841

Thz C arwdiut M ine ralo gis tVol.35, pp. U1-87409n)

CHEMOSTRATIGRAPH IC, ALTERATION, AN D OXYG E N ISOTOPIC TRE NDSIN A PROFILE THROUGH THE STRATIGRAPHIC SEOUENCE HOSTING

THE HEATH STEELE B ZONE MASSIVE SULFIDE DEPOSIT, NEW BRUNSWICK

DAVIDR.IENTZI

New BrunswickGeological Surveys Brarch P,O, Box 50,495 Riverside Drive, Baharst, New Brunswick E2A 3ZIand Deparmuu of Geology, University of New Bruncwiclg Fredcrictoa New Brunswick E3B 5A3

DOUGLAS C. HALL

Ekctmn Microscopy Unit, University of New Brwswicl<, Fred,ericton, New Brunswick E3B 6EI

LAWRENCED.HOY

Tallon Metal Techrwlngies, 1961, ru.e Cohzn, St. Ia.urent, Qudbec H4R 2M

AssrRAcr

This detailed study of a drill hole through the niddle Ordovician section that hosts the 25 Mt Heath Steele B zone massivesnlfide deposit shows that the local geology has been misi.uterpreted. Using immobile elements, their ratios, and orygen isotopesof quartz phenocryss, distinct stratigraphic footwall (FW) and hangrng wall (HW) are recognized in the sedinentary and felsiccrystal tutr (CT) sequence; This indicates that the two FW sedimentary packages and FW and HW CT packages do not representfold repetitions of each other, which has obvious exploration significance. Although extremely Eansposed, the stockwork andlaqger alteration system are recognizable with feldspar hydrolysis to phyllosilicates, al increasing proportion of cblorite relative!o K mica, and increasing disseminated and vein sulfides toward the ore horizon. These observations are consistent with increasing(>100 m) whole-rock (Fe + Mg/(K + Na) and AlzO/(AlzO: + KzO + NazO) toward the massive sulfides. In the FW, these trendsare coineident with increasing Sn Cu, Co, As, and Sb, reflecting sulfide saturation. The HW alteration is <50 m wide andmanifested by slichtly higber (Fe + Mg/(K + Na), Eu/Eu*, Fe, Mn, Mg, S, Ba, Co, G\Z&Pb, Sb, and Hg than rocls further upin sequence. The minsralegy ani mineral compositions reflect upper greenschist grade (450'C and 600 MPa) conditions with anoverall equilibrirrm disfibution of major and trace elements. In the least-altered FW CI, chessboard albite variably replacesalkali feldspar phenocrysts and, with increasing alteration, are hydrolyzed to nicas. The Fe(Fe + Mg) and Al contents of K-mica(phengite - muscovite) and chlorite (ferroan clinochlore to chamosite) increase, reflecting alkali-element leaching, variable silicaleaching, and Fe and Mg exchange reactions at low pH and high Fe/Mg in the fluid. In the HW hydrolysis of feldspar toBa-bearing phengite and Fe clinochlore is indicative of continued fluid venting through the CT and mixing with shallowlycirculatilg seawater. At an est'mated temperature of 400'C, stockwork cblorite compositions OLtmo1" = 0.8) indicate anFe/1Vlgnsi6 = 2@ for the buoyant mineralizing hydrothermal plume, whereas the distal chlorite alteration Qft5ae66 = Q.l)reflects local seawat€r-dominated alteration peripheral to themineralizingplume. Whole-rock 6180 values, closely reflecting cbloritecontent, decreasetoward the ore hot'uanta5.3Voo(FN chloritite). Atinfeiled tempemtures between 3fr) andzl$'C, the orc-formingfluid has ahigh r8O content (-5 to TVoo)indrcafive of extensively modiEed seawater, typical of those forming large VMS deposits.In the HV/, whole-rock 6leO values decrease toward the ore horizon from>llVooto 8.7/oon the altered rock.

Keywords: ma.ssive sulfide, VMS deposig lithogeochemistry, chemostratigraphy, hydrothermal alteration, orygen isotorpas, HeathSt€ele, Bathu$t Camp, New Brunswick.

Sonm{ene

D'aprds les r6sultats d'une 6tude d6teill6e de carottes de sondage traveaant la s€quence ordovicienne moyenne qui contientIe gisement de 5gffi1ps mas5if5 de Heath Steele, zone B (25 Mt), le contexte g6ologrque aumit 6t€ mal interpr6t6. Nous avonsutilis6 les teneurs en 6l6men8 immobiles, les rappors de celles-ci, et le rapport des isotopes d'oxygdne dans le quarE ph6ncristiquepour reconnafire les roches sfatigraphiquement sousjacenles et susjacentes dam Ia s6quence de m6as6dinents et de urfs felsiquesenrichis en cristaux. Nous ne croyons pas que les deux sdquences s6dimentaires sousjacentes et le.s s6quences de tufs I crisauxfragment6s sousjacente et susjacente (par rapport d la zone min6ralis€e) repr6sentetrt des unit6s r6p€t6as par plissemenq cetteinterp€tation a une si8nificstisn importante rlans les modeles d'exploration. Quoique la transposition d'unit6s peut Ctre eftreme,le stockwerk et le systime d'altdration plus dtendu sont reconnaissables grAce i I'hydrolyse du feldspath" pour donner des

I f,-mail address: dlenE@gov.nb.ca

842

phyllosilicat€s, une augmentation dans la proportion de chlorite par rapport au mica blanc, et une aupentatisl dans la proportionde sulfures diss6min6.s et en veinqs vers I'horizon min6ralis6. Ces observations rendent compte de l'aupentation, sur plus de1@ m, des valeurs (Fe + Mg)/(K + Na) et NzOzl(NzOz + KzO + Na2O) d,ns les roches globales en direction de I'horizonmin6ralis6. Dans le.s roches sousjacentes i cet horizon, ces ten.tenc€s progessent avec une auementation en S total, Cti, Co, As etSb, qui indique la safuration du systdme en sulfures. Dens les rochas susjacentes, I'enveloppe d'altdration, infdrieure i 50 m, semanifesrc p61'un rapport (Fe + MgV(K + Na) et Eu/Eu* plus 6lev6, et des teneun en Fe, Mn, Mg, S, Ba, Co, Cu, Zn, Pb, Sb et Hgl6gdrement plus 6lev6es, que plus haut dans la s6quence. Les assemblagqs de min6raux et leur composition concordent avec des

"oo616sn5 dans le facids schiste vert suffrieur (450'C, 6C[) MPa), et semblent indiquer l'6quilib're dars la distribution des 6l6ments

majeua et des 6l6ments traces. Dans les tufs I cristaux inf6rieurs les moins alt€r6s, I'albite I texure sa .lamier remplace lesph€nocristaux de feldspath alcalin i un degr6 variable et, avec augmentation du degr6 d'alt6ration, se voit Eansform6 enmicas. Le rapport Fd(Fe + Mg) et la teueur en Al du mica blanc (muscovite phengitique) et de Ia cblorite (clinocblore ferreuse ichamosite) augmentent, suite au lessivage des alcalins et de la silice, et aux r6actions d'6change impliquaat Fe et Mg i faible pHet rapport Fefivlg 6lev6. Dans les roches susjacentes, I'hydrolyse du feldsparh pour donner une phengite baryfdre et une clinochloreferreuse semble indiquer le flux soutenu d'une phase fluide d havers des trrfs i cristaux et un m6lange avec de I'eau de mer mis encirculation tr faible profondeur. A une temp6rature de 4fi)'C, la composition de la chlorite du stockwerk (X"lmmite = 0.8)indique une valeur Fe/Mg dans Ie fluide de f6vent d'environ 2@, tandis que la composition de la cblorite des zones .listalesd'alt6ration (&rm*l,= 0.3) sembleplutdtr6gie parl'eau de mer.les valeun de 6tb des roche,s globales, qui dEpendent directementdu contenu en chlorite, .liminuentjusqu'd 5.3%o (cbloritite sousjacente) rlans h dircgtion dle la zone min6ralis6e. Aune temp€rafirreprobable entre 3ff) et 400'C, Ia phase fluide responsable de la mindralisation aurait eu une teneur 61ev6e en 18O (ente 5 et7%o),et donc aurait 6t6 une saumure fortement modinde, telle que rlans le cas des gisenents de sulfiues volcanogdniques massifs plusimportants. Les valeurs 6180 des roches susjacentes alttirees diminuent de>|7Vood8.7Voo dans la direction de la zone min6ratis6e,

(ftaduit par la R6daction)

Mars-clls: sulfi:res massifs, gisement de type VMS, lithog€ahimie, chemostratigraphie, alt6ration hy&othermale, isotopes d'orygd,ne,Heath Steele, camp minier de Bathusq l\suveau-Brunswick.

hrmopucnoN

Hearh Steele, the secondlargestZn-Pb{u-Ag massivesulfide deposit in the Bathurst Mining Camp, is locatedabout 65 krn southwest of Bathurst, in northern NewBrunswick @g. 1). The Heath Steele B Zone, the largestdeposit known in the Heath Steele belt, has produced17 .9 Mt gradine 1.7 3Vo Pb, 4.67 Vo Zn, O.96Vo C.u, and63 g/tAg, mined intermittently between 1957 aadl997.As of 1993, ore reserves at the B 7on" letalled 3 Mt atgrades similar to historical values (McCutchan 1992,Hamifton et al. 1993).

The massive srlfide deposirs (A to E, Fig. 1) withinthe Heath Steele belt are hosted by crystal-rich felsicvolcaniclastic rocks and associated tuffaceous sedimen-tary rocks of the Nepisiguit FaJJs Formation, which formsthe basal part of the Mddle Ordovician Tetagouche Group(Skinnsl 1974, van Staal & Fyffe 1991, Wlson 1993).Theenclosing hostrocks and the sulfide deposits archighlydeformed (McBride 1976), with at least four phases ofdeformation (Moreton & Williams 1986, de Roo et aI.1990, I99l, l9V2,Motaon 194), and are meAmorphosedfrom lower to upper greenschist grade.

This whole-rock geochemical, mineralrchemical, andoxygen isotopic study ofthe B zone deposit (Fig.2) wasundertaken: 1) to investigate the relationship betweenfts hanging-wall (HW) quartz-crystal-rich tuff (QCT),which occurs immediately above the massive sulfldesand coeval iron-formation, and the quartz-feldsparcrystal-rich tuff (QFCT) that occurs 50 to 100 m higherinthe snatigraphy,2) to describ the alteration systematicsin the tIW and footwall GrilD, 3) to link the mineml-chemicalvariations with the whole-rock seochemical variations.

and4) to compare theHWCTto asimilarrocktype thatoccurs in the structural FW, as the la.fferhas recenflybeeninferred to be a structural repetition of the former (de Rooet al. 1991, Moreton 1994).Ia addition, all rrnits werecharactnizsd chemically in order to help correlate unitschemostratigraphically among the various massivesulfide deposits. With these objectives in mind, a recentunderground exploration diamond-drill-hole (DDHHSB3409) thaf transected much of the mine sequence wasselected for detailed analysis. The hole was collared@ig. 3) in the stratigraphic FW and drilled northward intothe HW CT in order to test for fold repetitions of the orehorizon.

The detailed results of this chemostratigraphic analysisconflict with structural interpretations of the Heath SteeleB zone area (deR:oo a aL 199l, Moreton 194). Therefore,the local mine stratigraphy is pnesented in revised form,and uses recognized suMivisions and nomenclature ofthe BathurstMining Camp (van Staal & Fytre 1991).

RrcroNer GEot ocIcAL SETTING

The stratigraphy around Heath Steele Mines consistsof intercalated quartz wackes and carbonaceous pelitesthat resemble the Miramichi Group (Fig. 1). However,the rocks locally contain fine-grained CT horizons and,therefore, by definition, are included in the NepisiguitFalls Formation of the Tetagouche Group. In the HeathSteele are4 the Tetagouche Group has been subdividedinto two parts, a lower part comprising volcanic,volcaniclastic, and sedimentary rocks (Nepisiguit FallsFormation, Fig. 4), and an upper part consisting ofrhyolite and hyaloclastic tuff (Flat Landing Brook

HEATTI STEELE B ZONE DEPOSIT. NEW BRUNSWICK

Frc. 1. Location of the Heath Steele A, B, C, D, E, and F zones and Stramat massive sulfide deposits (after I{amilton et al. 7993).

843

Formation, Fig. 4; van Staal & Fyffe l99l,vatStaal etal. I992,W'rIson 1993). Unlike the Brunswick No. 6 and12 deposits to the northeast, the Heath Steele massivesulfide deposis and associated iron-formation occur withinthe Nepisiguit Falls Formation (McCutsheon et al. 1993).

Intense deformation and metamorphism began duringthe Late Ordovician (Ashgiltian) with Dr thrusting andtight folding, but continued into ftre Devonian with theculmination of the Acadian Orogeny (van Staal & Fyffe1991, van Staal et al. 1992). At least five generations offolds have been identified in the Bathurst Mining Camp(van Sraal 1987, de R:oo et al. 1990, 1991).

LocALSErrtr{c

The rocks of the Heath Steele belt are, in part, boundedto the north and south by a sequence of massive rhyoliteand coarse pyroclastic rocks (lapilli tuff, breccia andagglomerate) of the Flat l,anding Brook Formation" whichare locally in fault contact to the south (Heath Steele fault,Fig. 2, Wilson 1993). This structure was first describedas abroad antiformal fold by Dechow (1960), although

deRoo et al. (1990) and Moreton (1994) suggested thatthe entire sequence is in thrust contact with the rhyolitesto the south. The position of the iron-formation and thesfyles of alteration (McMillian 1969, Whitehead 1973,McBride 1976, Owsiaki 1980) imply that the sequenceis north-younging at the B zone deposit.

