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MuellerAG(2020)StructureVariscanveins 1

SGAWEBMINERALDEPOSITARCHIVE

PRESENTATIONNOTES

TITLE:Structuralsettingandageofsyn-andpost-orogenicgoldandZn-Pb-Agveindeposits,Variscanslatebelt,Germany

Author:AndreasG.Mueller12aBelgraveStreet,MaylandsW.A.6051,Australia.E-mail:[email protected]

DISCLAIMER:Thispresentationisprovidedforfreebytheauthor,whoretainsthecopyright.TheSGAdistributestheMineralDepositArchiveonline(www.e-sga.org).Thepresentationhasbeenpeerreviewedtoensurescientificvaliditybuthasbeensubjectedtominimalcopy-editing.ThesepresentationnotesaccompanyaseriesofslidesintheVaricanVeins1-Slidespdffile.

Recommended citation: Mueller AG (2020) Structural setting and age of syn- and post-orogenic gold and Zn-Pb-Ag vein deposits, Variscan slate belt, Germany -- Slide presentation and explana-tory notes. Society for Geology Applied to Mineral Deposits (SGA): www.e-sga.org/Publications/Mineral Deposit Archive. Mueller AG (2020) Structural setting and age of syn- and post-orogenic gold and Zn-Pb-Ag vein deposits, Variscan slate belt, Germany -- Slide presentation and explanatory notes. Society for Geology Applied to Mineral Deposits (SGA): www.e-sga.org/Publications/Mineral Deposit Archive.

RECOMMENDEDCITATION:Thesepresentationnotesandtheircompanionslidesshouldbequotedtoas:AuthorN.N.(Year)Title.SGAMineralDepositArchive,http://www.e-sga.org.

Recommendedcitation:MuellerAG(2020)Structuralsettingandageofsyn-andpost-orogenicgoldandZn-Pb-Agveinde-posits,Variscanslatebelt,Germany--Slidepresentationandexplanatorynotes.SocietyforGeolo-gyAppliedtoMineralDeposits(SGA):www.e-sga.org/Publications/MineralDepositArchive.KEYWORDS:Slatebelt,veins,structure,gold,zinc,lead



ABSTRACTTheveinsdescribedarecontrolledbystructuresintheCarboniferousVariscanslatebeltof

centralEuropeexposedintheRhenishMassif,Harzblock,andRuhrcoaldistrictinGermany.Twosyn-orogenicdepositsformedduringfoldingatca.305MaintheoverturnedNW-limbsofregional anticlines. In the Eisenberg anticline, flexural slip at the contacts of thin limestonebedswithblackslateledtothecrack-sealdepositionoflaminatedcalciteveins.Bonanza-styledendritic gold is associated with hematite, chalcopyrite, clausthalite (PbSe) and accessoryborniteandnaumannite(Ag2Se).TheRamsbeckZn-Pb-Agdepositconsistsofveinscontrolledby theaxialplanecleavageand by flat reverse faults. Stacked pinch-and-swell veins in slateand thick breccia veins in quartziteweremined over a vertical extent of 700m, filledwithquartz,pyrite,sphalerite,galena(900g/tAg),andaccessorysiderite,chlorite,tetrahedriteandPbSb-sulfosalts.Zonesofquartz-sericite±ankeritealterationborderedveinsinslateanddia-base.Thedepositislocatedatthemarginofathermalanomalydefinedbyillitecrystallinity,vitrinitereflectanceandBouguergravityinterpretedtoindicateaburiedgranitepluton.

Twopost-orogenicdepositsformedafterfoldingatorpriorto260-240Ma,eitherinnormalfaultsreactivatedduringfold-beltupliftorinwrenchfaultsoftheElbestrike-slipzonegener-atedduringthewestwardmovementofGondwanarelativetoLaurussiaaftercontinentalcolli-sionintheUpperCarboniferous.TheAugusteVictoriaZn-Pb-Agdepositiscontrolledbya15-60mwidenormal fault,whichoffsets coalmeasures inananticline700mSW-blockdown.Stage1brecciaorecomposedofquartz,sphalerite,galena(1000-1200g/tAg),accessorysider-ite,ankerite,sericiteandchalcopyriteisconfinedtothenormalfault,whichisoffsetbybothdextral andsinistralwrench faults. Thedextral faults containStage2aquartz-sphaleriteore.ThesinistralfaultscontainminorStage2aoreoverprintedbyStage2bcalcite-barite-marcasiteveins. Continuous Zn-Pb mineralization constrains the hiatus between normal and wrenchfaultingtoashorttimeinterval.

IntheHarzblock,uplifted3-4kmattheNorthBoundaryFaultduringCretaceousandCeno-zoicAlpine stress,WNW-strikingwrench faultswestoftheBrockengranite (283±2Ma)hostZn-Pb-Agveins.Thetwolargestdeposits(11-19Mtofore)arecontrolledbyadextralexten-sionalsystematClausthal-Zellerfeld,andbyasinistralextensionalduplexatBadGrund.Lat-eraldisplacementonthemainfaultswas500-800m.Crosscuttingrelationshipsindicatethatdextral preceded sinistralmovement. Stage 1 hematite-pyritemineralizationwas associatedwithdolomite-quartz-illitereplacementatfluidtemperaturesofabout300°C.TheformationofbandedandbrecciaveinsprogressedfromStage2quartz-calcite-sphalerite-galenatoStage3siderite-barite-galena,fluidtemperaturefallingfromabout360°Cto220°Cwithtime.Stage3galenawassilver-rich(1000-2000g/t)duetoinclusionsoftetrahedrite,pyrargyrite,argentiteandnativesilver.Rb-Sragesofadularia(263±4Ma)fromveinsintheaureoleoftheBrockengranite,andof2M-illite fromStage1alterationatBadGrund (240±17Ma) indicateore for-mationinthePermianorTriassic.Isotopicresettingsuggestsreactivation(30-100moffset)ofsomefaultsatca.180,140and90Ma.



1 INTRODUCTION

These explanatory notes accompany colorslides illustrating the structural settingof syn-andpost-orogenicveindepositsintheRhenishMassif,HarzandRuhrcoaldistrict,partoftheVariscan slate belt inGermany. Both this textandtheslidepresentation(intablet4:3formatand Adobe 1998 color) are available free ofcharge as Adobe pdf-files from the SGAweb-site. They aredesigned as open access teach-ing tools for projection and the study on-screen. This text explains each slide step-by-step.

Four well-documented deposits were se-lected as structural type localities out of amuch larger group based on the personal ex-perienceof theauthor: (1) theEisenberggolddeposit, bedding-parallel veins in an anticline;(2)theRamsbeckZn-Pb-Agdeposit,veinscon-trolledbytheaxialplanecleavageandreversefaults in an anticline; (3) theAuguste VictoriaZn-Pb-Agdeposit,brecciaoreinanormalfaultdisplacing the folds; and (4) the ClausthalZellerfeldandBadGrundZn-Pb-Agdeposits inthe Upper Harz, banded and breccia veins inwrench faults displacing the regional folds.Muchof thepublished literature is inGermanand not easily accessible to the internationalpublic.Acomprehensivereviewofveindepos-its intheVariscanorogenisbeyondthescopeofthisstudy.

The term “syn-orogenic” is used as a timeconstraint, when structural relations indicatevein formation during Variscan folding, and“post-orogenic” when the host structurespostdatefolding.Localstratigraphicnomencla-ture(Westphalian,Stephanian) isretainedbutcorrelatedwithU-Pbageslistedinthechartofthe International Commission on Stratigraphy(ICS 2018). The Westphalian is equivalent totheMoscovian(315-307Ma),andtheStepha-nian to the Kasimovian and Gzhelian stages(307-299Ma)oftheCarboniferous.TheLowerPermianisdatedat299-273Ma(Cisuralianse-ries), and the Upper Permian at 273-252 Ma(Guadalupian and Lopingian series) in the ICSchart. The radiometric agesquoted arebased

on the decay constants of Steiger and Jäger(1977),recentlyrevisedfortheK-Ar(Renneetal.2011)andRb-Srsystems(Villaetal.2015).TherevisionswillresultinslightlyyoungerK-ArandolderRb-Srages(3-5Maat300Ma).Twokey Rb-Sr ages have been recalculated usingIsoplot3.75ofLudwig(2012)andthenewde-cayconstant.Mineralogical,fluidinclusionandisotopedataaresummarizedinthecontextofthestructuralframework.IntheAppendix,ge-neticmodelsfortheUpperHarz,thesubjectofmostspecializedstudiesarebrieflyreviewed.

2 SLIDESDESCRIPTION

2.1 Slide1.SGAdisclaimerandrecommendedcitation

2.2 Slide2.Titleslide.

Contents(1)Eisenberggolddeposit:page5(2)RamsbeckZn-Pb-Agdeposit:p.9(3)AugusteVictoriaZn-Pn-Agdeposit:p.13(4)UpperHarzZn-Pb-Agdeposits:p.19(5)Variscanveins.Keyfeatures:p.29(6)AppendixHarz.Fluidsources:p.29

2.3 Slide3.Europe: Cratons and orogenic belts

ThetectonicmapofEurope(modifiedfromMeinhold1971)showsthepresent-daytecton-ic setting. The Cenozoic Alpine orogen insouthern Europe (red, metamorphic massifsdarkred),partoftheNeo-Tethyanfoldbeltex-tending into Turkey and Iran, formed duringthe collision of the African-Arabian and Eura-siancontinents leavingtheMediterraneanseaasaremnantoceanicbasin.MostofEuropeisunderlain by the Precambrian Baltic craton(Baltica), shown in dark pink where outcrop-ping, lightpinkwhereunder thin sedimentarycover, and in yellow where covered by deepsedimentarybasins.Thecraton isboundedbytheCambrian-SilurianCaledonian (dark violet)and by the Devonian-Carboniferous Variscan(green)orogenicbelts.



TheVariscanbasementincentralandwest-ernEuropeistransectedbytwosetsofPermo-Carboniferousfaults:(1)NW-toWNW-strikingdextral strike-slip faults with 20-150 km dis-placement including the Tornquist-TeisseyreZone (TTZ), theElbe Zone (EZ), theBray Fault(BF), and the Amorican Faults (AF), and (2)subordinate north- to NNE-striking sinistralfaults such as the Sillon Houiller (SH) with alateral offset of 70 km in theMassif Central,France (Arthaud andMatte 1977; Holder andLeveridge1986;Ziegler1990).Thesefaultsareinterpreted as part of a Riedel-type mega-shearzone,whichdevelopedalongthesuturebetweenGondwanaandLaurussiashortlyafterCarboniferous folding in Europe ceased (Ar-thaudandMatte1977).

The TTZ is a broad fault zonemarking theboundarybetweentheconsolidatedBalticcra-ton and the fold belts to the southwest. TheOsloGraben(OG)attheterminationoftheTTZhasbeen interpretedas apull-apart structurerelated to dextral strike-slip (Ro et al. 1990;Ziegler 1990). The U-Pb ages of rift-relatedbasalt,syeniteandgraniteconstrainTTZstrike-slip to thePermo-Carboniferous (310-260Ma;peakat300-270Ma;Corfuetal.2017).Subse-quent movements include Mesozoic normalfaulting during the formation of the Danishsedimentarybasin, andbasin inversionduringthe Upper Cretaceous and Tertiary (Walter1995). The inversion was caused by Alpine-Tethyanfar-fieldstressduringtheNE-directedsubduction of oceanic crust at the southernmarginoftheEurasiancontinent.Stressculmi-natedintheEocenetoMioceneduringthecol-lision with the African-Arabian plate (e.g.MoritzandBaker2019).

2.4 Slide4.OrogenicbeltsincentralEurope

The geologicmapof central Europe (modi-fiedfromSchriel1930)showstheoutcropareaof the Variscan fold belt, limited by the Ger-man-PolishBasininthenorthandbytheCeno-zoic Alpine fold belt and its molasse basin inthe south. The Tornquist-Teisseyre (TTZ) andElbe fault zones (EZ) are boundaries to the

German-Polish basin, where the Variscanbasement is buried under Permo-Carboniferous volcanic and red-bed clasticrocks2-4kmthick,andUpperPermian toCe-nozoic sedimentary rocks up to 8 km thick(Breitkreuz and Kennedy 1999; HenningsenandKatzung2002).

SouthoftheElbeZone,thebasementcropsoutintheRhenishMassif(RM)andintheHarzblock (HZ), both part of the Rhenohercynianslate belt of folded Devonian sandstones andshales (dark brown) and Carboniferous grey-wacketurbiditesandcoalmeasures(grey).TheTaunus suture (TS) separates the slate beltfromthemetamorphicpartoftheorogen,ex-posed at the shoulders of the Rhine Graben(RG) and in the Bohemian Massif (BM). Theterranessouthofthesuture(Saxothuringikum,Moldanubikum)representtheriftedmarginofGondwana, accreted and metamorphosed togranulite facies during the collision with theLaurussian continent in theUpperCarbonifer-ous (Linnemann 2004). Syn- to post-tectonicgranites (red) were emplaced at 340-290 Ma(Walter1995;Sebastian2013).

LiketheTTZ,theElbeZone(EZ)andparallelfaults (blue lines) record twomain phases ofmovement: strike-slip in the Carboniferous toPermian, andAlpine-Tethyanuplift in theUp-perCretaceousandTertiary.AttheFlechtingenbasement horst (FH), seismic reflection dataindicate that the uplift amounts to 6 km(Schecketal.2002).Aminorphaseofdextralreactivation tookplaceat someEZ faultsdur-ing Atlantic rifting in the Upper Jurassic andLowerCretaceous(Ziegler1990).

In the Elbe valley near Dresden, the EZ isrepresentedby faults (EF)witha total dextraloffset of 60-120 km (Scheck et al. 2002). TheSaxonyFault inthesouthwest,azoneofcata-clasite and mylonite in gneiss and granitemovedat330to300Ma.Theolderageiscon-strainedbytheMeissenvolcano-plutoniccom-plex emplaced into an extensional fault step-over basin, and the younger age by rhyolitetuff at the base of the Döhlenmolasse. After300Ma, the Döhlenmolasse basin deepeneddue to anormal componentofmovementon



theboundingfaults.Incontrast,thereactivat-edLausitzFaultinthenortheastoverridesUp-per Cretaceous sandstone 1 km NE-block up(Sebastian2013).

East of the Elbe, the EZ is represented bytheSudeticfaults(SF)subdividedintothemainIntra-Sudetic Fault and the subsidiary SudeticBoundaryFault.AttheIntra-SudeticFault,dex-traldisplacementonthescaleofseveral10kmin theCarboniferouswas reversed in thePer-mo-Carboniferous by sinistral movement,whichpostdates theemplacementof theKar-konoszepluton(Cloos1922;Aleksandrowskietal.1997).TheKarkonoszegranitesaredatedat312±3to307±3Ma,andasulfide-bearingrhy-olitedykeemplacedintothefaultzoneisdat-edat300.7±2.4Ma(U-Pbzircon;Mikulskietal.2020).Aleft-lateraloffsetof10kmisestimat-ed by correlatingNNE-strikingmylonite zonesnorth(Niemcza)andsouth(Skrzynka)oftheIn-tra-Sudetic Fault, which both have a sinistralsenseofshear.AttheSudeticBoundaryFault,reactivation in the Tertiary lifted Cretaceousrocks 600 m NE-block up (Cloos 1922; Ale-ksandrowski et al. 1997). Faults at the south-westboundaryoftheBohemianMassifincludetheBavarianPfahl(BP),a200kmlongquartz-veined zoneofmylonite in gneiss and granitelinkedbyastep-overbasintotheFrankishLine(FL). Note the position of the KTB drill hole,which intersected fluid-filled faults of theFrankishLineat9.1kmdepth(Wöhrl2003).

2.5 Slide5.Rhenishslatebelt:Syn-andpost-orogenicveins

The geologic map (modified from Waltherand Zitzmann 1973) shows the location ofthree Variscan ore deposits described below:thesyn-orogenicEisenberg(EB)andRamsbeck(RB), and the post-orogenic Auguste Victoriadeposit (AV). The folded stratigraphic units intheRhenishMassifcompriseaLowerDevonianquartzite-sandstone ± shale succession (darkred-brown), a Middle Devonian sequence ofsand-banded and calcareous shales (brown-grey),minor basaltic spilites (dark green) andlimestone reefs (blue), Lower Carboniferous

black shale and greywacke turbidites (grey),andUpperCarboniferousdeltaicsand-andsilt-stoneswith coalmeasures (grey). In theRuhrcoaldistrict,partoftheVariscanforelandbasinat thenorthernmarginof theRhenishMassif,9 billionmetric tons of black coal wasmineduntilclosurein2018.

