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The Distribution and Mineral Hosts of Silver in Eastern

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The Distribution and Mineral Hosts of Silver in Eastern 529 The Canadian M ine ralo gist Vol.34, w. s29-s46(1996) THEDISTRIBUTION AND MINERALHOSTS OF SILVER IN EASTERNAUSTRALIAN VOLGANOGENIC MASSIVE SULFIDE DEPOSITS DAVID L. HUSTONI Centrefor OreDeposit a.nd Explnration Sndies, Uniyersity of Tasmania G.P.O.Box 252C, Hoban, Tanmania 7001, Australia WIESLAW JABLONSKI CentralScience Laboratory, University of Tasmania.G.P.O. Box 252C, Hoban, Tasmania 7001, Australia SOEYH. SIE CSIRODivision of ExplorationGeoscience, P.O. Box 136, North Ryde, NSW 2113, Australia ABSTRA T Silver, an importantby-product in volcanogenicmassive sulfide (VMS) depositsof easternAus[ali4 is emichedmainly in Zn-rich zones;in a few depositsit is enrichedin Cu-rich zones.Minerals that containsignificant a.mountsofAg include galena, tetrahedriteand chalcopyrite.The contribution of Ag sulfosalts,native silver and Ag tellurides to the total Ag budget is generally small. The hosts of Ag in VMS deposis vary spatially as follows: (1) in Cu-rich zones, Ag occurs mainly in chalcopyriteor Birich galena;(2) in overlying Zn-rich zones,Ag occursmainly in galenaand to a lesserextent, tetahedrite; (3) in barite-bearingzones, Ag occws mainly in Ag-rich tetraheddte.The geochemicalfactors that seemto influence the mineralogical distribution of Ag in VMS depositsinclude: (1) temperature,(2) the reLativeabundances of semi-metalsin fte mineralizing fluids, (3) fractional crystallization of tsfahedrite-tennantiteminerals, and (4) redox conditions during ore deposition.Higher t€mperatuesand more reducedconditions favor partitioning ofAg into chalcopyrite,and then galena.Silver partitions into tetrahedriteunder lower temperature,oxidized conditions,assisted by fractional crystallization,hence enriching later-precipitatedtetrahedrite in Ag and Sb. Keywords:silver, mineral hosts,volcanogenic massive sutfide deposic, eastemAustralia. SorrnueRe L'argent, important produit secondairedans I'exploitation de gisementsvolcanog6niques de sulfures massifs,est surtout concenf6 dans les zones enrichies en Zn. D:ns quelquesgisements, il est plutdt associ6aux zones cuprifdres.Parmi les min6raux qui renfermentde quantit6simportantes d'argent figurent galbne,t6tra6drite et chalcopyrite.Les contributionsdes sulfoselsargentifbres, I'argent natif et les tellururesde Ag au bilan global de I'argentsont mineures,en g6n6ral.l,es min6raux hOtesvarient dansI'espace dans ce type de gisementcornme suit (1) dansles zonesenrichies en Cu, on trouve l'axgentsurtout dansla chalcopy'riteou la galdnebismuthifdre; (2) da.* les zonessutrt'rieures enrichies en Zn, l'argent se trouve surtout dans la galbneet i un degr6moindre, danstra tdtra6drite; (3) dansles zonesn barite, I'argent se fouve surtout dansla t6tra6drite argentifdre.Parmi les facteursg6ochimiques qui r6gissentune telle distribution seraienfl(1) temp6rature,(2) abonda:rcerelative des semi-mdtauxdans la phasefluide, (3) cristallisation ftactionn6edes min6raux du groupe de la t€tra6drite-tennantite,et (4) conditionsd'oxydation au coursde la formation du minerai.Aux tempdraturesplus 6lev6eset