Mnve STRATIGRAPHY

The mine sftatigraphy has been described in detail byMcBride (196) andMoreton &WiUiams (1986), butwasrevised on the basis of structural observations by de Rooet al. (199t) and Moreton (194) (Fig. 4). McBnde, Qn 6)suggested that ahorizon of CT occurs inthe stratigaphicfootwall, whereas de Roo et al. (L991) suggested that itrepresents infolded hangrng-wall, an interpretation thathas major implications for possible repetition of themineralized hor2on. In contrast to the model of de Rooet al. (1991), the geochemical evidence presenled laterclosely resembles McBride's (1976) earlier stratigaphicinterpretation; therefore, a revised stratigraphic columnis proposed (Fig. 4).The detailed geology in Figure 2

844 TIIB CANADIAN MINERAI{reIST

Hc. 2. Geological map bf the Heath Steele B-zone orebodies (afterl€nE & Wilson 199), with the location of theA-B cross sectionillustrated in Figure 3. Abbreviations' plll plnl [snrling Brook Formation (Tetagouche Group), NF: Nepisiguit Falls Forma-tion (fetagouche Group), Mir. Gp: Miramichi Group.

reflects these revisions, based on firther chemostatigr4hicwork in the area (Lentz & Wilsott997).

lowe r foonvall ( FW) sedimentary paclcage

McBride (1976) described a sequence of locallygraphitic, interlayered mudstones and quarEose siltstonesand sandstones @g. 5) in the lower stratigraphic footwallto the B zone deposit. Overall, this unit resembles rocksof the Miramichi Group (see van Sraal & Fyffe 1991,I angton &Mccutcheon 1D3) thaf typicallyunderliefelsicCT and related sedimentary rocks of the Nepisiguit FallsFormation, although a few occurrences of CT wirhin itindicate that it belongs in the Tetagouche Group.

Footwall crystal-rbh taff (FW CT)

This unit contains 15 to 30 vol.% reworked crystalsdomina1B616t noartz, but locally also with feldspar (relictmicrocline and albite) (Fig. 6). As recognized by McBride( I 97O, this unit locally comes in contact with the ore zxre;the upper FW sedimentary package forms sub-basins oneither side of the CT. This depositional relationship,evident in mine plans and sectionso implies that this isnot the same CT that occurs in the stratigraphic andstructural HW. Avolcanic origin forthis unit is supportedby the occurrence ofvitreous quartz paramorphs afterp-quartz phenocrysts, embayed phenocrysts, and brokencrystals, theposition of this porphyritic unitbetween fwo

HEAIH STEELE B ZONE DEPOSII. NEW BRUNSWICK 845

different sedimentary units, and the occurrence ofvolcaniclastic material in the overlying (upper FW)sedimentary rocks.

Upper footwall (FW) sedimentary package

This unit is composed of relatively homogeneousmudstones (now phyllites and fine-grained schists)and local volcaniclastic layers with quartz crystals(phenocrysts), and resembles the characteristic NepisiguitFalls rocks (Wilson 1993). The intensity of the greencoloration increases towrdthe massive sulfidebody, whichrepresents an increasiug proportion of chlorite that iscoincidentally bec6ming more Fe-rich. These tuffaceoussedimentary rocks form the immediate footwallsequence to the massive sulfide deposis and host minorchalcopyrite - sphalerite - pynhotite - pyrite sringer veinsin a dark green chloritic groundmass @ig. 7). A leucocraticunit, which underlies the ore lenses, is described as acidnrff (McBride 1 97 6,Wahl.l97 8, Moreton & Williams 1986,Moreton 1994); however, it represents sulfidic Mg-richfootwall sedimentary rocks that underwent secondaryalteration processes of variable intensity.

Massive sulfides

The massive sulfides and intervening exhalativesedimentary rocks (iron-formation) are generally coevalamong all the known deposits in the Heath Steele area-The massive sulfides were described in detail by Lusk(1969, 1992) and Chen & Petruk (1980). The B Zonedeposit has three dominant ore-t54)es, massive pyrite,banded pyrite - sphalerite - galen4 and pyrrhotite -chalcopyrite fragmental ore with, overall, Cu, Co, andAs contents higher and Zn, Pbo and Ag lower than inthe Brunswick No. 12 deposit (Hamilton et al. 1993).The Heath Steele B Zone deposit is discontinuouslyoverlain by iron-formation (McMillian 1969) that ismineralogically very similar to that between theBrunswick No. 6 and 12 deposits. Lusk (1969, 1992)outlined a pattern of base-metal zoning from thestratigraphic footwall to the hanging wall of theB Zone deposit, and also noted two Cu-rich basalzones associated with the thickest'?orphyry" beneaththe footwall sedimentary rocks. However, deRoo et aI.(I99I,1992)refuted the interpretation of the base-metal2sning because of the tightFl folding within the sulfidelayer (see also Moreton 1994) and the high concentrationsof chalcopyrite in the Dr structurally remobilized sulfidebreccia (McDonald 1984).

Hanging-wall crystal-rich tuff GIW Cf)

Overlying the massive sulfides and associated bandediron-formation is a horizon of QCT that is concordant tolayering and that passes vertically into QFCT (NepisiguitFalls Formation) away fromthe deposit. The quartz andK-feldspar crystals comprise L5 to 25 vol . 7a of the rocko

although within 50 m of the ore horizon, the feldsparcrystals disappear over a 5 m vertical interval (Frg. 8).The size of the feldspar crystals decreases from 5 mmto <l mm ia this interval, but this may be an alteration-induced phenomenon. Within the zone of alterationstratigraphically above the ore, pyrite is present, butusuallyin amounts less than afew modal percent Sideritealso is present in this zone, but locally occurs elsewherein the hanging wall.

Srnuc"nins

McBride (1976) and Moreton (1994) have defined atleast five deformation events in detailed structuralanalyses of the B zone deposit. McBride (1976)suggested that the 51 foliation associated with isoclinalfolds conrains a steep, west-plunging lineation (Zr) thatwas folded around the Fz folds. Moreton (1994) foundthat the tight to isoclinal recumbent folds (Fr) havesheath-like profiles and probably forrned in a high-strainfold-and-tbrust environment. In contrast to McBride(1976), Moreton (1994) suggested that the vergence ofthe Fr folds is toward the southeast.

F2 folds are open to tight folds of the earlier layering,with moderate westerly plunge and a moderate (45')south-dipping axial-planar foliation. The ,Sz foliationgenerally obliterates the ̂S1 cleavage tbrough transposition.In general, the enveloping surface to the Fz folds definesthe tabular nature of the sulfide deposit, which lies onthe short limb of an overturned Fz fold.

Post-Fz deformation events are characterized by openfolds of the main ,S1,S2 composite foliation. Horizontalfolds with flat to shallowly dipping axial surfaces (F: orF11: de Roo et al.1990,1991) define the third event ofdeformation and cause the local variability in the dip ofSz.

Lmtoceoctuv[srRy

C hemo s natig raphic interp retarton

In order to ascertain the geochemical variationsaround the deposit, the raw data for hole HSB3409(available a.t the Depository of Unpublished Dat4 CISTI,National Research Council, Ottawq Ontario KIA 0S2)were plotted as a function of depth using differentsymbols for the major lithological units (Figs. 9a, b).Table I presents the average composition and standarddeviation of each of therecognizedunits, including samplesthat are considerablv altered. Onlv relativelv immobileelements weie used io identify compositional differencesin the lithologic sequence. In general, Al, Ga, Ti, Sc, Z,Hf, heavy rare-earth elements (HREE),Y,Th, and Nb areconsidered to be relatively immobile in the weatheringenvironment (Iaylor & Mcknnan I 985) and are, therefore,useful for petrogenetic studies of sedimentary rocks. Inaltered and metamorphosed volcanic rockso these semeelements are generally found to be relatively immobile

846 THE CANADIAN MINERALOGIST

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fi';:::,:1iffi"4il..lii]-iiii-iiil;iii-ii!1:;.ii(ip"rphrnvi (HF rm) ln u' Vl .'\l'.':#*i'1-:'i"i,.r".-j'-r-''-)'i".)'-r'n'l \ . " 1 :

f i<aD upper (HW)a l te redcrys ta t t r t? ' ' ' : ' ; " 'Nr-;<l>/ &ror B€dimentary rccke (NF Fm)

'' ;'.':\'.:Fl'I eoNi;';..;: i';-;r i'2r j';-;1 i'i-:1 jt:':"<\,UAi i;ll i;ll ijl;l ijli

^.---:. --/- geological contact,n.Qi"*>r".1)1"..)l'i-.').r+) masalvesulffdes&/orexhalllaa >r, .\-<,lr ;<,1. ;1'-,t;1i,t':

./,/./ ddlholes/drltt hole \),::j).:1j),:1ji.z-'iit>:.

lmentarv rodce </ sections with pierce pointe \^ ;iii i;ii i

ql'-J upper(FW) sed lilr rmy Tetagouche/Mtramtcht croup .K);".;:-.,".

,-a--i--\q:-, rower(Fw)*1mff.\ . i?,; i .' ! \ ; . / / \

; {tower (FW) sedlmentary rod<s

'$lit1:l

z '

(NFFm) y z (NF Fm/PB Fm)- : ' \ ; ' )

ocioct

octoo.q'

Hc. 3. Geological cross-section through the B-zone deposit illustrating the location of diamond drill-hole (DDII) HS83409.

Abbreviations: IIW: hanging wall, FW: footwall, NF: Nepisiguit Falls Formation (Ietagouche Group), PB: Patrick Brook

Forrnation (Miramichi Group).

McBr lde (1976) Moro ton (1994) th ls s tudy

HEATTI STEELEB ZONE DEPOSTT, NEWBRIJNSWICK 847

:

- - T

100 mlI

:t

5

3I

Ego=trl

= =| ! . J-;=lrJ

L E G E N D

Tetagouch€ Group

l-l nnyotttes, brecctas andLll tuffaceous sedlmentary rocks (FLB Fm)

ffi or"rtr-feldspar crystal-rrch tutflavas /[f3=l porphyrles and tuffltes (NF Fm)t t i l t t i l t t r -l l l l l l l l l l l l ron fo rmet lonuutuuf M"""t""

"rtftd""I

ffi ,rn"""ous sodtmentaryl--l rocke/mudstones (NF Fm)

lTl or"rtr (*fetdspa4 crystall4:l tutflres (NF Fm)

Mlramlchl Group / Tetagouche Group

[T] ou"urose stttstonee andlal shal€o (PB Fm) t tutfiteE

* ! . . . . do ts ln te rmlxedwl thpat te rnsIndlcates hydrothernial alterafl on

Frc. 4. Schematic stratigraphic columns of the Heath Steele area showing the two previous interpretations of the mine stratigraphy(McBride 1976, Moreton & Williams 1986, de Roo et al. 1991, Moreton 1994) compared with that proposed in this study.Lsed: lower FW sedimentary rock, FW CI: FW cryshl nrff, Used: upper FW sedimentary rock, HW CT: hanging-wall crystaltuff, NF Fm: Nepisiguit Fa[s Formation, FLB Fm: Flat l,anding Brook Formation.

@avies et aI. 1979, Davies & Whitehead 1980, Dostal& Strong L983,1*ntz & Goodfellow l993uMacl.,ear.& Barren 1993,1*ntz l996ub).

As shown in Figure 10, the Ti contents in theIower sedimentary package (0.9 to l.l wt.VoTtO) aredistinct from the upper footwall sedimentary package(0.4 to 0.7 wt.Vo TiO). Al contents are also greaterin the lower (>15 *.Vo Al2O3) compared to the upper(<15 wt.Vo Al2O3) sedimentary package. The relativelyhigh contents of Al and Ti in the lower sedimentarysection resemble those ofthe quarfzose siltstone and slatesof the Miramichi Group (I-entz e t al. 1996), although thepresence of minor in[ercalated, fine-grained CT horizonsby definition indicates that it is part of the Nepisiguit FaIsForrnation (Wilson 193). The variation inTi andAl contentsof the upper sedimentary unit relative to the lowersedimentary unit and the footwaX CT (Flg. l0) indicatescontinued pelagic sedimentation during deposition ofthe tuffaceous (upper) sedimentary rocks, particularlyat the top of the sedimentary section. Like TiO2, Cr, Sc,and V contents @g. 11) are also much higher in the lowersedimentary sequence, although they increaseupward nearthe top of the uni! where the most iitensely altered rocksoccur. The high Cr, Ni, and Y as well as other immobileelements (i.e.,Ti, Sc, A1, Zr), at the top of the uppersedimentary sequence indicates an increase in pelagicMiramichi Group sedimentation and a decreased inputof tuff just before the massive sulfide was deposited.

The overall difference in composition between thefootwall sedimentary packages indicates that they havedifferent provenances, The composition of the lowersedimentary sequence is very similar to quartzose rocksoftheMramichi Group attheFAB zonebetween BrunswickNo. 6 and 12 deposits (I-rlltz & Goodfellow L994a), atKeyAnacon (kntz I995b), and at Middle River, locatednorth of the Brunswick No. 12 deposit (Lentz et aL 1996).The upper sequence is compositionally similar totuffaceous sedimentary rocks of the Nepisiguit FaUsFormation Q-angton & McCutcheon 1993, Wilson 1993,Lentz & Goodfellow 1996). However, the upper packageof sedimentary rocks also is chemically distinct (i.e., triglelTiOz, Sc, Zr, Cr) from the lower footwall CT, indicativeof a different felsic volcanic or mixed tuff-pelite source.

There are important chemical differences befween thefoonrall and hanging wall, particularly in their levels ofincompatible high-field-strength elements (Y, HREE,Tb, andZ). Overall, the SiO2 (>70wt7o) and alkali elements(6 to 7 wLVo K2O + NazO) indicate a rhyolite compositionQ-nBas et al. 1986). However, they fall in the rhyodacitecompositional field of the Winchester & Floyd (1977)(Fig. l2a), similar to the CT between Brunswick andHeath Steele (Lentz & Goodfellow l992a,b,Langton &McCutcheon 1993, Wilson lgg3,Lenlv. 1996a). ThehigherZr and lower TiO2 in the hanging-wall CT sequencecompared to the FW sequence (Fig. 12a) reflecs increasedchemical evolution of the HW CT.