TheregionalfoldsstrikeN50-60°E,haveaxi-alplanes inclined towards thenorthwest, andhorizontal to gently plunging fold axes. TheNW-limbs of some anticlines are overturned.The Eisenberg and Ramsbeck veins are con-trolledbystructuresrelatedtothemainphaseofCarboniferousfoldingatca.305Ma.Rams-beckrepresentsamineralizationstylecommonin the Rhenish slate belt: Zn-Pb-Ag veins con-trolled by the axial plane cleavage and by re-verse faults. Such veinswere alsomined in a60 km long zone extending from Holzappel(HO)southwestacrosstheriverRhinetoWer-lau(WL)andthecityofTrier.Themainquartz-siderite-sphalerite-galena vein at Holzappelwasminedovera strikeof3.4kmand>1kmdown dip. In the Zn-Pb districts centered onBad Ems (BE), Lüderich (LD) andVelbert (VB),fault zones crosscutting the folds controlledvein and breccia ore (Beyschlag et al. 1916;Schneiderhöhn 1941). The Zn-Pb-Ag depositsat Ramsbeck, in the Holzappel-Trier zone andat Auguste Victoria are characterized by Var-iscanuranogenic(206Pb/204Pb=18.206-18.330)and thorogenic (208Pb/204Pb = 38.093-38.341)lead isotoperatios (LargeandSchaeffer1983;Diedel and Baumann 1988; Krahn and Bau-mann1996;WagnerandSchneider2002).

2.6 Slide6.TheEisenbergveinandEderplacergolddeposits

The gold-bearing Eisenberg anticline inLower Carboniferous black slate, chert andlimestone is located 5 km southwest of Kor-bach. The deposit is the principal source ofgold placers, which extend via tributarystreams to theEderover adistanceof 50 km(Beyschlag and Schriel 1923). Theplacers sur-rounding the 562 m high Eisenberg occur inPermian fluviatile red beds andmarine shore



conglomerates,andinPleistocenegravels.Thegold in these proximal placers consists ofrounded detrital grains, and of newly formeddendritic crystals precipitated by acidicgroundwater (Kulick et al. 1997). The detritalgold in Permian Zechstein 1marine conglom-erateindicatesthattheprimarydepositisold-er than 260 Ma (Lopingian series; ICS 2018).Thegoldcontentoftheproximalplacersises-timatedat0.5-2g/m3.ThedistalplacersintheEdervalleycontain0.16-0.95g/m3infinegoldflakes(BeyschlagandSchriel1923;Kulicketal.1997).

The Meissen chronicle of 1250 AD is theoldest record of mining at the Eisenberg. In1480, duke Phillip of Waldeck regulated themines.Until1585,whenthemaindrainagead-it collapsed, 8-10 km of drifts, 80 adits, andmore than50 shaftsweredevelopedor sunk.Gradesof137-384g/tgoldinhand-sortedbulkorewererecorded inthe localmint.Thetotalgoldintheoreminedundergroundisestimat-edat2.5metrictons,ofwhichabout40%wererecoveredbyamalgamation.Intermittentplac-er mining lasted until the 19th century(BeyschlagandSchriel1923;Kulicketal.1997).

2.7 Slide7.StrataboundgoldveinsintheEisenberganticline

TheEisenberganticline(mapmodifiedfromKulicketal.1997) consistsofa coreofUpperDevoniansilt-andsand-bandedgreyslate,andouterbituminousrocksoftheLowerCarbonif-erousKulmsuccession.Illitecrystallinityintheanticline indicatesmetamorphic temperaturesofabout250°C(Weberetal.1987).Theaurif-erous Kulm succession is subdivided into (Ku-licketal.1997):

(1) TheKulm1 LowerAluminousSlate (30-40m) composedmainly of quartz, illite, chlo-rite, and bitumen (up to 4.3 wt.% Corg), andmarkedbythinbedsofillite-richfelsictuff.Theupperhalf is enriched in framboidalpyrite (3-10 vol.%) associated with chalcopyrite andtracebornite.Backgroundcoppercontentsare100-500ppmbutspacedhorizonsareenrichedten-fold(0.27-0.45wt.%Cuover80cm).Lead,

zinc (both 10-50 ppm) and gold (0.01-0.05ppm)contentsarelow.

(2) The Kulm 2 chert-limestone-slate suc-cession,thelowerpart(10-24m)composedofblackradiolarianchertandsiliceousslate,andthe upper part (40m) of grey-green slate al-ternatingwithsiliceouslimestoneandamark-erbedoflithictuff1-10mthick.

(3)TheKulm3UpperAluminousSlate(8-15m)consistsofblackbituminousslate(25vol.%Corg + pyrite), siliceous-calcareous slate (3-12vol.%Corg+pyrite)and limestone intercalatedon a decimeter- to meter-scale. Felsic tuffs(0.5-5cmbeds)arecomposedof illite,kaolin-ite, quartz, and remnant orthoclase, plagio-clase,chloriteandbiotite.

(4) The Kulm 3 slate-greywacke succession(>250m), grey silt-banded slates low inbitu-mengradeupwardsintoslatewiththickerandmore abundant greywacke beds, which formthe core of the syncline northwest of the Ei-senberganticline.

Goldmineralization:TheUpper AluminousSlatesoutheastofGoldhausenisthehostunitofbedding-parallelveinsconfinedtotheover-turnedNW-limboftheanticline.Theworkingsin this unit, accessible from the Georg andPreussag (PS) shafts, are continuous over astrikeofmorethan1km.Scatteredminesfur-thernortheastextendstrataboundmineraliza-tion to 2 km. Minor production came fromstrike-parallel reverse faults in thecoreof theanticline. Two barren fault systems crosscutthe ore: (1) strike-slip faults (N65-90°W/60-85°S)withdextralmovementnorthblockeast;and (2) normal faults (N40°W/65-90° NE orSW) oriented perpendicular to the fold axis(Kulicketal.1997).

2.8 Slide8.Eisenberganticline:Mineworkingsincrosssection

The cross sections A-B and C-D (see Slide2.7), modified from Kulick and Theuerjahr(1983), show selectedmineworkings. The su-pergene copper ore at Victor is unrelated togold, and derived from diagenetic sulfides inthe Lower Aluminous Slate. Copper dissolved



ingroundwaterduringsulfideoxidationprecip-itated as malachite, azurite and chalcocite inadjacent limestone. In 1545, productionamounted to 24 t Cu (Beyschlag and Schriel1923;Kulicketal.1997).

SectionA-B:TheWaterAdit(Wasserstollen)intersects strike-parallel reverse faults of theSchlossbergsystem,whichdip40-60°SEatsur-facebutsteepento65-80°atdepth.Grade inthe 1.6-m-thickmain fault decreased from19g/tintheWasserstollento0.5g/tAuinanadit27 m below. The faults consist of cataclasitecemented by gold-bearing carbonate andquartz. Near surface, the carbonate cementwas leachedand the faultscontainedredclaysuggesting secondary enrichment. TheSchlossberg faults in the Kulm 2 successionwereminedoverastrike lengthof380mandverticaldepthof38m(Kulicketal.1997).

SectionC-D:TheStGeorgmine,drainedviatheUrstollenadit56mbelowshaftcollar,rep-resentsthebedding-parallelveinssoutheastofGoldhausen. The collapse of the Urstollen in1585 caused the shutdown ofmostmines. In1919-1929,theshaftandothermedievalwork-ings were refurbished (Rauschenbusch andRauschenbusch 1929). In 1932, the Preussagsunka70mdeepnewshafttoaccessorebe-lowtheseworkingsandin1974-1978,theGeo-logical Survey of Hessen carried out under-groundsamplinganddiamonddrilling.Onthe70 m level, scattered grades ≤ 5.5 g/t goldweredetected(Kulicketal.1997).

2.9 Slide9.Eisenberganticline:Bedding-parallelveins

Photographs A to C show late medievalworkings from1585orearlier in theStGeorgand St Sebastian mines southeast of Gold-hausen.

(A)StGeorgminemodel,Korbachmuseum,section looking northeast. At least 5 sets ofbedding-parallel veins (Lager 1 to 5), spreadoverahorizontaldistanceof7mintheKulm3UpperAluminousSlate,wereselectivelymineddown to theUrstollenadit.One "Lager" com-prisedlaminatedveins(5-10mmthick)atlime-

stone-slate contacts plus crackle and ladderveins crossing the limestone in between. Theore handpicked by the medieval miners con-sistedof:(1)asingleveinedlimestonebed10-15cmthickor (2) severalcloselyspacedbedsgrading 24-35 g/t gold over a width of 30-80cm(Ramdohr1932;Kulicketal.1997).

Crosscutting relationships in the St Georgmine(Kulicketal.1997)constrainthetimingofstructuresfromtheoldesttotheyoungest:(1)laminated Lager veins controlling main-stagegold;vertical striations indicate flexural slipatlimestone contacts, (2) flat thrust faults sub-parallel in strike tobedding,whichdip10-25°SE and displace the HW-block up to 20 cmnorthwest, some mineralized at the intersec-tionwithLagerveins,and(3)barrennormaloroblique-slip faults perpendicular in strike tobedding,whichdip65-90°NEorSW.

(B)StSebastianmine,thestopeabovethe-33mlevelis0.8-1.0mwide.Thegreyillite-richtuff in the center of the crown pillar was re-movedfirst tobreakblackslate intotheopenspace.TheLager5ore,a10-mm-thickcalcite-hematite vein in contact with limestone wasminedlast.

(C) St Sebastianmine -33m level, crosscutdrivenwithhammerandchiselintoblackslateoftheUpperAluminousKulm3formation,thehammeris32cmtall.

2.10 Slide10.EisenbergStGeorg:Bedding-parallelveins

Theore samples inphotographsB toEarefromLager1ontheGeorgshaft-38mlevel.

(A)Georgshaft-34mlevel,crownpillar15m southwest of the shaft, looking northeast:the Lager 1 ore consists of three laminated,hematite-stained calcite ± quartz ± dolomiteveins bound to the contacts of grey siliceouslimestone (whitearrows); the laminatedveinsare linked by thin veins (white) crossing thelimestone bed, most mineralized with nativegold.Theblackbituminousslatecontains lightgreyillite-richtuff.Thehammeris32cmlong.

(B) Footwall partof Lager1: the laminatedcalcite±quartz±hematiteveinisboundtothe



contactslate-limestone, the limestonestainedred by dispersed hematite. One of the cross-cuttingcalciteveinscontainsnativegold.Notethe thinmarker band of sand-sized felsic tuff(quartz,orthoclase,plagioclase,biotite)at thebottom of the specimen. The matchstick is 4cmlong,collectionRauschenbusch/Kulick.

(C) Hanging wall part of Lager 1, sketchmodified from Ramdohr (1932). Laminatedcrack-sealveinsmarktheflexuralslipsurfaces.In the laminations, the carbonate is recrystal-lized and the quartz brecciated, whereas thegangue in crackle and ladder veins is un-strained.Multiple stages of calcite ± quartz ±Fe-dolomite ± hematite fill are evident. Goldwasdeposited late.The felsic tuff is thesameasin(B).

(D)Lager1ore:aggregatesofnativegoldfillpart of a laminated calcite-quartz vein at thecontact slate-limestone. Some of the whitecalcite is stained pink by dispersed hematite.Thecalcitelaminationsareseparatedbystylo-lites of illite, and by thin lenses of slate andlimestone.Thescalebarisinmillimeter,collec-tionRauschenbusch/Kulick.

(E)Lager1ore:aggregatesofnativegoldina ladder vein crossing a laminated calcite-quartzveinatthecontactslate-limestone.Theladderveinhasthinredrimsofhematite,andisfilledwithcalciteandFe-dolomite(collectionRauschenbusch/Kulick).

2.11 Slide11.EisenbergStGeorg:OxidizedAu-Cu-Pb-Seore

The ore mineralogy is based on samplesfromtheStGeorgminedescribedinRamdohr(1932),MaucherandRehwald(1961),andKu-lick et al. (1997). The native gold is very fine-grained(0.5-5mm).Needlesandflakesofgold(11 wt.% Ag) occur disseminated in thegangue,formfeltedorbranchingdendriticag-gregates,andflower-ormoss-shapedmasses,which fill up to half the volume of a crackleveinorcrack-seal lamination.Manygrainsarezoned to thin silver-rich rims. Associated ox-ides, sulfides and selenides are less abundantthan gold (Ramdohr 1932): chalcopyrite,

clausthalite, goethite-lepidocrocite, hematite,bornite, pyrite, sphalerite, digenite and mag-netite, in the order of abundance. Chalcopy-rite,clausthaliteandgoldformmyrmekiticag-gregates.Bornitecontainsorientedlamellaeofchalcopyriteandfillstheintersticesindigenitetrellis, textures interpreted to indicate>200°Cfluid temperature (Ramdohr 1932). Primaryfluid inclusions inveinquartzhomogenizedat180-230°C(Sohl1990).Crystallinegoethiteandlepidocrocite are early hypogene oxides,whereas hematite occurs in both early- andlate-stageveins,locallyinspecularcrystals.

(A)Georgshaft-34mlevel,crownpillar15m southwest of the shaft, Lager 1 ore:moss-shaped and branching dendritic aggregates ofnative gold on the surface of a crackle veincrossing siliceous limestone. The calciteganguewasdissolvedinacid.Thematchstickis3cmlong,collectionKulick.

(B)Georgshaft-34mlevel,crownpillar15msouthwestoftheshaft,Lager1ore:dendrit-icaggregateofnativegoldonthesurfaceofabedding-parallel laminated vein at the lime-stonecontact.Thecalcitewasdissolved inac-id.Theaggregateisabout10mmlong,collec-tionKulick.

(C) Georg shaft -38 m level, Lager 1 ore:Syn-kinematic, snowball-shaped aggregates ofclausthalite (PbSe) with inclusions of darkernaumannite(Ag2Se)incontactwithnativegold(white), tiny crystals of gold are disseminatedinthegangue.Reflectedlightphotomicrographmodified fromMaucher and Rehwald (1961),collectionRauschenbusch.

Ramdohr(1932)concludedthatthedepositformedfromanascendinghydrothermalfluid.A source-distal setting is consistent with thepresence of selenides, the estimated fluidtemperature(about230°C),and lackofvisiblewall-rockalteration,exceptperhapsfor illite±kaolinite intuffclosetotheveins.Theassem-blage native gold + hematite in the bitumen-richUpper Aluminous Slate indicates that thehydrothermal fluid was oxidized. Fluid reduc-tionprobablycontributedtothebonanza-styleprecipitationofdendriticgold.



2.12 Slide12.SaddleReefsinfolds:TypelocalityBendigo

The bedding-parallel veins at spaced lime-stone-slatecontacts in theoverturned limbofthe Eisenberg anticline are structurally identi-caltothoseformedbyflexuralslipduringfold-ing (Ramsay1974; Tanner 1989). The type lo-cality for gold deposits of this "Saddle Reef"style is the Bendigo goldfield in the PaleozoicLachlanfoldbelt,southeastAustralia (mapA),where the Re-Os isochron age (438±6Ma) ofarsenopyriteandpyrite(n=5,MSWD=1.7)linksgoldmineralizationtoSilurianfolding(Arneetal.2001;Houghetal.2007).

(A)GeologicmapoftheBendigoareaintheLachlan fold belt, Australia, modified fromWillman (2007). The Devonian Harcourt gran-odiorite-granitebatholithseparatestheBendi-go and Castlemaine gold deposits. Syn-orogenic vein formation preceded the em-placement of the post-folding batholith at ca.375Ma.Granite-relatedAu-Bi-Tequartzbrec-ciaandpyroxeneskarninhornfelswereminedatMaldon (67 t Au). The insetmap of south-east Australia shows the Bendigo Zone (BZ)separated by regional faults from the Stawell(SZ)andMelbourne (MZ)Zones.Ageandpro-duction data: Cherry and Wilkinson (1994),Bierleinetal.2000,Arneetal.(2001),Willman(2007).

TheBendigodeposits (1851-2007:697tAuincl. 157 t fromplacers) arehostedby anOr-dovicianslate-greywackesuccessionfolded in-tonorth-trendingtightanticlinesandsynclinesof shallow plunge. A sub-vertical axial planecleavage iswidelydeveloped (Coxetal.1991;Willman2007).Mesothermalgoldquartzveins(reefs) form stacked ore bodies in anticlinesminedtoadepthof1400m,whereasthesyn-clinesarepoorlymineralized. Three structuraltypesofveinarecommon:(1)bedding-parallellaminated "leg reefs" inanticlinal limbs,oftenassociatedwithtensionalspurveinsextendingintocompetentbeds;(2)thick"saddlereefs"inthedilatedanticlinalhinge,someextendingin-to "neck reefs" crosscutting the beds; and (3)"fault reefs" with footwall tensional veins instrike-parallel reverse faults,whichdevelopat

steeply dipping bedding planes but flattenwhere theycrosscut the foldhinge (Coxetal.1991;CherryandWilkinson1994;Leaderetal.2013).

(B)Lookingnorthatacrosssectionthrougha Bendigo anticline illustrating the structuraltypesofgoldquartzvein,modifiedfromLead-eretal.(2013).

(C)Stackedsaddlereefs(red)inworkingsoftheHustlersmine,Bendigo,crosssectionlook-ing north (modified from Baragwanath 1930).Thepost-orelamprophyredyke(blue)isJuras-sic (159±6 Ma K-Ar; Cherry and Wilkinson1994).

