Native antimony in the Baogutu gold deposit (west Junggar,NW China): Its occurrence and origin |
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| Authors: | Fang An Yongfeng Zhu |
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| Institution: | 1. Université de Rennes 1, Géosciences Rennes - UMR CNRS 6118, OSUR, 35042 Rennes Cedex, France;2. UMR CNRS 6524, Laboratoire Magmas et Volcans, Université Blaise Pascal, 63038 Clermont-Ferrand Cedex, France;1. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada;2. National Research Center for Geoanalysis, Chinese Academy of Geological Sciences, Beijing 100037, PR China;3. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China;4. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, PR China |
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| Abstract: | The Baogutu gold deposit, West Junggar (Xinjiang, NW China), is composed of quartz–sulfide veins and their stockworks and is hosted within an Early Carboniferous volcanic–sedimentary sequence. Three ore-forming paragenetic stages can be identified: coarse-grained quartz–sulfide vein (stage I), gold-bearing fine-grained quartz–sulfide vein (stage II), and native antimony-bearing calcite–sulfide veinlets (stage III). The estimated formation temperatures (approximately 360 to 220 °C), fS2 (? 7 to ? 15 log units), and fO2 (? 26 to ? 43 log units) decrease from stage I, through stage II, to stage III. The nature of the hydrothermal fluid changed from weakly acidic (pH: 5 to 6 at stage I) to alkaline (pH: > 7 at stage III).Two different occurrences of native antimony could be identified: one coexists with chalcopyrite and pyrrhotite, whereas the other occurs as isolate grains within calcite veins. Native antimony (up to 100 μm in size) contains minor amounts of As (2.0 to 2.7 wt.%); empirical formula Sb0.95–0.96As0.03–0.04. Decrease of temperature and fO2 at high pH and low fS2 conditions favored co-precipitation of native antimony–ullmannite assemblages and the decomposition of tetrahedrite. Native antimony crystallized later than the native gold, suggesting fractionation between Au and Sb during the hydrothermal evolution of the deposit. |
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