Canadian Mineralogist Yol.26, pp. 487-504(1988)
SULFIDE_SULFATECHIMNEYS ON THE EAST PACIFICRISE, 11o AND 13oN LAflTUDES. PARTt: MtNERALOcy AND PARAGENESTS
URSULAM. GRAHAM, GREGGJ. BLUTHaNo HIRoSHI oHMoTo Department of Geosciences,The Pennsylvonia State University, University Park, Pennsylvania 16802,U.S.A.
ASSTRACT speciesfor FeS2,but also recrystallization and replacernent of earlier minerals in warmer conditions. Hydrothermal fluids up to -350.C emerge . o from vent sitesar I I and I3"N latitudes,East pacific Rise. Varia_ Keywords: chimneys, hydrothermal, sulfides, sulfates, tions in the morphology, zoning and mtneralogyof 27 chim_ mineralogy, zoning, paragenesis.East Pacific Rise. neys from I I vent sites can be representedby three active a1{ ge eltinctdogged chimney. Microscopii observation SoMMAIRE of 127 polished sections of these four chimneys has rev_ ealedfour types eachofmarcasite, pyrite and wurtzite, and Des fluides hydrothermaux atteignant une temp6rature lwg.types of sphalerite, which are distinct in their crystal d'environ 350oCsont 6mis des€vents aux latitudes llo et habits. Th€ consistency in the parageneticsequ.n.. und io l3oN, le long de la ride Est-Pacifique.Les variations en the spatial distribution with respect to the exterior chim_ morphologie, zonation et mindralogiede 27 chemin6espro- ney wall of theseFe and Zn sulfides, as well as anhydrite, venant de I I sites sont bien repr6sentdespar trois chemi- cialcopyrite and bornite in these four chimneys ,r,ggot, ndesactives et une €teinte qui est engorgdede d6p6ts. Un all chimneys tha-t in the ll vent sites ,epresent sililar examen par microscopie de 127 sections prdlevdesde ces hydrothermal processes.The variation among the chimneys quatre chemindesr6vble la prdsencede quatre g6n6ralions reflects simply the difference in the maturity (ongevity of de marcasite, pyrite et wurtzite, et deux de sphal6rite, dis- vgnting) preservation and of a complete liaeirty ctrlmney, tingudespar leur habitus. La concordancedans la sdquence which is comprisedof 8 mineralogicalzones. Formation paragen6tiquede ces sulfures de Fe et de Zn, de l,anhy- of zone-l gugerals (anhydrite with minor subhefual pyrite, drite, de la chalcopyrite a de la bornite, aussibien que dans and anhedral marcasiteand wurtzite) takes place during leur distribution par rapport d Ia paroi externe, fait penser mixing of hydrothermal fluids and cold seawaterwhen the que toute chemin6edes I I sitesd,€vents r€sulte de proces- rate of mineral precipitation exceedsmineral dissolution sus hydrothermaux semblables,et que les variations enrre by cold seawater. During outward growth of a chimney, les chemindess'expliquent simplement par les diff6rences zone-l minerals are continuously dissolved by later en maturit6 (durdede l'€mission)et en degr6de prdserva- hydrothermal fl uids, and also metasomaticallytransiormed tion d'une chemin6ecomplbte iddate, qui comprendhuit successively to zone2 (mostly large colloform marcasiteand zones min6ralogiques. Les mindraux de la zone I (anhy- wyt?ite), (mostly zone 3 cubesof pyrite and colloform drite, pyrite sub-idiomorpheaccessoire, avec marcasite non- sphalerite),zone (mostly 4 bomite), and zone 5 (mostly chal_ idiomorphe et wurtzite) sesont form& lors du m6langeentre copyrite); some new minerals (e.g., cubes of iyrite, le fluide hydrothermal et l'eau de mer froide, lorsque le sphalerite, chalcopyrite) also precipitate directly from the taux de pr6cipitation est superieur au taur( de dissolution hydrothermal fluids within the pore space created by the desmin6raux dansI'eau de mer ambiante. Pendantla crois- dissolution of zone-I.minerals. With continued u.n'tiog, sanceexcentrique d'une chemin6e,les mindraux delazone I channel openings enlarge, imd each sulfide zone tends ro sont continuellement redissous par les fluides hydrother- become wider and monomineralic; the width of the maux plus jeunes, ainsi que transform6s par m6tasomato- anhydrite-rich zone l, however,becomes larger during early sessuccessives en assemblagesdes zones 2 (principalement venting and then decreaseswith time. Clogging of a-chim_ de la marcasite colloforme d grains grossierset de la wun- ney occurs during the waning stageofhydrothermal activiry, zite), 3 (principalement des cubesde pyrite et de Ia sphal6- by precipitation -8 of zone-7 and minerals (wurtzite, mar_ rite colloforme), 4 (principalementde la bornite), et 5 casite pyrite) and along the inner chalcopyriie wall oizone (principalementde la chalcopyrite). Certainsmin€raux (par 5, and recrystallization in time to form zone6 (mostly pyrite exemple, cubes de pyrite, sphal6rite et chalcopyrite) sont a1d sphalerite). With decreasinghydrothermal activlty, tne aussidirectement pr6cipit& desfluidc hydrothermauxdans chimney walls begin to dissolve fiom the outside bv?ac_ les pores cr6espar la dissolution des min6raux de la zone tion with cold se:rwater.The observedparagenesis suggests l. A mesureque l'6mission progresse,les orifices s'€lar- that the ratesof cooling and oxidation, as will as tt . -.:tut_ gissent,et chaquezone de sulfures tend i devenir plus large sulfur chemistry of hydrothermal fluids, are important et monomindralique,except€ la zone l, qui s'6largit pen- parameters that control the chimney mineralogy. Quench- dant les stadespr6coces pour ensuite diminuer au cours de ing of H2S-rich fluids, causedby rapid mixing wiih cold l'€volution d'un 6vent. L'engorgement d'une chemin€e seawater, may result in precipitation of pyrrhotite and wun_ caracteriseles stadesterminaux de I'activitd hydrothermale, zite, while anhydrite precipitatesby incorporating SOr2- lors de la pr6cipitation desmin6raux deszones 7 ef 8 (wun- oI locat s€awater. Anhydrite layersformed by zucha process zite, marcasiteet pyrite) le long de la paroi interne'de chal- may play important roles both physically and chemically copyrite de la zone5, et de leur recristallisationdventuelle in the development of sulfide mineralogywithin the chim- pour former la zone 6 (principalement de la pyrite et de ney_walls by creating environments that promote not only Ia sphal6rite).Au cours de la diminution de I'activit€, les oxidation of hydrothermal H2S to generate polysulfide parois d'une chemindesont progressivementdissous par 481 488 THE CANADIAN MINERALOGIST
rfuction avecI'eau de mer froide. La s6quenceparag6n6ti- by Haymon & Kastner(1981), Oudin (1983),Gold- que observ6eindique que les taux de refroidissementet farb et ol. (1983),and Haymon (1983).Lareer, struc- d'oxydation,aussi bien que les relations chimiques entre turally more complex sulfide deposits than those m6tauxet soufredans les fluides hydrothermau(, exercent from 21oN have been found on the Endeavor and un contr6leimportant sur la compositionmindralogique of the Juan de Fuca Ridge, d'unechemin€e. Un refroidissementbrutal de fluides riches Middle Valley Segments en H2Spar m6langerapide avec l'eau de merpourrart cau- and are described respectively by Tivey & Delaney serla prdcipitationde pyrrhotite et dewurzite, tandisque (1986)and Tunnicliffe et al. (1986).The chemical I'anhydriteserait precipit€e par incorporationdu SOa2- evolution of ocean-ridgehot springsis describedby provenantde l'eau demer ambiante.Les niveaux d'anhy- Bowers et al, (1985), and a laboratory and theoreti- drite ainsiform6s pourrart jouer desr6les physique et chi- cal study of the growh of black-smokerchimneys miqueimportants dans le d6veloppementde la mindralogre is given by Turner & Campbell (1987). dessulfures i I'int6rizurdes parois d'une cheminde en cr6ant Chimney samples from the vent sites studied by qui, provoquent du desmilieux non seulement l'oxydatron previousworkers are similar in many respects.For pour permettrela formationd'espdces H2Shydrothermal of chal- polysulfur€esaux d6pensdu FeS2,mais aussi facilitent la example,the chimneysconsist dominantly recristallisationet le remplacementdes min6raux pr6coces copyrite, pyrite, wurtzite (sphalerite),and anhydrite, dansles milieux plus chauds. although their proportions vary greatly among the (Traduit par la R6daction) chimneys. There are regularities in mineralogical zonation, with a nearly monomineralic chalcopyrite Mots-cl&: chemindes,hydrothermal, sulfures, sulfates, layer at the interior walls of the chimneys, and an mindralogie,zonation, paragendse, ride Est-Pacifique. increasetowards the exteriorsin the abundanceof disseminated Fe and Zn sulfides