Eisenberg:Bedding-parallelveinsformedintheoverturnedNW-limboftheEisenberganti-cline during folding in the Stephanian, con-strainedby theK-Arageofmetamorphic illiteat297±9Ma (Ahrendtetal.1983).ErosionoftheVariscanmountainchaintookplace intheLower Permian (ca. 295-275 Ma), when the"saddle reef" position of the Kulm 3 slate-limestone succession was removed. Some re-verse faults of possible "fault reef" geometry(Schlossberg system)werepreserved. The an-ticline remained above sea level in theUpperPermianat 260Mabutwas coveredbymorethan400mof sedimentduring theMesozoic.UpliftbeganintheUpperCretaceousandcon-tinuedduringtheTertiary(Kulicketal.1997).

2.13 Slide13.RamsbeckZn-Pb-Agveins:Settinginaregionalanticline

The Ramsbeck mine (1840-1974: 16.7 mil-lionmetrictonsat4.4%Zn,2.1%Pband50-60g/tAg;BehrendandPaeckelmann1937;Baueretal.1979)closedin1974butremainsopentotourists via the Eickhoff tunnel(www.sauerlaender-besucherbergwerk.de).The geologic map of the northeast RhenishMassif(modifiedfromWeber1977)showstheRamsbeck vein system (white double arrow)relative to the GivetianMeggen sedimentary-exhalative Zn-Pb-Ba deposit (Mueller 2019),whichoutcropsinasubsidiarysyncline(red)atthenorthwestlimboftheEastSauerlandAnti-cline (ESA). The coordinates are latitude and



longitude.The insetshowsthemaparearela-tivetoGermanandDutchcities.

TheRamsbeckveinsarelocatedatthemar-ginofa thermalanomalydefinedby thecrys-tallinity of illite (white lines 105-115) in 633polished slate samplesmeasuredbyX-raydif-fraction at the half-height of the 10Å {001}peakrelativetoquartz(Hb-illite001x100/Hb-quartz100). Lower values correspond to in-creased illite crystallinity (Weber 1972a;1972b;Werner 1988). This anomaly coincideswith a regional high of vitrinite reflectance(magenta line V = 6%) and with a low inBouguer gravity most likely caused by buriedgranite. Peak temperatures of 300-350°C at304±10Ma(n=4) intheaureoleofthisplutonare constrained by actinolite-pumpellyite as-semblages in basaltic dykes and by illite K-Arages,respectively(Ahrendtetal.1983;Werner1988).The thermalanomaly isdisplaced1000mNE-blockdownattheAltenbürenFault(AF;Weber1977).

Primary inclusions inRamsbeckveinquartzand sphalerite contain NaCl-KCl-H2O fluids oflow to moderate salinity (3-14 wt.% NaCleq),which homogenize into liquid at 140-210°C(Langhoff 1997). The correction to trappingtemperature isplus80-90°C(Behretal.1987)givenatleast3kmburialdepthandalithostat-ic pressure of about 100MPa (1 kbar) duringoreformation(Baueretal.1979).Thecompo-sition of late-stage chlorite (in Behrend andPaeckelmann1937) indicates a fluid tempera-tureof306±50°CusingtheAlIVthermometerofCathelineau (1988). Early-stage sphalerite andgalena have d34S values of +6.5 to +7.7‰,whereas late-stage sphalerite (+2.4 to+8.7‰)and boulangerite (-0.5 to +7.7‰) display agreaterrange(WagnerandBoyce2001).Thesevalues overlap those of sulfides in mantle-derivedmagmatic rocks (0±3‰)but are closeto theaveraged34S (+7‰)of thepresent-daycrust suggesting assimilation of country rocksulfur, a feature of granitoids in Nova Scotia,TasmaniaandJapan(Ohmoto1986).

2.14 Slide14.RamsbeckZn-Pb-Agveinsinfoliatedquartziteandslate

The geologic map (modified from Behrendand Paeckelmann 1937) shows the N60-70°EstrikingDevonianquartzite-slate successionatthe NW-limb of the East Sauerland Anticline(ESA), the host formation of themines in thedistrict: Alexander (AX), Bastenberg (BA),Wil-libald (WB), Dörnberg (DB), Aurora (AR), Juno(JN)andPluto (PL).TheRamsbeck succession,shown in lithologic units, separates the ESAfrom the Nuttla Syncline. Veins of economicthickness (2-4m)andgradewere confined tothe80-100mthickMainQuartzite,whichper-sists for more than 7 km across the district,andtothe40-80mthickFootwallQuartzitere-stricted to the Dörnberg area. Both quartziteunitsarehighlightedbrightgreen.IntheDörn-berg area, stacked veins were mined over avertical extentof700m.Diamonddrillingbe-foreclosurein1974indicatedresourcesof2.8million metric tons below sea level (PodufalandWellmer1979). TheRamsbeck successionforms a hard quartzite-rich range in monoto-nous Middle Devonian grey to black slates3000 m thick, which vary from calcareous tosandyandcontainfelsic tuffsanddiabasesillsor dykes (Weber 1977). Two trends of Zn-Pbveins parallel to the slaty cleavage occur 1.0and1.5kmsoutheastof theRamsbeck range.Theseveinswereminedupto1911intheRiessystem(RS).

Post-orefaults:NW-toNNW-strikingjointsandfaults(bluelines)crosstheRamsbecksuc-cession.Dipsvaryfrom45-80°SWorNE.IntheBastenbergmine,a1.5-m-widejointextendingSSE from themain cleavage-parallel vein wasminedoveradistanceof100mindicatingthatsome cross joints / faults developed prior toore formation, initially as tensional surfacesperpendicular to the fold axes (Behrend andPaeckelmann1937).However,mostNW-faultsoffsetthecleavage-parallelveins, locallyupto300m down as in the graben separating theBastenbergandDörnbergmines.Somenormalfaultscontainveinfillupto2mthick,whichissubdivided into: Stage 1 barite with minorgersdorffite,andStage2calcite+Fe-dolomite



with minor pyrite, marcasite, chalcopyrite,low-Aggalena,low-Fesphalerite,andaccesso-ry pyrargyrite, stephanite, acanthite and mil-lerite(Baueretal.1979).

Thepost-orefaultingandmineralizationhasbeenattributedtoTertiaryreactivation(Baueretal.1979).Alternatively, it tookplaceduringpost-foldingupliftinthePermo-Carboniferous,asconstrainedbynormalplusstrike-slipfault-ingintheAugusteVictoriaarea(seebelow).AtRamsbeck, WNW-striking dextral strike-slipfaultswithupto60mapparentoffsetoccurintheDörnbergarea.NNE-strikingsinistralfaultswithupto400mapparentoffsetcontainedli-monite iron ore grading into pyrite at depth(BehrendandPaeckelmann1937).

2.15 Slide15.RamsbeckZn-Pb-Agveinsinslatycleavageandfaults

Cross-section through theBastenbergmine(Section "e" in Slide2.14;modified fromBeh-rend andPaeckelmann1937) illustrating foldsin the Ramsbeck quartzite-slate succession atthe NW-limb of the ESA. In the overturnedlimb,whichdips20-30°SSE, theMainQuartz-ite is thrustovertheCrinoidSlate. Inthesub-horizontal normal limb below, the lithologicunitsfacetherightwayup.Foldsofthisgeom-etrystepdownto>1.5kmdepth,asthehingeof the regional Nuttla Synclinewas not inter-sected in the 1.1 km deep Valme drill hole 3kmsoutheastofRamsbeck(Baueretal.1979).The Bastenberg is the site of the 130m longVenetianadit(1.4mhigh,0.2mattop,0.7mat base), whichmay date back to the BronzeAge. Most of the mining took place in theBastenbergVein at the faulted contact of theMainQuartzitewiththeCrinoidSlate(BehrendandPaeckelmann1937).

2.16 Slide16.RamsbeckZn-Pb-Agveins:Dörnbergsection

Cross-section through the Dörnberg minelooking east (modified from Podufal 1977)showing stacked Zn-Pb-Ag veins in the foldedMain Quartzite below the Eickhoff adit, themain drainage tunnel. A limestone bed (blue)

marks the stratigraphic top of the quartziteunit, which strikes N60-70°E. Overturned foldlimbsdip30-50°SSEandalternatewithnormallimbsdippingflatlysouth.Thefoldaxesplunge5-10°SW(PodufalandWellmer1979).

Like the slates, the quartzite displays acleavage sub-parallel to theaxial planeof thefolds,whichismoderatelyfannedinthickbeds(Weber 1977; Bauer et al. 1979). Cleavageplanes reactivated as reverse faults are theprincipalstructurescontrollingtheveins.TheystrikeN65-75°E,dip10-45°SSE(average:30°),andhaveoffsetsvaryingfromafewmeterstomorethan100m(FWVein1).Striationsare±parallel to the dip direction (Podufal andWellmer 1979). Not all veins are located infaults.Thecorrelationofbedsacrossveinsandthe jig-saw fit of wall-rock fragments suggestthatsomecleavageplanesweresimplyforcedopen by fluid pressure and filledwith gangueandsulfides(BehrendandPaeckelmann1937).

The veins are offset by numerous flat re-verse faults, which moved the hanging wallblockNNWanddip15°SSEto10°NNW(aver-age: 5° SSE). Some are dome-shaped in crosssection. The offsets vary from a few decime-terstotensofmeters.Mostflatfaultsarebar-ren or weakly mineralized between the sec-tions of vein displaced. The exception is theAuroraFault,whichoffsettheDörnberg,Auro-raandthreeminorveinsupto80mandcon-tainedhigh-gradeoreoveradistanceof140m(Behrend and Paeckelmann 1937; Podufal1977).

Thethirdsyn-mineralstructuresarenormalfaults (notshown),whichareparallel instriketo the veins but dip steeply SSE. They persistseveraltenmetersinstrike,haveoffsetsofupto5m,andarelocallymineralizedwithsphal-eriteandgalena.Theyareinterpretedasrelat-ed to the relaxation of Variscan compression(Weber1977).

2.17 Slide17.Ramsbeck:Veinsintheaxialplanecleavageandinflatreversefaults

The syn-orogenic mineralization at Rams-becktookplaceinstagesseparatedbyperiods



ofreversefaulting(BehrendandPaeckelmann1937;ScherpinBaueretal.1979;WagnerandCook1998). STAGE1 is confined to thecleav-age-parallel veins and faults, and consists ofquartz, minor siderite (6-8 wt.% Mn), pyrite,andaccessoryarsenopyrite.

STAGE 2 fills both the cleavage-parallelveins and some of the flat reverse faults andconsistsofquartz,sphalerite(6.1-9.6wt.%Fe),minorgalena,andaccessorychalcopyrite.Thesphalerite contains inclusions of chalcopyriteand, rarely, stanniteandpyrrhotite.Thesilvercontentofgalenavariedfrom400to1400g/tandaveraged900g/t(Baueretal.1979).

STAGE 3 is separated in time from Stage 2by the formationoforemylonites inboththecleavage-parallelveinsandtheflatfaultsclosetotheintersectionofbothstructures.Themy-lonitesconsistofroundedorcorrodedclastsofveinquartz,quartzite,andlesserFe-richsphal-eritecementedbyrecrystallizedsphaleriteandgalena.Manyoremylonitesareenrichedinsil-ver (250-492 g/t) and antimony (up to 0.25wt.%) indicating the presence of tetrahedrite,bournonite and boulangerite. These sulfosaltsandlatesphalerite(1.7-4.5%Fe),chalcopyrite,galena and quartz also form weakly strainedvein fill. Late minor minerals also include py-rite, arsenopyrite, calcite, ankerite, chlorite,kaoliniteanddickite.

(A) Looking east at theDörnbergVein ori-entedparallel to theaxialplane cleavage (dip30°SSE) ingreyquartzitewithpartingsofdarkgrey phyllite. Striations on the footwall veinsurface pitch 80-90° consistent with dip-slip.The vein is composed of white quartz, minordark brown sphalerite and accessory chlorite,andisoffset1-2msouth-sidedownatastrike-parallel fault dipping 70°SSE (broken whiteline).Dörnbergmine,stopeabovetheEickhofflevelclosetotheinternalshaft1,thehammeris32cmtall.

(B) Footwall Vein 1 composed of Stage 1massivepyrite,minorquartzandaccessorysi-derite oriented parallel to the axial planecleavageindarkgreyphyllite.AsecondveinofStage 2 sphalerite andwhite quartz, orientedparallel to a flat reverse fault, crosscuts the

cleavage planes and the pyrite vein. Displayspecimen in the Ramsbeck visitor center col-lectedfromthe300to360mleveloftheDö-rnbergmine,stopebetweencrosscuts2and6,theSwissknifeis8.5cmlong.

(C) Looking northeast at a cross sectionthrough the Aurora Vein oriented parallel tocleavage planes in theMain Quartzite (modi-fiedfromBornhardt1912).Theangularquartz-ite fragments arequartz-veinedandborderedby sparse sulfide seams (in bottom right cor-ner) indicating repeat fracturing and sulfidedeposition. The fragments are cemented byStage2quartzandaccessorysphalerite,whichform a banded vein at the hanging wall con-tact,where theyarecrosscutbyStage3gale-na-richmylonitemarked by quartz clasts. Ga-lena and minor sphalerite form replacementaggregates below the mylonite. Exposure inthe stope above the Willibald 3 adit, photo-graphed and colored by Bruno Baumgärtel,August1910.

2.18 Slide18.Ramsbeck:Vein-faultsysteminplansection

ProjectionoftheFootwallVein4withintheMain Quartzite unit to a horizontal plane(modified fromPodufal andWellmer1979) il-lustrating the structure of the vein-fault sys-tem: steeper cleavage-parallel vein segmentsare linked by flat reverse faults. The averagedip of the mineralized surface is 23° SSE be-tween+3mabove(360mminelevel)and-300mbelow sea level.Mineable orewas definedbyacompositethicknessof≥15cmsphaleriteequivalent. In the stopes below the Eickhoffadit, barren or weakly mineralized flat faultsamountedto25-30vol.%dilutingthegradeofthecrudeoreextracted.

2.19 Slide19.Ramsbeck:Vein-faultsystemincrosssection

(A)North-southsectionoftheAuroravein-faultsysteminMainQuartzitewestoftheAu-rorashaftbetweentheChristianandWillibald4 adits (not to scale; modified from BehrendandPaeckelmann1937).Thecleavage-parallel



AuroraVeinisoffsetatareversefaultmineral-ized with 1-10 cm thick ore mylonite in itssteeperpartsandwithunstrainedZn-Pboreinits central flat part, which opened duringmovement. Flat reverse faultswereonlymin-eralized between the veins they offset. TheylackStage1pyritebutcontainStage2-3sphal-eriteandgalenaaswellasStage3bournonite,boulangerite and tetrahedrite (Behrend andPaeckelmann1937;Baueretal.1979).

(B) Steel-grey ore mylonite, rounded andembayedclastsofwhitequartzare cementedbyfine-grainedgalenaandsphalerite.Notetheirregular replacement front in older veinquartz.Dörnbergmine,FootwallVein1,300to360mlevel,stopebetweencrosscuts2and6,the lens cap is 52 mm across, collectionPodufal.

(C) Looking northeast at a cross section oftheAuroraVeinorientedparalleltocleavageintheMain Quartzite (modified from Bornhardt1912).ThebandedveiniscomposedofStage2iron-rich sphalerite, quartz, minor galena andrarechalcopyrite.ExposureinthestopeabovetheWillibald3adit,photographedandcoloredbyBrunoBaumgärtel,August1910.

(D) Stage 2 sphalerite (ZnS), white quartzand rare calcite in veins parallel to the axialplanecleavageinphyllite.Thepinch-and-swellquartz veins are interpreted to reflect the in-crementalopeningofthecleavageplanesdueto supra-lithostatic fluid pressure. Dörnbergmine, Footwall Vein 1, 300 to 360 m level,stope between crosscuts 2 and 6, thematch-stickis42mmlong,collectionAGM.

2.20 Slide20.Ramsbeck:Zn-Pbgrade,veintextures,alteration

LEFT: Themap shows the contoured Zn-Pbgrade(assulfidethicknessinZnSequivalent)oftheFootwallVein1betweencrosscuts2and4onthe360mleveloftheDörnbergmine(mod-ified from Podufal and Wellmer 1979). Notethescissor-typemovementonsomeoftheflatfaults,whicharebarrenatthislocationindicat-ingthatthereversefaultingoutlastedmineral-ization.

(A) Footwall Vein 1: breccia in the MainQuartzite, angular fragments of fine-grainedquartzite are cemented by Stage 2 whitequartz, brown iron-rich sphalerite, and minorgalena and pyrite. Quartz is the oldest veinmineral rimming the fragments. Dörnbergmine, 300 to 360 m level, stope betweencrosscuts 2 and 6, the Swiss knife is 8.5 cmlong, collection Podufal. Wall-rock alteration:Quartziteadjacenttotheveinswaspartlysilici-fiedandcontainedsparsedisseminatedpyrite(ScherpinBaueretal.1979).

