The Spectrum of Ore Deposit Types, Volcanic Environments, Alteration Halos, and Related Exploration Vectors in Submarine Volcanic Successions: Some Examples from Australia

Ross R. LARGE,+JOCELYN MCPHIE, J. BRUCEGEMMELL, WALTER HERRMANN, AND GARRY1. DAV~DSON Centre for Ore Deposit Research, School of Earth Sciences, Uniuersity of Tosmonia, GPO Box 252-79, Hobart, Tasmania, Australia

Abstract Variations in shape, metal content, alteration mineralogy, and volcanic host rocks of the ore deposits in the two major volcanic-hosted luassive sulfide (VHMS) districts of eastern Anstralia, the Cambrian Mount Read Volcanics and the Camhro-Ordovician Mount Windsor snbprovince, strongly reflect their volcanic environ- ment, conditions of ore forination. and hvdrothermal alteration orocesses.

prol,~l,lyiorn.rJ rttl~~r,I. the sed flojr r ,:, Hrllvrr Qltc lli\.er or hy rcpl~crmrntof pun,~tsvolcnnicl~snc IIU,,+, Jirrzdv Irlo\r. thr s,u f.wr T e., H,n.l,cn . The, iounrull ulrrrdi<)n ~cs,ci~rrdunh rhccr .nolvmrtrlllc . \'HhlS Jc~>u\ltsu,n\ controllrd I.! hoit-rock pc;lllc.~l,rl~ty.r~d iroro\tty which arc it1 turn rr!,t+d n) n)lcxn>c Cicirs r\pv deucr oiir~zu.nl.c.111d ~\?.voI~.t~~iz~~u~r~trnl nrchitccturc Fucustneof llvurotllrrrnulfluids ihlno synvold&c sGctures has resurted in well-zoned chlorite-sericite footwall aheracon p;pes within footwall la"; at Hellyer. On the other hand, diffnse fluid flow through veIy thick pninice breccia at RosebeIy and Hercules has resulted in strata-hound, sericite-dominated footwall alteration zones parallel to the paleosea floor and the ore lenses. Massive and disseininated, pyitic Cu-Au deposits, such as those in the Mount Lyell field and at Highway- Reward. formed by subsea-floor replacement and are associated with only minor nnc-lead massive sulfide ore. These deposits formed from higher temperature fluids (>30OeC),in which copper transport is enhanced, and are commonly located in felsic volcanic centers do~nh~atedby shallow porphyitic intrusions (e.g., Highway- Reward). The Cn-An ore lenses may be strata-bound (e.g., Mount Lyell) or crosscutting pipes (e.g., Highway- Reward) depending on the structure and permeability characteristics of the felsic volcanic host rocks. The pres- ence of high-sulfidation alteration minerals (e.g., pyrophyllite, zunyite) in some of the Cu-An deposits (e.g., Mount Lyell field) indicates that fluids were relatively acidic and snggests the possibility of magmatic fluid input into the hydrothemal system. Alteration zonation associated with the Cu-An VHMS deposits is more symmetrical than that of the Zn-rich deposits, with sericite-rich alteration extending into the hanging wall, in keeping with the subsnrface replacement origin of these de osits Synvolcanic gold-rich deposits, with high gold/base met J ratlos.' are less common than the Cu-Au and Zn- rich VHMS ore types. The gold-rich ores (e.g., Henty, South Hercules) are strata bonnd in nature, have low sulfide contents, and are associated with central zones of intense silicification, surrounded hy envelopes of sericite-pyite and carbonate alteration. Volcanological and geochemical studies at Hen? indicate the gold-rich ore formed by the replacement of particular volcanic units deposited in a relatively shallow water environment dominated by volcaniclastic facies, lavas, and limestones. This spectrum of Cu-Au, Zn-rich, and Au-only deposits in the Mount Read Volcanics and the Mount Wind- sor subprovince is interpreted to represent a continunm from classic sea-floor VHMS ores toward those with features more akin to porphry Cu-Au and cpithermal An-Ag deposits. This spectrum relates to the inte~play between factors in the snbn~arinevolcanic environment and the character of the hydrothermal fluid as follows: (1)proportions of volcaniclastic, lava, and subvolcanic intrusive facies; (2)depth of seawater; (3) permeability and porosity of volcanic host rock;; (4) balance behveen magmatic components and seawater components in the ore fluid; and (5) temperature and acidity of the ore fluid. Mineralogical, lithogeochemical, and isotopic studies have revealed a range of alteration vectors usefnl in exploration for both the Zn-rich and Cu-An VHMS deposits. Carbonate and white mica compositional varia- tions are highlighted as important mineralogical vectors; thallium and antimony halos may be nseful trace element vectors; and oxygen and sulfur provide important isotope vectors toward the center of the hydro- thermal system.

Introduction Oueensland, contain a range of base metal and gold-bearing THETWO principal submarine volcanic successions in Aus- sulfide deposits (Table 1). fhe aims of this paper >e to bliefl; tralia that host volcanic.hosted massive sulfide (VHMS) de. review the geological features, volcanic environments, and posits, the Cambrian Morlnt Read Volcanics in Tasmania and genesis the 'pectNm of svlesand, based On the the ~~~b~~.~~d~~~~~~M~~~~ windsor subpro~ncein contributions to this special issue, to compare their patterns of hydrothermal alteration. From this analysis we propose a 'Corresponding author: e-mail. Ross.LargeOutas.edu.au selies of alteration vectors useful for minerd explo;ati&n ayr leql pm rgmo18 punour alqeua oj asuap ooj sem pmU alo aql jkyr isa%ans 04 aauappa uo!snlau? p!nu pas" 'pueq raqo aql uo '(6661) M~ZU!TI pue uouro~os.(ca61) .I" $9 a$up[a Xq s~!sodapoyolnx dueur loj paquasap jeq+ 0%uo!qsej lel!ur!s e u! '8u~ugaiauoz puuaqlo~pXqXq padolahap uogeuoz Iejaur q~m\'uo!ssardap IOOU-ease u! punour e se mar% Xpoqaro aprjIns aqsseur arp leg* papnpuoa '(~661)a81 pue nam -"a3 PU" (Z66I) a2187 '(9661 '6861)"qW3R '~~XII~H?V .ajeqap aIqelap!suoa jo ~aalqnsaq, uaaq seq uognlona iyodap alo pue uoqsodap aprjlns jo amleu as!said aql

asu+o~dq~lsraspuim .&w uadswj ~asua~sw a'l!~aaqs 6'0 ciz SO z-z a's 9'1 U~O~UO!T aou+o~dqusLOSprr!M lyy rampard ased sasusl sw ay!iaa=~s PO 69 9.1 9.8 V8 9.9 a%ue~~~ sa!uea[o~peay ~"~npo~dJSB~ sasual SN aid!&[n~ 82 691 PO PS r PC sap~a~ 13!~t~3p~poaa '2~ au!m juaun3 waqs sw ardgp~ cz PI 9.0 PP CPT L'IC Xraqasay sapqo~psaa .qq laanpard ]sea sw P~PIOB PC wz 9.0 S.L 1 I'C 'an!~~and S~!U~JIOApea8 'IN ppasop au!~ sual sw ale8~013. r.z 091 PO CI z'sr la41an n3-qd-UZ

uogeoa~ snle~s was (mdd) (add) (% W) (% W) (% W) (&w) acl(l ilsodaa nV % "3 'Id uz aluuql. EXPLORATION IN SUBMARINE VOLCANIC SUCCESSIONS: EXAMPLES FROM AUSTRALIA 915 metal sulfides precipitated within a brine pod1 ponded within fig. 3) has recognized a zonation throughout the Mount Lyell a sea-floor depression. A potential problem with the brine district, from large disseminated pyrite-chalcopyrite ores at pool model for Hellyer is the source of the high-salinity ore depth (with elevated magnetite-apatite-REE), passing up- fluids. Solo~nonand Groves (2000) point out the lack of evi- ward to bomite-rich ores in a zone of intense massive and dence for evaporitic sediments in the Cambrian and Precam- vuggy silica alteration (including enargite and pyrophyllite) brian basement source region and conclude that the most below the paleosea floor, followed by an uppennost zone of likely reason for the high salinities is the presence of signifi- small, massive sulfide Zn-Pb-Cu lenses intelpreted as exhala- cant magmatic fluid iuput, as previously suggested by Khin tive sea-floor deposits. Zaw et al. (1996). However, no other evidence exists for the Subvolcanic intrusions in the Mount Lgell dktrict: A series involvement of magmatic fluids at Hellyer. of granitic sill-like intrusions occur at depth along the eastem Solornon and Walsl~e (1979) and Solo~non and Groves margin of the Mount Read Volcanics (Fig. 1). Research by (1994) considered that the sheetlike form, stratiform sulfide Mike Solomon and his students (Solomon, 1976; Polya et al., banding, large size, and high Zn-Pb metal content of the 1986; Eastoe et al., 1987) proposed a relationship between Rosebery deposit set it apart from the classical mound-style synvolcanic granite emplacement, district-scale alteration, Kuroko massive sulfide deposits. They argue that Rosebelyis seawater circulation, and massive sulfide formation. More re- more like the large VHMS de osits in the Bathurst district, cently, Large et al. (1996) suggested the possibility of a di~ect Canada, than tlle smaller KuroP, o deposits of Japan. In some input of magmatic fluids carvng gold, copper, iron, and respects Rosebery could be considered to possess some of the phosphorous to form the copper-gold VHMS deposits in the features of a SEDEX deposit (e.g., banded sheetlike form, Mount Lyell district. Geophysical evidence (magnetics and high Zn/Cu ratio, high tonnage, lack of a well-developed gravity) indicates that the granite(s) form a narrow discontin- stringer zone) located within a volcanic rather than a sedi- uous body or series of bodies about 60 km long and 2 to 4 km mentary setting. wide toward the base and eastern margin of the volcanic pile Solomon and Groves (1994) proposed that Rosebely and that hosts the deposits (Large et al., 1996, fig 4). The two out- similar sheetlike, banded, large tonnage andlor grade VHMS cropping parts of the elongate composite granite body (the deposits formed within a brine pool from relatively high salin- Murchison and Danvin granites) are strongly altered, higb K, ity fluids that nndenvent reverse buoyancy on mixing with magnetite series granites. The Murchison granite varies in seawater. In marked contrast to this model, Allen (1994a, b) composition from diorite to granite (58-78 wt % Sz02;Polya provided volcanological and textural evidence to suggest that et al., 1986). whereas the Darwin granite is composed of two the sheetlike form and mineral banding in some of the Rose- highly fractionated phases (Jones, 1993) with an SiOl content bery ore lenses are due to subsea-floor replacement of from 74 to 78 wt percent. The depth of the granite below the pumice-rich units below impermeable quartz-porphyritic lowest VHMS horizon is difficult to determine due to later rhyodacitic synvolcanic sills. A similar process of subsea-floor structural events. Various reconstructions place the granites replacement was also proposed by Khin Zaw and Large at a depth of 3 to 7 km below the ore horizon. (1992) for the South Hercules deposit, situated to the south The coeval and comagmatic nature of the granites and vol- of Rosebely. canic~is based on geology (Polya et al., 1986; Corbett, 1992; In snmmaly, the july is still out on the exact process of the Jones, 1993), geochenlistly (Crawford et al., 1992; Wyinan, formation of ~osebelyand Hellyer, but most workers agree 2000), and geochronology (Perkins and Walshe, 1993). Ra- that the ores are synvolcanic and formed on, or just below, the diometric dating gives an age of 508 ? 6 Ma coinpared to the sea floor, from moderate- to high-salinity ore fluids (5-15 wt range of the Mount Read Volcanics of 501 to 510 + 7 Ma W NaCl and 160"320°C: Khin Zaw et al.. 1996). (Perkins and Walshe. 1993). The datin~is not sufficientlv precise to establish &e exact timing of the- Cambrian granilitk Mnssiue and clissewtinoted strata-bound . -.. intrusion with respect to Cu-Au mineralization at Mount I.yell. pyntic cu-Au deposits Based on reg& alteration studies, complimented by The Mount Lyell district (Fig. 1) contains 22 Cu-Au de- gravity and magnetic patterns, Large et al. (1996) suggested posits wid1 a total of 312 Mt of 1.0 percent Cu and 0.3g/t Au that the Mount Lyell hydrothermal alteration system was con- hosted within rhvolitic and dacitic volcanic facies. Previous nected to a deewseated maematic-hvdrothermal" alteration studies (e.g., CO;, 1981; Walshe and Solomon, 1981; Large, system related to the elongate Cambrian granite(s) that crop 1992) considered the Cu-Au deposits to be largely subsea- out south of Mount Lyell in the Jukes and Darwin areas. Low- floor replacement VHMS ores; however, recent research grade polphyry Cu-style mineralization has been recognized (Corbett, 2001; Huston and Ka~nprad,2001) has demon- in places surrounding the Cambrian granites (Hunns, 1987; strated that the ores have mineralogical and alteration affini- Doyle, 1990, Large et al., 19961, where it is associated with ties with high-sulfidatiou epithermal deposits and may thus magnetite-chlorite and tourmaline-quartz veins that overprint represent a hybrid type between VHMS and epithermal de- early K feldspar alteration (Wyman, 2000). posits, developed within a submarine volcanic successsion. Convincing evidence for magmatic fluid and metal input There is disagreement on the timiug of the Cu-Au mineral- into the hydrothermal system at Mount Lyell is difficult to ization and high-sulfidation alteration event. Huston and document, probably because the system has been swamped Kampred (2001) argue for an Ordovician age for the mineral- by seawater convection over the life of the hydrothemal cell. ization and alteration (-460 Ma), whereas Corbett (2001) However, evidence in favor of the Cambrian granites acting provides convincing evidence for a Cambrian age similar to as a thernlal source and contributing a magmatic component other deposits in the Mount Read Volcanics. Corbett (2001, to the ore fluidincludes (see also Solomon and Groves, 2000): 916 LARGE ET AL.

