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

A new period of volcanogenic massive sulfide formation in the Yilgarn: a volcanological study of theca2.76 Ga Hollandaire VMS deposit, Yilgarn Craton, Western Australia

“…The sphalerite-rich zone, between 120 and 135 m, is notable for enrichment in Zr and Mn and complete loss of K. Similar gains (Mn, Fe and Mg) and losses (Na, K) have been described for a number of VMS deposits (e.g. Franklin et al 1981;Large et al 2001b;Dube et al 2007).…”

Age and petrogenesis of Anisian magnesian alkali basalts and their genetic association with the Kafang stratiform Cu deposit in the Gejiu supergiant tin-polymetallic district, SW China

“…VMS deposits are accumulations of sulfide minerals that precipitated at or near the seafloor in spatial, temporal, and genetic association with contemporaneous volcanism (Franklin et al, 1981;Barrie and Hannington, 1999;Large et al, 2001). VMS deposits consist of a concordant massive sulfide lens and discordant vein-type sulfide mineralization located in the footwall rocks.…”

3D modelling of hydrothermal alteration associated with VHMS deposits in the Kristineberg area, Skellefte district, northern Sweden

“…In some cases, these alteration zones can extend into the stratigraphic hangingwall to envelop the deposit. In both cases, the alteration zones are typically mineralogically and chemically zoned and also volumetrically more extensive than the ore lenses themselves (Sangster 1972;Kranidiotis and MacLean 1987;Galley 1993;Ohmoto 1996;Hannington et al 1998;Large et al 2001b;Goodfellow et al 2003). Documenting the geometry, zonation patterns and intensities of such alteration zones is an important step in exploring for new VHMS deposits and also helps to constrain genetic models for the deposits.…”

“…Large et al 2001b; Barrett et al 2005;Zuo et al 2009;Lotfolah Hamedani et al 2012;Li et al 2013). However, only in recent years has it become possible to contour geochemical data in three dimensions (3D) using techniques such as polyharmonic radial basis functions (Carr et al 2001) to interpolate smooth surfaces from scattered data points.…”