*!*t rf l trF "atkJ

a'. r '

J{. ' ::. '_a "'

*.;-

i : - :

848 TI{B CANADIAN MINERAI'GIST

Frc. 5. Quartzose siltstone with interlayered graphitic pelite folded by Fr (very tight) andFz (n*t to open). This unit (lower FW sedimentary package) is most similar to theMimmichi Group. These sedimentary rocks represent the upper part of the MiramichiGroup sequence (van Staal & Fytre 1991) @DH HSB3409, 100.6 m).

Ftc. 6. Light green, fire- to medium-gaine4 FW CT with vireous high-temperature quartzphenocrysts and whitish (mitky) quaffz t mica t feldspar (relict feldspar phenoclasts)(DDH HSB3409, 230 m).

. 3St

$h

. : - i* , , . :

"*{ ! , f' * , , ' *

.s

HEATII STEELE B ZONE DEPOSTT. NEW BRT'NSWICK

FIc. 7. Dark green (chloritic), texturally homogeneous FW sedimentary rocks (upper FWsedimentary package) with chalcopyrite - pynhotite - pyrite sulfide layers and veinslocated at the base of the massive sulfide. Folding of the sulfide veins and layers isevident (DDH HSB3409,400 m).

849

':.;:i:ii ,.

850 TTIE CANADIAN MINERALOGIST

Ftc. 8. Parchy chloritic alteration in the transition zone between the altered QCT and QFCIin the IIW (DDH HS83409,459.4m).

The Nb/Y ratio of less than 0.8 is indicative of asubalkaline composition (Figs. 12a, b), consistent withthe low Zr contents (100 to 250 ppm) in both tuffunits(see Leat et al.1986). The Nb + Y contents indicatethat these felsic magmas are transitional betweenvolcanic arc and within-plate compositional fields(Figs. 12c, { Pearce et al. Lg84),W@lof intracontinentalbackarc environments O-enE 1996a). The low Ga/AI value(on average 2.3), derived fromWlson (1D3), is inconsistentwith an anorogenic origin (Whalen et al. I987).T\eYand Z;r contents in the hanging-wall CT (on average43 ppm and 146 ppm, respectively) are slightly higherthan the footwall CT (on average 35 ppm and 130 ppm,respectively) (Fig. 13a) and plot in the "tholeiitic" rhyolitefield thaf is normally associared with bimodal magmatism-

The footwall CT has less than 140 ppm 7r, andthehanging-wal unithas greater th4n this 26eun1 (Fig. l3b).Thori L m contents are also different (FW CT: 9 to 1 I ppmTh, IIWCT 13 to 14ppmTh). The LREEandHREEcontents are slightly higher in the HW CT than in theFW CT (Figs. I 3c, 14). The LaN/LuN of the hanging-wallCT (on average 6.4) is higher than that of the FW tuff(on average 5.7).

Overall, the distinct compositions of the hanging-walland footwall tuffs imply that they do not represent thesame CT units; this inference contrasts with the structuralinterpretations of de Roo e t al. ( I 990, I 99 I ) and Moreton(1994).

Alteration

At the Brunsvrick No. 12 deposit, a primary halo ofalteration and stringer-sulfide stockwork zone havetreen recognized (Goodfellow 1975, Juras l98l,Luff etaI. 1992,Lentz & Goodfellow 1993a, b, c, 1.994b,1996); these are predeformational in origin Q-ttff et al.1992,Lenz & van Staal 1995). Major-element andbase-metal compositional changes have been studiedaround the Heath Steele deposits by Whitehead (1973),Whitehead & Goveft (197 4), Goodfellow & Wahl (1976),and Wahl (1978).

In this study, a numerical designation ofthe alterationzones w:ts used (Alteration Index, Fig. 9b) to help mapalteration at Heath Steele; that designation was originallydeveloped in the Brunswick No. 12 study (Lentz &Goodfellow 1994b). It is based on the presence or absenceof feldspar, intensity of green coloration, presence ofstockwork sulfides, and degree of silicification, witha transition from least-altered type (distal zone 5) tomost-altered type (proxfunal zone 1), typically a silicifiedsulfide stockwork zone. QFCT and sedimentary rocksin the strucurral footwall of the Heafh Steele massive sulfidedeposits are altered wirhin tle vicinity (>100 m) of thedeposits. Alkali feldspar is altered to a chlorite-sericiteassemblage, although albite is still Iocally preserved (Wahl1978). Some of the most intense alteration in the area isassociated with the orebodies of the C zone (Wahl 1978).

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Ftc. 10. TiOz versus AlzOg contents of samples from DDHHSB3409 (open symbols), as well as lvve lrrlk ssmples ofthe lower and upper sedimentary rock packagas (solid sym-bols). Ahypothetical mixing linebetween FWvolcaniclasticrocks and the lower sedimentary package may give rise tothe compositional spectrum of the upper FW sedimentarypackage inferred to be tuffaceous in origin. The alterationfend depicts the dilution of immobile comFoDents due tomass addition to the rock.

Using discriminant analysis, Whitehead & Govett(1974) found that Pb contents are higher (>30 ppm) inthe hanging-wall rocks above the B zone deposit.Whitehead (1973) also found that the Mn/Fe value isrelatively low in the foorwall of the ore zone, but higherin the iron-formation and in the hanging-wall rocks thatboth overlie the deposits and are also distal with respectto the sulfides. Wahl (1978) showed that Fe, K and Mgare enriched in the footwall porphyry and sedimentaryrocks of the B zone deposit, with Na and Ca depleted in

o,2 0.4 0.6 0.8 1 1,2

IlOz gi.7d

Ftc. ll.TrOzverszs Y Cr, and Sc variation diagrams of lower(lvliramichi Group) and upper Q.{episiguit Falls Fm)sedimentary rocks from DDH HS83409, as well as a bulksample of the lower and upper sedimentary rock packages(large symbols).

HEATTI STEELE B ZONE DEPOSII. NEW BRUNSWICK

1

10@

100

1 0

thealteration zonerelativetodeterminedbackgroundvalues.In addition, Cu, Pb, 7n,Co,Ag, Cr, and P contents in thefootwall increase with increasing intensity of chloriticalteration toward the massive sulfide deposit @gs. 9a, b).

Nb/Y

1000

.......- o o

.";r61*erye'3"-"'- oqff"""*- v v

i . vv -.'' tr HW turl,i llraso ...."' V Upper s

,t -Ro$' -..'v

-rs{.--- a Fw tufftz .."O Lowersdlments

(\l

ot=l_ 0.1N

0.01

Fb_ 100g-o(E lo

Eo-o_

-oz

FE[ lo0goaof

oso

10 100 1000Y + Nb (ppm)

c)within-plategranite

volcanic arc & \./ Dsyn-collisional

orogenic rldgea / granite

1' 1 10 100 1000

Y (ppm)

Frc. 12. Geochemical compositions of the FW and HW CT ofthe Nepisiguit Falls Formation. a) T.rfhOz versas Nb/Ycompositional disctimination diagram (Wrnchester & FloydL977),b) Rb versas Y + Nb, and c) Nb versus Y tectonicdiscrimination diagrams for granitic rocks (Pearce et aL 1,9M).

a) corn/panr

Andeslb/Basal ../ | Af-Sas

b) syn-collisionalgranle

wlthin-plategranite

orogenic ddgegranite

volcanic arcgranile

A Oysildlull(q) . .

v tFp€rra(trnento lowers€dnFnf Ol.clgErryfdrob,"ril"ni'uLr-np"u YV .

, ^E o $VY

Q? ,vs 4v

' 9 v

o {ofo&-" o B

854 TTIE CANADIAN MINERAI-OGIST

80

100 200 300Zr (ppm)

b ) n Ef [ A

A I A

AA

A A

F ootw all ( FW ) alteration

The identity of the original feldspar phenocrysts isuncertain. In the footwall, microcline has been replacedby albite or phyllosilicates or both, but high in thehanging wallo coarse translucent albite is partiallyaltered to microcline. The nature of these low-temper;aturefeldspathization reactions is not well understood. Inany case, the least-altered rocks have intermediate Na/I(contents within the normal igneous spectrum of Hughes(1973) (Fie. 1s).

The intensity of the chloritic alterationo and the ironcontents of chlorite, increase toward the exhalative horizon.In the relatively homogeneous footwall CT, there is atransition fromQFCTto QCL In thin section, themicroclineis prtiallyreplacedby albite, and less commonlyby chloriteand sericite. The albite has poorly formed albit€ twinsthat are locally chessboard-texure4 and is, in uun, replacedby quartz-chlorite-sericite that mimics the originalalkali feldspar crystal in habit and size (see also lrntz &Goodfellow 1993a). The hydrolysis of albite marks thealmost complete removal of sodium from the rock(Frg. l5).Analogous to the Brunswick No. 12 deposit,the QCT, orlowerquartz porphyry in mine temrinology,represents an alteration product ofthe QFCT and occursalong its upper contact adjacent to the upper footwallsedimentary package.

The upper footwall sedimentary rocks are verysimilal mineralogically to the altered footwall QCT,except they are generally devoid ofphenocrysts and havea higher proportion of cblorite. These two rock types arechemically very similar, but on the basis of immobileelements and ratios of immohile elements (Macl,ean 1990,Maclean & Barrett 1993), the sedimentary rocks arecornpositionally more het€rogeneous. The higberproportionof chlorite in the sedimentary rocks results in lowerSiOz, KzO, and MnO, and higher MgO and FezOg(total) cont€nts (Fig. 9a). KzO, Ba, Rb, and Sr contentsdecrease gradually toward the massive sulfides (Fig. 9a).The enrichment in total Fe coincides with increasingS contents from disseminated pyrite and, to a lesserexten! pyrrhotite, chalg6p''riL and sphalerite. CO2 andCaO contents aregenerally low. As withAlzOg, mostotherimmobile elements (Ti, Zr, Th, HREE, Y, and Sc,Fig. 9a) are diluted. Overall, there is approximately30 to sOEo mass addition in the most-altered footwallsamples if Al is considered immobile (cf. Lentz &Goodfellow 1993a). As mentioned earlier, the footwallsedimentary rock at the top of the package (samples 16and 17) may be more aluminous (pelagic?), which wouldmake the calculated mass-change values underestimates.Nonetleless, these mass-change values are high andtypical of chloritites in footwall sedimentary rocks atBrunswick No. 12 (see data in lcitch & l,entz 1994),bvtare considerably less than the intensely silicified (up to3@7o mass addition) footwall sedimelrtryrocks rhat occursin the near-surface core of the discharge system (Lentz& Goodfellow 1990.

60Eo-t9+o

Eo--9 to-cF

Eo-o-

alJ

a),f

.."'{"';ffiflcalc-alkaline

400

20

od

1 5

5b100 150 200 250 300

Zr (ppm)

o.4 0.5 0.6 0.7

[-u (ppm)

Ftc. 13. Geochemical compositions of the FW and HW CT ofthe Nepisiguit Falls Formation. a) Y versus Z.r variattor.diagram (Barreu & Maclean 1994), b) Th versus 7,r,and c) La versus Ltt variation diagrams. Symbols as inFieure 10.

0.3

HEAII{ STEET.B B ZONE DEPOSIT. NEW BRIJNSWICK 855

100

10

The Co, Cu, As, and Sb contents progressively increase1suril{ fts massive sulfide lens (Fig. 9b), which, at Bruns-wickNo. 12, was interpreted (rnv & Goodfellow 1993c)to reflect the high temperature-dependent solubility of

K2o (wt %)

Ftc. 15. K2O versus Na2O diagram illustrating the range inalkali compositions of the FW volcaniclastic and sedimen-tary rocks (NF Fm) and HW volcaniclastic rocks (NF Fm).A least-altered field is illustrated on tle basis of petro-graphic observations. Veclors ofNa-K exchange, and Fe +Mg - K exchange show the principal a.lteration processesthat acted on these rocks. Symbols as in Figure 10.

theirrespective sulfidephases (tleimish ft Fgrlington 1986,Wood e/ aI. 1987). Zn, Pb, Hg, and Sn contents alsoincreaseo but are locally erratic, like in the alteration zoneat Brunswick N o. 12 (Lentz & Goodfellow I 993c). The

o+rt-IttroEooaEGat,

Lo Ce Nd Sm Eu ed'Tb Yb Lu

FIc. 14. Chondrite-normalized rare-earth-element (REE) abundances for the FW and HWCT. Values used in normalization are from Anders & Ebihara (1982). Gd was calculatedby a Sm-Tb interpolation (Gd').

s=

o(\I(Uz

6

5

4

3

Cn/(Cu + Pb + Zn) value increases from 0.1 to near 1within 50 m of the massive sulfide lens. Au is alsostghtly enriched (20 times background). TheEu/Eu* ratioincreases continually toward theorehorizon. This panemof enricbment has also been idenffied at the HalfrniieLake deposit to the west (Adair 1992,1*ntz 1996b) andcorrelates strongly with Pb.

In Figure 9b, the Fel@e + Mg) value increases from0.5 to 0.9 upward in the footwall CT, decreases sharplyinto the upper footwall sediment package, and thenincreases toward the massive sulfides, Similarly,IV(K +Na) increases ftomtheleast-alteredCTto the WI,decreases in sample 012, but otherwise remains elevated.TheCIA [AlzO/(AlzOg +NazO+ KzO, molar] increase,sprogressively from0.55 fleas-altered) to 1 artheorehorizon,which indicates a leaching of alkali elements. Like thealteration index, (Fe + Mg/(K + Na) increases p'rogressivelytoward the ore horizon, from values <1 to almost 100,indicative of increasing chlorite at the expense of micaand feldspars. The Fe/lVIn value consistently increasesfrom near 10 to >200 near the ore horizon, similar toWhitehead's (1973) observations. The Mg/Ca valueincreases irregularly from about 3 in the least-alteredrocks to nearly 20 in the altered rocks.