(1)the whole-rock and trace element geocheniistry indicates e ithennal style ores with a connection to a low-grade por- the granitoids are comagmatic with the suite 1 volcanics that p! yry environment at depth (e.g., Jukes Pty. prospect) and an host and underlie most of the deposits (Crawford, et al. 1992); exhalative Zn-Pb massive sulfide at the sea floor above (e.g., (2) the preseuce of alteration minerals (e.g., pyrophyllite, al- Comstock deposit). The formation processes and geological lunite tpes) adjacent to the ores indicates a very acidic hy- environment of Cu-Au deposits in the Mount LyeU field may drothermal fluid (Huston and Kamprad, 2001); (3) the pres- be similar to that suggested by Sillitoe et al. (1996, fig. 2) for ence of magnetite-apatite + pyrite assemblages at Prince high-sulfidation volcanogenic massive sulfide deposits. LyeU aud a correlation between Cu, P, and Fe in the ores (Large et al., 1996); (4) the 018-enriched hydrothermal mag- Disseminated strata-bamd gold-rich ores netite of about 4 per mil at Prince Lye11 indicates a magmatic There are several synvolcanic gold-rich deposits in the origin (Raymond, 1992); (5)the Nd-Sm isotope data support Mount Read Volcanics that coutain a high goldlbase metal a link between apatites in the magnetite-apatite assemblages ratio and are composed principally of disseminated mineral- at Priuce Lyell and the Cambrian g~anites(Wyman, 2000); (6) ization rather than massive sulfide. lenses. The Henty deposit the recent fluid inclusion studies by Khin Zaw et al.(in press) (Halley and Roberts, 1997; Callaghan, 2001), a current pro- in the Western Tharsis deposit, Mt. Lyell, indicate salinities ducing mine (1.7 Mt at 11 g/t Au), is the best known example, much higher than seawater-in the range 6 to 34 wt percent but others include South Hercules (Khin Zaw and Large, NaC1; and (7) the high (Cu + Au)/(Zn t Pb + Ag) ratios in the 1992) and the footwall precious metal zone at Que. River (Mc- ores are compatible with high-temperature,- acidic ore fluids Goldrick and Large, 1992). of magmatic origin. Henty is a low-sulfide strata-bound gold deposit within an Our current model for the Mount LyeU field (Fig. 2) de- intensely silicified mne adjacent to the region all^ extensive ~ictsthe maior disseminated Cu-Au ores. such as Prince Henty fault system. Although the deposit is synvolcanic and, kyell and ~e'sternTharsis, as hybrid VHMS-high-sidfidation based on Pb isotope and stratigraphic evidence (Halley and

canglomerale and sandstone Heliyer barail Granile (rnagnelile sene$ Owen Conglomerale

Rhyolilic mlcaniclastics, volcanogenic sadimenlr Andesitic lavas and Que-Hellyer GranlPicporphyry 4 and lavas - While Spur Formation volcanlclasPics volcanics

Rhyolilic lavas, volcaniclastics, ignimbriler. Dacite lavas and domes K-leldrpar-magnetilealleration limestone -TyndaI Group

Backshalesand voicanogenicsediments RhgIigc pumic-rich mass Seiici&hlarite-pyritealleration

Rhpu?e la daeibc lavas and Dirreminate4and stringer sulfides A voI~~n!das~~~

Hornblende anderlle lavas MaS~lvesulfide ores and inliuriver

Fic. 2. Schenvstic long section for the Mount Read Volcanirs showing the interpreted loeations md morphologies of V1-IMS deposits and their associatedaltrrntion zones (bmedon Large et al., 1996; Halley and Roberts, 1997; Callagllan, 2MI: Corhett, 2001). EXPLORATION IN SUB"dARINE VOLCANIC SUCCESSIONS: EXAiUPLES FROM AUSTRALIA 917

Roberts, 1997), roughly the same age as the other felsic vol- 1992; Callaghan, 2001) have noted that Henty and the Com- canic-hosted deposits at Rosebery and Mount Lyell, features stock deposits at the top of the Mount Lyell system lie at the which make it significantly different from the other VHMS same stratigraphic level at the base of the Tyndall Group. A deposits in the belt include the following: (1) it is a low sul- number of other Cu-Au and Zn-Ph prospects lie at this strati- fide disseminated style with only nlinor lenses of massive graphic position between Henty and Mount Lyell, suggesting polymetallic sulfide; (2) it is hosted by a relatively shallow the possibility that the gold-rich ores at Henty represent the water facies association, including igmmbrite and limestone, top of a magmatic-hydrothermal system similar to the copper- at the base of the Tyodall Group (White and McPhie, 1996); gold system at Mount Lyell (Fig. 2). and (3) the gold-silver-tellurium-rich core of the deposit is surrounded by a zone of copper-lead-bismuth and an outer Coniparisons to depositr in the Morrtlt LVindsor mbprovinca: halo of zinc (Callaghan, 2001). Queensland Halley and Robexts (1979) compared Henty to other gold- Three significant massive sulfide deposits (Thalanga, High- rich massive sulfides described by Poulsen and Hannington way-Reward, and Liontown) and another five small massive (1995) and'concludedthat Henty was a shallow-water exhalative sulfide lenses (Waterloo, Argincourt, Magpie, Handcuff, and VHMS deposit witb high gold and low base metal grades related Warrawee) are known from the Cambro-Ordovician Mount to boiling of the hydrothermal fluid. Recent work by Beckton Windsor subprovince (Fig. 3). Except for Highway-Reward, (1999) and Callaghan (1998, 2001) has shown that the strata- all the deposits are stratiform poly~netallic(Zn-Pb-Cu-Au-Ag) bound gold ores fonned by replacement rather than exhalation. massive sulfide lenses, showing some similarities to the Rose- Callaghan (2001) argues that the metal association (Au-Cu-Bi- hery and Hellyer deposits in the Mount Read Volcanics. In Te), extensive carbonate alteration halo, and replacement tex- contrast, Highway-Reward consists of several discordant mas- tures suggest that the deposit fonned by subsea-floor replace- sive pyritic Cu-An pipe-shaped bodies and has some features ment of paticular volcruuc and carbonate-rich umts during in common with the Mount Lyell deposits in Tasmania. For mixing of a magmatic-hydrothermal fluid with seawater. the purposes of this coinparison we will discuss the charac- In most respects EIenty has little in common with typical teristics and origin of the two principal deposits at Thalanga VHMS deposits, such as Hellyer and Rosehery, and is more and Highway-Reward. akin to a shallow marine strata-bound epither~nalAu-Ag re- Thalarrga deposit: Thalanga comprises several sheetlike, placement deposit (Fig. 2). Previous workers (e.g., Corbett, steeply dipping, sulfide lenses extending over about 3 km of

+++++

Cu. 94gltAg. 2gItAu

undifferentiated Tertiary Carnpaspe ~rn Lower Ordovician- Triassic Warang Sandstone Upper Cambrian Devonian- Q Lolworth- Ordovician Ravenswood Batholith Puddler Creek Fm

Townsville

Towers

Frc. 3. Locations of VI-IMS deposits in the Mount Windsor subprovince, eartern Queensland. 918 LARGE ET AL strike a11d containing a total of ab,out 7 Mt of ore. The ore mainly by subsea-floor replacement of the penneable m lenses are strata bound within a single stratigraphic interval gins of adjacent felsic cryptodomes. that is dominated by coarsely volcaniclastic facies and sills w?th quartz phenoc~ytsabove a thick Foohvall sequence of Spect~umof Volcanic Environments rhyolitic lavas and intn~sionsand beneath a hanging-wall se- Hosting VHMS Deposits quence of dacitic lavas andvolcaniclastic units. The ore lenses The Cambrian Mount Rcad Volcanics in westem Tasma~ and enclosing rocks were deformed and metamorphosed to md the Cambro-Ordovician Mount Windsor subprovince upper greenschist-grade assemblages during the Mid-Late Queensland host important massive sulfide deposits that d Ordovician period (Berry et al., 1992). Remobilization has play a range or lextural, mineralogical, and compositioi complicated metal zonation in the sulfide lenses. but they are 'characteristics. Both of these successions comprise camp generally pyritic and copper rich at the stratigraphic base and assemblages of texturally and compositionally diverse volca~ zinc-lead rich elsewhere. Seniimassivc barite * magnetite ex- facies that also illustrate a wide spectrum in the volcanic E ists in the lateral and upper fringes of some ore lenses. The vironments of massive sulfide ore formation. Research co~ sheetlike morphology and metal zonation at Thalanga are bining volcanic facies analyses and alteration studies has be similar to that exhihiled by the Rosebery deposit in the undertal

1, arated by intervals of volcanic. siltstone, sandstone, aAd Lava flows and domcs consist of hbth collerent and auto- pun~iceousand polymictic breccia (Doyle and McPhie, 2000; clastic (autobreccia, hyaloclastite, I-esedimentedhyaloclastite Doyle, 2001). Doyle and Huston (1999) concluded that the and intrusive hyaloclastite) facies. Flows and domes commonlj massive pyite pipes, although essentially synvolcanic, forrncd occur in associatio~~with synvolcanic intrusions, mainly sill: E.YPLOMTION IN SUBMARINE VOLCANIC SUCCESSIONS EXAMPLES FROM AUSTMLIA 919 and ctyptodomes. Margins of the extrusions and intrusions the time of emplacement. A below wave base, moderate to are typically glassy and in some cases, pumiceous; formerly rzl,~~i\,cl!t1tt.p sul~rnnrin<.,<.[tino, i., inl'zrrcd 10]I;\,(. przv~ilcd glassy domains are commonly perlitic. Interiors are typically fi~rrnc.sl oi rhz ~II(c(.sslon adis in(li( s~ztlby rlnc nrt.r(.nct: oi ~ ~, L microcrystalline, spherulitic, or micropoildlitic. Although the trilobite and other marine fossils, turbidites, and black pyritic volcaniclastic facies range widely in textural characteristics, mudstone in the sedimentary facies association. This inter- there are four particularly common types: (1)very thick (tens pretation is consistent with the presence of very thick vol- of meters), massive to graded beds of rhyolitic pumice brec- caniclastic mass-flow units, hyaloclastite, peperite, and pillow cia; (2) very thick, massive to diffusely stratified units of c~ys- lava in the volcanic facies association. The Rosebery, Her- tal-rich (feldspar, quartz, clinopyroxene) sandstone; (3) thick cules, Hellyer, and Que River orebodies probably all formed to vety thick, massive to graded beds of polymictic volcanic in such moderate- to deep-water environments. No conclu- conglo~nerateor breccia; and (4) pale, massive or laminated sive evidence for the exact water depth at the time of miner- shard-rich mudstone. alization is available, but based on the lack of evidence of boil- The facies architecture of the Mount Read Volcanics shows ing in fluid inclusions at Hellyer and Rosebery (Khin Zaw, distinct regional variations in the proportions of volcanic ver- 1991; Khin Zaw et al., 1996) and by anolo with present-day sus sedimentary facies. The volcanic facies association locally sea-floor massive sulfides, it is speculativerassumed that the dominates the succession, but elsewhere the volcanic facies depth ranged from about 500 to greater than 1,000 m. In con- are interbedded with, or subordinate to, sedimentary facies. trast, a shallower water setting, at or just below storm wave For example, sections about 800 m thick through the Mount base, is most likely to have existed for much of the region dur- Read Volcanics at Mount Black near Rosebery are composed ing deposition of the youngest hthostratigraphic unit, the Tyn- almost entirely of volcanic facies (felsic lavas, intrusions, dall Group, when the Au-rich Henty deposit and the upper- pumice breccia), whereas at Hellyer sedimentary facies most parts of the Cu-Au Mount Lyell deposits were fonned. (black mudstone and lnicaceous mudstone) up to 700 m thick The evidence for a shallower setting at Henty includes the dominate hanging-wall sections. local presence of limestone that contains a shallow-water The volcanic facies association exhibits considerable diver- fauna and in situ welded ignimbrite (White and McPhie, sity in eruption and emplacement processes. The spectrum 1997) ranges from the products of exclusively effusive, intrabasinal eruptions, such as the andesitic lavas and domes in the foot- Setting of Hellyer wall of the Hellyer massive sulfide orebody, to the products of The Hellyer massive sulfide orebody occurs within a sub- explosive eruptions, possibly from vents located at the basin stantial, intermediate to mafic volcanic succession known as margin, such as the pumice breccia units in the hanging wall the Que-Hellyer Volcanics, which is part of the Mount Char- at Hellyer. Among the volcaniclastic facies, there is a spec- ter Group (Corbett and Komyshan, 1989). The massive sul- trum from facies that are clearly syneruptive, having been fide occurs above a footwall comprising andesitic and basaltic generated by a coeval explosive emption, to posteruptive fa- lava and sills with quartz phenocryts, together with associated cie~that exhibit evidence for temporary storage and rework- autoclastic breccia (mainly hyaloclastite) and peperite (Wa- ing plior to redeposition. Syneruptive facies are characterized ters and Wallace 1992; Fig. 4a). The hanging wall is domi- by the dominance of unmodified juvenile components of uni- nated by basalt (Hellyer Basalt). The abundance of basalt- form composition and very thick, mass-flow sedimentation mudstone peperite indicates that most of the basalt units are units. The very thick rhyolitic pumice breccia units of the sills that inhuded black mudstone (Que River Shale). Very footwall to the Rosebery and Hercules massive sulfide ore- thick, graded units of rhyolitic pumiceous and volcanic lithic bodies are excellent examples of syneruptive facies that breccia interbedded with turbidites and mudstone occur in record a major explosive eruption. Massive to graded beds of the upper parts of the hanging wall (Southwell Subgroup). polymictic volcanic conglomerate with significant proportions Along strike from the massive sulfide, the ore position is of rounded clasts occur in the Rosebely-Hercules hanging marked by coarse polymictic volcanic breccia, sandstone, and wall and are good examples of volcaniclastic facies thought to mudstone, and dacitic lavas and domes. be posteruptive, generated by more complex and lengthy Trilobites in the Que River Shale, very thick sections of transport and reworking histories. black mudstone, and the abundance of graded mass-flow The volcanic fzies association in the Mount Read Vol- units collectively indicate that the Hellyer massive sulfide canic~also displays marked regional variations in the propor- formed in a moderate to deep (>1,000 m?) submarine setting tions of magma compositions represented. Much of the suc- The volcanic facies association indicates proximity to intra- cession is dominated by rhyolite and dacite. For example, basinal vents for effusive basaltic and andesitic eruptions and primary and syneruptive volcanic facies in the host succession synvolcanic intrusions. to the Rosebery and Hercules massive sulfide deposits are al- The hydrothennal system responsible for the Hellyer mas- most exclusively rhyolitic to dacitic. However, intermediate to sive sulfide was hosted by a lava- and intrusion4ominated mafic volcanic facies are important at several locations, some volcanic succession. In such successions, permeability can be of which host massive sulfide deposits. For example, at very high but is commonly fracture controlled and is also Hellyer, the volcanic facies in the footwall are mainly an- strongly influenced by facies geometry, especially the margins desitic, facies coeval with the orebody are dacitic, and the of lavas or domes. These controls are reflected in the well-de- hanging wall includes thick (-100 m) basaltic sills. fined and pipelike footwall alteration (GemmeU and Large, Another aspect of the geology ofthe Mount Read Volcanics 1992) that suggests fluid flow was strongly focused by a verti- that shows important variation is the inferred water depth at cal synvolcanic fault. LARGE ET AL b Hercules-Rosebely slratigraphy : Hellyer stratigraphy :

SouUlwell Subgroup massive rhyolite and dacite, pumice breccia; flow banded aUlOc1adc breccla rhyolhe; wlcanic limic breccia and mnglomerate: black pyrilic and grey mlraceous mudstone

Que River Shale black mudstone "hangingwall pyroclastics" crystal- andlor pumice-rich Heliyer Basalt sandstone and bremia mas~iveand pillow basalt. hyaloclashte breccia, peperite: black mudstone

dacite, autocladc breccia: polymidicwlcanic $ breccia, volcanic sandstone: massbe sulfide

Iddspar-phyric andeste; a~lmlasticbreccia: minor polymmic volcanic breccia "foolwall pyroclastics" very thickiy bedded, massive wealdy graded, feldspar-bearing pumice breccia: massive dacite and aut0claStic breccia pillow basalt, basallic hyaiodastlts

graded, micaceous sandsme UrbidRes In6 2 64mm

FIG. 4. Stlatigraphic columns showing volcanic facie$ relatianships in the (a) Rosebery-Hercules, and (b) Hellyer-Que River area of the Mount Read Volcm~ics,The $ sign dcnates the stt-atigmphic position of massive sulfide deposits.

