Mineralogy, Textures, and Relative Age Relationships of Massive Sulfide Ore in the West Shasta District, California

Econom/cGeo/og• Vol. 80, 1985, pp. 2114-2127

Mineralogy, Textures, and Relative Age Relationshipsof MassiveSulfide Ore in the West ShastaDistrict, California

STEPHEN S. HOWE

U.S. GeologicalSurvey, 345 MiddlefieldRoad, Mail Stop901, MenloPark, California 94025

Abstract

The Devonian massive sulfide orebodies of the West Shasta district in northern California are composedprimarily of pyrite, with lesseramounts of other sulfideand gangueminerals. Examinationof polishedthin sectionsof more than 100 samplesfrom the Mammoth,Shasta King, Early Bird, Balaklala,Keystone, and Iron Mountainmines suggests that mineralization may be dividedinto six parageneticstages, the last five each separatedby an episodeof deformation:(1) precipitationof fine-grained,locally colloformand framboidalpyrite and sphalerite;(2) depositionof fine-grainedarsenopyrite and coarse-grainedpyrite, the latter enclosingtiny inclusionsof pyrrhotite;(3) penetrationand local replacement of sulfideminerals of stages1 and 2 alonggrowth zones and fracturesby chalcopyrite,sphalerite, galena, tennantite, pyrrhotite, bornite, and idaite; (4) recrystallizationand remobilizationof existing minerals,locally increasingtheir size and euhedralismand promotingtheir aggregation;(5) depositionof quartz, white mica, chlorite, and calcite;and (6) formationof bornite, digenite, chalcocite,and covellite during supergene enrichment of severalorebodies at the Iron Mountain mine.Despite regional greenschist facies metamorphism and local heating by intrusivebodies, enoughof the originaldepositional features of the ore remainto suggestthat the depositsin the districtformed by processessimilar to thosethat formedKuroko- and Besshi-type massive sulfidedeposits. Mineralogic and textural evidence do not supporta secondmajor episode of massivesulfide mineralization during the Permian.

Introduction mineralogyand texturesof the ore in mostof the ma- IN recent years, detailed studiesby Barton (1978), jor massivesulfide deposits in the districtand incor- Eldridge (1981), and Eldridge et al. (1983) of the porates these observationsinto a parageneticse- mineralogyand texturesof ore in the relativelypris- quencesummarizing the relativeage relationships of tine Kuroko-typemassive sulfide deposits have re- the sulfide and nonsulfide minerals. These features of suitedin a dramaticrevision in the understandingof the West Shastaore are comparedwith thoseof Ku- the paragenesisof thesedeposits. This modification roko- and Besshi-typemassive sulfide deposits, and hasplayed an importantrole in the developmentof the bearingof thesecharacteristics on depositional the most recent model for the formation of Kuroko- processesis examined.Finally, recentK-Ar datingof type deposits(cf. Ohmoto and Skinner, 1983). The the West Shastaore by Kistler et al. (1985) is exam- success of these studies has stimulated a reexamination inedin light of the relativeage relationships outlined of ore mineralsand texturesin metamorphosedmas- here. sive sulfidedeposits, including Besshi-type deposits General Features of the West Shasta (Yui, 1983) and the more intenselydeformed Appa- Orebodies and Ore lachiandeposits (Craig, 1983), in an attempt to un- The geologicsetting of the massivesulfide deposits ravel their depositionaland metamorphichistories. in the West Shastadistrict is well describedby Kinkel As Craig (1983) points out, this challengemay be et al. (1956), Alberset al. (1981), Caseyand Taylor overwhelming in highly metamorphoseddeposits (1982), Reed(1984), andAlbers and Bain (1985) and containingsulfide minerals that reequilibratereadily. is onlybriefly summarizedhere. The orebodiesoccur On the other hand, microscopicexamination of de- within the upperpart of the middleunit of the Early positsdominated by refractorysulfide minerals, such DevonianBalaklala Rhyolite, on or near the axesof as pyrite and sphalerite,which have not been sub- broad synclinal,and lesscommonly anticlinal, folds jected to metamorphismabove greenschistfacies, alonga northeast-trendingzone 13 km longby 3 km shouldreveal a wealth of information. For this reason, wide (Fig. 1). The largestdeposits consist of massive, a microscopicinvestigation of ore in the massivesul- generallylenticular and fiat-lying, pyritic bodies with fide depositsof the West Shastacopper-zinc district lengthsand widths commonly an order of magnitude in northernCalifornia was initiated as part of a broader greaterthan their thicknesses;contacts between these studyof the district (Albers,1985). bodiesand barren or weaklypyritized wall rocksare The present paper describesand illustratesthe sharp.Stockworklike sulfide veins and disseminations

0361-0128/85/478/2114-1452.50 2114 MASSIVE SULFIDE MINERALOGY, TEXTURES & AGE RELATIONS 2115

122030 ' MASSIVE sulfideminerals, in decreasingabundance, are pyrite, SULFIDE MINES SAMPLED chalcopyrite, sphalerite, galena, tetrahedrite-ten- GOLINSKY nantite (hereafter referred to as tennantite), arsenopyrite, pyrrhotite, bornite, idaite, and two unidenti- BIRD fied phases.The nonsulfideminerals, in decreasing HASTA KING abundance,are quartz, white mica, calcite, chlorite, ,KLALA and iron oxides. Digenite, bornite, covellite, and 4Oø45' KEYSTONE chalcocitecomprise the secondarysulfide minerals. MOUNTAIN The growthhabits, textures, and associations of the mineralscomprising the ore are alsobroadly similar