Overall, the footwall alteration described herein andby Wahl (1978) is less intense than that found at the A,C, and D zones. The less intense stringer-sulfide miner-alizatiorl the continuity of cbloritic alteration in the fmtwall,and the general absence of silicic near-vent alteration, asat Brunswick No . 12, ndicate thatthe deposit is extemelyattenuale4 as inferredby deRao etaL (1991) andMoreton(1994). However, it is still considered a proximal-auto-chthonous deposit (Jambor 199) on the basis of the intensityof chloritization and theCu-richbase to much of the deposir

856 TIIE CANADIAN MINERALOGIST

H anging -w all ( HW ) alte ration

The hanging-wall unit is texturally homogeneous,

chessboard albite is partially replaced by turbid alkalifeldspar and vice versa,

The QCT and QFCT have identical immobile-elementalthough within 50 m of the sulfide contac! alteration has contents and ratios, such as ZrffiOz, MAi, and Lalluremoved the alkali feldspar from the QFCT. There is a (Fig. 9b). As in the footwall, there is a considerabletransition zone about 5 m wide characterized by the decrease in Nq K Ca, Rb, and Sr @g. 9a) toward the oredecreasing size of whitish alkali feldspar. In contrast to horizono consistent with chloritization. Fe-Mn-Mg-Stle footwall, quartz-mica pseudomorphs are absent; covariations (Ftg. 9a) indicate that the Fe in the altered

TABLE I. COMPOSITIONAL AVERAGES OF VARIOUS ROCKUNTTSIN DRILLHOLEHSB34O9,

HEATH STEELE BZONE VMS DEPOSIT,NEWBRI.NSWICK

Sampls LFWb FWCT UFW99 5

l s X L e E l s E L C5.4 73.2 3.0 61.0 14.5 73.4 1.03 61.5 66.20.08 0.31 0.15 0.55 0.11 0.25 0.O2 1.12 0.683.07 13.1 0.88 9.35 2.76 13.03 0.s3 17.7 13.90.84 3.87 1.88 20.16 11.30 2.55 1.20 7.96 9.560.01 0.12 0.07 0.07 0.(B 0.03 0.o2 0.08 0.060.19 1.m 0.49 2.24 1.11 1.52 0.61 1.93 1.720.10 0.41 0.39 0.18 0.08 0.41 0.16 0.28 0.290.54 0.89 0.88 0.47 0.97 1.31 1.14 1.75 0.26o.71 4.51 1.35 0.75 0.95 s.Oo 0.92 3.3:l 3.320.04 0.13 0.0'r 0.09 0.04 0.13 0.01 0.08 0.140.5 1.7 0.5 3.4 1.0 1.35 0.62 3.1 3.00.01 0.10 0.14 0.03 0.02 0.31 0.36 0.08 0.120.16 0.24 0.31 4.6 5.3 0.05 0.07 0.86 1.09

r{wcT LFW8 UFW8I bulk' buk*n

wL%stqrqAlro.FqonMnOMsoCaONqolGoPrO,l-tO+co,sppmAS o.25As 20Au ppb 1.8B 4 0Ba 496B€ 5.7Bl 4.3Br 1.7Co 19Cr 80Cs 4.7Cu 4SHf 4.7Hg 2.5u 1 7Nb 17Nf 44Pb 2.OPd o.7P t 5Rb 160sb 0.7Sc 19.4Sn 8.7Sr 97Th 14.0u 4.5v 134w 3.1Y 3 77i 1?2Zt 180La 4.7Ce 94.3Nd 42.0Sm 8.1Eu 1.73Tb 1.1Yb 3.4Lu 0.50

3x

58.61.U

19.738.890.072.25o.252.103.s80.103.30.051.00

0.@ 0.31 0.18 1.42 8 7 9 1 5 71.9 2.3 4.4 ',18.7

7 8 5 575 659 97 1U0.6 3.0 0.7 3.24.9 3.2 2.3 1030.6 2.0 0.5 2.O2 3.5 2.9 15:l

18 10 3.3 271.2 2.7 0.9 1.2

12 17 21 13430.6 4.O 1.3 4.60.0 3.9 3.0 7.02 7 3 50.6 11 5 12.68 6 2 U . 41.7 U 59 13.40.3 2.6 1.9 1.40 1 1 5 7 . 4

3:t 182 2, 37o.2 0.52 0.39 4.44.3 5.1 4.6 9.46.4 13 5 93

2. 56 21 212.6 10.4 1.2 7.6'1.'l 4.2 0.5 2.2

24 25 24 551.4 2.1 1.0 2.62 3 4 5 2 7 . 4

14 504 807 96a 130 & 19253.9 8.E 0.5 35.212.7 4A.6 11.9 68.85.2 ?2.7 s.2 31.41.3 4.8 1.0 6.40.31 0.68 0.31 3.120.1 0.8 0.1 0.70.3 2.9 0.5 2.50.00 0.37 0.o7 0.37

0.5 0.4It o.42 0.4 <0.1137 'l.4 0.7 7.1 38.018.8 0.E 0.5 <2 70 8 5 1 9 1 3

179 1U7 1070 456 341.1 3.1 0.6 4 3

109 2.7 1.8 0.8 4.80 1 . 6 0 . 5 4 3

1 4 2 2 2 1 8 3 81 8 8 2 8 / . 3 81.0 2.8 1.5 4 3

1160 I 15 52 7l2.3 4.1 0.35 7.3 7.66.9 9.1 10.9 <5 70 6 . 8 3 . 3 7 49.0 13.9 5.8 20 109.2 3.6 0.9 39 13

16.6 371 711 2 21.1 0.5 0 -3 . 4 5 0

43 179 15 159 1555.0 3.5 6.0 0.6 1.93.5 4.1 0.2 16 10

158 '12 5 13 271 7 6 1 ? 2 9 3 2 92.2 13.5 0.5 16.0 13.00.8 4.A 0.3 4.9 4.4

20 15 1 130 671 . ' t 2 1 2 3

12.0 43 2 43 3760 592 987 149 73886 16 6 257 21310.2 28.1 1.6 50.5 3!t.919.6 tt.1 2.9 105 76.010.1 26.1 1.4 rc.7 33.12.0 5.6 0.3 9.2 7.31.91 o.txi 0.26 1.49 2.05o.2 0.89 0.13 1.4 1.',|0.9 3.2 0.'17 4.o 3.50.15 0.49 0.03 0.59 0.49

HEATTT STEELB B ZONE DEPOSIT, NEW BRUNSWICK

Notres: LFWs: losrerf@tvruI sstinerrs,UFWs: r4perfotwall sedimentg FWCT: footwall crystalbfl, TIWCT: hmging-wall crystal ffi.FerO" is the ertpression of total irm r mem, ls: onestandard deviation, n: number of vmFles aoal:zed bulk*: 8 smples at 50 m intervals (10 cmlog), bulk**: 6 smFles at 50 m int€rvals (10 on long). -: uo malysis. The rmks were malyzeda X-Ray Assay Iabortoies using a multi-element pankage. Concenfados of the majcn eleins'ltsmd Bq Nb, Rb, Sr, Y, md Zr were determined by X-Ray Fluorescence Specno*opy ffiF) onfirsed disks. The ccncenraim of Sn v/Bs det€roined by pre*sed powder )tRF, that of Au, by fireasssyDirect Coupled Plasma, and that of Li, Be, B, V, Co, Ni Cr\ Za Ge, Mo, Ag C4 Pb, mdBi, by in<hrctively coupled emission spectroscopy (ICP-ES). The concentraticn of Sc, Cr, Sb, Cs,

REE, f4 Ta, W ft, and U was determined by insrumental neuron activation analysis (INAA).

The proportion ofFeO was deternined by aomodum metBvanadate titrarion, S, by the l-ecomethod, CO, by the coulometsy methd, and tlO., by the Penfield method The accwacy of themalyse was determined Am m irt€rDal $md6d (94-RI{Y, L€nu 1995a). The XRFdeterninedmajor elemerrts ae gpically wiein 2% ofthe recomended value, and conceffiations of the traceelemeds Q(RF) are within 5% ofthe accepted values, except for CaO end Sr, which are presentat loq' ccnc€Dradorc The remaining taoe elenreots re within 15% of the acceptd values, except

for Sn, Bi, Ag Zq srd Ni, whioh are below their detection limit in the stmclard for the malyticalmethod used

857

Et+rq()

0

1 0 0

200

3 0 0

400

500

600

700

8 0 0

9 0 00 . 2 0 . 6 1 . 0

5'o9 o +

Fe/ Mn/(Fe+Mg+Mn) (Fe+Mg+Mn)

ZnO (wt.Vo) BaO (wt.%)

s s: asTi02

s { s

(wt.%)s'.=

s \ s s9ss

s \

Frc. 16. Mineral compositional profiles along DDH HSB3z109 illusrating Fe/(Fe + Mg + Mn), Mn/(Fe + Mg + Mn), TiOz, ZnO,and BaO contents of chlorite (O), phengite (A), biotite (tr), and gamet (Q), as determined from resule of electron-microprobeanalyses (Table 2).

hanging-wall is mainly present as pyrite, with less in thechlorite [Fe/(Fe + Mg) < 0.5]. Barium contents in tlealtered CT are locally 2 to 5 times background,reflecting Ba-bearing phengitic muscovite (samples18, L9, 20). Levels of Co, Cu, Zn, Pbo Sb, and Hgincrease with sulfur toward the massive sulfides. butCu/(Cu + Pb + Zn) decreases toward the ore zone(Frg. 9b).There is a slight increase in the Eu/Eu* value

(0.4 to l) toward the ore horizon (Ftg. 9b). The ratrotrV(K + Na) increasas from the least-altered to most-alteredrocks @g. 9b). The ratio (Fe + Mg)/(K + Na) increasesfrom least-altered (0.3) toward the ore horizon @g. 9b).The ratio Mg/Ca increases five-fold toward the ore zone(Fig. 9b). All the chemical changes observed are consistentwith hydrolysis offeldspar and an increasing proportionof chlorite and pyrite to white mica toward the ore zone.

J". L sed".

N ! N V A

,FW tuff;

r i . r \ r i / / \ , i.il ),,.11 i,,'- \ : \ \ J \ .

:1j ),:1i i-:i l i , . ; ( , , . ; ,: HW tu frlij:l;ijj! \ a \ \ : - \ '

i< ' / \ ; ( ' / \ ; ,;1j ; , ;1j ) , :i < / , \ ; { , , \ ; i

858 THE CANADIAN MINERALOGIST

TABII 2a" SELECTED RESULTS OF ELECTRON-MICROPROBE AI.IALYSES OF CHIORITE IN SAMPLES FROMDRILL HOLE HSB3/+09, HEATH STEET,E B ZONE VMII DEPOSIT, NEW BRUNSWICK

No. 1 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18 19 m 21 2. A ESO, 2,l.rF 2424 24:lE 24.8 n.& 25.51 .@ 21.12 2& z'j.98 24.75 A.@ ZL|O 2&.24.31 24.$ 8.4 21.76 6.52 n.8 25.@ 8.74no, 0.10 0.12 0.01 0.@ 0.$ o.14 0.10 0.08 0.@ 0.@ 0.q, 0.@ o.$ o.12 0.(x) 0.08 0.00 0.10 0.08 0.13 0.10 o.@Ato! 2266 A.42 21.@.21AS 17.8 1527 19.e m.g 21.87 2127 21.N 2U A21 28 n.49 21.51 21.01 20.52 19.S 1923 l9.8[} 19.97Feo 2&16 8.4 E.1S 29.16 28.@ 29.98 31.73 3ZO4 39.@ g.E1 .76 3.&t 38.18 38.Ag g4 27.17 24.@ 16.8 2gl ?2.35 8.8 4.76MnO 025 0.19 0.48 28 O.75 2.8 213 1.@ 05/ 0.16 0.35 026 0.10 0.14 0.13 0.OO 0.52 0.84 020 027 024 0.6?iO 0.06 0.@ 0.@ 0.1 0.01 0.15 0.01 0.1 0.01 0.01 0.03 0.(b 0.01 0.01 0.01 0.12 0.08 0.01 0.01 0.6 0.10 0.02WO 1275 12.4 1236 fA $.% 11.17 9.3O 9.94 4.51 8.98 15..t2 E.4E 520 4.9:l 9.04 14.55 15.87 21.54 19.39 1825 13.90 15.,14CaO 0.@ 0.02 0.@ 0.02 026 0.01 0.01 0.(E 0.01 - 0.0'l 0.07 0.01 0.@ 0.(E - 0.6 0.Ol 0.(B 0.03 0.00 -NarO 0.6 0.@ 0.@ 0.@ 0.07 0.00 0.15 0.@ 0.02 0.05 0.Ol 0.@ 0.@ 0.oB 0.@ 0.@ 0.05 0.01 0.@ 0.@ 0.01 0.q)KrO 0.@ 0.01 0.@ 0.@ 0-6 0.@ 0.15 0.@ 0.00 0.@ - 0.@ 0.(I, 0.@ 0.@ 0.@ 0.@ 0.(x, 0.@ 0.00 0.07 0.@tfro 1t.at f.g f a f.P 1125 11.11 11.01 10.@ to.d} 10.95 11.37 10.@ 10.76 10.75 10.6 11.37 11.49 11.@, 11.67 11.@, 118 11.4F 0.05 - 0.q, 0.02 0.(E 0.(x, 0.05 0.@ 0.08 0.00 0.14 o.dl 0.oo 0.(x) o.Gt 0.@ 0.@ - 0.@ 0.08 0.@ 0.00cf o.cz - - 0.01 0.01 0.01 0.01 0.@ - 0.02 - - 0.01 0.01 0.01 0.14 - 0.01O-F 0.02 - 0.@ 0.01 0.01 0.q, 0.@ 0.OO 0.03 0.q, 0.(E 0.01 0.00 0.@ 0.01 0.00 0.@ - o.(xt 0.@ 0.@ 0.@O=Cl 0.(x) - - 0.@ 0.@ 0.@ 0.@ 0.01 - 0.(X, - - 0.@ - - 0.@ 0.(x! o.(ts - 0.00 - -

