the ada tepe deposit: a sediment-hosted, detachment …pmarchev/5.pdfschweizerische mineralogische...
TRANSCRIPT
Schweizerische Mineralogische und Petrographische Mitteilungen 84 59ndash78 2004
0036-769904008459 copy2004 Schweiz Mineral Petrogr Ges
The Ada Tepe deposit a sediment-hosted detachment fault-controlled low-sulfidation gold deposit in the
Eastern Rhodopes SE Bulgaria
Peter Marchev1 Brad S Singer 2 Danko Jelev 3 Sean Hasson 3 Robert Moritz4 and Nikolay Bonev5
Abstract
The Ada Tepe gold deposit 230 km SE of Sofia formed in the eastern part of the Rhodope Mountains that under-went extension and metamorphic core complex formation followed by normal faulting basin subsidence and silicicto mafic magmatism during the MaastrichtianndashOligocene The region comprises numerous volcanic-hosted epi-thermal and base-metal vein deposits spatially and temporally associated with the Oligocene magmatism Ada Tepeis a typical low-sulfidation epithermal gold deposit unusual in that it is older than adjacent magmatic-related depos-its and is hosted in MaastrichtianndashPaleocene sedimentary rocks above a detachment fault contact with underlyingPaleozoic metamorphic rocksGold mineralization is located in (1) a massive tabular ore body above the detachment fault and (2) open space-filling ores along predominantly eastndashwest oriented listric faults The ores are zones of intensive silicification andbrecciation synchronous with detachment faulting Brittle deformation opened spaces in which bands of opalinesilica and electrum quartz pyrite massive and bladed carbonates were deposited Mineralization is exclusively a Ausystem with AuAg ~3 trace As and no base metals Alteration consists of quartz adularia chlorite sericite calcitepyrite and clay minerals Adularia and abundant bladed carbonates indicate boiling within the entire span of thedeposit whereas bands of opaline silica with dendritic gold suggest that silica and gold were transported as colloidsThe physical setting of formation of the Ada Tepe deposit was very shallow and low temperature The Sr and Pbisotope ratios of carbonates and pyrite reflect hydrothermal fluid signatures derived predominantly from the meta-morphic rocksThe age of mineralization and association with the detachment fault suggest that gold mineralization at Ada Tepe ismore closely linked to the Kessebir metamorphic core complex rather than to local magmatism
Keywords detachment fault sediment-hosted low-sulfidation epithermal Eastern Rhodopes Bulgaria
1 Introduction
The Rhodope metallogenic province (Stoyanov1979) comprises numerous volcanic-hosted epi-thermal (Madjarovo Chala Zvezdel Losen Per-ama Hill Sappes) and base-metal vein (MadanLuki Popsko Thermes) deposits hosted by meta-morphic basement (Marchev et al 2000) Thespatial and temporal association of these depositswith Oligocene magmatic centers is documentedby the radioisotopic dating of Singer and Marchev(2000) Marchev and Singer (2002) Rohrmeier etal (2002) and Ovtcharova et al (2003)
The Ada Tepe deposit is one of a newly discov-ered group of gold deposits in the Eastern Rho-
dopes These share many features with the adu-laria class of epithermal deposits but they areatypical in that they are hosted mostly in sedi-mentary rocks and do not show direct relation-ships to local magmatic activity Three of them in-cluding Ada Tepe Rozino and Stremtsi (Fig 1)are major targets for commercial exploration Ex-ploration carried out in the last 2 years shows thatAda Tepe is the major potential economic depositin the region
The Ada Tepe low-sulfidation epithermal golddeposit is located 4 km SE of Krumovgrad in theEastern Rhodopes 230 km SE of Sofia (Fig 1)Balkan Minerals and Mining AD (BMM ownedby Dundee Precious Acquisitions Inc) operates
1 Geological Institute Bulgarian Academy of Sciences Acad G Bonchev St 1113 Sofia Bulgarialtpmarchevgeologybasbggt
2 Department of Geology and Geophysics University of Wisconsin-Madison 1215 West Dayton St Madison WI53706 USA
3 Balkan Mineral and Mining AD 24 Saedinenie St Krumovgrad Bulgaria4 Section des Sciences de la Terre Universiteacute de Genegraveve rue des Maraicircchers 13 CH 1211 Genegraveve Switzerland5 Department of Geology and Paleontology Faculty of Geology and Geography Sofia University ldquoSt Kliment
Ohridskirdquo 15 Tzar Osvoboditel Bd 1504 Sofia Bulgaria
P Marchev et al60
this project The deposit is unusual in that it is lo-cated along a regional detachment fault More-over it is geochemically distinctive with respect tothe adjacent deposits owing to high AuAg ratiosand low base metal content (Marchev et al 2003)
Here we summarize results from recent stud-ies on the surface geology structure alteration
types and textural and mineralogical characteris-tics of the gold mineralization The paper provideslimited Sr and Pb isotope data for Ada Tepe anddiscusses the age relationships among gold miner-alization local igneous activity and thermalevents in the nearby Kessebir metamorphic dome(Figs 1 2)
Fig 1 Schematic geological map of the Eastern Rhodope showing metamorphic dome structures major volcanicareas and dyke swarms Compiled from Ricou et al (1998) Yanev et al (1998a) and Marchev et al (2004) Insetshows location of Krumovgrad within Bulgaria
61Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
2 Historical background and previous studies
Small adits and large dumps at the eastern part ofthe Ada Tepe hill (Fig 3a) provide tangible evi-dence for the historical mining activity probablyof Thracian and Roman times Regional map-ping of the Krumovgrad area was conducted in1965 (Shabatov et al 1965) and recently be-tween 1995 and 1996 (Sarov et al 1996) by theState exploration Company ldquoGeology and Geo-
physicsrdquo at a 125 000 scale Studies by Goranovand Atanassov (1992) and a PhD thesis byBonev (2002) have clarified the stratigraphicand tectonic relationships of the Krumovgradarea The latter work advocates a detachment-fault model for the formation of the Kessebirmetamorphic dome Limited exploration in thearea of the Ada Tepe deposit was followed by thefirst description of its alteration and mineraliza-tion and its classification as AundashAg-polymetallic
Fig 2 Geological map of Kessebir dome (after Bonev 2002) and location of Ada Tepe deposit and Synap prospect
P Marchev et al62
Fig 3 (a) 3D view of Ada Tepe deposit (b) Cross section of Ada Tepe deposit Major ore bodies (c) Massivetabular ore body (ldquoThe Wallrdquo) above the detachment fault (d) Open space-filling ores along predominantly EndashWoriented listric faults
63Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
occurrence of the adularia-sericite type (Kunovet al 2001)
Since June 2000 the Ada Tepe deposit hasbeen included in the Krumovgrad license areaand is explored by Balkan Mineral and MiningAD Based on the results of regional mapping andsurface sampling BMM conducted two drillingprograms with 145 drill holes using both diamondand reverse circulation drilling techniques for atotal length of 12 440 m A total of 10 218 m ofsurface channel samples were also collected dur-ing 2001ndash2002 Resource calculations by RSGGlobal of Perth Australia show that Ada Tepe isa high-grade AundashAg deposit containing 615 Mt ofore at 46 gt Au for 910 000 ounces of Au using a10 gt cutoff grade
On the basis of initial results from the explora-tion program and the geographical proximity ofthe Ada Tepe deposit to the base metal mineraliza-tion at the Oligocene Zvezdel volcano Crummy(2002) suggested a direct genetic link between thebase and precious metal districts Marchev et al(2003) favoured an Upper Eocene age based onprecise 40Ar39Ar data and a detachment faultingmodel for the origin of the Ada Tepe deposit
3 Geologic setting
31 District geology
Basement metamorphic rocks in the Krumovgradarea build up the elongated Kessebir dome in NndashNE direction (Kozhoukharov et al 1988 Ricou etal 1998 Bonev 2002) (Figs 1 2) Two major tec-tonostratigraphic units (complexes) have beenrecognized on the basis of composition and tec-tonic setting of the metamorphic rocks a Gneiss-migmatite complex and a Variegated Complex(Kozhoukharov et al 1988 Haydoutov et al2001) which correspond to the Continental andMixed units of Ricou et al (1998) respectivelyThe structurally lower Gneiss-migmatite complexcrops out in the core of the Kessebir metamorphicdome It is dominated by igneous protoliths in-cluding metagranites migmatites and migmatizedgneisses overlain by a series of pelitic gneissesand rare amphibolites Eclogites and eclogitic am-phibolites have been described in the Greek partof the Kessebir dome (Mposkos and Krohe2000) RbndashSr ages of 3346 plusmn 34 Ma (Mposkosand Wawrzenitz 1995) from metapegmatites inGreece and RbndashSr (328 plusmn 25 Ma) and UndashPb zir-con ages of 310 plusmn 55 Ma and 319 plusmn 9 Ma (Pey-tcheva et al 1995 1998) from metagranites of theKessebir dome in Bulgaria indicate that theGneiss-migmatite complex is formed of Variscanor older continental basement
The overlaying Variegated complex consists ofa heterogeneous assemblage of pelitic schists para-gneisses amphibolites marbles and ophiolitebodies (Kozhoukharova 1984 Kolcheva and Es-kenazi 1998) Metamorphosed ophiolitic peridot-ites and amphibolitized eclogites are intruded bygabbros gabbronorites plagiogranites and dio-rites UndashPb zircon dating of a gabbro from theneighbouring Biala Reka dome (Fig 1) yields aLate Neoproterozoic age of 572 plusmn 5 Ma for thecore and outer zone recording a Hercynian meta-morphic event at ~300ndash350 Ma (Carrigan et al2003) Volumetrically minor plutonic bodies ofpresumably Upper Cretaceous age intrude theVariegated complex and represent an importantphase of igneous activity in the area (Belmustako-va et al 1995) The rocks are medium to fine-grained light grey two-mica granites of massiveto slightly foliated structure
The rocks of the Variegated complex in theKrumovgrad area are overlain by the Maastrich-tianndashPaleocene syndetachment Shavarovo For-mation (Goranov and Atanasov 1992 see be-low) which is in turn overlain by Upper EocenendashLower Oligocene coal-bearing-sandstone andmarl-limestone formations Lava flows anddomes of the ~35 Ma andesites (Lilov et al1987) of the Iran Tepe volcano are exposednortheast of Krumovgrad (Fig 1) This magmaticactivity was followed by scarce dykes of latitic torhyolitic composition in the northern part of theKessebir dome dated at 3182 plusmn 020 Ma and fi-nally by 26ndash28 Ma old intra-plate basaltic mag-matism in the southern part of the dome(Marchev et al 1997 1998)
32 Deposit geology
The Ada Tepe deposit is hosted by the syndetach-ment MaastrichtianndashPaleocene Shavarovo For-mation overlaying the northeastern closure ofthe Kessebir metamorphic core complex (Fig 2)The contact between poorly consolidated sedi-mentary rocks and underlying metamorphicrocks corresponds to the location of a regionallydeveloped low-angle normal fault named theTockachka detachment fault (TDF) by Bonev(1996) The fault dips 10ndash15deg to the north-north-east It can be traced further southwest for morethan 40 km from Krumovgrad to the Bulgarian-Greek frontier and is well exposed in the areasouthwest of Synap village about 2 km west ofAda Tepe In the latter area the rocks in the hang-ing wall of the TDF consist of metamorphicblocks breccia conglomerates sandstone marlsand argillaceous limestone This unit was first rec-ognized by Atanasov and Goranov (1984) in the
P Marchev et al64
Fig 4 Mineralization of The Wall showing multiple periods of silicification and veining (a) Brecciated early micro-crystalline silica (early stage) with a single gneiss fragment (b) Breccia of the microcrystalline silica (early stage)cemented by calcite (third stage) (c) Subvertical colloform finely banded vein Early stage gray (g) microcrystallinesilica on the margins of the veins followed by the massive microcrystalline (mq) cross-cut by the third stage sugaryquartz and massive and bladed calcite (qc) Late veinlets of dolomite-ankerite (da) cut early vein mineralization(d) Transition of subhorizontal opaline carbonate vein into subvertical step-like vein in the overlying sediments
65Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Krumovgrad area and described as the ShavarovoFormation of the Krumovgrad Group in a laterpaper (Goranov and Atanasov 1992) The totalthickness of the type section of the ShavarovoFormation (~350 m) was measured along the Kal-djic river near the Shavar village Blocks andclasts of breccia and conglomerate are mixtures ofgneiss amphibolite and marble derived primarilyfrom the Variegated complex
4 Structure
The dominant structure in the Ada Tepe prospectis the TDF It is a mapable tectonic contact bestexpressed along the western slope of Ada Tepehill (Fig 3a) In outcrop and drill cores the fault isrecognized as a contact between Paleozoic meta-morphic rocks and MaastrichtianndashPaleocene sed-imentary rocks of the Shavarovo Formation Im-mediately above the detachment fault there is a05 to 20 m thick zone of massive silicification Indrill core the lower limit of the structure ismarked by a 10ndash20 cm-thick layer of tectonic clayGneiss migmatite marble and the amphibolite ofthe metamorphic basement beneath the detach-ment surface are transformed into a cataclasticrock over a thickness of several meters Thesouthwestern slope of the Ada Tepe hill is cut by aNWndashSE-oriented high-angle fault (Fig 2) whichformed a small half graben fill by older Maas-trichtianndashPaleocene syndetachment sedimentaryrocks overlain in the eastern part by younger Pria-bonianndashOligocene sedimentary rocks
Major structures cutting the basement rocks ofthe Ada Tepe deposit are rare although severalEndashW and NndashS-oriented subvertical faults markedby a zone of silicification occur to the south eastand west of the Ada Tepe deposit The longest NndashS-striking zone has been traced for almost 200 mThe EndashW and NndashS faults coincide with the majordirections of the mineralized veins in the sedi-mentary cover and can be interpreted as feederstructures for the mineralizing fluids
5 Mineralization
51 Ore geometry and ore bodies
The Ada Tepe deposit is 600 m along strike and300ndash350 m wide Gold mineralization occurs as(1) a massive tabular body located immediatelyabove the detachment fault (Figs 3b c) and (2)open space-filling within the breccia-conglomer-ate and sandstone along predominantly east-westoriented subvertical listric faults within the hang-
ing wall (Figs 3b d) In cross section the tabularbody dips (10ndash15deg) to the north-northeast whichis consistent with the low angle TDF The orebody is so strongly silicified company geologistsrefer to it as ldquoThe Wallrdquo Detailed observations onThe Wall indicate a complicated sequence ofevents with multiple periods of silicification andveining Silicification began with the deposition ofmassive white to light grey silica above the de-tachment fault partly or totally replacing the orig-inal rocks Original rock textures were destroyedwith the exception of ghosted gneiss fragments(Fig 4a) The latter are rounded with veins ofquartz or carbonate cutting or surrounding theclasts Early microcrystalline silica was commonlyveined by subvertical banded veins or brecciatedby later fault movements and cemented by calcitesugary quartz (Fig 5b) or by pyrite
In the less silicified parts The Wall consists ofnumerous differently oriented veins ranging inwidth from less than 1 cm up to 30 cm (Fig 4c)Subvertical veins which were formed by deposi-tion of colloform silica layers in open space canbe traced from The Wall into the listric faults inthe overlying sedimentary rocks (Fig 4d) On thesurface they form EndashW-trending ridges separatedby argillic zones (Figs 3a b d)
52 Ore and gangue mineralogy andstages of mineralization
The ore mineralogy of the Ada Tepe deposit is sim-ple consisting mainly of electrum and subordinatepyrite with traces of galena and gold-silver tellu-rides Gangue minerals consist of silica polymorphs(microcrystalline fine-grained sugary quartz andopaline silica) various carbonates (calcite dolo-mite ankerite and siderite) and adularia Telluridesinclude hessite (Ag2Te) and petzite (Ag3AuTe2) Allsamples with Au content higher than 1 gt have al-most constant AuAg ratios ~ 3 reflecting the com-position of electrum (76ndash73 wt Au)
Unlike the massive silicification of The Wallbanded veins in and above it provide an excellentframework for identifying the different stages ofmineralization Mineralization in Ada Tepe canbe subdivided into 4 broad generally overlappingstages of quartz and carbonate veins on the basisof cross-cutting relationships changes in mineral-ogy texture and gold grades
The earliest stage is characterized by deposi-tion of microcrystalline to fine-grained grayish towhite massive or banded quartz with rare pyriteand adularia (Figs 5andashd) In some veins silica depo-sition starts with a thin band of almost isotropicopaline (Fig 4 c) followed by thin band of quartzwith rare bladed calcite Breccia texture is typical
P Marchev et al66
for the massive silicification of The Wall Theproducts of the early stage form microfracturefilling in the host rocks near the margins of the
Fig 5 Microphotographs and SEM images of silica and bonanza ore textures (a) Bands of early stage microcrystal-line (mq) and jigsaw quartz (jq) (b) Electrum band (e) deposited on the interface between early microcrystallinequartz (mq) and third stage sugary quartz and radiating bladed calcite (qc) (c) Band of electrum (e) and isotropicopaline Electrum is located on the bottom of the band (d) Third stage coarse crystalline quartz (ccq) cutting theopaline (o) and microcrystalline quartz (mq) which in turn is cut by calcite (c) (e) Subparallel bands of electrum (e)and microcrystalline adularia and silica separated by a calcite vein (c) The arrow shows the vertical direction (f)SEM image of the outlined area
veins or rock fragments in The Wall causing thesilica-adularia-pyrite replacement in them Thegold grade of this stage is unknown
67Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
The economic gold is related to the secondstage of mineralization It starts at the end of themicrocrystalline quartz and the beginning of thecoarser grained (sugary) quartz of the third stagebelow (Fig 5b) Usually it forms black millimeter-scale bands of opaline or microcrystalline chal-cedony-adularia and electrum (Figs 5cndashf) Locallyopaline silica crosscuts the microcrystallinequartz (Figs 5cndashd) of the early stage and in turn iscut by the coarser grained quartz and carbonatesof the third and forth stages (Figs 5dndashe) Petro-graphic examination of the electrum-rich bandsreveals that electrum commonly occurs towardsthe bottom of the opaline or microcrystallinebands (Figs 5c e) Where opaline bands are notpresent electrum precipitates at the boundary offirst and third stages (Fig 5b) The electrum hasirregular forms as the result of crystallization inthe quartz interstices being relatively well-shapedin the coarser-grained quartz crystals The size ofelectrum grains ranges from less than 1 to 20 micromHowever the single crystals form chains reachingup to 650 microm (Figs 5b 6a) Electrum in gold-richbands etched with HF is characterized by botryoi-dal surfaces that appear to have formed by theaggregation of spherical electrum particles (Figs6andashb) as observed in the Sleeper deposit Nevada(Saunders 1990 1994) Electrum in bonanza veinscan occupy 50 vol (Figs 5f 6c) accompanied byrare As-bearing pyrite Occasionally micron orsubmicron size electrum inclusions form zoneswithin the As-bearing pyrite (Figs 6d) Tiny AundashAg tellurides have been observed at the contactsbetween electrum grains and small galena crystals(Fig 6f)
The third stage starts with deposition of sugaryquartz (up to 15 mm large Figs 5d 7a) followedby bands of quartz and bladed calcite (Figs 5b 7b)and finally by massive calcite with small amountof quartz (Fig 5d) Locally calcite fills quartz ge-odes or forms small veins (Fig 7a) Microscopical-ly the late calcite corrodes and replaces quartzcrystals Small amount of adularia and pyrite arealso typical for this stage
The hydrothermal mineralization ended withthe deposition of pinkish ankerite-dolomite andsiderite which was preceded by precipitation ofmassive pyrite in some parts of the deposit (Figs7cndashd)
The mineralization of Ada Tepe exhibits sever-al important spatial and textural features thatprovide insights to the physical environment ofore deposition In its upper part quartz becomesthe predominant gangue mineral whereas car-bonates are subordinate This is particularly obvi-ous in the last stage where in the surface samplesdolomite and ankerite are absent in the geodes
and bladed minerals consist of microcrystallinequartz only Another spatial variation is the di-minishing of banding textures with the decreasein grade of Au mineralization to the north Animportant feature is the absence of bladed car-bonates in the veinlets beneath The Wall in con-trast to the entire extent of the deposit above thedetachment surface
53 Oxidized zone
The uppermost part of the Ada Tepe deposit hasbeen oxidized by supergene processes with thedepth of oxidation being dependent upon inten-sity of faulting Due to extensive silicification TheWall itself is generally not oxidized however a 2to 5 m thick zone of oxidation invariably occursabove The Wall Narrow zones of oxidation occurdown to this zone utilizing high angle listric faultsThese faults and fractures most likely acted asconduits for the surface waters to reach the im-permeable silicified zone forming the oxidizedzone above The Wall
Most of the pyrite in the oxidized zones hasbeen converted into limonite identified asgoethite Kaolinite is widely distributed in thiszone forming locally small veinlets Electrum inthe oxidized zone however shows no evidence ofAu enrichment
6 Alteration
In the poorly mineralized zones hydrothermal al-teration is weak with most of the detrital minerals(quartz muscovite and feldspars) remaining unal-tered Alteration consists of chlorite calcite kaoli-nite and subordinate albite pyrite and ankerite-dolomite It seems that calcite and ankerite-dolo-mite are late however it is difficult to distinguishreplacement calcite from vein calcite Quartzadularia calcite pyrite and dolomite-ankerite-siderite plusmn sericite and clay minerals in variableproportions occur in The Wall and immediateproximity to the subvertical quartz and carbonateveins in the strongly mineralized zones Theyformed through replacement of the original meta-morphic minerals included in the sandstone andconglomerate and are associated with relict de-trital quartz and muscovite This complex mineralassemblage is the result of the evolution of thehydrothermal activity
Hydrothermal alteration of the basementmetamorphic rocks is developed within a haloseveral meters in extent beneath The Wall and ismore pronounced around the subvertical veinsThe alteration assemblage includes quartz adu-
P Marchev et al68
Fig 6 (a) SEM images of electrum dendrite etched with HF (b) Negative forms of quartz removed by HFand spherical colloidal particles (c) Opal-electrum band containing ~ 50 electrum and small amount ofpyrite Dark crystals between electrum are adularia and silica (d) Pyrite with a zone of submicron-size elec-trum (e) Former Py converted to goethite with inclusions of Au (f) AundashAg tellurides between larger elec-trum and galena crystals
69Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
laria illite or sericite pyrite kaolinite and latestage ankerite-dolomite-siderite
Clay minerals are more abundant and betterdeveloped in the alteration close to the surfacewhere they form argillic zones between the EndashW-oriented swarms of veins Kaolinite and quartzpredominate in the argillic zones and illite chlo-rite adularia and carbonate are subordinate ac-companied locally by illite-montmorillonite Partof the shallow-level kaolinite may be supergenebut its association with unoxidized pyrite beneathand within The Wall indicates that a hypogene ori-gin is likely at least for the deeper kaolinite
7 Geochronology
40Ar39Ar ages from adularia and sanidine sam-ples were determined to constrain the timing ofmineralization and volcanic activity in the Kesse-bir dome Sample AT01-2 from which adulariawas extracted for dating is from a drill-hole at725 m depth It represents a quartz-adularia-car-bonate banded vein filled with finely veinedgneiss clasts It is a mixture of completely replaceddetrital K-feldspar and directly deposited adular-ia crystals The rhyolite dyke (sample AT01-17) isemplaced within the core orthogneisses of theKessebir dome located 4 km southwest from AdaTepe (Fig 2) It comprises 2 cm diameter sanidinephenocrysts that were separated for dating plusplagioclase biotite and quartz
40Ar39Ar experiments were conducted at UW-Madison Rare Gas Geochronology LaboratoryMinerals were separated from 100ndash250 micronsieve fractions using standard magnetic densityand handpicking methods Five milligrams of eachmineral were irradiated at Oregon State Univer-sity USA for 12 hours along with 2834 Ma sani-dine from the Taylor Creek rhyolite as the neu-tron fluence monitor Analytical procedures in-cluding mass spectrometry procedural blanks re-actor corrections and estimation of uncertaintiesare given in Singer and Brown (2002) Isotopicmeasurements were made of the gas extracted byincrementally heating of 2ndash3 mg multi-crystal ali-
quots using a defocused CO2 laser beam Resultsof incremental heating experiments along withthe 40Ar39Ar ages of muscovite and biotite fromthe lower plate of the metamorphic basementrocks taken from Bonev et al (accepted) are inTable 1 Incremental heating experiments and agespectra of the sanidine and adularia are presentedin Table 2 and Fig 8 Uncertainties in the agesinclude analytical contributions only at plusmn2
The plateau age of the adularia based on793 of the gas released is 3499 plusmn 023 Ma (Fig8) and is indistinguishable from the total fusionage of 3505 plusmn 023 Ma Sanidine from the rhyolitedyke yielded a plateau age of 3182 plusmn 020 Mabased on 60 percent of the gas released which isindistinguishable from the total fusion age of3188 plusmn 020 Ma As is the case for the adulariathis indicates that argon loss due to weathering oralteration is negligible Moreover the inverse iso-chron ages of 3511 plusmn 037 Ma for the adularaiaand 3191 plusmn 027 Ma for the sanidine are indistin-guishable from the plateau ages and the 40Ar36Arintercept values indicate that there is virtually noexcess argon present
Lavas from the Iran Tepe volcano four kmnortheast of Ada Tepe give KndashAr ages of ~35 Mabut their stratigraphic position above the UpperPriabonianndashLower Oligocene marl-limestone for-mation suggests that they are younger than 34Ma
40Ar39Ar measurements on muscovite and bi-otite (Bonev et al accepted) from the Gneiss-migmatite complex record ages of 3813 plusmn 036and 3773 plusmn 023 Ma respectively (Table 1) Theseages are broadly in agreement with the published40Ar39Ar ages for muscovite (422 plusmn 50 and 361 plusmn50 Ma Lips et al 2000) and muscovite and am-phibole (39 plusmn 1 and 45 plusmn 2 Ma respectively Muka-sa et al 2003) from the Biala Reka metamorphiccore complex Similar ages (39ndash35 Ma) have beenobtained by Peytcheva et al (1992) for the closingof Sr isotope system in the metagranites from theBiala Reka dome
The relative age of the mineralization was de-termined based on its relationship with the hostKrumovgrad group and the overlying Upper
Sample Mineral Weighted Plateau Total Fusion Sourceage (Ma) age (Ma)
AT01-2 adularia 3499 plusmn 023 3505 plusmn 023 this studyAT01-17 sanidine 3182 plusmn 020 3188 plusmn 020 this studyH6 biotite 3773 plusmn 025 3756 plusmn 024 Bonev et al (accepted)H706 muscovite 3813 plusmn 036 3834 plusmn 031 Bonev et al (accepted)
Table 1 Summary of 40Ar39Ar incremental heating experiments on adularia sanidinebiotite and muscovite from Ada Tepe deposit and Kessebir dome
P Marchev et al70
Exp
erim
ent
Las
er p
ower
36A
r37
Ara
38A
r39
Ara
40A
r40
Ar
39A
rK
Ca
Age
plusmn 2
num
ber
(Wat
ts)
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
()
()
(Ma)
b
AT
01-2
adu
lari
a J
= 0
002
987
plusmn 0
0000
09 m
ass
disc
rim
inat
ion
per
amu
10
022
plusmn 0
0004
A
B21
21 0
04
W 0
012
604
00
0003
0 0
000
159
00
0000
5 0
002
772
00
0002
1 0
029
850
00
0007
7 3
871
564
00
0155
74
70
46
132
72
plusmn 3
84A
B21
22 0
10
W 0
009
696
00
0002
2 0
004
566
00
0004
6 0
004
738
00
0002
0 0
239
380
00
0013
1 4
348
793
00
0312
034
92
91
633
85
plusmn 0
38A
B21
23 0
16
W 0
008
804
00
0001
5 0
005
107
00
0003
2 0
006
792
00
0003
0 0
427
709
00
0033
7 5
368
227
00
0278
052
25
32
634
93
plusmn 0
18A
B21
24 0
22
W 0
003
814
00
0001
1 0
000
564
00
0001
0 0
003
949
00
0001
2 0
268
571
00
0011
2 2
865
288
00
0078
961
33
315
034
83
plusmn 0
16A
B21
26 0
30
W 0
008
692
00
0001
1 0
000
261
00
0000
2 0
009
565
00
0002
0 0
650
692
00
0034
7 6
809
601
00
0275
562
78
079
935
01
plusmn 0
11A
B21
27 0
45
W 0
011
765
00
0001
5 0
000
226
00
0000
6 0
017
464
00
0003
5 1
258
986
00
0031
211
697
117
00
0648
770
524
817
70
350
0plusmn
009
AB
2128
06
9 W
00
1320
9 0
000
022
00
0019
9 0
000
003
00
1740
1 0
000
014
12
3066
3 0
001
217
119
6079
5 0
012
113
676
379
195
935
11
plusmn 0
15A
B21
29 1
25
W 0
012
274
00
0002
1 0
000
249
00
0000
3 0
017
405
00
0003
7 1
255
200
00
0080
311
896
055
00
0449
369
817
316
11
353
2plusmn
010
Pla
teau
age
349
9plusmn
023
MSW
D (
n =
5 o
f 8)
186
Tota
l Fus
ion
Age
350
5plusmn
023
AT
01-1
7a s
anid
ine
J =
00
0297
6 plusmn
000
0009
mas
s di
scri
min
atio
n pe
r am
u 1
002
2 plusmn
000
04
AB
2132
00
4 W
00
0055
1 0
000
005
00
0001
4 0
000
006
00
0017
5 0
000
005
00
0362
1 0
000
024
01
8252
2 0
000
076
118
00
456
313
1plusmn
456
AB
2133
00
6 W
00
0019
3 0
000
004
00
0002
6 0
000
003
00
0034
3 0
000
006
00
2579
1 0
000
046
02
1431
6 0
000
110
745
03
447
326
0plusmn
051
AB
2134
01
2 W
00
0018
8 0
000
004
00
0011
6 0
000
007
00
0251
1 0
000
023
02
0468
8 0
000
253
12
8821
1 0
000
967
959
20
568
320
8plusmn
012
AB
2136
01
8 W
00
0050
3 0
000
004
00
0056
8 0
000
012
00
1520
7 0
000
032
12
5179
3 0
000
404
76
2511
3 0
002
510
980
124
678
318
1plusmn
004
AB
2137
02
4 W
00
0056
0 0
000
005
00
0084
3 0
000
018
00
2351
2 0
000
025
19
2193
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000
651
116
3788
5 0
004
597
985
190
700
317
9plusmn
004
AB
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02
7 W
00
0036
1 0
000
008
00
0070
7 0
000
010
00
1915
2 0
000
024
15
7872
8 0
000
654
95
5607
9 0
004
091
988
156
686
318
7plusmn
005
AB
2139
03
1 W
00
0036
3 0
000
001
00
0052
2 0
000
008
00
1472
7 0
000
035
12
0293
6 0
000
478
73
0039
4 0
003
784
985
119
709
318
4plusmn
005
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2141
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5 W
00
0031
1 0
000
007
00
0037
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000
008
00
1054
1 0
000
029
08
7899
6 0
000
319
53
5364
2 0
002
077
983
87
716
318
8plusmn
005
AB
2142
04
5 W
00
0032
8 0
000
004
00
0055
3 0
000
015
00
1592
7 0
000
034
13
0785
9 0
000
548
79
4703
7 0
003
239
987
129
726
319
6plusmn
005
AB
2143
05
9 W
00
0028
5 0
000
005
00
0039
4 0
000
012
00
1085
1 0
000
045
08
9161
3 0
000
557
54
3036
7 0
002
402
984
88
696
319
3plusmn
006
AB
2145
08
4 W
00
0016
0 0
000
004
00
0019
6 0
000
007
00
0560
3 0
000
028
04
5183
5 0
000
332
27
6009
9 0
001
984
983
45
706
319
7plusmn
008
AB
2146
13
5 W
00
0016
6 0
000
005
00
0018
3 0
000
004
00
0462
0 0
000
018
03
8294
7 0
000
252
23
5385
3 0
001
397
980
38
647
320
5plusmn
008
Pla
teau
age
318
2plusmn
020
MSW
D (
4 of
12)
279
Tota
l Fus
ion
Age
318
8plusmn
020
aC
orre
cted
for
37A
r an
d 39
Ar
deca
yb
Age
s ca
lcul
ated
rel
ativ
e to
28
34 M
a Ta
ylor
Cre
ek R
hyol
ite
stan
dard
ita
lics
indi
cate
ste
ps o
mit
ted
from
the
plat
eau
age
calc
ulat
ion
see
text
for
deta
ils
Tabl
e 2
40A
r39
Ar
incr
emen
tal-
heat
ing
anal
yses
of a
dula
ria
and
sani
dine
from
Ada
Tep
e
71Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
EocenendashOligocene sedimentary rocks The latteris represented by sandstones unaffected by hy-drothermal alteration which cover the northernpart of the deposit
8 Sr and Pb isotope compositionsof carbonates and pyrite
Sr and Pb isotopes were measured by standardTIMS procedures at the University of GenevaSwitzerland following the methods of Valenza etal (2000) and Chiaradia and Fontboteacute (2002) Srisotope ratios on carbonate and Pb isotope ratiosfrom pyrite at Ada Tepe along with whole rock Srand Pb isotope ratios of the leachate fraction of asample from Synap prospect 2 km west of AdaTepe are presented in Table 3 and Figs 9 and 10The Ada Tepe carbonate is from a late stage an-kerite-dolomite vein taken from a drill-core sam-ple (AT01-22) at 996 m depth The bulk rock(sample Sin2000-28) from Synap is from sericite-adularia alteration from the surface Pyrite fromAda Tepe is from a strongly silicified sample(Km2000-6) Pyrite from Synap is from the samehand sample Sin2000-28 on which the Sr wasmeasured Both samples belong to the early alter-
ation The initial 87Sr86Sr ratio of the whole rockcorrected for 35 Ma is 070809 The pyrite sampleand whole rock leachate show identical 207Pb204Pb (1568) and 208Pb204Pb (3885) ratios andslightly different 206Pb204Pb ratios (1871 in AdaTepe and 1866 in Synap) The Sr and Pb isotopedata are compared with those of local Paleogenevolcanic rocks and dykes and the Rhodope meta-morphic rocks in Figs 9 and 10
9 Discussion
91 Physical environment
Epithermal quartz from the Ada Tepe deposit ispoor in fluid inclusions particularly the early mi-crocrystalline quartz and opal Euhedral late sug-ary quartz is the only phase which contains largerfluid inclusions but with no reliable characteris-tics that may allow to classify them as primary in-clusions For the similar Sleeper deposit USASaunders (1994) suggested that quartz formed bytransformation of poorly ordered silica may ex-clude trapped fluids thus precluding the use ofmicrothermometry to constrain the physicochem-ical conditions of silica and gold deposition
Fig 7 (a) Geode of coarse-crystalline quartz with carbonate infill (third stage) (b) Third stage coarse-crystallinequartz (ccq) and bladed parallel type calcite (c) (c) Late vein (forth stage) composed by pyrite on its margins fol-lowed by dolomite-ankerite (da) (d) Same fracture Dolomite-ankerite forms a halo overlapping quartz-adularia-pyrite alteration
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
P Marchev et al60
this project The deposit is unusual in that it is lo-cated along a regional detachment fault More-over it is geochemically distinctive with respect tothe adjacent deposits owing to high AuAg ratiosand low base metal content (Marchev et al 2003)
Here we summarize results from recent stud-ies on the surface geology structure alteration
types and textural and mineralogical characteris-tics of the gold mineralization The paper provideslimited Sr and Pb isotope data for Ada Tepe anddiscusses the age relationships among gold miner-alization local igneous activity and thermalevents in the nearby Kessebir metamorphic dome(Figs 1 2)
Fig 1 Schematic geological map of the Eastern Rhodope showing metamorphic dome structures major volcanicareas and dyke swarms Compiled from Ricou et al (1998) Yanev et al (1998a) and Marchev et al (2004) Insetshows location of Krumovgrad within Bulgaria
61Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
2 Historical background and previous studies
Small adits and large dumps at the eastern part ofthe Ada Tepe hill (Fig 3a) provide tangible evi-dence for the historical mining activity probablyof Thracian and Roman times Regional map-ping of the Krumovgrad area was conducted in1965 (Shabatov et al 1965) and recently be-tween 1995 and 1996 (Sarov et al 1996) by theState exploration Company ldquoGeology and Geo-