BIOTITE QUARTZ DIORITE throughoutthe district,allowing the depositionaland metamorphichistories of the depositsto be divided

ALBITE GRANITE into six parageneticstages (Fig. 2): (1) "primitive" pyrite + sphalerite;(2) pyrite ___arsenopyrite; (3) 40o30, • PALEOZOIC chalcopyrite + sphalerite + galena + tennantite SEDIMENTARY ROCKS + quartz + white mica; (4) recrystallizationand remobilization;(5) quartz + white mica + calcite;and BALAKLALA RHYOLITE (6) supergeneenrichment. These stages are described below. COPLEY GREENSTONE ß Stage1: "Primitive" pyrite + sphalerite 0 5 MILES MINES Mineralization in the West Shastadistrict appears FIC. 1. Locationmap of principalmines and the generalized to have begunwith the precipitationof framboidal, geologicsetting of the West Shastadistrict. The Mule Mountain colloform,and very fine grainedpyrite, collectively stockis shownhere asalbite graniteand the ShastaBally batholith termed "primitive" pyrite after Barton (1978). asbiotite quartz diorite. Framboids,a largeproportion preserved as iron oxide pseudomorphs,have been observedin ore from the occurlocally beneath the massivelenses. The Balak- Mammothmine where they reach a maximumdiam- lalaRhyolite is intrudedby the EarlyDevonian Mule eter of 25 ttm. Colloformpyrite occursin ore from Mountain stock,which is itself intrudedby the Late the Mammoth and Keystonemines as aggregatesof JurassicShasta Bally batholith.The districthas un- curvilinearbands up to 2 mm in length (Fig. 3A) or dergoneregional greenschist facies metamorphism. asindividual spheroids 15 to 90 ttmin diameter.Some The ore is composedmainly of massivepyrite with spheroidshave been selectivelyreplaced by chalco- relativelyminor amounts of chalcopyrite,sphalerite, pyrite,sphalerite, and galena along concentric growth galena,and quartz. Compositional layering is present zones (Fig. 3B) whereasother spheroidshave been locally.The orehas been deformed and recrystallized completely replaced, leaving circular voidsentirely to varying degrees,compromising the preservation filled by later sulfides(termed here "bullet hole tex- of originaldepositional textures and resultingin a ture") (Fig. 3C). Porousand pitted aggregatesup to somewhatchaotic mixture ofbreccia fragments, crys- 4 mm in diameterof very fine grained(•10 ttm)sub- tal aggregates,and minor crosscutting veins. hedralto euhedralpyrite crystalsconstitute the most The ore graderanges from 2.0 to 6.0 percentCu abundantand widespreadprimitive pyrite. andfrom 1.3 to 8.9 percentZn. Accordingto Kinkel Similaraggregates of fine-grainedsphalerite, up to et al. (1956), the lack of zinc assaysat many of the 4 mm in diameterand locallyporous and pitted, also mines preventsthe determinationof Cu/Zn ratios. appearto be earlyformed or primitive.The temporal Minor amountsof goldand silver have been recovered relationshipbetween primitive pyrite and sphalerite from the massivesulfide ore and from overlying is not clear, but both phasespredate stage2. gossan.

Mineralogy,Texture, and Paragenesis T•_BLE1. Locationand Number of SamplesExamined Singlypolished thick and thin sections,and doubly polishedthin sections,of 137 samplesfrom six mines Mine Number in the districtwere examined(see Table 1) usingre- Mammoth 10 flectedand transmitted light microscopes. A scanning ShastaKing 2 electronmicroscope and an electron microprobe were Early Bird 2 not availableduring this study. Balaklala 9 Keystone 1 The mineralogyof the ore is relativelysimple and Iron Mountain 113 consistentin all of the samplesexamined. The primary 2116 STEPHEN S. HOWE

