Abstract

Bedded disseminations. No evidence for hydrothermal alteration. The disseminated sulfides have a delta 34 S range of -17.3 to 15.8 per mil, consistent with bacterial reduction of sulfate. Veinlet sulfides have a similar but smaller delta 34 S range, in accord with formation by remobilization of the disseminated sulfides. No significant delta 13 C differences between bedded and veinlet carbonates; marked variations in delta 18 O values, with magnesite values being generally higher than dolomite, and the median value for bedded carbonates being around 23 per mil, some 3 per mil higher than the median value for veinlet carbonates. Low-temperature oxygen isotope equilibration during early diagenetic carbonate reactions. Low-grade regional metamorphism caused minor recrystallization and formation of additional veinlets but did not extensively overprint the diagenetic isotopic trends. Isotopic similarities between the cupriferous and the unmineralized lithologies support introduction of the copper during sedimentation and/or early diagenesis. Veinlet carbonates contain small NaCl-rich fluid inclusions, formed at around 300 degrees C and 4 km depth, during the metamorphism. General trend of increasing mean delta 34 S values with decreasing age of the late Proterozoic strata in the Adelaide geosyncline and Stuart shelf. This trend may be the product of local environmental conditions which resulted in sulfate reduction outweighing sulfate replenishment; alternatively, it could be reflecting global processes which caused major 34 S enrichment of seawater sulfate.--Modified journal abstract.

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