physicsrdquo at a 125 000 scale Studies by Goranovand Atanassov (1992) and a PhD thesis byBonev (2002) have clarified the stratigraphicand tectonic relationships of the Krumovgradarea The latter work advocates a detachment-fault model for the formation of the Kessebirmetamorphic dome Limited exploration in thearea of the Ada Tepe deposit was followed by thefirst description of its alteration and mineraliza-tion and its classification as AundashAg-polymetallic
Fig 2 Geological map of Kessebir dome (after Bonev 2002) and location of Ada Tepe deposit and Synap prospect
P Marchev et al62
Fig 3 (a) 3D view of Ada Tepe deposit (b) Cross section of Ada Tepe deposit Major ore bodies (c) Massivetabular ore body (ldquoThe Wallrdquo) above the detachment fault (d) Open space-filling ores along predominantly EndashWoriented listric faults
63Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
occurrence of the adularia-sericite type (Kunovet al 2001)
Since June 2000 the Ada Tepe deposit hasbeen included in the Krumovgrad license areaand is explored by Balkan Mineral and MiningAD Based on the results of regional mapping andsurface sampling BMM conducted two drillingprograms with 145 drill holes using both diamondand reverse circulation drilling techniques for atotal length of 12 440 m A total of 10 218 m ofsurface channel samples were also collected dur-ing 2001ndash2002 Resource calculations by RSGGlobal of Perth Australia show that Ada Tepe isa high-grade AundashAg deposit containing 615 Mt ofore at 46 gt Au for 910 000 ounces of Au using a10 gt cutoff grade
On the basis of initial results from the explora-tion program and the geographical proximity ofthe Ada Tepe deposit to the base metal mineraliza-tion at the Oligocene Zvezdel volcano Crummy(2002) suggested a direct genetic link between thebase and precious metal districts Marchev et al(2003) favoured an Upper Eocene age based onprecise 40Ar39Ar data and a detachment faultingmodel for the origin of the Ada Tepe deposit
3 Geologic setting
31 District geology
Basement metamorphic rocks in the Krumovgradarea build up the elongated Kessebir dome in NndashNE direction (Kozhoukharov et al 1988 Ricou etal 1998 Bonev 2002) (Figs 1 2) Two major tec-tonostratigraphic units (complexes) have beenrecognized on the basis of composition and tec-tonic setting of the metamorphic rocks a Gneiss-migmatite complex and a Variegated Complex(Kozhoukharov et al 1988 Haydoutov et al2001) which correspond to the Continental andMixed units of Ricou et al (1998) respectivelyThe structurally lower Gneiss-migmatite complexcrops out in the core of the Kessebir metamorphicdome It is dominated by igneous protoliths in-cluding metagranites migmatites and migmatizedgneisses overlain by a series of pelitic gneissesand rare amphibolites Eclogites and eclogitic am-phibolites have been described in the Greek partof the Kessebir dome (Mposkos and Krohe2000) RbndashSr ages of 3346 plusmn 34 Ma (Mposkosand Wawrzenitz 1995) from metapegmatites inGreece and RbndashSr (328 plusmn 25 Ma) and UndashPb zir-con ages of 310 plusmn 55 Ma and 319 plusmn 9 Ma (Pey-tcheva et al 1995 1998) from metagranites of theKessebir dome in Bulgaria indicate that theGneiss-migmatite complex is formed of Variscanor older continental basement
The overlaying Variegated complex consists ofa heterogeneous assemblage of pelitic schists para-gneisses amphibolites marbles and ophiolitebodies (Kozhoukharova 1984 Kolcheva and Es-kenazi 1998) Metamorphosed ophiolitic peridot-ites and amphibolitized eclogites are intruded bygabbros gabbronorites plagiogranites and dio-rites UndashPb zircon dating of a gabbro from theneighbouring Biala Reka dome (Fig 1) yields aLate Neoproterozoic age of 572 plusmn 5 Ma for thecore and outer zone recording a Hercynian meta-morphic event at ~300ndash350 Ma (Carrigan et al2003) Volumetrically minor plutonic bodies ofpresumably Upper Cretaceous age intrude theVariegated complex and represent an importantphase of igneous activity in the area (Belmustako-va et al 1995) The rocks are medium to fine-grained light grey two-mica granites of massiveto slightly foliated structure
The rocks of the Variegated complex in theKrumovgrad area are overlain by the Maastrich-tianndashPaleocene syndetachment Shavarovo For-mation (Goranov and Atanasov 1992 see be-low) which is in turn overlain by Upper EocenendashLower Oligocene coal-bearing-sandstone andmarl-limestone formations Lava flows anddomes of the ~35 Ma andesites (Lilov et al1987) of the Iran Tepe volcano are exposednortheast of Krumovgrad (Fig 1) This magmaticactivity was followed by scarce dykes of latitic torhyolitic composition in the northern part of theKessebir dome dated at 3182 plusmn 020 Ma and fi-nally by 26ndash28 Ma old intra-plate basaltic mag-matism in the southern part of the dome(Marchev et al 1997 1998)
32 Deposit geology
The Ada Tepe deposit is hosted by the syndetach-ment MaastrichtianndashPaleocene Shavarovo For-mation overlaying the northeastern closure ofthe Kessebir metamorphic core complex (Fig 2)The contact between poorly consolidated sedi-mentary rocks and underlying metamorphicrocks corresponds to the location of a regionallydeveloped low-angle normal fault named theTockachka detachment fault (TDF) by Bonev(1996) The fault dips 10ndash15deg to the north-north-east It can be traced further southwest for morethan 40 km from Krumovgrad to the Bulgarian-Greek frontier and is well exposed in the areasouthwest of Synap village about 2 km west ofAda Tepe In the latter area the rocks in the hang-ing wall of the TDF consist of metamorphicblocks breccia conglomerates sandstone marlsand argillaceous limestone This unit was first rec-ognized by Atanasov and Goranov (1984) in the
P Marchev et al64
Fig 4 Mineralization of The Wall showing multiple periods of silicification and veining (a) Brecciated early micro-crystalline silica (early stage) with a single gneiss fragment (b) Breccia of the microcrystalline silica (early stage)cemented by calcite (third stage) (c) Subvertical colloform finely banded vein Early stage gray (g) microcrystallinesilica on the margins of the veins followed by the massive microcrystalline (mq) cross-cut by the third stage sugaryquartz and massive and bladed calcite (qc) Late veinlets of dolomite-ankerite (da) cut early vein mineralization(d) Transition of subhorizontal opaline carbonate vein into subvertical step-like vein in the overlying sediments
65Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Krumovgrad area and described as the ShavarovoFormation of the Krumovgrad Group in a laterpaper (Goranov and Atanasov 1992) The totalthickness of the type section of the ShavarovoFormation (~350 m) was measured along the Kal-djic river near the Shavar village Blocks andclasts of breccia and conglomerate are mixtures ofgneiss amphibolite and marble derived primarilyfrom the Variegated complex
4 Structure
The dominant structure in the Ada Tepe prospectis the TDF It is a mapable tectonic contact bestexpressed along the western slope of Ada Tepehill (Fig 3a) In outcrop and drill cores the fault isrecognized as a contact between Paleozoic meta-morphic rocks and MaastrichtianndashPaleocene sed-imentary rocks of the Shavarovo Formation Im-mediately above the detachment fault there is a05 to 20 m thick zone of massive silicification Indrill core the lower limit of the structure ismarked by a 10ndash20 cm-thick layer of tectonic clayGneiss migmatite marble and the amphibolite ofthe metamorphic basement beneath the detach-ment surface are transformed into a cataclasticrock over a thickness of several meters Thesouthwestern slope of the Ada Tepe hill is cut by aNWndashSE-oriented high-angle fault (Fig 2) whichformed a small half graben fill by older Maas-trichtianndashPaleocene syndetachment sedimentaryrocks overlain in the eastern part by younger Pria-bonianndashOligocene sedimentary rocks
Major structures cutting the basement rocks ofthe Ada Tepe deposit are rare although severalEndashW and NndashS-oriented subvertical faults markedby a zone of silicification occur to the south eastand west of the Ada Tepe deposit The longest NndashS-striking zone has been traced for almost 200 mThe EndashW and NndashS faults coincide with the majordirections of the mineralized veins in the sedi-mentary cover and can be interpreted as feederstructures for the mineralizing fluids
5 Mineralization
51 Ore geometry and ore bodies
The Ada Tepe deposit is 600 m along strike and300ndash350 m wide Gold mineralization occurs as(1) a massive tabular body located immediatelyabove the detachment fault (Figs 3b c) and (2)open space-filling within the breccia-conglomer-ate and sandstone along predominantly east-westoriented subvertical listric faults within the hang-
ing wall (Figs 3b d) In cross section the tabularbody dips (10ndash15deg) to the north-northeast whichis consistent with the low angle TDF The orebody is so strongly silicified company geologistsrefer to it as ldquoThe Wallrdquo Detailed observations onThe Wall indicate a complicated sequence ofevents with multiple periods of silicification andveining Silicification began with the deposition ofmassive white to light grey silica above the de-tachment fault partly or totally replacing the orig-inal rocks Original rock textures were destroyedwith the exception of ghosted gneiss fragments(Fig 4a) The latter are rounded with veins ofquartz or carbonate cutting or surrounding theclasts Early microcrystalline silica was commonlyveined by subvertical banded veins or brecciatedby later fault movements and cemented by calcitesugary quartz (Fig 5b) or by pyrite
In the less silicified parts The Wall consists ofnumerous differently oriented veins ranging inwidth from less than 1 cm up to 30 cm (Fig 4c)Subvertical veins which were formed by deposi-tion of colloform silica layers in open space canbe traced from The Wall into the listric faults inthe overlying sedimentary rocks (Fig 4d) On thesurface they form EndashW-trending ridges separatedby argillic zones (Figs 3a b d)
52 Ore and gangue mineralogy andstages of mineralization
The ore mineralogy of the Ada Tepe deposit is sim-ple consisting mainly of electrum and subordinatepyrite with traces of galena and gold-silver tellu-rides Gangue minerals consist of silica polymorphs(microcrystalline fine-grained sugary quartz andopaline silica) various carbonates (calcite dolo-mite ankerite and siderite) and adularia Telluridesinclude hessite (Ag2Te) and petzite (Ag3AuTe2) Allsamples with Au content higher than 1 gt have al-most constant AuAg ratios ~ 3 reflecting the com-position of electrum (76ndash73 wt Au)
Unlike the massive silicification of The Wallbanded veins in and above it provide an excellentframework for identifying the different stages ofmineralization Mineralization in Ada Tepe canbe subdivided into 4 broad generally overlappingstages of quartz and carbonate veins on the basisof cross-cutting relationships changes in mineral-ogy texture and gold grades
The earliest stage is characterized by deposi-tion of microcrystalline to fine-grained grayish towhite massive or banded quartz with rare pyriteand adularia (Figs 5andashd) In some veins silica depo-sition starts with a thin band of almost isotropicopaline (Fig 4 c) followed by thin band of quartzwith rare bladed calcite Breccia texture is typical
P Marchev et al66
for the massive silicification of The Wall Theproducts of the early stage form microfracturefilling in the host rocks near the margins of the
Fig 5 Microphotographs and SEM images of silica and bonanza ore textures (a) Bands of early stage microcrystal-line (mq) and jigsaw quartz (jq) (b) Electrum band (e) deposited on the interface between early microcrystallinequartz (mq) and third stage sugary quartz and radiating bladed calcite (qc) (c) Band of electrum (e) and isotropicopaline Electrum is located on the bottom of the band (d) Third stage coarse crystalline quartz (ccq) cutting theopaline (o) and microcrystalline quartz (mq) which in turn is cut by calcite (c) (e) Subparallel bands of electrum (e)and microcrystalline adularia and silica separated by a calcite vein (c) The arrow shows the vertical direction (f)SEM image of the outlined area
veins or rock fragments in The Wall causing thesilica-adularia-pyrite replacement in them Thegold grade of this stage is unknown
67Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
The economic gold is related to the secondstage of mineralization It starts at the end of themicrocrystalline quartz and the beginning of thecoarser grained (sugary) quartz of the third stagebelow (Fig 5b) Usually it forms black millimeter-scale bands of opaline or microcrystalline chal-cedony-adularia and electrum (Figs 5cndashf) Locallyopaline silica crosscuts the microcrystallinequartz (Figs 5cndashd) of the early stage and in turn iscut by the coarser grained quartz and carbonatesof the third and forth stages (Figs 5dndashe) Petro-graphic examination of the electrum-rich bandsreveals that electrum commonly occurs towardsthe bottom of the opaline or microcrystallinebands (Figs 5c e) Where opaline bands are notpresent electrum precipitates at the boundary offirst and third stages (Fig 5b) The electrum hasirregular forms as the result of crystallization inthe quartz interstices being relatively well-shapedin the coarser-grained quartz crystals The size ofelectrum grains ranges from less than 1 to 20 micromHowever the single crystals form chains reachingup to 650 microm (Figs 5b 6a) Electrum in gold-richbands etched with HF is characterized by botryoi-dal surfaces that appear to have formed by theaggregation of spherical electrum particles (Figs6andashb) as observed in the Sleeper deposit Nevada(Saunders 1990 1994) Electrum in bonanza veinscan occupy 50 vol (Figs 5f 6c) accompanied byrare As-bearing pyrite Occasionally micron orsubmicron size electrum inclusions form zoneswithin the As-bearing pyrite (Figs 6d) Tiny AundashAg tellurides have been observed at the contactsbetween electrum grains and small galena crystals(Fig 6f)
The third stage starts with deposition of sugaryquartz (up to 15 mm large Figs 5d 7a) followedby bands of quartz and bladed calcite (Figs 5b 7b)and finally by massive calcite with small amountof quartz (Fig 5d) Locally calcite fills quartz ge-odes or forms small veins (Fig 7a) Microscopical-ly the late calcite corrodes and replaces quartzcrystals Small amount of adularia and pyrite arealso typical for this stage
The hydrothermal mineralization ended withthe deposition of pinkish ankerite-dolomite andsiderite which was preceded by precipitation ofmassive pyrite in some parts of the deposit (Figs7cndashd)
The mineralization of Ada Tepe exhibits sever-al important spatial and textural features thatprovide insights to the physical environment ofore deposition In its upper part quartz becomesthe predominant gangue mineral whereas car-bonates are subordinate This is particularly obvi-ous in the last stage where in the surface samplesdolomite and ankerite are absent in the geodes
and bladed minerals consist of microcrystallinequartz only Another spatial variation is the di-minishing of banding textures with the decreasein grade of Au mineralization to the north Animportant feature is the absence of bladed car-bonates in the veinlets beneath The Wall in con-trast to the entire extent of the deposit above thedetachment surface
53 Oxidized zone
The uppermost part of the Ada Tepe deposit hasbeen oxidized by supergene processes with thedepth of oxidation being dependent upon inten-sity of faulting Due to extensive silicification TheWall itself is generally not oxidized however a 2to 5 m thick zone of oxidation invariably occursabove The Wall Narrow zones of oxidation occurdown to this zone utilizing high angle listric faultsThese faults and fractures most likely acted asconduits for the surface waters to reach the im-permeable silicified zone forming the oxidizedzone above The Wall
Most of the pyrite in the oxidized zones hasbeen converted into limonite identified asgoethite Kaolinite is widely distributed in thiszone forming locally small veinlets Electrum inthe oxidized zone however shows no evidence ofAu enrichment
6 Alteration
In the poorly mineralized zones hydrothermal al-teration is weak with most of the detrital minerals(quartz muscovite and feldspars) remaining unal-tered Alteration consists of chlorite calcite kaoli-nite and subordinate albite pyrite and ankerite-dolomite It seems that calcite and ankerite-dolo-mite are late however it is difficult to distinguishreplacement calcite from vein calcite Quartzadularia calcite pyrite and dolomite-ankerite-siderite plusmn sericite and clay minerals in variableproportions occur in The Wall and immediateproximity to the subvertical quartz and carbonateveins in the strongly mineralized zones Theyformed through replacement of the original meta-morphic minerals included in the sandstone andconglomerate and are associated with relict de-trital quartz and muscovite This complex mineralassemblage is the result of the evolution of thehydrothermal activity
Hydrothermal alteration of the basementmetamorphic rocks is developed within a haloseveral meters in extent beneath The Wall and ismore pronounced around the subvertical veinsThe alteration assemblage includes quartz adu-
P Marchev et al68
Fig 6 (a) SEM images of electrum dendrite etched with HF (b) Negative forms of quartz removed by HFand spherical colloidal particles (c) Opal-electrum band containing ~ 50 electrum and small amount ofpyrite Dark crystals between electrum are adularia and silica (d) Pyrite with a zone of submicron-size elec-trum (e) Former Py converted to goethite with inclusions of Au (f) AundashAg tellurides between larger elec-trum and galena crystals
69Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
laria illite or sericite pyrite kaolinite and latestage ankerite-dolomite-siderite
Clay minerals are more abundant and betterdeveloped in the alteration close to the surfacewhere they form argillic zones between the EndashW-oriented swarms of veins Kaolinite and quartzpredominate in the argillic zones and illite chlo-rite adularia and carbonate are subordinate ac-companied locally by illite-montmorillonite Partof the shallow-level kaolinite may be supergenebut its association with unoxidized pyrite beneathand within The Wall indicates that a hypogene ori-gin is likely at least for the deeper kaolinite
7 Geochronology
40Ar39Ar ages from adularia and sanidine sam-ples were determined to constrain the timing ofmineralization and volcanic activity in the Kesse-bir dome Sample AT01-2 from which adulariawas extracted for dating is from a drill-hole at725 m depth It represents a quartz-adularia-car-bonate banded vein filled with finely veinedgneiss clasts It is a mixture of completely replaceddetrital K-feldspar and directly deposited adular-ia crystals The rhyolite dyke (sample AT01-17) isemplaced within the core orthogneisses of theKessebir dome located 4 km southwest from AdaTepe (Fig 2) It comprises 2 cm diameter sanidinephenocrysts that were separated for dating plusplagioclase biotite and quartz
40Ar39Ar experiments were conducted at UW-Madison Rare Gas Geochronology LaboratoryMinerals were separated from 100ndash250 micronsieve fractions using standard magnetic densityand handpicking methods Five milligrams of eachmineral were irradiated at Oregon State Univer-sity USA for 12 hours along with 2834 Ma sani-dine from the Taylor Creek rhyolite as the neu-tron fluence monitor Analytical procedures in-cluding mass spectrometry procedural blanks re-actor corrections and estimation of uncertaintiesare given in Singer and Brown (2002) Isotopicmeasurements were made of the gas extracted byincrementally heating of 2ndash3 mg multi-crystal ali-
quots using a defocused CO2 laser beam Resultsof incremental heating experiments along withthe 40Ar39Ar ages of muscovite and biotite fromthe lower plate of the metamorphic basementrocks taken from Bonev et al (accepted) are inTable 1 Incremental heating experiments and agespectra of the sanidine and adularia are presentedin Table 2 and Fig 8 Uncertainties in the agesinclude analytical contributions only at plusmn2
The plateau age of the adularia based on793 of the gas released is 3499 plusmn 023 Ma (Fig8) and is indistinguishable from the total fusionage of 3505 plusmn 023 Ma Sanidine from the rhyolitedyke yielded a plateau age of 3182 plusmn 020 Mabased on 60 percent of the gas released which isindistinguishable from the total fusion age of3188 plusmn 020 Ma As is the case for the adulariathis indicates that argon loss due to weathering oralteration is negligible Moreover the inverse iso-chron ages of 3511 plusmn 037 Ma for the adularaiaand 3191 plusmn 027 Ma for the sanidine are indistin-guishable from the plateau ages and the 40Ar36Arintercept values indicate that there is virtually noexcess argon present
Lavas from the Iran Tepe volcano four kmnortheast of Ada Tepe give KndashAr ages of ~35 Mabut their stratigraphic position above the UpperPriabonianndashLower Oligocene marl-limestone for-mation suggests that they are younger than 34Ma
40Ar39Ar measurements on muscovite and bi-otite (Bonev et al accepted) from the Gneiss-migmatite complex record ages of 3813 plusmn 036and 3773 plusmn 023 Ma respectively (Table 1) Theseages are broadly in agreement with the published40Ar39Ar ages for muscovite (422 plusmn 50 and 361 plusmn50 Ma Lips et al 2000) and muscovite and am-phibole (39 plusmn 1 and 45 plusmn 2 Ma respectively Muka-sa et al 2003) from the Biala Reka metamorphiccore complex Similar ages (39ndash35 Ma) have beenobtained by Peytcheva et al (1992) for the closingof Sr isotope system in the metagranites from theBiala Reka dome
The relative age of the mineralization was de-termined based on its relationship with the hostKrumovgrad group and the overlying Upper
Sample Mineral Weighted Plateau Total Fusion Sourceage (Ma) age (Ma)
AT01-2 adularia 3499 plusmn 023 3505 plusmn 023 this studyAT01-17 sanidine 3182 plusmn 020 3188 plusmn 020 this studyH6 biotite 3773 plusmn 025 3756 plusmn 024 Bonev et al (accepted)H706 muscovite 3813 plusmn 036 3834 plusmn 031 Bonev et al (accepted)
Table 1 Summary of 40Ar39Ar incremental heating experiments on adularia sanidinebiotite and muscovite from Ada Tepe deposit and Kessebir dome
P Marchev et al70
Exp
erim
ent
Las
er p
ower
36A
r37
Ara
38A
r39
Ara
40A
r40
Ar
39A
rK
Ca
Age
plusmn 2
num
ber
(Wat
ts)
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
()
()
(Ma)
b
AT
01-2
adu
lari
a J
= 0
002
987
plusmn 0
0000
09 m
ass
disc
rim
inat
ion
per
amu
10
022
plusmn 0
0004
A
B21
21 0
04
W 0
012
604
00
0003
0 0
000
159
00
0000
5 0
002
772
00
0002
1 0
029
850
00
0007
7 3
871
564
00
0155
74
70
46
132
72
plusmn 3
84A
B21
22 0
10
W 0
009
696
00
0002
2 0
004
566
00
0004
6 0
004
738
00
0002
0 0
239
380
00
0013
1 4
348
793
00
0312
034
92
91
633
85
plusmn 0
38A
B21
23 0
16
W 0
008
804
00
0001
5 0
005
107
00
0003
2 0
006
792
00
0003
0 0
427
709
00
0033
7 5
368
227
00
0278
052
25
32
634
93
plusmn 0
18A
B21
24 0
22
W 0
003
814
00
0001
1 0
000
564
00
0001
0 0
003
949
00
0001
2 0
268
571
00
0011
2 2
865
288
00
0078
961
33
315
034
83
plusmn 0
16A
B21
26 0
30
W 0
008
692
00
0001
1 0
000
261
00
0000
2 0
009
565
00
0002
0 0
650
692
00
0034
7 6
809
601
00
0275
562
78
079
935
01
plusmn 0
11A
B21
27 0
45
W 0
011
765
00
0001
5 0
000
226
00
0000
6 0
017
464
00
0003
5 1
258
986
00
0031
211
697
117
00
0648
770
524
817
70
350
0plusmn
009
AB
2128
06
9 W
00
1320
9 0
000
022
00
0019
9 0
000
003
00
1740
1 0
000
014
12
3066
3 0
001
217
119
6079
5 0
012
113
676
379
195
935
11
plusmn 0
15A
B21
29 1
25
W 0
012
274
00
0002
1 0
000
249
00
0000
3 0
017
405
00
0003
7 1
255
200
00
0080
311
896
055
00
0449
369
817
316
11
353
2plusmn
010
Pla
teau
age
349
9plusmn
023
MSW
D (
n =
5 o
f 8)
186
Tota
l Fus
ion
Age
350
5plusmn
023
AT
01-1
7a s
anid
ine
J =
00
0297
6 plusmn
000
0009
mas
s di
scri
min
atio
n pe
r am
u 1
002
2 plusmn
000
04
AB
2132
00
4 W
00
0055
1 0
000
005
00
0001
4 0
000
006
00
0017
5 0
000
005
00
0362
1 0
000
024
01
8252
2 0
000
076
118
00
456
313
1plusmn
456
AB
2133
00
6 W
00
0019
3 0
000
004
00
0002
6 0
000
003
00
0034
3 0
000
006
00
2579
1 0
000
046
02
1431
6 0
000
110
745
03
447
326
0plusmn
051
AB
2134
01
2 W
00
0018
8 0
000
004
00
0011
6 0
000
007
00
0251
1 0
000
023
02
0468
8 0
000
253
12
8821
1 0
000
967
959
20
568
320
8plusmn
012
AB
2136
01
8 W
00
0050
3 0
000
004
00
0056
8 0
000
012
00
1520
7 0
000
032
12
5179
3 0
000
404
76
2511
3 0
002
510
980
124
678
318
1plusmn
004
AB
2137
02
4 W
00
0056
0 0
000
005
00
0084
3 0
000
018
00
2351
2 0
000
025
19
2193
9 0
000
651
116
3788
5 0
004
597
985
190
700
317
9plusmn
004
AB
2138
02
7 W
00
0036
1 0
000
008
00
0070
7 0
000
010
00
1915
2 0
000
024
15
7872
8 0
000
654
95
5607
9 0
004
091
988
156
686
318
7plusmn
005
AB
2139
03
1 W
00
0036
3 0
000
001
00
0052
2 0
000
008
00
1472
7 0
000
035
12
0293
6 0
000
478
73
0039
4 0
003
784
985
119
709
318
4plusmn
005
AB
2141
03
5 W
00
0031
1 0
000
007
00
0037
7 0
000
008
00
1054
1 0
000
029
08
7899
6 0
000
319
53
5364
2 0
002
077
983
87
716
318
8plusmn
005
AB
2142
04
5 W
00
0032
8 0
000
004
00
0055
3 0
000
015
00
1592
7 0
000
034
13
0785
9 0
000
548
79
4703
7 0
003
239
987
129
726
319
6plusmn
005
AB
2143
05
9 W
00
0028
5 0
000
005
00
0039
4 0
000
012
00
1085
1 0
000
045
08
9161
3 0
000
557
54
3036
7 0
002
402
984
88
696
319
3plusmn
006
AB
2145
08
4 W
00
0016
0 0
000
004
00
0019
6 0
000
007
00
0560
3 0
000
028
04
5183
5 0
000
332
27
6009
9 0
001
984
983
45
706
319
7plusmn
008
AB
2146
13
5 W
00
0016
6 0
000
005
00
0018
3 0
000
004
00
0462
0 0
000
018
03
8294
7 0
000
252
23
5385
3 0
001
397
980
38
647
320
5plusmn
008
Pla
teau
age
318
2plusmn
020
MSW
D (
4 of
12)
279
Tota
l Fus
ion
Age
318
8plusmn
020
aC
orre
cted
for
37A
r an
d 39
Ar
deca
yb
Age
s ca
lcul
ated
rel
ativ
e to
28
34 M
a Ta
ylor
Cre
ek R
hyol
ite
stan
dard
ita
lics
indi
cate
ste
ps o
mit
ted
from
the
plat
eau
age
calc
ulat
ion
see
text
for
deta
ils
Tabl
e 2
40A
r39
Ar
incr
emen
tal-
heat
ing
anal
yses
of a
dula
ria
and
sani
dine
from
Ada
Tep
e
71Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
EocenendashOligocene sedimentary rocks The latteris represented by sandstones unaffected by hy-drothermal alteration which cover the northernpart of the deposit
8 Sr and Pb isotope compositionsof carbonates and pyrite
Sr and Pb isotopes were measured by standardTIMS procedures at the University of GenevaSwitzerland following the methods of Valenza etal (2000) and Chiaradia and Fontboteacute (2002) Srisotope ratios on carbonate and Pb isotope ratiosfrom pyrite at Ada Tepe along with whole rock Srand Pb isotope ratios of the leachate fraction of asample from Synap prospect 2 km west of AdaTepe are presented in Table 3 and Figs 9 and 10The Ada Tepe carbonate is from a late stage an-kerite-dolomite vein taken from a drill-core sam-ple (AT01-22) at 996 m depth The bulk rock(sample Sin2000-28) from Synap is from sericite-adularia alteration from the surface Pyrite fromAda Tepe is from a strongly silicified sample(Km2000-6) Pyrite from Synap is from the samehand sample Sin2000-28 on which the Sr wasmeasured Both samples belong to the early alter-
ation The initial 87Sr86Sr ratio of the whole rockcorrected for 35 Ma is 070809 The pyrite sampleand whole rock leachate show identical 207Pb204Pb (1568) and 208Pb204Pb (3885) ratios andslightly different 206Pb204Pb ratios (1871 in AdaTepe and 1866 in Synap) The Sr and Pb isotopedata are compared with those of local Paleogenevolcanic rocks and dykes and the Rhodope meta-morphic rocks in Figs 9 and 10
9 Discussion
91 Physical environment
Epithermal quartz from the Ada Tepe deposit ispoor in fluid inclusions particularly the early mi-crocrystalline quartz and opal Euhedral late sug-ary quartz is the only phase which contains largerfluid inclusions but with no reliable characteris-tics that may allow to classify them as primary in-clusions For the similar Sleeper deposit USASaunders (1994) suggested that quartz formed bytransformation of poorly ordered silica may ex-clude trapped fluids thus precluding the use ofmicrothermometry to constrain the physicochem-ical conditions of silica and gold deposition
Fig 7 (a) Geode of coarse-crystalline quartz with carbonate infill (third stage) (b) Third stage coarse-crystallinequartz (ccq) and bladed parallel type calcite (c) (c) Late vein (forth stage) composed by pyrite on its margins fol-lowed by dolomite-ankerite (da) (d) Same fracture Dolomite-ankerite forms a halo overlapping quartz-adularia-pyrite alteration
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
61Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
2 Historical background and previous studies
Small adits and large dumps at the eastern part ofthe Ada Tepe hill (Fig 3a) provide tangible evi-dence for the historical mining activity probablyof Thracian and Roman times Regional map-ping of the Krumovgrad area was conducted in1965 (Shabatov et al 1965) and recently be-tween 1995 and 1996 (Sarov et al 1996) by theState exploration Company ldquoGeology and Geo-
physicsrdquo at a 125 000 scale Studies by Goranovand Atanassov (1992) and a PhD thesis byBonev (2002) have clarified the stratigraphicand tectonic relationships of the Krumovgradarea The latter work advocates a detachment-fault model for the formation of the Kessebirmetamorphic dome Limited exploration in thearea of the Ada Tepe deposit was followed by thefirst description of its alteration and mineraliza-tion and its classification as AundashAg-polymetallic
Fig 2 Geological map of Kessebir dome (after Bonev 2002) and location of Ada Tepe deposit and Synap prospect
P Marchev et al62
Fig 3 (a) 3D view of Ada Tepe deposit (b) Cross section of Ada Tepe deposit Major ore bodies (c) Massivetabular ore body (ldquoThe Wallrdquo) above the detachment fault (d) Open space-filling ores along predominantly EndashWoriented listric faults
63Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
occurrence of the adularia-sericite type (Kunovet al 2001)
Since June 2000 the Ada Tepe deposit hasbeen included in the Krumovgrad license areaand is explored by Balkan Mineral and MiningAD Based on the results of regional mapping andsurface sampling BMM conducted two drillingprograms with 145 drill holes using both diamondand reverse circulation drilling techniques for atotal length of 12 440 m A total of 10 218 m ofsurface channel samples were also collected dur-ing 2001ndash2002 Resource calculations by RSGGlobal of Perth Australia show that Ada Tepe isa high-grade AundashAg deposit containing 615 Mt ofore at 46 gt Au for 910 000 ounces of Au using a10 gt cutoff grade
On the basis of initial results from the explora-tion program and the geographical proximity ofthe Ada Tepe deposit to the base metal mineraliza-tion at the Oligocene Zvezdel volcano Crummy(2002) suggested a direct genetic link between thebase and precious metal districts Marchev et al(2003) favoured an Upper Eocene age based onprecise 40Ar39Ar data and a detachment faultingmodel for the origin of the Ada Tepe deposit
3 Geologic setting
31 District geology
Basement metamorphic rocks in the Krumovgradarea build up the elongated Kessebir dome in NndashNE direction (Kozhoukharov et al 1988 Ricou etal 1998 Bonev 2002) (Figs 1 2) Two major tec-tonostratigraphic units (complexes) have beenrecognized on the basis of composition and tec-tonic setting of the metamorphic rocks a Gneiss-migmatite complex and a Variegated Complex(Kozhoukharov et al 1988 Haydoutov et al2001) which correspond to the Continental andMixed units of Ricou et al (1998) respectivelyThe structurally lower Gneiss-migmatite complexcrops out in the core of the Kessebir metamorphicdome It is dominated by igneous protoliths in-cluding metagranites migmatites and migmatizedgneisses overlain by a series of pelitic gneissesand rare amphibolites Eclogites and eclogitic am-phibolites have been described in the Greek partof the Kessebir dome (Mposkos and Krohe2000) RbndashSr ages of 3346 plusmn 34 Ma (Mposkosand Wawrzenitz 1995) from metapegmatites inGreece and RbndashSr (328 plusmn 25 Ma) and UndashPb zir-con ages of 310 plusmn 55 Ma and 319 plusmn 9 Ma (Pey-tcheva et al 1995 1998) from metagranites of theKessebir dome in Bulgaria indicate that theGneiss-migmatite complex is formed of Variscanor older continental basement
The overlaying Variegated complex consists ofa heterogeneous assemblage of pelitic schists para-gneisses amphibolites marbles and ophiolitebodies (Kozhoukharova 1984 Kolcheva and Es-kenazi 1998) Metamorphosed ophiolitic peridot-ites and amphibolitized eclogites are intruded bygabbros gabbronorites plagiogranites and dio-rites UndashPb zircon dating of a gabbro from theneighbouring Biala Reka dome (Fig 1) yields aLate Neoproterozoic age of 572 plusmn 5 Ma for thecore and outer zone recording a Hercynian meta-morphic event at ~300ndash350 Ma (Carrigan et al2003) Volumetrically minor plutonic bodies ofpresumably Upper Cretaceous age intrude theVariegated complex and represent an importantphase of igneous activity in the area (Belmustako-va et al 1995) The rocks are medium to fine-grained light grey two-mica granites of massiveto slightly foliated structure
The rocks of the Variegated complex in theKrumovgrad area are overlain by the Maastrich-tianndashPaleocene syndetachment Shavarovo For-mation (Goranov and Atanasov 1992 see be-low) which is in turn overlain by Upper EocenendashLower Oligocene coal-bearing-sandstone andmarl-limestone formations Lava flows anddomes of the ~35 Ma andesites (Lilov et al1987) of the Iran Tepe volcano are exposednortheast of Krumovgrad (Fig 1) This magmaticactivity was followed by scarce dykes of latitic torhyolitic composition in the northern part of theKessebir dome dated at 3182 plusmn 020 Ma and fi-nally by 26ndash28 Ma old intra-plate basaltic mag-matism in the southern part of the dome(Marchev et al 1997 1998)
32 Deposit geology
The Ada Tepe deposit is hosted by the syndetach-ment MaastrichtianndashPaleocene Shavarovo For-mation overlaying the northeastern closure ofthe Kessebir metamorphic core complex (Fig 2)The contact between poorly consolidated sedi-mentary rocks and underlying metamorphicrocks corresponds to the location of a regionallydeveloped low-angle normal fault named theTockachka detachment fault (TDF) by Bonev(1996) The fault dips 10ndash15deg to the north-north-east It can be traced further southwest for morethan 40 km from Krumovgrad to the Bulgarian-Greek frontier and is well exposed in the areasouthwest of Synap village about 2 km west ofAda Tepe In the latter area the rocks in the hang-ing wall of the TDF consist of metamorphicblocks breccia conglomerates sandstone marlsand argillaceous limestone This unit was first rec-ognized by Atanasov and Goranov (1984) in the
P Marchev et al64
Fig 4 Mineralization of The Wall showing multiple periods of silicification and veining (a) Brecciated early micro-crystalline silica (early stage) with a single gneiss fragment (b) Breccia of the microcrystalline silica (early stage)cemented by calcite (third stage) (c) Subvertical colloform finely banded vein Early stage gray (g) microcrystallinesilica on the margins of the veins followed by the massive microcrystalline (mq) cross-cut by the third stage sugaryquartz and massive and bladed calcite (qc) Late veinlets of dolomite-ankerite (da) cut early vein mineralization(d) Transition of subhorizontal opaline carbonate vein into subvertical step-like vein in the overlying sediments
65Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Krumovgrad area and described as the ShavarovoFormation of the Krumovgrad Group in a laterpaper (Goranov and Atanasov 1992) The totalthickness of the type section of the ShavarovoFormation (~350 m) was measured along the Kal-djic river near the Shavar village Blocks andclasts of breccia and conglomerate are mixtures ofgneiss amphibolite and marble derived primarilyfrom the Variegated complex
4 Structure