(B)FootwallVein1:compositeveinparalleltotheaxialplanecleavageindarkgreyphyllite(Upper Crinoid Slate): Stage 1 massive pyritewithaccessoryquartz is separated fromStage2iron-richsphaleritebyathinband(arrow)ofbrown siderite. Quartz ladder veins segmentthe siderite band indicating extension. Thecleavage-parallel pinch-and-swell veins arecomposedofStage2quartzandminorsphaler-ite.Dörnbergmine,300 to360m level, stopebetween crosscuts 2 and 6, the Swiss knife is8.5 cm long, collection Podufal. Wall-rock al-teration:Atveincontacts,theslatewasalteredto quartz-sericite ± pyrite schist 1-2 cm thickreplacingmetamorphicillite,chlorite,andrarefeldspar(ScherpinBaueretal.1979).

Alteration in diabase: Vesicular diabasedykesrotatedparalleltotheaxialplanecleav-ageoccurlocallyintheDörnbergmine(Weber1977). They consist of metamorphic chlorite,albiteandcalcite.Alongthecontactwithveins,the dykes are foliated and altered to a lightgrey sericite-quartz-ankerite ± leucoxene as-semblage. Altered diabase contains 2.03-4.06wt.% TiO2, 1.71-9.98 % CO2, and 2.02-4.59 %K2O. K2O/Na2O ratios of 5:1 to 20:1 suggestthatthealterationmicaismuscovite(ScherpinBaueretal.1979).

2.21 Slide21.Ruhrcoaldistrict:Zn-Pb-Agoreinnormalfaults

TheRuhrcoal-miningdistrictinNorthRhineWestphalia contains three Zn-Pb-Ag depositscontrolled by post-orogenic faults. The Au-guste Victoria deposit produced 5.2 million



metrictons(Mt)oforeat7%Zn,4%Pb,0.04%Cu and 65 g/t Ag (1938-1962), and the Chris-tian Levin deposit 0.35Mt at 10.7% Pb, 0.3%Znand26g/tAg(1938-1958).TheKlara/GrafMoltkedeposit(2Mtat8%Zn,2%Pb)wasde-velopedbutnotminedduetolowmetalpricesin 1958 (Buschendorf et al. 1957; Pilger et al.1961;Krassmann2019).

LEFT:BedrockmapofthewesternRuhrdis-trict (modified from Pilger et al. 1961). TheRuhr and Lippe are tributaries of the riverRhine.UpperPermian,Triassic,andUpperCre-taceous sedimentary rocks cover the erosionsurface in the Carboniferous coal measures(dip:2-6°N).ThecoverrockspinchoutalongalineconnectingthecitiesofEssenandBochumbutincreasenorthwardtoathicknessof800min the Lippe valley.Oligocene sandstones andshalesinthewestrepresenttheeastboundaryof the Tertiary succession in the Rhine Basin(Henningsen and Katzung 2002). The 3.8 kmthickUpperCarboniferouscoalmeasuresover-lie 1-2 km thick Lower Carboniferous slate,greywackeandlimestonewithoutcoal.Onthemap,theNamurianCandWestphalianAunitsup to coal seam Katharina delineate NE-striking tight anticlines (grey), whereas theWestphalian B and C delineate broad opensynclines. The foldshavegentlyplungingaxesand vertical to steeply inclined axial surfaces.Theyaredisplacedbyfoursetsoffaults, fromthe oldest to youngest: (1) syn-orogenic re-verse faultswith up to 2000mdisplacement,some re-folded during progressive defor-mation; (2) post-orogenic NW-striking normalfaults (local term: Sprung)with up to 1000mdisplacement;(3)WNW-strikingdextralstrike-slipfaults,and(4)north-strikingsinistralstrike-slip faults subordinate to the dextral set(Hesemann and Pilger 1951; Henningsen andKatzung 2002). The Auguste Victoria (AV),Christian Levin (CL), Klara (KL), and the Zn-Pbdeposits in the Velbert district (VB) to thesouthare controlledbynormal faultsperpen-dicularinstriketothefoldaxes.

CENTER:Stratigraphiccolumnof theUpperCarboniferous (Pennsylvanian) coal measuresintheRuhrdistrict(modifiedfromHenningsen

and Katzung 2002) showing prominent coalseams (black) and sandstones (yellow) in thefluviatile-deltaic siltstone-shale succession (ca.320-305 Ma) of the Variscan foredeep. ThecoalmeasuresaresubdividedintotheNamuri-an C and Westphalian A to C units keyed totypelocalitiesatlocalcities.Coalcomprises4-5% of the succession in the southern andabout 2% in the northern part of the district.Out of 266 coal seams, 108 seams 0.5-2.8 mthick(FlözinGerman)weremined.Theuncon-formityattheendoftheWestphalianCmarksthe main phase of Variscan folding in theStephanianatca.305Ma.

RIGHT:Column illustrating the sedimentaryrocks inonecycleofcoal formation (modifiedfrom Drozdzewski 2011). The coal seams arenot strictly stratigraphic markers, as they aretraversed at low angles by thin layers of vol-canicashalteredtokaolinclay.Sandstoneas-sociatedwith theWestphalianAFinefraucoalseam contains detrital zircons eroded frommetamorphic rocks (410-2590 Ma) and gran-ites(327±3Ma,U-Pb)intheVariscanterranessoutheastoftheRhenishMassif(Linnemannetal.2019).SomeWestphalianBsandstonescon-tainclastsoflow-volatilecoalerodedfromex-posedNamurianCseams.Thehighcoalrankatclast deposition is attributed to elevatedheatflow, probably caused by granite plutons em-placed at depth (Henningsen and Katzung2002).

2.22 Slide22.Ruhrdistrict:Foldedcoalmeasures

(A) Cross section at Christian Levin lookingeast (modified from Buschendorf et al. 1957)showing folded and thrust-faulted major coalseams (e.g. Katharina, Finefrau) in the UpperCarboniferous basement (grey). The intensityof folding decreases to the north and up thestratigraphicsection.Thebasementisoverlainbyflatlynorth-dippingUpperCretaceoussand-and marlstones (green), and by Pleistoceneglacialsediments(orange).Theverticalscaleis4-timesthatofthehorizontal.



(B) Looking northeast at the unconformitybetweenfoldedUpperCarboniferousandflat-lyingUpperCretaceoussedimentaryrocks.TheWestphalianAbedsconsistoffine-grainedmi-ca-bearing sandstone, exposed below a re-verse fault (white arrow), and sand-bandedgreysiltstonewithaslatycleavage.Thepoorlysorted transgression conglomerate with goe-thiteandsandstonepebblesattheunconform-itygradesupwards intoglauconiticsandstone.GeologicalGardeninthecityofBochum,expo-sure in the former open pit of the Friedericamine, which produced coal and black-bandironstonefrom1750-1907.

(C)LookingNNWatasectionsub-paralleltostrikeincoalmeasuresformingthewalloftheDünkelberg quarry,Mutte valley south of theriver Ruhr. The coal seam Gleitling 3 (black-brown) isoverlainby theFinefrauconglomer-atic sandstone, and underlain by slates com-prising (top to bottom): carbonaceous mud-stonewithplantroots(2m),siltstone(8-10m),mudstone with plant roots (3-4 m), sand-banded siltstone (8-10 m). The coal seam isdisplacedattwonormalfaults(whitearrows).Thewall is about35mhigh.Muttentalopen-airmuseumattheformerNachtigallcoalmine,RuhrvalleyinthecityofWitten.

(D) Looking north at the position of seamDickebank,mined for coal and siderite,whichis overlain by the cross-bedded Dickebanksandstone and underlain by brown carbona-ceous mudstone with plant roots gradingdownward into grey sand-banded siltstone.The coal-bearing mudstone contains yellow-brownsideritenodulesandlensesupto20cmlong. From 1851-1912, about 9millionmetrictons of "black-band" siderite were mined asiron ore (25-40% Fe) in the Ruhr district(Wrede2006).GeologicalGardeninthecityofBochum, exposure in the former open pit oftheFriedericamine.TheopenSwissknifeis16cmtall.

2.23 Slide23.AugusteVictoria:Faultsinplanandcrosssection

LEFT:PlanofLevel3(743mbelowsurface)showingtheprincipalstructuresintheAugusteVictoria mine (modified from Hesemann andPilger 1951). Crosscutting relationships indi-cate, from theoldest toyoungest: (1) theup-rightAugusteVictoriaanticline (AVA)outlinedby the coal seamsmined; (2) the AV reversefault (AVRF) with > 600 m displacement; (3)the post-orogenic Blumenthal normal fault(BNF) controlling theWilliam Köhler Zn-Pb-Agdeposit (black), (4) themineralizedAVdextralstrike-slip fault (AVF) with 210 m horizontaland 15m vertical offset, and (5) themineral-izedHülssinistralstrike-slipfault(HUF).TheAVstrike-slip fault,markedby cataclasiteup to5m thick, contained uneconomic sphalerite-quartz cemented breccia and barite-calcite-marcasiteveinsattributedtothelatestagesofsulfidemineralization (Pilger et al. 1961). Thedrift linking the production shafts 1/2 to theman-and-supply shafts 4/5was chosen as theZerolinecrosscutintheoredeposit.

RIGHT: Section through the Blumenthalnormalfault(blue)atcrosscutZero,parallelinstrike to the coal seams (black), sandstones,sand-bandedsiltstones(bothyellow)andmud-stonesof theWestphalianAbeds.Thestopes(red)projected fromcrosscut2southaverage15-18m inwidth. Theoreextends to theup-permostminelevel.Galenawasintersectedina drill hole 1mbelow the Cretaceous uncon-formity (Hesemann and Pilger 1951; Pilger etal.1961).

TheBlumenthalFault consistsofa steppedzone15-60mwide,whichdips60-70°SW.Theverticaldisplacementatthemineis700mSW-blockdown,as indicatedbythecorrelationofCarboniferous strata across the fault, the up-warddragofcoalseams in theSW-block,andvertical striations (pitch 75-90°) on faultplanes. Half the displacement is attributed tothefootwallboundaryfault,onequartertothehangingwall boundary fault, and the remain-der to faultswithin thezone.Adiamondhole(DDH) drilled from the uppermost mine levelinto the Cretaceous sandstone showed that



theerosionsurfaceonthefaultis55mhigherthanelsewhereonthemininglease.About20-25misduetoapaleo-highformedbythesilic-ified fault zone, and 30-35 m to post-Cretaceousreversereactivationcausedbyfar-field stress in the foreland of the Alpine-Tethyan fold belt. The deposit is thus olderthantheCenomaniansandstonecover(ca.100Ma; ICS 2018), and probably older than theflat-lying Permian Zechstein 1 conglomerateandblackshale(ca.260Ma)onadjacentmin-ingleases(HesemannandPilger1951).

2.24 Slide24.AugusteVictoriaZn-Pbore:Structuralcontrols

TOP: Looking southwest at the longitudinalprojection of the Zn-Pb-Ag ore bodies in theBlumenthalFaultontotheAVanticline (modi-fiedfromHesemannandPilger1958;Pilgeretal1961).ThetopoftheNorthernOrebodywaseroded prior to the Cretaceousmarine trans-gression. Theapparent inclinationof the axialplanetothesoutheastiscausedbythechangein strike of the projection line. The Zn-Pb de-posits andmostprospects in theRuhrdistrictoccur where NW-striking normal faults crossNE-strikinganticlines.

BOTTOM:StructuralplanofLevel3(-743m)showing the Stage 1 sphalerite-galena ore intheBlumenthalnormalfault(black),theStage2asphaleriteorecontrolledbytheNorthZoneofdextralstrike-slipfaults(red),andtheStage2b barite-calcite-pyrite-marcasite mineraliza-tion in the Hüls system of sinistral strike-slipfaults (green; modified from Hesemann andPilger1958;Pilgeretal1961).

The150-m-wideNorthZoneconsistsof3-7shear zones, which strike N75°W, dip 70-85°SSW, and displace the Blumenthal Fault andStage 1 ore 10-20 m north block east. Stria-tionsonfaultplanesarehorizontalorpitchatshallow angles. Stage 2a replacement is con-fined to the intersectionwith the BlumenthalFault, and extends along normal fault planes.Some 2a sphalerite zones with minor dextraloffsets trend N55°W across the Blumenthal

Fault,aRiedelorientationrelativetotheNorthZoneshownintheSouthernOrebody.

The Hüls system has an overall strike ofN60-65°W, and consists of en-echelon sub-vertical faults (N70-75°W) and fissures(N90°W),thelatterformingopenspacesupto5mwide. The faults displace the southblockeast and have horizontal to moderately east-pitchingstriations.IntheSouthernOrebody,inparticular, theyoffset both Stage1 and Stage2a ore. In aggregate, these offsets cause thesigmoidaldeflectionoftheBlumenthalFaultinstrikeseparatingtheorebodies.Stage2bfaultfillconsistsmainlyofcalcite,pyriteandmarca-site(Pilgeretal.1961).

2.25 Slide25.AugusteVictoria:Oreformationduringfaulting

TOP: Geologic map of the Northern Ore-bodyonLevel3a(-833m)oftheAugusteVic-toria mine showing the mineralization stagescontrolledbytheBlumenthalnormalfault,theNorth Zone dextral strike-slip faults, and theHüls sinistral strike-slip faults (modified fromHesemann and Pilger 1951). Main stage orewas confined to the Blumenthal Fault, andcomprised wall-rock silicification plus low-grade quartz breccia along the footwallboundaryfault(Stage1a),sphalerite-richbrec-cia in the central part (Stage 1b), and galena-richbrecciainthehangingwallpart(Stage1c).FragmentsofStage1ainStage1bandofStage1b in Stage 1c indicate syn-tectonic sulfidedeposition, and the stepwise widening of theBlumenthalFaultfromearlymovementonthefootwall boundary to later movements on itshanging wall faults (Hesemann and Pilger1951).

The North Zone is part of the WNW-trendingstrike-slip systemrepresentedby theAVFault(Slide2.23).IntheNorthernOrebody,the dextral faults offset both the BlumenthalFault and the Stage 1 ore. They controlledStage 2a silica replacement and sphalerite-quartzore.ThesphaleriteinbothStage1band2a had low iron contents of 1.62-1.75% and1.35-1.60%,respectively(Pilgeretal.1961).



The Hüls sinistral strike-slip faults (Huels Ato C) control Stage 2b mineralization com-posed of barite, calcite, pyrite andmarcasite.Sparse sphalerite (1.32% Fe) and rare galenaare interpreted as remobilized fromolderore(Hesemann and Pilger 1951). Some Stage 2bveins extend along normal faults,whichwerereactivated as indicated by horizontal stria-tions overprinting steeply pitching ones. NotethedeflectionoftheBlumenthalFaultinstrikeby stepped sinistral offsets at the southeastendoftheNorthernOrebody.

(A) Stage 1a fault breccia: angular to sub-roundedfragmentsofsilicifiedblackslateandolderbreccia(abovethecoin)arecementedbywhite sugary quartz and by sparse brownsphalerite. Small open vugs are lined withquartz crystals. Sample 55, Auguste Victoriaminecollection.TheSwissknifeis8.5cmlong.

(B)Stage1bbrecciaore:fragmentsoffine-grained brown sandstone, black slate andwhite Stage 1a quartz are cemented by darkbrowncrystallinesphaleriteandbyminorfine-grainedgalena(atknife).Thecleargreyquartzof the top lines an open vug. Sample 15, Au-gusteVictoriaminecollection.TheSwissknifeis8.5cmlong.

(C) Stage 1c breccia ore: wall-rock frag-ments (dotted) are cemented by galena andaccessory sphalerite (black), which are partlyreplaced by Stage 2b calcite and marcasite(yellow)adjacenttoaHülsfault.Drawingofanexposure on Level 3, Crosscut Zero, in thehanging wall part of the Blumenthal Fault(modifiedfromHesemannandPilger1951).

2.26 Slide26.AugusteVictoria:Stage1oreinthenormalfault

Stage 1 sphalerite and galena in the Blu-menthalnormalfaultandlessabundantStage2a sphalerite in and adjacent to the NorthZone strike-slip faults are the principal oreminerals.Inbothstages,thesequenceofdep-ositionisquartz-sphalerite-chalcopyrite-ga-lena - quartz, repeated several times in thefaultbreccia.Theabundanceofquartzrelativetohydrothermalsericite,siderite,ankeriteand

latedickiteisreflectedintheaveragecomposi-tionoftheore(71wt.%SiO2;3.8%Al2O3;1.3%CaO).PyriteandmilleriteareabsentinStage1.