STAGE i 2 3 4 5 6 selectivereplacement of coresand growth zonesby MINERAL chalcopyrite(Fig. 3H), whereasother fragmentsare PYRITE ARSENOPYRITE extensivelyembayed (Fig. 4A). Chalcopyrite also PYRRHOTITE formsgashlike veins and fills V-shapedvoids in ag- BORNITE, IDAITE CHALCOPYRITE gregatesof primitive pyrite and sphaleritefrom the SPHALERITE GALENA Mammothmine during this episode of stage3. At the TENNANTITE Mammoth and ShastaKing mines,chalcopyrite re- UNKNOWN B QUARTZ places arsenopyrite euhedra formed in stage 2 WHITE MICA (Fig. 4B). CHLORITE CALCITE Minute, rounded,oval inclusions and thin stringers DIGENITE of pyrrhotite, bornRe, idaRe, and an unidentified CHALCOCITE COVELLITE bluish-gray mineral ("unknown A") with optical IRON OXIDES properties somewhatsimilar to rutRe and hematite, DEFORMATION BRECCIATION completelyenclosed by pyrite, appearto have been FRACTURING RECRYST., REMOB. depositedtoward the end of the early episodeof stage 3. Pyrrhotite and bornRe in separatestringers both FIG. 2. Generalized paragenesisof the massivesulfide min- replace pyrite and are in contactlocally with chal- eralization in the West Shasta district. Bar thickness indicates relative abundance of the mineral. Number of x's indicates relative copyrite and sphalerite(Fig. 4C). Idaite, in contact intensityof the deformationalepisode. Question marks indicate with bornite, was identified in two rounded inclusions uncertaintyin the durationof mineralprecipitation. < 5 •m in diameter. Sphaleritewas deposited during the middleepisode of stage3. Although it is neither as abundantnor as Stage 2: Pyrite 4- arsenopyrite widespreadas chalcopyrite, it comprisesthe majority of the bandedore from the Friday-Loudenportal at The depositionof the primitive sulfideswas fol- the Mammothmine and is locallythe mostabundant lowed by the main episodeof pyrite precipitation sulfidein somesamples from the Mammoth, Shasta during stage2. Subhedralto euhedralcrystals of py- King, and Iron Mountain mines.Kinkel et al. (1956) rite, mostlycubes and pyritohedrons < 1/•m to 2 mm noted that the Yolo and (;raton orebodies at the in diameter,were depositedduring stage2. Where Mammothmine were particularlyzinc rich. Sphalerite not recrystallized,pyrite occursmainly asdense dis- exhibitsmany of the sametextures and associations seminationsand in loosely packed clustersof ran- shownby chalcopyritedeposited during the earliest domly oriented crystalsand crystalfragments (Fig. episodeof stage3. Like chalcopyrite,sphalerite pen- 3D). The clusterslocally surroundclasts of primitive etratespyrite and replacesit along fractures.Sphal- pyrite. Severalpyrite crystalscompletely enclose a erite generally fills the more proximal portions of few small,isolated pyrrhotite subhedra. fracturesoccupied by both sphaleriteand chalcopy- Euhedral,rhombic to wedge-shapedcrystals of ar- rite, suggestingthat sphaleritepostdates chalcopy- senopyrite,up to 80/•m in lengthbut generallymuch rite depositedduring the earliestepisode of stage3. shorter,are sparselyintergrown with stage2 pyrite. Sphaleritealso selectively replaces cores (Fig. 4D) Stage2 mineralizationwas followed by an episode and growth zonesin somepyrite fragmentsand em- of district-widedeformation, the severity of which baysthe marginsof other fragments(Fig. 4E). rangedfrom moderatefracturing (Fig. 3D) to intense Galenaand tennantite were both depositedduring brecciationand shearing (Fig. 3E andF) that occurred the middle episodeof stage3, but their positionsin during at leasttwo separateevents (Fig. 3F). the parageneticsequence are not firmly established owingto their minorabundance in the ore. Bothmin- Stage3: Chalcopyrite+ sphalerite+ galena eralspenetrate and replacestage 2 pyrite alongfrac- + tennantite+ quartz + white mica tureswhich locallycontain chalcopyrite distally (Fig. Precipitationof base metal sulfidesand replace- 4F). At the Iron Mountain mine, galenapenetrates ment of stage 2 pyrite occurred in three episodes shearsin previously brecciated pyrite fragments. during stage3. During the earliest episode,chalco- Tennantite replaces arsenopyrite euhedra at the pyrite wasdeposited along fractures in pyrite andbe- Mammoth and ShastaKing mines (Fig. 4B). Galena tween breccia fragments.In somesamples, particu- and tennantite commonlyare intergrown with one larly those from the Iron Mountain mine, fractures anotherand with chalcopyriteand sphalerite. Locally havebeen filled without appreciablereplacement of chalcopyriteembays galena but is itself replacedby the host,resulting in matchingwalls of pyrite on each tennantite,suggesting that tennantitepostdates galena sideof the fracture.In other samples,however, frac- slightly. Both galena and tennantite vein stage 3 tures are enlargedby replacementof the pyrite by sphaleriteat the Iron Mountain mine. Dense clusters chalcopyrite(Fig. 3G). Somepyrite fragmentsshow of submicron-sized needles and blebs of tennantite in MASSIVESULFIDE MINERALOGY, TEXTURES & AGE RELATIONS 2117 stage3 sphalerite(Fig. 4G) formpatches that are red- inclusionsand chalcopyrite along fractures have been dish-brownin transmittedlight andresemble patches preserved.These markersare orientedin a different in Kurukoores observed by Barton(1978). directionfor nearly eachof the individualsphalerite In one samplefrom the Iron Mountain