The dominant structure in the Ada Tepe prospectis the TDF It is a mapable tectonic contact bestexpressed along the western slope of Ada Tepehill (Fig 3a) In outcrop and drill cores the fault isrecognized as a contact between Paleozoic meta-morphic rocks and MaastrichtianndashPaleocene sed-imentary rocks of the Shavarovo Formation Im-mediately above the detachment fault there is a05 to 20 m thick zone of massive silicification Indrill core the lower limit of the structure ismarked by a 10ndash20 cm-thick layer of tectonic clayGneiss migmatite marble and the amphibolite ofthe metamorphic basement beneath the detach-ment surface are transformed into a cataclasticrock over a thickness of several meters Thesouthwestern slope of the Ada Tepe hill is cut by aNWndashSE-oriented high-angle fault (Fig 2) whichformed a small half graben fill by older Maas-trichtianndashPaleocene syndetachment sedimentaryrocks overlain in the eastern part by younger Pria-bonianndashOligocene sedimentary rocks
Major structures cutting the basement rocks ofthe Ada Tepe deposit are rare although severalEndashW and NndashS-oriented subvertical faults markedby a zone of silicification occur to the south eastand west of the Ada Tepe deposit The longest NndashS-striking zone has been traced for almost 200 mThe EndashW and NndashS faults coincide with the majordirections of the mineralized veins in the sedi-mentary cover and can be interpreted as feederstructures for the mineralizing fluids
5 Mineralization
51 Ore geometry and ore bodies
The Ada Tepe deposit is 600 m along strike and300ndash350 m wide Gold mineralization occurs as(1) a massive tabular body located immediatelyabove the detachment fault (Figs 3b c) and (2)open space-filling within the breccia-conglomer-ate and sandstone along predominantly east-westoriented subvertical listric faults within the hang-
ing wall (Figs 3b d) In cross section the tabularbody dips (10ndash15deg) to the north-northeast whichis consistent with the low angle TDF The orebody is so strongly silicified company geologistsrefer to it as ldquoThe Wallrdquo Detailed observations onThe Wall indicate a complicated sequence ofevents with multiple periods of silicification andveining Silicification began with the deposition ofmassive white to light grey silica above the de-tachment fault partly or totally replacing the orig-inal rocks Original rock textures were destroyedwith the exception of ghosted gneiss fragments(Fig 4a) The latter are rounded with veins ofquartz or carbonate cutting or surrounding theclasts Early microcrystalline silica was commonlyveined by subvertical banded veins or brecciatedby later fault movements and cemented by calcitesugary quartz (Fig 5b) or by pyrite
In the less silicified parts The Wall consists ofnumerous differently oriented veins ranging inwidth from less than 1 cm up to 30 cm (Fig 4c)Subvertical veins which were formed by deposi-tion of colloform silica layers in open space canbe traced from The Wall into the listric faults inthe overlying sedimentary rocks (Fig 4d) On thesurface they form EndashW-trending ridges separatedby argillic zones (Figs 3a b d)
52 Ore and gangue mineralogy andstages of mineralization
The ore mineralogy of the Ada Tepe deposit is sim-ple consisting mainly of electrum and subordinatepyrite with traces of galena and gold-silver tellu-rides Gangue minerals consist of silica polymorphs(microcrystalline fine-grained sugary quartz andopaline silica) various carbonates (calcite dolo-mite ankerite and siderite) and adularia Telluridesinclude hessite (Ag2Te) and petzite (Ag3AuTe2) Allsamples with Au content higher than 1 gt have al-most constant AuAg ratios ~ 3 reflecting the com-position of electrum (76ndash73 wt Au)
Unlike the massive silicification of The Wallbanded veins in and above it provide an excellentframework for identifying the different stages ofmineralization Mineralization in Ada Tepe canbe subdivided into 4 broad generally overlappingstages of quartz and carbonate veins on the basisof cross-cutting relationships changes in mineral-ogy texture and gold grades
The earliest stage is characterized by deposi-tion of microcrystalline to fine-grained grayish towhite massive or banded quartz with rare pyriteand adularia (Figs 5andashd) In some veins silica depo-sition starts with a thin band of almost isotropicopaline (Fig 4 c) followed by thin band of quartzwith rare bladed calcite Breccia texture is typical
P Marchev et al66
for the massive silicification of The Wall Theproducts of the early stage form microfracturefilling in the host rocks near the margins of the
Fig 5 Microphotographs and SEM images of silica and bonanza ore textures (a) Bands of early stage microcrystal-line (mq) and jigsaw quartz (jq) (b) Electrum band (e) deposited on the interface between early microcrystallinequartz (mq) and third stage sugary quartz and radiating bladed calcite (qc) (c) Band of electrum (e) and isotropicopaline Electrum is located on the bottom of the band (d) Third stage coarse crystalline quartz (ccq) cutting theopaline (o) and microcrystalline quartz (mq) which in turn is cut by calcite (c) (e) Subparallel bands of electrum (e)and microcrystalline adularia and silica separated by a calcite vein (c) The arrow shows the vertical direction (f)SEM image of the outlined area
veins or rock fragments in The Wall causing thesilica-adularia-pyrite replacement in them Thegold grade of this stage is unknown
67Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
The economic gold is related to the secondstage of mineralization It starts at the end of themicrocrystalline quartz and the beginning of thecoarser grained (sugary) quartz of the third stagebelow (Fig 5b) Usually it forms black millimeter-scale bands of opaline or microcrystalline chal-cedony-adularia and electrum (Figs 5cndashf) Locallyopaline silica crosscuts the microcrystallinequartz (Figs 5cndashd) of the early stage and in turn iscut by the coarser grained quartz and carbonatesof the third and forth stages (Figs 5dndashe) Petro-graphic examination of the electrum-rich bandsreveals that electrum commonly occurs towardsthe bottom of the opaline or microcrystallinebands (Figs 5c e) Where opaline bands are notpresent electrum precipitates at the boundary offirst and third stages (Fig 5b) The electrum hasirregular forms as the result of crystallization inthe quartz interstices being relatively well-shapedin the coarser-grained quartz crystals The size ofelectrum grains ranges from less than 1 to 20 micromHowever the single crystals form chains reachingup to 650 microm (Figs 5b 6a) Electrum in gold-richbands etched with HF is characterized by botryoi-dal surfaces that appear to have formed by theaggregation of spherical electrum particles (Figs6andashb) as observed in the Sleeper deposit Nevada(Saunders 1990 1994) Electrum in bonanza veinscan occupy 50 vol (Figs 5f 6c) accompanied byrare As-bearing pyrite Occasionally micron orsubmicron size electrum inclusions form zoneswithin the As-bearing pyrite (Figs 6d) Tiny AundashAg tellurides have been observed at the contactsbetween electrum grains and small galena crystals(Fig 6f)
The third stage starts with deposition of sugaryquartz (up to 15 mm large Figs 5d 7a) followedby bands of quartz and bladed calcite (Figs 5b 7b)and finally by massive calcite with small amountof quartz (Fig 5d) Locally calcite fills quartz ge-odes or forms small veins (Fig 7a) Microscopical-ly the late calcite corrodes and replaces quartzcrystals Small amount of adularia and pyrite arealso typical for this stage
The hydrothermal mineralization ended withthe deposition of pinkish ankerite-dolomite andsiderite which was preceded by precipitation ofmassive pyrite in some parts of the deposit (Figs7cndashd)
The mineralization of Ada Tepe exhibits sever-al important spatial and textural features thatprovide insights to the physical environment ofore deposition In its upper part quartz becomesthe predominant gangue mineral whereas car-bonates are subordinate This is particularly obvi-ous in the last stage where in the surface samplesdolomite and ankerite are absent in the geodes
and bladed minerals consist of microcrystallinequartz only Another spatial variation is the di-minishing of banding textures with the decreasein grade of Au mineralization to the north Animportant feature is the absence of bladed car-bonates in the veinlets beneath The Wall in con-trast to the entire extent of the deposit above thedetachment surface
53 Oxidized zone
The uppermost part of the Ada Tepe deposit hasbeen oxidized by supergene processes with thedepth of oxidation being dependent upon inten-sity of faulting Due to extensive silicification TheWall itself is generally not oxidized however a 2to 5 m thick zone of oxidation invariably occursabove The Wall Narrow zones of oxidation occurdown to this zone utilizing high angle listric faultsThese faults and fractures most likely acted asconduits for the surface waters to reach the im-permeable silicified zone forming the oxidizedzone above The Wall
Most of the pyrite in the oxidized zones hasbeen converted into limonite identified asgoethite Kaolinite is widely distributed in thiszone forming locally small veinlets Electrum inthe oxidized zone however shows no evidence ofAu enrichment
6 Alteration
In the poorly mineralized zones hydrothermal al-teration is weak with most of the detrital minerals(quartz muscovite and feldspars) remaining unal-tered Alteration consists of chlorite calcite kaoli-nite and subordinate albite pyrite and ankerite-dolomite It seems that calcite and ankerite-dolo-mite are late however it is difficult to distinguishreplacement calcite from vein calcite Quartzadularia calcite pyrite and dolomite-ankerite-siderite plusmn sericite and clay minerals in variableproportions occur in The Wall and immediateproximity to the subvertical quartz and carbonateveins in the strongly mineralized zones Theyformed through replacement of the original meta-morphic minerals included in the sandstone andconglomerate and are associated with relict de-trital quartz and muscovite This complex mineralassemblage is the result of the evolution of thehydrothermal activity
Hydrothermal alteration of the basementmetamorphic rocks is developed within a haloseveral meters in extent beneath The Wall and ismore pronounced around the subvertical veinsThe alteration assemblage includes quartz adu-
P Marchev et al68
Fig 6 (a) SEM images of electrum dendrite etched with HF (b) Negative forms of quartz removed by HFand spherical colloidal particles (c) Opal-electrum band containing ~ 50 electrum and small amount ofpyrite Dark crystals between electrum are adularia and silica (d) Pyrite with a zone of submicron-size elec-trum (e) Former Py converted to goethite with inclusions of Au (f) AundashAg tellurides between larger elec-trum and galena crystals
69Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
laria illite or sericite pyrite kaolinite and latestage ankerite-dolomite-siderite
Clay minerals are more abundant and betterdeveloped in the alteration close to the surfacewhere they form argillic zones between the EndashW-oriented swarms of veins Kaolinite and quartzpredominate in the argillic zones and illite chlo-rite adularia and carbonate are subordinate ac-companied locally by illite-montmorillonite Partof the shallow-level kaolinite may be supergenebut its association with unoxidized pyrite beneathand within The Wall indicates that a hypogene ori-gin is likely at least for the deeper kaolinite
7 Geochronology
40Ar39Ar ages from adularia and sanidine sam-ples were determined to constrain the timing ofmineralization and volcanic activity in the Kesse-bir dome Sample AT01-2 from which adulariawas extracted for dating is from a drill-hole at725 m depth It represents a quartz-adularia-car-bonate banded vein filled with finely veinedgneiss clasts It is a mixture of completely replaceddetrital K-feldspar and directly deposited adular-ia crystals The rhyolite dyke (sample AT01-17) isemplaced within the core orthogneisses of theKessebir dome located 4 km southwest from AdaTepe (Fig 2) It comprises 2 cm diameter sanidinephenocrysts that were separated for dating plusplagioclase biotite and quartz
40Ar39Ar experiments were conducted at UW-Madison Rare Gas Geochronology LaboratoryMinerals were separated from 100ndash250 micronsieve fractions using standard magnetic densityand handpicking methods Five milligrams of eachmineral were irradiated at Oregon State Univer-sity USA for 12 hours along with 2834 Ma sani-dine from the Taylor Creek rhyolite as the neu-tron fluence monitor Analytical procedures in-cluding mass spectrometry procedural blanks re-actor corrections and estimation of uncertaintiesare given in Singer and Brown (2002) Isotopicmeasurements were made of the gas extracted byincrementally heating of 2ndash3 mg multi-crystal ali-
quots using a defocused CO2 laser beam Resultsof incremental heating experiments along withthe 40Ar39Ar ages of muscovite and biotite fromthe lower plate of the metamorphic basementrocks taken from Bonev et al (accepted) are inTable 1 Incremental heating experiments and agespectra of the sanidine and adularia are presentedin Table 2 and Fig 8 Uncertainties in the agesinclude analytical contributions only at plusmn2
The plateau age of the adularia based on793 of the gas released is 3499 plusmn 023 Ma (Fig8) and is indistinguishable from the total fusionage of 3505 plusmn 023 Ma Sanidine from the rhyolitedyke yielded a plateau age of 3182 plusmn 020 Mabased on 60 percent of the gas released which isindistinguishable from the total fusion age of3188 plusmn 020 Ma As is the case for the adulariathis indicates that argon loss due to weathering oralteration is negligible Moreover the inverse iso-chron ages of 3511 plusmn 037 Ma for the adularaiaand 3191 plusmn 027 Ma for the sanidine are indistin-guishable from the plateau ages and the 40Ar36Arintercept values indicate that there is virtually noexcess argon present
Lavas from the Iran Tepe volcano four kmnortheast of Ada Tepe give KndashAr ages of ~35 Mabut their stratigraphic position above the UpperPriabonianndashLower Oligocene marl-limestone for-mation suggests that they are younger than 34Ma
40Ar39Ar measurements on muscovite and bi-otite (Bonev et al accepted) from the Gneiss-migmatite complex record ages of 3813 plusmn 036and 3773 plusmn 023 Ma respectively (Table 1) Theseages are broadly in agreement with the published40Ar39Ar ages for muscovite (422 plusmn 50 and 361 plusmn50 Ma Lips et al 2000) and muscovite and am-phibole (39 plusmn 1 and 45 plusmn 2 Ma respectively Muka-sa et al 2003) from the Biala Reka metamorphiccore complex Similar ages (39ndash35 Ma) have beenobtained by Peytcheva et al (1992) for the closingof Sr isotope system in the metagranites from theBiala Reka dome
The relative age of the mineralization was de-termined based on its relationship with the hostKrumovgrad group and the overlying Upper
Sample Mineral Weighted Plateau Total Fusion Sourceage (Ma) age (Ma)
AT01-2 adularia 3499 plusmn 023 3505 plusmn 023 this studyAT01-17 sanidine 3182 plusmn 020 3188 plusmn 020 this studyH6 biotite 3773 plusmn 025 3756 plusmn 024 Bonev et al (accepted)H706 muscovite 3813 plusmn 036 3834 plusmn 031 Bonev et al (accepted)
Table 1 Summary of 40Ar39Ar incremental heating experiments on adularia sanidinebiotite and muscovite from Ada Tepe deposit and Kessebir dome
P Marchev et al70
Exp
erim
ent
Las
er p
ower
36A
r37
Ara
38A
r39
Ara
40A
r40
Ar
39A
rK
Ca
Age
plusmn 2
num
ber
(Wat
ts)
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
()
()
(Ma)
b
AT
01-2
adu
lari
a J
= 0
002
987
plusmn 0
0000
09 m
ass
disc
rim
inat
ion
per
amu
10
022
plusmn 0
0004
A
B21
21 0
04
W 0
012
604
00
0003
0 0
000
159
00
0000
5 0
002
772
00
0002
1 0
029
850
00
0007
7 3
871
564
00
0155
74
70
46
132
72
plusmn 3
84A
B21
22 0
10
W 0
009
696
00
0002
2 0
004
566
00
0004
6 0
004
738
00
0002
0 0
239
380
00
0013
1 4
348
793
00
0312
034
92
91
633
85
plusmn 0
38A
B21
23 0
16
W 0
008
804
00
0001
5 0
005
107
00
0003
2 0
006
792
00
0003
0 0
427
709
00
0033
7 5
368
227
00
0278
052
25
32
634
93
plusmn 0
18A
B21
24 0
22
W 0
003
814
00
0001
1 0
000
564
00
0001
0 0
003
949
00
0001
2 0
268
571
00
0011
2 2
865
288
00
0078
961
33
315
034
83
plusmn 0
16A
B21
26 0
30
W 0
008
692
00
0001
1 0
000
261
00
0000
2 0
009
565
00
0002
0 0
650
692
00
0034
7 6
809
601
00
0275
562
78
079
935
01
plusmn 0
11A
B21
27 0
45
W 0
011
765
00
0001
5 0
000
226
00
0000
6 0
017
464
00
0003
5 1
258
986
00
0031
211
697
117
00
0648
770
524
817
70
350
0plusmn
009
AB
2128
06
9 W
00
1320
9 0
000
022
00
0019
9 0
000
003
00
1740
1 0
000
014
12
3066
3 0
001
217
119
6079
5 0
012
113
676
379
195
935
11
plusmn 0
15A
B21
29 1
25
W 0
012
274
00
0002
1 0
000
249
00
0000
3 0
017
405
00
0003
7 1
255
200
00
0080
311
896
055
00
0449
369
817
316
11
353
2plusmn
010
Pla
teau
age
349
9plusmn
023
MSW
D (
n =
5 o
f 8)
186
Tota
l Fus
ion
Age
350
5plusmn
023
AT
01-1
7a s
anid
ine
J =
00
0297
6 plusmn
000
0009
mas
s di
scri
min
atio
n pe
r am
u 1
002
2 plusmn
000
04
AB
2132
00
4 W
00
0055
1 0
000
005
00
0001
4 0
000
006
00
0017
5 0
000
005
00
0362
1 0
000
024
01
8252
2 0
000
076
118
00
456
313
1plusmn
456
AB
2133
00
6 W
00
0019
3 0
000
004
00
0002
6 0
000
003
00
0034
3 0
000
006
00
2579
1 0
000
046
02
1431
6 0
000
110
745
03
447
326
0plusmn
051
AB
2134
01
2 W
00
0018
8 0
000
004
00
0011
6 0
000
007
00
0251
1 0
000
023
02
0468
8 0
000
253
12
8821
1 0
000
967
959
20
568
320
8plusmn
012
AB
2136
01
8 W
00
0050
3 0
000
004
00
0056
8 0
000
012
00
1520
7 0
000
032
12
5179
3 0
000
404
76
2511
3 0
002
510
980
124
678
318
1plusmn
004
AB
2137
02
4 W
00
0056
0 0
000
005
00
0084
3 0
000
018
00
2351
2 0
000
025
19
2193
9 0
000
651
116
3788
5 0
004
597
985
190
700
317
9plusmn
004
AB
2138
02
7 W
00
0036
1 0
000
008
00
0070
7 0
000
010
00
1915
2 0
000
024
15
7872
8 0
000
654
95
5607
9 0
004
091
988
156
686
318
7plusmn
005
AB
2139
03
1 W
00
0036
3 0
000
001
00
0052
2 0
000
008
00
1472
7 0
000
035
12
0293
6 0
000
478
73
0039
4 0
003
784
985
119
709
318
4plusmn
005
AB
2141
03
5 W
00
0031
1 0
000
007
00
0037
7 0
000
008
00
1054
1 0
000
029
08
7899
6 0
000
319
53
5364
2 0
002
077
983
87
716
318
8plusmn
005
AB
2142
04
5 W
00
0032
8 0
000
004
00
0055
3 0
000
015
00
1592
7 0
000
034
13
0785
9 0
000
548
79
4703
7 0
003
239
987
129
726
319
6plusmn
005
AB
2143
05
9 W
00
0028
5 0
000
005
00
0039
4 0
000
012
00
1085
1 0
000
045
08
9161
3 0
000
557
54
3036
7 0
002
402
984
88
696
319
3plusmn
006
AB
2145
08
4 W
00
0016
0 0
000
004
00
0019
6 0
000
007
00
0560
3 0
000
028
04
5183
5 0
000
332
27
6009
9 0
001
984
983
45
706
319
7plusmn
008
AB
2146
13
5 W
00
0016
6 0
000
005
00
0018
3 0
000
004
00
0462
0 0
000
018
03
8294
7 0
000
252
23
5385
3 0
001
397
980
38
647
320
5plusmn
008
Pla
teau
age
318
2plusmn
020
MSW
D (
4 of
12)
279
Tota
l Fus
ion
Age
318
8plusmn
020
aC
orre
cted
for
37A
r an
d 39
Ar
deca
yb
Age
s ca
lcul
ated
rel
ativ
e to
28
34 M
a Ta
ylor
Cre
ek R
hyol
ite
stan
dard
ita
lics
indi
cate
ste
ps o
mit
ted
from
the
plat
eau
age
calc
ulat
ion
see
text
for
deta
ils
Tabl
e 2
40A
r39
Ar
incr
emen
tal-
heat
ing
anal
yses
of a
dula
ria
and
sani
dine
from
Ada
Tep
e
71Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
EocenendashOligocene sedimentary rocks The latteris represented by sandstones unaffected by hy-drothermal alteration which cover the northernpart of the deposit
8 Sr and Pb isotope compositionsof carbonates and pyrite
Sr and Pb isotopes were measured by standardTIMS procedures at the University of GenevaSwitzerland following the methods of Valenza etal (2000) and Chiaradia and Fontboteacute (2002) Srisotope ratios on carbonate and Pb isotope ratiosfrom pyrite at Ada Tepe along with whole rock Srand Pb isotope ratios of the leachate fraction of asample from Synap prospect 2 km west of AdaTepe are presented in Table 3 and Figs 9 and 10The Ada Tepe carbonate is from a late stage an-kerite-dolomite vein taken from a drill-core sam-ple (AT01-22) at 996 m depth The bulk rock(sample Sin2000-28) from Synap is from sericite-adularia alteration from the surface Pyrite fromAda Tepe is from a strongly silicified sample(Km2000-6) Pyrite from Synap is from the samehand sample Sin2000-28 on which the Sr wasmeasured Both samples belong to the early alter-
ation The initial 87Sr86Sr ratio of the whole rockcorrected for 35 Ma is 070809 The pyrite sampleand whole rock leachate show identical 207Pb204Pb (1568) and 208Pb204Pb (3885) ratios andslightly different 206Pb204Pb ratios (1871 in AdaTepe and 1866 in Synap) The Sr and Pb isotopedata are compared with those of local Paleogenevolcanic rocks and dykes and the Rhodope meta-morphic rocks in Figs 9 and 10
9 Discussion
91 Physical environment
Epithermal quartz from the Ada Tepe deposit ispoor in fluid inclusions particularly the early mi-crocrystalline quartz and opal Euhedral late sug-ary quartz is the only phase which contains largerfluid inclusions but with no reliable characteris-tics that may allow to classify them as primary in-clusions For the similar Sleeper deposit USASaunders (1994) suggested that quartz formed bytransformation of poorly ordered silica may ex-clude trapped fluids thus precluding the use ofmicrothermometry to constrain the physicochem-ical conditions of silica and gold deposition
Fig 7 (a) Geode of coarse-crystalline quartz with carbonate infill (third stage) (b) Third stage coarse-crystallinequartz (ccq) and bladed parallel type calcite (c) (c) Late vein (forth stage) composed by pyrite on its margins fol-lowed by dolomite-ankerite (da) (d) Same fracture Dolomite-ankerite forms a halo overlapping quartz-adularia-pyrite alteration
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
P Marchev et al62
Fig 3 (a) 3D view of Ada Tepe deposit (b) Cross section of Ada Tepe deposit Major ore bodies (c) Massivetabular ore body (ldquoThe Wallrdquo) above the detachment fault (d) Open space-filling ores along predominantly EndashWoriented listric faults
63Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
occurrence of the adularia-sericite type (Kunovet al 2001)
Since June 2000 the Ada Tepe deposit hasbeen included in the Krumovgrad license areaand is explored by Balkan Mineral and MiningAD Based on the results of regional mapping andsurface sampling BMM conducted two drillingprograms with 145 drill holes using both diamondand reverse circulation drilling techniques for atotal length of 12 440 m A total of 10 218 m ofsurface channel samples were also collected dur-ing 2001ndash2002 Resource calculations by RSGGlobal of Perth Australia show that Ada Tepe isa high-grade AundashAg deposit containing 615 Mt ofore at 46 gt Au for 910 000 ounces of Au using a10 gt cutoff grade
On the basis of initial results from the explora-tion program and the geographical proximity ofthe Ada Tepe deposit to the base metal mineraliza-tion at the Oligocene Zvezdel volcano Crummy(2002) suggested a direct genetic link between thebase and precious metal districts Marchev et al(2003) favoured an Upper Eocene age based onprecise 40Ar39Ar data and a detachment faultingmodel for the origin of the Ada Tepe deposit
3 Geologic setting
31 District geology
Basement metamorphic rocks in the Krumovgradarea build up the elongated Kessebir dome in NndashNE direction (Kozhoukharov et al 1988 Ricou etal 1998 Bonev 2002) (Figs 1 2) Two major tec-tonostratigraphic units (complexes) have beenrecognized on the basis of composition and tec-tonic setting of the metamorphic rocks a Gneiss-migmatite complex and a Variegated Complex(Kozhoukharov et al 1988 Haydoutov et al2001) which correspond to the Continental andMixed units of Ricou et al (1998) respectivelyThe structurally lower Gneiss-migmatite complexcrops out in the core of the Kessebir metamorphicdome It is dominated by igneous protoliths in-cluding metagranites migmatites and migmatizedgneisses overlain by a series of pelitic gneissesand rare amphibolites Eclogites and eclogitic am-phibolites have been described in the Greek partof the Kessebir dome (Mposkos and Krohe2000) RbndashSr ages of 3346 plusmn 34 Ma (Mposkosand Wawrzenitz 1995) from metapegmatites inGreece and RbndashSr (328 plusmn 25 Ma) and UndashPb zir-con ages of 310 plusmn 55 Ma and 319 plusmn 9 Ma (Pey-tcheva et al 1995 1998) from metagranites of theKessebir dome in Bulgaria indicate that theGneiss-migmatite complex is formed of Variscanor older continental basement
The overlaying Variegated complex consists ofa heterogeneous assemblage of pelitic schists para-gneisses amphibolites marbles and ophiolitebodies (Kozhoukharova 1984 Kolcheva and Es-kenazi 1998) Metamorphosed ophiolitic peridot-ites and amphibolitized eclogites are intruded bygabbros gabbronorites plagiogranites and dio-rites UndashPb zircon dating of a gabbro from theneighbouring Biala Reka dome (Fig 1) yields aLate Neoproterozoic age of 572 plusmn 5 Ma for thecore and outer zone recording a Hercynian meta-morphic event at ~300ndash350 Ma (Carrigan et al2003) Volumetrically minor plutonic bodies ofpresumably Upper Cretaceous age intrude theVariegated complex and represent an importantphase of igneous activity in the area (Belmustako-va et al 1995) The rocks are medium to fine-grained light grey two-mica granites of massiveto slightly foliated structure
The rocks of the Variegated complex in theKrumovgrad area are overlain by the Maastrich-tianndashPaleocene syndetachment Shavarovo For-mation (Goranov and Atanasov 1992 see be-low) which is in turn overlain by Upper EocenendashLower Oligocene coal-bearing-sandstone andmarl-limestone formations Lava flows anddomes of the ~35 Ma andesites (Lilov et al1987) of the Iran Tepe volcano are exposednortheast of Krumovgrad (Fig 1) This magmaticactivity was followed by scarce dykes of latitic torhyolitic composition in the northern part of theKessebir dome dated at 3182 plusmn 020 Ma and fi-nally by 26ndash28 Ma old intra-plate basaltic mag-matism in the southern part of the dome(Marchev et al 1997 1998)
32 Deposit geology
The Ada Tepe deposit is hosted by the syndetach-ment MaastrichtianndashPaleocene Shavarovo For-mation overlaying the northeastern closure ofthe Kessebir metamorphic core complex (Fig 2)The contact between poorly consolidated sedi-mentary rocks and underlying metamorphicrocks corresponds to the location of a regionallydeveloped low-angle normal fault named theTockachka detachment fault (TDF) by Bonev(1996) The fault dips 10ndash15deg to the north-north-east It can be traced further southwest for morethan 40 km from Krumovgrad to the Bulgarian-Greek frontier and is well exposed in the areasouthwest of Synap village about 2 km west ofAda Tepe In the latter area the rocks in the hang-ing wall of the TDF consist of metamorphicblocks breccia conglomerates sandstone marlsand argillaceous limestone This unit was first rec-ognized by Atanasov and Goranov (1984) in the
P Marchev et al64
Fig 4 Mineralization of The Wall showing multiple periods of silicification and veining (a) Brecciated early micro-crystalline silica (early stage) with a single gneiss fragment (b) Breccia of the microcrystalline silica (early stage)cemented by calcite (third stage) (c) Subvertical colloform finely banded vein Early stage gray (g) microcrystallinesilica on the margins of the veins followed by the massive microcrystalline (mq) cross-cut by the third stage sugaryquartz and massive and bladed calcite (qc) Late veinlets of dolomite-ankerite (da) cut early vein mineralization(d) Transition of subhorizontal opaline carbonate vein into subvertical step-like vein in the overlying sediments
65Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Krumovgrad area and described as the ShavarovoFormation of the Krumovgrad Group in a laterpaper (Goranov and Atanasov 1992) The totalthickness of the type section of the ShavarovoFormation (~350 m) was measured along the Kal-djic river near the Shavar village Blocks andclasts of breccia and conglomerate are mixtures ofgneiss amphibolite and marble derived primarilyfrom the Variegated complex
4 Structure
The dominant structure in the Ada Tepe prospectis the TDF It is a mapable tectonic contact bestexpressed along the western slope of Ada Tepehill (Fig 3a) In outcrop and drill cores the fault isrecognized as a contact between Paleozoic meta-morphic rocks and MaastrichtianndashPaleocene sed-imentary rocks of the Shavarovo Formation Im-mediately above the detachment fault there is a05 to 20 m thick zone of massive silicification Indrill core the lower limit of the structure ismarked by a 10ndash20 cm-thick layer of tectonic clayGneiss migmatite marble and the amphibolite ofthe metamorphic basement beneath the detach-ment surface are transformed into a cataclasticrock over a thickness of several meters Thesouthwestern slope of the Ada Tepe hill is cut by aNWndashSE-oriented high-angle fault (Fig 2) whichformed a small half graben fill by older Maas-trichtianndashPaleocene syndetachment sedimentaryrocks overlain in the eastern part by younger Pria-bonianndashOligocene sedimentary rocks
Major structures cutting the basement rocks ofthe Ada Tepe deposit are rare although severalEndashW and NndashS-oriented subvertical faults markedby a zone of silicification occur to the south eastand west of the Ada Tepe deposit The longest NndashS-striking zone has been traced for almost 200 mThe EndashW and NndashS faults coincide with the majordirections of the mineralized veins in the sedi-mentary cover and can be interpreted as feederstructures for the mineralizing fluids
5 Mineralization
51 Ore geometry and ore bodies
The Ada Tepe deposit is 600 m along strike and300ndash350 m wide Gold mineralization occurs as(1) a massive tabular body located immediatelyabove the detachment fault (Figs 3b c) and (2)open space-filling within the breccia-conglomer-ate and sandstone along predominantly east-westoriented subvertical listric faults within the hang-
ing wall (Figs 3b d) In cross section the tabularbody dips (10ndash15deg) to the north-northeast whichis consistent with the low angle TDF The orebody is so strongly silicified company geologistsrefer to it as ldquoThe Wallrdquo Detailed observations onThe Wall indicate a complicated sequence ofevents with multiple periods of silicification andveining Silicification began with the deposition ofmassive white to light grey silica above the de-tachment fault partly or totally replacing the orig-inal rocks Original rock textures were destroyedwith the exception of ghosted gneiss fragments(Fig 4a) The latter are rounded with veins ofquartz or carbonate cutting or surrounding theclasts Early microcrystalline silica was commonlyveined by subvertical banded veins or brecciatedby later fault movements and cemented by calcitesugary quartz (Fig 5b) or by pyrite
In the less silicified parts The Wall consists ofnumerous differently oriented veins ranging inwidth from less than 1 cm up to 30 cm (Fig 4c)Subvertical veins which were formed by deposi-tion of colloform silica layers in open space canbe traced from The Wall into the listric faults inthe overlying sedimentary rocks (Fig 4d) On thesurface they form EndashW-trending ridges separatedby argillic zones (Figs 3a b d)
52 Ore and gangue mineralogy andstages of mineralization
The ore mineralogy of the Ada Tepe deposit is sim-ple consisting mainly of electrum and subordinatepyrite with traces of galena and gold-silver tellu-rides Gangue minerals consist of silica polymorphs(microcrystalline fine-grained sugary quartz andopaline silica) various carbonates (calcite dolo-mite ankerite and siderite) and adularia Telluridesinclude hessite (Ag2Te) and petzite (Ag3AuTe2) Allsamples with Au content higher than 1 gt have al-most constant AuAg ratios ~ 3 reflecting the com-position of electrum (76ndash73 wt Au)
Unlike the massive silicification of The Wallbanded veins in and above it provide an excellentframework for identifying the different stages ofmineralization Mineralization in Ada Tepe canbe subdivided into 4 broad generally overlappingstages of quartz and carbonate veins on the basisof cross-cutting relationships changes in mineral-ogy texture and gold grades
The earliest stage is characterized by deposi-tion of microcrystalline to fine-grained grayish towhite massive or banded quartz with rare pyriteand adularia (Figs 5andashd) In some veins silica depo-sition starts with a thin band of almost isotropicopaline (Fig 4 c) followed by thin band of quartzwith rare bladed calcite Breccia texture is typical
P Marchev et al66
for the massive silicification of The Wall Theproducts of the early stage form microfracturefilling in the host rocks near the margins of the
Fig 5 Microphotographs and SEM images of silica and bonanza ore textures (a) Bands of early stage microcrystal-line (mq) and jigsaw quartz (jq) (b) Electrum band (e) deposited on the interface between early microcrystallinequartz (mq) and third stage sugary quartz and radiating bladed calcite (qc) (c) Band of electrum (e) and isotropicopaline Electrum is located on the bottom of the band (d) Third stage coarse crystalline quartz (ccq) cutting theopaline (o) and microcrystalline quartz (mq) which in turn is cut by calcite (c) (e) Subparallel bands of electrum (e)and microcrystalline adularia and silica separated by a calcite vein (c) The arrow shows the vertical direction (f)SEM image of the outlined area
veins or rock fragments in The Wall causing thesilica-adularia-pyrite replacement in them Thegold grade of this stage is unknown
67Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
The economic gold is related to the secondstage of mineralization It starts at the end of themicrocrystalline quartz and the beginning of thecoarser grained (sugary) quartz of the third stagebelow (Fig 5b) Usually it forms black millimeter-scale bands of opaline or microcrystalline chal-cedony-adularia and electrum (Figs 5cndashf) Locallyopaline silica crosscuts the microcrystallinequartz (Figs 5cndashd) of the early stage and in turn iscut by the coarser grained quartz and carbonatesof the third and forth stages (Figs 5dndashe) Petro-graphic examination of the electrum-rich bandsreveals that electrum commonly occurs towardsthe bottom of the opaline or microcrystallinebands (Figs 5c e) Where opaline bands are notpresent electrum precipitates at the boundary offirst and third stages (Fig 5b) The electrum hasirregular forms as the result of crystallization inthe quartz interstices being relatively well-shapedin the coarser-grained quartz crystals The size ofelectrum grains ranges from less than 1 to 20 micromHowever the single crystals form chains reachingup to 650 microm (Figs 5b 6a) Electrum in gold-richbands etched with HF is characterized by botryoi-dal surfaces that appear to have formed by theaggregation of spherical electrum particles (Figs6andashb) as observed in the Sleeper deposit Nevada(Saunders 1990 1994) Electrum in bonanza veinscan occupy 50 vol (Figs 5f 6c) accompanied byrare As-bearing pyrite Occasionally micron orsubmicron size electrum inclusions form zoneswithin the As-bearing pyrite (Figs 6d) Tiny AundashAg tellurides have been observed at the contactsbetween electrum grains and small galena crystals(Fig 6f)
The third stage starts with deposition of sugaryquartz (up to 15 mm large Figs 5d 7a) followedby bands of quartz and bladed calcite (Figs 5b 7b)and finally by massive calcite with small amountof quartz (Fig 5d) Locally calcite fills quartz ge-odes or forms small veins (Fig 7a) Microscopical-ly the late calcite corrodes and replaces quartzcrystals Small amount of adularia and pyrite arealso typical for this stage
The hydrothermal mineralization ended withthe deposition of pinkish ankerite-dolomite andsiderite which was preceded by precipitation ofmassive pyrite in some parts of the deposit (Figs7cndashd)
The mineralization of Ada Tepe exhibits sever-al important spatial and textural features thatprovide insights to the physical environment ofore deposition In its upper part quartz becomesthe predominant gangue mineral whereas car-bonates are subordinate This is particularly obvi-ous in the last stage where in the surface samplesdolomite and ankerite are absent in the geodes
and bladed minerals consist of microcrystallinequartz only Another spatial variation is the di-minishing of banding textures with the decreasein grade of Au mineralization to the north Animportant feature is the absence of bladed car-bonates in the veinlets beneath The Wall in con-trast to the entire extent of the deposit above thedetachment surface
