Constraints on the mass independent sulfur isotope signature of Fimiston, Oroya and Mount Charlotte style pyrites at the Golden Mile Deposit, Western Australia

Marcelo Godefroy Rodriguez

    Research output: ThesisMaster's Thesis

    239 Downloads (Pure)

    Abstract

    The Archean Golden Mile deposit in the Kalgoorlie Terrane of the Yilgarn craton in Western Australia, has been exploited since 1985 and contains 1919 t Au (mined resource and proven reserve until 2014). The Golden Mile deposit comprises three major mineralization styles: Fimiston, Oroya and Mt Charlotte. Fimiston style gold-telluride mineralization is associated with ankerite-sericite-pyrite alteration. Oroya style telluride-gold mineralization is contained in irregular breccia bodies with ankerite-dolomite-sericite-pyrite±roescolite alteration and Mount Charlotte style mineralization is hosted in scheelite bearing quartz-carbonate-pyrite±scheelite veins and associated ankerite-sericite-pyrite±pyrrhotite alteration selvages. The Δ33S and δ34S analyses on pyrites from the different mineralization stages including oxidised and reduced sulphide-oxide assemblages revealed a large variation in δ34S and Δ33S values. The Δ33S values above and below the MDF field in all three mineralization styles suggest that at least part of the sulfur was derived from the mantle. Other sources for sulfur include seawater and reduced elemental sulfur. Negative δ34S values (predominantly in Fimiston style mineralization) are compatible with oxidised fluids (evidenced by hematite-pyrite-magnetite-gold assemblages) and phase separation during shear zone movement. Positive δ34S values are explained by reduced oxidation state due to host rock reactions (evidenced by pyrite-pyrrhotite-gold assemblages), particularly in the Mt Charlotte and Oroya styles. The multiple sulfur isotope results of pyrites from the three major mineralization styles in the Golden Mile indicate that sulfur sources and redox conditions shifted significantly during the mineralization stages. The MIF signature strongly indicates that the mantle played a significant role in the formation of the gold-bearing pyrites.
    Original languageEnglish
    QualificationMasters
    Publication statusUnpublished - Oct 2015

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