Hydrothermal alteration and ore-forming fluids associated with gold-tellurium mineralization in the Dongping gold deposit,China |
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| Institution: | 1. School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing, 100083, China;2. Department of Earth Sciences, University of Adelaide, Adelaide, SA 5005, Australia;3. Tianjin Geothermal Exploration and Development-Designing Institute, Tianjin, 300250, China;4. KalNorth Gold Mines Limited, 224 Dugan Street, Kalgoorlie, WA 6430, Australia;5. Xi''an Institute of Geological and Mineral exploration, Shanxi, 710100, China;1. MLR Key Laboratory of Metallogeny and Mineral Assessment Institute of Mineral Resources, CAGS, Beijing 100037, China;2. Centre for Exploration Targeting, ARC Centre of Excellence for Core to Crust Fluid Systems, The University of Western Australia, Crawley, WA 6009, Australia;3. National Research Center of Geoanalysis, Beijing 100037, China;4. China University of Geosciences, Beijing 100083, China;1. Key Laboratory of Orogen and Crustal Evolution, Peking University, Beijing, 100871, China;2. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China;3. State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, China |
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| Abstract: | The Dongping gold deposit hosted in syenites is one of the largest hydrothermal gold deposits in China and composed of ore veins in the upper parts and altered zones in the lower parts of the ore bodies. Pervasive potassic alteration and silicification overprint the wall rocks of the ore deposit. The alteration minerals include orthoclase, microcline, perthite, quartz, sericite, epidote, calcite, hematite and pyrite, with the quartz, pyrite and hematite assemblages closely associated with gold mineralization. The phases of hydrothermal alteration include: (i) potassic alteration, (ii) potassic alteration - silicification, (iii) silicification - epidotization - hematitization, (iv) silicification - sericitization - pyritization and (v) carbonation. Mass-balance calculations in potassic altered and silicified rocks reveal the gain of K2O, Na2O, SiO2, HFSEs and transition elements (TEs) and the loss of REEs. Most major elements were affected by intense mineral reactions, and the REE patterns of the ore are consistent with those of the syenites. Gold, silver and tellurium show positive correlation and close association with silicification. Fluid inclusion homogenization temperatures in quartz veins range from 154 °C to 382 °C (peak at 275 °C–325 °C), with salinities of 4–9 wt.% NaCl equiv. At temperatures of 325 °C the fluid is estimated to have pH = 3.70–5.86, log fO2 = ? 32.4 to ? 28.1, with Au and Te transported as Au (HS)2? and Te22 ? complexes. The ore forming fluids evolved from high pH and fO2 at moderate temperatures into moderate-low pH, low fO2 and low temperature conditions. The fineness of the precipitated native gold and the contents of the oxide minerals (e.g., magnetite and hematite) decreased, followed by precipitation of Au- and Ag-bearing tellurides. The hydrothermal system was derived from an alkaline magma and the deposit is defined as an alkaline rock-hosted hydrothermal gold deposit. |
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