associated with INTRODUCTION anhydrite. Replacement and overgrowth textures Within the past decade, hydrothermal systems among sulfides are also common to all chimney activelydepositing sulfides of Cu, Fe, and Zn have structures. been examinedat numerous locations along oceanic Previous investigators recognizedthat minerals in spreading ridges. The strongest manifestation of the chimneys were formed by two concurrent hydrothermal activity occurs within axial grabens processes:direct precipitation from the mixed solu- (H6kinian et al. 1983, Ballard et al. 1984). The tions of hot fluid and cold seawater,and replace- hydrothermal vents dischargemetal- and H2S-rich, ment or recrystallization of the earlier minerals acidic, high-temperature(up to -350"C) fluids into within the chimneywall (e.g., Goldfarb et ol. 1983, cold seawater; sulfide and sulfate minerals precipi- H6kinian et al. 1983,Tivey & Delaney1986). Initial tate from the mixtures of hydrothermal fluids and chimney growth starts with the rapid precipitation seawater. of anhydrite and minor sulfidesto establisha perme- Precipitates from high-temperature vents seemto able chimney wall (Goldfarb et al. 1983,Haymon representthe modern equivalentsof ancient massive 1983).The wall functions as a partial barrier between sulfide deposits, and as such, provide a unique hydrothermal fluid and $eawater, restricting their opportunity. to document ore-forming processes. mixing. At subsequenthigher temperatures within Similarities between ancient and modern massive the chimney, mineral precipitation and replacement Fe-Cu-Zn sulfide depositsinclude: (l) deposition on createthe observedsulfide-sulfate zoning sequences. the oceanfloor at depths >2000 m; (2) formation Variations in the relative abundanceof sulfide to sul- of the main sulfide phases by reactions of hot fate can be related to the growth stage$or relative (- 150-350'C)fluids with cold seawater;(3) sulfides maturity of the vent structures(Goldfarb et al. 1983), of Fe, Cu, ard Zn as the dominant metal-bearing These authors suggested that differences in the phases(Styrt et al. 1981,Ohmoto & Skinner 1983, Ot/Znratio in chimneysfrom 2loN were controlled Ohmoto 1988). The advantageof studying these by the thermal history of the hydrothermal fluids: modern systemsis that the processesand products Z*ichchimneys fonned from fluids of I < -300oC, of active mineralization can be observed, and the and Cu-rich chimneys formed from fluids of deposits can be sampled in their unaltered state r > -300'c. without the complexities introduced by metamor- Nevertheless, many questions about chimney phism and deformation. growth and sulfide mineralogy remained. Problems Sulfide depositsalong the East Pacific Rise (EPR) requiring further study involved: i) the temporal and near 11o,13o, and 2loN, and on the southernJuan spatial relationships between marcasite and pyrite, de Fuca Ridge have similar geological settings and between wurtzite and sphalerite; ii) the (H6kinian et al. 1980 1983, Hekinian & Fouquet dominanceof pyrrhotite in the smoke, but of mar- 1985,Ballard el al. L984,Koski el a/. 1983,McCona- casite and pyrite in the chimney walls; iii) the res- chy et al. 1986,Normark et al. 1986).The mineral- triction of abundant chalcopyrite to inner chimney ogy and chemistryof samplesfrom active and extinct walls and its near-absencefrom the smoke; and lv) hot-spring sitesalong 2l'N EPR havebeen studied the causesof both regularities and variability in the SULFIDE-SULFATE CHIMNEYS. EPR 489
mineral zoning. The major objecfives of this study NV were, therefore, to put constraints on the above NORTH problems by investigating in detail the mineralogy AIlERICA and paragenesis,both of active and extinct chimneys, from llo and l3'N. This study also servesas ihe framework for a sulfur isotope study reported in the accompanyingpaper by Bluth & Ohmoto (l9SS). PACIFIC 15. oCEAN
Sauplns The chimney samplesused in this study were col- lected by L.K. Reilly of The pennsylvania State University, J.M. Edmond of The Massachusetrs Institute of Technology, and other members of the 1984ALYIN - expedirionat l3oN (dives1366 through 0 5(}oi 1375),and ll'N (dives1377 through 1380)of the EPR. Their geologic settings are described ^ Aafvsvsrisfre8 by Bal- " (amD& l@!oB) lard et al. (1984)and McConachy et al. (1936). A Vodsao8otthb6tudy A total of 27 chimney samplesfrom I I vent sites (appu. lGlbE) was examinedmacroscopically for the preservation /\ of vent porosity, ) / *ts""o"n structures, mineral abundances, t) zonation, thicknessof individual mineral layers, and Ved6n6 Djtqj Chlmnoy crystallinity of minerals.The generalappearance of I 1388 2 1369 the chimneys varied, particularly the thickness and 3 1370 D relative positions of mineral 4 1975 layers; measureddis- 5 1371 chargetemperatures also differed at the active vents. 6 1971,2 7 1373 A Four chimneys,representative of the range of vent 8 1373 9 1379 C structuresat llo and l3oN, were selectedfor detailed 10 1377 B 0 looom investigation (locations in Fig. l). Three chimneys I I l3a0 (A, B, C) were active when sampled; the fourth (D) was extinct. Ftc. l. Locationsof chimneysamples collected from I I o and l3o N latitudes,EPR, during the ALVIN divesin Chimney A (onhydrite-rich) May-June,1984. After Ballardetal. (1984),L.K. Reilly (pers, This chimney was sampled from vent site comm.1985), and A.C. Campbell(pers. comm. #7 1986). (12" 49'N) where hydrothermal fluids were emitting at 380oC,although this temperaturehas beenques- tioned (Bowerset ql. 1988).The recoveredpart of the vent structure is 64 cm long, averages20 cm in (Frg. 3b). A bornite-rich zone (-0.5 cm) occurs diameter, and branchesupward into two indiiidual immediately externally to the chalcopyrite layer. conduits (Fig. 2a). The outer pafts of the chimney walls are composedlargely of anhydrite and dissemi- Chimney C (Cu-rich) nated (-590 in volume) sulfides (pyrite + marca- Chimney C was collected from vent site #9 site + wurtzite * chalcopyrite; Fig.3a). A l0- (11'14'N). The temperatureof the hydrothermal 50 pm-wide bornite-rich layer and a l-5 mm-thick fluids was not measured.The chimney consistsof chalcopyrite-rich layer line the inner wall. a single 69-cm-longconduit, and has an averagewall thickness of 15 cm (Fig. 2c); five auxiliary conduits Chimney B (Zn- and Fe-rich) are also present.The outer two-thirds of the chim- ChimneyB, collectedfrom vent site #10 (l0o5g,N), ney consists of massive sulfides of Zn and Fe, - consistsof four individual conduits (Fig. 2b). Only whereasthe interior one-third ( 5 cm) is rich in chal- one conduit was active when sampled;the fluids were copyrite (Fig. 3c). Anhydrite is not visible macro- dischargingat 347oC.This conduit was selectedfor scopically at the chimney exterior, but was recog- microscopicstudy. It is 30 cm long, with chimney nized microscopically and by X-ray diffraction walls averaging 6 cm in thickness. The active con- analyses. duit is characterizedby athin (- I mm) exterior layer of anhydrite, a thick ( - 4 cm) transition zone of mar- Chimney D (inversely zoned) 9as1te + wurtzite + pyrite, and an inner lining This e)fiinct chimney, from veirt site #3 (12.51,N), (-2 cm) of nearly monomineralic chalcopyrite is 25 cm long with walls -3 cm thick; the top is 490 T}IE CANADIAN MINERALOGIST
A (actlve) B (actlve) neys, followed by wurtzite. The Cu-Fe sulfides are primarily chalcopyrite, isocubanite, and bornite. Along the conduit (and the exterior wall of Chim- ney D), chalcopyrite is the dominant sulfide (up to 90 vol.9o). Isocubaniterepresents less than l09o of total Cu-Fe sulfides. Bornite and covellite can be tie dominant phasesin particular zones,but account for less than a few percent of total Cu-bearing sulfides in a chimney. Traces of digenite and chalcocite are present. Sphalerite constitutes between 0-8090 of different zones, and +37 cmr toial Zn sulfides within the generally occurs internally to the wurtzite, exceptin the extinct chimney. Pyrrhotite (< I q0) was observed c (actlve) D (extlnct) only in the innermost layer of Chimney C. The pyr- rhotite occurs as inclusions in chalcopyrite and in -28 cttFr 17 cn.r pyrite cubesas prismatic and strongly fractured crys- tals. Non-sulfide phasesinclude anhydrite, minor silica 25I cm barite (<590 of total sulfate)and amorphous (<590 of the total mineral assemblage);they occur only at the exterior walls of chimneys A and B.