53 Oxidized zone
The uppermost part of the Ada Tepe deposit hasbeen oxidized by supergene processes with thedepth of oxidation being dependent upon inten-sity of faulting Due to extensive silicification TheWall itself is generally not oxidized however a 2to 5 m thick zone of oxidation invariably occursabove The Wall Narrow zones of oxidation occurdown to this zone utilizing high angle listric faultsThese faults and fractures most likely acted asconduits for the surface waters to reach the im-permeable silicified zone forming the oxidizedzone above The Wall
Most of the pyrite in the oxidized zones hasbeen converted into limonite identified asgoethite Kaolinite is widely distributed in thiszone forming locally small veinlets Electrum inthe oxidized zone however shows no evidence ofAu enrichment
6 Alteration
In the poorly mineralized zones hydrothermal al-teration is weak with most of the detrital minerals(quartz muscovite and feldspars) remaining unal-tered Alteration consists of chlorite calcite kaoli-nite and subordinate albite pyrite and ankerite-dolomite It seems that calcite and ankerite-dolo-mite are late however it is difficult to distinguishreplacement calcite from vein calcite Quartzadularia calcite pyrite and dolomite-ankerite-siderite plusmn sericite and clay minerals in variableproportions occur in The Wall and immediateproximity to the subvertical quartz and carbonateveins in the strongly mineralized zones Theyformed through replacement of the original meta-morphic minerals included in the sandstone andconglomerate and are associated with relict de-trital quartz and muscovite This complex mineralassemblage is the result of the evolution of thehydrothermal activity
Hydrothermal alteration of the basementmetamorphic rocks is developed within a haloseveral meters in extent beneath The Wall and ismore pronounced around the subvertical veinsThe alteration assemblage includes quartz adu-
P Marchev et al68
Fig 6 (a) SEM images of electrum dendrite etched with HF (b) Negative forms of quartz removed by HFand spherical colloidal particles (c) Opal-electrum band containing ~ 50 electrum and small amount ofpyrite Dark crystals between electrum are adularia and silica (d) Pyrite with a zone of submicron-size elec-trum (e) Former Py converted to goethite with inclusions of Au (f) AundashAg tellurides between larger elec-trum and galena crystals
69Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
laria illite or sericite pyrite kaolinite and latestage ankerite-dolomite-siderite
Clay minerals are more abundant and betterdeveloped in the alteration close to the surfacewhere they form argillic zones between the EndashW-oriented swarms of veins Kaolinite and quartzpredominate in the argillic zones and illite chlo-rite adularia and carbonate are subordinate ac-companied locally by illite-montmorillonite Partof the shallow-level kaolinite may be supergenebut its association with unoxidized pyrite beneathand within The Wall indicates that a hypogene ori-gin is likely at least for the deeper kaolinite
7 Geochronology
40Ar39Ar ages from adularia and sanidine sam-ples were determined to constrain the timing ofmineralization and volcanic activity in the Kesse-bir dome Sample AT01-2 from which adulariawas extracted for dating is from a drill-hole at725 m depth It represents a quartz-adularia-car-bonate banded vein filled with finely veinedgneiss clasts It is a mixture of completely replaceddetrital K-feldspar and directly deposited adular-ia crystals The rhyolite dyke (sample AT01-17) isemplaced within the core orthogneisses of theKessebir dome located 4 km southwest from AdaTepe (Fig 2) It comprises 2 cm diameter sanidinephenocrysts that were separated for dating plusplagioclase biotite and quartz
40Ar39Ar experiments were conducted at UW-Madison Rare Gas Geochronology LaboratoryMinerals were separated from 100ndash250 micronsieve fractions using standard magnetic densityand handpicking methods Five milligrams of eachmineral were irradiated at Oregon State Univer-sity USA for 12 hours along with 2834 Ma sani-dine from the Taylor Creek rhyolite as the neu-tron fluence monitor Analytical procedures in-cluding mass spectrometry procedural blanks re-actor corrections and estimation of uncertaintiesare given in Singer and Brown (2002) Isotopicmeasurements were made of the gas extracted byincrementally heating of 2ndash3 mg multi-crystal ali-
quots using a defocused CO2 laser beam Resultsof incremental heating experiments along withthe 40Ar39Ar ages of muscovite and biotite fromthe lower plate of the metamorphic basementrocks taken from Bonev et al (accepted) are inTable 1 Incremental heating experiments and agespectra of the sanidine and adularia are presentedin Table 2 and Fig 8 Uncertainties in the agesinclude analytical contributions only at plusmn2
The plateau age of the adularia based on793 of the gas released is 3499 plusmn 023 Ma (Fig8) and is indistinguishable from the total fusionage of 3505 plusmn 023 Ma Sanidine from the rhyolitedyke yielded a plateau age of 3182 plusmn 020 Mabased on 60 percent of the gas released which isindistinguishable from the total fusion age of3188 plusmn 020 Ma As is the case for the adulariathis indicates that argon loss due to weathering oralteration is negligible Moreover the inverse iso-chron ages of 3511 plusmn 037 Ma for the adularaiaand 3191 plusmn 027 Ma for the sanidine are indistin-guishable from the plateau ages and the 40Ar36Arintercept values indicate that there is virtually noexcess argon present
Lavas from the Iran Tepe volcano four kmnortheast of Ada Tepe give KndashAr ages of ~35 Mabut their stratigraphic position above the UpperPriabonianndashLower Oligocene marl-limestone for-mation suggests that they are younger than 34Ma
40Ar39Ar measurements on muscovite and bi-otite (Bonev et al accepted) from the Gneiss-migmatite complex record ages of 3813 plusmn 036and 3773 plusmn 023 Ma respectively (Table 1) Theseages are broadly in agreement with the published40Ar39Ar ages for muscovite (422 plusmn 50 and 361 plusmn50 Ma Lips et al 2000) and muscovite and am-phibole (39 plusmn 1 and 45 plusmn 2 Ma respectively Muka-sa et al 2003) from the Biala Reka metamorphiccore complex Similar ages (39ndash35 Ma) have beenobtained by Peytcheva et al (1992) for the closingof Sr isotope system in the metagranites from theBiala Reka dome
The relative age of the mineralization was de-termined based on its relationship with the hostKrumovgrad group and the overlying Upper
Sample Mineral Weighted Plateau Total Fusion Sourceage (Ma) age (Ma)
AT01-2 adularia 3499 plusmn 023 3505 plusmn 023 this studyAT01-17 sanidine 3182 plusmn 020 3188 plusmn 020 this studyH6 biotite 3773 plusmn 025 3756 plusmn 024 Bonev et al (accepted)H706 muscovite 3813 plusmn 036 3834 plusmn 031 Bonev et al (accepted)
Table 1 Summary of 40Ar39Ar incremental heating experiments on adularia sanidinebiotite and muscovite from Ada Tepe deposit and Kessebir dome
P Marchev et al70
Exp
erim
ent
Las
er p
ower
36A
r37
Ara
38A
r39
Ara
40A
r40
Ar
39A
rK
Ca
Age
plusmn 2
num
ber
(Wat
ts)
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
()
()
(Ma)
b
AT
01-2
adu
lari
a J
= 0
002
987
plusmn 0
0000
09 m
ass
disc
rim
inat
ion
per
amu
10
022
plusmn 0
0004
A
B21
21 0
04
W 0
012
604
00
0003
0 0
000
159
00
0000
5 0
002
772
00
0002
1 0
029
850
00
0007
7 3
871
564
00
0155
74
70
46
132
72
plusmn 3
84A
B21
22 0
10
W 0
009
696
00
0002
2 0
004
566
00
0004
6 0
004
738
00
0002
0 0
239
380
00
0013
1 4
348
793
00
0312
034
92
91
633
85
plusmn 0
38A
B21
23 0
16
W 0
008
804
00
0001
5 0
005
107
00
0003
2 0
006
792
00
0003
0 0
427
709
00
0033
7 5
368
227
00
0278
052
25
32
634
93
plusmn 0
18A
B21
24 0
22
W 0
003
814
00
0001
1 0
000
564
00
0001
0 0
003
949
00
0001
2 0
268
571
00
0011
2 2
865
288
00
0078
961
33
315
034
83
plusmn 0
16A
B21
26 0
30
W 0
008
692
00
0001
1 0
000
261
00
0000
2 0
009
565
00
0002
0 0
650
692
00
0034
7 6
809
601
00
0275
562
78
079
935
01
plusmn 0
11A
B21
27 0
45
W 0
011
765
00
0001
5 0
000
226
00
0000
6 0
017
464
00
0003
5 1
258
986
00
0031
211
697
117
00
0648
770
524
817
70
350
0plusmn
009
AB
2128
06
9 W
00
1320
9 0
000
022
00
0019
9 0
000
003
00
1740
1 0
000
014
12
3066
3 0
001
217
119
6079
5 0
012
113
676
379
195
935
11
plusmn 0
15A
B21
29 1
25
W 0
012
274
00
0002
1 0
000
249
00
0000
3 0
017
405
00
0003
7 1
255
200
00
0080
311
896
055
00
0449
369
817
316
11
353
2plusmn
010
Pla
teau
age
349
9plusmn
023
MSW
D (
n =
5 o
f 8)
186
Tota
l Fus
ion
Age
350
5plusmn
023
AT
01-1
7a s
anid
ine
J =
00
0297
6 plusmn
000
0009
mas
s di
scri
min
atio
n pe
r am
u 1
002
2 plusmn
000
04
AB
2132
00
4 W
00
0055
1 0
000
005
00
0001
4 0
000
006
00
0017
5 0
000
005
00
0362
1 0
000
024
01
8252
2 0
000
076
118
00
456
313
1plusmn
456
AB
2133
00
6 W
00
0019
3 0
000
004
00
0002
6 0
000
003
00
0034
3 0
000
006
00
2579
1 0
000
046
02
1431
6 0
000
110
745
03
447
326
0plusmn
051
AB
2134
01
2 W
00
0018
8 0
000
004
00
0011
6 0
000
007
00
0251
1 0
000
023
02
0468
8 0
000
253
12
8821
1 0
000
967
959
20
568
320
8plusmn
012
AB
2136
01
8 W
00
0050
3 0
000
004
00
0056
8 0
000
012
00
1520
7 0
000
032
12
5179
3 0
000
404
76
2511
3 0
002
510
980
124
678
318
1plusmn
004
AB
2137
02
4 W
00
0056
0 0
000
005
00
0084
3 0
000
018
00
2351
2 0
000
025
19
2193
9 0
000
651
116
3788
5 0
004
597
985
190
700
317
9plusmn
004
AB
2138
02
7 W
00
0036
1 0
000
008
00
0070
7 0
000
010
00
1915
2 0
000
024
15
7872
8 0
000
654
95
5607
9 0
004
091
988
156
686
318
7plusmn
005
AB
2139
03
1 W
00
0036
3 0
000
001
00
0052
2 0
000
008
00
1472
7 0
000
035
12
0293
6 0
000
478
73
0039
4 0
003
784
985
119
709
318
4plusmn
005
AB
2141
03
5 W
00
0031
1 0
000
007
00
0037
7 0
000
008
00
1054
1 0
000
029
08
7899
6 0
000
319
53
5364
2 0
002
077
983
87
716
318
8plusmn
005
AB
2142
04
5 W
00
0032
8 0
000
004
00
0055
3 0
000
015
00
1592
7 0
000
034
13
0785
9 0
000
548
79
4703
7 0
003
239
987
129
726
319
6plusmn
005
AB
2143
05
9 W
00
0028
5 0
000
005
00
0039
4 0
000
012
00
1085
1 0
000
045
08
9161
3 0
000
557
54
3036
7 0
002
402
984
88
696
319
3plusmn
006
AB
2145
08
4 W
00
0016
0 0
000
004
00
0019
6 0
000
007
00
0560
3 0
000
028
04
5183
5 0
000
332
27
6009
9 0
001
984
983
45
706
319
7plusmn
008
AB
2146
13
5 W
00
0016
6 0
000
005
00
0018
3 0
000
004
00
0462
0 0
000
018
03
8294
7 0
000
252
23
5385
3 0
001
397
980
38
647
320
5plusmn
008
Pla
teau
age
318
2plusmn
020
MSW
D (
4 of
12)
279
Tota
l Fus
ion
Age
318
8plusmn
020
aC
orre
cted
for
37A
r an
d 39
Ar
deca
yb
Age
s ca
lcul
ated
rel
ativ
e to
28
34 M
a Ta
ylor
Cre
ek R
hyol
ite
stan
dard
ita
lics
indi
cate
ste
ps o
mit
ted
from
the
plat
eau
age
calc
ulat
ion
see
text
for
deta
ils
Tabl
e 2
40A
r39
Ar
incr
emen
tal-
heat
ing
anal
yses
of a
dula
ria
and
sani
dine
from
Ada
Tep
e
71Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
EocenendashOligocene sedimentary rocks The latteris represented by sandstones unaffected by hy-drothermal alteration which cover the northernpart of the deposit
8 Sr and Pb isotope compositionsof carbonates and pyrite
Sr and Pb isotopes were measured by standardTIMS procedures at the University of GenevaSwitzerland following the methods of Valenza etal (2000) and Chiaradia and Fontboteacute (2002) Srisotope ratios on carbonate and Pb isotope ratiosfrom pyrite at Ada Tepe along with whole rock Srand Pb isotope ratios of the leachate fraction of asample from Synap prospect 2 km west of AdaTepe are presented in Table 3 and Figs 9 and 10The Ada Tepe carbonate is from a late stage an-kerite-dolomite vein taken from a drill-core sam-ple (AT01-22) at 996 m depth The bulk rock(sample Sin2000-28) from Synap is from sericite-adularia alteration from the surface Pyrite fromAda Tepe is from a strongly silicified sample(Km2000-6) Pyrite from Synap is from the samehand sample Sin2000-28 on which the Sr wasmeasured Both samples belong to the early alter-
ation The initial 87Sr86Sr ratio of the whole rockcorrected for 35 Ma is 070809 The pyrite sampleand whole rock leachate show identical 207Pb204Pb (1568) and 208Pb204Pb (3885) ratios andslightly different 206Pb204Pb ratios (1871 in AdaTepe and 1866 in Synap) The Sr and Pb isotopedata are compared with those of local Paleogenevolcanic rocks and dykes and the Rhodope meta-morphic rocks in Figs 9 and 10
9 Discussion
91 Physical environment
Epithermal quartz from the Ada Tepe deposit ispoor in fluid inclusions particularly the early mi-crocrystalline quartz and opal Euhedral late sug-ary quartz is the only phase which contains largerfluid inclusions but with no reliable characteris-tics that may allow to classify them as primary in-clusions For the similar Sleeper deposit USASaunders (1994) suggested that quartz formed bytransformation of poorly ordered silica may ex-clude trapped fluids thus precluding the use ofmicrothermometry to constrain the physicochem-ical conditions of silica and gold deposition
Fig 7 (a) Geode of coarse-crystalline quartz with carbonate infill (third stage) (b) Third stage coarse-crystallinequartz (ccq) and bladed parallel type calcite (c) (c) Late vein (forth stage) composed by pyrite on its margins fol-lowed by dolomite-ankerite (da) (d) Same fracture Dolomite-ankerite forms a halo overlapping quartz-adularia-pyrite alteration
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
63Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
occurrence of the adularia-sericite type (Kunovet al 2001)
Since June 2000 the Ada Tepe deposit hasbeen included in the Krumovgrad license areaand is explored by Balkan Mineral and MiningAD Based on the results of regional mapping andsurface sampling BMM conducted two drillingprograms with 145 drill holes using both diamondand reverse circulation drilling techniques for atotal length of 12 440 m A total of 10 218 m ofsurface channel samples were also collected dur-ing 2001ndash2002 Resource calculations by RSGGlobal of Perth Australia show that Ada Tepe isa high-grade AundashAg deposit containing 615 Mt ofore at 46 gt Au for 910 000 ounces of Au using a10 gt cutoff grade
On the basis of initial results from the explora-tion program and the geographical proximity ofthe Ada Tepe deposit to the base metal mineraliza-tion at the Oligocene Zvezdel volcano Crummy(2002) suggested a direct genetic link between thebase and precious metal districts Marchev et al(2003) favoured an Upper Eocene age based onprecise 40Ar39Ar data and a detachment faultingmodel for the origin of the Ada Tepe deposit
3 Geologic setting
31 District geology
Basement metamorphic rocks in the Krumovgradarea build up the elongated Kessebir dome in NndashNE direction (Kozhoukharov et al 1988 Ricou etal 1998 Bonev 2002) (Figs 1 2) Two major tec-tonostratigraphic units (complexes) have beenrecognized on the basis of composition and tec-tonic setting of the metamorphic rocks a Gneiss-migmatite complex and a Variegated Complex(Kozhoukharov et al 1988 Haydoutov et al2001) which correspond to the Continental andMixed units of Ricou et al (1998) respectivelyThe structurally lower Gneiss-migmatite complexcrops out in the core of the Kessebir metamorphicdome It is dominated by igneous protoliths in-cluding metagranites migmatites and migmatizedgneisses overlain by a series of pelitic gneissesand rare amphibolites Eclogites and eclogitic am-phibolites have been described in the Greek partof the Kessebir dome (Mposkos and Krohe2000) RbndashSr ages of 3346 plusmn 34 Ma (Mposkosand Wawrzenitz 1995) from metapegmatites inGreece and RbndashSr (328 plusmn 25 Ma) and UndashPb zir-con ages of 310 plusmn 55 Ma and 319 plusmn 9 Ma (Pey-tcheva et al 1995 1998) from metagranites of theKessebir dome in Bulgaria indicate that theGneiss-migmatite complex is formed of Variscanor older continental basement
The overlaying Variegated complex consists ofa heterogeneous assemblage of pelitic schists para-gneisses amphibolites marbles and ophiolitebodies (Kozhoukharova 1984 Kolcheva and Es-kenazi 1998) Metamorphosed ophiolitic peridot-ites and amphibolitized eclogites are intruded bygabbros gabbronorites plagiogranites and dio-rites UndashPb zircon dating of a gabbro from theneighbouring Biala Reka dome (Fig 1) yields aLate Neoproterozoic age of 572 plusmn 5 Ma for thecore and outer zone recording a Hercynian meta-morphic event at ~300ndash350 Ma (Carrigan et al2003) Volumetrically minor plutonic bodies ofpresumably Upper Cretaceous age intrude theVariegated complex and represent an importantphase of igneous activity in the area (Belmustako-va et al 1995) The rocks are medium to fine-grained light grey two-mica granites of massiveto slightly foliated structure
The rocks of the Variegated complex in theKrumovgrad area are overlain by the Maastrich-tianndashPaleocene syndetachment Shavarovo For-mation (Goranov and Atanasov 1992 see be-low) which is in turn overlain by Upper EocenendashLower Oligocene coal-bearing-sandstone andmarl-limestone formations Lava flows anddomes of the ~35 Ma andesites (Lilov et al1987) of the Iran Tepe volcano are exposednortheast of Krumovgrad (Fig 1) This magmaticactivity was followed by scarce dykes of latitic torhyolitic composition in the northern part of theKessebir dome dated at 3182 plusmn 020 Ma and fi-nally by 26ndash28 Ma old intra-plate basaltic mag-matism in the southern part of the dome(Marchev et al 1997 1998)
32 Deposit geology
The Ada Tepe deposit is hosted by the syndetach-ment MaastrichtianndashPaleocene Shavarovo For-mation overlaying the northeastern closure ofthe Kessebir metamorphic core complex (Fig 2)The contact between poorly consolidated sedi-mentary rocks and underlying metamorphicrocks corresponds to the location of a regionallydeveloped low-angle normal fault named theTockachka detachment fault (TDF) by Bonev(1996) The fault dips 10ndash15deg to the north-north-east It can be traced further southwest for morethan 40 km from Krumovgrad to the Bulgarian-Greek frontier and is well exposed in the areasouthwest of Synap village about 2 km west ofAda Tepe In the latter area the rocks in the hang-ing wall of the TDF consist of metamorphicblocks breccia conglomerates sandstone marlsand argillaceous limestone This unit was first rec-ognized by Atanasov and Goranov (1984) in the
P Marchev et al64
Fig 4 Mineralization of The Wall showing multiple periods of silicification and veining (a) Brecciated early micro-crystalline silica (early stage) with a single gneiss fragment (b) Breccia of the microcrystalline silica (early stage)cemented by calcite (third stage) (c) Subvertical colloform finely banded vein Early stage gray (g) microcrystallinesilica on the margins of the veins followed by the massive microcrystalline (mq) cross-cut by the third stage sugaryquartz and massive and bladed calcite (qc) Late veinlets of dolomite-ankerite (da) cut early vein mineralization(d) Transition of subhorizontal opaline carbonate vein into subvertical step-like vein in the overlying sediments
65Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Krumovgrad area and described as the ShavarovoFormation of the Krumovgrad Group in a laterpaper (Goranov and Atanasov 1992) The totalthickness of the type section of the ShavarovoFormation (~350 m) was measured along the Kal-djic river near the Shavar village Blocks andclasts of breccia and conglomerate are mixtures ofgneiss amphibolite and marble derived primarilyfrom the Variegated complex
4 Structure
The dominant structure in the Ada Tepe prospectis the TDF It is a mapable tectonic contact bestexpressed along the western slope of Ada Tepehill (Fig 3a) In outcrop and drill cores the fault isrecognized as a contact between Paleozoic meta-morphic rocks and MaastrichtianndashPaleocene sed-imentary rocks of the Shavarovo Formation Im-mediately above the detachment fault there is a05 to 20 m thick zone of massive silicification Indrill core the lower limit of the structure ismarked by a 10ndash20 cm-thick layer of tectonic clayGneiss migmatite marble and the amphibolite ofthe metamorphic basement beneath the detach-ment surface are transformed into a cataclasticrock over a thickness of several meters Thesouthwestern slope of the Ada Tepe hill is cut by aNWndashSE-oriented high-angle fault (Fig 2) whichformed a small half graben fill by older Maas-trichtianndashPaleocene syndetachment sedimentaryrocks overlain in the eastern part by younger Pria-bonianndashOligocene sedimentary rocks
Major structures cutting the basement rocks ofthe Ada Tepe deposit are rare although severalEndashW and NndashS-oriented subvertical faults markedby a zone of silicification occur to the south eastand west of the Ada Tepe deposit The longest NndashS-striking zone has been traced for almost 200 mThe EndashW and NndashS faults coincide with the majordirections of the mineralized veins in the sedi-mentary cover and can be interpreted as feederstructures for the mineralizing fluids
5 Mineralization
51 Ore geometry and ore bodies
The Ada Tepe deposit is 600 m along strike and300ndash350 m wide Gold mineralization occurs as(1) a massive tabular body located immediatelyabove the detachment fault (Figs 3b c) and (2)open space-filling within the breccia-conglomer-ate and sandstone along predominantly east-westoriented subvertical listric faults within the hang-
ing wall (Figs 3b d) In cross section the tabularbody dips (10ndash15deg) to the north-northeast whichis consistent with the low angle TDF The orebody is so strongly silicified company geologistsrefer to it as ldquoThe Wallrdquo Detailed observations onThe Wall indicate a complicated sequence ofevents with multiple periods of silicification andveining Silicification began with the deposition ofmassive white to light grey silica above the de-tachment fault partly or totally replacing the orig-inal rocks Original rock textures were destroyedwith the exception of ghosted gneiss fragments(Fig 4a) The latter are rounded with veins ofquartz or carbonate cutting or surrounding theclasts Early microcrystalline silica was commonlyveined by subvertical banded veins or brecciatedby later fault movements and cemented by calcitesugary quartz (Fig 5b) or by pyrite
In the less silicified parts The Wall consists ofnumerous differently oriented veins ranging inwidth from less than 1 cm up to 30 cm (Fig 4c)Subvertical veins which were formed by deposi-tion of colloform silica layers in open space canbe traced from The Wall into the listric faults inthe overlying sedimentary rocks (Fig 4d) On thesurface they form EndashW-trending ridges separatedby argillic zones (Figs 3a b d)
52 Ore and gangue mineralogy andstages of mineralization
The ore mineralogy of the Ada Tepe deposit is sim-ple consisting mainly of electrum and subordinatepyrite with traces of galena and gold-silver tellu-rides Gangue minerals consist of silica polymorphs(microcrystalline fine-grained sugary quartz andopaline silica) various carbonates (calcite dolo-mite ankerite and siderite) and adularia Telluridesinclude hessite (Ag2Te) and petzite (Ag3AuTe2) Allsamples with Au content higher than 1 gt have al-most constant AuAg ratios ~ 3 reflecting the com-position of electrum (76ndash73 wt Au)
Unlike the massive silicification of The Wallbanded veins in and above it provide an excellentframework for identifying the different stages ofmineralization Mineralization in Ada Tepe canbe subdivided into 4 broad generally overlappingstages of quartz and carbonate veins on the basisof cross-cutting relationships changes in mineral-ogy texture and gold grades
The earliest stage is characterized by deposi-tion of microcrystalline to fine-grained grayish towhite massive or banded quartz with rare pyriteand adularia (Figs 5andashd) In some veins silica depo-sition starts with a thin band of almost isotropicopaline (Fig 4 c) followed by thin band of quartzwith rare bladed calcite Breccia texture is typical
P Marchev et al66
for the massive silicification of The Wall Theproducts of the early stage form microfracturefilling in the host rocks near the margins of the
Fig 5 Microphotographs and SEM images of silica and bonanza ore textures (a) Bands of early stage microcrystal-line (mq) and jigsaw quartz (jq) (b) Electrum band (e) deposited on the interface between early microcrystallinequartz (mq) and third stage sugary quartz and radiating bladed calcite (qc) (c) Band of electrum (e) and isotropicopaline Electrum is located on the bottom of the band (d) Third stage coarse crystalline quartz (ccq) cutting theopaline (o) and microcrystalline quartz (mq) which in turn is cut by calcite (c) (e) Subparallel bands of electrum (e)and microcrystalline adularia and silica separated by a calcite vein (c) The arrow shows the vertical direction (f)SEM image of the outlined area
veins or rock fragments in The Wall causing thesilica-adularia-pyrite replacement in them Thegold grade of this stage is unknown
67Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
The economic gold is related to the secondstage of mineralization It starts at the end of themicrocrystalline quartz and the beginning of thecoarser grained (sugary) quartz of the third stagebelow (Fig 5b) Usually it forms black millimeter-scale bands of opaline or microcrystalline chal-cedony-adularia and electrum (Figs 5cndashf) Locallyopaline silica crosscuts the microcrystallinequartz (Figs 5cndashd) of the early stage and in turn iscut by the coarser grained quartz and carbonatesof the third and forth stages (Figs 5dndashe) Petro-graphic examination of the electrum-rich bandsreveals that electrum commonly occurs towardsthe bottom of the opaline or microcrystallinebands (Figs 5c e) Where opaline bands are notpresent electrum precipitates at the boundary offirst and third stages (Fig 5b) The electrum hasirregular forms as the result of crystallization inthe quartz interstices being relatively well-shapedin the coarser-grained quartz crystals The size ofelectrum grains ranges from less than 1 to 20 micromHowever the single crystals form chains reachingup to 650 microm (Figs 5b 6a) Electrum in gold-richbands etched with HF is characterized by botryoi-dal surfaces that appear to have formed by theaggregation of spherical electrum particles (Figs6andashb) as observed in the Sleeper deposit Nevada(Saunders 1990 1994) Electrum in bonanza veinscan occupy 50 vol (Figs 5f 6c) accompanied byrare As-bearing pyrite Occasionally micron orsubmicron size electrum inclusions form zoneswithin the As-bearing pyrite (Figs 6d) Tiny AundashAg tellurides have been observed at the contactsbetween electrum grains and small galena crystals(Fig 6f)
The third stage starts with deposition of sugaryquartz (up to 15 mm large Figs 5d 7a) followedby bands of quartz and bladed calcite (Figs 5b 7b)and finally by massive calcite with small amountof quartz (Fig 5d) Locally calcite fills quartz ge-odes or forms small veins (Fig 7a) Microscopical-ly the late calcite corrodes and replaces quartzcrystals Small amount of adularia and pyrite arealso typical for this stage
The hydrothermal mineralization ended withthe deposition of pinkish ankerite-dolomite andsiderite which was preceded by precipitation ofmassive pyrite in some parts of the deposit (Figs7cndashd)
The mineralization of Ada Tepe exhibits sever-al important spatial and textural features thatprovide insights to the physical environment ofore deposition In its upper part quartz becomesthe predominant gangue mineral whereas car-bonates are subordinate This is particularly obvi-ous in the last stage where in the surface samplesdolomite and ankerite are absent in the geodes
and bladed minerals consist of microcrystallinequartz only Another spatial variation is the di-minishing of banding textures with the decreasein grade of Au mineralization to the north Animportant feature is the absence of bladed car-bonates in the veinlets beneath The Wall in con-trast to the entire extent of the deposit above thedetachment surface
53 Oxidized zone
The uppermost part of the Ada Tepe deposit hasbeen oxidized by supergene processes with thedepth of oxidation being dependent upon inten-sity of faulting Due to extensive silicification TheWall itself is generally not oxidized however a 2to 5 m thick zone of oxidation invariably occursabove The Wall Narrow zones of oxidation occurdown to this zone utilizing high angle listric faultsThese faults and fractures most likely acted asconduits for the surface waters to reach the im-permeable silicified zone forming the oxidizedzone above The Wall
Most of the pyrite in the oxidized zones hasbeen converted into limonite identified asgoethite Kaolinite is widely distributed in thiszone forming locally small veinlets Electrum inthe oxidized zone however shows no evidence ofAu enrichment
6 Alteration
In the poorly mineralized zones hydrothermal al-teration is weak with most of the detrital minerals(quartz muscovite and feldspars) remaining unal-tered Alteration consists of chlorite calcite kaoli-nite and subordinate albite pyrite and ankerite-dolomite It seems that calcite and ankerite-dolo-mite are late however it is difficult to distinguishreplacement calcite from vein calcite Quartzadularia calcite pyrite and dolomite-ankerite-siderite plusmn sericite and clay minerals in variableproportions occur in The Wall and immediateproximity to the subvertical quartz and carbonateveins in the strongly mineralized zones Theyformed through replacement of the original meta-morphic minerals included in the sandstone andconglomerate and are associated with relict de-trital quartz and muscovite This complex mineralassemblage is the result of the evolution of thehydrothermal activity
Hydrothermal alteration of the basementmetamorphic rocks is developed within a haloseveral meters in extent beneath The Wall and ismore pronounced around the subvertical veinsThe alteration assemblage includes quartz adu-
P Marchev et al68
Fig 6 (a) SEM images of electrum dendrite etched with HF (b) Negative forms of quartz removed by HFand spherical colloidal particles (c) Opal-electrum band containing ~ 50 electrum and small amount ofpyrite Dark crystals between electrum are adularia and silica (d) Pyrite with a zone of submicron-size elec-trum (e) Former Py converted to goethite with inclusions of Au (f) AundashAg tellurides between larger elec-trum and galena crystals
69Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
laria illite or sericite pyrite kaolinite and latestage ankerite-dolomite-siderite
Clay minerals are more abundant and betterdeveloped in the alteration close to the surfacewhere they form argillic zones between the EndashW-oriented swarms of veins Kaolinite and quartzpredominate in the argillic zones and illite chlo-rite adularia and carbonate are subordinate ac-companied locally by illite-montmorillonite Partof the shallow-level kaolinite may be supergenebut its association with unoxidized pyrite beneathand within The Wall indicates that a hypogene ori-gin is likely at least for the deeper kaolinite
7 Geochronology
40Ar39Ar ages from adularia and sanidine sam-ples were determined to constrain the timing ofmineralization and volcanic activity in the Kesse-bir dome Sample AT01-2 from which adulariawas extracted for dating is from a drill-hole at725 m depth It represents a quartz-adularia-car-bonate banded vein filled with finely veinedgneiss clasts It is a mixture of completely replaceddetrital K-feldspar and directly deposited adular-ia crystals The rhyolite dyke (sample AT01-17) isemplaced within the core orthogneisses of theKessebir dome located 4 km southwest from AdaTepe (Fig 2) It comprises 2 cm diameter sanidinephenocrysts that were separated for dating plusplagioclase biotite and quartz
40Ar39Ar experiments were conducted at UW-Madison Rare Gas Geochronology LaboratoryMinerals were separated from 100ndash250 micronsieve fractions using standard magnetic densityand handpicking methods Five milligrams of eachmineral were irradiated at Oregon State Univer-sity USA for 12 hours along with 2834 Ma sani-dine from the Taylor Creek rhyolite as the neu-tron fluence monitor Analytical procedures in-cluding mass spectrometry procedural blanks re-actor corrections and estimation of uncertaintiesare given in Singer and Brown (2002) Isotopicmeasurements were made of the gas extracted byincrementally heating of 2ndash3 mg multi-crystal ali-
quots using a defocused CO2 laser beam Resultsof incremental heating experiments along withthe 40Ar39Ar ages of muscovite and biotite fromthe lower plate of the metamorphic basementrocks taken from Bonev et al (accepted) are inTable 1 Incremental heating experiments and agespectra of the sanidine and adularia are presentedin Table 2 and Fig 8 Uncertainties in the agesinclude analytical contributions only at plusmn2
The plateau age of the adularia based on793 of the gas released is 3499 plusmn 023 Ma (Fig8) and is indistinguishable from the total fusionage of 3505 plusmn 023 Ma Sanidine from the rhyolitedyke yielded a plateau age of 3182 plusmn 020 Mabased on 60 percent of the gas released which isindistinguishable from the total fusion age of3188 plusmn 020 Ma As is the case for the adulariathis indicates that argon loss due to weathering oralteration is negligible Moreover the inverse iso-chron ages of 3511 plusmn 037 Ma for the adularaiaand 3191 plusmn 027 Ma for the sanidine are indistin-guishable from the plateau ages and the 40Ar36Arintercept values indicate that there is virtually noexcess argon present
Lavas from the Iran Tepe volcano four kmnortheast of Ada Tepe give KndashAr ages of ~35 Mabut their stratigraphic position above the UpperPriabonianndashLower Oligocene marl-limestone for-mation suggests that they are younger than 34Ma
40Ar39Ar measurements on muscovite and bi-otite (Bonev et al accepted) from the Gneiss-migmatite complex record ages of 3813 plusmn 036and 3773 plusmn 023 Ma respectively (Table 1) Theseages are broadly in agreement with the published40Ar39Ar ages for muscovite (422 plusmn 50 and 361 plusmn50 Ma Lips et al 2000) and muscovite and am-phibole (39 plusmn 1 and 45 plusmn 2 Ma respectively Muka-sa et al 2003) from the Biala Reka metamorphiccore complex Similar ages (39ndash35 Ma) have beenobtained by Peytcheva et al (1992) for the closingof Sr isotope system in the metagranites from theBiala Reka dome
The relative age of the mineralization was de-termined based on its relationship with the hostKrumovgrad group and the overlying Upper
Sample Mineral Weighted Plateau Total Fusion Sourceage (Ma) age (Ma)
AT01-2 adularia 3499 plusmn 023 3505 plusmn 023 this studyAT01-17 sanidine 3182 plusmn 020 3188 plusmn 020 this studyH6 biotite 3773 plusmn 025 3756 plusmn 024 Bonev et al (accepted)H706 muscovite 3813 plusmn 036 3834 plusmn 031 Bonev et al (accepted)
Table 1 Summary of 40Ar39Ar incremental heating experiments on adularia sanidinebiotite and muscovite from Ada Tepe deposit and Kessebir dome
P Marchev et al70
Exp
erim
ent
Las
er p
ower
36A
r37
Ara
38A
r39
Ara
40A
r40
Ar
39A
rK
Ca
Age
plusmn 2
num
ber
(Wat
ts)
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
()
()
(Ma)
b
AT
01-2
adu
lari
a J
= 0
002
987
plusmn 0
0000
09 m
ass
disc
rim
inat
ion
per
amu
10
022
plusmn 0
0004
A
B21
21 0
04
W 0
012
604
00
0003
0 0
000
159
00
0000
5 0
002
772
00
0002
1 0
029
850
00
0007
7 3
871
564
00
0155
74
70
46
132
72
plusmn 3
84A
B21
22 0
10
W 0
009
696
00
0002
2 0
004
566
00
0004
6 0
004
738
00
0002
0 0
239
380
00
0013
1 4
348
793
00
0312
034
92
91
633
85
plusmn 0
38A
B21
23 0
16
W 0
008
804
00
0001
5 0
005
107
00
0003
2 0
006
792
00
0003
0 0
427
709
00
0033
7 5
368
227
00
0278
052
25
32
634
93
plusmn 0
18A
B21
24 0
22
W 0
003
814
00
0001
1 0
000
564
00
0001
0 0
003
949
00
0001
2 0
268
571
00
0011
2 2
865
288
00
0078
961
33
315
034
83
plusmn 0
16A
B21
26 0
30
W 0
008
692
00
0001
1 0
000
261
00
0000
2 0
009
565
00
0002
0 0
650
692
00
0034
7 6
809
601
00
0275
562
78
079
935
01
plusmn 0
11A
B21
27 0
45
W 0
011
765
00
0001
5 0
000
226
00
0000
6 0
017
464
00
0003
5 1
258
986
00
0031
211
697
117
00
0648
770
524
817
70
350
0plusmn
009
AB
2128
06
9 W
00
1320
9 0
000
022
00
0019
9 0
000
003
00
1740
1 0
000