mine, an fragmentscomprising the aggregates,indicating that unidentifiedbrownish-gray mineral ("unknownB") the fragmentscoalesced in a crystallographicallyran- with opticalproperties somewhat similar to enargite domfashion. Original color banding in sphaleritehas occursas rounded inclusions• 10 #m in diameter in largelybeen obliterated in aggregatesby the homog- tennantitein contactwith sphalerite.The unidentified enizinginfluence of recrystallization.Only in sphal- phaseexsolves from or replacessphalerite but hasa erite that has been shielded from the effects of re- mutualboundary texture with tennantite. crystallizationby surroundingsulfide masses has color Quartz, white mica, and chloritewere alsodepos- bandingbeen preserved(Fig. 5E). ited duringstage 3, probablyduring the middleep- Originallyfine-grained white micaand chloritein isode.Unfractured euhedral quartz is surroundedby the groundmassof sparselymineralized host rocks chalcopyriteand tennantitein severalsamples from apparentlyincreased in size and locally acquireda the Iron Mountainmine. Locally the quartz margins preferred orientationduring stage4. Stage3 white are embayedby tennantite. micaalso increased in sizeduring stage 4, seemingly The last episodeof stage 3 is characterizedby at the expenseof sphaleriteand, less commonly, pyrite chalcopyritereplacement of sphaleritein a manner andchalcopyrite (Figs. 4E and 5F), suggestedby the resemblingthe chalcopyritedisease of Barton(1978). enclosureof fragmentsof the sulfideminerals by the Irregular, rounded,or lathlikeblebs of chalcopyrite, white mica.The crystalsare usuallyscattered without all • 5 #m, occuras fine dustings,trains, or myrmek- discernibleorientation within the recrystallizedsul- itic forms (Fig. 4H) concentratedalong crystal fide minerals(see fig. 8 in Craig, 1983), but in ore boundariesand minute fractures.Locally chalcopy- fromthe Friday-Loudenportal of the Mammothmine, rite-diseasedsphalerite embays larger masses of chal- white mica flakes in sphalerite are subparallelto copyritethat were depositedduring the earlyepisode megascopiccompositional layering (Fig. 5G). of stage3. The youngerchalcopyrite has no apparent A minor amountof stage3 chalcopyritehas been spatialrelationship to the older chalcopyrite. remobilizedinto previouslyunfilled fractures in stage œpyrite and into pressureshadows during stage4. Stage4: Recrystallizationand remobilization Chalcopyritederived from stage3 alsoreplaces the Stage4 is characterizednot by depositionof new marginsof recrystallizedpyrite euhedrathat contain mineralsbut by recrystallizationand remobilization blebsoftennantite annealed during stage 4 (Fig. 5D). of existingminerals. Harder, more brittle sulfidemin- eralssuch as pyrite and sphaleriteare recrystallized Stage5: Quartz q- white mica q- calcite while softer, more malleable minerals such as chal- Pyrite wasthe firstmineral deposited during stage copyrite,galena, and tennantiteare remobilized. 5. Euhedral crystalslocally coat previouslyrecrys- Recrystallizationpromoted the aggregationof py- tallizedpyrite aggregatesand project into vugsfilled rite fragmentsthat had been fracturedat the end of later by quartz. stageœ and penetrated and replaced by chalcopyrite, A major episodeof quartz precipitationfollowed sphalerite,galena, and tennantite during stage 3 (Fig. pyrite deposition.Quartz penetrates and replaces 5A). Recrystallizationalso increased the sizeand eu- stageœ pyrite alongfractures that were not filled by hedralismof stage2 pyrite, mostdramatically for stage3 sulfideminerals (Fig. 5H). It surroundspyrite crystalsthat are disseminatedor in looselypacked aggregates,locally embayingthe marginsof the re- clusterssurrounded by chalcopyrite,galena, or void crystallizedpyrite. Quartz veinsfrequently enclose space(Fig. 5B). Recrystallizationof more tightly fragmentsof stage2 pyrite that are crosscutand re- packed,nearly monomineralic aggregates of pyrite placedby stage3 sulfideminerals (Fig. 6A), indicating resultedin localinterpenetrations of fragmentsand that the quartzpostdates stage 3. Two samplesfrom the developmentof triplejunctions among fragments the Iron Mountainmine have textures suggesting that (Fig. 5C). Irregularinclusions and fracture fillings of the quartznot onlypostdates stage 3 but alsothe re- stage3 sulfideminerals and quartz in pyritehave been crystallizationduring stage 4. In one sample,quartz annealedlocally; all thatremain are roundedto myr- surroundspyrite euhedrathat in turn encloserounded mekiticblebs concentrated in the coresof the pyrite chalcopyriteblebs (Fig. 6B). In the other sample,a crystals(Fig. 5C andD). 