Anhydrite Anhydrite may form up to 70 vol. 9o of the wall I in Chirnney A. Anhydrite crystals (100-600 pm) are Frc. 2. Sketchesof the four chimneys(A-D) investigated predominantly perpendicular to channelways; in detail. banded structures and oval clusters up to I cm in diameter are also present. Anhydrite forms a broad outer wall in Chimney A, a thin rim in Chimney B, cloggedwith sulfides(Fig. 2d). The most striking fea- and a minor dissemination in the outermost zone of ture of this chimney is the reversemineralogical zon- Chimney C. Anhydrite is not observed in extinct ing comparedto active chimneysA, B, and C. The Chimney D. The anhydrite zone in chimneys B and exterior wall is a chalcopyrite-rich layer - lcm thick; C could haveoriginally beenas thick as that in Chim- the insideis filled by marcasite,pyrite, wurtzite and ney A, but appearto have eroded,probably due to sphalerite(Fig. 3d). Anhydrite is not present. the continuous reactions with hydrothermal fluids The preservationof anhydrite in the chimney walls and with seawater;corroded remnants and replace- and the spatial relationship among various sulfide ment textures (pseudomorphs)of anhydrite by mar- layers are the criteria on which we baseour estimate casite and wurtzite are common in the outermost of the relative agesof the chimneys.In our model, zone of chimneysB and C. ChimneyA is the youngestvent type, followed suc- cessivelyby B, C, and D. Chimneysof type A and Iron sulfides B are most common among the 27 samples.Type Four types of pyrite and four types of marcasite D is representedby only one sample. have been distinguishedbased on differencesin their grain size, crystal habit, crystallinity, porosity and TEXTURES, PARAGENESIS AND COMPOSITIONS inclusionsofother sulfides.In general,pyrite is the or CHilraNEv MINERALS most abundant Fe sulfide in all samples;it accounts Cross-sectionalslices of the base,center and top for about 40 vol.9o of ChimneYB. of eachchimney structure were prepared. A total of Important characteristics of the four types of 127polished and doubly polishedthin sectionswas pyrite are summarizedin Table l. Pyrite-l consists examined,representing 19 traversesfrom the out- of euhedralcubic and pyritohedral crystals, 5-50 pm side to the inside walls of chimneysA through D. across, but usually <10 pm. It occurs within the Reflected-and transmittedJight microscopy,X-ray anhydrite walls of Chimney A (Ftg. 4a) and is a diffraction, and electron-microprobe analyseswere minor constituentof the interior walls of active chim- usedfor mineral indentification and textural interpre- neys, but is absentfrom extinct Chimney D. tation. Microprobe analyseswere carried out on Pyrite-2, the most abundant type in the active wurtzite, Cu-Fe sulfides, pyrite and marcasitd. chimneys,occurs as coarse-grained(100-5@ pm), In general,pyrite and marcasiteare the most abun- subhedral to euhedral crystals and their clusters. dant sulfides in the outer parts of the active chirn- Sorheof the clustersform semilinearto curved bands SULFIDE_SULFATE CHIMNEYS, EPR 491 b
,II{TEFIOR EXTERIOR INTERIOB EIIEBIOF r-- Abn ,lhbn Dv2 = o FV2 o :f *ffiM*-. Pv1 -ffiilMffitrilMm.qY1 F (u f E' o (! c 3 c .ph1 !ph1 (! 3 o r{frfiftnprh o *milfrnllllMrn*- (! O o o o mc2 U' mc2 (mcl) a zffix ncl "x*lM!$Mmn uu2 wuz (wul) if$l[ltfihl'* uul *ffirffffiMMnmtm a:I#.'.-sf...{,ffi.. arhy Chlm.tA (Trruu -380t) ChhmyB (T1utd r34fO) c -INTENIOR EITERION ,lrrEnton ETTERIOR cHmEY srr I cflrlt{EY WALL X "*l bn -ffih. (l) o :t -ua PY' - PYzffisMfifiM a' (U 3 c ^- 3 (d (d (l) o o !ph'l O o --,antmfiillMktmmn a !ph2, -',*PjJ' ct) mc2 ffi-* uu2 Jbtort Chtmnoy C (T'l!ld unknoun) Chlnncy D (tirutd untnom, f nAssrvE Ar{HvDRlrE [#.ffi| m DtssnitnATED Ftc. 3. Representationof the occurrencesof major minerals in chimney cross- sections. up to severalmm in length. Cubesof pyrite-2 crys- tains inclusionsof marcasiteand wurtzite (Frg. 4d). tals commonly occur in the inner parts of the Fe- The size and texturesof somepyrite-2 crysali are and Zn-rich layers of ChimneysA and B (Fig. 4c,d), reminiscentof colloform marcasiteaggregates which but are lessabundant in the chalcopyrite-richzone. commonly form at the outer parts of the Fe- andZn- Pyrite-2 is the dominant sulfide at the exterior wall rich layersin Chimney B; etch testsof relatively large in Chimney C, and is the most abundantFe sulfide massesof pyrite-2 show small (<10 rr.m)cubes of at the exterior wall of Chimney D. Most pyrite-2 con- pyrite-l or colloform texturestypically observedin 492 THE CANADIAN MINERALOGIST of pyrite-4 are slightly curved; such textures appear growth of precur- trKrBrsosY cl\rN to have beenproduced during the SEoa) PBASBII BY sor twinned marcasite crYstals. ITRITB-I ffil 5-C) t0 @1, sl, ctry v2,qr The four typesof marcasiteare listed in Table l. PTBIII.z qh m-lm EO 8r9, vd,!pbf, q:t (5-20 pm) cpt Marcasite-l occurs as small anhedral PYRIIE.3 dffi lo-rm $3 grains, coprecipitated with pyrite-l in the anhydrite- }YRNE4 !odu&rO-S @1,St2 rich zone of Chimney A. Marcasite-2, which con- MARCA$Tts.1 amqd 5 -a l0 gtl,sl,qry N\qt (50-5m pm) grains with a col- MI\RCASTTB-2 oloh to-J(n gl e62,fr\w vr2,qy sistsof large anhedral MI|ICASIII'3 Omngh g)-6m 5 eu4,ot4,py4 @4,tY4 loform texture, is common in the outer parts on the b)!.6d16 l0-2U) Er4,!$ @4,!f4 MARCASTTB4 M&db&10-lO 5 @{,s@ I Fe- and Zn-ich zone of chimneys A (Fig. 4b) and walls wuRrzrftsl &l r50 10 pyl,@l,qrt qr B, and occurs in minor amounts in the interior vurrzrrB-2 dlee 5030 g) o!2,!t'2,sDbl, rpy,Ahr chimneys A, B, and C. Most marcasite-2 cst of active wurxzxr&3 cldg@ rGr0 t0 !t3 | grains have undergone replacement by pyrite-2 cteb WIJIIxZIB4 d Frc. 4. Photomicrographs illustrating the mineral textures in chimneys A through D under reflected light. A scale bar = is displayed at the bbttom of each photo: double horizontal bar = 50pm, single horizontal bar 300pm; !Y Pfrite, cpy chaliopyrite, mc marcasite, wu nurtzite, sph sphalerite, bn bornite, anhy anhydrite. The numbers following pi', *., wu and sph refer to subtypes. The dark grey areas are anhydrite crystals; the black spots are voids. ia) Characteristic mode of subhedral to euhedral pyrite-I, anhedral marcasite-l, and extremely fine-grained chal- copyrite occurrence within an anhydrite-rich wall (grey matrix). @) Precipitation of colloform marcasite-2 and wurtzite-2 with no replacement textures. grain Gj krge-zubhedral to euhedralpyrite-2 crystalsthat replacedcolloform marcasite-2at the interior. The marcasite- 2 textures show concentric layetringand onset of pyrite replacement as indicated by the color differencq within the layers. Small voids are disseminatedwithin the pyrite-2 crystal rrhich is partly replaced by chalcopyrite. 