stM 9s.8 l@.0 99.s 99.8 1(x).5 99.5 rd)2 9S2 't@.1 1d)2 99.6 @.7 99.8 S9.8 S.3 99.3 S.1 10'1.1 1(n.3 99.3 99.8 1@.4vsf z z zu 2i61 291 zv 278 z@ 2.58 2:62 ?;81 253 247 L6 Z@ 2.61 2.@ 2.n 275 ZU z'73 ZmNAf 1.41 1.4 1.36 1.3n 1.09 123 1.2. 1. 1.4 1. 1.s 1.17 1.53 t.4i 1.32 1.p 1.32 1.A 125 1.16 127 121T s f r e 4 4 4 1 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4uAf 1.43 1./A 1.8 1.U 1.14 1.A 1.12. 128 1.46 1.35 1.31 1.4 1.53 1.51 l.3:i 1.31 1.8 1.19 1.16 1.18 1.2. 124Tl 0.01 0.01 0.@ 0.@ 0.04 0.01 0.01 0.01 0.@ 0.@ 0.@ 0.@ 0.o2 0.01 0.(x, 0.01 0.00 0.01 0.01 0.01 0.01 0.00Fefl Zg 2.51 Z@ Zdl 2.6 272 288 2.95 3.7'i2, 3.18 227 3.10 3.57 3.@ 3.16 2.41 2.18 1.53 1.89 1.94 2.55 2.33Mn& 0.02 o.o2 0.04 o21 o.o? o21 o2o 0.i6 0.05 0.01 o.qr 0.02 0.01 0.01 0.01 0.@ 0.05 0.07 0.@ 0.02 0.02 0.@MS z@, 1.9 1.96 1.81 L10 1.51 1.51 1.63 0.76 1.,16 242 1.$ O.g7 o.@. 1.4 2.31 2.49 3.21 28 Z@. 2.21 2.4ca 0.m 0.@ 0.00 0.@ 0.@ 0.@ 0.00 0.@ 0.@ - 0.00 0.01 0.@ 0.00 0.@ - 0.01 0.@ 0.@ 0.0o 0.01Na 0.01 0.@ 0.@ 0.@ 0.01 0.(x) 0.(E 0.@ 0.0o 0.01 0.@ 0.d, O.@ 0.02 0.(x) 0.00 0.01 0.@ 0.@ 0.00 0.@ 0.@K 0.@ 0.@ 0.@ 0.@ 0.0/t 0.@ 0.02 0.@ 0.00 0.00 - 0.q, 0.d, 0.@ o.cE 0.00 0.00 0.@ o.cD 0.@ 0.01 0.@Oslto 5.99 5.97 5.99 6.(ts 5.s 5.99 5.97 6.@ 5.99 6.02 6.04 6.@ 5.99 5.97 6.@ 6.04 6.02 6.01 6.04 5.98 6.02 5.98o 10 10 10 10 10 10 10 10 10 10 10 l0 10 t0 10 10 10 10 10 10 '10 10oH 7.98 8.@ 8.00 7.S9 7.99 8.@ 7.98 7.99 7.97 7.Q 7.% 7.99 8.00 8.@ 7.99 8.@ 8.m 7.98 e.@ 7.97 8.@ 8.00F 0.02 - 0.(x, 0.01 0.01 0.c[) 0.02 0.@ 0.03 0.@ 0.05 0.01 0.@ 0.00 0.01 0.@ 0.@ 0.@ 0.03 0.@ 0.@ct 0.@ - 0.00 0.@ 0.(x) 0.00 0.01 - 0.@ 0.@ - - 0.(x) 0.00 0.@ - 0.00

NOIES: The proportion of HoO was catoilated fr@ the nh€ral formil& A JEOL-733 $paprobe with 15 kV accelerating voltage md l0 nAbeam current was used with a maximum zt0-secud counting int€rval. Analytical r€s{ts w€re cdrected for mtix e,fects.sing the CITZ\Fprogrsm" The remainder dihe dan is deposited md is available from CISITL

These features of alteration in the hanging wall occuron a much smaller scale than alteration at the ACD Zones(Wahl 1978) and the Brunswick No. 12 deposit (Lentz& fufellow 1994b). The 5Gm-wide alteiation halo maybe considerably attenuated owing to strain within these"weakened" rocks. Hanging-wall alleration at the HeathSteele B Zone could be relaled to continued hydrothermalreaction after the CT was deposited (cf the Millenbachdeposit, Rivedn & Hodgson 1980) orto diagenetic processes.

Svsrr.traarrc V,cRrATroNS rN MTNERAL CorwosrnoNs

Introdaction

The foliated and recrystallized groundmass of all therock types consists of variable proportions of quartz,K-rich white mic4 biotite, stilpnomelane, and garnet, aswell as feldspars in the less-altered samples. Many of thesame minerals occur in the partially altered feldsparcrystals and tensional pull-aparts and were analyzedfor comparison. The chemical compositions of chlorite,white mica, biotite, and garnet were determined(Table 2) . Locally, the very fine grain-size of some phasesprecluded chemical analysis.

FeWpar

Weakly turbid K-feldspar is locally preserved in thefootwall CT. Tartan 6a,'inning, indicative of microcline,is locally evident and seems to replace the opticallyhomogeneous alkali feldspar. At Brunswick No. 6, theoptically homogeneous alkali feldspar is orderedmicrocline (Nelson 1983). In most of the footwall CT,alkali feldspar is pafiiaUy to torally replaced by irregu-larly oriented, twinned albite crystals (Ana3; opticaldetermination) and chlorite showing bluish interferencecolors. In the intensely altered rocks, albite and anyremaining alkali feldspar are pseudomorphically replacedby a quartz - sericite - chlorite assemblage, which formmilky quartz-rich augen. These mi-lky quartz augen areffierentfrom the vitreous high-temp€rafire quartz crystalsanalogous to fhe two varieties ofquartz augen describedat the Brunswick No. 12 deposit Q'entz & Goodfellow1993a).

In the hanging-watl QFCT, the crystals of alkalifeldspar are turbid, with patches of albite (chessboardtexture4 not turbid) locally preserved. Such textures arenormally interpreted to result from albitization ofK-feldspar @aftey 1955, Starkey 1959, Nelson 1983).

HEATI{ STEELE B ZONE DEPOSIT. NEW BRTINSWICK

TABLE 2b. SELECTED RESULTS OF ELECTRON-MICROPROBE ANALYSESOF MUSCOVTTE IN SAMPLES FROM DRILL HOLE B3409,

HEATH STEELE B ZONE VMS DEPOSIT. NEW BRUNSWICK

No. 1 3 4 6 E 10 12 14 15 18 19 20 21 Z3 25slo, 47.64 45.73 47.80 47.80 50.60 47.@ 47.2A 6.@ 45.28 49.2A 47.59 47.98 49.26 8.14 49.43nO, 0.30 0.27 O.8 O2S 024 0.(X, O.41 On 0.02 0.33 0.39 0.81 0.61 o..lE 0.50Alro3 34.90 U.27 31.@ A.88 29.00 2A.X3 &.74 3524 35.37 30.31 29.78 .91 27.43 @.13 28.a2F%O. - 0.@ 0.@ 0.OO 0.OO - 0.(n - 0.00 0.00 0.@ - 0.00 0.0() -FeO 2.O7 1.8 2.17 3.W 3.31 5.18 4.$ 2.43 3.23 3.(E 3.23 4.O1 3.39 3.21 273MnO 0.03 0.00 0.C[, 0.18 0.12 0.09 0.01 0.(b 0.02 0.05 0.OO 0.06 0.00 0.00 0.00MSO 1.25 1.@ 1.73 2.73 2.01 2.O9 1.2. O.* 0.16 227 2.'19 4.61 3.66 2.10 233BaO O.A O27 0.@ 0.@ 021 0.39 0.@ 0.13 0.01 0.62 O.A7 O.41 0.11 0.00 0.03CaO 0.02 0.01 0.06 0.(E - 0.01 0.02 0.01 0.01 0.04 0.01 - 0.04N%O 0.38 O.47 0.n O27 O2O 0.00 0.27 0.4 O.74 0.3tt 0.27 0.16 0.12 0.1E 0.17l(ro 9.68 9.27 10.49 9.27 10.13 10.94 10.61 9.8S, 9.71 10.10 10.,13 10.76 10..72 'lO.U 11.OsfLo 4.52 4.9 4.W 4.45 4.49 4.4O 4.41 4.@ 4.8 4.n 4.8 4.41 4.8 4.45 4.47F 0.00 0.28 o.(xt 0.@ 0.@ 0.@ 0.(x, 0.(X) 0.05 0.38 0.30 0.00 0.c0 0.04 0.00cl - 0.01 - 0.15 0.01 - 0.11 - 0.01 . 0.01O=F 0.@ 0.12 0.@ 0.00 0.@ 0.@ 0.@ 0.@ 0.02 0.16 0.13 0.00 0.@ 0.02 0.00()=cl - 0.@ - 0.09 0.(x) - o.tz - 0.@ - 0.00suM101.1 97.8 99.1 98.6 1@.4 9S.0 e9.5 99.6 99.0 1q).9 992 1@2 99.8 99.7 99.6vst 6.2s 621 6.42 6.8 6.73 6.55 6.42 6.15 6.1i 6.ss 6./to 6.o1 6.6/t 6.49 6.65vAf 1.75 1.79 1.8 1.s2 127 1.4s l.sE 1.65 1.E9 1.45 .1.52 1.49 1.36 1.51 1.35T s l b S 8 8 I 8 I I I I 8 8 I I I I'Af 3.64 3.@ 3.118 3.26 327 3.14 3.U 3.71 3.74 3.n 3.25 2.81 3.@ 327 322vTi 0.0:' 0.G} 0.@ o.@ o.o2 o.@ o.o4 o.o3 o.@ o.@ o.o4 o.o8 0.06 o.o5 o.osFe* - 0.00 o.o0 0.q, o.oo - o.oo - 0.@ 0.@ 0.@ - 0.00 0.00 -F& 0.23 o.2. o.24 o.41 0.37 0.60 o.5o o.27 0.36 0.34 0.37 0.4{t o.3g 0.36 0.31Mn'z 0.@ 0.00 0.@ o.o2 o.o1 o.o1 o.oo o.oo o.ol o.oo o.ol o.qr o.ol o.@ o.ooMg 024 O.21 0.35 0.55 O.4O 0./€ O25 O.11 0.03 0.45 0.44 0.93 o.74 O.42 O.47Osfte 4.15 4.'15 41O 4.26 4.07 4j7 4.12 412 4.14 4.12 4.11 4.2A 4lA 4.11 4.MBa 0.01 0.01 0.@ 0.00 0.01 0.02 0.00 0.01 0.00 o.Gl 0.05 0.02 0.01 0.00 0.00Ca 0.00 0.@ - 0.01 0.01 0.@ 0.@ 0.00 0.(D - 0.01 0.00 - 0.01Na 0.10 0.12 0.05 0.07 0.05 0.@ 0.07 0.'14 0.19 0.08 0.07 0.04 0.G) 0.05 0.04K 1.62. 1.60 1.80 1.@ 1.72 1.C2 1.U 1.69 1.67 1.71 1.A1 1.&l 1.84 1.88 1.90Asne 1.73 1.74 1.85 1.68 1.79 1.94 1.91 1.U 1.gl '1.8:' 1.9:l l.gE| 1.68 1.9:i 1.95o 20 m 20 m 20 20 20 20 20 20 20 20 20 20 20oH 4.CrO 3.88 4.00 3.S 4.00 4.00 3.97 4.@ 3.98 3.84 3.87 4.00 4.00 3.98 4.00F 0.00 0.12 0.00 0.q) 0.00 0.@ 0.@ 0.00 0.02 0.16 0.13 0.00 0.(E 0.o2 0.00

859

cl - 0.oo - 0.G| 0.@ - 0.(E

Notes: The prroportion of FIrO was oalorlated fiom the mh€ral forula- See Table 2a for malyticalmethd. The remainder of fte rlat' is &posited md is available fi'm CIflTI.

Farther into the hanging wall, Carlsbad-twinnedchessboard albite (discontinuous a1611s lwlnning) isconunon, with networks of turbid alkali feldsparreplacing plagioclase phenoclasts. The hydrothermalreplacement of sodic ptagioclase by nrbid alkali feldsparcan occru at low temperatures in the presence of a fluidhaving a high Na+/K+ (30), similar to modem seawater${tnhd et al. 1980); thus plagioclase was probably theliquidus feldspar. This conclusion contrasts with mostother cases inferred for the Nepisiguit Falls Fonnation,butplagioclase phenocrysts have been described from theClearwaterStream Fonnation to the southwest @ffe 1995);therefore, sodic rhyodacite (ow-K) may have been presenl

Chlorite

The color of the rocks in drill core reflects theproportion and iron content of chlorite. The most Fe-richchlorite-enriched sedimentary rocks (very dark green inhand specimen) occur in the immediate footwall to themassive sulfides. The interference color of the chlorite

ranges from berlin blue to gold-brown, and is related toFe:Mg value (Kranidiotis & MacLean 1987). Thecompositions @gs. 16, 17) rangefromferroan clinocbloreto chamosite, using the nomenclature of Bayliss(1975) (see also Sutherland196T, Lewczuk 1990, Luffet al. L992,LE\tz & Goodfellow 1993a).

At constant metamorphic grade, the phyllosilicateassemblage reflects the variation in bulk composition,although high sulfide content increases theFe/@e + Mg) value of the whole rock relative to tleratio in minerals (Ftg. l8).