25-#m-widefracture filled by deformedquartz cuts Recrystallizationalso resulted in sphaleriteaggre- acrossa pyrite aggregatein which the coresof the gatesthat containcrystals or fragmentswhich have pyrite crystalscomprising the aggregateare replaced beenpreviously replaced by chalcopyrite.Although by roundedinclusions of chalcopyriteand sphalerite. recrystallizationincreased the sizeof the chalcopyrite Quartz depositedduring stage5 showsa variety of blebs,the originalorientation of rowsof chalcopyrite deformationtextures. Most commonis the develop- 2118 STEPHENS. HOWE ment of polycrystallinequartz with undulatoryex- locallyhorsetailing, fractures commonly cut stage5 tinction. Slightlyincreased deformation resulted in chalcopyrite. the suturingof contactsbetween crystallites through At the end of stage5, undeformedquartz filled the pressuresolution and a mottlingof crystallites(and voidslined by stage5 chalcopyrite.Trace amounts of theirextinctions) by the nucleationof submicron-sizedwhite mica fill hairline fractures that cut both feather protocrystallites.In rare instances,the intensityof and unstrainedquartz. the deformationproduced a cataclastictexture. One of the morecommon textures of the quartz(first noted Stage6: Supergeneenrichment by Kinkel et al., 1956) is a subparallelarrangement This stageincludes oxidation and supergeneen- of lathlikecrystallites with slightlysutured contacts, richmentof the ore.Oxidation is widespread but very termedhere "featherquartz." In placesit linesvein insignificant.Iron oxides,associated in placeswith walls,surrounding more equant polycrystalline quartz covellite,locally penetrate horsetailing hairline frac- in the interior of the veins.Elsewhere, it completely turesthat cut the ore and sparselymineralized host fillsveins where the opticalcontinuity of the individ- rocks. ual crystallitesis not interruptedby pyrite fragments Supergeneenrichment of the ore by formationof in the center of the veins. Feather quartz also sur- copper sulfideminerals occurred in the Brick Flat, roundsindividual crystals or fragmentsof pyrite and Mattie, and Old Mine orebodies at the Iron Mountain pyrite aggregates,the lathsusually oriented with their minebut is mostadvanced in the Old Mine orebody. long axesat right anglesto the marginof the pyrite Bornite, the first stage6 mineral to form, occursas (Fig. 6C). Often the quartzfeathers completely sur- irregularmasses locally embaying pyrite and is com- round the pyrite, but locally they developonly on pletely surroundedby digenite. Locally bornite en- oppositesides of the pyrite or near cornersof the closessubmicron-sized inclusions of chalcopyrite. pyrite crystalsor fragments.In sampleswhere both Digenite veinsand partly replaceschalcopyrite and relict quartzphenocrysts and pyrite crystalsor frag- bornite(Fig. 6H). It surrounds,but doesnot replace, mentsare surroundedby a groundmassof fine-grained roundedpyrite fragmentsthat were partly replaced quartz, white mica, and chlorite, quartz lathsextend by stage3 chalcopyrite.Minor amountsof chalcocite only from the marginsof the pyrite (Fig. 6D). Late have mutualboundary textures with digenitethat is fractureslocally cut acrossdeformed quartz, inter- associatedwith chalcopyriteand bornite. Covellite secting the submicron-sizedprotocrystallites and replaceschalcopyrite, sphalerite, and tennantite along larger crystalliteboundaries; they are marked by late hairlinefractures in samplesfrom the BrickFlat trains of secondarytwo-phase fluid inclusions.The and Mattie orebodies, but it is most abundant at the fracturesalso offset gashlike veins and pods filled with Old Mine orebody.It alsopenetrates hairline fractures deformedfeather quartz (Fig. 6E). in digniteand chalcocite. Covellite locally surrounds White mica and lesser amounts of chlorite were pyrite fragmentsthat havebeen previously replaced depositedwith quartz.As deformation and recrystal- by chalcopyrite;the covellite doesnot replace the lization of the quartzintensified, flakes of white mica pyrite but attacksthe chalcopyriteentensively. and chloriterecrystallized along the elongatequartz crystallitecontacts. In severalsamples, feather quartz Depositionaland Metamorphic Histories and intergranularwhite mica are both deformed,lo- of the Deposits cally with distinctkinking. The parageneticsequence outlined in this paper Calcitefills largevoids and fracturesin a sample summarizesthe relative age relationshipsof the sul- from the Early Bird mine (Fig. 6F) but hasnot been fide and nonsulfideminerals in mostof the majorde- recognizedelsewhere in the district. The calcite en- positsin the West Shastadistrict. Due to the regional closesfragments of pyrite replacedby chalcopyrite- greenschistfacies metamorphism and local heating diseasedsphalerite and surroundseuhedral pyrite by a variety of plutons,the depositionalhistories of with coresreplaced by roundedsphalerite blebs. The the depositsare somewhatobscured by metamorphic calciteexhibits prominent deformation lamellae and events. However, a careful study of the ore allows is cut locally by late fractures. the unravelingof portionsof both the depositional Recrystallizationand remobilizationduring stage and metamorphichistories of the deposits. 