dansles milieux plus fortement r6ducteurs,I'argent favorise La chalcopyrite, et ensuitela galbne.Aux tempdratuesplus faibles et dansles milieux plus oxydants, I'argentest davantager6parti dansla t6tra6drite;un facteur secondaire,la cristallisationfractionn6e, mbne i un enrichissement de I'argentet de I'antimoinealans la t6taddrite tardive. (Iraduit par la R6daction) Mots-cl6s:axgen! min&arxr h6tes,gisements volcanog6niques de sulfuresmassifs, Australie orientale. I Presentaddress: Australian Geological Survey Organisation, G.P.O. Box 378, Canbena ACT 260I, Australia. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/34/3/529/3435587/529.pdf by guest on 26 September 2021 530 TIIE CANADIAN MINERALOGIST TABII 1. MINBRA!)CICAL DTSTRII'LINON OF SILVER IN VOI..CANOCEMC INTRoDUCT'roN M.{SSIVB SULF'IDE DBPOSNS Of the major metals recoveredfrom volcanogenic Mob@ Quebe PFib:0.614@ ppm (t = 42 Ppn). 1 (VMS) Chal@I,FiE: 1-200 ppm (x = 29 PPn). massivesulfide deposits,Ag is uniquein that it Iaklike,I.IWT GrlcopyriE:-500ppd(T6Toofbbleilvs). occurs mainly as a trace or minor element in ore Galew 0.u74297o (9/' of bhl silver). minerals.As Ag is recoveredas a by-productin Pb or Kidd Cr@k, oatrio 7d-tich (\sl@ptrivn4-25ffi (s = 1047ppq n = Q. Cu concentrates.extensive research has been under- ll6iw PFi@: <7-2! ppn (n = 14; 10 b€Iry deHi@). sdfidc Gal@87-1167ppm(x=638ppun=E). taken on bulk samplesand metallurgical concentrates Sphalerirc:<123{tr (n = U;7 bclowdetecliotr). Othq nimls: uiw silwr, @thitg bEahcdritg sEphmitc, to determineits mineralogical hosts (e.9., Henley & pyfrr8)ldte, p€eie, ois.gtrnc dd dymir. Glrich ClElq}Pydto: x = 1E3 ppa; 59.6Vool Ag, Steveson1978. Jambor & Laflamme 1978. Chen Il6ieo Ild@: <? ppd (! = 6). & Petruk1980. Harris et al. L984.Laflamme sdfrdc caleE x = 3Ur,ppd; 0.257aof Ag. & Cabri SDha.lsi@:<12 mn (! = 2). 1986a, b). Less attention has been paid to spatial othcr mincEls: iitivi sisi ad ']mthiE (40.15% of Adt Bomib Gr.lopyrile: <1G57pp6 (D= 4; I bclw dc@ion)- variations in the occurrenceof Ag in VMS deposits, b& Plrirc: <7 ppm (D = 1). Splalcrttc: 36 ppn (r = 1). which fypically have well-developedzonation in the Othc! Bilorols: |ffimib. distribution of minerals and metals.The objectivesof Pyhelnl,Fioled Ctal@pyribedAgsudalB 4 this study are to presentnew data on tle mineralogical csrpcDbcrg Swcdcn Tdahcdriii @tbite ad nativq silvq. 5 Sab€rgel, Sw€den Maidly galeE dd cbdcopyriE silh re pynr&trilq @tlilq 6 distribution of Ag in spatially constrained samples sb@E&mwcSvq, from eastem Australian VMS Hellyq Tmia Teiahc.drilet l.*28.3Vo;{Jloof Ag. Md impoM d tbe Fp 7 deposits, to establish oI the ore lm Ac-rich blEhcdrik ru iu moblliad velD6. patternsef sening in this distributionnand to propose Cdeul!l.{.4tVo (4ry7ooIAg). More iepnkd @d Ag-rlch bMrls the be o! lhe o@le6, geologicaland geochemical controls on the distribution Pnile: 2@350 ppE in t[e hanghg wall p@ioB Bebl ane. Hdh-St@fe, New TetsahcdrilerI.5-34,07o (x -12.44/o);35VooIAs. 