The Granites gold deposits, Northern Territory, Australia: evidence for an early syn-tectonic ore genesis |
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| Authors: | G J Adams R A Both P James |
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| Institution: | (1) School of Earth and Environmental Sciences, University of Adelaide, Adelaide, South Australia, 5005, Australia;(2) Present address: Newmont, Jundee Operations, P.O. Box 1652, Subiaco, Western Australia, 6904, Australia;(3) Present address: School of Natural and Built Environments, University of South Australia, Adelaide, South Australia, 5005, Australia |
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| Abstract: | The ore deposits of The Granites goldfield are shear-hosted within Palaeoproterozoic amphibolite facies metasedimentary rocks
in the Tanami Region, Northern Territory, Australia. The ore bodies are located within a 5- to 35-m thick sequence of steeply
dipping unit of metamorphosed iron-rich metasedimentary rocks. Deformation at The Granites was complex and is characterized
by five successive deformation phases (D1–5). Shear veins (central and oblique) are the dominant type of vein geometry, with minor development of extensional veins and
reverse-fault related veins. Four generations of syn-tectonic veins, corresponding to D1, D3, D4, and D5, have been recognized and are comprised of quartz, quartz-carbonate, calc-silicate, and calcite. In addition, two generations
of disseminated sulfide–arsenide mineralization, dominated by pyrrhotite, arsenopyrite, and loellingite, with minor pyrite,
chalcopyrite and rare marcasite, formed syn-D1 and syn- to post-D3. Textural and structural evidence indicates deposition of gold was contemporaneous with the syn-D1 veins and sulfide–arsenide mineralization. Four hydrothermal phases are proposed for the formation of the veins and disseminated
sulfide–arsenide assemblages. The first phase (D1) was responsible for transport and deposition of the majority of the gold. Minor remobilization and deposition of gold occurred
during the D3 and D4 phases. Little is known about the nature of the D1 ore fluid, although a relatively low sulfur content is indicated by the assemblage pyrrhotite–arsenopyrite–loellingite+rare
pyrite. The growth of amphibolite facies metamorphic minerals andalusite and almandine garnet during D1 indicates a high temperature for the fluid. The D3 hydrothermal phase coincided with peak metamorphism. D4 fluids were hypersaline, high temperature, CO2-poor, and H2S-poor.
Editorial handling: L. Meinert |
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| Keywords: | Tanami region Proterozoic gold Structural control Shear veins Fluid inclusions Sulfur isotopes |
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