In1950,thesphaleriteflotationconcentratecontained57-60%Zn, 31.5%S, 1.75%Fe, 0.8-1.2%Pb,0.25%Cu,0.15%Sb(traceAs),95-135g/tAg, 590 g/tGa, 150 g/tGe, 300 g/t In, 50g/tCd,40-80g/tSn,40g/tMnand24g/tHg,andthegalenaconcentrate73-78%Pb,13.4%S,0.8-2%Zn,0.4%Cu,0.25%Sb (traceAs,noBi) and 1000-1200 g/t Ag (Hesemann and Pil-ger 1951; Pilger et al. 1961). The total metalrecoveredamountedto277,000tZn,169,000t Pb and 250 t Ag (1938-1962; GewerkschaftAugusteVictoria1997).

LEFT:LongitudinalprojectionofStage1orein the Northern Orebody looking southwest(modified from Hesemann and Pilger 1951).Thegradualchangefromsphalerite-richoreatdepthtogalena-richoreatthetopissimilartotheinner-outerCutoZntoPbzonationinoth-er hydrothermal ore deposits, controlled bychloride solubility in an H2S-bearing fluid andby temperature at about constant pressure(HemleyandHunt1992).TheupwardzonationofZntoPbinStage1oreindicatesanascend-ing fluid.Applicationof theempirical sphaler-itegeothermometerofFrenzeletal.(2016)tothe flotation concentrate composition resultsinanestimatedfluidtemperatureof259±17°Cduring sulfide deposition, which may beroundedto260±20°C.

(A) Stage1b Zn-Pb cockadeore: fragmentsof silicified black siltstone and quartz-sphaleritebrecciaorearemantledbyconcen-tric grey layers of fine-grained galena andquartz forming round to elliptical cockades,whicharecementedbydarkbrownsphaleriteand white quartz crystals lining interstitialvugs.Sample40,AugusteVictoriaminecollec-tion,theSwissknifeis8.5cmlong.

(B) Stage 1b/c lead cockade ore (25 wt.%PbS):closelypacked,fine-grainedgreygalena-quartzcockadeswithcentralfragmentsofsilic-ified siltstone or Stage 1b ore, which are ce-mentedbyquartzandinterstitialyellow-whiteclay. Note the light brown sandstone at the



knife.Sample38,AugusteVictoriaminecollec-tion,theSwissknifeis8.5cmlong.

(C)Transmittedlightphotographofaroundcockade surrounding an angular fragment ofsiltstone. The concentric shells are composedof galena-rich (black) and quartz-rich layers(white), modified from Stolze in Pilger et al.(1961).

Stage 1 cockade ore was confined to thelowerhalfof theNorthernOrebodyandcom-mononlevel3a(Slide2.25),whereitfilledfis-sures inbrecciaoreupto1mwideand28mlong.Thecockadesareinterpretedasgelstruc-tures recrystallized into radially oriented thinquartzcrystalswithmicron-sizedgalena inclu-sions and interstitial galena grains (0.1-0.3mm). The consistency of fine galena-quartzlayering in adjacent spheres and soft-layer in-dentations indicate that the cockades grewsuspendedinaviscousSiO2-PbScolloidalsolu-tion,probablyduringperiodsoftectonicquies-cence intheBlumenthalFault (Stolze inPilgeretal.1961).

2.27 Slide27.AugusteVictoria:Stage2oreinstrike-slipfaults

LEFT:LongitudinalprojectionofStage2orein the Northern Orebody looking southwest.Thedistributionofsyn-tectonicStage2miner-alization indicates the successive opening ofthe strike-slip faults during a short period oftime (Hesemann and Pilger 1951). Stage 2asphalerite-quartz±ankerite±sideriteorewasdeposited early from a fluid ascending in theNorth Zone faults, which infiltrated first theHülsAandthentheHülsBfaultatprogressive-lyhigher levels intheorebody.Minorgalena,pyriteandmilleriteweredepositedwithsphal-eriteonandaboveLevel2.

Stage 2b barite-calcite-pyrite-marcasitemineralization overprints Stage 2a and fills allthreeHülsstrike-slipfaultsinthelowerpartofthe ore body. In the upper part, Stage 2asphalerite-quartz ore restricted the ascent oftheStage2bfluidintheHülsAandBbutnotinthe Hüls C fault, which opened last and wasmineralized with marcasite and pyrite to the

uppermost level.Calciteandbaritearesparseabove Level 2. Latemarcasite is 2- to 3-timesmore abundant than pyrite, and forms collo-formaggregateswithpyriteandminorsphaler-ite.Galena (200-250 g/tAg), chalcopyrite andmilleriteareaccessory.

(A) Fragments of light brown Stage 2asphaleriteandofquartz-sphaleritebrecciaorearecementedbywhiteStage2bbarite,whichcontains interstitial marcasite (right margin).Sample 49, Auguste Victoria mine collection,the Swiss knife is 8 cm tall.Marcasite (0.03%As),calcite (0.3-0.4%Mn)andbarite(0.5%Sr)are the most abundant minerals in Stage 2b(StolzeinPilgeretal.1961).

(B) Fault breccia composed ofwhite baritefragments in yellow-grey marcasite cementcrosscuts massive Stage 2b barite indicatingthat mineral fill in the Hüls faults was syn-tectonic.Sample22,AugusteVictoriaminecol-lection,theSwissknifeis8.5cmlong.

Age constraints: Hesemann and Pilger(1951) interpret the relationship betweenfaulting and syn-tectonicmineralization to in-dicate a short-lived magmatic-hydrothermalsystem,whichoperated afterVariscan foldingbut before significant erosion in the LowerPermian. Ore formation took place at 3-4 kmdepth based on stratigraphic reconstruction.Normal faults initiatedduringfoldingwerere-activatedcausing700moffsetattheBlumen-thal Fault, followed by 100-m-scale dextralstrike-slipontheAugusteVictoriasystem,andthenbysinistralstrike-slipontheHülssysteminterpreted as stress release after dextral dis-placement.

Thisinterpretationisconsistentwiththere-gional pattern of Permo-Carboniferous strike-slip faults in Europe (Slides 2.3 and 2.4), andwith the lead isotope ratios in AV galena(Krahn and Baumann 1996), which matchthose at Ramsbeck where thermal and geo-physical anomalies delineate the related plu-ton.Incontrast,theradiogenicleadisotopera-tios in galena from the barite-rich ore atChristianLevinaremorecompatiblewithpost-orogenic basement-brine mineralization(DiedelandBaumann1988;Wrede2006).



2.28 Slide28.HarzBlock:Zn-Pb-Agoreinwrenchfaults

OreproductionfromtheUpperHarzdistrictwest of the Brocken granite amounts to 37.8millionmetrictons(Mt)atrecoveredgradesof5.1%Pb,3.9%Znand135g/tAg (1524-1992)equal to 1.910 Mt of lead, 1.463 Mt of zinc,and>5000tsilver(Stedingk2012).Afterape-riod of shallow shaft and open-cut mining in1200-1350AD,systematicundergrounddevel-opmentbegan in1524 initiatedbydukeHein-richtheYoungerofWolfenbüttel(Buschendorfetal.1971).

RIGHT:Geologicmapof theHarzblockup-lifted and tilted SSW at the North BoundaryFaultintheCretaceousandCenozoic(modifiedfromHinzeetal.1998).TheVariscanslatebeltisinlightgrey,andtheraftofbasementEckergneiss is black. The Devonian anticlinorium(brown) south of Goslar, NE-striking folds inDevonianbasalticspilite (darkgreen),andDe-vonian limestone reefs (dark blue) are high-lighted. Also colored are the post-foldingHarzburg norite-gabbro intrusion (G), theBrocken (B) and Ramberg (R) granite plutonsand theHarzdykeswarm(HD),all consideredpartofanunderlyingbatholith.Thedykesarefeeders to Permian rhyolite, minor andesiteandbasalt flows intercalatedwithredbedsatthe south rim of theHarz block. The Brockenand Ramberg granites (283±2 Ma and 283±3MaU-Pbzircon;Zechetal.2010)areyoungerthanthequartzporphyriesoftheHalleVolcan-icComplex(HVC;307±3to294±3MaU-Pbzir-con; Breitkreuz and Kennedy 1999). The Per-mo-Carboniferous volcanic and red bedsedimentarysuccession isoverlainbythePer-mian Zechstein formation (blue), representedby marine limestone, anhydrite and dolomiteattheHarzrim,andbyupto2000mofsaltinthebasins to thenorth and south coveredbyTriassic (pink), Jurassic (lightblue),Cretaceous(lightgreen)andyoungersedimentaryrocks.

LEFT: Geologic map of the Upper Harz(modified fromHinze et al. 1998) highlightingthe post-folding wrench faults sub-parallel to

the Harz North Boundary Fault (HNBF). TheN50-60°E striking folds are outlined by LowertoUpperDevonian(LDtoUD)sandstonesandslatesintheanticlinoriumsouthofGoslar,andbyMiddleDevonian (MD)diabase-spilite anti-clines.All foldshaveaxialsurfaces inclinedto-wards thenorthwest.TheCarboniferousgrey-wacke succession hosts the major fault-controlled Zn-Pb-Ag deposits centered on theminingtownsofClausthal-Zellerfeld(CLZ),BadGrund(BG)andLautenthal (LT).Thesilverde-posit at St Andreasberg (StA), famous for itscollector-itemminerals (Stedingk et al. 2016),is controlled by the dextral Edelleuter Fault(ELF),whichoffsetstightfoldsinDevoniandia-base 750m north block east. Post-folding in-trusions includetheultramafic-maficHarzburggabbro (G), theBrockendiorite-granitepluton(B),and thenorth-strikingkersantitedyke (K).Lamprophyres in the Erzgebirge block of theBohemian Massif are dated at 328±0.5 to294±6Ma (K-Ar and Ar-Ar phlogopite; Seifert2008).TheemplacementdepthoftheBrockenplutonprior toerosion isestimatedat3-6kmaccordingtomelt-inclusiondata(80-200MPa;740-560°C) frompost-orogenic granites in thenorthern Bohemian Massif (Thomas andKlemm1997).

2.29 Slide29.ElbeZone:HarzNorthBoundaryFault

(A)TheVariscanslatebeltintheHarzblockwas uplifted 3-4 kmat theWNW-striking and70° south dipping Harz North Boundary Fault(HNBF),whichispartoftheElbeZone(Schecket al. 2002). The onset of Alpine-Tethyan far-field stress is constrained by angular uncon-formities in the Mesozoic sedimentary rocks,which were tilted up and overturned at thefrontofthebasementblock(WagenbrethandSteiner1990).IntheUpperPermiantoMiddleTriassic, the NE-trending Hunsrück-Eichsfeld-Oberharzpaleo-high influencedsedimentation(Mohr1993).IntheUpperTriassic(ca.210-201Ma; ICS 2018), parts of the Harz were abovesea level, perhaps elevated at the HNBF, andshallow-marineoolitic ironorebedssuggesta



WNW-trending shoreline in the Jurassic. Thefirst unconformity (15°) is at the base of theLower Cretaceous Hauterivian sandstone (ca.135 Ma), and the main unconformity (up to90°) at the base of Santonian conglomeraticsandstone (ca. 85Ma).Granite clasts indicatethattheBrockencomplexwasunroofedatthistime.Majorphasesofupliftalsotookplace intheMioceneandPliocene(Mohr1993).

(B) In the Harz block, the N50°E-strikingfolds in theDevonianandCarboniferous sedi-mentaryrocksaremarkedbyaslatycleavage:Lookingnortheast atUpperDevonian calcare-ousslateformingtheverticallydippingSE-limbof a syncline in Middle Devonian black slate.Leached limestone nodules trace the verticalbedding. The axial plane cleavage dips 50-60°SE.MargaretenklippenoutcropintheGranetalnearGoslar,theSwissknifeis18cmtall.

(C)Whilemost folds areupright, overturn-ingofthestrataandthrustfaultingoccurlocal-ly, for example in the Devonian slates at theRammelsbergmine,Goslar.Thediagram(afterAbt 1958) illustrates an isoclinal syncline inWissenbach black slate looking northeast.Structuresinclude:subsidiarydragfoldsinduc-tilebeds(black),theaxialplanecleavage,fan-ning of the cleavage in competent limestoneandsandstonebeds,andthethinningofthesebedsonthefoldlimbsduetobedding-parallelflexuralslip.

2.30 Slide30.HarzBlock:Post-orogenicwrenchfaults

LEFT:StructuralmapoftheUpperHarzdis-trict (modified from Jacobsen and Schneider1950;SperlingandStoppel1981)showing thewrench faults parallel to the Harz NorthBoundaryFault (HNBF),and themining townsof Goslar, Lautenthal (LT), Clausthal-Zellerfeld(CLZ),andBadGrund(BG).ThefaultsoffsettheN50-60°E striking Variscan folds. Stahl (1920)recognized that the movement was eitherstrike-oroblique-slip.Richter(1941)suggestedthat themovementwas dextral with aminorcomponent south side down. Faults transect-ing theDevonian anticlinorium SSWofGoslar

offset a sub-vertical kersantite dyke (K) by acumulativeamountof2kmnorthblockeast.Incontrast, sinistral strike-slip of 800 m southblock east has been established at the Sil-bernaalFault (SNF;StedingkandEhling1995).FaultsbranchingofftheSNF,termedtheChar-lotter (CRF) and Burgstätter Ruschel (BRF),crosscut the dextral Zellerfeld-Rosenhof-Burgstätter fault system (ZEF-RHF-BUF). Ap-parently, the wrench faults progressed fromearly dextral to late sinistral movement, thedominantphaseevidentintheoffsetofmarkerfoldsanddykes.ThethreefaultsboundingtheDevonian anticlinorium to the SSE have asouth-side-down component, constrained bystratigraphiccorrelationto400-500matboththe sinistral Lautenthal (LTF) and the dextralBockswiese (BOF) faults.Mineralized faults in-clude the dextral ZEF-RHF-BUF system atClausthal-Zellerfeld(10.8Mtat3.8%Zn+4.6%Pb), the dextral oblique-slip BOF (2.15 Mt at1.4% Zn + 5.7% Pb), the sinistal SNF at BadGrund(19.1Mtat3.9%Zn+5.8%Pb),andthesinistraloblique-slip LTFat Lautenthal (4.2Mtat 6.7% Zn + 2.3% Pb; Sperling and Stoppel1981;Stedingk2012).

(A) Looking at thin-bedded black slate andgreywackeoftheLowerCarboniferousKulm3stratigraphicunit,themostcommonhostrockintheUpperHarzveindistrict.Exposureintheadit to theNewMain shaft, Lautenthalmuse-um and visitor mine (www.lautenthals-glueck.de).Thehammeris32cmtall.

(B) Looking northeast at folded Lower Car-boniferous greywacke: sandstone turbiditebeds (35-45% quartz, 15-35% feldspar, 5-20%chlorite, 1-5% sericite, 3-10% clay) are sepa-ratedbythinblack-greysiltstone.QuarryintheInnerstevalleyneartheMedingshaft.

Relative age constraints: The Goslar seg-ment of theHNBF extends east into theHarzblocktowardstheIlsestein,theNW-striking11km longbordergraniteof theBrockenplutoninterpreted as emplaced into the fault zone(Mohr 1993). The north-striking kersantitedyke(K)terminatesattheLautenthalFaultbutanotherkersantitewasemplacedintothisfault(Schulze 1968). Thus, the wrench faults post-



date Variscan folding at ca. 305 Ma but areolder than 283±2Ma, the U-Pb zircon age oftheBrockenpluton (Zechet al. 2010).On theother hand, the Weisser Hirsch Fault (WHF)offsets the Oker granite 600 m in a dextralsense, the Edelleuter Fault at St Andreasbergoffsets hornfels, and other faults offset thefeederdykestoPermianvolcanicrocksindicat-ing large-scale(500-800m)faultingcoincidentwithPermianmagmaticactivityat300-280Ma.

The Silbernaal (SNF) and Weisser Hirschfaults extend west into the Upper PermianZechstein limestone and dolomite, which un-conformably overlie the Variscan basementand dip 5-10° west. At both faults, the lime-stone was replaced by tabular siderite-bariteore,barrenofbasemetalsbutmined for iron(limonite)andbariteinopencuts(SperlingandStoppel 1979). At the Silbernaal Fault, thePermiancover rocksareoffset30-40msouthblockup.Dextralreverseoblique-slipof50-100mis indicatedbypost-sulfidefaults intheorebodies below the unconformity. These faultshadreverseoffsets(0.2-5m),wereconfinedtothe SNF and rotated anticlockwise in strike(Sperling1973).ThePermianZechstein1lime-stonecorrelateswiththebaseoftheLopingianformation dated at 259±0.5 Ma (ICS 2018;Oszczepalskietal.2019)indicatingfaultreacti-vation, probably during Alpine-Tethyan far-field stress. In contrast to the SNF andWHF,otherwrenchfaultshavenotbeentracedintothe Upper Permian cover rocks. In particular,there is not evidence for post-Permian faultmovement on the ZEF-RHF-BUF system atClausthal-Zellerfeld.