1d) Cubes of pyrite-2 with inclusions of wurtzite-2. Marcasite-2 in the right upper corner is almost entirely replaced by pynte-2. Chalcopyrite partly replaced both pyrite-2 and wurtzite-2. (i 3btraterite-t witliintenie chalcopyrite disease.Chalcopyrite replacement proceeded from the rims and growth zonei of sphalerite-l and penetrated towards grain interiors. Pyrite-2 is replaced by chalcopyrite. (f; Round6d and corroded isolated islands of pyrite-2 and less abundant sphalerite-l occur in the chalcopyrite-rich zone. Pyrite-2 in center forms atoll textures in the paragenetically later chalcopyrite. Sphalerite-l is free of chal- copyrite disease. record intense 19 itre field is dominated by elongate pyrrhotite crystals intergrown with chalcopyrite. The textur$ iia"toring of the pyrrhotite with rounded and corroded edgesdue to replacementby chalcopyrite, and the preserva- tion of small pyrrhotite grains inside pyrite-2 cubes. 493 '' .ir',i1 I i1 :f - pyrite"?..and.ffinor*ph6lerite-1. Pyrite-2 cubeshavb been copyrite along cracks. Somechalcopyrite grains are completely replacedby bornite and by later covellite (blue lines). (i) Cross-section olf shimney I). () Enlargement of (i): from right to left the textures record the growth of chalcopyrite by partial replacement of pyrite-2 cubes, a massivelayer of pyrite-4 blades, the inclusion of anhedral sphalerite-2within pyrite-4 blades, large colloform marcasite-3 aggregates,and the occurrence of subhedral rvurtzite-3. TIIE CANADIAN MINERALOCIST , .lrrkry#HFffill -, @4v&1t;iiqkstsi$asffisw€s_4Fffi**lres I I -rffid#ryr - (k) Intergrow.th of pyrite and chalcopyriJsr-fiffi+ bhdes include chalcopSnitelamellae in onFogGEl-and trian- gular arrays. Pyrite-4 blades are not replaced by chalcopyrite, but chalcopyrite lamellab are replaced by pyrite-4. @ Highly rounded pyrite-4 blade with chalcopyrite lamellae occuring perpendicular to the erowth surface of pyrite-4. (m) Selectivereplacementofamarcasite{gainbypyrite4asindicatedbythesameinterferenecolorofthemarcasite-4 remnants. Pyrite-4 blades form a massive layer. Pyrite-2 at the l€ft upper corner is reflaced by chalcopyrite. (n) A large marcasite-3grain partly replaced from the outside by pynte4 shows a seriesof sphalerite-2 inclusions. The interior has a fine-grained texture. Pyrite-4 blades at the lower rigbt are highly anisotropic. SULADE-SULFATE CHIMNEYS, EPR 495 1q-:W (oj Mareasite-3 is a conibination of aggregatesanq erongalecrystars. ,neffiy *ro.pu.", indicate a high porosity of marcasite-3. Somemarcasite-3 shows inclusions of extremely small wurtzite-4. Wurtzite- 3 occurs outside the marcasite-3 and shows no textural relationship to marcasite-3. , (p) Enlargement of (o): wurtzite-4 with a hexagonal crmtal habit occurs in a matrix of marcasite-3. (q) Marcasite-3 and pyrite4 in nearly monolninsl6[is zones; many voids occur at the interface of both zones. (r) The textures record the growth of dendritic pyrite-3 rvhich occurs in the paragenesiswith subhedral wurtzite-3. Some wurtzite grains are encrysted by dendritic pyrite. 496 TTIE CANADIAN MINERALOGIST ent forms'"of sphalerite have been'distinguished s)Fo92 microscopically. Wurtzite-l occurs as small (5- feS2.TYFE tot Cmt XII&Y Cqlrl l 50 pm) grains in association with pyrite-l and CTAINI marcasite-l within the anhydrite-rich zone of Chim- PYRTTE.I 2tA 0.05-0.10 0.6-010 4'02 ney A. It is not observed in the extinct chimney. PYRITts.2 25 A,B,C 0.6-0.13 0.10-03 4u2 PYRIIA.3 t7D 035-0J5 Table 3, Charactorlgtlc mlnoral A$omblagss and products of reaction betweenfacies-S sulfides and Spatlal Relatlonshlp of ll,lheral Facle3 later, cooler fluids. Zone 5. Massive, coarse-grained chalcopyrite FACIES intergrown with isocubanite.Pyrite-2 and sphalerite- Dlagnostlc Ulneral Phaseg I (+ wurtzite-2) are also presentwithin the pore 't (10-20 to be 7 5 4 2 space vol.9o). Facies-5minerals appear Chlmnoy replacementproducts of facies-3minerals. ru3 n03 ry4 ,Py rPy \12 naz ty3 ,u4 nc4 at tn ]ph1 ru2 )rl Zone 6. A massivepyrite layer composedprimarily Sample rphi ,,'2 tyz 1U2 rrt rul :py ]ph' rph :py ncl ncl of aggregates of pyrite4 blades with relicts of iv2 ru2 tyr :py rpy to nc2 marcasite4 (-10 vol.9o). Sphalerite-2occurs as rnht inclusions in pyrite4 and marcasite-4, and as over- #growth on the FeS2phases. D Zone 7. Marcasite-3 with minor (<0.1 vol.Vo) c hexagonal vrurtzite-4 inclusions. B Zone 8. Subhedral wurtzite-3 crystals with over- growths of dendritic pyrite-3. Zones6,7, and 8 are A {arestricted to the interior of extinct Chimney D. Facies-7 and -8 minerals appear to have grown Chlmnoy Wlll inward from a chimney wall composedof facies-5 minerals; facies-6sulfides appear to bethe recrystal- lization products of facies-7and -8 minerals. mineralogical zone is characterized by a distinct Our interpretation of the changewith time in the mineral assemblageand textures, and becausethe widths and the positions (relativeto the chimney con- mineralogicalzones €re not stationary during the his- duit) ofthe 8 mineralogical zones(facies) in an ideal- tory of a chimney; they may migrate outward or ized chimney is illustrated schematicallyin Figure 6. inward in a chimney, be replaced by other minera- Horizontal lines in Figure 6.represent the order of logical zones, or be dissolved away by later mineralogical zones which a fluid of a given stage hydrothermal fluids or by local seawater.The use of hydrothermal activity might encounter during its of "mineralogicalfacies", rather than "zones", has migration from the channelway, through the chim- beenjustified by Eldidge et ol. (1983)in their miner- ney'rvall, to the surrounding seawater.For example, alogical study of Kuroko and other volcanogenic the fluid discharged at time C may encounter suc- massivesulfide deposits. cessivelyfacies 5 + {+ !