Setting of Rosebey and Hercules with, at least initially, very high permeability and porosity As a result, hydrothermal alteration of the footwall and host The Rosebery and Hercules massive sulfide lenses occur in rocks is pervasive, widespread, conformable, and of variable part of the Central Volcanic Complex that is dominated by intensity (Large et al., 2001). In addition, it is likely that the very thick, weakly graded units of feldspar-porphyritic rhy- highly penneable host facies inhibited venting of hydrother- olitic pumice breccia. The ore lenses are located in the strat- mal fluids at the sea floor and instead favored a subsea-floor ified ~umiceoussandstone and mudstone to^ (host rock. Fie. re~lacementoridn for some of the ore lenses (Allen. 1994b). L " 4b) &very thick pumice breccia that forms most of the'fo;. wall (Allen, 1994a; Large et al., 2001). The hanging architecture Of the Windsor prises thick graded beds of variably crystal-rich and The regional lithostratigraphy of the Mount Windsor sub- pumiceous sandstone (hanging-wallpyroclastics) interbedded province was described by Henderson (1986) and refu~edby . with black mudstone. Berm et al. (1992). There are four formations: the Puddler A below-wave base submarine setting for the Rosebery- ~relkFormation at the base, the Mount Windsor Formation, Hercules successiou is clear from the presence of very hick the Trooper Creek Formation, and the Rollston Range For- graded beds and black mudstone, but there are no features matiou at the top (Fig 4). The middle two formations (Mt. that provide more precise constraints. The volcanic facies as- Windsor Formation and Trooper Creek Formation) are sociation is dominated by syneruptive pumiceous mass-flow domiuated by volcanic facies, whereas the lowest and topmost deposits generated by a voluminous rhyolitic explosive erup- formations are dominated by sedimentary facies, principally tion. The vent position has not been identified but was prob- turbidite and pelagic mudstone. The assemblage of volcanic ably not within the area encompassed by existing exposures. facies is typical of submarine volcanic successions elsewhere in The hydrothermal system that produced the Rosebery and comprising lava flows and domes, synvolcanic intrusions, and Hercules ore lenses operated in a volcaniclastic succession diverse volcamclastic facies. The Mount Windsor Formation is EXPLORATION IN SUBMARINE VOLCANIC SUCCESSIONS: EXAMPLES FROM AUSTRALIA 921 composed of quartz-porphyritic rhyolitic ldvas and intrusions, succession close to the contact between the Mount Windsor together with minor felsic volcaniclastic facies. The Trooper Formation and the Trooper Creek Formation. The footwall Creek Formation is more varied in the volcanic facies types succession is dominated by strong1 quartz- and feldspar- (lavas, sills, and cryptodomes and a wide variety of volcaniclas- porphyritic rhyolitic lavas, including [0th coherent and auto- tic facies) and in the coinpositions (basalt through to rhyolite). elastic facies (hyaloclastite, resedimented hyaloclastite, auto- The presence of turbidite, suspension-settled mudstone and breccia) on the order of 1,000 m thick. Despite strong alteration, graptolite, and pelagic trilobite fossils (Henderson 1986) implies diverse original textures (including perlite, spherulites, mi- that most of the succession was deposited in a below-wave base, cropoikilitic texture, flow banding) and separate units have probably moderately deep marine environment. However, shal- been identiiled (Paulick and McPhie 1999). The massive sul- low-water facies have recently been identified (Doyle 1997),in- fide lenses occur in a co~nplexsuccession of quartz- and dicating that water depths varied spatially ahd temporally feldspar-bearing, clystal-rich sandstone and breccia, quartz- Studies of the volcanic facies in the Mount Windsor sub- and feldspar-porphyritic rhyolitic lavas and synvolcanic sills, province are limited to detailed research at the Thalanga and and peperite. The hanging-wall volcanic succession is about Highway-Reward massive sulfide orebodies. These two ex- 200 m thick and dominated by feldspar-porphyritic dacitic amples extend the spectrum of volcanic environments in lavas with that include significant volumes of autoclastic facies which massive sulfides form and show interesting and impor- (hyaloclastite, resedimented hyaloclastite), polymictic felsic tant differences from Rosebery-Hercules and Hellyer in the volcanic breccia, feldspar crystal-rich sandstone, feldspar- and Mount Read Volcanics. Both deposits occur at felsic volcanic pyroxene-porphyritic andesitic sills, and nonvolcanic mud- centers, on one hand dominated by lavas and domes (Tha- stone and sandstone. Importantly, quartz-rich sandstone and langa) and on the other by synvolcanic intrusions (Highway- rhyolite with quartz phenocryts previously thought to be re- Reward). However, the two deposits contrast markedly in stricted to the ore horizon are now known to occur in the geometry in relationship to the host succession and in the pat- hanging-wall succession as well (Paulick and McPhie 1999). tern of hydrothermal alteration. Thalanga formed at or very The Thalanga massive sulfide deposits formed at a subma- close to the sea floor from exhaling hydrothermal fluids (Hill, rine volcanic center dominated by the products of effusive 19961, whereas Highway-Reward formed by subsea-floor re- rhyolitic eruptions, comprising lavas and domes, together placement, hydrothermal fluids being focused along the steep with lava- or dome-derived, mass-flow-emplaced clastic units margins of shallow intrusions (Doyle and Huston, 1999). and synvolcanic intrusions (Fig. 5). The crest of this volcanic center could have been up to 500 m above the surrounding Setting of Thalanga area, probably reflecting the constructional relief of the high- The Thalanga massive sulfide lenses occur more or less aspect ratio lavas and domes. This setting resembles that of conformably within a felsic lava- and dome-dominated the PACMANUS hydrothermal field in the eastern Manus

West Central East E W h

-Y -

dacite lavas and monomictic breccia massive sulfide ~ntrus~ons rd rhyolite lavas and polymictic breccia strong alteration lntrus~ons andesite intrusion a mudstone moderate alteration chemical sedimentary facies

FIG.5. Volcanic fawes recoustruction of the enviroment of the Thalanga massive silfide deposit, Mount Windsor snb- province, Qoeensland (after Paulick and McPhie, 1999). 922 LARGE ET AL basin (Papua New Guinea), which occnrs at -1,600 m below have peperitic upper margins that demonstrate their em- sea level on the top of a 400- to 600-m-high ridge composad placement into wet unconsolidated sediment as shallow sills predominantly of dacitic lava (Binns and Scott, 1993). After and cryptodomes. A single partly extrusive cryptodolne ore for~uation,the Thalanga mine area remained a center of emerged at the sca floor, but the presallce of additional lavas effusive volcanism and topographically high, although com- or partly extrusive cryptodomes is indicated by resedimented positions of lava flows and domes shifted to dacite. The mas- autoclastic breccia units. sive sutCides at Thalanga were bulied by dacite lavas, synvol- Paleosea-floor positions at Highway-Reward are difficult to canic intrusions, and thick, mass-flow-emplaced volcanic assign and'in any case, they do not appear to have been fa- breccias composed of locally derived clasts. Hemipelagic vored locations for massive sulfide formation. Instead, by- mudstone and tnrhidite sand, partly derived from an nn- drothermal fluids were constrained by the steep contacts of !mown possibly distal source, accumulated in surrounding intrusions and focused withi11 the porous and permeable, lower lying areas. glassy: brecciated margins, promoting the formation of sub- Mapping of alteration in the footwall at Thalanga (Panlick sea-floor massive snlfide pipes (Doyle and I-Iuston, 1999). 1999) bas shown that the zones of intense alteration do not This distinctive style of massive sulfide is also reflected in the coincide either with paficular facies boundaries or facies distribution of alteration, zones of strong hydrothermal alter- types and, instead, clearly crosscnt the Cacies arrangement ation, and p~ite-qua~tz-sericitestringer veins extending 150 (Fig. 5). Thalanga is important m this regard, illustrating a m into the footwall and at least 60 m above the snlfide pipes. case where the facies architecture apparently had minimal in fluence on the ore-forming hydrothermal system. Volcanic influences on VHMS sbyle Patterns shown by the deposits descrihcd above allow, syec- Snfting of Highway-Rcward ulation that volcanic setting may he a significant influence on The Highway-Reward massive sulfide pipes occur in a shal- the style and metal content of VHMS deposits. In simple low intmsion~dominatedfelsic volcaiiir: center (Doyle and terms the more copper rich deposits appear to be associated McPhie, 2000; Fig. 6). The intrusions are interleaved with with felsic volcanic centers dominated by subvolcanic intru- pumice breccia, crystal-rich sandstone, turbidites, and sns- sions (e.g., Highway-Reward),whereas the Inore zinc rich de- pension-settled mudstone. Contact relationships and phe- posits are associated with both felsic (e.g., Rosebeq, Tha- nocqst populations (mineralog, size, and percentages) indi- langa) and mafic-intermediate (e.g., Hellyer, Que River) cate the presence of at least 13 distinct porphpitic units in a \~olcaniccenters dominated by lavas andlor volca~~iclasticfa- volurne of 1 x 1 x 0.5 km3. More than 75 percent of the units cies. Studies by Amold and Sillitoe (1989) and Messenger et

pumice breccia-sandstone ambient sedimentary facies

I:;:/ resedimented autoclastic breccia strong alteration and veins

porphyritic intrusions massive pyrite-chalcopyrite

Frc 6. Volcanic facies reconstluction of the enviroment of the Highway-Reward massive silfide deposit, Mount Windsnr rubprovince, Quoonslmd (after Doyb aridMcPhie, 2000). EXPLORATION IN SUBhf.4RINE VOLCANIC SUCCESSIONS: EXAMPLES FROM AUSTRALIA 923 al. (1997) at Mount Morgan support this proposed relation- facies or located on the cooler flanks of volcanic edifices and ship between Cu-Au pyritic pipe ores and intrusion-related distal from swvolcanic intrusions. A, L L volcanic centers; however, the volcanic environment of Mount Lyell is too poorly understood to confirm the pattern. Spectrum of Deposits in the Mount Read Volcanics Previous workers (e.g., Poulson and Hannington, 1995; and the Mount Windsor Subprovince Halley and Roberts, 1997) have demonstrated that the water The deposit descriptions and genetic interpretations pre- depth can be an important control on goldJbase metal ratio; sented above suggest that the ores of the Mount Read Vol- gold-rich, base metal-poor deposits such as Henty typically canic~and the Mount Windsor subprovince do not all belong form in shallow-water volcanic settings, whereas the base to the same VHMS class. Rather, there is a continuum or metal-rich deposits (e.g., Hellyer, Rosebe~y,Thalanga) are spectrum from classical VHMS deposits (e.g., Hellyer, Tha- confined to deeper water volcanic settings (Fig. 3). The pri- langa), which formed on the sea floor in a moderate- to deep- mary shape of the deposit may also be influenced by volcanic water environment, to replacement, intrusion-related, cop- setting. Elongate mound-shaped deposits (e.g., Hellyer) form per-gold deposits, which appear to he transitional between above major spvolcanic structures, m low-permeability vol- VHMS and high-sulfidation epithermal (e.g., Mount Lyell canic facies that have focused hydrothermal fluid flow to the and Highway-Reward), to shallow-water gold-rich strata- sea floor (Large, 1992). Multiple stratiform sheetlike lenses bound replacement deposits that have some features akin to (e.g., Rosebery) are more likely to develop within permeable low-sulfidation epithermal ores. This spectrum is shown in a volcaniclastic facies, in which hydrothermal fluids are less fo- triangular diagram (Fig. 7) where the deposits have been cused and spread out laterally either below or onto the sea plotted in terms of their attributes relative to end-member floor, forming thinner sheetlike lenses at various stratigraphic VHMS, porphyry Cu-Au-Mo, and epithennal Au-Ag ores. levels. The spectrum encompasses deposit styles that we might ex- The relationship between ore metal ratios and nature of the pect in a suhmaIine volcanic setting, from shallow-water volcanic center probably relates to the temperatul-e of the as- (epithermal) to moderate- to deep-water (VHMS), and from sociated hydrothermal system. Thermodynamic modeling suhvolcanic intrusion-related replacement (porphyry) to snb- studies (e.g., Sato, 1973; Large, 1977, 1992; Ohmoto et al., sea-floor replacement and sea-floor exhalative systems. Al- 1983) and measurements of temperature of black smoker though we do not favor use of the term "high-sulfidation" vents on the sea floor (e.g., Goldfarb et al., 1.983; Scott, 1992) VHMS for these hybrid-style massive sulfide and dissemi- have shown that copper mineralizing vents are typically asso- nated deposits, as proposed by Sillitoe. et al. (1996), we do ciated with higher temperature fluids (>300°C) than the zinc agree that their formation involved subsea-floor re- mineralizing vents. Hydrothermal systems developed above placement, in relatively shallow water, with involvement of a or closer to synvolcanic intrusions are more likely to be hotter, magmatic fluid component. and thus generate Cu-Au-rich ores, compared to the hy- This spectrum of submaline volcanic-hosted deposits is not drothermal systems associated with lavas and volcaniclastic considered to be unique to the Mount Read Volcanics and the

Porphyry Cu-Au-Mo

Far South East

fluid input and Mt Lyell

Increasing component of //*Hig$y-Reward \\ sub-volconic idmives in volcanic succession

Hishikari VHMS 2"-~b-cuAU-~g 4 -,Low sulfidation submarine subaenal epithermal volcanics volcanics Au-Ag

7 Increasing meteoricfluid input andgold/barr metal ratio

FIG.5. T"angular representation sliowing the spectmm of ore deposits in volcaruc successions, ulng selected deposits from the Mouut Read Volcanics and Mount Windrar subprovince z examples. 924 LARGE ETAL.