2.31 Slide31.Clausthal-Zellerfeld:Zn-Pbveinsindextralfaults

LEFT: The structural map (modified fromStedingk 2012) shows the steeply dippingwrench faults controlling the Clausthal-Zellerfelddeposit,whichproduced10.8millionmetrictonsoforeatrecoveredgradesof3.8%Zn,4.6%Pband>100g/tAg(1524-1930;Sper-lingandStoppel1981).TheZellerfeld(ZEF)andRosenhof (RHF) boundary faults are linked by

the Burgstätter Fault (BUF), oriented 40°clockwiseinstrike,closetotheempiricaldirec-tionofextensioninadextralstrike-slipsystem(Sylvester1988).Atbothboundaryfaults,foldsin Devonian diabase are offset 600 m southblockwest, thestrike-slipcomplementedbyaminornormalcomponent.TheRosenhofFaultbranches into the Kranicher Fault (KRF) andotherstrandsattheOttiliaeshaft(OT)formingacomplexfaultpatternnearClausthal.TheSil-bernaalFault(SNF)southofthedextralsystemmoved in the opposite direction, and offsetsmarkerconglomerates800msouthblockeast(StedingkandEhling1995).TheCharlotterRu-schel (CRF) displaces the Zellerfeld Fault 250m, and the Burgstätter Ruschel (BRF) theBurgstätter Fault 50 m in a sinistral sense(SperlingandStoppel1979).

The ore bodies were initially developedfrominclinedshafts(StLorenz:SL)replacedinthe19thcenturywiththeverticalNewJohan-nes (NJ), Meding (MD), Ottiliae (OT), KaiserWilhelmII(WH)andKöniginMarie(KM)shafts.Orewasminedfromoutcropsdownto600min the Zellerfeld, 800m in the Rosenhof, and1000 m in the Burgstätter faults. The TieferGeorg (+307m; 1777-1799AD) and the ErnstAugustdrainageadits(+190m;1851-1864)stilldewater the mines to about 400 m depth(SperlingandStoppel1979;1981). Thewood-en wheels used to hoist the ore and pumpminewater to the lowest adit were poweredbywaterstoredin149artificiallakesconnect-ed by 500 km of ditches. This system (UpperHarz Water Regale) protected by royal right(regale) in the16th to19th centuriesbecameUNESCO world heritage in 2010(www.oberharz.de).

RIGHT: Vein from the Burgstätter Fault:Stage 2 banded ore enclosing sulfide-rimmedvein fragments, coarse-grained (2-5mm)darkbrownsphaleriteandgreygalena(60vol.%oftotal sulfide) in white-grey quartz and minorcalcite.Museumcollection,TechnicalUniversi-ty of Clausthal, Adolph Römer Strasse 2a,Clausthal-Zellerfeld, the Swiss knife is 8.5 cmlong.



2.32 Slide32.Clausthal-Zellerfeld:Burgstätterdextralfault

Syn-tectonicbandedandbrecciaveinsupto5 m thick and 300 m long in the BurgstätterFault account for 70% (7.46Mt at 4.4% Zn +3.6% Pb) of the total oremined at Clausthal-Zellerfeld.Aboutonethirdofthefaultsurfacecontained ore. Composite veins were minedoverawidthofupto10montheWilhelm19level(SperlingandStoppel1979).

(A) Structural plan of the Burgstätter Fault(modified from Stedingk 2012) at two minelevels660mapartshowingthe junctionswiththeKranicher(KRF)andRosenhof(RHF)faults,the sinistral displacement at the BurgstätterRuschel (BRF), and the locations of the St Lo-renz (SL),KaiserWilhelm II (WH),KöniginMa-rie (KM), and Caroline (CL) shafts. Sinistralmovement on the barren BRF postdatesmin-eralizationinthedextralBurgstätterFault.

(B) Cross section illustrating the steep SW-dip (75°) of the Burgstätter (BUF) andKranicher (KRF) faults at theKaiserWilhelm IIshaft, and the development of Zn-Pb-Ag oredowntothe24levelabout1000mbelowsur-face.

(C) Longitudinal projection of Zn-Pb-Ag orein the Burgstätter Fault (modified fromStedingk2012)showingtheWilhelm(W),Mar-garethe (M)andDorothea (D)orebodies, theintersectionlineswiththeKranicher(KRF)andRosenhof (RHF) dextral faults, and the sub-vertical intersection with the post-oreBurgstätterRuschel(BRF)strike-slipfault.NotetheTieferGeorgandErnstAugustdrainagead-its.

STAGE1hematite-dolomite-pyrite(+ illite?)alterationandsilicification inzonesup to1mwidewas prominent on theWilhelm 23 levelbut extended up to the Tiefer Georg adit,mainly along the footwall and hanging wallboundary faults. Associated quartz-chalcopyrite veins increased in thickness withdepth. On the Tiefer Georg level, Stage 1 an-keriteveinsinalteredgreywackeNWandSEofthe St Lorenz shaft contained hematite,clausthalite (PbSe), tiemannite (HgSe), minornaumannite (Ag2Se), pyrite and chalcopyrite.

Hematite-dolomite±talcalterationoccurredinthe Kranicher Fault (Sperling and Stoppel1979).

STAGE2 sphalerite, galena, accessory chal-copyrite,quartzandcalciteconstitutedtheZn-Pb-Agore.Stage3sideriteandbaritewerera-reorabsent.Sphalerite (1.4-5.3%Fe)was themost abundant sulfide below theWilhelm 17levelindicatinganupwardzonationZnStoPbSintheorebodies.Galenad34Svaluesincreasedwithdepthfrom-1.4‰ontheWilhelm3levelto+3.5‰on16leveland+4.7-5.8‰on20-23level(Nielsen1968),perhapsreflectingatem-peraturegradient.Galena fromtheupper lev-elsintheDorotheaorebodyhadhigherAg-Sbcontents (>0.23%Ag, 0.32-0.65%Sb) than ga-lena from the lower levels (0.07-0.09% Ag,0.17-0.33%Sb)duetoinclusionsofjamesonite,boulangerite, stibnite, tetrahedrite (9% Ag),pyrargyrite,stephaniteandnativesilver.Stage2orewasalsodominant in theZellerfeldandRosenhof boundary faults. Galena concen-trates from the Burgstätter Fault (0.06-0.20%Ag) were rich in silver relative to those fromthe Zellerfeld (0.03-0.10% Ag) and Rosenhoffaults(0.05-0.08%Ag;Wilke1952).

(D) Burgstätter Fault, Kranicher vein: Stage2 banded vein composed of sphalerite (darkbrown), calcite (yellow) and minor galena(blue), the wall rock (grey) is quartz-flooded(white).Wilhelmorebody, 23 level southeastof theKaiserWilhelm II shaft, between cross-cuts 1 and 2. The scale bar is 1 m long. Thehand-coloredphotographtakenbyMascherin1930showszinc-richoreonthedeepestactiveminelevelshortlybeforeclosure.

(E) Stage 2 breccia composed of angularfragments of grey sandy slate cemented bybrown sphalerite (2-5 mm) and white-greyquartz.Some fragmentsare rimmedbysphal-erite and quartz but others are not. Zinc-richore from the Margarethe ore body, lowerBurgstätter Fault. Museum collection, Tech-nical University of Clausthal, Adolph RömerStrasse2a,Clausthal-Zellerfeld,theSwissknifeis8.5cmlong.



2.33 Slide33.BadGrund:Zn-Pbveinsinasinistralextensionalduplex

Incontrasttootherdeposits inthedistrict,theorebodiesatBadGrundwereblindexceptfor smalloutcropsat theAchenbach (AB)andMeding (MD) shafts. The mine "SilbernerNagel" (silvernail)near theMeding shaftwasinoperationfrom1570to1733.From1831to1992,19.1millionmetrictonsoforeatrecov-eredgradesof5.8%Pb,3.9%Zn,0.07%Cuand117g/tAgweremined.Zincremainedinsignif-icant until 1930 (Stedingk 2012). The galenaconcentrate averaged 76.5% Pb, 1.0% Zn and1500 g/t Ag, and the zinc concentrate 59.1%Zn, 1.7%Pb, 40 g/tAg, 140 g/t In, 20 g/tGe,100g/tSnand600g/tHg(Sperling1973).

(A) Structural map of the Silbernaal faultsystem (SNF) showing the 500-m-wide exten-sional duplex at Bad Grund (modified fromStedingk 2012), and the Charlotter Ruschelbranch fault (CRF). TheSNFcontainsorebod-iesovera lengthof6.5kmbetweentheWest(WS), Achenbach (AB), Knesebeck (KB), Wie-mannsbucht (WB) and Meding (MD) shafts.ThestrandsoftheSNFdip60-80°southatsur-face. Many steepen to sub-vertical at depth.Themainfaultis15-20mwideonaveragebutwidensto70mattheWestshaftandto50meast of the Achenbach shaft. The other faultsvaryinwidthfrom2-12m(Sperling1973;Sper-ling and Stoppel 1979). The offset at the Sil-bernaal Fault is 800 m south block east(StedingkandEhling1995).ThedextralRosen-hofFault(RHF)hasa200-m-downcomponentat the Devonian limestone reef, whereasmovementattheLaubhütteFault (LHF) is700msouthblockwestand<50mdown(Sperling1973).

(B) Longitunal projection of Zn-Pb-Ag orebodiesinthemainSilbernaalFault(WestfeldIIand I, 800/900W, Achenbach, Ostfeld, Wie-mannsbucht, Silbernaal) excluding those inother faults of the system (modified fromStedingk2012).Stage1hematite-pyriteminer-alizationisparticularlywidespreadinthewestbutStage1dolomite-illitewall-rockalterationextends east to the Meding shaft. Stage 2sphalerite-galena-calciteoreispredominantin

Westfeld II and partly overprinted by Stage 3galena-siderite-barite in all other ore bodies(SperlingandStoppel1979;Stedingk2012).

2.34 Slide34.BadGrundWestfeld:Stage1hematite+pyrite

TOP LEFT: Longitudinal projection of Var-iscan folds in Carboniferous greywacke at thefootwall boundary of the Silbernaal Fault (dip65-70°SW),unconformablyoverlainbyPermi-anlimestone(Zechstein1/2)attheWestshaft(modifiedfromStedingkandEhling1995).Thecorrelation of slatemarker horizons and con-glomeratebeds(C1andC2)inthefootwallandhanging wall of the fault indicates strike-slipandalateraloffsetof800msouthblockeast.Stage1hematite-pyrite±chalcopyritemineral-izationandassociateddolomite-quartz-illiteal-teration iswidespread in and adjacent to thefaultenveloping theWestfeldorebodies.Redhematite staining, extensive on level 1 of theWest shaft, doesnotpersist into thePermianlimestone cover. The Stauffenburg drill holesintersected barren dolomite-ankerite, sideriteandanhydriteveins4to300cmthick ingrey-wackewest of the Zn-Pb ore bodies (SperlingandStoppel1979).

BOTTOM LEFT: Level plans illustrating thedistributionof Stage1hematite-pyrite ± chal-copyrite mineralization and dolomite-quartz-illite alteration associated with the SilbernaalFault(modifiedfromSperling1973).Wall-rockalteration was pervasive in greywacke andmostlyfracture-andbedding-controlledinsilt-bandedslate.TheWestfeldIorebodyextend-ed from 900-1550mW andWestfeld II from1450-2060mWcounted fromtheAchenbachshaft.Silicareplacementupto30mwidewasmainly confined to Westfeld II. Hematite oc-curred dispersed in dolomite but also formedspecular aggregates. Ankerite and Mg-rich si-deritewerelateStage1(Sperling1973).

(A) Looking east at quartz-illite alteredgreywacke crosscut by dark red hematite-staineddolomiteveins(1-10mm)containing1-2%disseminatedpyrite(Stage1).WhiteStage2 veins of calcite-sphalerite-chalcopyrite ore



crosscut the alteredwall rock and the brownankerite-sideriteveinat thebottom.WestfeldII ore body, Achenbach shaft 20 level, mainvein 10-20 m SW of the footwall boundaryfault, cut 4 in east drive at 1600 m W, thehammeris32cmlong.

(B)Stage1alteredgreywackesouthwestofathickStage2calcite-sphalerite±galenavein:crackle breccia composed of grey dolomite-quartz-illitealteredwall-rockfragments(70-80vol.%)anddarkred,hematite-staineddolomitecement containing 1% disseminated pyrite.Quartz, ferroan dolomite andwell crystallized2M-illite were identified by X-ray diffraction.Stage2veinlets(1-2mm)arefilledwithquartz,whitecalcite,andchalcopyrite.WestfeldIIorebody, Achenbach shaft 20 level, footwallbranchofthemainvein,cut11inwestdriveat1600mW,thematchstickis4cmlong.

Illite temperature estimates: Illite crystal-linity has been used to estimate temperaturein low-grademetamorphic rocks at Ramsbeck(Slide 13). At Bad Grund, a studywas carriedoutondrillcoreintersectingthesouthernandmainfaultsoftheextensionalduplexat960mEonlevel15oftheAchenbachshaft,andsam-plingleastalteredwallrockinthesouthcross-cutat1460mE(Schmidt1991).Thehostrocksat both locations are greywacke and slate ofthe Kulm 3b unit. The clay fraction (2-6mm)was separated and analyzed by X-ray diffrac-tionusingquartzasan internalstandard. Illiteinthefaultzonehadahalf-height(Hb=illite001x100/quartz100)peakwidthaveraging130(n=27;maximum110-120,n=7),whereas illitein the least-altered rocks to the south had ameanof195(n=7;Schmidt1991).Thehigherillite crystallinity in the Silbernaal fault zonecorresponds toa temperatureof about300°C(Schmidt1991).Hb-valuesof135 inpure illiteare equivalent to Hb = 105 in polished rocksamples (Werner 1988). The Stage1 estimateof300°CisthussupportedbythecasestudyatRamsbeck.

Illite Rb-Sr ages: Sevenbulk samples of al-tered greywacke enclosed in Stage 2 calcite-sulfide veins of theWestfeld II ore body, andfive drill core samples of unaltered slate and

greywacke were analyzed for their Rb-Sr iso-tope ratios, mineral modes, and major oxidecompositions (Boness et al. 1990). The unal-teredsamplesconsistedofquartz,albite,chlo-rite, minor calcite and illite, and had lowK2O/Na2O ratios (0.48-0.64) representative ofHarz greywacke (Visean: 346.7±0.4 to330.9±0.2Ma;ICS2018).

The altered greywacke consistedof quartz,illiteandcarbonate(dolomite,siderite,calcite).TheK2O/Na2Oratiosofthewholerocks(mean18.8;n=7)weremuchhigherthanthoseofun-altered greywacke indicating intense potassi-ummetasomatism. The clay consistedof 99%2M-illiteand1%1M-illite,thelatterresidinginthefinegrainfractions(100%0.1-0.2mm;45%0.2-0.6 mm). SEM imaging showed that the2M-illiteformeddiscretecrystals,whereasthe1M-illiteformedaggregatescomposedof<0.1mm grains (Boness et al. 1990). The 2M-illitehad an interlayer charge of K = 1.564-1.600andNa = 0.113 (for 22 oxygens), comparabletomuscovitefromtheprehnite-pumpellyitetogreenschist facies boundary (Hunziker et al.1986),andgaveRb-Srisochronagesof242±28Maand247±20Mausingthewholerock,grainfraction (>0.6 mm), HCl leachate and residueisotope ratios of two samples. As the regres-sion-line intercepts agreed within error withthe87Sr/86SrratiomeasuredinStage2/3gale-na(0.7138±0.0007),theTriassicageswerein-terpreted to date sulfide mineralization. TheRb-Sr data of the 1M-illite fractions (0.1-0.2mm;1%ofthetotalclay)wereregressedsepa-rately. The ages of 180±9Ma and 176±8Ma,and the 87Sr/86Sr intercept ratios of 0.7152 ±0.0013and0.7168±0.0008dateaneventun-relatedtooreformation(Bonessetal.1990).

The critical 2M-illite ages have been re-calculatedusing Isoplot3.45of Ludwig (2012)and the 87Rb decay constant in Villa et al.(2015). The 87Sr/86Sr intercept ratios obtainedby Model 3 regression are 0.7127 ± 0.0024(n=7, MSWD=35) and 0.7136 ± 0.0018 (n=7,MSWD=21). Both agree within error with themeasured 87Sr/86Sr ratios in calcite and barite(0.7133 ± 0.0005; n=45; Voigt 1984; LévêqueandHaack1993a)fromZn-Pb-Agore,confirm-



ing the conclusion of Boness et al. (1990) ofstrontiumderivation fromahomogenous res-ervoirduringsulfidedeposition(Stages1-3). Ifthe average calcite-barite 87Sr/86Sr ratio is in-cludedintheModel3regression,the2M-illiteages are 241±20 Ma (n=8, MSWD=30) and238±17Ma(n=8,MSWD=17).TheycorrespondtotheMiddleTriassic(247-237Ma;ICS2018),when the Upper Harz was part of the NE-trending Hunsrück-Eichsfeld-Oberharz paleo-high,anareaofcondensedPermianandTrias-sicsedimentation(Mohr1993).