5 resultedin the depositionof pyrite euhedraand The mineralogyof the West Shastaores is nearly massivechalcopyrite around the marginsof voidsin identicalto that of oresin Kuroko-typedeposits, al- olderpyrite andquartz aggregates, and the deposition though their proportionsare somewhatdifferent of chalcopyritein fracturesand along grain boundaries (Shimazaki,1974; Eldridge et al., 1983). More strik- in polycrystallinequartz (Fig. 6G). As the abundance ing is the similarityof mineraltextures in the West of thisstage 5 chalcopyriteis quite significant locally, Shastaores to thoseexhibited by Kuroko-and Besshi- someof it may have been newly precipitatedrather type deposits(see especially figs. 10 A-H, 11 A-H, thanjust remobilizedfrom existing masses. Hairline, and 23a in Eldridgeet al., 1983; figs.4, 5, 6 in Ko- MASSIVE SULFIDE MINERALOGY, TEXTURES & AGE RELATIONS 2119 muro, 1984; and figs. 10-12, 14, 15, and 17a-h in rathera recrystallizationand remobilization of earlier Yui, 1983). For the Kurokoores, the particularlygood minerals(and partial resetting of the olderK-Ar ages) geologiccontrol, the recognitionof severaldistinct due to heatingby the Pit River stock. ore types (e.g., tetsusekiei,massive black ore, pow- Acknowledgments dery yellow ore, and siliceousblack ore), and the preservationof primary depositionalfeatures allow The author is indebted to T. G. Theodore for mi- an especiallydetailed paragenesis to be constructed. croscopeand photographic facilities and to K. Di Lullo The use of the term "facies"rather than "stage"in for tirelesstyping and photographicassistance. Two the parageneticsequence in Eldridge et al. (1983) EconomicGeology reviewers are thanked for their reflectsthe high quality of the data on spatialrela- thoroughand insightful reviews of the manuscript. tionshipsin the Kuroko ores. Such stringentcon- REFERENCES straintson the paragenesisof the mineralizationin the West Shastadistrict are not possible,but a com- Albers,J.P., 1985, An issuedevoted to the West Shastamassive parisonof the paragenesisof the ores in the West deposits--Introduction:ECON. GEOL., v. 80, p. 2067--2071. Shasta and Hokuroko districts reveals a number of Albers,J.P., and Bain,J. H. C., 1985, Regionalsetting and new informationon somecritical geologic features of the West Shasta similarities.These include early precipitationof fine- district,California: ECON. GEOL., v. 80, p. 2072-2091. grainedand colloform(primitive) pyrite and sphal- Albers,J.P., Kistler,R. W., andKwak, L., 1981, The Mule Moun- erite, renewedprecipitation and coarseningof pyrite tain stock,an early Middle Devonianpluton in northernCali- andother iron sulfideminerals, replacement of earlier fornia:Isochron/West, no. 31, p. 17. Barton, P. B., Jr., 1978, Some ore texturesinvolving sphalerite formed sulfidesby later basemetal sulfides,and de- from the Furutobemine, Akita Prefecture,Japan: Mining Geol- positionof quartz toward the end of the sequence. ogy, v. 28, p. 293-300. These similaritiesin the mineralogy,textures, and Casey,W. H., and Taylor, B. E., 1982, Oxygen,hydrogen, and paragenesisamong the West Shasta,Kuroko, and sulfurisotope geochemistry of a portionof the West ShastaCu- Besshiores suggest that all three were formedby sim- Zn district, California: ECON.GEOL., v. 77, p. 38-49. Craig,J. R., 1983, Metamorphicfeatures in Appalachianmassive ilar depositionalprocesses. sulphides:Mineralog. Magazine, v. 47, p. 515-525. It is uncertain whether recrystallizationand re- Eldridge,C. S., 1981, Mineraltextures and parageneses of Kuroko mobilizationin the WestShasta deposits during stage oresfrom the Uwamuki No. 4 and someother Kurokodeposits, 4 (and continuingduring portions of stage5) were Hokurokudistrict, Japan: Unpub. M.S. thesis,The Pennsylvania State Univ., 104 p. caused by temperature increasesand dissolution Eldridge,C. S., Barton,P. B., Jr., andOhmoto, H., 1983, Mineral within the accumulatingsulfide sediment, by local texturesand their bearingon formationof the Kurokoorebodies: heating around plutons intruded after most of the ECON. GEOL. MON. 5, p. 241-281. mineralizationwas completed, by greenschistfacies Kinkel, A. R., Jr., Hall, W. E., and Albers, J.P., 1956, Geology metamorphism,or by some combinationof these andbase-metal deposits of the West Shastacopper-zinc district, ShastaCounty, California: U.S. Geol. SurveyProf. Paper 285, events.However, the bulk of the quartz,white mica, 156 p. and chloriteformed during stage 5, definitelypost- Kistler, R. W., McKee, E. H., Futa, K., Peterman, Z. E., and Zart- datingmain ore deposition. Kistler et al. (1985)report man, R. E., 1985, A reconnaissanceRb-Sr, Sm-Nd, UoPb, and K-Ar agesof about370 m.y. for mostof the samples K-Ar studyof somehost rocks and ore mineralsin the West of sericite from the massive ore in the Brick Flat ore- ShastaCuoZn district, California: ECON. GEOL., v. 80, p. 2128-- 2135. body at the Iron Mountainmine, 30 m.y. younger Komuro, K., 1984, Textures of the Kuroko ores from the Ezuri thanthe BalaklalaRhyolite. However, a few samples mine, Akita Prefecture:Mining Geology,v. 34, p. 251-262. fromthe BrickFlat orebodyyielded K-Ar agesof 290 Ohmoto,H., andSkinner, B. J., eds.,1983, The Kurokoand related to 252 m.y., leadingthem to suggesta secondepisode volcanogenicmassive sulfide deposits: ECON. GEOL. MON. 5, 604 p. ofmineralization,possibly related to theemplacement Reed, M. H., 1984, Geology, wall-rock alteration, and massive of the Pit River stockdated at about261 m.y. (J.P. sulfidemineralization in a portionof the West Shastadistrict, Albers,oral commun.,1985) eastof the West Shasta California: ECON.GEOL., v. 79, p. 1299-1318. district.The minoramounts of pyriteand chalcopyrite Shimazaki,Y., 1974, Ore mineralsof the Kuroko-typedeposits: Mining Geology Spec. Issue 6, p. 311-322. depositedwith quartz and white mica at the end of Yui, S., 1983, Textures of someJapanese Besshi-type ores and stage5 indicatethat thislater eventwas probably not their implicationsfor Kuroko deposits:ECON. GEOL. MON. 5, a secondepisode of massivesulfide mineralization but p. 231-240. 2120 STEPHEN S. HOWE