Mount Windsor subprovince, but other cases probably occur (Western Tharsis-Mt. Lyell and Highway-Reward) are shown in the major VHMS districts worldwide. Based on metal ra- in Figure 8, based on data from Doyle (20011, CemmcU and tios, alteration assemblages, morphology, and volcanic envi- Fulton (2001), Herrmann and Hill (2001), Huston and Kam- ronment, additioual examples of hybrid Cu-Au-bearing mas- prad (2001), Large et al. (2001). and Paulick et al. (2001). The sive sulfides that wollld plot within the tliangle in Figurc 7 are polynletallic zinc-rich deposits each have an alteration enve- possibly the Horne and Bousquet deposits in the Abitibi dis- lope, which is typically elongate parallel to volcanic stratigra- trict, Canada, the Gai and Kul-Yurt-Tau deposits in the phy, with the footwall alteration more intense and more ex- Soulher11 Urals, Russia, the Mount Morgan deposit in East- tensive than the hanging-wall alteration (Fig. 8a, b, c). In the em Australia, and the Boliden deposit in the Skellefte district, copper-gold-bearing deposits, the alteration halo extends a Sweden. grcater distance into tllr: hauging wall and appears to cut across volcanic facies boundaries (Fig. 8d, e). In all cases, Spectrum of Ore Deposit Alteration Halos there is a simple zonation from chlorite i- quattz-rich alter- The studies ul this special issue on the character, extent, ation close to the ore lenses, to sericite-rich alteration farther and composition of hydrothermal alteration and volcanic fa- away. In the polymetallic zinc-rich ores, the chlorite 3 qua&- cie~related to the Australian VHMS deposits discussed above rich zone is commonly present immerliately below the ore enables a comparison of hydrothermal alteration across the lenses (Fig. 8a, b, c) and is thickest and most intense below spectrum of deposits. copper-rich parts of the orebody. At Hellyer (Fig. 8b), the chlorite and sericite alteration forms a zoned pipe, similar to Mo,rphology, zonation, and eltent ofl~alos those described for many Archean deposits in Canada (e.g., The morphology and zonation of the hydrothermal alter- Sangster, 1972; Franklin et al., 1981); however, a1 Rusebery ation halos associated with the polymetallic ziuc-rich deposits (Fig. 8a) the alteration zones are strata bound, and at Tha- (Rosebery,Hellyer, and Thalanga) and the pylitic Cu-An deposits langa (Fig. 8c) there is evidence for a combination of pipes

a ROSEBERY Zn-Pb fCu b HELLYER Zn-PbfCu

c THALANGA Cu-Zn-Pb d WESTERN THARSIS Cu-Au

e HIGHWAY-REWARD Cu-Au f GOSSAN HILL Cu and Cu-Zn

Strong quartz-rich andlor moderate seridte f chlorite 1 chiorits-rich (At Z 90) EXPLORATION IN SUBMARINE VOLCANIC SUCCESSIONS EXAMPLES PROM AUSTMLIA 925

and strata-bound zones. Previous workers (e.g., Morton and Five alteratior~zones have been identified: fuchsite, chlorite, Franklin, 1987; Large, 1992) have discussed the importance carbonate (calcite), quartz-albite, and sericite. Fuchsite-dom- of permeability and faults in the footwall as controls on ore inated alteration occupies the central portiou of the hanging- fluid discharge and the formation of alteration pipes or strata- wall alteration plume. Chlorite and carbonate alter t'lon sur- bound zones. rounds the fuchsite zone with carbnuate zones forming near The copper-gold pyritic ores commonly show intense chlo- to the ore deposit, and chlorite zones extending above and lat- rite + quartz alteration within and immediately surrounding eral to the carbonate. Outward is quartz-albite alteratiou, the ore, both on the hanging-wall and footwall sides. The which extends laterally into distal sericite alteration. Afker sericite + chlorite halo can be very extensive and commonly rapid burial of the deposit by basalt, continuation of upward shows a symmetric pattern surrounding the chlorite + quartz- hydrotl~ermalflmd flow created the zoned hanging-wall al- rich zone (Fig. Sd, e). At Western Thasis in the Mount Lyell teration. Distributiou of hanging-wall alteratiou assemblages . field, Huston and Kamprad (2001, fig. 3) have recognized a

pyrophyllite-rich alteration zone, which foms an overprinting , L zone surrounding the Cu-bearing chlorite + quartz-rich core. sericite: Ge~nmelland Fulton:2001). The zone contains other minerals (topaz, fluorite, zunyite, In contrast to the crosscutting carbonate-bearing and and alunite types), which together with pyrophyllite indicate quartz-albite zones at Hellyer, similar, but strata-bound, car- advmced argillic alteration, similar to that found in high-sul- bonate and quartz-albite + chlorite alteration lenses are pre- fidation epithermal systems (White and Hedenquist, 1995). sent in the hanging wall of the Henty gold-rich volcanogenic Although Highway-Reward is a similar Cu-Au-bearing system ores (Large, C.P., 1995; Callaghan, 2001). It is significant to Mount Lyell, no advanced argillic assemblages have been from an exploration perspective, that whereas albite destruc- reported. tion is a ubiquitous feature of footwall alteration in the VHMS Alteration zonation related to the Henty strata-bound dis- system, albite addition may be present in the hanging wall of seminated gold cleposit is very different from that in the zinc- some Zn- and Au-rich VHMS deposits. and copper-rich VHMS deposit discussed above. In the gold orebodies the alteration is concentrically zoned, with a core of Carbonate alteration massive microcrystalline silica showing marked ahminum de- The distribution of carbonate alteration in the five deposits pletion, sul~oundedby an intermediate silica-sericite zone, studied is shown in Figure 9. lu the stratiform zinc-rich de- followed by an outer zone of silica-sericite-pyrite-chlorite posits, carbonate is commonly developed in either the chlo- (Callaghan, 2001). Footwall alteration consists of intense rite- or sericite-beariug zones cld& to ore (Fig. 9a, b, c). In sericite + pyrite i carbonate, whereas hanging-wall alteration coutrast the copper-gold ores sho$iess or no significant car- consists of albite-silica + chlorite in strata-bound zones mter- bonate alteration, and if present;,?t is developed within an calated with carbonate-altered volca~~iclasticsand bedded outer propyllitic-type alteration hdilo surrounding the sericite carbonate (Ilalley and Roberts, 1997; Callaghan, 2001). Thus, zone (Fig. 94). Hydrothermal carbonate is generally present compared to the zinc- and copper-bearing VHMS systems, as disseminated spots comprising 2 to 20 wt percent of the al- the Henty gold system shows more intense silica rich and alu- tered rock, although massive carbonate zones occur above, minum depleted alteration close to ore and extensive albite below, or lateral to zinc-lead ore at Rosebery and Thalanga. alteration within the hanging wall, consistent with a subsea- Textural evidence (e.g., Khin Zaw and Large, 1992; Sharp and floor re lacement origin. Callaghan (2001) interprets the in- Gemmell, 2001) and chemical evidence (e.g., Herrmann and tense siica enriched, aluminum depleted, alteration core to Hill, 2001; Large et al., 2001) indicate that the carbonate form from a highly acidic, possibly magmatic, flnid. zones form by infill of porosity and selective replacement of various components of the volcanic rocks, rather than by di- Hanging-wall alteration rect precipitation on the sea floor. Studies by Allen et al. As described above, the pyritic Cu-An deposits (Fig. Sd, e) (1998) of carbonate alteration m the Rosebery-Hercules area are associated with extensive hanging-wall alteration (up to of the Mount Read Volcanics indicate that carbonate alter- 200 m thick) of similar mineralogy but generdly less intensity ation distal to ore is generally low intensity m1d not texturally than the footwall alteration. This distribution reflects forma- destructive, ocuning as disseininatious, filling primary poros- tion by subsea-floor replacement rather than exhalation ity such as vesicles and replacing or rimming glass shards and (Large, 1992). The stratifom sheetlilie zinc-rich deposits at feldspar phenocrysts, in advanced stages. However, close to Rosebery and Thalanga (Fig. 8a, c) show little obvious visual ore, more intense carbonate alteration masks prima~yvol- hanging-wall alteration in drill core; however, lithogeochemi- canic textures, resulting in fine-grained massive homoge- cal studies at Rosebery (Large et al., 2001) have revealed a neous pale-colored rock. The alteratiou carbonate minerals weak chemical halo, indicated by the whole-rock BaISr ratio are commor~lycomplex mixtures of Fe-Mn-Mg-Ca carbon- and Mn content of carbonate, extending up to 100 m into the ates, as summarized in Figure 9. At Rosebery the carbonates hanging-wall volcaniclastics. No similar hanging-wall halo has are commonly Mn rich (Large et al., 2001), whereas at been defined at the Thalanga deposit (Paulick et al., 2001). Hellyer, Western Tharsis, and Gossan Hill ferroan dolomite, Hellyer is unusual as it is the only Paleozoic polymetallic ankerite, and siderite are the common species. VHMS deposit to exhibit a well-developed hanging-wall al- Chlorite-trenlolite-dolomite-calciteassemblages are promi- teration zone. Studies by Gemmell and Fulton (2001) have nent in thin strata-bound zones in, and laterally adjacent to, defined a distinctive and zoned alteration plume overlying the the western ore leuses at Thalanga. Their major elemeut, im- central part of the deposit within the hanging-wall basalts. mobile trace element, and isotopic compositions indicate they LARGE ETAL

a ROSEBERY , b HELLYER

Mn-rich carbonate ~F 1OOrn (kutnahorite, rhoclochrosite) - Mn canlent increases towards ore \ . j .Ferroan dolomite & \ . ankerite \ / Mn content increases lowards \' ore in i,angingwali

carbonate-trernolite -chlorite lenses d WESTERN THARSIS

100m .Calcite overprinting dolomite no chemlcal trend to ore

e GOSSAN HILL Ankerite & siderile ... no trends to ore s most Mn-rich carbonate zinc ore & veins 1 I .Ankerite & siderite . Fe conlent of ji,:i.i.i.i.: .... carbonate increases

1 ~ m,L-nm,- to ore

Fw. 9. Comparative sketches showing extent of carbonate alteratmn at Rosebery, Hellyer, Ttrdlanga, Western Tl~arsis,and Gossan Hill. are the metamolphic products of chlorite-dolomite assem- isotopic data on the carbonates at Henty to suggest that they blages that originated by h drothermal alteration of rhplitic resulted from a district-wide magmatic COBdevolatilization volcanics, close to the p 9eosea floor (Herrmann and Hill, event, which commenced during early hydrothermal activity 2001). The chlorite and tren~olitehave magnesian compositions and continued for a period beyond ore formation. Carbonate that do not show systematic lateral variations in relationship deposition resulted from mixing of small amounts of a mag- to ore. Dolomite and calcite have nearly ideal compositions. matic COz-rich fluid with seawater at, or below, the paleosea Dolomite contains up to 0.02 and 0.06 cations per formula floor (Callaghan, 2001). unit of iron and manganese. Iron content of dolomite increases slightly toward the central ore lens (<0.005-0.02 cations) but 1701canic influences on alteration styles in VHMS successions there is no systematic spatial variation in manganese. The facies architecture of submarine volcanic successions Bedded carbonates and carbonate-altered volcaniclastic fa- that host VHMS deposits is inherently complicated, and ad- cie~are features of the Henty deposit (Halley and Roberts, ditional stratigraphic and structural complexities may be in- 1997; Callaghan, 2001). The carbonate minerals (dominantly troduced by the synvolcanic intrusions and synvolcanic faults. calcite) occur both in the footwall alteration zone (sericite- Sites of ore deposition are highly variable and may comprise pyrite-carbonate) and as massive lenses in both the footwall thick lava and breccia successions (e.g., Hellyer, Thalanga), and hanging wall. synvolcanic intrusions (e.g., Highway-Reward), and volcani- Early studies of the carbonate lenses at Rosebery, Tha- clastic mass-flow units (e.g., Rosebery and Hercules). Ore- langa, and Henty (Braithwaite, 1974; Gregory et d., 1990; bodies may have formed in shallow subsea-floor settings as Halley and Roberts, 1997) concluded that they were of ex- replacements of volcaniclastic (e.g., Rosebery and Hercules) halative origin forming distal to the sea-floor sulfide lenses. or synvolcanic intrusions (e.g., Highway-Reward), or else at However, in each case, more recent work has demonstrated the sea floor (e.g., Hellyer). their infill and replacement origin, involving mixing of hy- Even though submarine volcanic successions are poten- drothermal fluid and seawater below the paleosea floor, in tially immensely complex, their initid response to alteration is permeable volcanic units (e.g., Herrmann and Hill, 2001). at least in part predictable. Factors that appear to influence Khin Zdw and Large (1992) used the isotopic composition of responses to alteration include the presence of volcanic glass, the ore-related carbonate minerals to interpret a seawater the porosity and permeability (including fracture density and source for both carbon and oxygen. Callaghan (2001) used faulting), the rock composition, and external conditions such EXPLORATION IA' SUBMARINE VOLCANIC ':CICCESSIONS. EXAMPLES FROM AtrSTRALIA as pressure, temperature, fluid composition, and fluidlrock domains in the same facies. This generalization ho ratio. Of particular importance is the presence of volcanic scales rangin from millimeters, such as in the case of glass and the porosity and permeability characteristics. versus clystalfi ne flow laminae in lavas, to meters, sucl Propoeion and distribution of glarsy versus ccryrlallina do- the case of glassy margins versus the crystalline inter mains: Submarine lavas, high-level intrusions, and some vol- lavas and synvolcanic intrusions. caniclastic facies are commonly initially glassy or at Irast Polosity and penncability characteristiis: The ext, partly glassy (Fig. 10). Once formed, both the texture and physical and chemical interaction of various volcanic composition of volcanic glass may be partially or completely with seawater, diagenetic fluids, andlor hydrotliennal modified by a variety uT processes, such as hydration, devitri- depends on the porosity and permeability. These pror fication (crystallization below the glass transition tempera- vaiy enormously among different volcanic facies ture), diagenetic alteration, and compaction. Thc ratc at tially within sorrle volcanic facies, and also tempor%? ly. which these modifications proceed is in general accelerated the time of emplacement through compaction and diag by the presence of water and by elevated temperature. In alteration. However, in simplest terms, cohcrcnt and contrast, clystalline components of volcanic facies are gener- volcanic facies show fundamentally different styles of p< ally unaffected by hydration and compaction and may remain and permeability (Fig. 10) largely stable during diagcnetic alteratioli. Tlms, glassv do- Coherent domains of lavas and intrusions are domina mains will undergo longer and more complex textural evolu- fracture-controlled porosity and permeability This style tion and e.&ibit greater compositional changes than crystalline in scale from vcry large (melers) quench fractures or c, joints to vev small (millimeters)perlitic fractures. The f generally prevail in the interior of lavas and synvolcar tmions, whereas the latter may occur in any glassy domai: in glassy clasts. In volcaniclastic facies, the interpartic] inlraparticle pores control porosity and permeabilty, so tpe (pumice or scoria versus nonvesicular clasts), graii and sorting are all important. Wcll-sorted pumice b~ such as that forming the footwall to the Rosebely and cules massive sulfide deposits, at least initially has unif high porosity and permeability Poorly sorted mixtures of s clystals, and dense volcanic clasts (for example, resedim autoclastic facies) have lower and more heterogeneous 1 ity and permeability. The matrix character and abundan particularly important in poorly sorted aggregates. Thus, there is a wide spectrum in the textural and ct sitional responses of different volcanic facies to &agent other alteration even within one succession. Glaswic more porous and permeable facies in submarine volcani cessions are the most easily affccted. The texLural and positional contrasts that initially exist between glassy an( talline domains will persist during, and influence, an) alteration, including alteration related to VHMS ore-fo hydrothermal activity. Chemical mass change.$ The intense hydrntlrermal alteration of the footwall of VHMS deposits may be associatedwithsignificant chan the mass of mobile chemical com onents (e.g., Barre MacLean, 1991, 1994; Barrett et af., 1993). Estimates mass changes in variably altered and spatially relate< samples have been uscd in lithogeoche~nical explo {MacLean and Barrett, 1993; Galley, 1995). This tecl~ has not been widely applied in Australian VHMS dir However, the available data for Australian deposits in that large net mass gains associated with silicification /-j matrix-controlled~orositv fracture-cantmlled oarositv footwall zones are tpical. This pattern contrasts with ne losses m the chloritic zones that exist beneath some Ca VHMS deposits (e.g., Noranda; Barrett and Machm, 191 Gernmell and Large (1992) applied a modified j ity in the principal volcarnc facirs wes found in rubrn&ne volcanic shes- sions. The coherent parts of lavas and intrusions have fracturz-controlled method to estimate mass chan es in the zoned alteratioi porosity, whcrwu the pu~usilyof volcanielastic fanes is rnahix mntrolled beneath the Hellyer deposit. T% ey found that alteration (after Mc Phie et al., 1993). stringer envelope, sericitic, chloritic, and siliceous core 928 LARGE ET AL involved net mass gains of 41100 g, 21100 g 181100 g, and entrainment of seawater into the hydrothermal system 108/100g, respectively. These zones reflect increasing alter- (Roberts and Reardon, 1978; Lydon, 1988). ation intensity frorn the onter shell to the inner core of the The idea of alteration zonation due to a decreasing thermal snbvertical feeder system. All the zones lost substantial Na,O and fluidhock ratio has been tested and refined by Schardt et and minor CaO. The major gains were in Fe203,S, and Si02, al.. (2001) in a thermodynamic model designed to reproduce with additional slight gains in K20in most zones, and MgO in the zonation present in the footwall alteration pipe at Hellyer, the sericitic and chloritic zones (Table 2). Paradoxically, the passing from the silica-rich core, through a chlorite-rich shell, chlorite zone appears to have lost Si02(-131100g ). That con- to the sericite-rich envelope. Schardt et al. (2001) have shown trasts with the SiO, gains in the adjacent sericitic and siliceous that alteration mineral zonation depends principally on varia- core zones (13 and 951100 g , respectively). tions in temperature, pH, redox state, and reaction progress At Thalanga, most footwall alteration zones were associated (or fluidhock ratio), as hydrothennal fluids move outward with net inass gains up to about 50/100g; mainly attributable from the center to edges of the alteration system. The classic to large gains in Si02(Hernnann and Hill, 2001). The pFtic footwall zonation of quartz -t chlorite -t sericite at Hellyer stringer zones also gained substantial Fe20, and S, and the was reproduced by reacting a fluid at 250' to 350°C (starting peripheral siliceous white rhyolite zones gained minor K20. temperatures) and pH of 4.5 to 5.0 with andesite over a de- In contrast, some volumetrically small footwall sericite-chlo- creasing flnid~rockratio from 50.000 down to 20. Reactions rite and chlorite-tremolite zones are characterized by net during cooling over the temperature range 350' to 100°C re- mass losses due to significant losses of SO2. AU Thalanga produced the fnll range of foohvall alteration assemblages. footwall alteration zones exhibit major or total loss of NazO. The pH of the reacting fluid showed little variation (4.54.0) Consideration of limited geochemical data from Rosebery during reaction progress (Schardt et al., 2001). Mg-rich chlo- (Large et al., 2001) suggests that the footwall alteration was rite formed in the inner chlorite-rich zone and Fe-rich chlo- also mainly associated with net mass gains, dominated by sig- rite developed in the outermost part of the sericite zone, sim- nificant gains in SiO,. Estimates of absolute mass changes for ilar to the pattern observed in many massive snlfide deposits variably altered samples from beneath the K lens reveal losses (Urabe et al., 1983). This modeling was carried out employ- of Na,O in all the footwall hydrothermal alteration assem- ing an Mg-bearing ore fluid, with the assumption that a com- blages (Table 2). With the exception of a slight loss of SiO, m ponent of seawater Mg was entrained into the ore fluid at the chloritic zone immediately below the ore, all other foot- depth. Further coupled fli~idflow-fluid chemical modeling is wall-altered samples exhihit minor to large gains of Si02 planned to study footwall chlorite formation related to the in- (Table 2). teraction of an upwelling Mg-free hydrothermal fluid with advected Mg-bearing seawater, as proposed by several work- Conditions offormotion ofht~drothemalalteration ers (e.g., Roberts and Reardon, 1978; Franklin et al., 1983). in VHMS stjstems The modeling by Schardt et al. (2001) demonstrated that, Previous workers (e.g., Large, 1977; Riverin and ITodgson, for the case of Mg-bearing hydrothennal fluids, extensive 1980; Lydon and Galley, 1986) have suggested that alteration chlorite alteration zones are favored by higher temperatures zonation in the footwall of VHMS deposits probably reflects (>250°C) and less acidic pH (4.55.5) fluids. Sericite-domi- fluidlrock interaction controlled by decreasiug temperature nated alteration, on the other hand, forms at lower tempera- with distance from the center of the hydrothermal upflow tures (<250°C) and Inore acidic conditions (pH = 4.04.5). At zones. However, the Mg-free nature of modem sea-floor hy- lower pH, kaobnite and pyrophyllite are stabilized, and at drothermal fluids suggests that Mg-bearing chlorite develop- higher pH and lower temperatures (<200°C),K feldspar be- ment in foohvall alteration zones most likely relates to the comes an important component of the outerinost alteration