2.35 Slide35.BadGrundWestfeld:Stage2Zn-Pbore

The Westfeld II ore body contained 5-6 tZn+Pb/m2veinsurfacebetweenlevel12and14, the highest base-metal grade in the BadGrund mine. Stage 2 ore was zoned from abroad sphalerite-rich core to a 20-40mwidegalena-rich rim. Chalcopyrite increased belowtheAchenbachshaftlevel18indicatingaverti-cal Cu-Zn-Pb zonation. Sphalerite veins were1.5-2.0mthickonaverage,andupto7mthickon level13 formingquartz-calcitebandedandbrecciaore500mlongand20mwideclosetothe footwall boundary of the Silbernaal Fault(Sperling1973;Stedingk2012).

LEFT:ThinStage3sideriteandbariteveins,probably formed during small-scale SW-blockdownmovement, crosscut Stage 2 sphalerite-calcite±quartzveinswithgalenamarginsandbarren calcite veins. Similar relationshipscaused by tectonic movement were used tosubdivide Stage 2 into four and Stage 3 intothree sub-stages (Sperling1973). Post-mineralreversefaultsoffsetallveins.WestfeldI,stopebetweentheAchenbachshaft11and12levelsat1400mW.

(A)Lookingwestatthefootwallpartofa6-m-thick vein composed of Stage 2b chalcopy-ritecrosscutbyStage2ccalcite-sphalerite±ga-lenaore.Thehostrockisbrecciated,dolomite-quartz-illite altered greywacke stained red bydisseminatedhematite andpyrite.Westfeld IIore body, Achenbach shaft 20 level, crosscutthrough the main vein 10-20 m SW of the

footwallboundaryfault,cut11inwestdriveat1600 m W. Photograph courtesy WolfgangWerner, January 1992, showing the author(left)andminegeologistKlausStedingk(right).

(B)LookingeastatthetransitionfromStage2c banded calcite-sphalerite-galena into brec-ciaore:fragmentsofStage1dolomite-quartz-illite altered greywacke are cemented by cal-cite and sphalerite. A post-mineral reversefaultoffsets thebandedvein intheupper leftcorner (arrow).Hangingwall part of the 6-m-thickveinin(A),thehammeris32cmtall.

(C)Stage2bandedandbrecciaore:angularfragments of Stage 1 dolomite-quartz-illite al-tered greywacke (left), and older bands ofwhite-grey quartz, yellow chalcopyrite, anddarkbrownsphaleriteareovergrownbymas-sivewhite quartz andpale yellow calcite. Thequartz-calcite gangue encloses 20-cm-thickcockadeorecomposedofgreygalenaandmi-nor brown sphalerite cementing fragments ofaltered greywacke, massive chalcopyrite, andquartz-chalcopyrite. Westfeld II ore body,Achenbachshaft20level,thepinkpenis14cmlong. Display at the mine museum Clausthal-Zellerfeld(www.oberharzerbergwerksmuseum.de).

Mineralogy: The principal ganguemineralsinStage2veinsarequartzandcalcite.Calcitecontains1.5%FeCO3and2.6-3.5%MnCO3andis strained due to fault movement. Least-strained quartz crystals and geopetal ZnS-quartz layers fillcavities inthecenterofveinsandrepresentthefinalStage2d.Sphalerite intheWestfeld II ore body has higher iron con-tents (3.0-4.7% Fe) than Stage 2 sphalerite inall other ore bodies (1.2-2.4% Fe). Silver andantimonyingalena(0.08-0.15%Ag;0.46-0.61%Sb) are related to inclusions and attachedgrains of tetrahedrite (Sperling 1973; SperlingandStoppel1979).

Temperature estimates: In theWestfeld IIore body, the Ga/Ge ratios in sphalerite indi-cate fluid temperatures of 270-240°C. Whenplotted in longitudinal projection, the ratiosoutlinevertical fluidascentbranching laterally(Möller and Dulski 1993; Stedingk 1993). Thed34Svaluesofsphalerite(+6to+10‰)andga-



lena(+4to+7‰)inWestfeldIIarehigherthanthose inallotherorebodies (+4 to+6‰sph;+2to+4‰gal).Sphalerite-galenapairsdisplayconsistent isotope fractionation d34SZnS >d34SPbS averaging 1.8‰ (Sperling and Nielsen1973), which equates to sulfide deposition at360±25°CusingthecalibrationinOhmotoandRye (1979). These results were confirmed byZhengandHoefs(1993a),whoanalyzedanad-ditional21sphalerite-galenapairs,establishedequilibrium, and obtained Stage 2 tempera-turesof400-220°Cusingthesamecalibration.

Fluid inclusions: Primary 2-phase fluid in-clusions in euhedral Stage 2d quartz (n=20)had salinities of 15.0-25.1 wt.% NaCleq, andhomogenizedintoliquidatTh=147-160°C.In-clusionsinStage2csphaleritehadsimilarsalin-ities and Th (Adeyemi 1982). Schmidt (1991)analyzed fluid inclusions (n=136) forming pla-nar arrays in quartz and calcite filling veins inthecentralSilbernaal faultsystem. Instrainedcalcite,secondary2-phase(2-10vol.%gas)and3-phaseinclusionswithsolidsallhomogenizedintoliquidat80-105°C.Secondaryandprimary(?) inclusions in quartz homogenized at 105-130°C, 140-165°C, 175-200°C, and 210-225°C,perhapstrappingdifferentgenerationsoffluid(Schmidt1991).Firstmelting(Te=-65to-60°C)and finalmelting temperatures (Tm = -35 to -25°C) indicated that the aqueous phase con-tained CaCl2 and NaCl (26-32 wt.% NaCleq).Therewasnoevidenceforphaseseparationorthe presence of CO2. Rare single-phase inclu-sionscontainedmethane(Schmidt1991).

2.36 Slide36.BadGrundEast:Stage3Pb-Agore

UndergroundminingatBadGrundbeganin1570near theMeding shaft following the 1.8kmlongSilbernaaloreshootdown-plungeun-tilthe1920s.Productionfrom1831-1899ises-timatedat1.6millionmetrictonsat9%Pband230g/tAg.Thesilvergradestillaveraged240g/t in 1924-1932 (Sperling 1973; Stedingk2012). Bituminous slate was abundant in thegreywackehosting this orebody. Stage1 car-bonate-quartz-pyrite ± illite (?) replacement,

locally stained by hematite, was extensive ingreywacke(König1923).Theorebodyconsist-edofStage3galenaandtracesphalerite.Bar-ite formedveinsup to4m thick in theupperpart(abovelevel10),andgavewaytosideriteand quartz at depth. Barite textures variedfromcataclastictocrystalline,andcolorsfromwhite (pure) to grey or red due to dispersedgalena or hematite, respectively. Quartz re-placed barite locally (König 1923). Stage 2sphaleritewasrestrictedtothelowerwesternpartoftheorebody(Stedingk2012).

LEFT: Stage 3 crackle-breccia Pb-Ag ore inalteredgreywacke,Silbernaalorebody1700mWof theMedingshaft,backofa stope25-30mabove level10 (modified fromKönig1923).Galena is intergrown with minor chalcedonyand quartz but also rims barite, which locallycuts across its galenamargin. Siderite formedsymmetric rims to barite veins in other expo-sures.Smallopenvugswerecommon.

(A) Achenbach Pb-Ag ore: Stage 3a in thecenteriscomposedoffine-grainedgalena,mi-nor sphalerite (1.2-3.0% Fe) and chalcopyritecementedbywhitequartzandcalcite.Stage3b(bottom)consistsofsiderite,calciteandsulfidebands,asideriteveincrossingStage3a.Stage3c (top) is represented by crystalline (5-10mm)yellow-whitebarite.Achenbachshaftlev-el19,VeinHat120mW,theredpenis14cmlong.

(B)WestfeldIPb-Agore:Stage3b/cbrecciacomposed of angular fragments of hematite-stainedalteredgreywacke(Stage1)rimmedbybrown siderite and blue-grey galena. Whitebarite fills the interstitial space. Achenbachshaft level19at1560mW,VeinL, thespeci-menis30cmlong.

Mineralogy: The Silbernaal hanging wallfault south of theWiemannsbucht shaft con-taineda400mlongand250mhighorebody,whichextendedfromlevels12to17andcon-sisted of a zoned Stage 3 galena vein 0.5 mthick. Galena was intergrown with calcite inthe central part, and with siderite and lesserbarite at themargin. The silver in galena de-creased from0.23-0.41wt.%at theperiphery



to0.12-0.19%Agintheinnerandlowerparts(SperlingandStoppel1979).

Common Stage 3 gangueminerals areMn-rich siderite and barite (2.7-10.5% SrSO4). Inplaces,baritecontainedcm-thickbandsoftet-rahedrite (4.3% Ag). Chalcopyrite was partlyreplaced by tetrahedrite and bournonite. Sil-ver-richgalenaenclosedgrainsofbournonite,boulangerite, tetrahedrite, pyrargyrite, argen-tite and rare native silver. Cavities in Stage 3veins were lined with quartz, siderite, barite,calcite, colloformmarcasite, and rare stibnite,native antimony, cinnabar, amalgam and na-tivemercury(Sperling1973).

Temperatureestimates:Thed34S valuesofStage 3 sphalerite (+2 to +4‰) and galena (±0‰) are lower than in Stage 2. Sphalerite-galena pairs display an average isotope frac-tionation of 3‰ (Sperling and Nielsen 1973),which equates to sulfide deposition at220±25°CusingthecalibrationinOhmotoandRye(1979).ZhengandHoefs(1993a)analyzedanadditional14sphalerite-galenapairs,estab-lishedequilibrium, andobtainedStage3 tem-peraturesof240-140°Cusingthesamecalibra-tion. Stage 3 barite d34S values have amodalmaximumat+13to+15‰(n=35).Isotopefrac-tionation between barite and coexisting sul-fides was not in equilibrium suggesting thatmost barite precipitated after the galena(Zheng and Hoefs 1993a). Fluid inclusions inearly Stage3aquartz and in latequartz liningvugs record decreasing homogenization tem-peratures (early 115-124°C to late 107-96°C)coupled with decreasing salinity (early 17 to12;late12to0wt.%NaCleq),valueslowerthaninStage2(Adeyemi1982).

2.37 Slide37.StAndreasbergveins:Wrenchfaultreversal

TheStAndreasbergsilverdepositisfamousfor its collector-item crystals of zeolite, tetra-hedrite,pyrargyriteanddyscrasite(Stedingketal. 2016). Metal production (1521-1910)amountsto313tAg,12500tPband2500tCufromcrudeoreestimatedat5-8%Pb,1-3%Zn,1%Cu,0.03-0.1%Ag,1%Co+Niand1%As+

Sb(Wilke1952).Theshaftbuildingsandwater-drivenhoist andpumpingwheelsof the Sam-son mine (www.grube-samson.de), and the16thto19thcenturyundergroundworkingsoftheRoterBärminearepopular touristattrac-tions (www.lehrbergwerk.de). The structuralsetting of the veins illustrates the reversal ofmovement from early dextral to late sinistralontheEdelleuterwrenchfault.

TOP:Blockdiagramof thebounding faults,main veins and inclined shafts projected ontotheleveloftheGrünerHirschleradit130mbe-low the Samson shaft collar (modified fromWilke1952).TheBrockengraniteunderliesthemineareaat>850mdepth.ThesuccessionofDevonian sandstone, calcareous and blackslate,diabase,andCarboniferousgreywackeiscontactmetamorphosedtohornfels,skarnandcordierite knotted schist. The folds are dis-placed by barren reverse faults (Neufanger,Abendröther), which strike N75°E, dip 50-75°SSE,andareinduratedtohornfels.ThereversefaultsareinturndisplacedbywrenchfaultsoftheEdelleutersystem,whichstrikeN70-80°W,dip60-80°SorN,andcontain0.3mthickfault-fill veins. Diagonal extension veins orientedN20-50°W/70-80°NEbranchoff theEdelleuterand its subsidiary faults. The extension veins,0.3-1.0m thick (Felicitas, Samson, Dorothee),aremarkedbyopenvugsandverticalstriationsattheirwalls(Wilke1952).Theclockwiseanglein strike (40°) between the Edelleuter faults(av. N75°W/70°S) and the diagonal veins (av.N35°W/75°NE)indicatesvein-fillduringdextralstrike-slip (see Sylvester 1988). This sense ofmovement, however, is inconsistent with thesinistraloffsetoftheAbendrötherreversefaultinterpreted to indicate a late phase of strike-oroblique-slipreversalonthewrenchfaults.

Vein-fillstages(Wilke1952):STAGE1com-prisesearlyhematite+quartz,siderite+anker-ite + Fe-Mn calcite, and accessory pyrrhotite,pyrite and chalcopyrite. Locally, late calcite-quartz-hematite veins contain clausthalite(PbSe), tiemannite (HgSe) and guanajuatite(Bi2Se3)associatedwithchalcopyrite,cobaltite,native gold (12-14wt.%Ag), Pd8Sb3 alloy and



PdCuBiSe3(GeilmannandRose1928;Cabraletal.2015).

STAGE 2 consists of an early Pb-Zn quartz-sulfide assemblage (galena, Fe-rich sphalerite,minor chalcopyrite, tetrahedrite, accessorybournonite, jamesonite) and a late Ag-Co-Nicalcite-arsenide assemblage (mainly safflorite-rammelsbergite,colloformnativearsenic,dys-crasite,pyrargyrite).

STAGE3comprisesearlyandradite,zeolites(stilbite, heulandite, analcime), hematite,quartzandcalcitecontainingpyrrhotite,pyrite,galena, low-Fe sphalerite, millerite, niccoliteand late pyrargyrite, stephanite, polybasite,nativesilver,argentite,andrealgar.

The stages recordpulsesofascending fluidcoolingfromaninitialhightemperature,whichmaybeestimated for theStage3assemblageandradite + quartz + wollastonite in contactwithStage2calcite(Wilke1952).Quartz+cal-citereacttowollastoniteat500°C,andquartz+calcite+hematitetoandraditeat400°C(P=50MPa,XCO2=0.1;Einaudi1982).Ontheoth-erhand,analcime+quartzisstablerelativetoalbiteatlessthan180°C(P=50-100MPa),andstilbite-Carelativetoheulandite-Caatlessthan150°C (P=100MPa;Deeretal. 2004).Minorfluoriteoccurredinallstages,bariteinStages2and 3, and anhydrite in Stage 3 at >600 mdepth(Wilke1952).Nielsen(1968)determinednegatived34SvaluesinStage2/3galena(-7to-23‰; n=29) suggesting sulfide-sulfate co-precipitation(Rye1993).

(A)EarlyStage2veinfilledwithbandsofga-lena,comb-texturedquartz,andminorcalcite.Theveinwallatthepen(14cmlong)issharp.The opposite wall is marked by a 2 cm thickbreccia cemented by grey silica and shearedgalena. The host rock is indurated, silty slate.Jacobsglückvein,Samsonshaftlevel8.

(B) Late Stage 2 vein filledwith calcite en-closing native arsenic (As; medium grey) anddyscrasite (Ag3Sb; tarnishedblack) rimmedbysilver-whiteCo-Niarsenides.Note theStage1breccia of hornfels fragments cemented bybrowncarbonateandquartz. Thehost rock iscarbonate-altered hornfels. Samsonmine, thematchstickis4cmlong.

(C) Stage 3 pseudo-hexagonal crystals ofcalcitecoatedwithgalenaandsilverminerals,perhapspyrargyrite,stephaniteandpolybasite.Thepen is14cm long.Samsonshaft33 level,openvugintheSamsonveinmeasuring3.5mlong, 2 m high, and 20-30 cm wide (Wilke1952).SamplesA,BandCarefromthemuse-um collection of the Technical University ofClausthal,AdolphRömerStrasse2a,Clausthal-Zellerfeld.

AdulariaK-ArandRb-Srages:AndreasbergadulariaassociatedwithStage3zeolitesgaveatotalfusion40Ar/39Arageof135.7±2.6Ma(2s),anda2-pointcalcite-adulariaRb-Srmodelageof123.9±1.2Ma(Mertzetal.1989).Acompa-rable study involved adularia from quartz-calciteveins in faultsatHasserode,whichoff-set hornfels and granite at the NE-margin ofthe Brocken pluton. These veins also containzeolites,hematite,Zn-PbsulfidesandCo-Niar-senides (Wilke 1952). The Hasserode adularia(0.5-2mm)had77-80%triclinicSi-Alorder.Us-ingcalcite87Sr/86Srastheinitialratio(0.71033± 0.00020), 2-point Rb-Sr isochrons gave Per-mian(260±7Ma,n=3)andTriassicages(223±4Ma,n=4;HagedornandLippolt1993).Thecrit-ical Permian age has been re-calculated usingIsoplot3.45ofLudwig(2012)andthe87Rbde-cayconstantinVillaetal.(2015).RegressionoftheHasserodecalciteandadulariaisotopeda-taresultsinaModel1Rb-Srageof263±4Ma(n=4,MSWD=1.3).