The variation of NSi in chlorite is a function ofcoupled Tschermak substitution (Mz+ + Si++ = vIAl3+ +rvAl3+). The Al content of chlorite is also stronglyaffected by the availability ofAl and degree of silicasaturation of the rock. Therefore, covariation of Fe andAl probably reflects the variation in silica content(NSi < 2.6 atoms per formula unit, Fig. 17), proximityto pyrophyllite (kyanite) saturation in the most-alteredrocks, and the crystal-chemical effects mentioned above.Lentz & Goodfellow (I993a\ also noted that the

860 THE CANADIAN MINERALOGIST

TABLE 2c. SELECTED RESULTS oF ELECTRON-MICROPROBE ANALYSES OF BIOTITE IN SAMPLES

FROMDRILLHOLEB34O9,HEATH STEEI^E B ZONE VMS DEPOSIT, NEW BRUNSWICK

No .567891020212224

sio2 35.4 35.6 U.2 35.s 39.1 35.8 38.2 35.4 37.3 37.5Tio, 0.78 1.86 1.73 0.62 0.19 0.39 1.39 1.71 1.53 1.62Af2o3 1 8.81 16.62 17 .7 I 17 .94 17 .62 18.22 16.40 1 6.83 1 6. 1 9 1 6.09CrrO. - - 0.06F eO 21 .82 21 .'l 1 23.94 21 .'l I 2,.20 25.07 1 4.41 21 .8O 17 .45 20.7 3MnO 1.30 1.21 1.01 1.M 1.6 0.52 0.40 0.12 0.14 0.00MgO 8.23 9.4710.28 9.05 8.10 8.4415.19 9.7712.6910.92ZnO 0.005 0.05 0.005 0.005 0.01 0.005 0.005 0.11 0.09 0.12BaO 0.0050.0050.00 0.00 0.00 0.17 0.00 0.00 0.00 0.18Cao 0.03 0.01 0.06 0.02 0.07 0.O4 0.02 - 0.01 0.03NarO 0.12 0.00 0.09 0.19 0.17 0.06 0.08 0.06 0.03 0.07KrO 9.27 8.63 6.28 9.25 6.81 8.20 9.94 9.36 9.78 9.65HrO 3.71 3.67 3.71 3.67 3.76 3.69 4.05 3.79 3.73 3.56F O.41 0.50 0.41 0.46 0.48 0.39 0.00 0.24 0.55 0.79cl - o.o2 0.02 0.03 0.02 0.02' 0.01 0.01 - 0.01O=F 0.17 O.21 O.17 019 0.20 0.16 0.00 0.10 0.23 0.33O=Cl - 0.00 0.00 0.01 0.00 0.00 0.00 0.00 - 0.00suM99.7 98.5 99.3 99.2 99.5100.8100.1 99.0 99.2100.9

vsi 5.45 5.s3 s.2T s.49 5.90 5.48 5.64 5.49 5.64 5.66rvAt z.ss z.4T 2.Tg 2.s1 2.10 2.52 2.36 2.51 2.36 2.uTs i t eS 8 I 8 I 8 8 I I 8vfAf 0.86 0.57 0.50 0.26 1.03 0.76 0.50 0.56 0.53 0.52T1 0.09 0.2. 0.20 0.o7 a.o2 0.04 0.15 0.20 0.17 0.18Fee 0.00 0.00 0.00 0.00Feb 2.81 2.74 3.08 2.74 2.80 3.21 1.78 2.A2 2.21 2.61Mne 0.17 0.16 0.13 0.19 0.14 0.07 0.05 0.02 0.02 0.00Mg 1.89 2.19 236 2.Og 1.82 1.93 3.34 2.25 2.6 2.45Oslte 5.82 5.88 6.28 5.85 5.82 6.01 5.82 5.85 5.79 5.77Ba 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.01Ca 0.00 0.00 0.01 0.00 0.01 0.01 0.00 - 0.00 0.00Na 0.04 0.00 0.03 0.06 0.05 0.02 0.02 0.02 0.01 0.02K 1.82 1.71 1.23 1.83 1.31 1.60 1.87 1.85 1.89 1.86Asite 1.86 1.71 1.27 1.89 1.37 1.64 1.90 1.87 1.90 1.89o 20 20 20 20 20 20 20 20 20 20oH 3.80 3.75 3.80 3.77 3.77 3.81 4.00 3.88 3.74 3.62F 0.20 0.25 0.20 0.23 0.23 0.19 0.00 0.12 0.26 0.38cl - 0.01 0.01 0.01 0.01 0.01 0.00 0.00 - 0.00

Notes: The proportion of IlO was calculated from the mineral formula. SeeTable2a for analytical method. The remaind€r ofthe data is deposited and isavailable from CISTI (see text for dctails). As in Tables 2a and 2b, results ofthe analyses are quoted in wt.%.

HEATTI STEELE B ZONEDEPOSTT. NEWBRI]NSWICK 861

CD=+oIL

blr

+ Hanglngo J ' Footwall

t

: t t .

tt:. + '

a

a

+ ++

proportion of rvSi decreases and that of total Alincreases with increasing alteration at BrunswickNo. 12. Crystal-chemical effects related to Fe and Mgcontents control the NAI content of chlorite (Kranidiotis& Maclean 1987). However, experimental data(Saccocia & Seyfried 1994) show that the wAI contentof chlorite is insensitive to temperature of formation.

(llsrite in thshangrng wall has alowerFd(Fe+ Mg)value than that in the foofwall. In both areas, chloritebecomes richer in Fe toward the ore horizon, althoughthe trend is more pronounced in the footwall (Figs. 16,L7 ,Table2).T\ebackground Fe/(Fe + Mg + IvIn) in cbloriteincreases near the exhalite, but decreases at the exhalitecontact, where disseminated sulfides are abundanL Therelatively low Fe(Fe + Mg) value of chlorite near theexhalite horizon (samples 16 and 17) is probably due tothe higherftHzS) (Bryndzia & Scos 1987), resultine insulfide formation at the expense of ferrous iron incblorite (see below).

The Mn/(Fe + Mg + Mn) value of cblorite (Ftg. 16)is low in the lower quartzose sedimentary package, butincreases ten-fold in the CT unit of the footwall, anddecreases to <O.01 in the upper footwall. In general, theMn contents of chlorite, sericite and biotite reflectwhole-rock Mn contents. The spessartine gamet (sample006) in the footwall CT with the highest Mn contentformed at the expense of Mn in some of the cblorite andpossibly carbonates. The low-T enrichment of Mn inthe least-altered rocks is consistent with the decreasingsolubility of Mn relative to Fe with increasing tempera-ture, based on fluid/chlorite distribution coefficients(Sverjensky 1985).

Inthefoorwall, Zn contents of cblorite are also irregular(40 to 1200 ppm), although the highest values occur insome of the least-altered rocks (Fig. 16). This parern mayreflectthe removal of Zn by leaching of altered rocks andits partition into sulfides at high sulfur fugacitias. Thisis consistent with thermodynamic calculations forcoexisting fluid and chlorite (Sverjensky 1985), whichsuggests thatzn partitions into a solution relative to Feand Mg. At the Mount Lyell deposit, Hendry (1981)found that the Zn content ofchlorite is also variable, butwith a greater range, up to 50C10 ppm. Mottl (1983) found187 to 2-62 ppmZn in cblorite from the mid-ocean ridges.

White mica

The white mica ranges from a muscovitic to aphengitic composition (Fig. 19, Table 2b). The mostphengitic compositions are the most Mg-rich, indicativeof the coupled Tschermak substitution (Mz+ + Si++ =vIAl3+ + IvAl3+, Fig. 20), which favors the incorporationofMgoverFe (rntz & Goodfellow 1993a).Withincreasingalteration, there is an increase inAl toward end-membermuscovite compositions (samples 011 to 015), as alsodocumented at Brunswick No. 12 (Irntz & Goodfellow193a) andseveral othermassive sulfide deposits (tlendry1981, Urabe et al. 1983, Scbmidt 1988). In general, the

311

lvsl4"

Hc. 17. rvsi4+ versas Fe/@e + Mg) in chlorite, illustrating thechlorite compositions in the HW and FW units Qable2a),

0.5 0.8 0,7 0.8Fe(Fe+Mg) whoto.ock

0 0.05 0.1 0.15 02 0.25MnO (rrL%) e661s 661

FIc. 18. Whole-rock yersus mineral a) Fe/(Fe + Mg) weightruio and b) MnO contents.

1 .0

E 0.eo

€ o.sE

I o.'+te o'o

,P 0'6

0.4

o

2 2E

:S.l

E, 1otr.

o

a)

og

t8

$c

.lF If:^$D

o oA A

oo

oo o o

oE

n oE

oo

Eo o

b)

E

o

A

o

o Eg 0 8 ^ : g a a A

vAt+uAl

862 THE CANADIAN MINERALOGIST

F\c.lg.vrMz+ _(IVAI + vIAl) _rySi niangulardiagram (Monio& Robert 1986) illustrating the composition of white micasfrom the FW and HW (Table 2b). Eas: eastonite, PhI:phlogopite, Ms: muscovite, Cel: celadonite.

Fe/(Fe + Mg + Mn) values of phengitic mica mimicthe whole-rock compositions (Frg. 16). The Mn/(Fe +Mg + Mn) value of muscovite is much less regular. TiOzcontents typically range ftom 0.1 to I wt.Vo (Fig. 16).The highest Ti values coincide with the highest Sicontents, which implies a relationship similar tophengite substitutions (wM2+ + \nTi4! = / vr[13+'

Guidotti 1984). In the footwall, Ba contents are very

+ Hanging vrallr Footwall

+I

+t +

a

. l t t t + '

a ol o .

a aI

lvsl4+

Fro.20. Plot of EMz+ versustvsi4+ of white micas illustratinggeneral emichment of divalent cations (Fe, Mg, Mn) withIvSi4+ contents that are relatetl to Tschermak substitution.

Eas

+ Hanglng urall. Footrvall

aa

ot

t

t t '++r

Phlogopfte

Fe(Fe+Mg)1.0Ann

Frc. 21. Plot of Fel@e + lNdg) versus \4A13+ illustrating thecomposition of biotite from the FW and Hw (fable 2c).Ann: annite, Phl: phlogopite, Sid: siderophyllite, Eas:eastonite.

irregular; values up to 0.5 wt.Vo BaO are common, butBa contents decrease toward the ore horizon. Thehighest Ba contents of phengitic mica occur in thealtered QCT of the hanging wall (0.7 to 0.9 wt.Vo),but the level of Ba decreases to va-lues less than0.I wt.Vo BaO further into the hanging wall (Fig. 16).

The IvSi content of phengite coexisting withK-feldspar, quartz, and phlogopite [X(Mg) = 0.6] rangesbetween 3.25 and 3.32 atoms per formula unit, whichcorresponds to pressures of about 500 to 700 MPa (5 to7 kbar), based on the phengite geobarometer (Massonne& Schreyer 1987). Sphalerite from the Heath Steeledeposits contains 13.7 to l4.l mole 7a FeS (Sutherland& Halls 1969), coexiss with a pyrrhotite-pyrite assemblage,and indicates comparable pressures of approximately600 MPa at an inferred temperature of 450"C, using theToulrnin et al. (1991) calibration.

Biotite

Biotite is locally present as alate to postJ2 metamorphicphase. The Fe/(Fe + Mg) value of biotite ranges between0.35 and 0.65, with a considerable siderophyllitecomponentin the Fe-rich member (Fig.21, Table 2c). TheFe-Mg-Al contents reflect the whole-rock compositionand the assemblage in which it formed. Similarly,Mn/(Fe + Mg + Mn) values are generally comparable tothose in chlorite. The Ti contents of biotite range between0.5 and 2wt%oTlOz, and are highest in biotite with tlelowest Fe/(Fe + Mg + Mn) value or highest Si content(Frg. 16). The extent of Ti incorporation is a function ofcomposition, but also of metamorphic grade and whethera phase such as titanite orrutile is present (Guidoui 1984,

std

+

= 1.05

0.0 L0.0

Pht

L ''o,i|

I*ntz 1994). The inverse relationship betwe€n Ti andsiderophyllite component implies that the Ti-Tschermaksubstitution (M2+ + uTi+. = 2 vIAl3+) controlled theTi contents of the biotite. T\e Zn content of biotitevaries greatly (40 to 1000 ppm), and is highest in theleast-altered rocks, which suggests that its abundanceis affected by leaching and sulfur fugacity.

Garnet

Although rare, garnet forms small euhedralporphyroblasts that overgrow the S1S2 fabric. It occursin rocks with a relatively high Mn content, particularlywithin the footwall QFCT. The garnet is spessartine-rich,with less than 1.5Vo almandine component (Fig. 16).Spessartine-rich gamet in a quartz - albite - muscovite- biotite assemblage generally forms at temperaturesgreater than 400'C depending on bulk composition(cl Symmes & Ferry 1992).The X(Mn)i1*k is 0.08 forsample 006 [X(Mn) = Mn/(Fe + Mg + Mn)]. At 5C]0 MPa(5 kbar), such compositions can form garnet at tempera-tures slightly less than 4O0'C.T\e2L mol.7o almandinecomponent in spessartine and the Fe(Fe + Mn) value ofcoexisting chlorite (0.98), which is high, are consistentwith atemperature of490'C (Krez 1993), although450"Cis more reasonable considering the absence of amphiboleand the low Ca content ofplagioclase.

Ivrrx.-MnsmerEqumnra

Innoduction

The compositions described above were generallydetermined on assemblages of coexisting minerals.Although the minerals were usually in proximity, i.e.,within I mnL they wererarely in mutual contacL However,most minerals have compositions indicative of equilibriumon the scale 6f 4 rhin section.

Element distributions are used to describe thesesystems in more detail. For major elements, elementratios, e.g.o Fe/(Fe + Mg), are used to compensate for theconstant-srm effect, whereas this is not required for traceelements. However, if solid-solution effects change themakeup of the exchange site in the mineral, then the traceelement should be normalized to the exchanging cationto define coherent distributions (e.9., Rb/K). The actualdistribution is described by the distribution coefficient,Kp (Kretz I 96 I ). For major elements, the Kp is (eq. 1)

[Fe] KoPuus = [XF"B(l -Xr.re)]/[(l -XFeBt)XFelIs] [1]where [Fe] = !e(pg + Mg) for Kp, and Xn" = Fe/(Fe + Mg).