8 of Ag in VMS deposits. B@ick Goleu 0.G0.97a(r = 0,15Vo\;nEo oL Ae. Agarclas witb Bi. olhs EiDcElr: kobcllik (0.6Co\ @elile (l.Gl,4Vd Pb-Bi.Sb(Ag) stni6al& 8@lhitc, stcphddb, pyftrgrie Gsorocv oF Tr{EDEPosrrs STUDED and olalBailn 397ooIAg, Csiboq Nfl TeEab€driE:0.G192%;687,ofAg, h lhe Ed oretedsAg 9 lrruBvick l4cls i!6w froo 0.G2,lo/' ilthebww7.9Vo arrhe @p. Galou <0.04{.2It7, (x = 0.1V/o); 2Ao/.ot ffit AA. Mineralogical observationsand electron-micro- Othq mio@ls: olffiq polybdiE, chol@pyril€, umlbne ud slepheite; 47" of Ag. probe analyseswere undertakenon samplesfrom the 'Ievahe&ittto,l-365Vo;&Voof BNick No. 12" Ag. 10 Mt. Chalmers,Waterloo, Agincourt, Balcooma, Dry NewB@ict Galw bo297o (x-o.077o); 307oof Ag; Ag (wlalq wilh Bi (r = 0.80. River South and Rosebery deposits in order to oll;r minerils: spMorirc, cbalcopyriteod pynhci E;7 'Vo ot Ag. determine the mineralogical distribution of Ag. The Cofer, Vilginia M4lnly bfrhldrib. 11 Hokuroku disiql Mainly braho&iE ald gafcq with miDd @fribui@ ftod 12 mineralogical hosts of Ag in these and other VMS Japatr @rhiF, jalpaitq tu6ery6ite EcHshyi@, smbaFt& depositsare summarizedin Table 1. polybslE, F$cilE pyEr$rib, pffiiE dd @iw silvd, DM su6: (l) L!ftpq@ et al (t99t; (2) Hui! et al. (1984) (3) Cabri ct al. (1981; cabd (t988I ud Walkq & lilaonard (1974); (4) Helmurl (1979); (5) Viwllo (1986); (O An@fr i il f 19E ; (7) RusdeD ot aL (1990) (8) Chen & Perul (1980): (9) J@bor & l2Jlmme (1978i; (10) kil@e & C€brl 0986qb) Chrrsulis & sEsd (1988), ud Gbd (1992); (1 1) Mfllq & crais (194); ud (12) Shinaaki (1974) aod sab (1974). FIc. 1. Cross sectionsshowing the geology of the (A) Ml ChalmersWest l,ode (modified from Large & Both 1980), and @) Roseberynorth-end orebody (modified after Huston & Large 1988). Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/34/3/529/3435587/529.pdf by guest on 26 September 2021 DISTRIBUTION OF SILVER. AUSTRALIAN VMS DEPOSITS 531 Mt Chalmers Silver gradesare highest (50-100 g/t) in the Zn-rich upper portion of the massivesulfide lens. In the Cu- The Mt. Chalmers deposit contains of two Cu- rich lower part of the massivesulfide lens and in the gold-rich massivesulfide lensesthat occur abovewell- stringer zone, Ag grades are 5-20 ppm. The disri- developedpydte - chalcopyritestringer zoneswithin bution of Ag correlatesbest with those of Zn and Pb the Permian Beserker Beds in central Queensland (Large& Both 1980). (Large& Both 1980,Taube & van der Helder 1983; Fig. lA). As Mt. Chalmersis one of the leastdefonned Rosebery VMS deposits in Australia, primary textures are commonly preservedin the ores. Massive sulfide and The Zn-Pb-rich Rosebery deposit consists of a stringer ore are dominatedby pyrite and chalcopyrite. seriesof sheet-likemassive sulfide and barite-bearing Sphalerite, galena and barite occur in the upper lenses within a lens of fine-grained tuffaceous portions of the massive sulfide lenses, along with sandstoneand siltstone above an extensive zone of minor tennantite. Electrum is a trace Ae-bearine pyrite-bearing qtuartiz- sericite t chlorite-bearing mineral. alteredfelsic volcaniclasticrocks in the CambrianMt. F.€Terrlgenous sandstones and conglomerates [SlArgllllteand chert Ffi Graywacke [i] Felslcvolcaniclastic rocks Fro.2. Crosssections show- ing the geology of the I Massivesulfi de/barite (A) Waterloo and WPyrltlc quartz'serlclteschlst (B) Agincourt deposits t-I N Pyritlc sericiterquartzschist (modified after Berry 50m [i]Andesite et al. 1992). Downloaded from
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