014
12
3066
3 0
001
217
119
6079
5 0
012
113
676
379
195
935
11
plusmn 0
15A
B21
29 1
25
W 0
012
274
00
0002
1 0
000
249
00
0000
3 0
017
405
00
0003
7 1
255
200
00
0080
311
896
055
00
0449
369
817
316
11
353
2plusmn
010
Pla
teau
age
349
9plusmn
023
MSW
D (
n =
5 o
f 8)
186
Tota
l Fus
ion
Age
350
5plusmn
023
AT
01-1
7a s
anid
ine
J =
00
0297
6 plusmn
000
0009
mas
s di
scri
min
atio
n pe
r am
u 1
002
2 plusmn
000
04
AB
2132
00
4 W
00
0055
1 0
000
005
00
0001
4 0
000
006
00
0017
5 0
000
005
00
0362
1 0
000
024
01
8252
2 0
000
076
118
00
456
313
1plusmn
456
AB
2133
00
6 W
00
0019
3 0
000
004
00
0002
6 0
000
003
00
0034
3 0
000
006
00
2579
1 0
000
046
02
1431
6 0
000
110
745
03
447
326
0plusmn
051
AB
2134
01
2 W
00
0018
8 0
000
004
00
0011
6 0
000
007
00
0251
1 0
000
023
02
0468
8 0
000
253
12
8821
1 0
000
967
959
20
568
320
8plusmn
012
AB
2136
01
8 W
00
0050
3 0
000
004
00
0056
8 0
000
012
00
1520
7 0
000
032
12
5179
3 0
000
404
76
2511
3 0
002
510
980
124
678
318
1plusmn
004
AB
2137
02
4 W
00
0056
0 0
000
005
00
0084
3 0
000
018
00
2351
2 0
000
025
19
2193
9 0
000
651
116
3788
5 0
004
597
985
190
700
317
9plusmn
004
AB
2138
02
7 W
00
0036
1 0
000
008
00
0070
7 0
000
010
00
1915
2 0
000
024
15
7872
8 0
000
654
95
5607
9 0
004
091
988
156
686
318
7plusmn
005
AB
2139
03
1 W
00
0036
3 0
000
001
00
0052
2 0
000
008
00
1472
7 0
000
035
12
0293
6 0
000
478
73
0039
4 0
003
784
985
119
709
318
4plusmn
005
AB
2141
03
5 W
00
0031
1 0
000
007
00
0037
7 0
000
008
00
1054
1 0
000
029
08
7899
6 0
000
319
53
5364
2 0
002
077
983
87
716
318
8plusmn
005
AB
2142
04
5 W
00
0032
8 0
000
004
00
0055
3 0
000
015
00
1592
7 0
000
034
13
0785
9 0
000
548
79
4703
7 0
003
239
987
129
726
319
6plusmn
005
AB
2143
05
9 W
00
0028
5 0
000
005
00
0039
4 0
000
012
00
1085
1 0
000
045
08
9161
3 0
000
557
54
3036
7 0
002
402
984
88
696
319
3plusmn
006
AB
2145
08
4 W
00
0016
0 0
000
004
00
0019
6 0
000
007
00
0560
3 0
000
028
04
5183
5 0
000
332
27
6009
9 0
001
984
983
45
706
319
7plusmn
008
AB
2146
13
5 W
00
0016
6 0
000
005
00
0018
3 0
000
004
00
0462
0 0
000
018
03
8294
7 0
000
252
23
5385
3 0
001
397
980
38
647
320
5plusmn
008
Pla
teau
age
318
2plusmn
020
MSW
D (
4 of
12)
279
Tota
l Fus
ion
Age
318
8plusmn
020
aC
orre
cted
for
37A
r an
d 39
Ar
deca
yb
Age
s ca
lcul
ated
rel
ativ
e to
28
34 M
a Ta
ylor
Cre
ek R
hyol
ite
stan
dard
ita
lics
indi
cate
ste
ps o
mit
ted
from
the
plat
eau
age
calc
ulat
ion
see
text
for
deta
ils
Tabl
e 2
40A
r39
Ar
incr
emen
tal-
heat
ing
anal
yses
of a
dula
ria
and
sani
dine
from
Ada
Tep
e
71Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
EocenendashOligocene sedimentary rocks The latteris represented by sandstones unaffected by hy-drothermal alteration which cover the northernpart of the deposit
8 Sr and Pb isotope compositionsof carbonates and pyrite
Sr and Pb isotopes were measured by standardTIMS procedures at the University of GenevaSwitzerland following the methods of Valenza etal (2000) and Chiaradia and Fontboteacute (2002) Srisotope ratios on carbonate and Pb isotope ratiosfrom pyrite at Ada Tepe along with whole rock Srand Pb isotope ratios of the leachate fraction of asample from Synap prospect 2 km west of AdaTepe are presented in Table 3 and Figs 9 and 10The Ada Tepe carbonate is from a late stage an-kerite-dolomite vein taken from a drill-core sam-ple (AT01-22) at 996 m depth The bulk rock(sample Sin2000-28) from Synap is from sericite-adularia alteration from the surface Pyrite fromAda Tepe is from a strongly silicified sample(Km2000-6) Pyrite from Synap is from the samehand sample Sin2000-28 on which the Sr wasmeasured Both samples belong to the early alter-
ation The initial 87Sr86Sr ratio of the whole rockcorrected for 35 Ma is 070809 The pyrite sampleand whole rock leachate show identical 207Pb204Pb (1568) and 208Pb204Pb (3885) ratios andslightly different 206Pb204Pb ratios (1871 in AdaTepe and 1866 in Synap) The Sr and Pb isotopedata are compared with those of local Paleogenevolcanic rocks and dykes and the Rhodope meta-morphic rocks in Figs 9 and 10
9 Discussion
91 Physical environment
Epithermal quartz from the Ada Tepe deposit ispoor in fluid inclusions particularly the early mi-crocrystalline quartz and opal Euhedral late sug-ary quartz is the only phase which contains largerfluid inclusions but with no reliable characteris-tics that may allow to classify them as primary in-clusions For the similar Sleeper deposit USASaunders (1994) suggested that quartz formed bytransformation of poorly ordered silica may ex-clude trapped fluids thus precluding the use ofmicrothermometry to constrain the physicochem-ical conditions of silica and gold deposition
Fig 7 (a) Geode of coarse-crystalline quartz with carbonate infill (third stage) (b) Third stage coarse-crystallinequartz (ccq) and bladed parallel type calcite (c) (c) Late vein (forth stage) composed by pyrite on its margins fol-lowed by dolomite-ankerite (da) (d) Same fracture Dolomite-ankerite forms a halo overlapping quartz-adularia-pyrite alteration
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
P Marchev et al64
Fig 4 Mineralization of The Wall showing multiple periods of silicification and veining (a) Brecciated early micro-crystalline silica (early stage) with a single gneiss fragment (b) Breccia of the microcrystalline silica (early stage)cemented by calcite (third stage) (c) Subvertical colloform finely banded vein Early stage gray (g) microcrystallinesilica on the margins of the veins followed by the massive microcrystalline (mq) cross-cut by the third stage sugaryquartz and massive and bladed calcite (qc) Late veinlets of dolomite-ankerite (da) cut early vein mineralization(d) Transition of subhorizontal opaline carbonate vein into subvertical step-like vein in the overlying sediments
65Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Krumovgrad area and described as the ShavarovoFormation of the Krumovgrad Group in a laterpaper (Goranov and Atanasov 1992) The totalthickness of the type section of the ShavarovoFormation (~350 m) was measured along the Kal-djic river near the Shavar village Blocks andclasts of breccia and conglomerate are mixtures ofgneiss amphibolite and marble derived primarilyfrom the Variegated complex
4 Structure
The dominant structure in the Ada Tepe prospectis the TDF It is a mapable tectonic contact bestexpressed along the western slope of Ada Tepehill (Fig 3a) In outcrop and drill cores the fault isrecognized as a contact between Paleozoic meta-morphic rocks and MaastrichtianndashPaleocene sed-imentary rocks of the Shavarovo Formation Im-mediately above the detachment fault there is a05 to 20 m thick zone of massive silicification Indrill core the lower limit of the structure ismarked by a 10ndash20 cm-thick layer of tectonic clayGneiss migmatite marble and the amphibolite ofthe metamorphic basement beneath the detach-ment surface are transformed into a cataclasticrock over a thickness of several meters Thesouthwestern slope of the Ada Tepe hill is cut by aNWndashSE-oriented high-angle fault (Fig 2) whichformed a small half graben fill by older Maas-trichtianndashPaleocene syndetachment sedimentaryrocks overlain in the eastern part by younger Pria-bonianndashOligocene sedimentary rocks
Major structures cutting the basement rocks ofthe Ada Tepe deposit are rare although severalEndashW and NndashS-oriented subvertical faults markedby a zone of silicification occur to the south eastand west of the Ada Tepe deposit The longest NndashS-striking zone has been traced for almost 200 mThe EndashW and NndashS faults coincide with the majordirections of the mineralized veins in the sedi-mentary cover and can be interpreted as feederstructures for the mineralizing fluids
5 Mineralization
51 Ore geometry and ore bodies
The Ada Tepe deposit is 600 m along strike and300ndash350 m wide Gold mineralization occurs as(1) a massive tabular body located immediatelyabove the detachment fault (Figs 3b c) and (2)open space-filling within the breccia-conglomer-ate and sandstone along predominantly east-westoriented subvertical listric faults within the hang-
ing wall (Figs 3b d) In cross section the tabularbody dips (10ndash15deg) to the north-northeast whichis consistent with the low angle TDF The orebody is so strongly silicified company geologistsrefer to it as ldquoThe Wallrdquo Detailed observations onThe Wall indicate a complicated sequence ofevents with multiple periods of silicification andveining Silicification began with the deposition ofmassive white to light grey silica above the de-tachment fault partly or totally replacing the orig-inal rocks Original rock textures were destroyedwith the exception of ghosted gneiss fragments(Fig 4a) The latter are rounded with veins ofquartz or carbonate cutting or surrounding theclasts Early microcrystalline silica was commonlyveined by subvertical banded veins or brecciatedby later fault movements and cemented by calcitesugary quartz (Fig 5b) or by pyrite
In the less silicified parts The Wall consists ofnumerous differently oriented veins ranging inwidth from less than 1 cm up to 30 cm (Fig 4c)Subvertical veins which were formed by deposi-tion of colloform silica layers in open space canbe traced from The Wall into the listric faults inthe overlying sedimentary rocks (Fig 4d) On thesurface they form EndashW-trending ridges separatedby argillic zones (Figs 3a b d)
52 Ore and gangue mineralogy andstages of mineralization
The ore mineralogy of the Ada Tepe deposit is sim-ple consisting mainly of electrum and subordinatepyrite with traces of galena and gold-silver tellu-rides Gangue minerals consist of silica polymorphs(microcrystalline fine-grained sugary quartz andopaline silica) various carbonates (calcite dolo-mite ankerite and siderite) and adularia Telluridesinclude hessite (Ag2Te) and petzite (Ag3AuTe2) Allsamples with Au content higher than 1 gt have al-most constant AuAg ratios ~ 3 reflecting the com-position of electrum (76ndash73 wt Au)
Unlike the massive silicification of The Wallbanded veins in and above it provide an excellentframework for identifying the different stages ofmineralization Mineralization in Ada Tepe canbe subdivided into 4 broad generally overlappingstages of quartz and carbonate veins on the basisof cross-cutting relationships changes in mineral-ogy texture and gold grades
The earliest stage is characterized by deposi-tion of microcrystalline to fine-grained grayish towhite massive or banded quartz with rare pyriteand adularia (Figs 5andashd) In some veins silica depo-sition starts with a thin band of almost isotropicopaline (Fig 4 c) followed by thin band of quartzwith rare bladed calcite Breccia texture is typical
P Marchev et al66
for the massive silicification of The Wall Theproducts of the early stage form microfracturefilling in the host rocks near the margins of the
Fig 5 Microphotographs and SEM images of silica and bonanza ore textures (a) Bands of early stage microcrystal-line (mq) and jigsaw quartz (jq) (b) Electrum band (e) deposited on the interface between early microcrystallinequartz (mq) and third stage sugary quartz and radiating bladed calcite (qc) (c) Band of electrum (e) and isotropicopaline Electrum is located on the bottom of the band (d) Third stage coarse crystalline quartz (ccq) cutting theopaline (o) and microcrystalline quartz (mq) which in turn is cut by calcite (c) (e) Subparallel bands of electrum (e)and microcrystalline adularia and silica separated by a calcite vein (c) The arrow shows the vertical direction (f)SEM image of the outlined area
veins or rock fragments in The Wall causing thesilica-adularia-pyrite replacement in them Thegold grade of this stage is unknown
67Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
The economic gold is related to the secondstage of mineralization It starts at the end of themicrocrystalline quartz and the beginning of thecoarser grained (sugary) quartz of the third stagebelow (Fig 5b) Usually it forms black millimeter-scale bands of opaline or microcrystalline chal-cedony-adularia and electrum (Figs 5cndashf) Locallyopaline silica crosscuts the microcrystallinequartz (Figs 5cndashd) of the early stage and in turn iscut by the coarser grained quartz and carbonatesof the third and forth stages (Figs 5dndashe) Petro-graphic examination of the electrum-rich bandsreveals that electrum commonly occurs towardsthe bottom of the opaline or microcrystallinebands (Figs 5c e) Where opaline bands are notpresent electrum precipitates at the boundary offirst and third stages (Fig 5b) The electrum hasirregular forms as the result of crystallization inthe quartz interstices being relatively well-shapedin the coarser-grained quartz crystals The size ofelectrum grains ranges from less than 1 to 20 micromHowever the single crystals form chains reachingup to 650 microm (Figs 5b 6a) Electrum in gold-richbands etched with HF is characterized by botryoi-dal surfaces that appear to have formed by theaggregation of spherical electrum particles (Figs6andashb) as observed in the Sleeper deposit Nevada(Saunders 1990 1994) Electrum in bonanza veinscan occupy 50 vol (Figs 5f 6c) accompanied byrare As-bearing pyrite Occasionally micron orsubmicron size electrum inclusions form zoneswithin the As-bearing pyrite (Figs 6d) Tiny AundashAg tellurides have been observed at the contactsbetween electrum grains and small galena crystals(Fig 6f)
The third stage starts with deposition of sugaryquartz (up to 15 mm large Figs 5d 7a) followedby bands of quartz and bladed calcite (Figs 5b 7b)and finally by massive calcite with small amountof quartz (Fig 5d) Locally calcite fills quartz ge-odes or forms small veins (Fig 7a) Microscopical-ly the late calcite corrodes and replaces quartzcrystals Small amount of adularia and pyrite arealso typical for this stage
The hydrothermal mineralization ended withthe deposition of pinkish ankerite-dolomite andsiderite which was preceded by precipitation ofmassive pyrite in some parts of the deposit (Figs7cndashd)
The mineralization of Ada Tepe exhibits sever-al important spatial and textural features thatprovide insights to the physical environment ofore deposition In its upper part quartz becomesthe predominant gangue mineral whereas car-bonates are subordinate This is particularly obvi-ous in the last stage where in the surface samplesdolomite and ankerite are absent in the geodes
and bladed minerals consist of microcrystallinequartz only Another spatial variation is the di-minishing of banding textures with the decreasein grade of Au mineralization to the north Animportant feature is the absence of bladed car-bonates in the veinlets beneath The Wall in con-trast to the entire extent of the deposit above thedetachment surface
53 Oxidized zone
The uppermost part of the Ada Tepe deposit hasbeen oxidized by supergene processes with thedepth of oxidation being dependent upon inten-sity of faulting Due to extensive silicification TheWall itself is generally not oxidized however a 2to 5 m thick zone of oxidation invariably occursabove The Wall Narrow zones of oxidation occurdown to this zone utilizing high angle listric faultsThese faults and fractures most likely acted asconduits for the surface waters to reach the im-permeable silicified zone forming the oxidizedzone above The Wall
Most of the pyrite in the oxidized zones hasbeen converted into limonite identified asgoethite Kaolinite is widely distributed in thiszone forming locally small veinlets Electrum inthe oxidized zone however shows no evidence ofAu enrichment
6 Alteration
In the poorly mineralized zones hydrothermal al-teration is weak with most of the detrital minerals(quartz muscovite and feldspars) remaining unal-tered Alteration consists of chlorite calcite kaoli-nite and subordinate albite pyrite and ankerite-dolomite It seems that calcite and ankerite-dolo-mite are late however it is difficult to distinguishreplacement calcite from vein calcite Quartzadularia calcite pyrite and dolomite-ankerite-siderite plusmn sericite and clay minerals in variableproportions occur in The Wall and immediateproximity to the subvertical quartz and carbonateveins in the strongly mineralized zones Theyformed through replacement of the original meta-morphic minerals included in the sandstone andconglomerate and are associated with relict de-trital quartz and muscovite This complex mineralassemblage is the result of the evolution of thehydrothermal activity
Hydrothermal alteration of the basementmetamorphic rocks is developed within a haloseveral meters in extent beneath The Wall and ismore pronounced around the subvertical veinsThe alteration assemblage includes quartz adu-
P Marchev et al68
Fig 6 (a) SEM images of electrum dendrite etched with HF (b) Negative forms of quartz removed by HFand spherical colloidal particles (c) Opal-electrum band containing ~ 50 electrum and small amount ofpyrite Dark crystals between electrum are adularia and silica (d) Pyrite with a zone of submicron-size elec-trum (e) Former Py converted to goethite with inclusions of Au (f) AundashAg tellurides between larger elec-trum and galena crystals
69Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
laria illite or sericite pyrite kaolinite and latestage ankerite-dolomite-siderite
Clay minerals are more abundant and betterdeveloped in the alteration close to the surfacewhere they form argillic zones between the EndashW-oriented swarms of veins Kaolinite and quartzpredominate in the argillic zones and illite chlo-rite adularia and carbonate are subordinate ac-companied locally by illite-montmorillonite Partof the shallow-level kaolinite may be supergenebut its association with unoxidized pyrite beneathand within The Wall indicates that a hypogene ori-gin is likely at least for the deeper kaolinite
7 Geochronology
40Ar39Ar ages from adularia and sanidine sam-ples were determined to constrain the timing ofmineralization and volcanic activity in the Kesse-bir dome Sample AT01-2 from which adulariawas extracted for dating is from a drill-hole at725 m depth It represents a quartz-adularia-car-bonate banded vein filled with finely veinedgneiss clasts It is a mixture of completely replaceddetrital K-feldspar and directly deposited adular-ia crystals The rhyolite dyke (sample AT01-17) isemplaced within the core orthogneisses of theKessebir dome located 4 km southwest from AdaTepe (Fig 2) It comprises 2 cm diameter sanidinephenocrysts that were separated for dating plusplagioclase biotite and quartz
40Ar39Ar experiments were conducted at UW-Madison Rare Gas Geochronology LaboratoryMinerals were separated from 100ndash250 micronsieve fractions using standard magnetic densityand handpicking methods Five milligrams of eachmineral were irradiated at Oregon State Univer-sity USA for 12 hours along with 2834 Ma sani-dine from the Taylor Creek rhyolite as the neu-tron fluence monitor Analytical procedures in-cluding mass spectrometry procedural blanks re-actor corrections and estimation of uncertaintiesare given in Singer and Brown (2002) Isotopicmeasurements were made of the gas extracted byincrementally heating of 2ndash3 mg multi-crystal ali-
quots using a defocused CO2 laser beam Resultsof incremental heating experiments along withthe 40Ar39Ar ages of muscovite and biotite fromthe lower plate of the metamorphic basementrocks taken from Bonev et al (accepted) are inTable 1 Incremental heating experiments and agespectra of the sanidine and adularia are presentedin Table 2 and Fig 8 Uncertainties in the agesinclude analytical contributions only at plusmn2
The plateau age of the adularia based on793 of the gas released is 3499 plusmn 023 Ma (Fig8) and is indistinguishable from the total fusionage of 3505 plusmn 023 Ma Sanidine from the rhyolitedyke yielded a plateau age of 3182 plusmn 020 Mabased on 60 percent of the gas released which isindistinguishable from the total fusion age of3188 plusmn 020 Ma As is the case for the adulariathis indicates that argon loss due to weathering oralteration is negligible Moreover the inverse iso-chron ages of 3511 plusmn 037 Ma for the adularaiaand 3191 plusmn 027 Ma for the sanidine are indistin-guishable from the plateau ages and the 40Ar36Arintercept values indicate that there is virtually noexcess argon present
Lavas from the Iran Tepe volcano four kmnortheast of Ada Tepe give KndashAr ages of ~35 Mabut their stratigraphic position above the UpperPriabonianndashLower Oligocene marl-limestone for-mation suggests that they are younger than 34Ma
40Ar39Ar measurements on muscovite and bi-otite (Bonev et al accepted) from the Gneiss-migmatite complex record ages of 3813 plusmn 036and 3773 plusmn 023 Ma respectively (Table 1) Theseages are broadly in agreement with the published40Ar39Ar ages for muscovite (422 plusmn 50 and 361 plusmn50 Ma Lips et al 2000) and muscovite and am-phibole (39 plusmn 1 and 45 plusmn 2 Ma respectively Muka-sa et al 2003) from the Biala Reka metamorphiccore complex Similar ages (39ndash35 Ma) have beenobtained by Peytcheva et al (1992) for the closingof Sr isotope system in the metagranites from theBiala Reka dome
The relative age of the mineralization was de-termined based on its relationship with the hostKrumovgrad group and the overlying Upper
Sample Mineral Weighted Plateau Total Fusion Sourceage (Ma) age (Ma)
AT01-2 adularia 3499 plusmn 023 3505 plusmn 023 this studyAT01-17 sanidine 3182 plusmn 020 3188 plusmn 020 this studyH6 biotite 3773 plusmn 025 3756 plusmn 024 Bonev et al (accepted)H706 muscovite 3813 plusmn 036 3834 plusmn 031 Bonev et al (accepted)
Table 1 Summary of 40Ar39Ar incremental heating experiments on adularia sanidinebiotite and muscovite from Ada Tepe deposit and Kessebir dome
P Marchev et al70
Exp
erim
ent
Las
er p
ower
36A
r37
Ara
38A
r39
Ara
40A
r40
Ar
39A
rK
Ca
Age
plusmn 2
num
ber
(Wat
ts)
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
()
()
(Ma)
b
AT
01-2
adu
lari
a J
= 0
002
987
plusmn 0
0000
09 m
ass
disc
rim
inat
ion
per
amu
10
022
plusmn 0
0004
A
B21
21 0
04
W 0
012
604
00
0003
0 0
000
159
00
0000
5 0
002
772
00
0002
1 0
029
850
00
0007
7 3
871
564
00
0155
74
70
46
132
72
plusmn 3
84A
B21
22 0
10
W 0
009
696
00
0002
2 0
004
566
00
0004
6 0
004
738
00
0002
0 0
239
380
00
0013
1 4
348
793
00
0312
034
92
91
633
85
plusmn 0
38A
B21
23 0
16
W 0
008
804
00
0001
5 0
005
107
00
0003
2 0
006
792
00
0003
0 0
427
709
00
0033
7 5
368
227
00
0278
052
25
32
634
93
plusmn 0
18A
B21
24 0
22
W 0
003
814
00
0001
1 0
000
564
00
0001
0 0
003
949
00
0001
2 0
268
571
00
0011
2 2
865
288
00
0078
961
33
315
034
83
plusmn 0
16A
B21
26 0
30
W 0
008
692
00
0001
1 0
000
261
00
0000
2 0
009
565
00
0002
0 0
650
692
00
0034
7 6
809
601
00
0275
562
78
079
935
01
plusmn 0
11A
B21
27 0
45
W 0
011
765
00
0001
5 0
000
226
00
0000
6 0
017
464
00
0003
5 1
258
986
00
0031
211
697
117
00
0648
770
524
817
70
350
0plusmn
009
AB
2128
06
9 W
00
1320
9 0
000
022
00
0019
9 0
000
003
00
1740
1 0
000
014
12
3066
3 0
001
217
119
6079
5 0
012
113
676
379
195
935
11
plusmn 0
15A
B21
29 1
25
W 0
012
274
00
0002
1 0
000
249
00
0000
3 0
017
405
00
0003
7 1
255
200
00
0080
311
896
055
00
0449
369
817
316
11
353
2plusmn
010
Pla
teau
age
349
9plusmn
023
MSW
D (
n =
5 o
f 8)
186
Tota
l Fus
ion
Age
350
5plusmn
023
AT
01-1
7a s
anid
ine
J =
00
0297
6 plusmn
000
0009
mas
s di
scri
min
atio
n pe
r am
u 1
002
2 plusmn
000
04
AB
2132
00
4 W
00
0055
1 0
000
005
00
0001
4 0
000
006
00
0017
5 0
000
005
00
0362
1 0
000
024
01
8252
2 0
000
076
118
00
456
313
1plusmn
456
AB
2133
00
6 W
00
0019
3 0
000
004
00
0002
6 0
000
003
00
0034
3 0
000
006
00
2579
1 0
000
046
02
1431
6 0
000
110
745
03
447
326
0plusmn
051
AB
2134
01
2 W
00
0018
8 0
000
004
00
0011
6 0
000
007
00
0251
1 0
000
023
02
0468
8 0
000
253
12
8821
1 0
000
967
959
20
568
320
8plusmn
012
AB
2136
01
8 W
00
0050
3 0
000
004
00
0056
8 0
000
012
00
1520
7 0
000
032
12
5179
3 0
000
404
76
2511
3 0
002
510
980
124
678
318
1plusmn
004
AB
2137
02
4 W
00
0056
0 0
000
005
00
0084
3 0
000
018
00
2351
2 0
000
025
19
2193
9 0
000
651
116
3788
5 0
004
597
985
190
700
317
9plusmn
004
AB
2138
02
7 W
00
0036
1 0
000
008
00
0070
7 0
000
010
00
1915
2 0
000
024
15
7872
8 0
000
654
95
5607
9 0
004
091
988
156
686
318
7plusmn
005
AB
2139
03
1 W
00
0036
3 0
000
001
00
0052
2 0
000
008
00
1472
7 0
000
035
12
0293
6 0
000
478
73
0039
4 0
003
784
985
119
709
318
4plusmn
005
AB
2141
03
5 W
00
0031
1 0
000
007
00
0037
7 0
000
008
00
1054
1 0
000
029
08
7899
6 0
000
319
53
5364
2 0
002
077
983
87
716
318
8plusmn
005
AB
2142
04
5 W
00
0032
8 0
000
004
00
0055
3 0
000
015
00
1592
7 0
000
034
13
0785
9 0
000
548
79
4703
7 0
003
239
987
129
726
319
6plusmn
005
AB
2143
05
9 W
00
0028
5 0
000
005
00
0039
4 0
000
012
00
1085
1 0
000
045
08
9161
3 0
000
557
54
3036
7 0
002
402
984
88
696
319
3plusmn
006
AB
2145
08
4 W
00
0016
0 0
000
004
00
0019
6 0
000
007
00
0560
3 0
000
028
04
5183
5 0
000
332
27
6009
9 0
001
984
983
45
706
319
7plusmn
008
AB
2146
13
5 W
00
0016
6 0
000
005
00
0018
3 0
000
004
00
0462
0 0
000
018
03
8294
7 0
000
252
23
5385
3 0
001
397
980
38
647
320
5plusmn
008
Pla
teau
age
318
2plusmn
020
MSW
D (
4 of
12)
279
Tota
l Fus
ion
Age
318
8plusmn
020
aC
orre
cted
for
37A
r an
d 39
Ar
deca
yb
Age
s ca
lcul
ated
rel
ativ
e to
28
34 M
a Ta
ylor
Cre
ek R
hyol
ite
stan
dard
ita
lics
indi
cate
ste
ps o
mit
ted
from
the
plat
eau
age
calc
ulat
ion
see
text
for
deta
ils
Tabl
e 2
40A
r39
Ar
incr
emen
tal-
heat
ing
anal
yses
of a
dula
ria
and
sani
dine
from
Ada
Tep
e
71Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
EocenendashOligocene sedimentary rocks The latteris represented by sandstones unaffected by hy-drothermal alteration which cover the northernpart of the deposit
8 Sr and Pb isotope compositionsof carbonates and pyrite
Sr and Pb isotopes were measured by standardTIMS procedures at the University of GenevaSwitzerland following the methods of Valenza etal (2000) and Chiaradia and Fontboteacute (2002) Srisotope ratios on carbonate and Pb isotope ratiosfrom pyrite at Ada Tepe along with whole rock Srand Pb isotope ratios of the leachate fraction of asample from Synap prospect 2 km west of AdaTepe are presented in Table 3 and Figs 9 and 10The Ada Tepe carbonate is from a late stage an-kerite-dolomite vein taken from a drill-core sam-ple (AT01-22) at 996 m depth The bulk rock(sample Sin2000-28) from Synap is from sericite-adularia alteration from the surface Pyrite fromAda Tepe is from a strongly silicified sample(Km2000-6) Pyrite from Synap is from the samehand sample Sin2000-28 on which the Sr wasmeasured Both samples belong to the early alter-
ation The initial 87Sr86Sr ratio of the whole rockcorrected for 35 Ma is 070809 The pyrite sampleand whole rock leachate show identical 207Pb204Pb (1568) and 208Pb204Pb (3885) ratios andslightly different 206Pb204Pb ratios (1871 in AdaTepe and 1866 in Synap) The Sr and Pb isotopedata are compared with those of local Paleogenevolcanic rocks and dykes and the Rhodope meta-morphic rocks in Figs 9 and 10
9 Discussion
91 Physical environment
Epithermal quartz from the Ada Tepe deposit ispoor in fluid inclusions particularly the early mi-crocrystalline quartz and opal Euhedral late sug-ary quartz is the only phase which contains largerfluid inclusions but with no reliable characteris-tics that may allow to classify them as primary in-clusions For the similar Sleeper deposit USASaunders (1994) suggested that quartz formed bytransformation of poorly ordered silica may ex-clude trapped fluids thus precluding the use ofmicrothermometry to constrain the physicochem-ical conditions of silica and gold deposition
Fig 7 (a) Geode of coarse-crystalline quartz with carbonate infill (third stage) (b) Third stage coarse-crystallinequartz (ccq) and bladed parallel type calcite (c) (c) Late vein (forth stage) composed by pyrite on its margins fol-lowed by dolomite-ankerite (da) (d) Same fracture Dolomite-ankerite forms a halo overlapping quartz-adularia-pyrite alteration
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
65Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Krumovgrad area and described as the ShavarovoFormation of the Krumovgrad Group in a laterpaper (Goranov and Atanasov 1992) The totalthickness of the type section of the ShavarovoFormation (~350 m) was measured along the Kal-djic river near the Shavar village Blocks andclasts of breccia and conglomerate are mixtures ofgneiss amphibolite and marble derived primarilyfrom the Variegated complex
4 Structure
The dominant structure in the Ada Tepe prospectis the TDF It is a mapable tectonic contact bestexpressed along the western slope of Ada Tepehill (Fig 3a) In outcrop and drill cores the fault isrecognized as a contact between Paleozoic meta-morphic rocks and MaastrichtianndashPaleocene sed-imentary rocks of the Shavarovo Formation Im-mediately above the detachment fault there is a05 to 20 m thick zone of massive silicification Indrill core the lower limit of the structure ismarked by a 10ndash20 cm-thick layer of tectonic clayGneiss migmatite marble and the amphibolite ofthe metamorphic basement beneath the detach-ment surface are transformed into a cataclasticrock over a thickness of several meters Thesouthwestern slope of the Ada Tepe hill is cut by aNWndashSE-oriented high-angle fault (Fig 2) whichformed a small half graben fill by older Maas-trichtianndashPaleocene syndetachment sedimentaryrocks overlain in the eastern part by younger Pria-bonianndashOligocene sedimentary rocks
Major structures cutting the basement rocks ofthe Ada Tepe deposit are rare although severalEndashW and NndashS-oriented subvertical faults markedby a zone of silicification occur to the south eastand west of the Ada Tepe deposit The longest NndashS-striking zone has been traced for almost 200 mThe EndashW and NndashS faults coincide with the majordirections of the mineralized veins in the sedi-mentary cover and can be interpreted as feederstructures for the mineralizing fluids
5 Mineralization
51 Ore geometry and ore bodies
The Ada Tepe deposit is 600 m along strike and300ndash350 m wide Gold mineralization occurs as(1) a massive tabular body located immediatelyabove the detachment fault (Figs 3b c) and (2)open space-filling within the breccia-conglomer-ate and sandstone along predominantly east-westoriented subvertical listric faults within the hang-
ing wall (Figs 3b d) In cross section the tabularbody dips (10ndash15deg) to the north-northeast whichis consistent with the low angle TDF The orebody is so strongly silicified company geologistsrefer to it as ldquoThe Wallrdquo Detailed observations onThe Wall indicate a complicated sequence ofevents with multiple periods of silicification andveining Silicification began with the deposition ofmassive white to light grey silica above the de-tachment fault partly or totally replacing the orig-inal rocks Original rock textures were destroyedwith the exception of ghosted gneiss fragments(Fig 4a) The latter are rounded with veins ofquartz or carbonate cutting or surrounding theclasts Early microcrystalline silica was commonlyveined by subvertical banded veins or brecciatedby later fault movements and cemented by calcitesugary quartz (Fig 5b) or by pyrite
In the less silicified parts The Wall consists ofnumerous differently oriented veins ranging inwidth from less than 1 cm up to 30 cm (Fig 4c)Subvertical veins which were formed by deposi-tion of colloform silica layers in open space canbe traced from The Wall into the listric faults inthe overlying sedimentary rocks (Fig 4d) On thesurface they form EndashW-trending ridges separatedby argillic zones (Figs 3a b d)
52 Ore and gangue mineralogy andstages of mineralization
The ore mineralogy of the Ada Tepe deposit is sim-ple consisting mainly of electrum and subordinatepyrite with traces of galena and gold-silver tellu-rides Gangue minerals consist of silica polymorphs(microcrystalline fine-grained sugary quartz andopaline silica) various carbonates (calcite dolo-mite ankerite and siderite) and adularia Telluridesinclude hessite (Ag2Te) and petzite (Ag3AuTe2) Allsamples with Au content higher than 1 gt have al-most constant AuAg ratios ~ 3 reflecting the com-position of electrum (76ndash73 wt Au)
Unlike the massive silicification of The Wallbanded veins in and above it provide an excellentframework for identifying the different stages ofmineralization Mineralization in Ada Tepe canbe subdivided into 4 broad generally overlappingstages of quartz and carbonate veins on the basisof cross-cutting relationships changes in mineral-ogy texture and gold grades
The earliest stage is characterized by deposi-tion of microcrystalline to fine-grained grayish towhite massive or banded quartz with rare pyriteand adularia (Figs 5andashd) In some veins silica depo-sition starts with a thin band of almost isotropicopaline (Fig 4 c) followed by thin band of quartzwith rare bladed calcite Breccia texture is typical
P Marchev et al66
for the massive silicification of The Wall Theproducts of the early stage form microfracturefilling in the host rocks near the margins of the
Fig 5 Microphotographs and SEM images of silica and bonanza ore textures (a) Bands of early stage microcrystal-line (mq) and jigsaw quartz (jq) (b) Electrum band (e) deposited on the interface between early microcrystallinequartz (mq) and third stage sugary quartz and radiating bladed calcite (qc) (c) Band of electrum (e) and isotropicopaline Electrum is located on the bottom of the band (d) Third stage coarse crystalline quartz (ccq) cutting theopaline (o) and microcrystalline quartz (mq) which in turn is cut by calcite (c) (e) Subparallel bands of electrum (e)and microcrystalline adularia and silica separated by a calcite vein (c) The arrow shows the vertical direction (f)SEM image of the outlined area
veins or rock fragments in The Wall causing thesilica-adularia-pyrite replacement in them Thegold grade of this stage is unknown
67Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
The economic gold is related to the secondstage of mineralization It starts at the end of themicrocrystalline quartz and the beginning of thecoarser grained (sugary) quartz of the third stagebelow (Fig 5b) Usually it forms black millimeter-scale bands of opaline or microcrystalline chal-cedony-adularia and electrum (Figs 5cndashf) Locallyopaline silica crosscuts the microcrystallinequartz (Figs 5cndashd) of the early stage and in turn iscut by the coarser grained quartz and carbonatesof the third and forth stages (Figs 5dndashe) Petro-graphic examination of the electrum-rich bandsreveals that electrum commonly occurs towardsthe bottom of the opaline or microcrystallinebands (Figs 5c e) Where opaline bands are notpresent electrum precipitates at the boundary offirst and third stages (Fig 5b) The electrum hasirregular forms as the result of crystallization inthe quartz interstices being relatively well-shapedin the coarser-grained quartz crystals The size ofelectrum grains ranges from less than 1 to 20 micromHowever the single crystals form chains reachingup to 650 microm (Figs 5b 6a) Electrum in gold-richbands etched with HF is characterized by botryoi-dal surfaces that appear to have formed by theaggregation of spherical electrum particles (Figs6andashb) as observed in the Sleeper deposit Nevada(Saunders 1990 1994) Electrum in bonanza veinscan occupy 50 vol (Figs 5f 6c) accompanied byrare As-bearing pyrite Occasionally micron orsubmicron size electrum inclusions form zoneswithin the As-bearing pyrite (Figs 6d) Tiny AundashAg tellurides have been observed at the contactsbetween electrum grains and small galena crystals(Fig 6f)
The third stage starts with deposition of sugaryquartz (up to 15 mm large Figs 5d 7a) followedby bands of quartz and bladed calcite (Figs 5b 7b)and finally by massive calcite with small amountof quartz (Fig 5d) Locally calcite fills quartz ge-odes or forms small veins (Fig 7a) Microscopical-ly the late calcite corrodes and replaces quartzcrystals Small amount of adularia and pyrite arealso typical for this stage
The hydrothermal mineralization ended withthe deposition of pinkish ankerite-dolomite andsiderite which was preceded by precipitation ofmassive pyrite in some parts of the deposit (Figs7cndashd)