1Xs slshange of trace elements with various cations isbest expressed as a simple ratio (eq. 2).

l7_nlKr3ttM"=ZnBVZnME l2lThe distribution of major-, minel-, and trace-elementcomponents describes the system in detail and assesses

HEATH STEELE B ZONEDEPOSIT. NEWBRUNSWICK

0.7

u.o

0

o.4

the extent ofequilibrium (or departures from it) betweenphases, and thus better defines fhe controls on alteration.

Chlarite -mascovite

The [Fe] K2ct'ulvts "u1o"s

generally vary between 1.5and I .(Frg. ?-?a). These values are lower tban those observedat Brunswick No. 12 ([Fe] Kpffi = 1.68; l*ntz &Goodfellow 1993a) and Kidd Creek ([FeJ KrrMs in theinterval 2.0 ta 2.5; Csmeron et aI. 1993), but similal 1ethose around the Mount Lyell stockwork Cu deposit in

a)

l l

iI,o.4 0.5 0.6 0.7 0.8 0.9

Fer(FelMg) Chlorlte

1.0

oE 0.8

oo o.7E

F o u-o= o.5d

!t

1.0

@

oo6-+ott

tstI.

b)

4

o.7

€oEooE-+o

tt

?tt

0.3 0.4 0.s (16 0.7 0.8 0.9Fsr(FelMg) Chlorlte

c)

i .

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Fe/(Fe+Mg) Blotlte

Ftc. 22. Fe(Fe + Mg) distribution [Fe] between coexisting a)white nica and chlorite, b) biotite and chlorite, and c) whitemica and biotite.

n 4

o.4

0.3

8g THE CANADIAN MINERALOGIST

Tasmania (Hendry 1981). The distribution of Fe(Fe +Mg) between these phase,s is partially a function of theirrespective Al content at greenschist grade (Kawachi eral.1983), although there are no overlapping tie-lines.

Mn is enriched in chlorite relative to muscovite(Ko= l5), although the Kp increases for muscovitesamples with very low Mn contents. This may be due tothe local formation of biotite where the most closelyassociated chlorite may not have been involved in thebiotite-forming reaction.

Chlorite - biotite

The [Fe] Koftvst value is very regular and close tounity (Fig. 22b), consistent with equilib'rium Commonly,there is a regular relationship for Fe-Mg exchangebetween these minerals (K, = 1) at various metamorphicgrades in meta-igneous rocks lRefaat &Abdallah(1979)and references therein]. However, the [Fe] exchangebetween these minerals is apparently insensitive tometamorphic grade paird (1988) andreferences thereinl.The Mn distribution befween these phases is irregular(0.6 < 6rcunt < 2.9), reflecting spatial sensitivity toexchange.

Biortte - muscovite

The [Fe] KDBlMs varies between I and 1.3 (Fig. 22c).In general, Fe is enriched in muscovite relative to biotiteat higher metamorphic grades (upper amphibolite), andthe Fe-Mg distribution is a function of the Al content ofmuscovite (celadonite) and biotite (siderophyllite)(Rambaldi 1973).The Mn Krntlras is about 4, if theMn-rich biotite samples are not considered. The spatialrelarionships between phases may be critical in evaluating1Un s;ehange. Rambaldi (1973) reported a similar Mndishibution (Ko=3) for these phases. In contrast, Dablet al. (1993) daermned adistribution of l4t 6 forrocksof similar grade. Therefore, it seems that Mn is sensitiveto otler substitutions, particularly Fe-Mg exchange.Thus, the Mn/Fe ratio may be more aprpropriate to calculare}In exchange, considering the chemical affnity of thesetwo elements in the divalent (reduced) state.

TheTiOz clisftibution is about 8 for muscovite samplesand 1.7 for phengite-rich muscovite. The overall abun-dance of Ti in these micas is a function of the presenceof a saturating phase like ilmgniteo titanite, or rutile, aswell as the composition of the respctive micas (Guidotti1984,|*ntz 1994). Siderophyllite-rich biotite is lowerin Ti, but phengitic muscovite is higher, implying thate,ot pled, M2+ + vTl = 2vIAl exchange occurred.

MwnnarEeu-mnre

An AFK diagram illustrates the general equilib'riumexhibited by the various phyllosilicares based on the prallelnature of tie-lines between minerals, and also shows theconsiderable extent ofTschermak substitution (Fig. 23).

An AFM diagram @ig. 2q illustrates the considerablerange in Fe(Fe + Mg) values of cblorite and phengiticmica- Biotite is generally much mote restricted in termsof Fe and Mg than the chlorite and phengitic mica Thereis a considerable increase in the Al content of phengitecoincident with lower Fe/Mg values (eq. 3):

3 KAlzSirAlOto(OlI)z + FesAlSi3AlOls(OHh =Ms Cbt

3 ffieSisAlOro(Oll)z + 7 SiOz + 4 AlzFe-rSLr + 4 HzO [3]Bt ae (Ms,Cbl,Bt)

Chlorite

Fic. 23. AFK riangular diagram tA= (AtzOgn - NazOn - KzOd,F = (FeOn + MgOn + MnOm), K = Kzoml illustrating themineral tie-lines linking cooxisting cblorite (Q), phengrte( ), biotite (r), and gamet (o) (Iable 2). m : molar.

FeQm MgOmFIc. 24. AFM triangular diagram [A = AlzOgm, F = FeOm,

M = MgOnl illustrating the mineral tie-lines linkingcoexis'ng chtorite (O), phengite (A), biotite (r), andgamet (o) (Iable 2).

KF

t-E-ii :

iii;t!

HEATH STEELE B ZONE DEPOSIT. NEq/ BRI,JNSWICK 865

TABLE 3. 6rEO ISOTOPIC COMPOSnONS (!)6)CRYSTALTUFF, IIEATH STEELE BZONE

Saryle WR

7.79.9

- 9.2E.4_ 8.7- 9.1- 9.5- 10.3- 11.3- l l .3

9.7

10.310.4

t2. l

Notes: WR: r*ole-roclq GM: grouodmasi Q,E: quartzphenocrysts. Using a binocular microsco'p€, largo (ctear)ptm:g cfqua2 md groundmass were separared by handafter fine cnrshing. Ths quartz phenocrysts wero more tbmE(F/o pre. Tb oxygen isctopic co'4ositions were dst€rminedat tho Universitd de Mo,ffal. Oxygeo was liberafed byreaction with BrFr (Clayton & Mayeda l%3). All Otb p*mil (!|6o) values are reported relative to dandard mean oceanvnder (SMOW: Craig 196l). NBS.28 quarb was used as minlsnal e[dcd In gpn*a! tho aoalytical procision ir within0.2%,

Biotite was not analyzed in several samples because ofis fine grain-size; it is absent in the intensely chloritizedrocks and the least-altered rmks. The prese,nce of cexisingchlorite and muscovite suggests that the Fe-rich chloriteand end-member muscovite are stable under theseconditions and that the biotite-forming reaction fromthese phases is incongruent.

The biotite - chlorite - muscovite geothermometer-geobarometer of Powell & Evans ( I 983) has been revisedby Bucher-Nurminen (1987). This geothermobarometeris represented by contours of equilibrium coetficient(ln K) of reaction 4:

3 celadonite+ clinochlore = muscovite + 3 pblogopite +

In sample 20, the mole fractions of muscovite (0.65),phlogoprte (0.60), celadonite (0.35), and clinocblore (0.68)with unit activity for K-feldspar and quartz at 450"CQn K= 3.7) correspond to a pressure of metamorphismbetween 350 to 400 MPa (3.5 and 4 kbar) for theassemblage at Heath Steele.

Crystallizafion of low-T metamorphic gamet is mainlya function of the Mn content in aluminous rocks. Theprobable gamet-formingreaction involves cblorite, quatqand aluminous components of various other phases(eq.5; l,aird 1988):

2 MnMgFe3AlSi3AlOro(OH)e + Alzlvlg-lSi-r + 4 SiO2 =chl (lvls,chl,B0 atz

3 (Mno.xFeo.zs)gAlzSigOrz + 8 HzO t5lGrt

This garnet-forming dehydration reaction is intendedto represent the 2I molVo almaldine component inspessartine and corresponds to a temperaore of formationof about 450:C.

Oxvcnq Isorope Svsruuxrcs

The 6180 values ofquare separatas ftom thefootwallCT range from 9.1 tn t0.2Voo, whereas quartz from thehanging-wall CT range ftom 9.7 to lZ.lVoo (lable 3, Fig.25).Tlne latter values approach the heavy 6180 values(l2.lVoo) of the footwall CT ftom the Brunswick No. 12deposit (I-en:tz & Goodfellow 1993a). Quartz separatesfrom the attered rocks ofboth CT packages are isotopicallylighter fhan in the least-altered samples, and may indicateisotopic modification of the quartz during hydrothermalalteration or partial re-equilib'ration during metamo4phism"The difference in the isotopic composition of the quartzphenocrysts from the hanging-wall and footwall CTpackages is consistent with our intelpretation of these asseprate lithological rmits. These ffierences are consistentwith slightly different crustal sources for their respectivemelts, and involvement of isotopically heavy sedimentaryrocks (O'Neil a aJ. 1977,Taylor 1980, Huston er al. 199A.

The whole-rock and groundmass 61EO values ofthefootwall CT range from 7.5 to 9.9Voo. The least-alteredsample has a whole-rock composition of 9 .2%o (lable 3 ,Fig. 25). In the upper-footwall sedimentary package,whole-rock 6180 values increasefrom 6.9 to T.9%ootnwardthe ore horizon, coincident with weak silicification of thechloritic sediments, but decreases to 5.3%o in the intenselychloritized sedimentary rocks directly beneath the deposirla fts hanging wall, thewhole-rock and groundmass 6180values (8.4 to ll.3%o) increase with distance fromminepJization, similarto the trend observed in the quartzseparates (fable 3, Fig.25).

In the least-altered CT from both footwall andhanging-wall sequences, the whole-rock and groundmass6180 values are consistently L to 2%o lighter than thecoexisting quartz separates, which is compatible with

atrGM

9.29.49.1

9.27.58.5

9.09-.2

6.97.37.67.97.86.t5.3

4A5A6A7t9l01 lt2l3t4l5t6t7l8t920z122232425

7 qtartz+4HzO t4l

!- sPd',i

:-f Wtuit-A ! A V A V

r )

i :

;j >' : !

-)' : ,

i1ji'i,i.iii-;. t \ : < t ) . - < t , \ -

i ),;1i f-,;1i:-a \ \ ; \ \ ; \

t . r i < ' | ; ( ' | ;j> , :1 j i , , :1 iZ

H W itiri ;> t z - t > t 2 _ t > t 2 .; \ \ \ - \ \ J -t . r t - < , , , l < t t ;

l . ),,-11 :,,-11:,,r - \ \ e . \ \ j - \

t , \ , - < t , \ : ! t , \ :

l ' : - .11 ' : - .11 ' t; \ \ r - \ \ j - \

ir \ti,: itl,: ;

866

0

100

2ffi

300

4m

500

600

700

E00

qx)

Groundmass orWhole-rock

61to5y6yy (Zrr)

10 11 12

Dttorro* (Z-)

Quartz

100

(Fe+Mg)(Na+K)Index

13L2l0

Ftc. 25. Oxygen isotopic compositions (6180) of goundmass (open slnbols) and whole rock (filled symbols), and quartzseparates expressed relative to Vienna standard mear ocean water (VSMOW). The isotopic values are compared to the(Fe + Mg/(Na + K) alterafion index and illustrated as profiles (Table 3). Symbols: lower sedimentary package (o), FW CT(^), upper sedimentary package (\z), and HW CT (u).

observafions from othervolcanic rocks (taylor 1968, 1980).The isotopic rlats for the whole-rock and groundmass areconsistent with the isotopic differences btwe€n the footwalland hanging wall defined by the quartz separates.

Whole-rock and groundmass 6180 variations are prin-cipally related to mineralogical changes resulting fromhydrothermal alteration and to variation in the isotopiccomposition and [emperature of the fluid involved. Inthe least-altered tuffs, whole-rock SiO2 contents decreaseslightly with decreasing 18O content @g. 26a), exceptfor the extemely chloritized samples. The 6180 decreaseswith KzO, re.flecting increasing degree of cbloritic alteration(Fig. 26b). This also is reflected by a decrease in l8O withincrease inAl2Ozl(NzOz + NazO + Kzo) (Fig. 26c) andincreasing Fe2O3 (total) (Fig. 26d), partly due ro increasingchlorite. These host-rock oxygen isotopic variations aresimilar to those from ottrer altered samples in VMSdeposits hosted by felsic volcanic rocks (e.g., Grenn etaI L983, Bwret & Mackan l99 l,Maclan &Hoy 1991,Hoy 1993, Huston et al. 1995).

6ssuming a fractionation value A"norit"-Hro betweenchlorite and water of about O to -2%oo at an estimatedformation tempemnre of 300 to400"C, respectively (Wenner& Taylor 1971), the 6taQ value ofthe hydrothennal fluidin equilibrium with cblorite in sample 17 should be 5 to7%o, i.e, well above the value for normal seawater. Thishigh valueis close to thatinfenedforthe rock-dominate4ore-forming fluid at Brunswick No. 12 (4.O%o).Nonetheless, these positive values are consistent withmodified seawaler coryositions, and are close to the infenedisotopic compositions of ore-forming fluids ftom someother major VMS deposis (Costa et al. 1 983, Barriga &Kerrich I 9 84, Munh6 e t al. 1986, Macl-earn & Hoy I 99 I,H!*otet aI 195). In contast, in many otherVMS deposits,the inferred values of the fluid are close to or even lessth an Vo o, refT*t'tng more pristine seawater compositions.A different reaction-path is responsible for the isotopicallyheavy ore-forming fluids (Munhlielal 1986), which affectsfluid temperatures, scavenging of metals, and transportwirhin the hydrothermal conduit.

