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Geochemistry: Exploration, Environment, Analysis
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Geochemistry: Exploration, Environment, Analysis; 2004; v. 4; issue.3; p. 191-211;
DOI: 10.1144/1467-7873/04-201
© 2004 Geological Society of London

Original Article

Stable isotope (C, O, S) systematics in alteration haloes associatedwith orogenic gold mineralization in the Victorian gold province,SE Australia

Frank P. Bierlein1, Dennis C. Arne2 & Ian Cartwright1

1 VIEPS School of Geosciences, Monash University, PO Box 28E, Melbourne, VIC 3800, Australia(e-mail: bierlein@mail.earth.monash.edu.au)
2 Western Australian School of Mines, Curtin University of Technology, PMB 22, Kalgoorlie, WA 6430, Australia

This study investigates whether hydrothermal alteration of metasedimentary rocks associated with orogenic gold mineralization in the Victorian gold province produces systematic changes in oxygen, carbon and sulphur isotope compositions that might provide explorationists with vectors towards ore. The presence of systematic isotopic trends across wallrock alteration haloes in gold deposits in the Stawell, Percydale, Ballarat, Bendigo and Fosterville goldfields clearly supports the interpreted hydrothermal origin of these haloes. General increases in carbonate {delta}13C towards the ore zones in all deposits record the influx of hydrothermal CO2. Whole-rock silicate and quartz {delta}18O, carbonate {delta}18O, and sulphide {delta}34S shifts equally mirror petrological and geochemical changes that resulted from prolonged and extensive interaction between externally derived hydrothermal fluids and the surrounding siliciclastic wallrocks. With the possible exception of sulphur, however, the isotopic enrichment/depletion trends are subtle and also vary significantly from deposit to deposit. Results of this study and comparisons with published data suggest that the oxygen and carbon isotopic ratios of silicates and carbonates in whole-rock samples within the alteration haloes are buffered by the wallrocks. Hydrothermal sulphides in Victorian orogenic gold deposits are characterized by {delta}34S values generally in the range –5 to +5{per thousand}. However, there is relatively little influx of hydrothermal sulphur beyond c. 5 to 10 m from the vein margins and disseminated pyrite well removed from the lode systems is characterized by either greatly negative or positive {delta}34S values typically greater than±10{per thousand}.

Key Words: Victorian gold province • orogenic gold • stable isotopes • wallrock alteration • exploration geochemistry