TABLE2. Summary 01Major (absolute) Mass Changes in Alteration Zones Associated with Hellyer Rosebery, and Thalanga Massive Sulfide Deposits

Deposit AlteraLion zone Net mass change (g1100g) Major mas gains Major mass losses

Hellye-er Siliceous core 108 Si, Fe, S. (K) N% (Ca) Chlorite 18 Fe, Mg, S Si, Na, (Ca) Seridte 2 Si, Fe, 5, (K) Na, (Ca) Stringer envelope 4 Si, S, Fe, (K) Na, (Ca)

Roseber). Quartz-sericite St, Fe, * (S, K, COz) Nu Sencite Si, (K, CO,) Na Chlorite Si, Na

Thalanga Chlotite~tremobte-carbo~~ate(CTC 2 and 3) 147 Ca, Mg, CO, (Fe, S, Zn) Na, K Chloritr~tree~olite(CTC 1) -28 Mg, (Fe, S) Si, Na

Qtz~Pystringer zones Si, Fe, S Na Qtz~Kswhite d~plite Si. K Na Qtz-SerChl moderately altered rhyolite 51, (Fe, S) Na Ser-Chl foliated rlyobte (Mg) Si. Na

Abbreviations: chl = chlorite, Ks = K feldspar, Py = pyite, qtz = quartz EXPLOPATION IN SUBMARINE VOLCANIC SUCCESSIONS. EXAMPLES FROM AUSTRALIA 929

zone (Schardt et al., 2001). The modeling Supports previous hydrothermal alteration (Ishikawa et al., 1976; Large et al., interpretations (e.g., Walshe and Solomon, 1981) that intense 2001); (2) Pearce element ratios (Stanley and Madeisky, chlorite and quartz rich alteration associated with copper- 1994),which involve mathematic treatment of the whole-rock gold VHMS deposits results from high-temperature hy- data to distinguish igneous fractionation and volcanic compo- I drothermal systems (>300°C),whereas sericite-dominated al- nent mixing trends from hydrothermal alteration associated teration associated with zinc-lead-silver ores results from with mineralization; and (3)determination of elemental mass lower temperature hydrothermal systems (<200"C).At inter- changes associated with hydrothermal alteration, using the mediate temperatures (200°300"C), mixed chlorite-sericite procedure of Gresens (1967), modified by Grant (19861, m , assemblages are typically developed. Carbonate alteration conjunction with immobile element chemostratigraphy (Bar- was not considered by Schardt et al. (2001); however, it is rett and MacLean 1994; Barrett et al., 2001). likely that significant carbonate alteration, particularly chlo- The first of these methods combines two alteration indices,

, rite-carbonate assemblages, indicates more alkaline condi- A1 and CCPI, to produce the alteration box plot and is simple tions that may develop where hot, near-neutral hydrothermal and easily applied m the exploration context. It has the added fluids have mixed with, and heated, entrained seawater, lead- advantage of relating chemical to mineralogical changes in a ing to saturation of carbonate at the periphery of the hy- graphic method, highlighting any trends that may be spatially drothermal upflow zones. related to VHMS ores (Fie. 11: Laree et al., 2001) .- , Figure 11 depicts the most common- alteiation trends gen- Alteration Vectors Useful for Exploration erated by hydrothermal systems associated with VHMS de- A summary of the alteration vectors discussed in the papers posits. ieait altered volckic samples plot within a central of this special issue is given below. The reader is also referred box with an A1 = 20 to 65 and a CCPI = 15 to 85, depending to an excellent review on this topic by Galley (19951, which is on primary composition (Large et al., 2001, fig. 7). Bydro- based plincipally on case studies of Canadian VHMS deposits. thermally altered samples define a trend to the right, de- A. pending'on the relative significance of sericite, Fhlorite, Mineral zonation vectors pyite, K feldspar, and carbonate alteration. Diagenetic alter- Zonation from sericite-rich alteration assemblages to more ation, which includes albite, epidote, paragonite, and calcite,

chlorite- or auartz-rich alteration has been recoemzed for and some bwes, of weak haneine-wallu u alteration., Lproduces some time as'an empirical vector toward the center of hy- trends to the .left on the box plot. drothermal systems ksociated with VHMS deposits (e.g., Sangster, 1972; Lydon, 1984). Chlorite-rich alteration is more Mineral conlposition vectors common close to copper-rich ores, especially those containing Previous studies have emphasized the composition of chlo- magnetite or pyrrhotite, such as the Archean Noranda-type rite, n~particular the variation in FeIMg ratio, as a vector to Cu-Zn deposits (e.g., Franklin, 1995); and quartz-rich alter- mineralization (e.g., Urabe and Scott, 1983; McLeod and ation may be present close to gold-rich ores (e.g., Henty). Stanton, 1984; Lydon, 1988). However, research in the Carbonate alteration may occur in both the chlorite and Mount Windsor and Mount Read volcanic successions sug- sericite zones but is more commonly associated with the zinc- gests that subtle changes in the composition of white mica (e.g., Rosebery, Thalanga) and gold-rich deposits (e.g., may be just as useful (Herrmann et al., 2001; Hustou and Henty) than the copper-rich deposits. Kamprad, 2001; Large et al., 2001). The most intense carbonate alteration is commonly later- Herrrnann et al. (2001) have shown that spectral analysis of ally adjacent to inferred fluid upflow zones and probably de- rock samples by short wavelength infrared analysis (SWIR) veloped in porous volcanic units where the hydrothermal flu- using the PIMA can reveal changes in the Fe and Mg content ids mixed with seawater (e.g., Thalanga; Herrmann and Hill, ("phengicity"), Si/Al ratios, and the Nal(Na + K) ratios of 2001). white mica. White mica in the svmmetrical hydrothermal al- teration zones surrounding the p@c Cu-Au deposits at Mnjor element lit~~.ogeochemicalvectors Western Tharsis (Mt. Lyell, Tasmania) and Highway Reward All deposits studied in this investigation show zones of pla- (Mt. Windsor subpro\ii~ce,Queensland) valy systematically gioclase destruction and sodium depletion in the foohvall. in composition from phengite at the outer edge of the alter- Similar zones of sodium depletion have been known about, ation to sodic muscovite close to ore. At Rosebery, a zone of and applied in, mineral exploration for the Kuroko deposits of phengitic white mica sul~ounhthe ore zone, and a zone of Japan and the Archean massive sulfide deposits of Canada for sodic white mica occurs in a volcaniclastic unit above the over 30 yr (Franklin et a]., 1981). These zones are commonly highest grade ore. The most barium rich mica (between 5 and associated with iron and magnesium enrichment, depending 10% Ba ion substituting for K) occurs close to ore in th~~m-' on the degree of pwte and chlorite alteration, the FeIMg mediate hanging-wall and footwall positions. ratio of the chlorite, and the original composition of the vol- Although our research shows that there are significant vari- canic rock. Potassium may be enriched or depleted within the ations in chlorite con~positionsurrounding VHMS deposits, alteration zone, depending on the ratio of sericite to chlorite. there is no common and systematic pattern related to the dis- The following three lithogeochemical approaches based on tance from the ore. This is at variance with studies elsewhere variations in whole-rock composition may serve to define vec- which have shown that the Mg content of Fe-Mg chlorite tors to ore: (1) ratios such as the Ishikawa alteration index commonly increases passing from the margin to the core of (AI) and the chlorite-carbonate-pyrite index (CCPI), which the footwall alteration system (e.g., Seneca, Southbay, and track the chemical and mineralogical changes associated with Corbet deposits; Urabe et al., 1983). In contrast, in the dglomite 1 snkerite 100 *ll.,l:l-.. , + chlorite epidote .- *4-c/ll-ca;- ore - pyrlte calclte 80

9. sericite

albite

0 2 0 4 0 6 0 8 0 100 Alteration Index FIG.11. Aller~tionindex (All-cblo~ite-carbonate-p)~itemdex (CCPI; box plot showng principal hy3mthernral and dio- genetic alteration trends in snhmarine volcanics msociolnl with VHMS deposds (from Large et al., 2001). A1 = lOO(Mg0 + KzO)/(MgO + K,O + NnsO + CaO), CCPl = lOO(Fe0 + MgO)l(FeO + MgO + Na&I + K,O).