Photomicrographsof the West ShastaMineralization

Figures3 through6 were taken in reflectedlight unlessindicated otherwise. The abbreviationsfor the mineralsare as follows: ap = arsenopyrite,bn = bornite,ca = calcite,cp -- chalcopyrite,cv -- eovellite, dg = digenite,gn = galena,po = pyrrhotite,py = pyrite, qz = quartz,sp = sphalerite,tn = tennantite, wm = white mica.

FIG. 3. A. Aggregateof curvilinearbands of stageI colloformpyrite selectivelyreplaced by stage 3 chalcopyrite.G4, Keystonemine. Scale bar -- 52 #m. B. Spheroidsof stage1 colloformpyrite selectively replacedby stage3 chalcopyriteand sphaleritealong concentric growth zones.FL1, Mammothmine. Scalebar = 104 #m. C. Complete replacementof spheroidsof stage1 colloformpyrite; the resulting circularvoids are entirely filled by stage3 chalcopyrite(bullet hole texture). G4, Keystonemine. Scale bar = 52 #m.D. Fractured stage2 pyrite crystals.Note nearly perfectly matchingwalls of pyrite fragments,left center. Stage5 quartz surroundsthe pyrite fragments.661, Iron Mountainmine. Scale bar = 104 #m. E. Intenselybrecciated stage 2 pyrite showinga wide range in fragmentsizes. The largermasses are aggregatesof smallerfragments. Stage 5 quartzsurrounds the fragments.IM-28, Iron Mountainmine. Scalebar = 207 #m. F. Rebrecciationof stage2 pyrite fragments.Note shearingof largefragment in the centerof the photographand presence of manysmaller pyrite fragmentsbetween the two piecesof the largefragment. Stage 5 quartzsurrounds the pyrite fragments.IM-5, Iron Mountain mine. Scale bar -- 52 #m. G. Fractured stage 2 pyrite replaced by stage 3 chalcopyrite.Note late fracturerunning from the top to the bottomof the photograph,cutting both the pyrite and the chalcopyrite. G2, Mammoth mine. Scalebar = 104 #m. H. Stage 3 chalcopyriteand very minor stage3 galenaand sphaleritehave selectivelyreplaced stage 2 pyrite alongconcentric growth zones.IM-26, Iron Mountain mine. Scale bar = 52 #m. MASSIV• SULFIDE MINERALOGY, TEXTURES& AGE RELA•r•o•s 2121 2122 STEPHEH S. HOWE

FIG. 4. A. Subhedralstage 2 pyrite extensivelyembayed by stage3 chalcopyrite,tennantite, and sphalerite.658, Iron Mountainmine. Scalebar = 52 •m. B. Rhombicto wedge-shapedcrystals of stage 2 arsenopyritereplaced by stage3 chalcopyrite,tennantite, and galena.Note the scallopedmargins of the arsenopyriteeuhedra in contactwith chalcopyrite.Tennantite appearsto have replaced selectively the arsenopyritealong growth zones. 671, Mammothmine. Scalebar -- 52 •m. C. Stringersof stage3 pyrrhotite, in contact with stage 3 sphalerite, have replaced stage 2 pyrite. IM-46, Iron Mountain mine. Scalebar = 21 •m. D. Stage3 sphaleritehas selectivelyreplaced the core of subhedralstage 2 pyrite. Stage5 quartz surroundsthe pyrite. IM-37, Iron Mountain mine. Scalebar = 52 •m. E. Stage 3 sphaleriteembaying margins of stage2 pyrite subhedra.Flakes of stage3 white mica are enclosed within sphalerite.658, Iron Mountain mine. Scalebar = 52 •m. F. Stage3 tennantite and chalcopyrite havepenetrated and replaced stage 2 pyritealong fractures. Stage 3 galenanot visiblein thisphotograph. IM-19, Iron Mountain mine. Scale bar = 21 •m. G. Submicron-sizedneedles and blebs of stage 3 tennantitein stage3 sphalerite.IM-23, Iron Mountainmine. Scale bar = 21 •m. H. Tiny lathlikeblebs of late stage3 chalcopyritehave replaced middle stage 3 sphaleritein the centerof the photograph. More massiveearly stage3 chalcopyritehas replaced stage 2 pyrite subhedraaround the marginsof the field but is itself embayedby the sphalerite.IM-19, Iron Mountainmine. Scalebar = 21 •m. MASSIVESULFIDE MINERALOGY, •'EX•S & AGE RELATIONS 2123

