The fault-controlled skarn W–Mo polymetallic mineralization during the main India–Eurasia collision: Example from Hahaigang deposit of Gangdese metallogenic belt of Tibet |
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| Institution: | 1. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou 550002, China;2. University of Maine at Presque Isle, Presque Isle, ME 04769, USA;3. Guilin Research Institute of Geology for Mineral Resources, Guilin, Guangxi 541004, China;1. Institute of Mineral Resources, Chinese Academy of Geological Sciences (CAGS), Beijing 100037, China;2. China University of Geosciences, Beijing 100083, China;3. Chengdu University of Technology, Chengdu 610059, China;1. MNR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS, Beijing 100037, China;2. Geomathematics Key Laboratory of Sichuan Province (Chengdu University of Technology), Chengdu 610059, China;3. School of Natural and Built Environment, Queen''s University Belfast, BT7 1NN, UK;4. Geological Survey of Northern Ireland, Dundonald House, Upper Newtownards Road, Belfast BT4 3SB, UK;5. Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Chengdu 611756, China;6. Central South Geological Survey Institute of China Metallurgical Geology Bureau, Wuhan 430081, China;1. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;1. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, PR China;2. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China;1. State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;2. State Key Laboratory of Geological Processes and Mineral Resources, and Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China |
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| Abstract: | The Hahaigang W–Mo polymetallic skarn deposit is located in the central-eastern part of Gangdese tectono-magmatic belt in Lhasa terrane, Tibet. The deposit was discovered in 2007 with currently proven 46 million tons of WO3 ores, 12 million tons of Mo ores, and 1.31 million tons of combined Cu–Pb–Zn ores, at an average grade of 0.20% WO3, 0.07% Mo, 0.026% Cu, 0.49% Pb, and 3.1% Zn. Ore bodies occur in veins or disseminations, and are confined within the NE-striking Dalong fault zone which is hosted by the Lower-Permian Pangna Group of dominantly quartz sandstone and slate. Several granitic plutons are exposed in the area or known from drill-holes. Ages of these granitic plutons are determined by using zircon U–Pb LA–ICP–MS method. For example, the biotite monzogranite yields a 206Pb/238U–207Pb/238U concordia age of 58.66 ± 0.90 Ma and a weighted mean 206Pb/238U age of 57.02 ± 0.42 Ma. The granite porphyry yields a 206Pb/238U–207Pb/238U concordia age of 109.1 ± 8.9 Ma and a weighted mean 206Pb/238U age of 114.0 ± 2.6 Ma. The biotite monzogranite yields a weighted mean 206Pb/238U age of 56.1 ± 1.1 Ma. Re–Os isochron age of 63.2 ± 3.2 Ma from 5 molybdenite samples collected from the W–Mo skarn ores is also obtained in this study. The zircon U–Pb and molybdenite Re–Os geochronological data suggest that the W–Mo mineralization was not temporally associated with any of the dated igneous plutons. However, the molybdenite Re–Os age of 63.2 ± 3.2 Ma indicates that the W–Mo mineralization might have occurred during the main India–Eurasia collision that was initiated around 65 Ma. Microprobe analysis of ilvaite that occurs in two generations in the W–Mo skarn ores reveals a close relationship to Ca–Fe–F-rich hydrothermal fluids, which were probably derived from deeply-seated magmas. We suggest that ascent of the fluids was strictly controlled by the ore-controlling Dalong fault zone, and that chemical interaction and metasomatism between the fluids and the Lower-Permian Pangna quartz-feldspathic host rocks produced the ilvaite and the W–Mo polymetallic skarn deposit during the main India–Eurasia collision. Although the majority of the polymetallic deposits in the Gangdese belt are reported to be either pre- or post-main collision, it is evident from this study that the main collision also produced W–Mo polymetallic mineralization within the belt. |
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