The Geology and Origin of the Rosebery Ore Deposit, Tasmania

Brathwaite, Robert L.

doi:10.2113/gsecongeo.69.7.1086

Cited by 45 publications

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“…Early studies of the carbonate lenses at Rosebery, Thalanga, and Henty (Braithwaite, 1974;Gregory et d., 1990;Halley and Roberts, 1997) concluded that they were of exhalative origin forming distal to the sea-floor sulfide lenses. However, in each case, more recent work has demonstrated their infill and replacement origin, involving mixing of hydrothermal fluid and seawater below the paleosea floor, in permeable volcanic units (e.g., Herrmann and Hill, 2001).…”

Section: Carbonate Alterationmentioning

confidence: 99%

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

Large¹

2001

Economic Geology

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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 environment, conditions of ore forination. and hvdrothermal alteration orocesses.prol,~l,ly iorn.rJ r t t l~~r ,I. the sed flojr r ,:, Hrllvrr Qltc lli\.er or hy rcpl~crmrnt of pun,~ts volcnnicl~snc IIU,,+, Jirrzdv Irlo\r. thr s,u f.wr T e., H,n.l,cn . The, iounrull ulrrrdi<)n ~cs,ci~rrd unh rhccr nolvmrtrlllc . . \'HhlS Jc~>u\lts u,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 ~\ ? . v o I~. t~~i z~~u~r~t r n l nrchitccturc Fucustneof llvurotllrrrnul fluids ihlno synvold&c sGctures has resurted in well-zoned chlorite-sericite footwall aheracon p;pes within footwall l a"; 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 HighwayReward. 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~ated by shallow porphyitic intrusions (e.g., HighwayReward). The Cn-An ore lenses may be strata-bound (e.g., Mount Lyell) or crosscutting pipes (e.g., HighwayReward) depending on the structure and permeability characteristics of the felsic volcanic host rocks. The presence 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 J . ' Synvolcanic gold-rich deposits, with high gold/base met ratlos are less common than the Cu-Au and Znrich 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 ...

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Section: Carbonate Alterationmentioning

confidence: 99%

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

Large¹

2001

Economic Geology

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“…Sphalerite, galena, chalcopyrite, barite, and quartz form a fine-grained polygonal matrix in which pyrite and arsenopyrite occur as porphyroblasts (Brathwaite, 1970(Brathwaite, , 1974. Deformational textures such as cataclastic brecciation of pyrite and ar-F•½;.…”

Section: Ore Texturesmentioning

confidence: 99%

“…There is no evidence of a chlorite-rich alteration pipe similar to those found beneath some of the Canadian Archean deposits (e.g., Sangster and Scott, 1976). However, Brathwaite (1970Brathwaite ( , 1974 Table 2). Sample numbers for the H lens are prefixed by 100, the remainder by 1051.…”

Section: Geological and Textural Relationshipsmentioning

confidence: 99%

The formation of the volcanic-hosted massive sulfide ore deposit at Rosebery, Tasmania

Green¹,

Solomon²,

Walshe³

1981

Economic Geology

109

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The Rosebery pyritic zinc-lead-copper-silver-gold orebody occurs in dominantly felsic volcanic rocks of Cambrian age in western Tasmania. Ore formation occurred in a marine environment following eruption of a thick pyroclastic unit consisting mainly of welded, ashflow tuffs, and subsequent subsidence. The main orebody consists of a discontinuous massive sulfide horizon and in the southern part of the mine there is a generalized metal zonation with a lower and central Cu-Fe-rich zone surrounded and overlain by Zn-Pb-Ag-rich ore. Barite-sulfide ore occurs as separate lenses higher in the sequence separated from the sulfide orebody by unmineralized, cleaved siltstone. The orebody is underlain by an extensive zone of alteration marked by depletion of Na and Sr and enrichment in Rb, K, Mg, Mn, and H20. The pyrite and chalcopyrite content of the altered footwall tuff and the Co content of the pyrite is highest beneath the Fe-and Cu-rich zones in the sulfide orebody and a feeder is inferred in this area.The •a4S values for sulfides in the sulfide orebody are higher in the richest Zn-Pb-Ag ore (>14.1%0) than the Fe-Cu ore (>7.8•), a pattern paralleled by a decrease in the Fe/Fe + Mg + Mn ratio of chlorite and a decrease in the FeS content of sphalerite. The •$48 values for sulfides in the barite ore are even higher (14.5 to 19.8%0) and the FeS content of sphalerite lower. Barite throughout the barite and sulfide orebodies is fairly constant between 84.6 and 41.2 per mil, but that in the sulfide ore appears to be epigenetic. The/i34S values for baritesulfide pairs indicate a temperature range of 255 ø to 298øC for the barite orebody, but the temperature of barite ore formation was probably about 250øC.The use of $a4S values for sulfides as stratigraphic markers indicates that the sulfide orebody is diachronous. It is possible to account for the metal and $a4S distribution by assuming that the ore solutions are buoyant on reaching the sea floor during the Fe-and Cu-rich phases but show reversing buoyancy during the PboZn-rich phase.The coexisting arsenopyrite-pyrite-chlorite-quartz assemblage in the sulfide orebody defines a range of aO2-T conditions using the six-component solid solution chlorite model of Walshe and Solomon (1981). The maximum indicated temperature of $00øC is consistent with the minimum temperature required by iron and copper solubilities. However, the chlorite compositions may be postdepositional, as seems to be the case for the FeS contents of sphalerite. The $a4Szs for the sulfide orebody is probably derived by almost complete reduction of Cambrian seawater sulfate mixed with sulfur leached from underlying rocks. The/ia4S values for the barite orebody may represent partial reduction of seawater sulfate.The ore fluid is supposed to have been generated by convective circulation of seawater in a rock pile heated by a Cambrian granitoid pluton.