867

r = 0.63

r' = 0.44

6 ttorro* (%o)

5 6 7 8 9 1 0 1 1 l : 2

Dttorro* (%oo)

HypnornrnverArrmeuoN

The least-altered samples of CT have irregular Na,/Kvalues and Mg contents that probably reflect post-depositional devitrification, also observed al BrunswickNo. 12 (Lentz & Goodfellow 1993a). It is uncertainwhether the chessboard albite and alkali feldspar repre-sentprimary phasas orproducts of alteration (ct Munhliet al. 1980).Both K-feldspar replacement of plagioclaseand albitization of plagioclase have been observed inthe outer (montmorillonite zone) around the Kurokodeposits (Green et aL 1983, and references therein), inthe Iberian Pyrite Belt (Munfu1 et al. L98O), and someother ma-ssive sulfide deposits. Although the Na/K value

EO

70

8

7

6

S

4

3

2

1

0

40

30

20

b)

r =O.74

r'= 0.78

s+iF(\

U)

Nv+

N6lz+

n)

at

3.{a

FI

?

s+5Fnt

AN(D

l=

Flc. 26. Whole-rock SiO:, KzO, [A1zO:(AlzO: + NazO + KzO)], and FezOg (total) ver.rrrs 6l8Osuow of goundmass (open symbols)and whole-rock samples (filled symbols) (Iable 3). r is the Pearson Product correlation coefficient, and r'is ttte Spearmaa'sRank correlation coefficient. Symbols as per Fig. 25.

t21t10

50

40

30

1.0

0.9

0.E

0.7

0.6

05

7 E 9 1 0 1 1 1 2

6ttorro* (%o)

'd) j=:;:

^No'o\ t

OoI

"{r

rYtHW

Fw

5 6 7 8 9 1 0 1 1 1 2

Dttor*nor" (/so)

of infiltrating seawater can be expected to shift byexchange with the footwall sequence, albitization usuallypredominates in the Bathurst Camp, at least until, withincreasing alteration, the pH ofthe altering fluid decreasesto stabilize white mica and chlorite (f I.enz & Goodfellow1993a).

The enricbment of Mg in the lower-footwall sedimentmyrocks (distal) and occurrence of Mg-rich phengitic micaand Fe-rich clinochlore probably reflect relatively low-temperatue conditions of formation (<2C0'C), as aresultof distal bntrainment of seawater. The deposition ofMg(OH)2a in clays in felsic volcanicrocks has conributedto a pronounced decrease of the fluid's pH @ischoff eral. L981, Hajash & Chandler 1981, Shiraki et aL 1987).

HEATTI STEELE B ZONE DEPOSIT. NEW BRIJNSS/ICK

s+JB

6lv

r=4.74

r' = -0.75

HW

A r :

ffiffi\

^A

868

Toward the proximal alteration zone at the HeathSteele B zone, there is an increase in chlorite abundancerelative to white mic4 as was also observed at BrunswickNo. 12 (,entz & Goodfellow 1993a). The chlorite com-positions also become moreFe-rich toward thestockworkzone, as atBrunswickNo. 12 (Juras [98l,Lttff et aI 1992,Lenz & fufellow 1993a, 1996, and references therein)aud Half Mile Lake, New Brunswick (Adair 1992,1*tE1996b), as well as many other ma.ssive sulfide deposis(e.9., Roberts & Reardon 1978, Hendry 1981, Mcl-eod& Stanton 1984, Kranidiotis & Macl-ean 1987, Slack &Coad 1989, I-Eitchl992).The chlorite in some depositsdisplays an Mg-enricbment trrid (Urutr, et aL. 1983, Morton& Franktin 1987).

The chlorite-forming reaction at the expense of whitemica is indicative of high Fe aud Mg activities relativeto K activify in the hydrothermal fluid, with the Feend-member reaction given in equation 6.

KzFe2+AleSizAlOzo(OII)+ + 9 FeClzao + 16 HzO -+phengite

Fe2* roAlzSi o{l zO zo(Otl)re + HaSiOagq + 2 KCI aoFe-rich chlorite

+ 16 HCI t6l

This end-member reaction was formula.ted assuming Alimmobility to illustrate the relative behavior of mobilecomponents. The ssns 'mFtion of phengite occurs in anenvironment with a high activity of divalent metals andhigh temperature-dependent solubility of quartz. Thegeneral absence of free quartz in the chloritite impliesSiO2 leaching, although the fluid may be locally SiO2-saturated. However, cbloritization may not necessarilyalways indicate leaching (eq.7) at every srage of thealteration process:

2KAlgSirOro(OH)2 + 15FeCl2 + 3SiOz + 24HzO =Muscovite

3FesAlzSisOro(OH)e + 2KCl + 28HClChlorite l7l

Figure2T illustrates the possible reactions that formcblorite based on an aNa+/aK+ value equal to 10, typicalof an ore-forming fluid originally dominated byseawater. The temperature of the probable end-memberreaction for the more distal alteration should be less than350'C (Fig. 27a) comparel, to the higher-temperatureproximal stockwork alteration (350 to 400'C;Fig. nO. These reactions are near saturation with analnminosilicate, on thebasis of theAl-rich compositionsof the cblorite. The stability of biotite is significantlyreduced for the quartz-undersaturated equilibria;therefore, it rvould not have become a stable primaryhydrothermal alteration phase in the stockworko even ifmuscovite is present,

The inferred moderate- to high-temperature alterationtrend at Heath Steele B zone is illustrated on Fig:lre2:7a

and b, respectively. The distal alteration zone (IV)generally contains ferroan clinochlore [Fe(Fe + Mg) inthe range 0.3 -0.4, Fig. 27 al, qtaftz and feldspar, and thehighest component of phengite in the white mica. In the

3 4l o g a p o + / a r a

2 3 4

l o g a p u + / a " *

F\c. 27. l-o9 o(F&+l &(kI*) versrs log a(Na+)/a(H9 ilustratinehypothetical conditions of hydrothermal alteration at 3@'C(a) and 4CX)'C (b) at 50 MPa (modified from Saccocia &Seyfried 1994) for assemblages found in tle most proximal(tr), the intermediat€ (II!, and the distal (IY) alterationzones observed in this section at the Heath Steele B zone.The stability fields of muscovite and annite were estimatedfor a fluid with an aNa+/aK+ of 10 (Bowers et al. 1984'I

intermediate alteration zone (III), chlorite typically hasan Fe/(Fe + Mg) value of 0.5 to 0.6, and feldspar isabsent @g. 27a). The proximal alteration zones @ andI) are dominated by chamosite [Fe/(Fe + Mg) > 0.7];quartz and muscovite are not always present Gig.z7b).This trend indicates relatively high activity ratios for Fe/Mg, Fe/IL and Fe/Na in the discharging hydrothermalfluid. The increase in Fe/(Fe + Mg) content of chlorite

+

N

-d

bo

ao

+F' t 3

+d

€c l z

@

L) \* 30o"C+QuarE \. -._..-- 50 MPa

"i"*1"** = ro \.Biotite iso,ou*l

-.--..--. o.5 -.----.--...

.------ 0.1.---'----

b)+ QuartzaNa+/aK+ = l0

Cham$itJe

4m"c50MPa(5m bars)

Biotile

.'--.--'. 05..------".-

- . . . - . . . - . - . 0.1

and phengitic mica toward the main hydrothermalconduit at Heath Steele B zone is indicative of hishaF&+laM{+ (cf.Shikazono & Kawahata 1987, Saccdra& Seyfried 1994). For the mole fraction of chamosite(0.8) observed in the stockwork zone, the Fe/Mgsui6 ratiois estimated to have been about 2@ aI4ffJ'C, Le., FTlicalof the buoyant mineralizing fluid whereas the Fe{Vlgqui6approaches 0.5 for the distal alteration (at 300'C) forsalinity conditions of normal seawater (Saccocia &Seyfrid I D4). In general, these estimates indicate mqinalinteraction of low-T shallowly circulating seawaterwithhigh-T modified seawater derived at depth (i.e., fluidmixing) or intermediate compositions of fluid obtainedby altering Mg-rich (seawater-altered) rocks at themargins of the stockworkmne.

CoNcLusrons

This whole-rock geochemical, mineral-chemical, andoxygen isotopic sfidy dscrfoes geological and geochemicalfeatures of primary igneous and sedimentary rocks andthe effecs of hydrothermal alteration ofthoserocks hostingthe Heath Steele B zone deposit. Overallo the principalresults are:

1) Whole-rock composition of the fmtwall md hanging-wall CTpackages are slightly but significantly differen!on the basis ofI/FSE contents and ratios; they, therefore,do not represenl fts sams rrnif.

2) Contents of immslils transition metals of thetwo footwall serlimentary packages are considerablydifferent; the lower package petrographically andcompositionally resembles rocks of the MiramichiGroup, whereas the upper footwall sedimentary package,for the most part, resembles tuffaceous rocks of theNepisiguit Falts Formation.

3) In the altered footwa[ in particular the stockworkzone, there is an increase in the proportion of chlorite andsulfides, including pyrite and pynhotite, at the expenseof groundmass components, feldspar and phyllosilicates,as the ore horizon is approached; these changes also arereflected in the whole-rock chemistry. The overall widthof the recognizable altered zone is relatively small(-200 m), because it has been telescoped owing toextensive D1 transposition. There is also a coosistentincrease in (Fe + Mg/(K + Na) and AlzO/(Al zOt + KzO+ NazO) toward the massive sulfides, which reflectsthe combined effects of alkali leaching and the increasein ratio of chlorite to white mica. These trends arecoincident with an increase in whole-rock S, Cu, Co, As,and Sb, which reflects saturation in sulfides,

4) In this drill-hole section, the hanging-wall altera-tion is less than 50 m wide, with recognizably higher(Fe + Mg)(K + Na), Eu./Eu*, Fe, Mn, Mg, S, and B4Coo Cu, 7n,Pb, Sb, and Hg, and lower AlzO/(AlzOt +K2O + NazO) than rocks further up in the hanging-wallsequence.

5) The low Mn contents in the most-altered footwallrocks are indicative of low/(O2) conditions compared

HEATI{ STEELE B ZONE DEPOSIT. NEW BRUNSWICK 869

to the underlying CT, which probably represents a distalfeature considering the transposition involved. Thehigher Mn contents in the altered CT of the hanging wallare consistent with previous studies at Heath Steele.

Q The mineml assemblages and their relativerefl ect primary and secondary lithogeochemical variationsand upper greenschist-grade met4morphism. On thebasis ofselected mineral equilibri4 these rocks reachedapproximately 450'C and 600 MPa during peakmetamorphism, with the minerals generally showing anequilibrium distribution of major and trace elements.

7) QuarE phenocryst separates from the CT horizonsin the footwall and hanging wall have slightly differenr6180 values. The whole-rock values for least-alteredfootwall and hanging wall are 7.5 to 9.5%o and 10.3 toll.3Vo o, respectively.

8) Whole-rock 6180 values decrease with increasedintensity ofchloritic alteration toward the ore horizon.A sample of footwall chloritite has a [lEg of 5.3Voo; atthe inferred temperature of formation (between 3@ and4(D'C), this value should appnoximarethatof ore-formingfluid (-5 toTVoo), indicative of an extensively modifiedseawater composition, Whole-rock 61EO values decreasefrom greater th an l.lVoo rn the l"*1-a11ssd fuangi ng wallto8.7%onthealteration zone immediately above the ore.

9) Distal alteration in the footwall is manifested bychessboard albite, which variably replaces alkali feldsparphenocrysts. With increasing alteration (intermediateto proximal), the feldspar grains are progressivelyhydrolyzed to micas, and there is an increase in theFe/(Fe + Mg) ratio and Al contents of the white mica(phengite - muscovite) and cblorite (fenoan clinochlore- magnesian chamosite). These changes reflect alkaliand silica leaching at low pH and a high Fe/LIg in thefluid. For an esrimated temperature of 400'C, chloritecompositions (Xcbmo"it = 0.8) near the stockworkindicates an Fe./Mgsuia = 200 (modified seawater). At alower inferred temperafure (300'C), the chlorite(Xcnamostt" = 0.3) from the distal alteration indicates amajor decrease in the Fe/Mg of the fluid, reflectinglow-T, shallow infiltration of seawater into the peripheralenvironment of alteration.

10) Feldspar hydrolysis to Ba-bearing phengite andferroan clinochlore in the immediate hanging-wall CTis indicative ofcontinued venting offluid through the CTand mixing with shallowly circulating Mg-rich seawater.

AcK\owrEDGm/E\TS

The authors thank the staff of Noranda ExplorationLimited for the financial support and cooperation withthis phase of the Heath Steele research project. ArtHamilton, chief geologist atHeath Steele Mines, helpedfamiliarize the first author with the vast amount ofinformation on the Heath Steele deposits. Discussionswith Wayne Godfellow (GSO, Chris Moreton (Noranda),and Reg Wilson (NBGSB) are greatly appreciated.

870 TIIE CANADIAN MINERALOGIST

Comments on a preliminary version of the manuscriptby Steven McCutcheon (NBGSB) were helpful. Thismanuscript benefitted from critical reviews byDrs. Timothy J. Barrett, Craig H.B. Leitch, and RobertF. Martin. This contribution forms part of the five-year'federal-provincial EXTECH tr Agreement.

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Received May I 4, I 996, revised manuscript accepted March 6,1997.

Note addcd in proof, Further follow-up research (Ifltz 1997) and exploration (Art Hamitton, pers. commun.) ln the Heath Steele

B-B5 area have shown that the exhalative Heath Steele horizon seems to be structually repeated by folding on the south limb of

the overturned" doubly plunging, isoclinal Fro fotd (see Fig. 2), as implied by the stratigraphic and structural revisions proposed

in this study and by I.enz & Wils on (1997). Furthermore, the contact between the Heath Steele belt and the Flat Landing Brook

rhyolites (Fig. 2) is probably alate Dr thrust, as indicated by de Roo et al. (1990) and Moreton (1994), in conEast to a locally

faulted (Heath Steele Fault), conformable relationship as shown here (-entz 1997).