In contrast, the K-Ar method yielded totaland 40Ar/39Ar plateau ages of 141.5±2.2 to138±3.0 Ma at Hasserode. Adularia from achalcopyrite-actinolite vein in the aureole ofthe Ramberg granite, located at GernrodeclosetotheHarzNorthBoundaryFault,gaveaK-Ar age of 92.5±2.0 Ma. An argon diffusionstudyoftheturbidveinadulariaindicatedclo-suretemperaturesaslowas100°C.Inaddition,progressiveSi-Alorderingmayhavecausedar-gonloss(HagedornandLippolt1993).



2.38 Slide38.Variscanveins:Keygeneticfeatures

Structuralsetting:Syn-orogenicinbedding-parallel "saddle reefs" and in the axial planecleavage of anticlines (Eisenberg, Ramsbeck).Post-orogenicinnormalandwrenchfaultsdis-placingfoldsintheVariscanslatebelt(AugusteVictoria, Upper Harz). Normal faulting duringfold-beltupliftprecededwrenchfaultingalongthe WNW-striking Elbe Zone. The hiatus wasshort as syn-tectonic breccia ore formed inboth structures at Auguste Victoria. Themin-eralization in wrench faults took place duringthetransitionfromearlydextralandlatesinis-trallateralmovement.

Absolute age: The syn-orogenic EisenbergandRamsbeckveinsformedatca.305Madur-ingmain-stageVariscan folding.Post-orogenicmineralization in the normal fault at AugusteVictoriaandinthewrenchfaultsoftheUpperHarzprobablytookplacebeforetheZechstein1marinetransgressionatca.260Ma.Howev-er,therearenoradiometricageconstraintsatAuguste Victoria and few in the Upper Harz,where Rb-Sr illite and adularia ages indicateore formation at or before 260-240 Ma. Thereactivation of regional faults at 140-135 and90-85MaduringAlpinefar-fieldstresswasmi-nor (30-100m) relative to the LowerPermianmovement (500-800m),anddidnotaffectallwrenchfaultsintheHarz.

Ore deposits: Gold-hematite-chalcopyrite-clausthalite (PbSe) in carbonate veins (Eisen-berg), and sphalerite-galena ± chalcopyrite inquartz-carbonate ± barite veins and breccia(Ramsbeck,AugusteVictoria,UpperHarz).TheEisenberg deposit represents a group of oxi-dized gold-selenide ± PdSb alloy veins in theVariscan slate belt including occurrences pre-ceding Zn-Pb-Ag mineralization at Clausthal-Zellerfeld and St Andreasberg. The silver-richgalena in the Zn-Pb veins (900-2000 g/t Ag inconcentrates) contrasts with the silver-poorgalenaintheMississippiValley-typeZn-Pbde-posits (200-500Mt of ore) related to the dis-chargeofbrinesfromtheGerman-Polishbasin:Mechernich-Maubach in Triassic sandstone(80-140g/tAg;Behrend1950),andUpperSile-

sia in Triassic limestone (64-260 g/t Ag; Stap-penbeck1928).

Ore formation: At the Eisenberg, oxidizednativegoldandCu-Pbsulfide-selenidedeposi-tionat>200°Cinreducedblackslate,probablydistaltothefluidsource.AtRamsbeck,Zn-Pb-Agsulfidemineralizationat>300°C,thesourcegraniteoutlinedbyanomaliesinillitecrystallin-ity, vitrinite reflectance and Bouguer gravity.AtAugusteVictoria,Zn-Pb-Agsulfideminerali-zation at 260°C in reduced coal measures. IntheUpperHarz,earlyoxidizedFe±Cu-Pbsul-fide-selenidemineralization at 300°C followedbymain-stageZn-Pb-Agsulfidedepositiondur-ing fluid cooling from 360 to 220°C (>400 to150°C at St Andreasberg). The fluid tempera-tures estimated by mineral and isotope ther-mometry are higher than those measured byphase homogenization in inclusions (110-180°C;max.225°CatBadGrund).

Appendix: Harz veins, discussion of fluidsources

The Zn-Pb-Ag veins in the Upper Harz dis-trict remained in production until 1992, andthus have been subject to more specializedchronological,isotopeandfluidinclusionstud-ies than the other deposits described above.Earlygeneticmodelsrelatedveinformationtomagmatic fluids sourced in the Brocken andRamberg plutons (Schneiderhöhn 1941;Buschendorf et al. 1971; Mohr 1993). Bothgranites represent feeder intrusions to theLower Permian volcanic rocks and, perhaps,cupolasandlaccolithsofadeeperbatholith.IntheGerman-Polishbasin,deepdrillholesinter-sectedPermo-Carboniferous rhyodacite flows,ignimbrites, minor andesite and basalt up to2.5kmthick,partofa"largeigneousprovince"comprising 70,000-80,000 km3 of volcanicproducts (Paulick and Breitkreuz 2005).Morerecently, mineralization has been related tobasin-derived brines circulating in the faultsduringMesozoicreactivation(Behretal.1987;Lüders et al. 1993; de Graaf et al. 2020). Forthose interested, the alternative models arediscussed below given ongoing research on



similar Zn-Pb deposits elsewhere (Yu et al.2020).

K-Ar and Rb-Sr ages: The chronologicalstudies at Bad Grund, St Andreasberg, Hasse-rodeandGernroderesultedinawiderangeofpossible vein-formation ages: 263±4 Ma,240±17Ma, 223±4Ma, 180±9Ma, 141.5±2.2Ma,135.7±2.6Ma,123.9±1.2Maand92.5±2.0Ma. Some interpreted these results to recordmultipleepisodesofsulfide,bariteandfluoritedeposition lasting from Triassic to Cretaceoustime (Lüders et al. 1993). Others selected aspecific age. Haack and Lauterjung (1993) ap-pliedamixingmodel tothedataofBonessetal. (1990) fromBadGrund.Theyregardedthe2M-illiteas inheritedandthe1M-illiteascrys-tallized during ore formationmixingwall rockandfluidstrontium.Consequently,theTriassicage defined by 99% of the clay fraction(240±17 Ma) was considered inherited fromtheCarboniferousgreywacke,andtheJurassicage (180±9Ma) defined by the remaining 1%of ultra-fine 1M-illite (< 0.1 mm) was inter-pretedtodatesulfidedeposition.

KandRbarelattice-boundinilliteandadu-laria crystals, whereas the daughter productsof 40K and 87Rb decay are not. The daughterisotopes (40Ar and 87Sr)may leave the crystaldue to thermally activated volume diffusion,whichisgrainsizedependent,orduetolatticerestructuring.Bothprocessesgenerateyoung-erages.IlliteK-Aragesarecompletelyresetat260±30°CandilliteRb-Sragesatabout300°C,low-grademetamorphicconditionseliminating1M-illite (Hunzikeretal.1986). In fault zones,argon and strontium retention in illite is alsocontrolled by neo-crystallization duringmove-ment(Kirschneretal.1996).

IntheSilbernaalFault,thehighillitecrystal-linity,Stage1-2temperatureestimatesof300-360°C, and the predominance of K-rich 2M-illite/muscovite(99vol.%)suggestthattheTri-assic Rb-Sr age records Zn-Pb mineralization.However, as neither the Stage 1 hematite-pyrite nor Stage 2 sphalerite-galena minerali-zation persists into the Zechstein cover rocks,ore formation is probably older than260Ma,thestratigraphicageoftheZ1limestone.AtSt

Andreasberg,HasserodeandGernrode,allK-ArandsomeRb-SradulariaagesareresetduetoSi-Al ordering to a triclinic symmetry, andbe-cause argon diffusion did not close until theterranecooledbelowabout100°C.Theyoung-er agesof ca. 140-124and92Mamaybe re-latedtoupliftattheHarzNorthBoundaryFaultrecorded by unconformities (at 135 and 85Ma)intheCretaceoussedimentarysuccession.The Permian and Triassic Rb-Sr adularia ages,too,mightbeminimagiven3-4 kmburialbe-fore the un-roofing of the Brocken granite at85Ma,andheatflowinthewakeoftheLowerPermian"largeigneousprovince".

Magmatic fluids: The hematite-pyrite as-semblages at Bad Grund, Clausthal-ZellerfeldandStAndreasbergcontrastwiththereducednature of the Devonian-Carboniferous hostrocks,mainly sandstone, greywacke and bitu-minousshale,whichcannotbufferfluidtosuchhighoxidationstate.Little isknownaboutthecrystallinebasement.UpliftedraftssuchastheEcker gneiss are not marked by widely dis-persed ironoxides.MostBrockengranitesaregreybuttheNW-striking, late Ilsesteingraniteat thenorthrim isbrightredduetohematitein abundant K-feldspar (Mohr 1993). Sericite-quartzalterationandhematite-pyrite±fluoritemineralization are present in parts of theBrockenroofgranite(FrieseandHaack1993).

Additional evidence is based on strontium,leadandstableisotopedata.Strontiumsubsti-tutesforCaincarbonate(60-350ppmSr)andforBainbarite(>1wt.%Sr).Asthesemineralscontain little Rb (most < 0.6 ppm), they pre-serve the initial 87Sr/86Sr ratio of the hydro-thermal fluid. Stage 1 dolomite (0.7132 ±0.0018), and Stage 2/3 calcite and barite(0.7133 ± 0.0005; n=45; Voigt 1984; LévêqueandHaack1993a)atBadGrundhavehomoge-nousratiosindicatingacommonsourceforSr,CaandBainanevolvinghydrothermalsystem.TheStAndreasberg(0.7118±0.0024;n=9)andHasserodeveins(0.7103±0.0002;n=1)attheperiphery of the Brocken have slightly lowerratios. All values agree within 2-sigma errorwiththeinitial87Sr/86Srratiodefinedbydiorite



andgranitewhole rock samples fromtheplu-ton(0.713±0.002;Schoell1986).

Non-radiogenic Pb-rich minerals are inter-preted to preserve the initial lead isotopecompositionat thetimeof formation.Stage3galenaatBadGrundhasaverageratios(n=10)of206Pb/204Pb=18.463±0.042(2s),207Pb/204Pb= 15.535 ± 0.044 and 208Pb/204Pb = 38.486 ±0.136 (Wedepohl et al. 1978; Lévêque andHaack1993b).TheseratiosagreewiththoseofStage2galenaandareclosetothoseinleast-radiogenic K-feldspar (n=7) of the Brockengranite: 206Pb/204Pb = 18.540 ± 0.036 (2s),207Pb/204Pb=15.531±0.018and208Pb/204Pb=38.423 ± 0.064 (Wedepohl et al. 1978; Frieseand Haack 1993). The K-feldspars analyzedwereacid-washedbutnotleachedinhydroflu-oricacidtoremoveunsupported206Pbderivedfrom the migration and accumulation of theradioactive daughters of 238U (Ludwig and Sil-ver1977).Thelowest206Pb/204PbmeasuredingraniteK-feldsparswas18.519suggestingthattheseratios,too,approachthosemeasuredinBadGrundgalena.

ZhengandHoefs (1993b,c)determined thestable isotope composition of Stage 2/3 veincalcite (n=130; d13CPDB = -8.8 to -4.9‰;d18OSMOW = +16.4 to +21.7‰) and Stage 3 si-derite(n=20;d13C=-7.5to-3.7‰;d18O=+18.7to +23.0‰) at Bad Grund. The data definetightly clustered positive correlation trends ind13C versus d18O space. Stage 2 calcite-sulfideveinshadanarrowerrange(d13CPDB=-8.8to-7.8‰; d18O = +16.4 to +17.7‰). Samplesacrossthick(2.2-3.6m)veinsintheWestfeldIandWiemannsbuchtorebodiesshowedanin-crease in d13C and d18O from the center tobothmargins, trends not consistent with car-bonate deposition during themixing of NaCl-CaCl2-KCl brine with meteoric water or withCO2degassing. Instead, thecorrelated isotopedatarepresentfractionationduringcalciteandsideriteprecipitationfromanH2CO3-dominantmagmatic or deep crustal fluid (d13C = -7‰;d18O = +10‰) cooling from 280°C to 170°C.Changes in fluid composition duringwall-rockinteraction (Stage 1) triggered vein formation(ZhengandHoefs1993b,c).

Basin and basement brines: The barite-siderite replacement in Zechstein 1 limestoneat the Silbernaal Fault, and the present-dayprecipitation of barite and aragonite close tothe Wiemannsbucht shaft are proof of post-Permianmineralization,albeitone freeof sul-fides (Stedingk 2012). Studies of fluid inclu-sionsfilledwithNaCl-CaCl2-KClbrineinalteredpartsoftheBrockengraniteandinveinsoftheUpperHarzprovided thebasisof the "basinalbrine"modelforZn-Pb-AgoreformationintheUpperHarz(Behretal.1987;LüdersandMöl-ler 1992; Lüders et al. 1993; de Graaf et al.2020). The low homogenization temperatures(Th=110-180°C)ofmost inclusions, similar tothose measured in MVT deposits (100-150°C,rarely 210°C; Leach et al. 2005) were consid-eredcriticalevidence.Themodel requires thegravity-driven descent of brines derived fromsaltintheGerman-Polishsedimentarybasinin-to the faultsduringMesozoic-Cenozoic reacti-vation, the leaching of Ca, Sr, Ba and basemetalsduetohydrolysisreactions inthemet-amorphicbasementat8-12kmdepth,andthesubsequent ascent of the evolved brines dur-ingseismicactivity.Atcrustal levelsof1-2kmbelowsurface,theascendingbrinewasdilutedduringmixingwith groundwater, which intro-duced H2S or SO4

2- during sulfide and baritedeposition, respectively, the sulfur sourcedfrom Permian Zechstein anhydrite (Lüders etal.1993).However,suchasulfursourcewouldalso introduce significant amounts of stronti-um, consideredunlikelygiven the lowstronti-umisotoperatiosoftheZechsteinmarinesuc-cession(87Sr/86Sr=0.7068-0.7078;KrammandWedepohl 1991). Alternatively, the H2S re-quired to precipitate sulfide from basementbrinemaybesourcedfromthePaleozoicsed-imentary succession in the foldbelt (deGraafetal.2020),aninterpretationatoddswiththehighoxidationstateofStage1hematite-pyritemineralizationintheUpperHarz.

TheKTBdeepdrillholecollaredatthewestmargin of the BohemianMassif intersected areducedsuccessionofparagneissandamphib-olite,andgraphiticcataclasitesoftheFrankishLine (Slide 4), a Permo-Carboniferous fault



zone reactivated in the Triassic (245Ma) andCretaceous.Low-salinitygroundwaterwaspre-sent until 1.5 km and CaCl2-NaCl brine below3.1 km depth, the expected stratification ac-cordingtodensity.Thebrinecontainedsignifi-cantamountsofdissolvedN2andCH4butlittlezinc (0.2 mg/litre) and no H2S, although thefaultsweremineralizedwithpyriteandpyrrho-tite.Brineinfluxpersistedtothefinaldepthof9.1km,wherethetemperaturereached275°C(Wöhrl 2003). Whether intermittent seismicactivityissufficienttocausebasementbrinetoascendandforma6.5kmlongoredepositre-mains an open question. A local heat sourcemay be required to overcome the densitystratification.

The maximum fluid-inclusion homogeniza-tiontemperaturesmeasuredintheUpperHarzdistrictare225°CintheSilbernaaland254°Cinthe Weisser Hirsch faults, which may be in-creased by a pressure correction of at least30°C (Schmidt 1991; Lüders et al. 1993). Themuch lower temperatures (Th = 110-180°C) inthe vast majority of fluid inclusions suggestthatmostaresecondary(Table2inLüdersandMöller1992),trappedduringthewaningstageof the hydrothermal system or after sulfidedeposition,whencoolerbrinecirculatedinthefaults.AtBadGrund,thereisatrendtolowerfluid salinitywith timeapproaching zerowt.%NaCleq in quartz crystals lining Stage 3 openvugs. The hydrogen-oxygen isotope ratios offluid released fromprimaryand secondary in-clusions in crushed vein quartz plot close tothe meteoric water line and seawater (deGraaf et al. 2020) suggesting the presence oflow-densitygroundwater inthewrenchfaults.Laser ablation ICP-MS analyses targeted atprimaryinclusions,andmeasurementsoftheirzincandleadconcentrationsareneededtore-solveoutstandingissues.

3 ACKNOWLEDGEMENTS

TheauthorisgratefultoJensKulickandPe-terPodufal,whoprovidedadviceandmentor-ingearlyinhiscareer,andallowedthephotog-raphy of samples they collected in the

Eisenberg and Ramsbeck mines. This SGAopen-access contribution is an attempt atmentoringonline,andpromotingthecentury-old tradition of economic geology in Europe.Special thanksgotoKlausStedingk,myfriendsince university times in Clausthal-Zellerfeld,who guided several tours in undergroundmines, provided local background data, andcontributedmapsandphotographstotheHarzsection. Klaus is shown togetherwith the au-thor in a photograph graciously provided byWolfgangWerner. Suggestions by Bernd Leh-mann, Friedrich Wellmer, Wolfgang WernerandMathias Schöpel helped to improve bothcontentandpresentation.

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