+ 2' I during migration The 8 mineralogical zones (facies), aligned from outward. Therefore, a horizontal line is equivalent the exterior to the interior in an idealized chimney, to the representationof a cross-sectionof a chim- have the following characteristics: ney wall at a given stage of its growth history. Zone 1. A porous framework of anhydrite crys- Horizontal linesA, B, C, and D representthe cross- tals with <5 vol.Vo of disserninatedsulfides (pyrite-t sectionsof chimneysA, B, C, and D, respectively. + marcasite-l + wurtzite-l t chalcopyrite). Facies- Their relative positions with respect to the / (time) I minerals are very fine grained, suggestingthat they axis imply that these chimneys represent different formed rapidly by mixing of hot fluids and cold sea- stages of the development of an ideal chimney. waxer. Our chimney-growth model (Fig. 6) incorporates Zone 2, Aggregatesof marcasite-2 and wurtzite- the following major conceptsconcerning the growth 2 (up to 80 vol.9o) with minor pyrite-l, marcasite-l and preservation of chimney structures: and relicts of anhydrite. Some facies-2 minerals 1) The chimneys grow outward when the rate of appear to have formed as recrystallization products precipitation on the exterior wall of facies-l minerals of facies-l minerals;the others appearto be direct (anhydrite + wurtzite-l + pyrite-l) exceedsthat of precipitatesfrorh hydrothermal fluids within the pore mineral dissolution by the surrounding seawater. spacesin zone l. During and after waning of hydrothermal activity, Zone 3. Coarse-grainedpyrite-2 (> 60 vol.Vo), chimneys are dissolvedby cold seawaterand dimin- sphalerite-I, and wurtzite-2with minor amountsof ish in size becauseseawater is undersaturated with pyrite-l and marcasite-2.All Fe-Zn phasesare partly respectto the chimneysulfides and sulfates.Disso- (-3090) replacedby chalcopyrite.Facies-3 minerals lution continues until the chimneys are covered by appeaxto be mostly the recrystallization products of sediments or oxidized to ferric oxides (or both). facies-2sulfides, but some may have precipitated 2) During the outward growth of chimneys,'the directly from hydrothermal fluids. earlier formed minerals on the inner wall are con- Zone 4. Sulfur-rich Cu sulfides(bornite t covel- tinuously dissolved by later hydrothermal fluids, lite t digenite) with chalcopyrite, pyrite-2, and becausethe fluids are initially undersaturated with sphalerite-I. Facies-4 minerals appear to be the respectto the chimney minerals. The larger conduit SULFIDE-SULFATE CHIMNEYS, EPR 499 6l l. l FACIES ol trl E 1. anhydilte-rlch EI ct 22. marcaslte+ wurzlte ol I lllll3. pyrlto ol tl E 4. bo?nlte-rlch o' o Nl 5. chalcopyrlte 'r o 6. pyrlte c fl ! Nl ?. marcaslie ()E El 8. wurtzlte --- E A, B, C, D = ChlmneYTYPe t E 2.t >rl ol gl EI gl ol I ol ttt I cl irl ol INSIDE OUTSIDE (Scale Varlable) Ftc. 6. Schematicdiagram illustrating the growth and dissolution history of a model (ideal) chimney. The spatial rela- tionships of different mineralogical zonesor facies of chimneysA, B, C and D are compared. Maturity of the chim- neys is indicated by the vertical axis. The horizontal axis shows the relative distance from the chimney conduits to the exterior walls, which simply reflects the width of the chimney wall. Chimney A is interpreted as the least mature and Chimney D as the most mature. PPT: mineral precipitation rate; DISS: mineral dissolutionrate. Seetext for further explanation of the model. diameter of Chimney C relative to Chimney A during skarn mineralization, with a major difference (*7 cm versus *3 cm) suggeststhat the rate of that the material replaced is anhydrite instead of mineral dissolution at the inner wall exceededthat limestone. of mineral precipitation in the active chimneys. 4) Conduits fill when the rate of mineral precipita- 3) The hydrothermal fluids that migrate through the tion on the interior wall exceedsthat of mineral dis- chimney wall react with the earlier minerals, dissolv- solution during the waning stage of hydrothermal ing them or transforming them (or both) successively activity. Some of theseminerals transform to more to the mineral assemblagesthat are more stable at stablephases during interaction with later fluids. For higher temperatures(e.9., facies | - 2 - 3 - 5 * 4). example, facies-6 minerals (pynte4.) of Chimney D Some of the dissolvedmaterials from the interior are probably the products of transformation of zonesmay reprecipitatein the pore spaceofthe outer facies-7 and -8 minerals. zonesor on the exterior surface. That is, eachminer- processes growth alogical zone contains the old materials (sulfur and Chemical of chimney metals), which were fixed there as earlier minerals, Anhydrite. The precipitation of anhydrite as well as the younger materialsthat wereintroduced (CaSO) during the mixing of hydrothermal fluid there by later hydrothermal fluids. The proportion and cold seawaterhas been noted by many investi- of older to younger materials increasestoward the gators (Spiesset al, 1980,Ohmoto et al. 1983).The outer zone; the outermost zone (anhydrite-rich zone) Ca2* in anhydrite is derived largely from the contains the highest proportion of the oldest hydrothermal fluids; sulfur isotopeevidence indicates materials. This is in good agreementwith sulfur iso- that the SOa2- is derived from local seawater tope data obtained in thesechimney zones(Bluth & (Kusakabeet al.1982). Ohmoto 1988).The chimney-growthprocesses are, The anhydrite of facies I is continuously dissolved therefore, analogousto the migrating reaction front from chimney interiors by later hydrothermai fluids 500 THE CANADIAN MINERALOCIST becausethese fluids are nearly sulfate-free (e.g., (and FeS) produced from reactions (3) and ( ) Edmond et ol. 1979,Styrt e/ ol. 1981,Von Damm would not exceed- l}a m, However, the O, con- et al. 1983, Ohmoto et al. 1983). The anhydrite is tent of normal (oxic) seawater in deep oceans also dissolvedfrom the chimney efierior by cold sea- ( - tO-''t m; Drever 1982)and the H2 content of the water becauseseawater is undersaturatedwith respect EPR fluids (-10-''trz; Welhan & Craig 1983, to anhydrite. Ohmoto 1988)are lessthan the H2S content of the Fe sulfides. High-temperaturehydrothermal fluids hydrothermal fluids (l0r - l0-t m), but they are developedin basaltic rocks are typically at or near sufficiently high to becomequantitatively important the saturation conditions of both pyrrhotite and in the formation of FeS2via reactions (3) and (4). pyrite; they typically have H2S contentsof l0-3 - Normal seawater contains large amount of SOo2- l0-t moles/kg I{2O and DSOnz-contents of < l0-3 (- ltrt't m; Dreva 1982).The ratesof reactions(3) moles/kg HrO at T -- 250_4f0C (e.9., Edmond e/ - (6) appear to increaserapidly with increasingtem- al. 1979,Slyrt e/ al. 1981,Von Damm et al, 1983, perature(f>" 150"C), and with decreasingpH (.