Bathurst district also in Canada, the reverse pattern has been recorded in thc footwall alteration zone of the MattabiVHMS recordcd, with the Fe content of chlorite increasing toward deposit, Canada (Franklin et al., 1975). the alteration core (e.g., Hcath Steele, Lentz et al., 1997; Brunswick 2, Luffet al., 1992). Thalanga is the only deposit Thallium and antimony l~ulus in this program of study uhere a consistent trend of chlorite Certain volatile ele~uentssuch as thallium, mercury, and composition 11;~sbeen recorded. Paulick et al. (2001) have antimony are know to form extenshe halos surroundingpar- identified an increase in the Mg/(Mg + Fe) ratio of hy- ticular types of vein- and massive sulfide-style deposits (c.g., drothermal chlorite toward the ore from values of 40 to 50 in Shaw, 1952; Ikrauddin et al., 1983; Smith and Huston, 1992). the least altered footwall rhyolites to 85 to 95 in the. fontwall Smith (1873) was tlie first to record TI dispersion around a rhyolites close to ore. Although no trends were defined at VHMS deposit, later described in detail by Smith and Huston Rosebery and Hellyer, our research indicates that chlorite (1992) for the Rosebery deposit, and considered further hy close to ore, or within the nre host stratigraphy, tends to be Large et al. (2001). Our recent research on several L'HMS de- Mg rich, whereas chlorite outside the alteration zones tends posits in Australia has shown that the stratiform Zn-rich de- tobe Fe rich (Genlmelland Fulton, 2001; Large et al., 2001). posits, such a< Rosebely, Hcllpr, and Thalanga, have signifi- Studies in the Mount ReadVolcarrics (Herrmann et al., 2001) cant thallium and antimony halos, whereas thc Cu-hu have shown that in most regional and wcnkly altered zones deposits (Western Tharsis, Hi hway Reward, and Gossan distal to massive sulfides where fluidlrock ratios are low. the Hill) show nu llalos (Figs. 12 an2 13). - chlorite composition is controlled by the bulk-rock composi- Both Rosehery and Hellycr exhibit lidos extending several tion, rather than a position relative to mineralization. hundred meters into the hanging wall in which T1 and Sb are Of all minerals studied here, carbonates seem lo have the greater than 1 ppm. Within and close to the ores, values most potential as vectors to ore, both in hanging-wall and greater tllar~10 ppm are common, with a systematic decrease foohvdll alteration. Distal carbonate, in small amounts (2-10 outward and stratigraphically upward from the ore lenses wt %), within least altered volcanic samples commonly has a (Figs. 12 and 13). The halo at Thalanga is less well developed, relatively pure dolomite or calcite compositior~.Alteration extending less than 50 m into the hanging wall and footwall. dolomite cornmonly shows an increase in irnn and/or man- There is a variation in TVSb ratio for the three Zn-rich de- ganese content as it approaches the ore. For example, at posits with significant halos (Fig. 13): Rosebery has aT1/Sb -1, Rosebery thc MnC03 content of dolomite increases system- cam ared to Hellyer. which has a T11Sb -0.1, and Thdlanga, atically from values of 1 to 10 molc percenl UL the outer al- whic?I has a TVSb -5. Overall the halo data for all six deposits teration envelope to dues of 50 to 95 mole percent close to (Figs. 12 and 13; suggest a relationship between the mean the ore (Large et al., 2001). At Hellyer, the Mn content of Zflu ratio of thc orebodieh and the extent and magnitude of dolomite and ankerile in the hanging wall increases toward the T1 halo. U7esternTharsis, Highway-Rewal-d, and Gossan the ore (Gemmell and Fulton, 2001), whereas at Western Hill have ZdCu ratios <1and no significant TI halo, Thalanga Tharsis, the Fe content of ankerite and siderite in thc outer with a ZdCu -6 has a weakly developed halo, and Hellyer envelope of the alteration system increases toward the ore and Rosebery have ZdCu ratios >30 and well-developed (Huston and Karnprad, 2001). Similar trends in carbonate halos. This trend may also be extendcd to include the HYC composition (dolomite to Mn-bealing siderite) have been SEDEX deposit, northern Australia. with a Zm'Cu >SO, and a and also highlighted the potential use of' carbon and sulfur a ROSEBERY isotopes (Solomon et al., 1988; Green and Taheri, 1992;

~ ~-~ .,-%\\\\\\ .,-%\\\\\\ Calla~han.~D , 2001). Lead isotones have been shown to be a dis- criminant for s)mvolcmic versus epigenetic mineralization styles in the belt (Gulson and Porritt, 1987). However, case ...- studies, the fonndation of ore vectors. are not well advanced 10Om for the isotopic systems in comparisor~to trace elements. - Altered v6lcanics beneath t6e stratifom Zn-rich deposits b HELLYER display low SL80values (6.5-10%0; Green and Taheri, 1992), and these extend beyond the obvious Na depletion and An- Cu-Pb-Zn enrichment of the visible alteration (e.g., Que River; Stolz and Large, 1992). This is typical of VHMS min- eralization (e.g., Green et al., 1983; Cathles, 1993). It~lnes higher than general footwall background occur within 500 m of the visible edge of alteration, forming a 900-m-wide zone at Hellyer with SIBO= 12.0 to 13.8 per mil and a 150-m-wide 200m zone with S180 = 14.0 to 15.6 per mi1,lOO m beyond visible al- no data in footwall - teration at Hercules (Green and Taheri, 1992). Low-grade pyritic mineralization does not display values below back- c THAMNGA ground (Green and Taheri, 1992). Miller et al. (2001) outline and apply a method for the conversion of S180 values in the . Thalanga Range, Mount Windsor subprovince, to a pseudo- - temperature profile. using XRD-determined mineral abun- TI > 0.7 ppm massive ore @ - u for isoto~evector internretation but relies on (1). . the accuracv of the assumed valnes, (2) a lack of isotouic resettine: during later events, and (3) mini~nalinfluence of irheritedovgeg d McARTHUR RIVER Zn-Pb-Ag I' during water-rock reaction. Sulfur isotope vectors have only been stndied at Rosebery, Hellyer, and, to a limited extent, Que River. By conlparison, the sulfur isotope composition of the ores and stringer zone sulfides in most districts is very well known (e.g., Green et al., 1981; Solomon et al.. 1988).The overa1lS"S composition for mineral prospects has been proposed to be an economic discriminant for Cambrian deposits (Green and Taheri, 1992). For instance, economic stratifom mineralization in the Mount Read Volcanics has 8% >G per mil and com- Rc. 12. Extent of thallium halos associated with thee zinc-rich VHMS monly in the range of 8 to 12 per mil, probably reflecting the deposits: Rosehely. Hellyer, and Thalanga compared ta the McArthur River mixing of reduced Cambrian seawater sulfate (8"'s -30%0; SEDEX ZII-Pb-Ag deposit (Lage et el., 2000). Note the scale change For McA~thurRiver, where the halo extends for over 20 km compared to the Claypool et al., 1980) with leached rock sulfur. Strata-bound VHMS deposits, where the halos eaeud for less than 1 Lrn b~andthe are pyrite with S3% ~5 per mil, such as the Boco prospect , is zones. suggested to have fonned at <200°C, which would prevent both sulfate reduction and base metal leaching (Solomon et al., 1998; Green and Taheri, 1992). However, some mineral- T1 halo which extends hundreds of meters into the hanging ization in the Mount Read Volcanics, with S"S <5 per mil wall and tens of idlometers along strike (Fig. 12d; Large et al., has recently been shown to relate to Au-Cu-bearing, high- 2000). The lack of T1 in the Cu-rich ores and their associated sulfidation fluids, possibly derived from oxidized synvolcanic alteration halos may relate to their higher temperature of for- granites (e.g., Boda, 1991; fluston and Kamprad, 2001). This mation. TI and Sh tend to concentrate in the lower tempera- is an alternative explanation for the low S34Svalnes, and thus ture Zn-rich systems but are probably too soluble for precip- the P4S discriminant requires modification to incorporate itation in the higher temperature copper-rich systems. mineralogy. The sulfur isotope composition of disseminated Fe sulfide Isotope discrimination and vectors in the footwall is emerging as a useful vector to the stratiform Previous studies (e.g., Green et al., 1983; Cathles, 1993; Zn-rich ores. Although the footwall stringer veins and dis- Taylor et al., 2000) have de~nonstratedthe use of whole-rock seminations have S34Svalues similar to overlying ore, zones of oxygen isotopes to define hydrothermal fluid/rock interaction high 6% dues occur lateral to the main footwall alteration and provide vectors to massive sulfide ores in volcanic suc- at the three largest Zn-rich deposits in the Mount Read Vol- cessions. Research in the Mount Read Volcanics has con- canic~.At Hellyer, Jack (1989) and Ge~n~nelland Large fnmed the value of whole-rock oxygen isotopes in exploration (1993) found 6% values of 11.9 to 40.7 per mil (avg of e D W 2 --. C 5i B 'f: " i 6 3 rn m-0 a - - 8 - 0 - - Wdd I1 Wdd IJ ;@ P 2 3 3 5 $ E -0 Ery g6 g% 2 2 z 3 B U 2 s m -C c E c: g.8 .--E 2" $ g gErn i. d % & H .9 2s - c EXPLORATION IN SUBMARINE VOLCANIC SUCCESSIONS: EXAMPLES FROM AUSTRALIA 933

25.0%0) in coarse pyrite up to 200 In from the central intense clastic elements such as Zr, Ti, and A1 are evident, the clastic alteration. Similar eurich~nenthas been discovered at Rose- REE signal must be quantified before the REE composition bery but is confined to a distinct, tabular 70-m-thick zone of the marker bed can be used as an exploration vector. -100 m from the ore that extends up to 500 In away from the hydrothermal vent (Davidson et al., 2000). These %-en- Sunlmuy on exploration vectors riched zones approach and even exceed the isotopic compo- Schematic summaries of the mineralogical, lithogeochemi- sition of Cambrian seawater sulfate and probably formed by cal, and isotopic vectors useful for exploration are given for partial in situ seawater sulfate reduction. The values require Zn-rich stratiform polymetallic ores nl Fignre 14 and for ' that sulfate reduction occurred under closed or partly closed pyritic Cu-Au ores in Figure 15. Our recent research indi- conditions that must have differed markedly from those of the cates that the most useful vectors for Zn-rich ores are Na de- main hydrothermal upflow stringer zones. Their precise rela- pletion; the alteration index (AI); the chlorite-carbonate- tionship to associated whole-rock oxygen isotope values has pyrite index (CCPI); Mn content of carbonate; whole-rock TI, not been established. They have the potential to significantly Sb, and BdSr ratio; and 634Sof pyrite and whole-rock 6180 expand the isotopic halo of large systems and are predicted to (Fig. 14). The most useful vectors for pyritic Cu-Au ores are be more tabular in porous volcaniclastic units (e.g., Rosebely) Na depletion, AI, CCPI, S/Na20 ratio, Na content of white than m lavas (e.g., Hellyer, Que River). We speculate that mica, and Fe content of carbonate (Fig. 15). Insufficient data similar zones may occur in other VHMS deposits but have not is available to comment on the nsefulness of whole-rock 6180 been detected because few studies have examined the iso- and 634Spyrite as vectors in the pyritic Cu-Au hydrotherlnal topic composition of sulfides lateral to footwall vents, and systems. ! such sulfides are fine grained requiring bulk sulfur dissolution or microanalyhcal techniques, both of which are not com- Conclusions monly applied. The most significant conclusions to emerge from recent re- search on the nature and alteration of Australian VHMS de- Rare earth elemen,t vectors oosits and their host volcanic rocks include the followiue: The rare earth elements (REE) in Fe-Si-bearing ore- equivalent lateral marker beds and footwall alteration have 1. There is a spectrum of sulfide deposits in submarine vol- been employed as vectors in massive sulfide districts (Lotter- canic successions in Australia, including lens and sheet-style moser, 1989; Peter and Goodfellow, 1996; Spry et al., in press). Zn-rich polymetallic deposits, massive and disseminated To date, the ore-equivalent beds have proven most useful for pyritic Cu-Au deposits, and disseminated strata-bound Au- this purpose, although Huston and Kamprad (2001) show only deposits. there to be significant REE mobility in the very acid alter- 2. The Zn-rich polymetallic deposits forin either on, or just ation zones of some Cu-Au systems, such as Western Tl~arsis. below, the sea floor, whereas the Cu-Au and Au-only deposits The chemistry of Fe-Si lateral marker beds such as form subsea floor by replacement of particular volcanic units. heinatitic cherts can only be used in exploration wliere such 3. The pyrite Cu-Au deposits wically form in felsic vol- units are. common, as in the Mount Windsor subprovince. canic centers donlinated by synvolcanic intrusions, whereas The REE composition of hematitic chert was successfully the zinc-rich polymetallic deposits for111 in both felsic and used as an exploration filtering tool by Miller et al. (2001) to mafic, moderate- to deep-water volcanic successions, domi- discover satellite Zn-Pb ore in the Mount Windsor sub- nated by lavas, volcaniclastic facies, and volcanogenic sedi- province. Chert bodies above and along strike from the Tha- mentary facies. The gold-only deposits are confmed to shal- langa Zn-Pb-Cu deposit exhibit strong positive Eu anolnalies low-water volcanic sequences. and LREE enrichment (Duhig et al., 1992). Davidson et al. 4. Alteratiou zoned outward from qua& + Mg-Fe chlorite (2001) show that positive Eu anomalies are not a feature of all -t sericite + carbonate is typical of VHMS deposits across the hematitic chert bodies m the district, supporting the view that spectrum. Quartz and carbonate alteration is dominant in the they are a valuable screening tool for exploration. Although gold-only systems, whereas chlorite alteration is com~nonly soine chert bodies developed from fluids that were suffi- developed close to copper-rich ores. Sericite and carbonate ciently acid to destroy feldspar and mobilize Eu2', others alteration zones are well develo~edin the stratiform zinc-rich have soine features inherited from seawater, such as negative ores. Ce anomalies, and probably originated from cooler recharge- 5. Thermodynamic modeling indicates that chlorite-rich dominated fluids (Davidson et d. 2001). Most examples fornled alteration is generated by higher temperature (>250°C) and/ in sitn above diffuse alteration zones or within subsurface al- or less acidic (pH >5) hydrothermal fluids, whereas sericite- teration zones (Doyle, 1997) and are very different from the rich alteration forms from lower temperature, slightly acidic extensive ore-equivalent lnarker beds that characterize other fluids. Pyrophyllite associated with Cu-Au ores is indicative of massive sulfide districts, such as the Bathmst district (Peter strongly acidic fluids (pH <4), possibly related to involvement and Goodfellow, 1996). However, in all of these cases, high of a magmatic fluid. concentrations of host-rock REE, whether incolporated clas- 6. The variation in molphologies, metal ratios, volcanic en- tically or by replacement of wall rock, may mask the hy- vironments, and alteration features in Australian volcanic- drothermal REE signature of the marker bed. Clastic REE hosted ores indicates that a spectrum of deposits may exist- are commonly held in resistate mineral phases that will sur- from those that fit the classic VHMS model to those that are vive reaction with most hydrothermal fluids (Davidson, 1998; hybrids between VHMS porphyry Cu and VIIMS epithermal Spry et al., in press). Consequently, if high concentrations of end members, developed in submarine volcanic successions.

EXPLORATION IN SUBMARINE VOLCANIC SUCCESSIONS: EXAMPLES FROM AUSTRALIA

I Massive pqlitic Cu-Au ore I Chlorite silica zone (chlorite-quartz-se-le-pyrite) 1 ( - Selicile zone (sericite-calbonale-chlorite~pyrite)

Pymphqilite zone (pymphylble-sericite-pyrite)

Calbonate zone ( carbonatechlolite-sericife) Similar to propyilitic alteration

FIG. 15. Model of alteration zonation and key alteration vedan useful for exploration for pydtic Cu-Au VHMS deposits Based on Doyle (2001), Herrmann et al. (2001). Huston and Kamprad (2001), and hrge et al. (2M)l).