The mineralization of Ada Tepe exhibits sever-al important spatial and textural features thatprovide insights to the physical environment ofore deposition In its upper part quartz becomesthe predominant gangue mineral whereas car-bonates are subordinate This is particularly obvi-ous in the last stage where in the surface samplesdolomite and ankerite are absent in the geodes
and bladed minerals consist of microcrystallinequartz only Another spatial variation is the di-minishing of banding textures with the decreasein grade of Au mineralization to the north Animportant feature is the absence of bladed car-bonates in the veinlets beneath The Wall in con-trast to the entire extent of the deposit above thedetachment surface
53 Oxidized zone
The uppermost part of the Ada Tepe deposit hasbeen oxidized by supergene processes with thedepth of oxidation being dependent upon inten-sity of faulting Due to extensive silicification TheWall itself is generally not oxidized however a 2to 5 m thick zone of oxidation invariably occursabove The Wall Narrow zones of oxidation occurdown to this zone utilizing high angle listric faultsThese faults and fractures most likely acted asconduits for the surface waters to reach the im-permeable silicified zone forming the oxidizedzone above The Wall
Most of the pyrite in the oxidized zones hasbeen converted into limonite identified asgoethite Kaolinite is widely distributed in thiszone forming locally small veinlets Electrum inthe oxidized zone however shows no evidence ofAu enrichment
6 Alteration
In the poorly mineralized zones hydrothermal al-teration is weak with most of the detrital minerals(quartz muscovite and feldspars) remaining unal-tered Alteration consists of chlorite calcite kaoli-nite and subordinate albite pyrite and ankerite-dolomite It seems that calcite and ankerite-dolo-mite are late however it is difficult to distinguishreplacement calcite from vein calcite Quartzadularia calcite pyrite and dolomite-ankerite-siderite plusmn sericite and clay minerals in variableproportions occur in The Wall and immediateproximity to the subvertical quartz and carbonateveins in the strongly mineralized zones Theyformed through replacement of the original meta-morphic minerals included in the sandstone andconglomerate and are associated with relict de-trital quartz and muscovite This complex mineralassemblage is the result of the evolution of thehydrothermal activity
Hydrothermal alteration of the basementmetamorphic rocks is developed within a haloseveral meters in extent beneath The Wall and ismore pronounced around the subvertical veinsThe alteration assemblage includes quartz adu-
P Marchev et al68
Fig 6 (a) SEM images of electrum dendrite etched with HF (b) Negative forms of quartz removed by HFand spherical colloidal particles (c) Opal-electrum band containing ~ 50 electrum and small amount ofpyrite Dark crystals between electrum are adularia and silica (d) Pyrite with a zone of submicron-size elec-trum (e) Former Py converted to goethite with inclusions of Au (f) AundashAg tellurides between larger elec-trum and galena crystals
69Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
laria illite or sericite pyrite kaolinite and latestage ankerite-dolomite-siderite
Clay minerals are more abundant and betterdeveloped in the alteration close to the surfacewhere they form argillic zones between the EndashW-oriented swarms of veins Kaolinite and quartzpredominate in the argillic zones and illite chlo-rite adularia and carbonate are subordinate ac-companied locally by illite-montmorillonite Partof the shallow-level kaolinite may be supergenebut its association with unoxidized pyrite beneathand within The Wall indicates that a hypogene ori-gin is likely at least for the deeper kaolinite
7 Geochronology
40Ar39Ar ages from adularia and sanidine sam-ples were determined to constrain the timing ofmineralization and volcanic activity in the Kesse-bir dome Sample AT01-2 from which adulariawas extracted for dating is from a drill-hole at725 m depth It represents a quartz-adularia-car-bonate banded vein filled with finely veinedgneiss clasts It is a mixture of completely replaceddetrital K-feldspar and directly deposited adular-ia crystals The rhyolite dyke (sample AT01-17) isemplaced within the core orthogneisses of theKessebir dome located 4 km southwest from AdaTepe (Fig 2) It comprises 2 cm diameter sanidinephenocrysts that were separated for dating plusplagioclase biotite and quartz
40Ar39Ar experiments were conducted at UW-Madison Rare Gas Geochronology LaboratoryMinerals were separated from 100ndash250 micronsieve fractions using standard magnetic densityand handpicking methods Five milligrams of eachmineral were irradiated at Oregon State Univer-sity USA for 12 hours along with 2834 Ma sani-dine from the Taylor Creek rhyolite as the neu-tron fluence monitor Analytical procedures in-cluding mass spectrometry procedural blanks re-actor corrections and estimation of uncertaintiesare given in Singer and Brown (2002) Isotopicmeasurements were made of the gas extracted byincrementally heating of 2ndash3 mg multi-crystal ali-
quots using a defocused CO2 laser beam Resultsof incremental heating experiments along withthe 40Ar39Ar ages of muscovite and biotite fromthe lower plate of the metamorphic basementrocks taken from Bonev et al (accepted) are inTable 1 Incremental heating experiments and agespectra of the sanidine and adularia are presentedin Table 2 and Fig 8 Uncertainties in the agesinclude analytical contributions only at plusmn2
The plateau age of the adularia based on793 of the gas released is 3499 plusmn 023 Ma (Fig8) and is indistinguishable from the total fusionage of 3505 plusmn 023 Ma Sanidine from the rhyolitedyke yielded a plateau age of 3182 plusmn 020 Mabased on 60 percent of the gas released which isindistinguishable from the total fusion age of3188 plusmn 020 Ma As is the case for the adulariathis indicates that argon loss due to weathering oralteration is negligible Moreover the inverse iso-chron ages of 3511 plusmn 037 Ma for the adularaiaand 3191 plusmn 027 Ma for the sanidine are indistin-guishable from the plateau ages and the 40Ar36Arintercept values indicate that there is virtually noexcess argon present
Lavas from the Iran Tepe volcano four kmnortheast of Ada Tepe give KndashAr ages of ~35 Mabut their stratigraphic position above the UpperPriabonianndashLower Oligocene marl-limestone for-mation suggests that they are younger than 34Ma
40Ar39Ar measurements on muscovite and bi-otite (Bonev et al accepted) from the Gneiss-migmatite complex record ages of 3813 plusmn 036and 3773 plusmn 023 Ma respectively (Table 1) Theseages are broadly in agreement with the published40Ar39Ar ages for muscovite (422 plusmn 50 and 361 plusmn50 Ma Lips et al 2000) and muscovite and am-phibole (39 plusmn 1 and 45 plusmn 2 Ma respectively Muka-sa et al 2003) from the Biala Reka metamorphiccore complex Similar ages (39ndash35 Ma) have beenobtained by Peytcheva et al (1992) for the closingof Sr isotope system in the metagranites from theBiala Reka dome
The relative age of the mineralization was de-termined based on its relationship with the hostKrumovgrad group and the overlying Upper
Sample Mineral Weighted Plateau Total Fusion Sourceage (Ma) age (Ma)
AT01-2 adularia 3499 plusmn 023 3505 plusmn 023 this studyAT01-17 sanidine 3182 plusmn 020 3188 plusmn 020 this studyH6 biotite 3773 plusmn 025 3756 plusmn 024 Bonev et al (accepted)H706 muscovite 3813 plusmn 036 3834 plusmn 031 Bonev et al (accepted)
Table 1 Summary of 40Ar39Ar incremental heating experiments on adularia sanidinebiotite and muscovite from Ada Tepe deposit and Kessebir dome
P Marchev et al70
Exp
erim
ent
Las
er p
ower
36A
r37
Ara
38A
r39
Ara
40A
r40
Ar
39A
rK
Ca
Age
plusmn 2
num
ber
(Wat
ts)
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
()
()
(Ma)
b
AT
01-2
adu
lari
a J
= 0
002
987
plusmn 0
0000
09 m
ass
disc
rim
inat
ion
per
amu
10
022
plusmn 0
0004
A
B21
21 0
04
W 0
012
604
00
0003
0 0
000
159
00
0000
5 0
002
772
00
0002
1 0
029
850
00
0007
7 3
871
564
00
0155
74
70
46
132
72
plusmn 3
84A
B21
22 0
10
W 0
009
696
00
0002
2 0
004
566
00
0004
6 0
004
738
00
0002
0 0
239
380
00
0013
1 4
348
793
00
0312
034
92
91
633
85
plusmn 0
38A
B21
23 0
16
W 0
008
804
00
0001
5 0
005
107
00
0003
2 0
006
792
00
0003
0 0
427
709
00
0033
7 5
368
227
00
0278
052
25
32
634
93
plusmn 0
18A
B21
24 0
22
W 0
003
814
00
0001
1 0
000
564
00
0001
0 0
003
949
00
0001
2 0
268
571
00
0011
2 2
865
288
00
0078
961
33
315
034
83
plusmn 0
16A
B21
26 0
30
W 0
008
692
00
0001
1 0
000
261
00
0000
2 0
009
565
00
0002
0 0
650
692
00
0034
7 6
809
601
00
0275
562
78
079
935
01
plusmn 0
11A
B21
27 0
45
W 0
011
765
00
0001
5 0
000
226
00
0000
6 0
017
464
00
0003
5 1
258
986
00
0031
211
697
117
00
0648
770
524
817
70
350
0plusmn
009
AB
2128
06
9 W
00
1320
9 0
000
022
00
0019
9 0
000
003
00
1740
1 0
000
014
12
3066
3 0
001
217
119
6079
5 0
012
113
676
379
195
935
11
plusmn 0
15A
B21
29 1
25
W 0
012
274
00
0002
1 0
000
249
00
0000
3 0
017
405
00
0003
7 1
255
200
00
0080
311
896
055
00
0449
369
817
316
11
353
2plusmn
010
Pla
teau
age
349
9plusmn
023
MSW
D (
n =
5 o
f 8)
186
Tota
l Fus
ion
Age
350
5plusmn
023
AT
01-1
7a s
anid
ine
J =
00
0297
6 plusmn
000
0009
mas
s di
scri
min
atio
n pe
r am
u 1
002
2 plusmn
000
04
AB
2132
00
4 W
00
0055
1 0
000
005
00
0001
4 0
000
006
00
0017
5 0
000
005
00
0362
1 0
000
024
01
8252
2 0
000
076
118
00
456
313
1plusmn
456
AB
2133
00
6 W
00
0019
3 0
000
004
00
0002
6 0
000
003
00
0034
3 0
000
006
00
2579
1 0
000
046
02
1431
6 0
000
110
745
03
447
326
0plusmn
051
AB
2134
01
2 W
00
0018
8 0
000
004
00
0011
6 0
000
007
00
0251
1 0
000
023
02
0468
8 0
000
253
12
8821
1 0
000
967
959
20
568
320
8plusmn
012
AB
2136
01
8 W
00
0050
3 0
000
004
00
0056
8 0
000
012
00
1520
7 0
000
032
12
5179
3 0
000
404
76
2511
3 0
002
510
980
124
678
318
1plusmn
004
AB
2137
02
4 W
00
0056
0 0
000
005
00
0084
3 0
000
018
00
2351
2 0
000
025
19
2193
9 0
000
651
116
3788
5 0
004
597
985
190
700
317
9plusmn
004
AB
2138
02
7 W
00
0036
1 0
000
008
00
0070
7 0
000
010
00
1915
2 0
000
024
15
7872
8 0
000
654
95
5607
9 0
004
091
988
156
686
318
7plusmn
005
AB
2139
03
1 W
00
0036
3 0
000
001
00
0052
2 0
000
008
00
1472
7 0
000
035
12
0293
6 0
000
478
73
0039
4 0
003
784
985
119
709
318
4plusmn
005
AB
2141
03
5 W
00
0031
1 0
000
007
00
0037
7 0
000
008
00
1054
1 0
000
029
08
7899
6 0
000
319
53
5364
2 0
002
077
983
87
716
318
8plusmn
005
AB
2142
04
5 W
00
0032
8 0
000
004
00
0055
3 0
000
015
00
1592
7 0
000
034
13
0785
9 0
000
548
79
4703
7 0
003
239
987
129
726
319
6plusmn
005
AB
2143
05
9 W
00
0028
5 0
000
005
00
0039
4 0
000
012
00
1085
1 0
000
045
08
9161
3 0
000
557
54
3036
7 0
002
402
984
88
696
319
3plusmn
006
AB
2145
08
4 W
00
0016
0 0
000
004
00
0019
6 0
000
007
00
0560
3 0
000
028
04
5183
5 0
000
332
27
6009
9 0
001
984
983
45
706
319
7plusmn
008
AB
2146
13
5 W
00
0016
6 0
000
005
00
0018
3 0
000
004
00
0462
0 0
000
018
03
8294
7 0
000
252
23
5385
3 0
001
397
980
38
647
320
5plusmn
008
Pla
teau
age
318
2plusmn
020
MSW
D (
4 of
12)
279
Tota
l Fus
ion
Age
318
8plusmn
020
aC
orre
cted
for
37A
r an
d 39
Ar
deca
yb
Age
s ca
lcul
ated
rel
ativ
e to
28
34 M
a Ta
ylor
Cre
ek R
hyol
ite
stan
dard
ita
lics
indi
cate
ste
ps o
mit
ted
from
the
plat
eau
age
calc
ulat
ion
see
text
for
deta
ils
Tabl
e 2
40A
r39
Ar
incr
emen
tal-
heat
ing
anal
yses
of a
dula
ria
and
sani
dine
from
Ada
Tep
e
71Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
EocenendashOligocene sedimentary rocks The latteris represented by sandstones unaffected by hy-drothermal alteration which cover the northernpart of the deposit
8 Sr and Pb isotope compositionsof carbonates and pyrite
Sr and Pb isotopes were measured by standardTIMS procedures at the University of GenevaSwitzerland following the methods of Valenza etal (2000) and Chiaradia and Fontboteacute (2002) Srisotope ratios on carbonate and Pb isotope ratiosfrom pyrite at Ada Tepe along with whole rock Srand Pb isotope ratios of the leachate fraction of asample from Synap prospect 2 km west of AdaTepe are presented in Table 3 and Figs 9 and 10The Ada Tepe carbonate is from a late stage an-kerite-dolomite vein taken from a drill-core sam-ple (AT01-22) at 996 m depth The bulk rock(sample Sin2000-28) from Synap is from sericite-adularia alteration from the surface Pyrite fromAda Tepe is from a strongly silicified sample(Km2000-6) Pyrite from Synap is from the samehand sample Sin2000-28 on which the Sr wasmeasured Both samples belong to the early alter-
ation The initial 87Sr86Sr ratio of the whole rockcorrected for 35 Ma is 070809 The pyrite sampleand whole rock leachate show identical 207Pb204Pb (1568) and 208Pb204Pb (3885) ratios andslightly different 206Pb204Pb ratios (1871 in AdaTepe and 1866 in Synap) The Sr and Pb isotopedata are compared with those of local Paleogenevolcanic rocks and dykes and the Rhodope meta-morphic rocks in Figs 9 and 10
9 Discussion
91 Physical environment
Epithermal quartz from the Ada Tepe deposit ispoor in fluid inclusions particularly the early mi-crocrystalline quartz and opal Euhedral late sug-ary quartz is the only phase which contains largerfluid inclusions but with no reliable characteris-tics that may allow to classify them as primary in-clusions For the similar Sleeper deposit USASaunders (1994) suggested that quartz formed bytransformation of poorly ordered silica may ex-clude trapped fluids thus precluding the use ofmicrothermometry to constrain the physicochem-ical conditions of silica and gold deposition
Fig 7 (a) Geode of coarse-crystalline quartz with carbonate infill (third stage) (b) Third stage coarse-crystallinequartz (ccq) and bladed parallel type calcite (c) (c) Late vein (forth stage) composed by pyrite on its margins fol-lowed by dolomite-ankerite (da) (d) Same fracture Dolomite-ankerite forms a halo overlapping quartz-adularia-pyrite alteration
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
P Marchev et al66
for the massive silicification of The Wall Theproducts of the early stage form microfracturefilling in the host rocks near the margins of the
Fig 5 Microphotographs and SEM images of silica and bonanza ore textures (a) Bands of early stage microcrystal-line (mq) and jigsaw quartz (jq) (b) Electrum band (e) deposited on the interface between early microcrystallinequartz (mq) and third stage sugary quartz and radiating bladed calcite (qc) (c) Band of electrum (e) and isotropicopaline Electrum is located on the bottom of the band (d) Third stage coarse crystalline quartz (ccq) cutting theopaline (o) and microcrystalline quartz (mq) which in turn is cut by calcite (c) (e) Subparallel bands of electrum (e)and microcrystalline adularia and silica separated by a calcite vein (c) The arrow shows the vertical direction (f)SEM image of the outlined area
veins or rock fragments in The Wall causing thesilica-adularia-pyrite replacement in them Thegold grade of this stage is unknown
67Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
The economic gold is related to the secondstage of mineralization It starts at the end of themicrocrystalline quartz and the beginning of thecoarser grained (sugary) quartz of the third stagebelow (Fig 5b) Usually it forms black millimeter-scale bands of opaline or microcrystalline chal-cedony-adularia and electrum (Figs 5cndashf) Locallyopaline silica crosscuts the microcrystallinequartz (Figs 5cndashd) of the early stage and in turn iscut by the coarser grained quartz and carbonatesof the third and forth stages (Figs 5dndashe) Petro-graphic examination of the electrum-rich bandsreveals that electrum commonly occurs towardsthe bottom of the opaline or microcrystallinebands (Figs 5c e) Where opaline bands are notpresent electrum precipitates at the boundary offirst and third stages (Fig 5b) The electrum hasirregular forms as the result of crystallization inthe quartz interstices being relatively well-shapedin the coarser-grained quartz crystals The size ofelectrum grains ranges from less than 1 to 20 micromHowever the single crystals form chains reachingup to 650 microm (Figs 5b 6a) Electrum in gold-richbands etched with HF is characterized by botryoi-dal surfaces that appear to have formed by theaggregation of spherical electrum particles (Figs6andashb) as observed in the Sleeper deposit Nevada(Saunders 1990 1994) Electrum in bonanza veinscan occupy 50 vol (Figs 5f 6c) accompanied byrare As-bearing pyrite Occasionally micron orsubmicron size electrum inclusions form zoneswithin the As-bearing pyrite (Figs 6d) Tiny AundashAg tellurides have been observed at the contactsbetween electrum grains and small galena crystals(Fig 6f)
The third stage starts with deposition of sugaryquartz (up to 15 mm large Figs 5d 7a) followedby bands of quartz and bladed calcite (Figs 5b 7b)and finally by massive calcite with small amountof quartz (Fig 5d) Locally calcite fills quartz ge-odes or forms small veins (Fig 7a) Microscopical-ly the late calcite corrodes and replaces quartzcrystals Small amount of adularia and pyrite arealso typical for this stage
The hydrothermal mineralization ended withthe deposition of pinkish ankerite-dolomite andsiderite which was preceded by precipitation ofmassive pyrite in some parts of the deposit (Figs7cndashd)
The mineralization of Ada Tepe exhibits sever-al important spatial and textural features thatprovide insights to the physical environment ofore deposition In its upper part quartz becomesthe predominant gangue mineral whereas car-bonates are subordinate This is particularly obvi-ous in the last stage where in the surface samplesdolomite and ankerite are absent in the geodes
and bladed minerals consist of microcrystallinequartz only Another spatial variation is the di-minishing of banding textures with the decreasein grade of Au mineralization to the north Animportant feature is the absence of bladed car-bonates in the veinlets beneath The Wall in con-trast to the entire extent of the deposit above thedetachment surface
53 Oxidized zone
The uppermost part of the Ada Tepe deposit hasbeen oxidized by supergene processes with thedepth of oxidation being dependent upon inten-sity of faulting Due to extensive silicification TheWall itself is generally not oxidized however a 2to 5 m thick zone of oxidation invariably occursabove The Wall Narrow zones of oxidation occurdown to this zone utilizing high angle listric faultsThese faults and fractures most likely acted asconduits for the surface waters to reach the im-permeable silicified zone forming the oxidizedzone above The Wall
Most of the pyrite in the oxidized zones hasbeen converted into limonite identified asgoethite Kaolinite is widely distributed in thiszone forming locally small veinlets Electrum inthe oxidized zone however shows no evidence ofAu enrichment
6 Alteration
In the poorly mineralized zones hydrothermal al-teration is weak with most of the detrital minerals(quartz muscovite and feldspars) remaining unal-tered Alteration consists of chlorite calcite kaoli-nite and subordinate albite pyrite and ankerite-dolomite It seems that calcite and ankerite-dolo-mite are late however it is difficult to distinguishreplacement calcite from vein calcite Quartzadularia calcite pyrite and dolomite-ankerite-siderite plusmn sericite and clay minerals in variableproportions occur in The Wall and immediateproximity to the subvertical quartz and carbonateveins in the strongly mineralized zones Theyformed through replacement of the original meta-morphic minerals included in the sandstone andconglomerate and are associated with relict de-trital quartz and muscovite This complex mineralassemblage is the result of the evolution of thehydrothermal activity
Hydrothermal alteration of the basementmetamorphic rocks is developed within a haloseveral meters in extent beneath The Wall and ismore pronounced around the subvertical veinsThe alteration assemblage includes quartz adu-
P Marchev et al68
Fig 6 (a) SEM images of electrum dendrite etched with HF (b) Negative forms of quartz removed by HFand spherical colloidal particles (c) Opal-electrum band containing ~ 50 electrum and small amount ofpyrite Dark crystals between electrum are adularia and silica (d) Pyrite with a zone of submicron-size elec-trum (e) Former Py converted to goethite with inclusions of Au (f) AundashAg tellurides between larger elec-trum and galena crystals
69Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
laria illite or sericite pyrite kaolinite and latestage ankerite-dolomite-siderite
Clay minerals are more abundant and betterdeveloped in the alteration close to the surfacewhere they form argillic zones between the EndashW-oriented swarms of veins Kaolinite and quartzpredominate in the argillic zones and illite chlo-rite adularia and carbonate are subordinate ac-companied locally by illite-montmorillonite Partof the shallow-level kaolinite may be supergenebut its association with unoxidized pyrite beneathand within The Wall indicates that a hypogene ori-gin is likely at least for the deeper kaolinite
7 Geochronology
40Ar39Ar ages from adularia and sanidine sam-ples were determined to constrain the timing ofmineralization and volcanic activity in the Kesse-bir dome Sample AT01-2 from which adulariawas extracted for dating is from a drill-hole at725 m depth It represents a quartz-adularia-car-bonate banded vein filled with finely veinedgneiss clasts It is a mixture of completely replaceddetrital K-feldspar and directly deposited adular-ia crystals The rhyolite dyke (sample AT01-17) isemplaced within the core orthogneisses of theKessebir dome located 4 km southwest from AdaTepe (Fig 2) It comprises 2 cm diameter sanidinephenocrysts that were separated for dating plusplagioclase biotite and quartz
40Ar39Ar experiments were conducted at UW-Madison Rare Gas Geochronology LaboratoryMinerals were separated from 100ndash250 micronsieve fractions using standard magnetic densityand handpicking methods Five milligrams of eachmineral were irradiated at Oregon State Univer-sity USA for 12 hours along with 2834 Ma sani-dine from the Taylor Creek rhyolite as the neu-tron fluence monitor Analytical procedures in-cluding mass spectrometry procedural blanks re-actor corrections and estimation of uncertaintiesare given in Singer and Brown (2002) Isotopicmeasurements were made of the gas extracted byincrementally heating of 2ndash3 mg multi-crystal ali-
quots using a defocused CO2 laser beam Resultsof incremental heating experiments along withthe 40Ar39Ar ages of muscovite and biotite fromthe lower plate of the metamorphic basementrocks taken from Bonev et al (accepted) are inTable 1 Incremental heating experiments and agespectra of the sanidine and adularia are presentedin Table 2 and Fig 8 Uncertainties in the agesinclude analytical contributions only at plusmn2
The plateau age of the adularia based on793 of the gas released is 3499 plusmn 023 Ma (Fig8) and is indistinguishable from the total fusionage of 3505 plusmn 023 Ma Sanidine from the rhyolitedyke yielded a plateau age of 3182 plusmn 020 Mabased on 60 percent of the gas released which isindistinguishable from the total fusion age of3188 plusmn 020 Ma As is the case for the adulariathis indicates that argon loss due to weathering oralteration is negligible Moreover the inverse iso-chron ages of 3511 plusmn 037 Ma for the adularaiaand 3191 plusmn 027 Ma for the sanidine are indistin-guishable from the plateau ages and the 40Ar36Arintercept values indicate that there is virtually noexcess argon present
Lavas from the Iran Tepe volcano four kmnortheast of Ada Tepe give KndashAr ages of ~35 Mabut their stratigraphic position above the UpperPriabonianndashLower Oligocene marl-limestone for-mation suggests that they are younger than 34Ma
40Ar39Ar measurements on muscovite and bi-otite (Bonev et al accepted) from the Gneiss-migmatite complex record ages of 3813 plusmn 036and 3773 plusmn 023 Ma respectively (Table 1) Theseages are broadly in agreement with the published40Ar39Ar ages for muscovite (422 plusmn 50 and 361 plusmn50 Ma Lips et al 2000) and muscovite and am-phibole (39 plusmn 1 and 45 plusmn 2 Ma respectively Muka-sa et al 2003) from the Biala Reka metamorphiccore complex Similar ages (39ndash35 Ma) have beenobtained by Peytcheva et al (1992) for the closingof Sr isotope system in the metagranites from theBiala Reka dome
The relative age of the mineralization was de-termined based on its relationship with the hostKrumovgrad group and the overlying Upper
Sample Mineral Weighted Plateau Total Fusion Sourceage (Ma) age (Ma)
AT01-2 adularia 3499 plusmn 023 3505 plusmn 023 this studyAT01-17 sanidine 3182 plusmn 020 3188 plusmn 020 this studyH6 biotite 3773 plusmn 025 3756 plusmn 024 Bonev et al (accepted)H706 muscovite 3813 plusmn 036 3834 plusmn 031 Bonev et al (accepted)
Table 1 Summary of 40Ar39Ar incremental heating experiments on adularia sanidinebiotite and muscovite from Ada Tepe deposit and Kessebir dome
P Marchev et al70
Exp
erim
ent
Las
er p
ower
36A
r37
Ara
38A
r39
Ara
40A
r40
Ar
39A
rK
Ca
Age
plusmn 2
num
ber
(Wat
ts)
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
()
()
(Ma)
b
AT
01-2
adu
lari
a J
= 0
002
987
plusmn 0
0000
09 m
ass
disc
rim
inat
ion
per
amu
10
022
plusmn 0
0004
A
B21
21 0
04
W 0
012
604
00
0003
0 0
000
159
00
0000
5 0
002
772
00
0002
1 0
029
850
00
0007
7 3
871
564
00
0155
74
70
46
132
72
plusmn 3
84A
B21
22 0
10
W 0
009
696
00
0002
2 0
004
566
00
0004
6 0
004
738
00
0002
0 0
239
380
00
0013
1 4
348
793
00
0312
034
92
91
633
85
plusmn 0
38A
B21
23 0
16
W 0
008
804
00
0001
5 0
005
107
00
0003
2 0
006
792
00
0003
0 0
427
709
00
0033
7 5
368
227
00
0278
052
25
32
634
93
plusmn 0
18A
B21
24 0
22
W 0
003
814
00
0001
1 0
000
564
00
0001
0 0
003
949
00
0001
2 0
268
571
00
0011
2 2
865
288
00
0078
961
33
315
034
83
plusmn 0
16A
B21
26 0
30
W 0
008
692
00
0001
1 0
000
261
00
0000
2 0
009
565
00
0002
0 0
650
692
00
0034
7 6
809
601
00
0275
562
78
079
935
01
plusmn 0
11A
B21
27 0
45
W 0
011
765
00
0001
5 0
000
226
00
0000
6 0
017
464
00
0003
5 1
258
986
00
0031
211
697
117
00
0648
770
524
817
70
350
0plusmn
009
AB
2128
06
9 W
00
1320
9 0
000
022
00
0019
9 0
000
003
00
1740
1 0
000
014
12
3066
3 0
001
217
119
6079
5 0
012
113
676
379
195
935
11
plusmn 0
15A
B21
29 1
25
W 0
012
274
00
0002
1 0
000
249
00
0000
3 0
017
405
00
0003
7 1
255
200
00
0080
311
896
055
00
0449
369
817
316
11
353
2plusmn
010
Pla
teau
age
349
9plusmn
023
MSW
D (
n =
5 o
f 8)
186
Tota
l Fus
ion
Age
350
5plusmn
023
AT
01-1
7a s
anid
ine
J =
00
0297
6 plusmn
000
0009
mas
s di
scri
min
atio
n pe
r am
u 1
002
2 plusmn
000
04
AB
2132
00
4 W
00
0055
1 0
000
005
00
0001
4 0
000
006
00
0017
5 0
000
005
00
0362
1 0
000
024
01
8252
2 0
000
076
118
00
456
313
1plusmn
456
AB
2133
00
6 W
00
0019
3 0
000
004
00
0002
6 0
000
003
00
0034
3 0
000
006
00
2579
1 0
000
046
02
1431
6 0
000
110
745
03
447
326
0plusmn
051
AB
2134
01
2 W
00
0018
8 0
000
004
00
0011
6 0
000
007
00
0251
1 0
000
023
02
0468
8 0
000
253
12
8821
1 0
000
967
959
20
568
320
8plusmn
012
AB
2136
01
8 W
00
0050
3 0
000
004
00
0056
8 0
000
012
00
1520
7 0
000
032
12
5179
3 0
000
404
76
2511
3 0
002
510
980
124
678
318
1plusmn
004
AB
2137
02
4 W
00
0056
0 0
000
005
00
0084
3 0
000
018
00
2351
2 0
000
025
19
2193
9 0
000
651
116
3788
5 0
004
597
985
190
700
317
9plusmn
004
AB
2138
02
7 W
00
0036
1 0
000
008
00
0070
7 0
000
010
00
1915
2 0
000
024
15
7872
8 0
000
654
95
5607
9 0
004
091
988
156
686
318
7plusmn
005
AB
2139
03
1 W
00
0036
3 0
000
001
00
0052
2 0
000
008
00
1472
7 0
000
035
12
0293
6 0
000
478
73
0039
4 0
003
784
985
119
709
318
4plusmn
005
AB
2141
03
5 W
00
0031
1 0
000
007
00
0037
7 0
000
008
00
1054
1 0
000
029
08
7899
6 0
000
319
53
5364
2 0
002
077
983
87
716
318
8plusmn
005
AB
2142
04
5 W
00
0032
8 0
000
004
00
0055
3 0
000
015
00
1592
7 0
000
034
13
0785
9 0
000
548
79
4703
7 0
003
239
987
129
726
319
6plusmn
005
AB
2143
05
9 W
00
0028
5 0
000
005
00
0039
4 0
000
012
00
1085
1 0
000
045
08
9161
3 0
000
557
54
3036
7 0
002
402
984
88
696
319
3plusmn
006
AB
2145
08
4 W
00
0016
0 0
000
004
00
0019
6 0
000
007
00
0560
3 0
000
028
04
5183
5 0
000
332
27
6009
9 0
001
984
983
45
706
319
7plusmn
008
AB
2146
13
5 W
00
0016
6 0
000
005
00
0018
3 0
000
004
00
0462
0 0
000
018
03
8294
7 0
000
252
23
5385
3 0
001
397
980
38
647
320
5plusmn
008
Pla
teau
age
318
2plusmn
020
MSW
D (
4 of
12)
279
Tota
l Fus
ion
Age
318
8plusmn
020
aC
orre
cted
for
37A
r an
d 39
Ar
deca
yb
Age
s ca
lcul
ated
rel
ativ
e to
28
34 M
a Ta
ylor
Cre
ek R
hyol
ite
stan
dard
ita
lics
indi
cate
ste
ps o
mit
ted
from
the
plat
eau
age
calc
ulat
ion
see
text
for
deta
ils
Tabl
e 2
40A
r39
Ar
incr
emen
tal-
heat
ing
anal
yses
of a
dula
ria
and
sani
dine
from
Ada
Tep
e
71Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
EocenendashOligocene sedimentary rocks The latteris represented by sandstones unaffected by hy-drothermal alteration which cover the northernpart of the deposit
8 Sr and Pb isotope compositionsof carbonates and pyrite
Sr and Pb isotopes were measured by standardTIMS procedures at the University of GenevaSwitzerland following the methods of Valenza etal (2000) and Chiaradia and Fontboteacute (2002) Srisotope ratios on carbonate and Pb isotope ratiosfrom pyrite at Ada Tepe along with whole rock Srand Pb isotope ratios of the leachate fraction of asample from Synap prospect 2 km west of AdaTepe are presented in Table 3 and Figs 9 and 10The Ada Tepe carbonate is from a late stage an-kerite-dolomite vein taken from a drill-core sam-ple (AT01-22) at 996 m depth The bulk rock(sample Sin2000-28) from Synap is from sericite-adularia alteration from the surface Pyrite fromAda Tepe is from a strongly silicified sample(Km2000-6) Pyrite from Synap is from the samehand sample Sin2000-28 on which the Sr wasmeasured Both samples belong to the early alter-
ation The initial 87Sr86Sr ratio of the whole rockcorrected for 35 Ma is 070809 The pyrite sampleand whole rock leachate show identical 207Pb204Pb (1568) and 208Pb204Pb (3885) ratios andslightly different 206Pb204Pb ratios (1871 in AdaTepe and 1866 in Synap) The Sr and Pb isotopedata are compared with those of local Paleogenevolcanic rocks and dykes and the Rhodope meta-morphic rocks in Figs 9 and 10
9 Discussion
91 Physical environment
Epithermal quartz from the Ada Tepe deposit ispoor in fluid inclusions particularly the early mi-crocrystalline quartz and opal Euhedral late sug-ary quartz is the only phase which contains largerfluid inclusions but with no reliable characteris-tics that may allow to classify them as primary in-clusions For the similar Sleeper deposit USASaunders (1994) suggested that quartz formed bytransformation of poorly ordered silica may ex-clude trapped fluids thus precluding the use ofmicrothermometry to constrain the physicochem-ical conditions of silica and gold deposition
Fig 7 (a) Geode of coarse-crystalline quartz with carbonate infill (third stage) (b) Third stage coarse-crystallinequartz (ccq) and bladed parallel type calcite (c) (c) Late vein (forth stage) composed by pyrite on its margins fol-lowed by dolomite-ankerite (da) (d) Same fracture Dolomite-ankerite forms a halo overlapping quartz-adularia-pyrite alteration
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
67Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
The economic gold is related to the secondstage of mineralization It starts at the end of themicrocrystalline quartz and the beginning of thecoarser grained (sugary) quartz of the third stagebelow (Fig 5b) Usually it forms black millimeter-scale bands of opaline or microcrystalline chal-cedony-adularia and electrum (Figs 5cndashf) Locallyopaline silica crosscuts the microcrystallinequartz (Figs 5cndashd) of the early stage and in turn iscut by the coarser grained quartz and carbonatesof the third and forth stages (Figs 5dndashe) Petro-graphic examination of the electrum-rich bandsreveals that electrum commonly occurs towardsthe bottom of the opaline or microcrystallinebands (Figs 5c e) Where opaline bands are notpresent electrum precipitates at the boundary offirst and third stages (Fig 5b) The electrum hasirregular forms as the result of crystallization inthe quartz interstices being relatively well-shapedin the coarser-grained quartz crystals The size ofelectrum grains ranges from less than 1 to 20 micromHowever the single crystals form chains reachingup to 650 microm (Figs 5b 6a) Electrum in gold-richbands etched with HF is characterized by botryoi-dal surfaces that appear to have formed by theaggregation of spherical electrum particles (Figs6andashb) as observed in the Sleeper deposit Nevada(Saunders 1990 1994) Electrum in bonanza veinscan occupy 50 vol (Figs 5f 6c) accompanied byrare As-bearing pyrite Occasionally micron orsubmicron size electrum inclusions form zoneswithin the As-bearing pyrite (Figs 6d) Tiny AundashAg tellurides have been observed at the contactsbetween electrum grains and small galena crystals(Fig 6f)
The third stage starts with deposition of sugaryquartz (up to 15 mm large Figs 5d 7a) followedby bands of quartz and bladed calcite (Figs 5b 7b)and finally by massive calcite with small amountof quartz (Fig 5d) Locally calcite fills quartz ge-odes or forms small veins (Fig 7a) Microscopical-ly the late calcite corrodes and replaces quartzcrystals Small amount of adularia and pyrite arealso typical for this stage
The hydrothermal mineralization ended withthe deposition of pinkish ankerite-dolomite andsiderite which was preceded by precipitation ofmassive pyrite in some parts of the deposit (Figs7cndashd)
The mineralization of Ada Tepe exhibits sever-al important spatial and textural features thatprovide insights to the physical environment ofore deposition In its upper part quartz becomesthe predominant gangue mineral whereas car-bonates are subordinate This is particularly obvi-ous in the last stage where in the surface samplesdolomite and ankerite are absent in the geodes
and bladed minerals consist of microcrystallinequartz only Another spatial variation is the di-minishing of banding textures with the decreasein grade of Au mineralization to the north Animportant feature is the absence of bladed car-bonates in the veinlets beneath The Wall in con-trast to the entire extent of the deposit above thedetachment surface
53 Oxidized zone
The uppermost part of the Ada Tepe deposit hasbeen oxidized by supergene processes with thedepth of oxidation being dependent upon inten-sity of faulting Due to extensive silicification TheWall itself is generally not oxidized however a 2to 5 m thick zone of oxidation invariably occursabove The Wall Narrow zones of oxidation occurdown to this zone utilizing high angle listric faultsThese faults and fractures most likely acted asconduits for the surface waters to reach the im-permeable silicified zone forming the oxidizedzone above The Wall
Most of the pyrite in the oxidized zones hasbeen converted into limonite identified asgoethite Kaolinite is widely distributed in thiszone forming locally small veinlets Electrum inthe oxidized zone however shows no evidence ofAu enrichment
6 Alteration
In the poorly mineralized zones hydrothermal al-teration is weak with most of the detrital minerals(quartz muscovite and feldspars) remaining unal-tered Alteration consists of chlorite calcite kaoli-nite and subordinate albite pyrite and ankerite-dolomite It seems that calcite and ankerite-dolo-mite are late however it is difficult to distinguishreplacement calcite from vein calcite Quartzadularia calcite pyrite and dolomite-ankerite-siderite plusmn sericite and clay minerals in variableproportions occur in The Wall and immediateproximity to the subvertical quartz and carbonateveins in the strongly mineralized zones Theyformed through replacement of the original meta-morphic minerals included in the sandstone andconglomerate and are associated with relict de-trital quartz and muscovite This complex mineralassemblage is the result of the evolution of thehydrothermal activity