<4; Von Damm 1988,Ohmoto 1988).It hasbeen demon- ohmoto 1988). strated experimentally by Murowchick & Barnes During the rapid cooling of hydrothermal fluid (1986a)that simplecooling of such fluids resultsin (from -350oC10 -zoc in -seconds)due to mix- precipitation of pyrrhotite (FeS), rather than pyrite ing with cold seawaterabove the chimneys,the reac- or marcasite(FeSJ: tion rates of (3)-(6) are probably much slower than Fd*+HoS*FeS+2H+ (t) the reaction rate of (l), explainingwhy pyrrhotite, Thus, simple cooling of the hydrothermal fluids can rather than FeS, minerals, is the dominant Fe- explain the presenceof pynhotite in the black smoke sulfide phasein the black smoke(Ohmoto 1988).If (e.9., Haymon & Kastner l98l) and also in the fluid mixing occurs slowly within warm chimney interior of Chimney C. structures, formation of polysulfide species (and Formation of FeS2minerals requires polysulfide FeS2minerals) via reactions (3) through (6) may be species,such as H2S2and HSr- (Murowchick & facilitated. Barnes 1986b): The presenceof different types and proportions Fd+ + HzSz- FeS, + 2H+ Q) of marcasite and pyrite in the different chimney Since the equilibrium concentration of H2S2 (and zone$suggests that more than one mechanismof other polysulfide species)in hydrothermal fluids is polysulfide generationoccurs in the chimneyenviron- many orders of magnitude less than that of HrS ment. Precipitation of marcasiteapparently requires (e.9., Murowchick & Barnes 1986b),a sienificant acidic conditions(pH <-4.5 at T <-200oC), quantity of FeS2 would form only if polysulfide whereaspyrite precipitation is favored at higher pH speciesare continously generatedatthe depositionol conditions (Murowchick & Barnes1986b, Goldhaber sile from more abundant sulfur species,such as H2S & Stanton 1987).The fact that the pH ofthe EPR in the hydrothermal fluids and/or SOo2- in sea- fluids is typically < - 4.5 (e.9., at 21oN: Von Damm water (and anhydrite which formed from seawater et al. l9S3,Campbelletal. 1988;at 11-13oN:Bowers SOot-). Severalpossible mechanisms exist for the et al. 1988), and that marcasite is the dominant generationofpolysulfide speciesin the depositional FeS2phase in the outermost zone of active chim- environment of the chimneys(Ohmoto 1988): neys (marcasite-l in zone l) and in the innermost (i) Oxidation of hydrothermal H2S by dissolved 02 zone of the cloggedchimney (marcasite-3in zone 7), in seawater: suggeststhat the less abundant marcasite phases 2H2S + YzOz- H2S2+ H2O (3) formed primarily by reactions(3) or (4) (or both). (ii) Oxidation of hydrothermal HzS by diffusive loss The more abundant marcasite-2and -4, which occur of hydrothermal H2: mostly in the interior parts of the chimneys (zones 2H2S'H2S2+H2(l) (4) 2,3, and 6), may havebeen formed by reaction (5), (iii) Reaction between hydrothermal I{2S and sea- i.e., the reaction betweenhydrothermal HrS and water SOa2-: SOn2- that is constantly supplied by the dissolution 7H2S + 2H+ + SOa2- - 4H252 + 4H2O (5) of earlier anhydrite by warmer hydrothermal fluids. (iv) Reduction of seawaterSOr2- by hydrothermal Primary pyrite phases(pyrite-I, pyrite-3, and some H2: plrite-2) in the chimneysmay have formed because 7IJt + 4H+ + zSOf- - HzSz + 8H2O (6) the hydrothermal fluids were neutralized by disso- The relative im.portanceof the abovefour mechan- lution of earlier anhydrite and sulfide minerals. Con- isms of polysulfide generation dependspartly on the tinuous heating of the chimney wall by later fluids, relative abundancesof H2S, 02, H2, H* and SOnz- together with the tendencyof increasingpH of fluids in the hydrothermal fluids and seawater.For exam- inside the chimney structure, are probably respon- ple, if the mixing seawatercontained only -lV6 m sible for the conversion of marcasite and primary of dissolved 02 or if the hydrothermal fluids con- pyrite phasesto larger grained pyrite phases(pyrite- tained only -10-6 m of Hr, the amounts of H2S2 2 and 4). SULFIDE-SULFATE CHIMNEYS. EPR 501 ZnS. The observed trend of increasing wurt- pyrite observed between zones 5 and 6 in extinct zitelsphalerite ratio from the chalcopyrite wall both Chimney D (Frg. 4k) may be a reversal of reaction to the outside walls (in the active chimneys) and (9). Note that the direction of reaction (9) depends inside wall (extinct chimney) as illustrated in Figure on the concentration of Cu' in the fluids, as well 5b suggeststhat the rate of nucleation is an impor- as on Z, pH, and the availability of redox mechan- tant factor controlling the ZnS mineralogy: rapid isms: lower concentration of Cu* in later lower nucleation causedby quenching apparently leadsto temperature fluids and the availability of oxidation the formation of wurtzite, whereas slower nuclea- mechanismsmay have promoted pyrite formation tion in warrner environments (e.g., chimney-wall over chalcopyrite. interiors) leads to the precipitation of sphalerite. Srich CuwWes. Fluids in equilibrium with chal- Chalcopyrite. Precipitation of chalcopyrite from copyrite tend to move into the stability fields of the hydrothermal fluid bearing Cu*, Fd* and H2S S-rich Cu sulfides (e.9., bornite, covellite) during requires an oxidation mechanism: cooling (Ohmoto et ql. 1983).Given a sufficient sup- Cu* + Fe2* + 2HrS + %Oz - CuFeS2+ ply of HrS, an oxidation mechanism,and a temper- 3H* + y2}I2O (7) ature gradient acrossthe chimney wall, the follow- Slow rates of oxidation reactions during rapid mix- ing reactionstend to proceedto the right: ing of hot fluids and cold seawater (seeabove dis- 5CuFeS2+ 2H2S * 02 n Cu5FeSa* 4FeS2 -r cussion on pyrite) explain why chalcopyrite is not 2H2O (ll) abundantin the black smoke.In contrast,the avail- ability of various oxidation mechanismsin the chim- cu5FeSn+ 3H2S + %Oz - 5CuS + FeS, + ney environment,and the prolongedcontact ofthe 3H2O 02) hydrothermal fluids with theseoxidants, explain the Thesereactions can explain the occurrenceof a S-rich occurence of a small amount of chalcopyrite, espe- Cu sulfide assemblage(facies 4) in the outer parts cially in the anhydrite-rich zone l. of the chalcopyrite-rich zone 5. Chalcopyrite in facies 5 appears to have formed largely by reaction of a Cu- and Fe-bearing SutvttrtenY hydrothermal fluid with pre-existing (i.e. facies l- 3) ZnS or FeS2minerals (or both) though reactions Important observations and suggestionsmade in such as: this study are summarized below: Cu+ + Fd* + H+ + /nO, + 2Zr$ ' CuFeSz 1) Variations in the mineralogy, texture, and zon- + 2Z*+ + y2HzO (8) ngof X chimneysfrom 11vent sitesat 11" and l3oN on the EPR are representedby 3 active and I extinct Cu+ + FeS, + Y2H2O - CuFeS2+ H+ + chimneys. %oz (9) 2) The three active chimneysshow the cornmon zon- The combination of reactions(8) and (9) represents ing: an anhydrite-rich outer zone, a transition zone replacementof both FeS2and ZnS by chalcopyrite: rich in Fe and Zn sulfides, and a chalcopyrite-rich 2Cu+ + Fd* + TZIS + FeS2 - 2CuFeS2+ innermost zone, althougb the thicknessof eachzone 22fr* (10) varies among the chimneys. Two types eachof mar- which is manifest as chalcopyrite disease. The casite,pyrite, and wurtzite, and one type of sphalerite stoichiometry of reaction (10) implies that ZnS is are observed in all three active chimneys. consumedat a faster rate than FeS2during replace- 3) The extinct chimney lacks the outer anhydrite-rich ment by chalcopyrite and thus can explain the trend and Fe-Zn-rich zones, probably becauseof dissolu- of increasing FeS2/ZnS ratios inward in the chim- tion by cold seawater. The exterior wall is a ney structure.TheZn releasedby reaction(10) may chalcopyrite-rich layer; the conduit is clogged by partly reprecipitate in zones 2 and l. pyrite, marcasite,wurtzite and sphaleritewhich have Reactions (8) - (10) suggestthat the formation of different crystal habits compared to those in the chalcopyrite and dissolution of FeS2may c€aseonce active chimneys. all the ZnS is consumed,unless a reduction mechan- 4) Similarities in the temporal and spatial relation- ism exists within the chimney (seereaction 9). This ships among different types of Fe and Zn sulfides, is probably the reason why the nearly monominer- anhydrite, and chalcopyrite in the active chimneys, alic pyrite zone (zone 3) is developed between the and the relationships between the size of conduit inner monomineralic chalcopyrite zone (zone 5) and opening and the thicknessesand composition ofvar- the outer zone rich in Zn and Fe sulfides(zone 3). ious mineralogical zones in both the active and Therefore, more mature chimneys would tend to extinct chimneyssuggest that the processesof chim- have higher CulFe, Cu/Zn, Fe/Zn, and Dsul- ney growth were similar at all vent sites of I I " and fide/anhydrite ratios, and also develop more 13oN,and that eachchimney repre$ents a different monomineralic zones. stage of maturity and preservation of a complete The "replacement" texture of chalcopyrite by (ideal) chimney. 502 THE CANADIAN MINERALOGIST 5) A complete chimney consists of 8 mineralogical Acmowt-BpcEMENTS zones(or facies).From outsideto insideof the chim- cntrcalcomments ano sugges- ney, they ate, i (anhydritewith minor marcasite+ -,-y-t-1t-,{1:lulJortl made bv H'D' Hol- pyrite + wurrzite),2 (marcasite+ wurrzire * minor land,i1"-1t c' l!:,:1li:t$-uscriptKaiser' s'R' Poulson' H'L' Barnes' R'A' anhydrite), 3 (pyrite + sphalerite), a (neari., Discussionswith P'B' Bar- monomineraricbornire), 5 (nearry .ono-ir,..utit 5-"-tki,-"i1T'l*T:""' were most helpful' chalcopyrite),6 (pyrite + sphalerite),z (marcasiil !on,-J-r' q9"J'?'.Murowchick sectionswere preparedat the * wurrzire), and 8 (wurtzire + pyrire). zones t tJ University.ofP:Ptl^f-:l*?1-thin Heidelberg' This study was supported 5 developduring the outward gxowth(waxing stagef Grantno' of chimneys,ri.r"* ,ooes6 ro s divelopdurin-! ScienceFoundation under the filling (waning stage)of chimney conduits. Bt",ff T|!ff 6) The growth of chimneys is initiated by the for- mation of the facies-l assemblage,which takes place RplrnsNcss as a result of rapidrarixing of hydrothermal fluids and cold seawater.The outwardgrowth of chimneys BALLaRD,R.C., HErrNrar, R. & FneNcunrrau,J. occursby: (i) successivetransformation of facies-l (1984):Geological setting ofhydrothermal activity mineralsinto facies-2,-3, -5, and -4 mineralsby reac- at 12'50'N-onthe EastPacific Rise: a submersible tions with Fe-, Z\-, Cu- and H2S-bearingnuias in study.Earth Planet. Sci.Lett. 69' 176'186. the interior of the chimneys;and (fi) formation of nBenron' ^__^-. D P'B"Jn' D r_ (1973):,, n Solid solutions in the system new layersof facies-l mineralsat the exterior of th" andcu-Fe-s join' chimneys.rherefore, all mineralogicalzones (r-sj Ei;Xit;.i.Tr, lr$?rlt-t inherit, to a varying degree,the fluid characteristics (Zand metal compositions)of the entire stage(rather (1928):Some ore texturesinvolving sphalerite than a particular stage) of hydrothermal activity; from the Furutobe mine, Akita Prefecture,Japan. mineralsin tJreouter zonesinherit higher proportions Mining Geol. 28,293-300. of the earlier fluid characteristics.The chimney- (1964): growth processesare analogousto skarn formation, . !. Tou.LMlN,P', III The electrum- witn a major difference in the marerial that ii grylg:tggforthedeterminationof thefugac- repracedby surrideminerals (anhydrite v"rsusrinnl '3r:t:l;n:h';fr:?,;:H$: *'tems'Geochim' stone). 7) Previous researchers@ldridge et al. 1983) have & - (1966): Phase relations involving suggestedthat anhydrite-rich layers play an impor- sphaleriteLlerite in the Fe-Zn-S system. Econ..Econ. Geol. 61, tant role in the developmentof sulfide chimneysand 815-849. volcanogenicmassive sulfide depositsby acting as a BurrH, G. & Ornroro, H. (1988): Sulfide-sulfate chim- thermal blanket for sulfide ore. Our model sug- o gests that anhydrite may also play an important neys on the East Pacific Rise, I I and 13'N latitudes. chemical role for the development of FeSr-rich sul- Part II: sulfur isotopes. Can. Mineral.26, 505-515. fide ores by providing various oxidation mechanisms Bowrns, T.S., VoN Davv, K.L. EouoNo, produce & J.M. to polysulfide speciesfrom hydrothermal (1985): Chemical evolution of mid-ocean ridge hot HzS. springs. Geochim. Cosmochim. Acta 49, 22392252. 8) Kinetics of various oxidation reactionsseem to control the mineralogy of Fe sulfides (pyrrhotite, -, CalFnELL, A.C., Measunrs, C.I., Servacr, marcasite and pyrite) in a chimney. The kinetics of A.J., KrnoBu, M. & EovoNn, J.M. (1988):Chem- nucleation are also important in the formation of ical controls on the composition of vent fluids at wurtzite versas sphalerite. l3o-11oN and 21oN, East Pacific Rise. J. Geophys. Res. 93, 45224536. 9) Monomineralic zones of chalcopyrite and pyrite develop becauseof the preferential replacement of Cannr, L.J. (1973): New data on phase relations in the ZnS over FeS2by chalcopyrite during the chimney Cu-Fe-S system. Econ. Geol. 68,443454. grofih stage. Replacementof chalcopyrite by FeS2 may occur during the waning stageof hydrothermal -, Hall, S.R., Szvuarisrr, J.T. & Srswanr, J.M. activity. (1973): On the transformation of qtbanite, Can. l0) Chimneys of higher maturity are characterized Mineral. 