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“…Recent work (Green 1983) suggests that the Rosebery 'Group' consists of a number of tectonic slices, and that previous stratigraphic columns (e.g. Loftus-Hill et al 1967;Brathwaite 1970) are of doubtful significance. The sequence is faulted against the Crimson Creek Formation to the W (Green 1983), and the best lithological correlation appears to be with the Dundas Group (Williams et al 1976a;Corbett 1981;Green 1983).…”

Section: Crimson Creek Formationmentioning

confidence: 99%

“…Correlates of the sequence overlie the Rosebery orebody and have been referred to as the Mt Black Volcanics (Brathwaite 1974;Green etal 1981). Samples for Rb-Sr analysis were collected over a 1.5 km interval of the old tramway E of Farrell Siding.…”

Section: Mt Black Volcanics Central Sequence Mt Read Volcanicsmentioning

confidence: 99%

Reconnaissance isotopic studies bearing on the tectonothermal history of Early Palaeozoic and Late Proterozoic sequences in western Tasmania

Adams

Black

Corbett³

et al. 1985

Australian Journal of Earth Sciences

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Reconnaissance isotopic dating (K-Ar, Rb-Sr, U-Pb) of over 20 different units of Early Palaeozoic and Late Proterozoic age in western and northern Tasmania has assisted in clarifying some ages and relationships but has met with many problems. The Rb-Sr systems in most Cambrian rocks have been re-set or partially re-set by post-Cambrian tectonothermal events, particularly the midDevonian Tabberabberan Orogeny, and U-Pb zircon data show considerable scatter due to contamination by older zircon and to post-crystallization Pb loss. K-Ar dating, mainly of slates and schists, has been more successful in delineating major tectonothermal events, but spreads of ages due to incomplete re-setting are again evident in some cases. The investigation has demonstrated some of the difficulties involved in dating in this complex region. Slate ages from the Late Proterozoic Burnie and Oonah Formations and Rocky Cape Group fall in the 630-690 Ma range, and confirm that the Penguin Orogeny was a Proterozoic event which, although protracted, was not related to the generation of the Cambrian Mt Read Volcanics. Slates and schists from the Proterozoic metasedimentary sequences of the Tyennan Region give ages in the 540-610 Ma range, suggesting independence from the Rocky Cape Region and confirming the importance of the D3 event of Råheim and Compston (Lithos 10, 271-90, 1977). A considerable number of Ordovician ages (450-490 Ma) have been recorded from known Cambrian units, not all of which can reasonably be ascribed to partial Tabberabberan re-setting. Some of these are interpreted as indicating a significant thermal event, associated with some folding and cleavage formation, in the Late CambrianEarly Ordovician. Slates and schists produced by the Tabberabberan Orogeny show a spread of ages from about 390 Ma, near the indicated biostratigraphic position of the orogeny, to about 420 Ma (e.g. Rosebery Mine schists), suggesting that the Devonian tectonothermal activity may have been spread over some 30 Ma.

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The Geology and Origin of the Rosebery Ore Deposit, Tasmania

Cited by 45 publications

References 0 publications

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

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

The formation of the volcanic-hosted massive sulfide ore deposit at Rosebery, Tasmania

Reconnaissance isotopic studies bearing on the tectonothermal history of Early Palaeozoic and Late Proterozoic sequences in western Tasmania

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