Council SPIRT Scheme. Thanks to many of the contributors Barrett, TJ.,md MacLean, WH., 1991, Chemical, mnm, and oxygen isotope to this special issue for providing advanced copies of their pa- changes during extreme h"drothema1 alteration of an Archean rhyolite, Noranda, Quebec: EcoNoMrC GEOLOGY,v. 86, p. 406414. pers to enahle this review to be completed. -1994, Mass changes in liydrathermal alteration zones associated with VMS deposits of the Noranda area: Exploration and Mining Geology v 3, REFERENCES p. 131-160. Allen, R.L., 1994a, Volcanic facies ilnalysis indicates large pyoclastic erup- Barrett, T.J., Cattalsni, S., and MacLean, W.H., 1993, Volcanic lithogto- L tions, sill complexis, SF-volcantc grabens, and subtle thrusts in the Cam- chemishy and alterution at the Delbridge massive sulfide deposit, Noranda, brian "Central Volcanic Complex" volcanic centre, western Tasmania: Quebec: Journal af Geochemical Erploratian, v. 48, p. 135-173. Contentiaus Issnes in Tasmanian Geology Symposium, Geological Soci- Barrett, T.J., MacLenn, W.H., and Tennant, S.C., 2W1, Volcanic seqnence ety of Australia Tasmanian Division, Extended Abstracts Volume, 0. and alteration at the Pqs Monntain volcanic-hosted massive snlfide de- aide. posit, Wales, United Kingdom: Applications af immobile element lithogeo~ Men, R.L., 1994b. SF-volcanic, snbseafloor replacement model for Rose- chemistry: EwNoMrc GEOLOGY,v. 96, p. 1279-1305. hew and other massive sulfide ares: Contentious lssnes in Tasmanian Ge- Berktan, J., 1999, Gold distributionwitl~inthe Zone 96 gold deposit, western ology Symposium, Geological Society of Australia Tasmanian Division, Ex- Tasmania: lnflnence of protolit11 and structural remobilisatian: Unpub- tended Abstracts Volnme, p. 89-91. lisl~edMastefs thesis in Economic Geology, flabart, Tasmania, University Allen, R.L., Gindns, C.C., Large, R.R., and Hemnann, W, 1998, Discrimi- of Tasmania, 133 p. nation af diagenetic, hydrothermal and metamorphic alteration: Hobart, Berq R.F., Hnston, DL.. Stolz, A.J., Hill, A.P., Beams, S.D., Knranen, U., Tasmania. University of Tasmania. CODES-Anstratian Mineral Indnstv and Taube, A,, 1992, Stratigraphy, struckre, and volcanic-hosted mineral- Research Association (AMIRA) project P439, Unpnhlirhed final report, p~ ization of the Mount Windsor subpravince, North Queenrland, Austr.da: 01 110 ""-LL". ECONOMICGEOLOGY, v. 87, p. 739-763. Arnold, G.O. and Sillitoe. R.H., 1989, Mt Morgan gold-copper deposit Binns, R.A., and Smtt, S.D., 1993, Actively farming polymetallic snlfide de- Queemland, Australia: Evlderlce for an intrnsion~~.elatedreplacement ori- posits arsociated with felsic vo1cm.c rocks in the eastern Manns back-ac gin: ECONOMICGEOLOGY, v 84, p. 180%1816. basin, Papua New Gninea: ECONOMICGEOLOGY, v. 88, p. 2222-2232. 936 L4RGE ET AL.

Boda, S.P., 1991, The geology, structural Fetting and genesis of the Chester Franklin, J.M., Sangster, D.F., and Lydan, J.W., 1981, Valcauic-associated mine, uorthwest Tasmnaia: Unpublished tlonorn~thenir,Canberra, ACT, massive sulfide de~orits:ECONOMIC GEOLOGY 758~1A~~~~~~~~~~ VOLUME, Australian Nillioual Uuiversity, Ill p. p. 48M27. Braithwaite, B.L., 1974, The geology and origin of the Rosebey Ore De- Galley, A.G., 1995, Ta$et vectoling using hthogeochemisty. Applications to pont, Tasmania: ECONOM~CGEOLOCY, v 69, p. 1086-1101. the exploration far volcanic l~urtedmassive sulfide deposits: CIM Bulletin, Callaghan, T, 1998, Geology and alteration of the Mouut Jdia deposit, v. 88, no. 990: p. 15-B. Henty gold mine. Tasmania: Unpublished Master? thesir iu Economic Ge- Gemrnell. J.B., and Fultan, R., 2001, Gcalogy, genesis, and exploration im- olom Hobart, Tasmauia, liniversity of Tasmania. 78 p. pliuations of the footwall and hanging-wall alteration associated with the -2001, Geology and host-rack alteration of the Henly and Mount Jdia Hellyer volcanic-hosted massive sulfide deposit. Tasmania, Aushalia: Eco- gold deposits, Western Tasmania: ECONOMICGEOLOGY, v 96, p. 107LL1088. NoMlC GEOLOGY,v 96, p. 100LL1035. Cnthles, L.M., 1993, Oxygen iaatope dteratiurr ill the Naranda miniug &- Gemrnell, J.B.. and Large, R.R., 1992, htinger system and alteratian zones hict, Abitibi Greenstone belt, Quebec: ECONOMICGEOLOGY, v 88, p, underlying the Hellyer volcauagenic massive sulfide deposit, Tasmania, 148LL1511, Australia: ECONOMICGEOLOGY, 87, p. 690449. I.W.. Clav~oul.,. . G.E.. Halser.. W.T...L.. Kaolau. Sakai. . H... and Zak I.. 1980. The -19%. Evolution of a VHMS hvdrothennal swtem. Hellver, deoosit. Tas- age curves of sulfur and oxygen isotopes in marine sulfate and their muhlal mania. Australin: Sulfur isotope dvidence: Resiurce Geology Special lssue iuterpretation: Chemical Geology, v. 28, p. 199-260. 17.. n., 10&118. Corbett, K.D., 1992, Stratigraphic-volcimic setting of massive sulfide de- (,.Tma~.s [: C. , ,#.I.411cr, HI.,Ict I l;xt>.rdl ,nd .I#,,,. ><,I cl.ar>TC~I$TI.>C f posits in the Cambrian Mouut Read Volcanics, Tasmania: ECONOMICGE- d~.,.!~n?t~~~nt. h!dm.cl..r~t~ ,I Alc~r,ci~r..n gl~Lw vn.;, n~; ru.k\ l'~,~~r.pl~. OLOCY, v 87, p. 56GR6. . t.I. h.. i. I: ..r..*!r'CFL. .> 76, p .-.I I,> -2001. New mapping and interpretations of the Mount LyeU miuing dis- " . - A - -, trict, TasmanL-a large hybrid Cu-Au system with an ed~alatlvePb-.4n Goldfarb, M.S., Couvene, DR.. Holland, H.D., and Edmond, J.M, 1083, top: ECONOMICCEOLOCY, v. 96, p. 1089-1122. The genesis of hot spring deporits an the East Pacific Rise, 21-N: Eco- Corbett, K.D, and Komyrhan, P, 1989, Geology of the Hellyer-Mt Charier NOMlC GEOLOGYMONOGRAPH 5. p. 184197. area: Tasmania De~altmerrtof Miues. Mount Read Valcanics Praiect Ge- Grant, J.4, 19R6, The lsocou dingram: A simple solution tu Gresens equa- oloky Report l, 45 p. tion for metasomatic alteration: ECONOMICGEOwCr, v 81, p. 1976-1982. Cox, S.F., 1981. The stmtigraphic and structural setting of the Mount Lyell Green, GR.. md Taheti. J., 1992. Stable isotopes and geochemishy as elplo- volcanic-hosted sulfide deposits: ECONOMICGEOLOGY, v. 76, p. 231-245. mtion indicators. Gcolugical Survey of Tasmania Bulletiu, v. 70, p. 8C91. Crawford A.J., Corbett K.D., and Everad, J.L., 1992, Geochemky of the Green, G.R., Solomon, M., aud Wfilshe. J.L., 1981, The hrlnatioll of rl~evol- Cambdan-licl~volcaniohosted massix sulfide Mount RedVolcanics, Tasma- cnnic-hasted massive sulfide ore deposit at Rosebery, Tasmania: ECoNnMrr nia, and some tectonic implirntions. ECONOMICGEOLOGY, v 87, p. 597--619. GE~LOGY,v 76, p. 304338. Davidson G.J., 1998, Application of silica iron deposit geochemistry to ex- Gregaiy, PW., Hartley, IS., and Wills, JA., 1990, Thalanga zinc-lead-copper ploratiou hr VHMS deposits in the Mount Windsor volcanic belb Habat, silver deposit: Australacian Institute of Mining and Metdura Mauogmph University oi'rmmania, CODES-Auslollian Minerd ludustiy Hesearch As- 14, p. 1527-1537. sociatiou (AMIRA) project P439, L'npublished fiual repart, p. 135-188. Greseus, R.L., 1967, Camposition-volume relationship of metasomatism: Davidsou, G.J, Garven. G., Kitto, P, aud Beny, R.F., 2000, Geochemically Chemiml Ceolog, v. 2, p. 47-65. diacrcta fluid bodies formed by canvectiau at the heated edge of porous Gulsou, B.L., and Ponitt. P.M., 1987, Base metal exploration of the Mount scafloor aquifer [eb-bs.]: Beyond 2000: New Frontiers iu lsotope Geoscience, Read Volcanics, western Tasmania: Pt 11. Lead isotope signatures and ge- Lome, 3000,Abstracts and Proceedings, p. 394 nctic implications. ECONOMICGEOLOGY, v. 82, p. 291307. Oaridsou, G.J., Stalz, A.J., and Eggios, S.M., 2001, Geochemical anatomy of Halley, S.W., and Roberts, R.H., 1997, Renty- A shallow-water gold-richvol- silica iron erhalites: Eviden6.e for hydrothermal oxyaniau cycling in re- cauagenic massive sulfide dcpasit in western Tasmania: ECONnMlc C.rro~- spouse to vent flnid redox and thermnl ovoluho~~(Mt. Wildrur sub- OGY,x 92, p. 438447. province, Australia): ECONOMICGEOLOGY, v. 96, p. 1201-1226. Henderson, R.A.,1986, Geolop of the Mount Windsor subprovince-s Doyle M., 199i. A Cambro-Ordovician volcanic succession hosting massive lower Palaeozoic volcano-sedimentary terrane in the northern Tvrman oro- sulfide mincralisution: Mount Wi~rdsur subprowice, Qld: Unpublished genic zoue: Australia, Journal of Earth Sciences, v. 33, p. 343364. Ph.D thesis, Hobad, Tasmania, University of Tasmania, 305 p. Hermann, W., and I-lill, AP, 2001, Thearigiu of chlotite-tremolite-carbon- Doyle, M.G., 1990, The geology of the Jukes Proprietary prorped. Mouut ate rocks associated with the Thslnngr volcanic-l~usladmasslve sulfide de- naadVulcanics: Unpublished Honors thesis, Hobart, Tasmania, University posit, No& Queensland, Austnlia: ECONOMICGEOWCY, v 96, p. 114%1173. of Tasmania, 114 p. Herrmann, W, Blake, M., Doyle, M., Hustou, D., Kamprod, J., Merry, N., -2001, Volcanic influences on hydrathermal and diagenetic alteration: md Pontud, S., 2001, Sl~ortwavelength infrared (SWIR) spectral anabis Evidence fmm the Highway-Reward deposit, Mount Windsor subprovince, of hydrothermal alteration zones associated with base metal sulfide de- Austraha: ECONOMICGEOLOGY, v. 96, p. 1133-1148. posits at Rosebery and Western Tharsis, Tasmauia, and Highway-Reward, Doyle. M.G., and Hnston, D.L., 1999, The subsca-floor replacelrlc~rtorigin Queensland: ECONOMICGEOLOGY, v. 96, p. 93%955. of the Ordoviciau Highw~y-Rewardvolcanic-associated massive sulfide de- Hill, A.P.. 1996, Structure. volcanic setting, hydrothermal alteratiau and gen- posit, Mount Windsor subprovince, Australia: ECONOMICGEOLOGY, v. 94, esis of the Thalanga massive snlphidc dcposit: Upuhlishcd PhD. thesis, p. 8158*3. Hobart, Tasmania, University of Tasmania, 404 p. Doyle, M.G., and McPhie, J., 2000, Facies architecture of a silicic intrusiou- Hunus, S.R., 1987, MineralisaSon of the Lake Selinaprasped: Unpublished dominated volcanic centre at Highway-Reward, Queensland, Aushalia: Master'? thesis, Hahart, Tasmania, Uuiverrity aCTasnr~rtia,126 p. f Journal ofVocauology and Geothermal Research, v 99, p. 79-96. Hustan, DL., and Kampnd, J., 2001, Zonation of alteration facies at West- Duhig, N.C., Stalz, I.,Davi&on, G.J.. and Large, R.R., 1992, Cambrian mi- em Tharris: Implications for the genet-is of Cu-Au deposits in the Mount crobial and silica el textures preselved in silica iron exhaliten of the Mouut Lyell field, wesleru Tumania: Eco~ohlrcGEOLOCY, v. 96, p. 112%1132. Windsor dcanic belt, Australia: Their petrography, geochemistry, and oti- Ihanluddin, M., Asmeron, Y. Nordatron!, P.M., Kinart, S.P., Martin, W.M., giu: ECONOMICGEOIDGY, v. 67, p. 764784. Digby, S.J.M., Elder, D.D., Nijak. W.F. andAfemari,A.A., 1963, Thalli~lm: Eastoe. C.J.. Solomnn. M., and Wlrhe, J.L., 1087, District-scale altsrstiou a potential guide to mineral deposits: Journal of Geochemical Exploration, associatedwith massive sulfide deposits in the Mount Read Volcanics, west- v. 19, p. 465490. em Tacmniil: EcoNohlrc GEOLOGY,v. 82, p. 1239-1258. Isliikaws, Y., Sawaguchi, T., lwayn, S., and Horiuchi, M , 1976, Delineation Eldtidge, C.S., Barton, P.B., Jr. illd Ohrnoto, H., 1983, Mineral textures aud of prospecting targets for Kumko deposits based an modes afvalcanism of their bearing on formatiou of the Kurako orebodier: ECONOMICGEOLOCY underlyiug dacite and alteration halos: Mining Geology, v. 26. p. 105-117 MoNocrtppa 5. p. 241-281. (in Japanese with English abs.). Franklin, J.M., 1995, Volcanic-associated massive sulfide base metals: Geo- Jack, D., 1989. Hellyer host rock alteration: Uupublished M.Sc thesis, Ho- logical Survey of Canada, Geology af Canada, uo. 8, p. 158-183. bart, Tasmania, L-niversity of Tasmania, 182 p. Franklin. J.M., Kasarda, J., andPaulsen, K.H., 1975, Petrolo~andchemistry Jones, A.T., 1993, Tlm geology, geochemistry and stmcture of the Mount of the alteration zone of the Mattabi massive sulfide deposit: ECONOMIC Dah-South Daruln Peak area, westem Tasmania: Uupublished Honors GEoLms, v. 70, p. 63-79. thesis, Hobart, Tasmania. University of Tasmania. 120 p. ESPLORATION IN SUBMARlNE VOLCANIC :iUCCESSIONS: ESAMPLES FROM AUSTRALIA 937