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G 2124 STEPHEN $. HOWE

FIG. 5. A. Partial aggregationof stage2 pyrite fragmentscontaining irregular stage3 chalcopyrite andsphalerite inclusions resulting from recrystallizationin stage4. Stage5 quartzsurrounds aggregates. IM-8, Iron Mountainmine. Scale bar -- 52 •m. B. Aggregatesof stage2 pyrite fragmentspartly replaced by stage3 chalcopyrite.Recrystallization increased most dramaticallythe size and euhedralismof crystalsprojecting into voidswhich were later filled by stage5 quartz. Note the roundednature of the chalcopyrite inclusionsin the pyrite crystals. IM-38, Iron Mountain mine. Scale bar -- 52 •m. C. Roundedto myrmekiticblebs of stage3 sphaleriteconcentrated in the coresof stage2 pyrite fragments in recrystallizedaggregates. Note obliterationof pyrite fragmentmargins, interpenetration of fragments, and the formationof triple junctionsamong fragments. IM-15, Iron Mountainmine. Scalebar -- 21 •m. D. Roundedto myrmekiticblebs of stage3 tennantiteconcentrated in the core of a recrystallized stage2 pyrite crystal. The crystal originally projected into a void which has been filled by stage5 quartz. Note replacementof the pyrite and intersectionof the annealedtennantite blebs by stage3 chalcopyritewhich wasremobilized during stage4. IM-26, Iron Mountainmine. Scalebar -- 21 •m. E. Stage3 sphaleritefilling bullet hole voidsin stagei colloformpyrite. Reddish-browncolor banding is preservedin the outer margin. G4, Keystonemine. Transmittedlight. Scalebar = 52 •m. F. Laths of stage3 white mica apparentlyreplacing stage 3 chalcopyrite.Note projection of laths into the chalcopyriteand the fragmentsof chalcopyriteenclosed by the white mica. Minor pyrite, galena, tennantite, and sphaleritealso present. IM-26, Iron Mountain mine. Scalebar = 52 •m. G. White mica flakesin stage3 sphaleritesubparallel to megascopiccompositional layering. FL1, Mammothmine. Scalebar = 104 •m. H. Fracturedstage 2 pyrite penetratedand replacedby stage3 chalcopyriteand stage5 quartz. Note offsetof one of the chalcopyrite-filledfractures in the center of the photograph. IM-5, Iron Mountain mine. Scale bar -- 52 •m. MASSIVESULFIDE MINEBALOC¾,TEXTURES • ACE RELATIONS 2125

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G 2126 STEPHEN S. HOWE

FIG. 6. A. Stage5 quartz vein enclosingfragments of stage2 pyrite. Thesefragments are penetrated and replacedby stage3 sulfideminerals elsewhere in the sample.A late fracture, not clearly visible in this photograph,cuts the quartz vein. IM-23, Iron Mountain mine. Scalebar = 207 •m. B. Stage 5 quartzsurrounds recrystailiz•d stage 2 pyriteeuhedra that in turn encloserounded blebs of stage3 chaicopyrite.IM-13, Iron Mountain mine. Scalebar -- 52 •m. C. Lathlike crystallitesof stage5 feather quartz with their long axessubperpendicular to the margin of a stage 2 pyrite crystal. Stage 5 white mica is intergrownwith and locallyreplaces the quartz. IM-46, Iron Mountainmine. Transmittedlight, crossedpolars. Scale bar -- 132 •m. D. Stage5 feather quartz extendingfrom marginsof stage2 pyrite crystalswhereas margins of relict quartzphenocrysts are barren of featherquartz. IM-42A, Iron Mountain mine. Transmittedlight, crossedpolars. Scale bar -- 334 •m. E. Late fracturesoffset gashlike veins and podsfilled with deformedfeather quartz in aggregateof fine-grainedbrecciated stage 2 pyrite. IM-9, Iron Mountainmine. Scalebar -- 207 •m. F. Stage5 calcite fills void into which projectsa large recrystailizedstage 2 pyrite crystal, penetratingthe pyrite along fracturesrunning from the top to the bottomof the photograph.Deformation lamellae in calcitenot visible in photograph.Stage 3 chaicopyrite replacesthe pyrite. 566, Early Bird mine. Scale bar = 104 •m. G. Massiveand vein chalcopyrite depositedduring stage5 in voids,fractures, and alonggrain boundariesin polycrystallinequartz. IM- 25, Iron Mountain mine. Scalebar = 207 •m. H. Anastamosingveinlets of stage 6 digenite replacing stage3 chalcopyriteand stage6 bornite. Digenite surrounds,but doesnot replace, rounded stage2 pyrite fragmentspreviously corroded by chaicopyrite.Trace amountsof stage6 coveilite alsopresent. 651, Iron Mountain mine. Scale bar -- 52 •m. MASSIVESULFIDE MINERALOGY, TEXTURES & AGE RELATIONS 2127

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