Hydrothermal alteration of the basementmetamorphic rocks is developed within a haloseveral meters in extent beneath The Wall and ismore pronounced around the subvertical veinsThe alteration assemblage includes quartz adu-
P Marchev et al68
Fig 6 (a) SEM images of electrum dendrite etched with HF (b) Negative forms of quartz removed by HFand spherical colloidal particles (c) Opal-electrum band containing ~ 50 electrum and small amount ofpyrite Dark crystals between electrum are adularia and silica (d) Pyrite with a zone of submicron-size elec-trum (e) Former Py converted to goethite with inclusions of Au (f) AundashAg tellurides between larger elec-trum and galena crystals
69Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
laria illite or sericite pyrite kaolinite and latestage ankerite-dolomite-siderite
Clay minerals are more abundant and betterdeveloped in the alteration close to the surfacewhere they form argillic zones between the EndashW-oriented swarms of veins Kaolinite and quartzpredominate in the argillic zones and illite chlo-rite adularia and carbonate are subordinate ac-companied locally by illite-montmorillonite Partof the shallow-level kaolinite may be supergenebut its association with unoxidized pyrite beneathand within The Wall indicates that a hypogene ori-gin is likely at least for the deeper kaolinite
7 Geochronology
40Ar39Ar ages from adularia and sanidine sam-ples were determined to constrain the timing ofmineralization and volcanic activity in the Kesse-bir dome Sample AT01-2 from which adulariawas extracted for dating is from a drill-hole at725 m depth It represents a quartz-adularia-car-bonate banded vein filled with finely veinedgneiss clasts It is a mixture of completely replaceddetrital K-feldspar and directly deposited adular-ia crystals The rhyolite dyke (sample AT01-17) isemplaced within the core orthogneisses of theKessebir dome located 4 km southwest from AdaTepe (Fig 2) It comprises 2 cm diameter sanidinephenocrysts that were separated for dating plusplagioclase biotite and quartz
40Ar39Ar experiments were conducted at UW-Madison Rare Gas Geochronology LaboratoryMinerals were separated from 100ndash250 micronsieve fractions using standard magnetic densityand handpicking methods Five milligrams of eachmineral were irradiated at Oregon State Univer-sity USA for 12 hours along with 2834 Ma sani-dine from the Taylor Creek rhyolite as the neu-tron fluence monitor Analytical procedures in-cluding mass spectrometry procedural blanks re-actor corrections and estimation of uncertaintiesare given in Singer and Brown (2002) Isotopicmeasurements were made of the gas extracted byincrementally heating of 2ndash3 mg multi-crystal ali-
quots using a defocused CO2 laser beam Resultsof incremental heating experiments along withthe 40Ar39Ar ages of muscovite and biotite fromthe lower plate of the metamorphic basementrocks taken from Bonev et al (accepted) are inTable 1 Incremental heating experiments and agespectra of the sanidine and adularia are presentedin Table 2 and Fig 8 Uncertainties in the agesinclude analytical contributions only at plusmn2
The plateau age of the adularia based on793 of the gas released is 3499 plusmn 023 Ma (Fig8) and is indistinguishable from the total fusionage of 3505 plusmn 023 Ma Sanidine from the rhyolitedyke yielded a plateau age of 3182 plusmn 020 Mabased on 60 percent of the gas released which isindistinguishable from the total fusion age of3188 plusmn 020 Ma As is the case for the adulariathis indicates that argon loss due to weathering oralteration is negligible Moreover the inverse iso-chron ages of 3511 plusmn 037 Ma for the adularaiaand 3191 plusmn 027 Ma for the sanidine are indistin-guishable from the plateau ages and the 40Ar36Arintercept values indicate that there is virtually noexcess argon present
Lavas from the Iran Tepe volcano four kmnortheast of Ada Tepe give KndashAr ages of ~35 Mabut their stratigraphic position above the UpperPriabonianndashLower Oligocene marl-limestone for-mation suggests that they are younger than 34Ma
40Ar39Ar measurements on muscovite and bi-otite (Bonev et al accepted) from the Gneiss-migmatite complex record ages of 3813 plusmn 036and 3773 plusmn 023 Ma respectively (Table 1) Theseages are broadly in agreement with the published40Ar39Ar ages for muscovite (422 plusmn 50 and 361 plusmn50 Ma Lips et al 2000) and muscovite and am-phibole (39 plusmn 1 and 45 plusmn 2 Ma respectively Muka-sa et al 2003) from the Biala Reka metamorphiccore complex Similar ages (39ndash35 Ma) have beenobtained by Peytcheva et al (1992) for the closingof Sr isotope system in the metagranites from theBiala Reka dome
The relative age of the mineralization was de-termined based on its relationship with the hostKrumovgrad group and the overlying Upper
Sample Mineral Weighted Plateau Total Fusion Sourceage (Ma) age (Ma)
AT01-2 adularia 3499 plusmn 023 3505 plusmn 023 this studyAT01-17 sanidine 3182 plusmn 020 3188 plusmn 020 this studyH6 biotite 3773 plusmn 025 3756 plusmn 024 Bonev et al (accepted)H706 muscovite 3813 plusmn 036 3834 plusmn 031 Bonev et al (accepted)
Table 1 Summary of 40Ar39Ar incremental heating experiments on adularia sanidinebiotite and muscovite from Ada Tepe deposit and Kessebir dome
P Marchev et al70
Exp
erim
ent
Las
er p
ower
36A
r37
Ara
38A
r39
Ara
40A
r40
Ar
39A
rK
Ca
Age
plusmn 2
num
ber
(Wat
ts)
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
()
()
(Ma)
b
AT
01-2
adu
lari
a J
= 0
002
987
plusmn 0
0000
09 m
ass
disc
rim
inat
ion
per
amu
10
022
plusmn 0
0004
A
B21
21 0
04
W 0
012
604
00
0003
0 0
000
159
00
0000
5 0
002
772
00
0002
1 0
029
850
00
0007
7 3
871
564
00
0155
74
70
46
132
72
plusmn 3
84A
B21
22 0
10
W 0
009
696
00
0002
2 0
004
566
00
0004
6 0
004
738
00
0002
0 0
239
380
00
0013
1 4
348
793
00
0312
034
92
91
633
85
plusmn 0
38A
B21
23 0
16
W 0
008
804
00
0001
5 0
005
107
00
0003
2 0
006
792
00
0003
0 0
427
709
00
0033
7 5
368
227
00
0278
052
25
32
634
93
plusmn 0
18A
B21
24 0
22
W 0
003
814
00
0001
1 0
000
564
00
0001
0 0
003
949
00
0001
2 0
268
571
00
0011
2 2
865
288
00
0078
961
33
315
034
83
plusmn 0
16A
B21
26 0
30
W 0
008
692
00
0001
1 0
000
261
00
0000
2 0
009
565
00
0002
0 0
650
692
00
0034
7 6
809
601
00
0275
562
78
079
935
01
plusmn 0
11A
B21
27 0
45
W 0
011
765
00
0001
5 0
000
226
00
0000
6 0
017
464
00
0003
5 1
258
986
00
0031
211
697
117
00
0648
770
524
817
70
350
0plusmn
009
AB
2128
06
9 W
00
1320
9 0
000
022
00
0019
9 0
000
003
00
1740
1 0
000
014
12
3066
3 0
001
217
119
6079
5 0
012
113
676
379
195
935
11
plusmn 0
15A
B21
29 1
25
W 0
012
274
00
0002
1 0
000
249
00
0000
3 0
017
405
00
0003
7 1
255
200
00
0080
311
896
055
00
0449
369
817
316
11
353
2plusmn
010
Pla
teau
age
349
9plusmn
023
MSW
D (
n =
5 o
f 8)
186
Tota
l Fus
ion
Age
350
5plusmn
023
AT
01-1
7a s
anid
ine
J =
00
0297
6 plusmn
000
0009
mas
s di
scri
min
atio
n pe
r am
u 1
002
2 plusmn
000
04
AB
2132
00
4 W
00
0055
1 0
000
005
00
0001
4 0
000
006
00
0017
5 0
000
005
00
0362
1 0
000
024
01
8252
2 0
000
076
118
00
456
313
1plusmn
456
AB
2133
00
6 W
00
0019
3 0
000
004
00
0002
6 0
000
003
00
0034
3 0
000
006
00
2579
1 0
000
046
02
1431
6 0
000
110
745
03
447
326
0plusmn
051
AB
2134
01
2 W
00
0018
8 0
000
004
00
0011
6 0
000
007
00
0251
1 0
000
023
02
0468
8 0
000
253
12
8821
1 0
000
967
959
20
568
320
8plusmn
012
AB
2136
01
8 W
00
0050
3 0
000
004
00
0056
8 0
000
012
00
1520
7 0
000
032
12
5179
3 0
000
404
76
2511
3 0
002
510
980
124
678
318
1plusmn
004
AB
2137
02
4 W
00
0056
0 0
000
005
00
0084
3 0
000
018
00
2351
2 0
000
025
19
2193
9 0
000
651
116
3788
5 0
004
597
985
190
700
317
9plusmn
004
AB
2138
02
7 W
00
0036
1 0
000
008
00
0070
7 0
000
010
00
1915
2 0
000
024
15
7872
8 0
000
654
95
5607
9 0
004
091
988
156
686
318
7plusmn
005
AB
2139
03
1 W
00
0036
3 0
000
001
00
0052
2 0
000
008
00
1472
7 0
000
035
12
0293
6 0
000
478
73
0039
4 0
003
784
985
119
709
318
4plusmn
005
AB
2141
03
5 W
00
0031
1 0
000
007
00
0037
7 0
000
008
00
1054
1 0
000
029
08
7899
6 0
000
319
53
5364
2 0
002
077
983
87
716
318
8plusmn
005
AB
2142
04
5 W
00
0032
8 0
000
004
00
0055
3 0
000
015
00
1592
7 0
000
034
13
0785
9 0
000
548
79
4703
7 0
003
239
987
129
726
319
6plusmn
005
AB
2143
05
9 W
00
0028
5 0
000
005
00
0039
4 0
000
012
00
1085
1 0
000
045
08
9161
3 0
000
557
54
3036
7 0
002
402
984
88
696
319
3plusmn
006
AB
2145
08
4 W
00
0016
0 0
000
004
00
0019
6 0
000
007
00
0560
3 0
000
028
04
5183
5 0
000
332
27
6009
9 0
001
984
983
45
706
319
7plusmn
008
AB
2146
13
5 W
00
0016
6 0
000
005
00
0018
3 0
000
004
00
0462
0 0
000
018
03
8294
7 0
000
252
23
5385
3 0
001
397
980
38
647
320
5plusmn
008
Pla
teau
age
318
2plusmn
020
MSW
D (
4 of
12)
279
Tota
l Fus
ion
Age
318
8plusmn
020
aC
orre
cted
for
37A
r an
d 39
Ar
deca
yb
Age
s ca
lcul
ated
rel
ativ
e to
28
34 M
a Ta
ylor
Cre
ek R
hyol
ite
stan
dard
ita
lics
indi
cate
ste
ps o
mit
ted
from
the
plat
eau
age
calc
ulat
ion
see
text
for
deta
ils
Tabl
e 2
40A
r39
Ar
incr
emen
tal-
heat
ing
anal
yses
of a
dula
ria
and
sani
dine
from
Ada
Tep
e
71Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
EocenendashOligocene sedimentary rocks The latteris represented by sandstones unaffected by hy-drothermal alteration which cover the northernpart of the deposit
8 Sr and Pb isotope compositionsof carbonates and pyrite
Sr and Pb isotopes were measured by standardTIMS procedures at the University of GenevaSwitzerland following the methods of Valenza etal (2000) and Chiaradia and Fontboteacute (2002) Srisotope ratios on carbonate and Pb isotope ratiosfrom pyrite at Ada Tepe along with whole rock Srand Pb isotope ratios of the leachate fraction of asample from Synap prospect 2 km west of AdaTepe are presented in Table 3 and Figs 9 and 10The Ada Tepe carbonate is from a late stage an-kerite-dolomite vein taken from a drill-core sam-ple (AT01-22) at 996 m depth The bulk rock(sample Sin2000-28) from Synap is from sericite-adularia alteration from the surface Pyrite fromAda Tepe is from a strongly silicified sample(Km2000-6) Pyrite from Synap is from the samehand sample Sin2000-28 on which the Sr wasmeasured Both samples belong to the early alter-
ation The initial 87Sr86Sr ratio of the whole rockcorrected for 35 Ma is 070809 The pyrite sampleand whole rock leachate show identical 207Pb204Pb (1568) and 208Pb204Pb (3885) ratios andslightly different 206Pb204Pb ratios (1871 in AdaTepe and 1866 in Synap) The Sr and Pb isotopedata are compared with those of local Paleogenevolcanic rocks and dykes and the Rhodope meta-morphic rocks in Figs 9 and 10
9 Discussion
91 Physical environment
Epithermal quartz from the Ada Tepe deposit ispoor in fluid inclusions particularly the early mi-crocrystalline quartz and opal Euhedral late sug-ary quartz is the only phase which contains largerfluid inclusions but with no reliable characteris-tics that may allow to classify them as primary in-clusions For the similar Sleeper deposit USASaunders (1994) suggested that quartz formed bytransformation of poorly ordered silica may ex-clude trapped fluids thus precluding the use ofmicrothermometry to constrain the physicochem-ical conditions of silica and gold deposition
Fig 7 (a) Geode of coarse-crystalline quartz with carbonate infill (third stage) (b) Third stage coarse-crystallinequartz (ccq) and bladed parallel type calcite (c) (c) Late vein (forth stage) composed by pyrite on its margins fol-lowed by dolomite-ankerite (da) (d) Same fracture Dolomite-ankerite forms a halo overlapping quartz-adularia-pyrite alteration
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
P Marchev et al68
Fig 6 (a) SEM images of electrum dendrite etched with HF (b) Negative forms of quartz removed by HFand spherical colloidal particles (c) Opal-electrum band containing ~ 50 electrum and small amount ofpyrite Dark crystals between electrum are adularia and silica (d) Pyrite with a zone of submicron-size elec-trum (e) Former Py converted to goethite with inclusions of Au (f) AundashAg tellurides between larger elec-trum and galena crystals
69Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
laria illite or sericite pyrite kaolinite and latestage ankerite-dolomite-siderite
Clay minerals are more abundant and betterdeveloped in the alteration close to the surfacewhere they form argillic zones between the EndashW-oriented swarms of veins Kaolinite and quartzpredominate in the argillic zones and illite chlo-rite adularia and carbonate are subordinate ac-companied locally by illite-montmorillonite Partof the shallow-level kaolinite may be supergenebut its association with unoxidized pyrite beneathand within The Wall indicates that a hypogene ori-gin is likely at least for the deeper kaolinite
7 Geochronology
40Ar39Ar ages from adularia and sanidine sam-ples were determined to constrain the timing ofmineralization and volcanic activity in the Kesse-bir dome Sample AT01-2 from which adulariawas extracted for dating is from a drill-hole at725 m depth It represents a quartz-adularia-car-bonate banded vein filled with finely veinedgneiss clasts It is a mixture of completely replaceddetrital K-feldspar and directly deposited adular-ia crystals The rhyolite dyke (sample AT01-17) isemplaced within the core orthogneisses of theKessebir dome located 4 km southwest from AdaTepe (Fig 2) It comprises 2 cm diameter sanidinephenocrysts that were separated for dating plusplagioclase biotite and quartz
40Ar39Ar experiments were conducted at UW-Madison Rare Gas Geochronology LaboratoryMinerals were separated from 100ndash250 micronsieve fractions using standard magnetic densityand handpicking methods Five milligrams of eachmineral were irradiated at Oregon State Univer-sity USA for 12 hours along with 2834 Ma sani-dine from the Taylor Creek rhyolite as the neu-tron fluence monitor Analytical procedures in-cluding mass spectrometry procedural blanks re-actor corrections and estimation of uncertaintiesare given in Singer and Brown (2002) Isotopicmeasurements were made of the gas extracted byincrementally heating of 2ndash3 mg multi-crystal ali-
quots using a defocused CO2 laser beam Resultsof incremental heating experiments along withthe 40Ar39Ar ages of muscovite and biotite fromthe lower plate of the metamorphic basementrocks taken from Bonev et al (accepted) are inTable 1 Incremental heating experiments and agespectra of the sanidine and adularia are presentedin Table 2 and Fig 8 Uncertainties in the agesinclude analytical contributions only at plusmn2
The plateau age of the adularia based on793 of the gas released is 3499 plusmn 023 Ma (Fig8) and is indistinguishable from the total fusionage of 3505 plusmn 023 Ma Sanidine from the rhyolitedyke yielded a plateau age of 3182 plusmn 020 Mabased on 60 percent of the gas released which isindistinguishable from the total fusion age of3188 plusmn 020 Ma As is the case for the adulariathis indicates that argon loss due to weathering oralteration is negligible Moreover the inverse iso-chron ages of 3511 plusmn 037 Ma for the adularaiaand 3191 plusmn 027 Ma for the sanidine are indistin-guishable from the plateau ages and the 40Ar36Arintercept values indicate that there is virtually noexcess argon present
Lavas from the Iran Tepe volcano four kmnortheast of Ada Tepe give KndashAr ages of ~35 Mabut their stratigraphic position above the UpperPriabonianndashLower Oligocene marl-limestone for-mation suggests that they are younger than 34Ma
40Ar39Ar measurements on muscovite and bi-otite (Bonev et al accepted) from the Gneiss-migmatite complex record ages of 3813 plusmn 036and 3773 plusmn 023 Ma respectively (Table 1) Theseages are broadly in agreement with the published40Ar39Ar ages for muscovite (422 plusmn 50 and 361 plusmn50 Ma Lips et al 2000) and muscovite and am-phibole (39 plusmn 1 and 45 plusmn 2 Ma respectively Muka-sa et al 2003) from the Biala Reka metamorphiccore complex Similar ages (39ndash35 Ma) have beenobtained by Peytcheva et al (1992) for the closingof Sr isotope system in the metagranites from theBiala Reka dome
The relative age of the mineralization was de-termined based on its relationship with the hostKrumovgrad group and the overlying Upper
Sample Mineral Weighted Plateau Total Fusion Sourceage (Ma) age (Ma)
AT01-2 adularia 3499 plusmn 023 3505 plusmn 023 this studyAT01-17 sanidine 3182 plusmn 020 3188 plusmn 020 this studyH6 biotite 3773 plusmn 025 3756 plusmn 024 Bonev et al (accepted)H706 muscovite 3813 plusmn 036 3834 plusmn 031 Bonev et al (accepted)
Table 1 Summary of 40Ar39Ar incremental heating experiments on adularia sanidinebiotite and muscovite from Ada Tepe deposit and Kessebir dome
P Marchev et al70
Exp
erim
ent
Las
er p
ower
36A
r37
Ara
38A
r39
Ara
40A
r40
Ar
39A
rK
Ca
Age
plusmn 2
num
ber
(Wat
ts)
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
()
()
(Ma)
b
AT
01-2
adu
lari
a J
= 0
002
987
plusmn 0
0000
09 m
ass
disc
rim
inat
ion
per
amu
10
022
plusmn 0
0004
A
B21
21 0
04
W 0
012
604
00
0003
0 0
000
159
00
0000
5 0
002
772
00
0002
1 0
029
850
00
0007
7 3
871
564
00
0155
74
70
46
132
72
plusmn 3
84A
B21
22 0
10
W 0
009
696
00
0002
2 0
004
566
00
0004
6 0
004
738
00
0002
0 0
239
380
00
0013
1 4
348
793
00
0312
034
92
91
633
85
plusmn 0
38A
B21
23 0
16
W 0
008
804
00
0001
5 0
005
107
00
0003
2 0
006
792
00
0003
0 0
427
709
00
0033
7 5
368
227
00
0278
052
25
32
634
93
plusmn 0
18A
B21
24 0
22
W 0
003
814
00
0001
1 0
000
564
00
0001
0 0
003
949
00
0001
2 0
268
571
00
0011
2 2
865
288
00
0078
961
33
315
034
83
plusmn 0
16A
B21
26 0
30
W 0
008
692
00
0001
1 0
000
261
00
0000
2 0
009
565
00
0002
0 0
650
692
00
0034
7 6
809
601
00
0275
562
78
079
935
01
plusmn 0
11A
B21
27 0
45
W 0
011
765
00
0001
5 0
000
226
00
0000
6 0
017
464
00
0003
5 1
258
986
00
0031
211
697
117
00
0648
770
524
817
70
350
0plusmn
009
AB
2128
06
9 W
00
1320
9 0
000
022
00
0019
9 0
000
003
00
1740
1 0
000
014
12
3066
3 0
001
217
119
6079
5 0
012
113
676
379
195
935
11
plusmn 0
15A
B21
29 1
25
W 0
012
274
00
0002
1 0
000
249
00
0000
3 0
017
405
00
0003
7 1
255
200
00
0080
311
896
055
00
0449
369
817
316
11
353
2plusmn
010
Pla
teau
age
349
9plusmn
023
MSW
D (
n =
5 o
f 8)
186
Tota
l Fus
ion
Age
350
5plusmn
023
AT
01-1
7a s
anid
ine
J =
00
0297
6 plusmn
000
0009
mas
s di
scri
min
atio
n pe
r am
u 1
002
2 plusmn
000
04
AB
2132
00
4 W
00
0055
1 0
000
005
00
0001
4 0
000
006
00
0017
5 0
000
005
00
0362
1 0
000
024
01
8252
2 0
000
076
118
00
456
313
1plusmn
456
AB
2133
00
6 W
00
0019
3 0
000
004
00
0002
6 0
000
003
00
0034
3 0
000
006
00
2579
1 0
000
046
02
1431
6 0
000
110
745
03
447
326
0plusmn
051
AB
2134
01
2 W
00
0018
8 0
000
004
00
0011
6 0
000
007
00
0251
1 0
000
023
02
0468
8 0
000
253
12
8821
1 0
000
967
959
20
568
320
8plusmn
012
AB
2136
01
8 W
00
0050
3 0
000
004
00
0056
8 0
000
012
00
1520
7 0
000
032
12
5179
3 0
000
404
76
2511
3 0
002
510
980
124
678
318
1plusmn
004
AB
2137
02
4 W
00
0056
0 0
000
005
00
0084
3 0
000
018
00
2351
2 0
000
025
19
2193
9 0
000
651
116
3788
5 0
004
597
985
190
700
317
9plusmn
004
AB
2138
02
7 W
00
0036
1 0
000
008
00
0070
7 0
000
010
00
1915
2 0
000
024
15
7872
8 0
000
654
95
5607
9 0
004
091
988
156
686
318
7plusmn
005
AB
2139
03
1 W
00
0036
3 0
000
001
00
0052
2 0
000
008
00
1472
7 0
000
035
12
0293
6 0
000
478
73
0039
4 0
003
784
985
119
709
318
4plusmn
005
AB
2141
03
5 W
00
0031
1 0
000
007
00
0037
7 0
000
008
00
1054
1 0
000
029
08
7899
6 0
000
319
53
5364
2 0
002
077
983
87
716
318
8plusmn
005
AB
2142
04
5 W
00
0032
8 0
000
004
00
0055
3 0
000
015
00
1592
7 0
000
034
13
0785
9 0
000
548
79
4703
7 0
003
239
987
129
726
319
6plusmn
005
AB
2143
05
9 W
00
0028
5 0
000
005
00
0039
4 0
000
012
00
1085
1 0
000
045
08
9161
3 0
000
557
54
3036
7 0
002
402
984
88
696
319
3plusmn
006
AB
2145
08
4 W
00
0016
0 0
000
004
00
0019
6 0
000
007
00
0560
3 0
000
028
04
5183
5 0
000
332
27
6009
9 0
001
984
983
45
706
319
7plusmn
008
AB
2146
13
5 W
00
0016
6 0
000
005
00
0018
3 0
000
004
00
0462
0 0
000
018
03
8294
7 0
000
252
23
5385
3 0
001
397
980
38
647
320
5plusmn
008
Pla
teau
age
318
2plusmn
020
MSW
D (
4 of
12)
279
Tota
l Fus
ion
Age
318
8plusmn
020
aC
orre
cted
for
37A
r an
d 39
Ar
deca
yb
Age
s ca
lcul
ated
rel
ativ
e to
28
34 M
a Ta
ylor
Cre
ek R
hyol
ite
stan
dard
ita
lics
indi
cate
ste
ps o
mit
ted
from
the
plat
eau
age
calc
ulat
ion
see
text
for
deta
ils
Tabl
e 2
40A
r39
Ar
incr
emen
tal-
heat
ing
anal
yses
of a
dula
ria
and
sani
dine
from
Ada
Tep
e
71Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
EocenendashOligocene sedimentary rocks The latteris represented by sandstones unaffected by hy-drothermal alteration which cover the northernpart of the deposit
8 Sr and Pb isotope compositionsof carbonates and pyrite
Sr and Pb isotopes were measured by standardTIMS procedures at the University of GenevaSwitzerland following the methods of Valenza etal (2000) and Chiaradia and Fontboteacute (2002) Srisotope ratios on carbonate and Pb isotope ratiosfrom pyrite at Ada Tepe along with whole rock Srand Pb isotope ratios of the leachate fraction of asample from Synap prospect 2 km west of AdaTepe are presented in Table 3 and Figs 9 and 10The Ada Tepe carbonate is from a late stage an-kerite-dolomite vein taken from a drill-core sam-ple (AT01-22) at 996 m depth The bulk rock(sample Sin2000-28) from Synap is from sericite-adularia alteration from the surface Pyrite fromAda Tepe is from a strongly silicified sample(Km2000-6) Pyrite from Synap is from the samehand sample Sin2000-28 on which the Sr wasmeasured Both samples belong to the early alter-
ation The initial 87Sr86Sr ratio of the whole rockcorrected for 35 Ma is 070809 The pyrite sampleand whole rock leachate show identical 207Pb204Pb (1568) and 208Pb204Pb (3885) ratios andslightly different 206Pb204Pb ratios (1871 in AdaTepe and 1866 in Synap) The Sr and Pb isotopedata are compared with those of local Paleogenevolcanic rocks and dykes and the Rhodope meta-morphic rocks in Figs 9 and 10
9 Discussion
91 Physical environment
Epithermal quartz from the Ada Tepe deposit ispoor in fluid inclusions particularly the early mi-crocrystalline quartz and opal Euhedral late sug-ary quartz is the only phase which contains largerfluid inclusions but with no reliable characteris-tics that may allow to classify them as primary in-clusions For the similar Sleeper deposit USASaunders (1994) suggested that quartz formed bytransformation of poorly ordered silica may ex-clude trapped fluids thus precluding the use ofmicrothermometry to constrain the physicochem-ical conditions of silica and gold deposition
Fig 7 (a) Geode of coarse-crystalline quartz with carbonate infill (third stage) (b) Third stage coarse-crystallinequartz (ccq) and bladed parallel type calcite (c) (c) Late vein (forth stage) composed by pyrite on its margins fol-lowed by dolomite-ankerite (da) (d) Same fracture Dolomite-ankerite forms a halo overlapping quartz-adularia-pyrite alteration
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
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Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
69Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
laria illite or sericite pyrite kaolinite and latestage ankerite-dolomite-siderite
Clay minerals are more abundant and betterdeveloped in the alteration close to the surfacewhere they form argillic zones between the EndashW-oriented swarms of veins Kaolinite and quartzpredominate in the argillic zones and illite chlo-rite adularia and carbonate are subordinate ac-companied locally by illite-montmorillonite Partof the shallow-level kaolinite may be supergenebut its association with unoxidized pyrite beneathand within The Wall indicates that a hypogene ori-gin is likely at least for the deeper kaolinite
7 Geochronology
40Ar39Ar ages from adularia and sanidine sam-ples were determined to constrain the timing ofmineralization and volcanic activity in the Kesse-bir dome Sample AT01-2 from which adulariawas extracted for dating is from a drill-hole at725 m depth It represents a quartz-adularia-car-bonate banded vein filled with finely veinedgneiss clasts It is a mixture of completely replaceddetrital K-feldspar and directly deposited adular-ia crystals The rhyolite dyke (sample AT01-17) isemplaced within the core orthogneisses of theKessebir dome located 4 km southwest from AdaTepe (Fig 2) It comprises 2 cm diameter sanidinephenocrysts that were separated for dating plusplagioclase biotite and quartz
40Ar39Ar experiments were conducted at UW-Madison Rare Gas Geochronology LaboratoryMinerals were separated from 100ndash250 micronsieve fractions using standard magnetic densityand handpicking methods Five milligrams of eachmineral were irradiated at Oregon State Univer-sity USA for 12 hours along with 2834 Ma sani-dine from the Taylor Creek rhyolite as the neu-tron fluence monitor Analytical procedures in-cluding mass spectrometry procedural blanks re-actor corrections and estimation of uncertaintiesare given in Singer and Brown (2002) Isotopicmeasurements were made of the gas extracted byincrementally heating of 2ndash3 mg multi-crystal ali-
quots using a defocused CO2 laser beam Resultsof incremental heating experiments along withthe 40Ar39Ar ages of muscovite and biotite fromthe lower plate of the metamorphic basementrocks taken from Bonev et al (accepted) are inTable 1 Incremental heating experiments and agespectra of the sanidine and adularia are presentedin Table 2 and Fig 8 Uncertainties in the agesinclude analytical contributions only at plusmn2
The plateau age of the adularia based on793 of the gas released is 3499 plusmn 023 Ma (Fig8) and is indistinguishable from the total fusionage of 3505 plusmn 023 Ma Sanidine from the rhyolitedyke yielded a plateau age of 3182 plusmn 020 Mabased on 60 percent of the gas released which isindistinguishable from the total fusion age of3188 plusmn 020 Ma As is the case for the adulariathis indicates that argon loss due to weathering oralteration is negligible Moreover the inverse iso-chron ages of 3511 plusmn 037 Ma for the adularaiaand 3191 plusmn 027 Ma for the sanidine are indistin-guishable from the plateau ages and the 40Ar36Arintercept values indicate that there is virtually noexcess argon present
Lavas from the Iran Tepe volcano four kmnortheast of Ada Tepe give KndashAr ages of ~35 Mabut their stratigraphic position above the UpperPriabonianndashLower Oligocene marl-limestone for-mation suggests that they are younger than 34Ma
40Ar39Ar measurements on muscovite and bi-otite (Bonev et al accepted) from the Gneiss-migmatite complex record ages of 3813 plusmn 036and 3773 plusmn 023 Ma respectively (Table 1) Theseages are broadly in agreement with the published40Ar39Ar ages for muscovite (422 plusmn 50 and 361 plusmn50 Ma Lips et al 2000) and muscovite and am-phibole (39 plusmn 1 and 45 plusmn 2 Ma respectively Muka-sa et al 2003) from the Biala Reka metamorphiccore complex Similar ages (39ndash35 Ma) have beenobtained by Peytcheva et al (1992) for the closingof Sr isotope system in the metagranites from theBiala Reka dome
The relative age of the mineralization was de-termined based on its relationship with the hostKrumovgrad group and the overlying Upper
Sample Mineral Weighted Plateau Total Fusion Sourceage (Ma) age (Ma)
AT01-2 adularia 3499 plusmn 023 3505 plusmn 023 this studyAT01-17 sanidine 3182 plusmn 020 3188 plusmn 020 this studyH6 biotite 3773 plusmn 025 3756 plusmn 024 Bonev et al (accepted)H706 muscovite 3813 plusmn 036 3834 plusmn 031 Bonev et al (accepted)
Table 1 Summary of 40Ar39Ar incremental heating experiments on adularia sanidinebiotite and muscovite from Ada Tepe deposit and Kessebir dome
P Marchev et al70
Exp
erim
ent
Las
er p
ower
36A
r37
Ara
38A
r39
Ara
40A
r40
Ar
39A
rK
Ca
Age
plusmn 2
num
ber
(Wat
ts)
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
()
()
(Ma)
b
AT
01-2
adu
lari
a J
= 0
002
987
plusmn 0
0000
09 m
ass
disc
rim
inat
ion
per
amu
10
022
plusmn 0
0004
A
B21
21 0
04
W 0
012
604
00
0003
0 0
000
159
00
0000
5 0
002
772
00
0002
1 0
029
850
00
0007
7 3
871
564
00
0155
74
70
46
132
72
plusmn 3
84A
B21
22 0
10
W 0
009
696
00
0002
2 0
004
566
00
0004
6 0
004
738
00
0002
0 0
239
380
00
0013
1 4
348
793
00
0312
034
92
91
633
85
plusmn 0
38A
B21
23 0
16
W 0
008
804
00
0001
5 0
005
107
00
0003
2 0
006
792
00
0003
0 0
427
709
00
0033
7 5
368
227
00
0278
052
25
32
634
93
plusmn 0
18A
B21
24 0
22
W 0
003
814
00
0001
1 0
000
564
00
0001
0 0
003
949
00
0001
2 0
268
571
00
0011
2 2
865
288
00
0078
961
33
315
034
83
plusmn 0
16A
B21
26 0
30
W 0
008
692
00
0001
1 0
000
261
00
0000
2 0
009
565
00
0002
0 0
650
692
00
0034
7 6
809
601
00
0275
562
78
079
935
01
plusmn 0
11A
B21
27 0
45
W 0
011
765
00
0001
5 0
000
226
00
0000
6 0
017
464
00
0003
5 1
258
986
00
0031
211
697
117
00
0648
770
524
817
70
350
0plusmn
009
AB
2128
06
9 W
00
1320
9 0
000
022
00
0019
9 0
000
003
00
1740
1 0
000
014
12
3066
3 0
001
217
119
6079
5 0
012
113
676
379
195
935
11
plusmn 0
15A
B21
29 1
25
W 0
012
274
00
0002
1 0
000
249
00
0000
3 0
017
405
00
0003
7 1
255
200
00
0080
311
896
055
00
0449
369
817
316
11
353
2plusmn
010
Pla
teau
age
349
9plusmn
023
MSW
D (
n =
5 o
f 8)
186
Tota
l Fus
ion
Age
350
5plusmn
023
AT
01-1
7a s
anid
ine
J =
00
0297
6 plusmn
000
0009
mas
s di
scri
min
atio
n pe
r am
u 1
002
2 plusmn
000
04
AB
2132
00
4 W
00
0055
1 0
000
005
00
0001
4 0
000
006
00
0017
5 0
000
005
00
0362
1 0
000
024
01
8252
2 0
000
076
118
00
456
313
1plusmn
456
AB
2133
00
6 W
00
0019
3 0
000
004
00
0002
6 0
000
003
00
0034
3 0
000
006
00
2579
1 0
000
046
02
1431
6 0
000
110
745
03
447
326
0plusmn
051
AB
2134
01
2 W
00
0018
8 0
000
004
00
0011
6 0
000
007
00
0251
1 0
000
023
02
0468
8 0
000
253
12
8821
1 0
000
967
959
20
568
320
8plusmn
012
AB
2136
01
8 W
00
0050
3 0
000
004
00
0056
8 0
000
012
00
1520
7 0
000
032
12
5179
3 0
000
404
76
2511
3 0
002
510
980
124
678
318
1plusmn
004
AB
2137
02
4 W
00
0056
0 0
000
005
00
0084
3 0
000
018
00
2351
2 0
000
025
19
2193
9 0
000
651
116
3788
5 0
004
597
985
190
700
317
9plusmn
004
AB
2138
02
7 W
00
0036
1 0
000
008
00
0070
7 0
000
010
00
1915
2 0
000
024
15
7872
8 0
000
654
95
5607
9 0
004
091
988
156
686
318
7plusmn
005
AB
2139
03
1 W
00
0036
3 0
000
001
00
0052
2 0
000
008
00
1472
7 0
000
035
12
0293
6 0
000
478
73
0039
4 0
003
784
985
119
709
318
4plusmn
005
AB
2141
03
5 W
00
0031
1 0
000
007
00
0037
7 0
000
008
00
1054
1 0
000
029
08
7899
6 0
000
319
53
5364
2 0
002
077
983
87
716
318
8plusmn
005
AB
2142
04
5 W
00
0032
8 0
000
004
00
0055
3 0
000
015
00
1592
7 0
000
034
13
0785
9 0
000
548
79
4703
7 0
003
239
987
129
726
319
6plusmn
005
AB
2143
05
9 W
00
0028
5 0
000
005
00
0039
4 0
000
012
00
1085
1 0
000
045
08
9161
3 0
000
557
54
3036
7 0
002
402
984
88
696
319
3plusmn
006
AB
2145
08
4 W
00
0016
0 0
000
004
00
0019
6 0
000
007
00
0560
3 0
000
028
04
5183
5 0
000
332
27
6009
9 0
001
984
983
45
706
319
7plusmn
008
AB
2146
13
5 W
00
0016
6 0
000
005
00
0018
3 0
000
004
00
0462
0 0
000
018
03
8294
7 0
000
252
23
5385
3 0
001
397
980
38
647
320
5plusmn
008
Pla
teau
age
318
2plusmn
020
MSW
D (
4 of
12)
279
Tota
l Fus
ion
Age
318
8plusmn
020
aC
orre
cted
for
37A
r an
d 39
Ar
deca
yb
Age
s ca
lcul
ated
rel
ativ
e to
28
34 M
a Ta
ylor
Cre
ek R
hyol
ite
stan
dard
ita
lics
indi
cate
ste
ps o
mit
ted
from
the
plat
eau
age
calc
ulat
ion
see
text
for
deta
ils
Tabl
e 2
40A
r39
Ar
incr
emen
tal-
heat
ing
anal
yses
of a
dula
ria
and
sani
dine
from
Ada
Tep
e
71Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
EocenendashOligocene sedimentary rocks The latteris represented by sandstones unaffected by hy-drothermal alteration which cover the northernpart of the deposit
8 Sr and Pb isotope compositionsof carbonates and pyrite
Sr and Pb isotopes were measured by standardTIMS procedures at the University of GenevaSwitzerland following the methods of Valenza etal (2000) and Chiaradia and Fontboteacute (2002) Srisotope ratios on carbonate and Pb isotope ratiosfrom pyrite at Ada Tepe along with whole rock Srand Pb isotope ratios of the leachate fraction of asample from Synap prospect 2 km west of AdaTepe are presented in Table 3 and Figs 9 and 10The Ada Tepe carbonate is from a late stage an-kerite-dolomite vein taken from a drill-core sam-ple (AT01-22) at 996 m depth The bulk rock(sample Sin2000-28) from Synap is from sericite-adularia alteration from the surface Pyrite fromAda Tepe is from a strongly silicified sample(Km2000-6) Pyrite from Synap is from the samehand sample Sin2000-28 on which the Sr wasmeasured Both samples belong to the early alter-
ation The initial 87Sr86Sr ratio of the whole rockcorrected for 35 Ma is 070809 The pyrite sampleand whole rock leachate show identical 207Pb204Pb (1568) and 208Pb204Pb (3885) ratios andslightly different 206Pb204Pb ratios (1871 in AdaTepe and 1866 in Synap) The Sr and Pb isotopedata are compared with those of local Paleogenevolcanic rocks and dykes and the Rhodope meta-morphic rocks in Figs 9 and 10
9 Discussion
91 Physical environment
Epithermal quartz from the Ada Tepe deposit ispoor in fluid inclusions particularly the early mi-crocrystalline quartz and opal Euhedral late sug-ary quartz is the only phase which contains largerfluid inclusions but with no reliable characteris-tics that may allow to classify them as primary in-clusions For the similar Sleeper deposit USASaunders (1994) suggested that quartz formed bytransformation of poorly ordered silica may ex-clude trapped fluids thus precluding the use ofmicrothermometry to constrain the physicochem-ical conditions of silica and gold deposition
Fig 7 (a) Geode of coarse-crystalline quartz with carbonate infill (third stage) (b) Third stage coarse-crystallinequartz (ccq) and bladed parallel type calcite (c) (c) Late vein (forth stage) composed by pyrite on its margins fol-lowed by dolomite-ankerite (da) (d) Same fracture Dolomite-ankerite forms a halo overlapping quartz-adularia-pyrite alteration
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
P Marchev et al70
Exp
erim
ent
Las
er p
ower
36A
r37
Ara
38A
r39
Ara
40A
r40
Ar
39A
rK
Ca
Age
plusmn 2
num
ber
(Wat
ts)
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
(Vol
ts)
plusmn 1
()
()
(Ma)
b
AT
01-2
adu
lari
a J
= 0
002
987
plusmn 0
0000
09 m
ass
disc
rim
inat
ion
per
amu
10
022
plusmn 0
0004
A
B21
21 0
04
W 0
012
604
00
0003
0 0
000
159
00
0000
5 0
002
772
00
0002
1 0
029
850
00
0007
7 3
871
564
00
0155
74
70
46
132
72
plusmn 3
84A
B21
22 0
10
W 0
009
696
00
0002
2 0
004
566
00
0004
6 0
004
738
00
0002
0 0
239
380
00
0013
1 4
348
793
00
0312
034
92
91
633
85
plusmn 0
38A
B21
23 0
16
W 0
008
804
00
0001
5 0
005
107
00
0003
2 0
006
792
00
0003
0 0
427
709
00
0033
7 5
368
227
00
0278
052
25
32
634
93
plusmn 0
18A
B21
24 0
22
W 0
003
814
00
0001
1 0
000
564
00
0001
0 0
003
949
00
0001
2 0
268
571
00
0011
2 2
865
288
00
0078
961
33
315
034
83
plusmn 0
16A
B21
26 0
30
W 0
008
692
00
0001
1 0
000
261
00
0000
2 0
009
565
00
0002
0 0
650
692
00
0034
7 6
809
601
00
0275
562
78
079
935
01
plusmn 0
11A
B21
27 0
45
W 0
011
765
00
0001
5 0
000
226
00
0000
6 0
017
464
00
0003
5 1
258
986
00
0031
211
697
117
00
0648
770
524
817
70
350
0plusmn
009
AB
2128
06
9 W
00
1320
9 0
000
022
00
0019
9 0
000
003
00
1740
1 0
000
014
12
3066
3 0
001
217
119
6079
5 0
012
113
676
379
195
935
11
plusmn 0
15A
B21
29 1
25
W 0
012
274
00
0002
1 0
000
249
00
0000
3 0
017
405
00
0003
7 1
255
200
00
0080
311
896
055
00
0449
369
817
316
11
353
2plusmn
010
Pla
teau
age
349
9plusmn
023
MSW
D (
n =
5 o
f 8)
186
Tota
l Fus
ion
Age
350
5plusmn
023
AT
01-1
7a s
anid
ine
J =
00
0297
6 plusmn
000
0009
mas
s di
scri
min
atio
n pe
r am
u 1
002
2 plusmn
000
04
AB
2132
00
4 W
00
0055
1 0
000
005
00
0001
4 0
000
006
00
0017
5 0
000
005
00
0362
1 0
000
024
01
8252
2 0
000
076
118
00
456
313
1plusmn
456
AB
2133
00
6 W
00
0019
3 0
000
004
00
0002
6 0
000
003
00
0034
3 0
000
006
00
2579
1 0
000
046
02
1431
6 0
000
110
745
03
447
326
0plusmn
051
AB
2134
01
2 W
00
0018
8 0
000
004
00
0011
6 0
000
007
00
0251
1 0
000
023
02
0468
8 0
000
253
12
8821
1 0
000
967
959
20
568
320
8plusmn
012
AB
2136
01
8 W
00
0050
3 0
000
004
00
0056
8 0
000
012
00
1520
7 0
000
032
12
5179
3 0
000
404
76
2511
3 0
002
510
980
124
678
318
1plusmn
004
AB
2137
02
4 W
00
0056
0 0
000
005
00
0084
3 0
000
018
00
2351
2 0
000
025
19
2193
9 0
000
651
116
3788
5 0
004
597
985
190
700
317
9plusmn
004
AB