12,33-38. by larger conduit openings, better developed monomineralic zonesof pyrite, chalcopyriteand bor- Carunnell, A.C., Bownns, T.S., Mrasunns, C.1., Fetrxnn, K.K., Krnoev, M. & Enuoxo, J.M. nite, and higher ratios of Esulfide,/anhydrite, Cu/Fe (1988): A time seriesof vent fluid compositions from and Fe/ Zn. Differences between the Zn-rich versus 21oN, East Pacific Rise(1979,1981,1985), and the Cu-rich chimneys may be a function of the matu- (1982, Guaymas Basin, Gulf of California 198t. "f. rity of a chimney,rather than of fluid temperature. Geophys. J?es. 93, 45374549. SULFIDE_SULFATE CHIMNEYS, EPR 503 Cnerc,J.R. & Vaucuan,D.J. (1981):Ore Microscopy Kusarass, M., CHTBA,H. & Onuoro, H. (1982): Sta- and Ore Petrography, John Wiley & Sons, New ble isotopes and fluid inclusion study of anhydrite York. from the East Pacific Rise at 21"N. Geochem. J. 16, 89-95. Cnenen,D.A. & Benres, H.L. (1976):Ore solution chemistryV. Solubilitiesof chalcopyriteand chal- McCosecHv, T.F., Bellano, R.C., Mottl, M.J. & cocite assemblagesin hydrothermal solutions at VoN Henznn, R.P. (1980: Geological form and set- 2@oCto 350"C.Econ. Ceol. 11,772-194. ting of a hydrothermal vent field at lat 10o56'N, East Pacific Rise: a detailed study using Angus and DnevrR, J.I. (1982): The Geochemistryof Natural AJvin, Geology 14, 295-298. Waters.Prentice-Hall, Englewood Cliff, N.J. Munowqucr, J.B. & BanNss,H.L. (1984): The recog- Durrzec, J.E. (lW6): Reactionsin cubaniteand chal- _nition and significance of porous pyite. Geol. Soc. copyrite. Can. Mineral. 14, 112-181. Amer. Progrom Abstr. 16,6M. Elomocr, C.S., BarroN, P.B., Jn. & Ouuoro, H. & - (1986a):Formation of cubic FeS. (1983):Mineral texturesand their bearingon for- Amer. Mineral. 71, 1243-1246. mation of the Kuroko orebodies.Econ. Geol. (1986b):Marcasite precipitation from Monogr. 5,241-281. & - hydrothermal solutions. Geochim. Cosmochim. 50,2615-2629. Eonaoro,J.M., Mnasunns,C., Malcuu, B., GRANT, Acta B., ScLanEn,F.R., Corlmn, R., HuDsoN,A., Gon- Nonuem, W.R., MonroN, J.L., BtscHorr, J.L., ooN,L.I. & Conr-rss,J.B. (1979):On the formation BREfi, R., HoLcoun, R.T., Karert, E.S., Kosrr, of metal-rich depositsat ridge crests.Earth Planet. R.A., Ross,S.L., SneNrs,W.C., Slncr, J.F., VoN Sci.Lett. 6, 19-30. Deuu, K.L. & ZrsneNsenc,R.A. (U.S.G.S. Juan de Fuca Study Group) (1986): Submarine fissure Golnrans,M.S., CoNwnsE,D.R., HoLLIND,H.D. & eruptions and hydrothermal vents along the southern Eolvror.ro,J.M. (1983):The genesisof hot spring Juan de Fuca Ridge: Preliminary observations oN. depositsin the EastPacific Rise,2l Econ. Geol. from the submersible ALYIN.Geologyl4,823-827. Monogr. 5, 184-197. Outvtoto, H. (1988): Formational processesof volcano- Golouenrn, M.B. & SreNror, M.R. (1987): genic massive sulfide deposits. 1z Hydrothermal Experimentalformation of marcasiteat 150-2@'C; Processes - Applications to Ore Genesis (H.L. implicationsfor carbonatehosted PblZn deposits. Barnes & H. Ohmoto, eds.). D. Reidel Publishing Geol. Soc.Amer. Program Abstr. 19. Co., Dordrecht, Holland (in press). , MtzuKAMl, M., Dnuuuouo, S.E., Et.onroce, HavuoN, R.M. (1983):Growth history of hydrother- C.S., Prsurua-Anuown, V. & LeNecH, T.C. (1983): mal black smokerchimneys. Nature 301,695-698. Chemical processes of Kuroko formation. Econ. Geol. Monogr. 5, 570-567. & KesrNen,M. (1981):Hot spring depositson (1983): The Kuroko and the EastPacific Rise at 2loN: preliminarydescrip- & SrnNnn, B.J. massive sulfide deposits: tion of mineralogyand genesis.Earth Planet. Sci. related volcanogenic Lett. 53,363-381. Introduction and summary of new findings. Econ. Geol. Monogr. 5, l-8. HErlNnn, R., Frvnrcn,M., BrscuonR,J.L., Ptcor, P. OuorN, E. (1983): Hydrothermal sulfide depositsof the & Snanrs,W.C. (1980):Sulfide deposits from the East Pacific Rise (21"N). Part 1: descriptiveminer- EastPacific Rise near 2loN. ScienceZW,1433-1444. alow. Mar. Mining 4,39-72. , FnaNcuntrau, J., RrNano, V., BALLARD, Srrrss, F.N., Macoouaro, K.C., Arwartn, T., Bel R.D., Cnournoure,P., CunumEr,J.L., Arnannor, I-A.RD,R., CenaNzA, A., Connoaa, D., Cox, C., F., Mrugrnn,J.F., Cueuou, J.L., Menrv, J.C. & Dnz Gancn, V.M., FnaNcutrseu, J., Gunnnrno, Boumcun, J. (1983):Iniense hydrothermal activity J., HawrtNs, J., HavuoN, R., Hesslen, R., at the axisof the EastPacific Rise near 13oN:sub- Jurseu, T., KasrNER,M., LensoN, R., LrrrBwpvr, mersiblewitnesses the growth of a sulfide chimney. 8., Mecooucer,l, J.D., Mrllnn, S., Nonuam, W., Marine Geophys. Res.6, l-14. Oncurr, J. & RercrN, C. (1980): East Pacific Rise: hot springs and geophysical experiments. Science & Foueuer,Y. (1985):Volcanism and metal- 207, l42t-1433. logenesisof axial and offaxial structureson the East Pacific Risenear l3oN. Econ. Geol. 80,221-U9. Srvnr, M.M., BRAcrunus, A.J., Hot-lero, H.D., Cnm, B.C., Prsmre-AruoND, V., Er,or.rocn,C.S. Kosrr, R.A., Clecun, D.A. & OuorN,E. (1983): & OHrr,roro,H. (1981): The minerology and the iso- Mineralogy and chemistry of massive sulfide topic composition of sulfur in hydrothermal sul- depositsfrom the Juan de Fuca Ridge. Geol. Soc. fide,/sulfate deposits on the East Pacific Rise, 2loN Amer. Bull. 95, 930-945. latitude. Earth Planet. Sci. Lett. 53,382-390. 504 TIIE CANADIAN MINERALOGIST Trvev,M.D. & Dn-emv, J.R. (1986):Growth of large Gnan{r,B. & Eouono,J.M. (1983):Prelimi sulfide structureson the EndeavourSegment of the nary report on the chemistryof hydrothermalsolu- Juan de Fuca Ridge.Earth Planet. Sci.Lett.77, tions at 2loN, EastPacific Rise. .fu Hydrothermal 303-317. Processesat SeafloorSpreading Centers @.A. Rona, K. Bdstrom,L. Laubier& K.L. Smith,Jr., eds.). TunNtclrre, V., Botnos,M., Dn Buncu,M.E., Dnrr, PlenumPress, New York, 369-390. A., JotntsoN,H.P., JuNrran,S.K. & McDun, R.E. (1986): Hydrothermal vents of Explorer Ridge, WerHeN,J.A. & Cnerc, H. (1983):Methane, hydro- northeast Pacific. Deep-SeaRes. 33, 401412. genand heliumin hydrothermalfluids at 2loN on the East Pacific Rise. .lz Hydrothermal Processes Tununn,J.S. & Cervrparu,I.H. (1987):A laboratory at SeafloorSpreading Centers @.A. Rona,K. Bds- and theoretical study of the growth of "black trom, L. Laubier& K.L. Smith,Jr., eds.).Plenum smoker" chimneys. Earth Planet. Sci. Lett. 87n- Press,New York, 391-410. 3648. Vou Dauu, K.L. (1988):Systematics of andpostulated controls on submarine hydrothermal solution ReceivedAugust 31, 1987;revised rnanuscript accepted chemistry.J. Geophys.Rar. 93,45514561. June24, 1988.