Oxygen and carbon isotope abundances in carbonates of spilitic rocks from Glarus, Switzerland

Schidlowski, Manfred

doi:10.1007/bf00625323

Cited by 6 publications

(1 citation statement)

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“…In the Kalgoorlie-Norseman region, seafloor-altered metabasalts, which are only weakly carbonated, dominate the stratigraphy (Hallberg 1972). Modern analogues with such low degrees of seafloor carbonation typically have carbonates with ~13C of -6 to -2%0 (Schidlowski et al 1970;Muehlenbachs and Clayton 1972;Muehlenbachs 1977). These values overlap with carbon isotope compositions in some Archaean gold deposits including Racetrack, and potentially negate earlier arguments against such carbon sources for Archaean mesothermal gold deposits (cf.…”

Section: Stable Isotope Datamentioning

confidence: 75%

Archaean Au−Ag mineralisation at Racetrack, near Kalgoorlie, Western Australia: a high crustal-level expression of the Archaean composite lode-gold system

et al. 1993

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Abstract. The Racetrack Au-Ag deposit, in the ArchaeanYilgarn Block, Western Australia, is hosted by a porphyritic basalt in a low greenschist facies setting and is associated with a brittle strike-slip fault system. Three distinct and successive stages of hydrothermal activity and late quartz-carbonate veining resulted in multiple veining and/or brecciation: Stages I and II are Au-bearing, whereas Stage III and late veins are barren. The ore shows features of both classic epithermal and mesothermal deposits. Alteration assemblages, typified by sericitization, carbonization, silicification and chloritization, are similar to those of mesothermal gold deposits, whereas the quartz vein-textures including comb, rosette, plumose and banded, ore mineralogy of arsenopyrite, pyrite, chalcopyrite, sphalerite, galena, freibergite, tetrahedrite, tennantite, fahlore, electrum and gold, and metal associations (Cu, As, Ag, Sn, Sb, W, Au and Pb) are more characteristic of epithermal deposits. Fluid inclusions related to Stage II are two phase and aqueous with 1-8 (average 4) wt. % NaC1 equiv, and CO2 content of < 0.85 molal. Pressure-corrected homogenisation temperatures range from 190~ to 260~ Mineral assemblages indicate that ore fluid pH ranged between 4.2 and 5.3, fo2 between 10 -38.8 and 10 -39"6 bars, and mrs between 10 -3.2 and 10-3.6. Calculated chemical and stable isotope compositions require a component of surface water in the ore fluid depositing the mineralisation, but evidence for deep crustal Pb indicates that deeply sourced fluids were also involved.The deposit is interpreted to" have formed in a shallow environment via mixing of deeply sourced fluids, from at least as deep as the base of the greenstone belt, with surface waters. It therefore represents the upper crustal end-member of the crustal depth spectrtim of Archaean lode-gold mineralisation.Archaean lode-gold deposits are sited in granulite to subgreenschist facies metamorphic terranes Groves -this issue). Deposits at the upper and lower end of the spectrum are relatively rare, and documentation has been dominated by those so-called mesothermal deposits from greenschist and lower-amphibolite fades environments. The principal objective of this paper is to present data on the previously undocumented Archaean Racetrack Au-Ag deposit, with production and resources of approximately 12.6 t Au. The deposit shows features characteristic of both Archaean lode-gold mesothermal deposit, and epithermal precious-metal mineralisation. It is interpreted that mineralisation occurred at a high crustal level, in a near surface environment, and that the deposit represents an upper crustal end-member of a spectrum of Archaean lode-gold mineralisation.

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