2138
02
7 W
00
0036
1 0
000
008
00
0070
7 0
000
010
00
1915
2 0
000
024
15
7872
8 0
000
654
95
5607
9 0
004
091
988
156
686
318
7plusmn
005
AB
2139
03
1 W
00
0036
3 0
000
001
00
0052
2 0
000
008
00
1472
7 0
000
035
12
0293
6 0
000
478
73
0039
4 0
003
784
985
119
709
318
4plusmn
005
AB
2141
03
5 W
00
0031
1 0
000
007
00
0037
7 0
000
008
00
1054
1 0
000
029
08
7899
6 0
000
319
53
5364
2 0
002
077
983
87
716
318
8plusmn
005
AB
2142
04
5 W
00
0032
8 0
000
004
00
0055
3 0
000
015
00
1592
7 0
000
034
13
0785
9 0
000
548
79
4703
7 0
003
239
987
129
726
319
6plusmn
005
AB
2143
05
9 W
00
0028
5 0
000
005
00
0039
4 0
000
012
00
1085
1 0
000
045
08
9161
3 0
000
557
54
3036
7 0
002
402
984
88
696
319
3plusmn
006
AB
2145
08
4 W
00
0016
0 0
000
004
00
0019
6 0
000
007
00
0560
3 0
000
028
04
5183
5 0
000
332
27
6009
9 0
001
984
983
45
706
319
7plusmn
008
AB
2146
13
5 W
00
0016
6 0
000
005
00
0018
3 0
000
004
00
0462
0 0
000
018
03
8294
7 0
000
252
23
5385
3 0
001
397
980
38
647
320
5plusmn
008
Pla
teau
age
318
2plusmn
020
MSW
D (
4 of
12)
279
Tota
l Fus
ion
Age
318
8plusmn
020
aC
orre
cted
for
37A
r an
d 39
Ar
deca
yb
Age
s ca
lcul
ated
rel
ativ
e to
28
34 M
a Ta
ylor
Cre
ek R
hyol
ite
stan
dard
ita
lics
indi
cate
ste
ps o
mit
ted
from
the
plat
eau
age
calc
ulat
ion
see
text
for
deta
ils
Tabl
e 2
40A
r39
Ar
incr
emen
tal-
heat
ing
anal
yses
of a
dula
ria
and
sani
dine
from
Ada
Tep
e
71Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
EocenendashOligocene sedimentary rocks The latteris represented by sandstones unaffected by hy-drothermal alteration which cover the northernpart of the deposit
8 Sr and Pb isotope compositionsof carbonates and pyrite
Sr and Pb isotopes were measured by standardTIMS procedures at the University of GenevaSwitzerland following the methods of Valenza etal (2000) and Chiaradia and Fontboteacute (2002) Srisotope ratios on carbonate and Pb isotope ratiosfrom pyrite at Ada Tepe along with whole rock Srand Pb isotope ratios of the leachate fraction of asample from Synap prospect 2 km west of AdaTepe are presented in Table 3 and Figs 9 and 10The Ada Tepe carbonate is from a late stage an-kerite-dolomite vein taken from a drill-core sam-ple (AT01-22) at 996 m depth The bulk rock(sample Sin2000-28) from Synap is from sericite-adularia alteration from the surface Pyrite fromAda Tepe is from a strongly silicified sample(Km2000-6) Pyrite from Synap is from the samehand sample Sin2000-28 on which the Sr wasmeasured Both samples belong to the early alter-
ation The initial 87Sr86Sr ratio of the whole rockcorrected for 35 Ma is 070809 The pyrite sampleand whole rock leachate show identical 207Pb204Pb (1568) and 208Pb204Pb (3885) ratios andslightly different 206Pb204Pb ratios (1871 in AdaTepe and 1866 in Synap) The Sr and Pb isotopedata are compared with those of local Paleogenevolcanic rocks and dykes and the Rhodope meta-morphic rocks in Figs 9 and 10
9 Discussion
91 Physical environment
Epithermal quartz from the Ada Tepe deposit ispoor in fluid inclusions particularly the early mi-crocrystalline quartz and opal Euhedral late sug-ary quartz is the only phase which contains largerfluid inclusions but with no reliable characteris-tics that may allow to classify them as primary in-clusions For the similar Sleeper deposit USASaunders (1994) suggested that quartz formed bytransformation of poorly ordered silica may ex-clude trapped fluids thus precluding the use ofmicrothermometry to constrain the physicochem-ical conditions of silica and gold deposition
Fig 7 (a) Geode of coarse-crystalline quartz with carbonate infill (third stage) (b) Third stage coarse-crystallinequartz (ccq) and bladed parallel type calcite (c) (c) Late vein (forth stage) composed by pyrite on its margins fol-lowed by dolomite-ankerite (da) (d) Same fracture Dolomite-ankerite forms a halo overlapping quartz-adularia-pyrite alteration
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
71Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
EocenendashOligocene sedimentary rocks The latteris represented by sandstones unaffected by hy-drothermal alteration which cover the northernpart of the deposit
8 Sr and Pb isotope compositionsof carbonates and pyrite
Sr and Pb isotopes were measured by standardTIMS procedures at the University of GenevaSwitzerland following the methods of Valenza etal (2000) and Chiaradia and Fontboteacute (2002) Srisotope ratios on carbonate and Pb isotope ratiosfrom pyrite at Ada Tepe along with whole rock Srand Pb isotope ratios of the leachate fraction of asample from Synap prospect 2 km west of AdaTepe are presented in Table 3 and Figs 9 and 10The Ada Tepe carbonate is from a late stage an-kerite-dolomite vein taken from a drill-core sam-ple (AT01-22) at 996 m depth The bulk rock(sample Sin2000-28) from Synap is from sericite-adularia alteration from the surface Pyrite fromAda Tepe is from a strongly silicified sample(Km2000-6) Pyrite from Synap is from the samehand sample Sin2000-28 on which the Sr wasmeasured Both samples belong to the early alter-
ation The initial 87Sr86Sr ratio of the whole rockcorrected for 35 Ma is 070809 The pyrite sampleand whole rock leachate show identical 207Pb204Pb (1568) and 208Pb204Pb (3885) ratios andslightly different 206Pb204Pb ratios (1871 in AdaTepe and 1866 in Synap) The Sr and Pb isotopedata are compared with those of local Paleogenevolcanic rocks and dykes and the Rhodope meta-morphic rocks in Figs 9 and 10
9 Discussion
91 Physical environment
Epithermal quartz from the Ada Tepe deposit ispoor in fluid inclusions particularly the early mi-crocrystalline quartz and opal Euhedral late sug-ary quartz is the only phase which contains largerfluid inclusions but with no reliable characteris-tics that may allow to classify them as primary in-clusions For the similar Sleeper deposit USASaunders (1994) suggested that quartz formed bytransformation of poorly ordered silica may ex-clude trapped fluids thus precluding the use ofmicrothermometry to constrain the physicochem-ical conditions of silica and gold deposition
Fig 7 (a) Geode of coarse-crystalline quartz with carbonate infill (third stage) (b) Third stage coarse-crystallinequartz (ccq) and bladed parallel type calcite (c) (c) Late vein (forth stage) composed by pyrite on its margins fol-lowed by dolomite-ankerite (da) (d) Same fracture Dolomite-ankerite forms a halo overlapping quartz-adularia-pyrite alteration
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
P Marchev et al72
The presence of adularia that spans the time ofhydrothermal mineralization from the early mi-crocrystalline stage to deposition of bonanza elec-trum bands accompanied by early bladed calciteand followed by late bladed CandashMgndashFe carbon-ates is consistent with boiling during most of thehydrothermal process (Izava et al 1990 Sim-mons and Christenson 1994) Evidence for boil-ing occurs throughout the Ada Tepe deposit fromthe present-day surface down to the detachmentsurface The absence of bladed calcite in the vein-lets beneath the detachment however suggeststhat boiling started as the fluid reached the sedi-mentary sequence Boiling cools the fluid andconcentrates dissolved silica leading to precipita-tion of silica colloids (Saunders 1994) Thus muchof the mineralization in The Wall appears to coin-cide with the onset of boiling
Thermal conditions can be roughly evaluatedon the basis of the distribution of temperature-sensitive minerals The absence of epidote in thehost-rock alteration can be interpreted in favor ofa low-temperature (lt240 degC) for the initial fluids(Bird et al 1984 Rayes 1990) This is confirmedby the large distribution of kaolinite crystallizingat temperatures lt200 degC (Simmons and Browne2000) and deposition of microcrystalline silica(chalcedony) or its transformation to jigsawquartz in the stage of massive silicification whichoccurs at temperature of gt180 degC (Fournier1985) Thus the temperature of the early fluidseems to have been 200ndash180 degC Deposition ofbonanza opal-electrum bands however requiresconsiderably lower temperatures (100ndash150 degCHedenquist et al 2000) suggesting a significantdrop of temperature (see also Saunders 1994)Such cooling can be attributed to simple boilingcausing cooling during decompression and in-crease in pH and ƒO2 which accompanies the lossof dissolved gasses Alternatively it can be the re-
sult of mixing with cooler meteoric groundwaterin a manner similar to that described for theHishikari low-sulfidation deposit (Izawa et al1990) Mixing of cool oxidized meteoric waterwith a hot reduced deep crustal fluid has beenproposed for low-angle faults bounding severalmetamorphic core complexes (Kerrich and Reh-ring 1987 Kerrich and Hyndman 1987 Spencerand Welty 1986 Beaudoin et al 1991)
92 Paleodepth
Mineralogical and textural characteristics such asbladed carbonates and crustiform and colloformbanded chalcedony and opaline silica plus adular-ia (Izawa et al 1990 Cook and Simmons 2000)suggest that the depth for the formation of miner-alization at Ada Tepe deposit was shallow In theabsence of precise temperature and salinity datafrom fluid inclusion studies the paleodepth of theAda Tepe deposit cannot be precisely con-strained A minimum depth can be roughly esti-mated assuming boiling of low salinity solutions(lt1 wt NaCl equivalent) at a temperature of200 degC The depth of boiling of such a fluid belowthe water table is about 160ndash170 m (Haas 1971)
Fig 8 40Ar39Ar incremental-heating age spectra for adularia from Ada Tepe and sanidine from rhyolite dyke fromKessebir dome
Sample AT 01-22 Sin2000-28 KM 2000-6carbonate bulk rock pyrite
Rb 218Sr 8287Rb86Sr 7695087Sr86Sr 0709270plusmn14 0711911plusmn10(87Sr86Sr)i 070809206Pb204Pb 18663 18707207Pb204Pb 15682 15684208Pb204Pb 38849 38843
Table 3 Sr and Pb isotope compositions of carbonatepyrite and whole rock from Ada Tepe deposit and Synapmineralization
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
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Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
73Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
For fluids under a hydrodynamic gradient andcontaining dissolved CO2 the depth of boilingwould be somewhat deeper (Hedenquist andHenley 1985) This is consistent with the 350 mthickness of the host Shavarovo Formation(Goranov and Atanasov 1992) which implies thatthe overlying coal-bearing-sandstone and marl-limestone formations had not yet been depositedwhen the ore formed
93 Sources and relationships among minerali-zation extension and magmatism
The new 40Ar39Ar ages from adularia and sani-dine have been compared with those from musco-vite and biotite in the Kessebir dome (Bonev etal accepted) KndashAr ages of nearby Iran Tepe vol-cano (Lilov et al 1987) and intra-plate alkalinebasalts (Marchev et al 1997 1998) to clarify rela-tionships between volcanism thermal events inthe Kessebir dome and mineralization in the AdaTepe deposit As discussed above the 40Ar39Artotal fusion age of adularia (Marchev et al 2003)shows that the mineralization at Ada Tepe formedat 35 Ma Mineralization may have been coevalwith 35 Ma lavas of the Iran Tepe paleovolcano(Lilov et al 1987 Pecskay pers comm) howeverthe uncertainties of the dating methods do notrule out differences in age on the order of several100 kyr Notwithstanding field relationships indi-cate that volcanic activity of the Iran Tepe volca-no is younger than the Krumovgrad group
Another possible source of fluids and metals isthe magmatism of the Kessebir dome itself Com-parison of the timing of Ada Tepe mineralization(35 Ma) the Kessebir rhyolite dyke (3182 plusmn 020Ma) and KndashAr ages of intra-plate alkaline basalts(28ndash26 Ma) show that mineralization preceded byat least 3 Ma the rhyolitic magmatism and at least6 Ma the intra-plate basalts Thus it is highly un-
likely that this younger igneous activity was thesource of Ada Tepe mineralizing fluids or heat
Mineralization at Ada Tepe is ca 3 Ma young-er than the 40Ar39Ar ages of the muscovite (3813plusmn 036) and biotite (3773 plusmn 025 Ma) from thelower plate of the Kessebir dome Recently ob-tained older 40Ar39Ar age for amphibole (45 plusmn 2Ma) and similar age for the muscovite (39 plusmn 1 Ma)in the Biala Reka dome (Mukasa et al 2003)have been interpreted as cooling ages for the up-per plate Therefore muscovite and biotite agesfrom Kessebir can be interpreted as cooling of thelower plate rocks to below 350ndash300 degC followingthe MaastrichtianndashPaleocene metamorphism(Marchev et al 2004) The latter ages are general-ly consistent with a 42ndash35 Ma range of ages ob-tained earlier by Peytcheva (1997) for the closingof RbndashSr system in the granitoids in Biala Rekaand Kessebir after a presumable amphibolitefacies metamorphism Ore deposit formation at~35 Ma in the hanging wall of the Tokachka de-tachment coincides with late stage brittle exten-sion after cooling of the basement rocks at tem-peratures lt 200 degC (Bonev et al accepted) Thehighest grade portion of the ore mineralization(The Wall) is dominated by multiple phases ofveining and brecciation suggesting a syndetach-ment evolution of the hydrothermal process Thepresence of several unconformities in the overly-ing Upper EocenendashLower Oligocene coal-bear-ing-sandstone and marl-limestone formations(Goranov and Atanassov 1992 Boyanov andGoranov 1994 2001) suggests a continuation ofthe uplift and exhumation of the Kessebir domeeven several million years after the formation ofthe Ada Tepe deposit
Probable source rocks for the Sr (Ca) and Pbcan be constrained by comparison of the Sr andPb isotope ratios of carbonates and pyrites fromAda Tepe with the major source rocks (Figs 9 and
Fig 9 Sr isotope composition of calcite from Ada Tepe and whole rock sample from Synap compared withKrumovgrad area igneous and metamorphic rocks Data for the intra-plate basalts ndash Marchev et al 1998 for theZvezdel and Iran Tepe lavas ndash Marchev unpublished data for the metamorphic rocks ndash Peytcheva et al 1992 andPljusnin et al 1988)
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
P Marchev et al74
10) Bulk rock and carbonate Sr isotope data(070809ndash070927) lie within the lower range ofpresent-day 87Sr86Sr isotopic ratios between0708ndash0737 for the prevailing gneissic metamor-phic rock within the Eastern Rhodopes (Peytch-eva et al 1992) and are higher than the Sr isoto-pic values of the nearby younger igneous rocksfrom Iran Tepe and Zvezdel volcanoes (070641ndash070741 Marchev et al unpubl data) It appearslikely that the hydrothermal Sr and by inferenceCa is mostly of metamorphic origin or represent amixture of metamorphic and small amount of oldmagmatic source isotopically similar to Iran Tepeand Zvezdel magmas (see below)
Pyrite Pb isotope ratios overlap with the fieldof feldspars from Zvezdel igneous rocks howeverthe leachate fraction of the whole rock sample
from Synap has a slightly lower 206Pb204Pb ratiothan the feldspars Collectively the two samplesplot in the fields of the Rhodope metamorphicrocks From these data it is not possible to dis-criminate between a metamorphic and an igneousorigin of Pb in the hydrothermal fluid This is notsurprising as orogenic igneous rocks of the East-ern Rhodopes were strongly contaminated withcrustal Pb (Marchev et al 1998 and 2004) and dif-fer isotopically from the asthenospheric-derivedKrumovgrad intra-plate basalts (Fig 10) There-fore isotopic homogenization of the orogenic ig-neous and metamorphic rocks in the region limitsthe possibility to discriminate between these twosources Nevertheless it may be suggested thatfluid circulation through the metamorphic base-ment rocks and metamorphic-derived sediments
Fig 10 Pb isotope composition of pyrite (Ada Tepe) and whole rock alteration (Synap) compared with feldsparsand whole rocks from Zvezdel Oligocene volcano (Marchev et al unpubl data) and whole rocks from Krumovgradintra-plate basalts (Marchev et al (1998) and Rhodope metamorphic rocks from Frei (1995)
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
75Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
would cause a large contribution from metamor-phic lead
Thus the simplest genetic model to explain thegeology geochronology and Sr and Pb isotopesinvolves hydrothermal convection through thePaleozoic metamorphic basement The close tem-poral association of mineralization at Ada Tepewith the exhumation processes and formation ofthe Kessebir dome favours a genetic link betweenthem We propose that the metamorphic base-ment rocks provided the heat to drive the hydro-thermal system During exhumation however thelower plate of the Kessebir metamorphic corecomplex experienced cooling and decompressionsince the Upper Cretaceous (Marchev et al2004) This has been used in other metamorphiccomplexes (Smith et al 1991) to argue that pro-grade metamorphic devolatilization of the lowerplate is unlikely to generate fluid responsible formineralization during extension These authorssuggested that igneous rather than metamorphicfluid source is more likely for the metamorphiccore complex-related mineralization This appar-ent contradiction can be explained by astheno-spheric upwelling that was operating in the East-ern Rhodope area (Marchev et al 2004) causingretrograde metamorphism at shallow levels andat the same time resulting in prograde metamor-phism at deeper levels observed by the high heatflow in the region Although magmatic activityseems to be younger than the ore mineralizationthe first erupted lavas of Iran Tepe were close intime The beginning of this volcanism was proba-bly preceded by accumulation of magma at great-er depths Under such conditions fluids liberatedby deep prograde devolatilization reactions andor mantle degassing could ascend to form lowtemperature fluids
94 Gold deposits associatedwith detachment faults
Different types of mineralization in low-angle de-tachment faults associated with metamorphiccore complexes are described mostly in the south-western United States These include Picacho(Drobeck et al 1986 Liebler 1988) and BullardPeak (Roddy et al 1988) Southwestern Arizonaand Riverside Pass (Wilkinson et al 1988) andWhipple-Buckskin-Rawhide (Spencer and Welty1986) Southeastern California Another exampleis in the Kokanee Range Southern British Co-lumbia Canada (Beaudoin et al 1991)
These kinds of deposits are divided by Eng etal (1988) into two categories base-metal en-riched (Whipple-Buckskin-Rawhide and Koka-nee deposits) and base-metal poor (Picacho and
Riverside Pass) In the base-metal poor depositsgold is typically associated with silicification andhematite (Picacho) or hematite and chrisocolla(Riverside Pass) Pyrite which is entirely oxidizedin Riverside Pass is the principal sulfide mineralQuartz and lesser calcite are the main gangueminerals
Mineralization at Ada Tepe deposit sharesmany characteristics with Picacho and RiversidePass including association of gold with multipleepisodes of silicification and veining within shal-lowly dipping detachment faults and a low con-tent of base-metals and As However comparisonof the characteristics of Ada Tepe to other base-metal poor detachment-related mineralizationsreveals several notable differences These includelack of copper and specular hematite a relativelyhigh content of adularia and various silica poly-morphs and carbonates These features may re-flect differences in crustal compositions and his-tory the nature of the ore-forming hydrothermalfluids and physico-chemical conditions at the fo-cus of ore deposition
10 Conclusions
(1) Based on alteration mineralization andtextures we classify Ada Tepe as a low-sulfidationepithermal gold deposit hosted in sedimentaryrocks
(2) The Tokachka low-angle detachment faultand the steep listric faults in the Maastrichtian-Paleocene sedimentary sequence were the majorsites of gold mineralization There are many indi-cators including breccias that synmineralizationmovement took place along the detachment sur-face
(3) The deposit formed at shallow depth lessthan 200ndash250 m below the paleosurface Micro-crystalline quartz and opal which are the main sil-ica polymorphs crystallizing with the electrumbands preclude the use of fluid inclusion to con-strain the conditions of gold deposition Fromother alteration minerals temperature of forma-tion is evaluated to lt200 degC The mineralogy sug-gests that the fluid boiled throughout the deposit
(4) Mineralization is an exclusively Au systemwith traces of As and with no base metals Themajority of the gold occurs as electrum with 73ndash76 Au which is reflected in the average AuAgratio (~3) of the deposit
(5) The 40Ar39Ar age of adularia indicates thatthe ore was deposited at Ada Tepe at 350 plusmn 02Ma This age is ~3 Ma younger than the closure ofmetamorphic muscovite and biotite at ~350 degC inthe underlying basement and 3 Ma older than sa-
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
P Marchev et al76
nidine in the nearest rhyolite thereby precludinglocal magmatism as a source of fluids or heat
(6) Sr and Pb isotope ratios are consistent withthe idea that metals and carbonates were proba-bly derived from the metamorphic basementrocks with a possible contribution from an igne-ous source
(7) Collectively these data suggest an intimateassociation of Ada Tepe Au mineralization to themetamorphic core-complex formation rather thanto the local magmatism
Acknowledgments
This is a contribution to the ABCD-GEODE programof the European Science Foundation Supported by theSwiss National Science Foundation Joint ResearchProject 7BUPJ062276 and grants 21-5904199 and200020-101853 40Ar39Ar analyses at UW-Madison sup-ported by US NSF grants EAR-10114055 and EAR-0337667 to Singer BMM gave permission to publishthese results and provided financial support The au-thors appreciate the comments and helpful reviews ofthe journal reviewers D Altherton N Skarpelis and Al-brecht von Quadt Denis Fontignie and Massimo Chi-aradia (Universities of Geneva Switzerland and LeedsUK) are thanked for the Sr and Pb isotope analysesThanks are owed to Albrecht von Quadt and IvanBonev for etching of gold samples and the SEM picturesof the etched samples respectively
References
Atanasov G and Goranov A (1984) On the Palaeo-geography of the East Rhodopes C R Acad bulgSci 37(6) 783ndash784
Beaudoin G Taylor BE and Sangster DF (1991) Sil-ver-lead-zinc veins metamorphic core complexesand hydraulic regimes during crustal extensionGeology 19 1217ndash1220
Belmustakova H Boyanov I Ivanov I and Lilov P(1995) Granitoid bodies in the Byala Reka dome CR Acad bulg Sci 48 (4) 37ndash40 (in Russian)
Bird DK Schiffman P Elders WA Williams AEand McDowell SD (1984) Calc-silicate mineraliza-tion in active geothermal systems Econ Geol 79671ndash695
Bonev N (1996) Tokachka shear zone southwest ofKrumovgrad in Eastern Rhodopes Bulgaria an ex-tensional detachment Ann Univ Sofia 89 97ndash106
Bonev N (2002) Structure and evolution of the Kesse-bir gneiss dome Eastern Rodopes PhD thesis Univof Sofia unpubl 282 pp (in Bulgarian)
Bonev N Marchev P and Singer B (accepted) Inter-ference between tectonic ore-forming and magmat-ic processes during the Tertiary extensional exhuma-tion in the Eastern Rhodope (Bulgaria) 40Ar39Argeochronology constraints Geodin Acta
Boyanov I and Goranov A (1994) PaleocenendashEocenesediments from the Northern periphery of theBorovica depression and their correlation with simi-lar sediments in the East Rhodopean Paleogene de-pression Rev Bulg Geol Soc 55(1) 83ndash102 (in Bul-garian with English abstract)
Boyanov I and Goranov A (2001) Late Alpine (Paleo-gene) superimposed depressions in parts of South-east Bulgaria Geol Balc 34(3ndash4) 3ndash36
Carrigan C Mukasa S Haydoutov I and Kolcheva K(2003) Ion microprobe UndashPb zircon ages of pre-Al-pine rocks in the Balkan Sredna Gora and Rho-dope terranes of Bulgaria Constraints on Neopro-terozoic and Variscan tectonic evolution J CzechGeol Soc Abstract volume 481ndash2 32ndash33
Chiaradia M and Fontboteacute L (2002) Separate leadisotope analyses of leachate and residue rock frac-tions implications for metal source tracing in oredeposit studies Mineral Deposita 38 185ndash195
Cook DR and Simmons SF (2000) Characteristics andgenesis of epithermal gold deposits Reviews EconGeol 13 221ndash224
Crummy J (2002) A speculative genetic model for thelocation of gold mineralization on the Krumovgradlicense SE Rhodope Bulgaria Geol Mineral Res1 20ndash24
Duffield W and Dalrymple GB (1990) The TaylorCreek Rhyolite of New Mexico a rapidly emplacedfield of lava domes and flows Bull Volcanol 52475ndash487
Drobeck PA Hillemeyer JL Frost EG and LieblerGS (1986) The Picacho Mine a gold mineralizeddetachment in southeastern California In Beatty Band Wilkinson PAK (eds) Frontiers in geologyand ore deposits of Arizona and the Southwest Ari-zona Geol Soc Digest XVI Tucson 187ndash221
Eng T Boden DR Reischman MR and Biggs JO(1995) Geology and mineralization of the BullfrogMine and vicinity Nye County Nevada In CoynerAR and Fahey PL (eds) Geology and ore depos-its of the American Cordillera Symposium Proceed-ings Geol Soc Nevada RenoSparks Nevada Vol1353ndash400
Fournier RO (1985) Silica minerals as indicators ofconditions during gold deposition US Geol SurveyBull 1646 15ndash26
Frei R (1995) Evolution of mineralizing fluid in theporphyry copper system of the Scouries depositNortheast Chalkidiki (Greece) Evidence from com-bined PbndashSr and stable isotope data Econ Geol 90746ndash762
Goranov A and Atanasov G (1992) Lithostratigraphyand formation conditions of Maastrichtian-Paleo-cene deposit in Krumovgrad District Geol Balc22(3) 71ndash82
Haas JL Jr (1971) The effect of salinity on the maxi-mum thermal gradient of a hydrothermal system athydrostatic pressure Econ Geol 66 940ndash946
Hedenquist JW and Henley RW (1985) The impor-tance of CO2 on freezing point measurment of fluidinclusions evidence from active geothermal systemsand implications for epithermal ore depositionEcon Geol 80 1379ndash1399
Hedenquist JW Arribas AR and Gonzales-Urien E(2000) Exploration for epithermal gold depositsSoc Econ Geol Reviews 13 245ndash277
Izawa E Urashima Y Ibaraki K Suzuki R Yokoya-ma T Kawasaki K Koga A and Taguchi S (1990)The Hishikari gold deposit High grade epithermalveins in Quaternary volcanics of southern KyushuJapan J Geochem Explor 36 1ndash56
Kerrich R and Rehring W (1987) Fluid motion associ-ated with Tertiary mylonitization and detachmentfaulting 18O16O evidence from the Picacho meta-morphic core complex Arizona Geology 15 58ndash62
Kerrich R and Hyndman D (1987) Thermal and fluidregimes in the Bitteroot lobe-Sapphire block de-tachment zone Montana Evidence from 18O16Oand geologic relations Geol Soc Am Bull 97 147ndash155
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
77Ada Tepe gold deposit in the Eastern Rhodopes SE Bulgaria
Kolcheva K and Eskenazy G (1988) Geochemistry ofmetaeclogites from the Central and Eastern Rho-dope Mts (Bulgaria) Geol Balc 18 61ndash78
Kozhoukharov D Kozhoukharova E and Papaniko-laou D (1988) Precambrian in the Rhodope massifIn Zoubek V (ed) Precambrian in Younger FoldBelts Chichester 723ndash778
Kozhoukharova E (1984) Origin and structural posi-tion of the serpentinized ultrabasic rocks of the Pre-cambrian ophiolitic association in the RhodopeMassif I Geologic position and composition ofophiolite association Geol Balc 14 9ndash36 (in Rus-sian)
Kunov A Stamatova V Atanasova R and Petrova P(2001) The Ada Tepe Au-Ag-polymetallic occur-rence of low-sulfidation (adularia-sericite) type inKrumovgrad district Mining and Geol 2001(4) 16ndash20 (in Bulgarian)
Liebler GS (1988) Geology and gold mineralization atthe Picacho mine Imperial County California InSchafer RW Cooper JJ and Vikre PG (eds) Bulkmineable precious metal deposits of the WesternUnited States Symposium Proceedings Geol SocNevada RenoSparks Nevada Part IV Gold-silverdeposits associated with detachment faults 453ndash504
Lilov P Yanev Y and Marchev P (1987) KAr dating ofthe Eastern Rhodopes Paleogene magmatism GeolBalc 17(6) 49ndash58
Lips ALW White SH and Wijbrans JR (2000) Mid-dle-Late Alpine thermotectonic evolution of thesouthern Rhodope Massif Greece Geodin Acta 13281ndash292
Marchev P Harkovska A Pecskay Z Vaselli O andDownes H (1997) Nature and age of the alkalinebasaltic magmatism south-east of Krumovgrad SE-Bulgaria C R Acad bulg Sci 50(4) 77ndash80
Marchev P Vaselli O Downes H Pinarelli L IngramG Rogers G and Raicheva R (1998) Petrologyand geochemistry of alkaline basalts and lampro-phyres implications for the chemical composition ofthe upper mantle beneath the Eastern Rhodopes(Bulgaria) In Christofides G Marchev P and SerriG (eds) Tertiary magmatism of the Rhodopian re-gion Acta Vulcanologica 102 233ndash242
Marchev P and Singer B (2002) 40Ar39Ar geochronol-ogy of magmatism and hydrothermal activity of theMadjarovo base-precious metal ore district easternRhodopes Bulgaria In Blundell D Neubauer Fand von Quadt A (eds) The timing and location ofmajor ore deposits in an evolving orogen Geol SocLondon Spec Publ 204 137ndash150
Marchev P Singer B Andrew C Hasson A MoritzR and Bonev N (2003) Characteristics and prelim-inary 40Ar39Ar and 87Sr86Sr data of the UpperEocene sedimentary-hosted low-sulfidation golddeposits Ada Tepe and Rosino SE Bulgaria possi-ble relation with core complex formation In Elio-poulos et al (eds) Mineral Exploration and Sus-tainable Development Millpress Rotterdam 1193ndash1196
Marchev P Raicheva R Downes H Vaselli O Massi-mo C and Moritz R (2004) Compositional diversi-ty of Eocene-Oligocene basaltic magmatism in theEastern Rhodopes SE Bulgaria implications for itsgenesis and geological setting Tectonophysics 393301ndash328
Marchev P Raicheva R Singer B Downes H AmovB and Moritz R (2000) Isotopic evidence for theorigin of Paleogene magmatism and epithermal oredeposits of the Rhodope Massif In Geodynamicsand Ore Deposit Evolution of the Alpine-Balkan-Carpathian-Dinaride-Province Borovets Abstracts
ABCD-GEODE 2000 workshop Borovets Bulga-ria p 47
Mposkos E and Krohe A (2000) Petrological andstructural evolution of continental high pressure(HP) metamorphic rocks in the Alpine RhodopeDomain (N Greece) In Panayides I XenopontosC and Malpas J (eds) Proceedings of the 3rd Inter-national Conf on the Geology of the Eastern Medi-terranean (Nicosia Cyprus) Geol Survey NicosiaCyprus 221ndash232
Mposkos E and Wawrzenitz N (1995) Metapegmatitesand pegmatites bracketing the time of high P meta-morphism in polymetamorphic rocks of the E-Rho-dope N Greece Petrological and geochronologicalconstraints Geol Soc Greece Spec Publ 4(2) 602ndash608
Mukasa S Haydoutov I Carrigan C and Kolcheva K(2003) Thermobarometry and 40Ar39Ar ages of ec-logitic and gneissic rocks in the Sredna Gora andRhodope terranes of Bulgaria J Czech Geol SocAbstract volume 481ndash2 94ndash95
Ovtcharova M Quadt A von Heinrich CA FrankM and Kaiser-Rohrmeier M (2003) Triggering ofhydrothermal ore mineralization in the CentralRhodopean Core Complex (Bulgaria) ndash Insightfrom isotope and geochronological studies on Terti-ary magmatism and migmatization In Eliopoulos etal (eds) Mineral Exploration and Sustainable De-velopment Millpress Rotterdam 367ndash370
Peytcheva I (1997) The Alpine metamorphism in East-ern Rhodopes ndash RbndashSr isotope data Rev Bulg GeolSoc 58(3) 157ndash165 (in Bulgarian with English ab-stract)
Peytcheva I Kostitsin Y Salnikova E OvtcharovaM and von Quadt A (1999) The Variscan orogen inBulgaria ndash new isotope-geochemical data RomJour tectonics and regional geology 77 Abstract vol-ume p 72
Peytcheva I Kostitsin JA and Shukolyukov JA(1992) RbndashSr isotope system of gneisses in theSouth-Eastern Rhodopes (Bulgaria) C R Acadbulg Sci 45(10) 65ndash68 (in Russian)
Peytcheva I Ovcharova M Sarov S and Kostitsin Y(1998) Age and metamorphic evolution of meta-granites from Kessebir reka region Eastern Rho-dopes ndash RbndashSr isotope data Abstracts XVI Con-gress CBGA Austria Vienna
Peytcheva I and von Quadt A (1995) UndashPb dating ofmetagranites from Byala-Reka region in the EastRhodopes Bulgaria Geol Soc Greece Spec Publ4(2) 637ndash642
Plyusnin GS Marchev PG and Antipin VS (1988)Rubidium-Strontium age and genesis of the sho-shonite-latite series in the Eastern-Rhodope Bul-garia Dokl Akad Nauk SSSR 303(3) 719ndash724
Reyes AG (1990) Petrology of Philippine geothermalsystems and the application of alteration mineralogyto their assessment J Volcanol Geotherm Res 43279ndash309
Ricou LE Burg JP Godfriaux I and Ivanov Z (1998)Rhodope and Vardar the metamorphic and the olis-tostromic paired belts related to the Cretaceous sub-duction under Europe Geodin Acta 11 285ndash309
Roddy MS Reynolds SJ Smith BM and Ruiz J(1988) K metasomatism and detachment-relatedmineralization Harcuvar Mountains Arizona GeolSoc Am Bull 100 1627ndash1639
Rohrmeier M Quadt Avon Handler R OvtcharovaM Ivanov Z and Heinrich C (2002) The geody-namic evolution of hydrothermal vein deposits inthe Madan metamorphic core complex BulgariaGeochim Cosmochim Acta Special Supplement
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt
P Marchev et al78
Abstracts of the 12th Ann Goldschmidt Confer-ence Davos Switzerland 66 S1 A645
Sarov S and twelve others (1996) Report for the resultsof execution of the geological task ldquoGeological map-ping in scale 125 000 and geomorphologic mappingin scale 150 000 with complex prognostic evaluationof the mineral resources in the area of Krumovgradand villages Gornoseltsi Popsko Djanka and Nano-vitsa (Eastern Rhodopes) on area of 485 km2 Na-tional geofond IV-438
Saunders JA (1990) Colloidal transport of gold and sil-ica in epithermal precious-metal systems Evidencefrom the Sleeper deposit Nevada Geology 18 757ndash760
Shabatov Y and eight others (1965) Report for the geo-logical mapping accompanied with prospecting forore mineralizations in scale 125 000 in 1963ndash1964 inpart of the SE Rhodopes Geofond of Committee ofGeology IV-217
Saunders JA (1994) Silica and gold texture in bonanzaores of the Sleeper deposit Humbolt county Ne-vada Evidence for colloids and implications for epi-thermal ore-forming processes Econ Geol 89 628ndash638
Simmons SF and Browne PRL (2000) Hydrothermalminerals and precious metals in the Broadlands-Ohaaki geothermal system Implications for under-standing low-sulfidation epithermal environmentsEcon Geol 95 971ndash999
Simmons SF and Christenson BW (1994) Origins ofcalcite in a boiling geothermal system Am J Sci294 361ndash400
Singer B and Brown LL (2002) The Santa Rosa Event40Ar39Ar and paleomagnetic results from the Valesrhyolite near Jaramillo Creek Jemez Mountains NewMexico Earth Planet Sci Lett 197 51ndash64
Singer B and Marchev P (2000) Temporal evolution ofarc magmatism and hydrothermal activity includingepithermal gold veins Borovitsa caldera southernBulgaria Econ Geol 95 1155ndash1164
Smith BM Reynolds SJ Day HW and Bodnar RJ(1991) Deep-seated fluid involvement in ductile-brit-tle deformation and mineralization South Mountainmetamorphic core complex Arizona Geol Soc AmBull 103 559ndash569
Spencer JE and Welty JW (1986) Possible controls ofbase- and precious-metal mineralization associatedwith Tertiary detachment faults in the lower Colora-do River trough Arizona and California Geology14 195ndash198
Stoyanov R (1979) Metallogeny of the Rhodope Cen-tral Massif Nedra Moscow 180 pp (in Russian)
Valenza K Moritz R Mouttaqi A Fontignie D andSharp Z (2000) Vein and karstic barite deposits inthe Western Jebilet of Morocco Fluid inclusion andisotope (SOSr) evidence for regional fluid mixingrelated to Central Atlantic rifting Econ Geol 95587ndash605
Wilkinson WH Wendt CJ and Dennis MD (1988)Gold mineralization along Riverside Mountains De-tachment Fault Riverside County California InSchafer RW Cooper JJ and Vikre PG (eds)Bulk mineable precious metal deposits of the West-ern United States Symposium Proceedings GeolSoc Nevada RenoSparks Nevada Part IV Gold-silver deposits associated with detachment faults487ndash504
Received 24 March 2003Accepted in revised form 23 July 2004Editorial handling A von Quadt