KbZaw, 1991, The etl'ect of Devonian metamo~ptlismand metasamatism Me4rthur. G.J., 1989. Hellyer: Geological Society of Australia Special Pnbli- an the mineralogy and geochemistry of the Csmblian VMS deposits in the cation 15, p. 16148. Rosebely-Hercnles disttict, western Tasmania: Unpublished Ph.D. thesis, 1996,Textural Evolntia of the Hellyer ncassive snlphide deposit: Un- Hobart, Tasmania, University of Tasmania, 302 p. published P11.D. thesis, Hoba~r,Tasmania, University of Tasmania. 272 p. Khin Zaw, and Large, R.R., 1992, The prsdans metal-lich Sonth Hercules McGoldrick, P.J., and Large, R.R., 1992, Geologic and geochemical controls mineralization, western Tasmania: A possible snbsea-floor replacement on gold-tich stringer mineralization in the Que River deposit, Tasmania: valcanic-hosted massive rnliide deposit: EcoNoMrC GEOLOGY,v. 87, p. ECONOMICGEOLOGY, v. 87. p. 667-685. 931-952. McPhie. I., and Allen, R.L., 1992, Facies arclntecturc of mineralized snbma~ Khin Zaw, Gemmell, I.B., Large, R.R., Mernagh, T., and Ryan, C.G., 1996, tine volcanic seqnences: Cambliarl Mount Read Valcanics, western Tasma- Miciothrrmometv and geochemistq of fluid inclnsions in the stringer nia: ECONOMIC GEOWGY,v 87, p. 587596. zone, Hrllyer VHMS deposit. Tasmania, .4untrdia: Ore Geologj Reviews, McPhie, J., Doyle. M., and Allen, R., 1993, Volcanic textures. A gnide lo the < v. 10, p. 251-278. intelpretation of textures in volcanic rock: Hobart, Tasmania, Centre for KhinZaw, Huston, D.L., Gemmell, J.B., Hnnns, S.R., Large, R.R., Ryan, C.G., Ore Deposit Research, University of Tasmania, Hobart, 198 p. and Mernagh, TP, in prms, Microthermometry and geochemistry of ore Messenger, PA, Golding, S.D., and Taube, A,, 1997. Volcanic setting ofthe fluids healing on the genesis ofVHMS deposits: Water depth and source of Mount Morgan Au-Cn deposit, central Queenrland: Implications for ore P metals [abs.]: ECROFl Conference, 16th. Portugal, 2001, Abstracts. genesis: Geological Society ofAustralia Special Publication 19, p. 109-127. Khin Zaw, Huston. D.L., and Large, R.R., 1999, A ehemicd model for the Miller, C., Malley, S., Green. G., and Jones, M., 2001, Discovery of the West Devonian remobiliseion process in the Cambrian volcanic-hosted massive 45 volcanic-hosted massive sulfide deposit nsing oxygen isotopes and REE sulfide Rosebery deposit, wertemTasmarrka: ECONOMICGEOLOCY, v 94, p. geochemirtv: ECONOMICGEOLOGY, v. 96, p. 1227-1237. 529-546. Morton, R.L., and Franklin, J.M., 1987, Two-fold classification of Archean Khin Zaw, Iluston, D.L.. Gemmell, J.B., Hunns, SR., Large, R.R., Ryan, volcanic-associated niarnive sulfide deposits: ECoNohlIc GEOLOGY,v 82, p. C.G., and Mernagh, TP, 2001, Microthermometry and geochemistry of -.I flS7-lOfid. . .. - - . ore fluids bealing on the genesir of VHMS deposits: Water depth and Ohmoto, H., Mizukami, M., Dmmmond, S.E., Eldlidge, C.S., Pisntha- source of metals: ECROFl Conference, European Current Research on Amond, Y, and Lenagh, T.C., 1983, Cllemical processes of Kuroko forma- Flud Inclnsions, 16th. Porto, Portng.11, Abstracts, p. 463466. tion: ECONOMIC GEOLOGYMONOG~APH 5. p. 57S604. Large, C.', 1995, Stratigraphy and alteration of the Tyndall Group at Henty: Paulick, I-I., 1999, The Thalmga sequence-facies architecture. geochem- Unpublished B.Sc, llonors thesis, Hobart, Tasmania, University of Tarma- istry, alteration and metamorphism of felsic volcanics hosting the Thalanga uia, 119 p. massive sulkde deposit: Unpnblished Ph.D thesis, Hobart, Tasmania, Uni- Large, R.R., 1977, Chemical evolntion and zonation of massive sulfide ds- versitv of Tasmania. 220 o. posits in volcanic termins: ECONOMICGEOLOCY, v. 72, p. 549572. Pr:~lak.Ii, .nd .\l I'IIc. 1 1%~ Fwvq Jr.l.~c:.~~.r.L( (I., i~l~..I \*. -1092, Australian volcanic-hosted massive sulfide deposits: Featnres, 40) >c>.~~J .\~.*rr.,l~,n 1, 1.tr1.1 ,fElr:.. ;..,I.,~\ v -1997, Variability is the key to understanding the genesis of Anstrdian 46, p. 391405. Palaeoroic volcanic hosted massive sulfide deposits [abs.]: SEG Neves Cawo Paulick, H., Henmann, W, and Gemmell, J.B., 2001, Alteration offelsicvol- Field Conference, Lisbon, May ll-14,1997, .4bstracts and Program, p. 54. cmics hosting the Thalanga massive snlfide deposit, North Qneensland, Large, R.R., Doyle, M., Raymond, 0..Cooke, D., lanes, A, and Heasman, Australia: Geochemical proximity indicators to are: Eco~oh$lcGEOLOGY, v. L., 1996, Evalnation of the role of Camblian granites in the gen~siraf 96, p. 1175-1200. world class VHMS deposits in Tasmania: Ore Geolop Reviews, v. 10, p. Perkins, C., and Walshe, J.L., 1993, Geochronologj of the Mount Read Vol- 215-230. canic~,Tarmania, Australia: ECONOMICGEOLOGY, v. 88, p. 11761197. Large, R.R., Bull, S.W., and McGaldrick PJ,2000, Lithogeachemical halos Peter, J.M., and Goodfellow, W.D., 1096, Mineralogy, bulkand rare earth el- and geochemical vectors to str&tiform sediment hosted Zn-Pb.4g deposits, ement geochemistry of massive snlphide-associated hydrothermal sedi- Part 2: HYC Deposit, Northern Territov Jou~malof Geochemical Explo~ ments of the Brunswick horizon, Bathurst mining camp, New Brunswick: ration, v. 64, 1-2, p. 105-126. Canadian Journal af Earth Sciences, v. 33, p. 252-283. Largc, R.R., Allen. R.L.. Blake, M.D., and Hen.mann, W.. 2001a, Hy- Polya, D.A., Solomon, M., Eastoe, C.J., andVTaIshe,J.L., 1986, The Mmrhi- drothern~alalteration and wlatile element llalos for the Rosebery K lens son Gorge, Tasmania-a possible cmsr section through a Camblian mas- volcanic-hosted massive sulfide deposit, western Tasmania: ECONO~IICGE- sive sulfide system: EcoNohqrc GEoLocr, 4 81, p. 1341-1355. OLOCY, r 96, p. 1055-1072. Poulson. K.H.. and Hannineton. M.D.. 1995. Volcanic-associated massive sul- Large, R.R., Gemmell, J.B.. Paulick, H., and Huston. D.L., 2001b. The alter ation box plot: A simple approach to understanding the relationship be- tween alteration mineralogy and litilogeochemistry associated with volcanic- hasted massive sulfide deposits: ECONOMICGEOLOGY, v. 96, p. 957-971. nia, University of Tasmania, 161 p. Lentz, D.R., Hall. D.C., and Hoy, L.D., 1997, Chemostratigraphic, alteration Rivertn, G., and Hodgson, CT., 1980, WallLrock alteration at the Millenbach and oxygen isotope trends in a profile through the stratigraphic sequence CuZn mine. Noranda, ~nebec:ECONOMIC GEOLOGY,v. 75, p. 42G414. hosting the Heath Steele B zone massive sulfide deposit, New Brunswick: Roberts, R.G., and Realdon, E.J., 1978, Alteration and ore formingprocesses

Canadian Mineralogist, v. 35, p. 841474. at Mattaesmiu Lake mine. Ouebec: Canadian Toumd of Ealth Sciences. r Lattermoser, B., 1989, Rare ealth element study af exhalites within thc 15, p. 1-21. WiUyama Snpergoup, Broken Hill block, Auslralia: Minerdium Deposita, Sangster, D.F., 1972, Precamblian volcanogenic rnzsive sulphide deposits in v. 24, p. 9L99. Canada: A review: Gealo@cal Snrvey of Canada Paper 72-22,44 p. Luff; W, GoodfeUow, W.D., and Jurar, S.J.. 1991, Evidence for afeederpipe Sato, T., 1973, A chloride complex model for Kurako mineralisation: Geo- and associated alteration at the Brunswick no. 12 massive snlfids deposit: chemical Journal, v 7, p. 245-270. I Exploration and Mining Geology, v. 1, p. 167-185. Schardt, C., Coake, D.R., GemmeU, J.B., and Large, R.R., 2001, Geochemi- Lydon, J.W., 1984, Some obsemtionr an the mineralogical and chemical cal modeling of the zoned foohvall alteration pipe, Hellyer volcanic-hosted zonation patterns of volcanogenic sulphide deposits of Q~rns:Geological massive sulfide deposit, western Tasmania, Anrtralia: ECONOMICGEOLOGY, Survey of Canada Paper 84-IA, p. 611-616. v. 96, p. 1037-1054. -1988, Volcanogenic massive sulpllide depsitr, Part 2: Genetic models: Scott. S.D., 1992, Polymetallic sulfide licller from the deep: Fact or fallacy?, Geoscience Canada Reprints Series 3, p. 155-182. in Hsn, K.J., and Thied~,I., eds., Uses and misuses of the seafloor: New Lydan, J.W., and Galley, A,, 1986, Cl~emicaland mineralogical rollation of York, NY, John Wiley and Sons, p. 87-115. the Mathati alteration pipe, Cyprus. and its genetic sipificance, in Gal- Shqe, R., and Gemmell, J.B., 3001, Alteration charactelistics of the lagher, M.I., Iner, R.A., Neary, C.R., and Plichard, H.M., eds., Metallogeny Archean Golden Grove Formation at tlre Gossan Hill deposit, Western afbasic and nltrabasic rock: London, Institute of Mining and Metallogen3 Austrslia: Indnration as a focusing mechanism for mineralizing hydrothrr- p. 49-68. mal fluids: ECONOMICGEOLOGY, v. 96, p. 1239-1262. MacLem, WH., and Bnrrett, T J., 1993, Lithageochemical trchniqnes using Shw, D.M., 1952, The geochemistry of thallium: Gcochimica et Cos- immobile elements: Journal of Geochemical Exploration, v. 48, p. 109-133. mochimica Acta, v. 2, p. 118-154. 938 LARGE: ETAL

Sillitoe, R.H., Hanningtan, M.D., and Thompson. J.F.H., 1996, High sulfl- Taylor, B.E., Holk, G.J., and Hnston, D.L., 2000, Oxygen isotope milppirrg dation dcpoaitn in the volcanogenic massive sulfide environment Eco- and evaluation of palaeo-hydrothenmi sytems associated~thsymvolcmic NOMIC GEOMCY,V. 91, p. 20&212. intmsions and VMS deposits [abs.]: Hobart, Tasmania, Uni\~aityui Tas- Satilll, R.N , 1973, Trace element distributions within some major stratiform mania, CODES Sprcial Publication 3, Program and Abstracts, p. 207-208. orebodies: Unpublished BSc (Hons) thesis. University of Melbourne, 189 Urabe, T., and Scott, S.D., 1983, Geochemistq and fodwall alteration afthe - t' South Bay massive rulfide deposit, noltlwcrtcm Ontuiio, Canad;!: Ciora- Snridl, R.N., and I-lustan, U.L., 1982, Distribution and association of se- &an Ionmal of Earth Sciences. v 20. a. 1882-1879. lected traee elemmts at the Rosebeq deposit, Tasmania: ECONOMICGE- OLOGY,a 87, p. 706719. Solutt~ozl,M., 1976, Volcmic" massive sulphidc deposits and their hart mcks-a review and an eqlanation, ia Wolf, K.B., ed., Handbook ofstrata- 5, p 345-364 bound and stratiform ore deposits: 11: Regional studies and specific de~ Walslre, J L.. and Solomon. M , 1'381, An invcstigatian into thc envirn~n~~er~t * pusils: Amsterdam. Elsewer, 32U p. of formation of the rolcanic-hosted Yt. Lyell copper deposits nsing seal- . Solomon, M., and Groves, D.I., 1991, The geoloa and an'gin of Australia's ogy, mineralogv. stable isotopes, and a SLY-componentchlorite ralid-solution mineral deposits: Monagrnphs in Geology and Geophysics 24, Orford, Ox- model: EcoNoMlc C,Eo~or:v:v. 76, p. 246-264. ,I fold University Press, 951 p. Waters, J.C., and Wallace, D.B., 1992, Volcanology and sedimentolog of the -WOO, The geology and origin of Australla5 mineral deposits. Reprinted host succession to the Hellyer and Que River volcarric-hosted massive sul- with additional material: ?lobart, Tasmania, University of Tasmania. Centre fide depsitr, northwestern Tarmania: ECONOMICCCOLOCY, v. 87, p. fo, Ore Depusit Research, and Nedlands, WA, University of Western Aus- ASG6Afi~-.~ tralia, Centre for Global MetaUogeny, 1002p. Wldte. M.J.. and McPhie, J., 1996, Stratigaphy and palaeavolcanology ofthe Solomon, M., and Khin Zaw, 1999, Formation on the sea floor of the Hellyer Cambrian Tymdall Cmnp. Mt Read Volcanics, wostcrn T-unia. Aus- volcanoge~tic irrassive sulfide depask EcoNoulc GEoMcY, v, 92, p. tdan Journal af Earth Sciences. v. 43. p. 147-156. 68M95. -1997, A submarine welded ipimhiite-crystal-rieh sandstone facies asso- Solomon, M., and U'alshe, J.L., 1979, The formation of massive sulfide de- ciation in the Camhnm Tyndail Gmup, western Tnsmanin: Australii!. Jour- posits on the %a floor: ECONOMICGEOLOGY, v. 74, p. 797-813. nal of \~olcanology and Geothermal Research, v. 76, p. 377-295. Solomon, M.,Eastoe, C.J., U'alshe, J.L., and Green, G.R., 1988, Mineral de- White, N.C., and Hedenquist, JW, 1995, Epithemal gold deposits: Styles, posits and rulfnr isotope abundu~eesin the Mo~mtRead Volcanics between charactelirtics. and exploration: Society of Emnonlic Ccologrts Newslet- Que niver and Mulult Darwin, Tasmania: ticoaoMic GEOLOGY,v. 83, p. ter 23. o. 9-13. 1307-1328. Spry. PG., Peter, J.M., and Slack J.F., 2000, Meta-exhahtes as exploration prides to acs: Reviews in Econoric Ceolog v 11. p. 163-201. Stanley, C.R, and Macleisb H.E., 1994, Lithageochemical e.qlomtion for hydmthcrmal are deposit using Pearce element ratio analysis: Geologic4 Association of Canada Sl~unCourse Notes, v. 11, p. 18S212. Stolz, J., and Large, R.R., 1992, Evaluation of the source-rack cantml an pre- cions metal grades in volcaruc-hosted massive sulfide deposits from west- cm Tasmania: ECONOMIC:GEOLOCY; v, 87, p. 72U-738.