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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• 作者：Xiaofeng Li ; Chunzeng Wang ; Wei Mao ; Qinghong Xu ; Yaohui Liu
• 关键词：W&ndash ; Mo polymetallic mineralization ; Skarn ; Ilvaite ; Geochronology ; India&ndash ; Eurasia collision ; Hahaigang deposit ; Gangdese Belt ; Tibet
• 刊名：Ore Geology Reviews
• 出版年：April, 2014
• 年：2014
• 卷：58
• 期：Complete
• 页码：27-40
• 全文大小：2621 K

文摘

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 卤 0.90 Ma and a weighted mean ²⁰⁶Pb/²³⁸U age of 57.02 卤 0.42 Ma. The granite porphyry yields a ²⁰⁶Pb/²³⁸U-²⁰⁷Pb/²³⁸U concordia age of 109.1 卤 8.9 Ma and a weighted mean ²⁰⁶Pb/²³⁸U age of 114.0 卤 2.6 Ma. The biotite monzogranite yields a weighted mean ²⁰⁶Pb/²³⁸U age of 56.1 卤 1.1 Ma. Re-Os isochron age of 63.2 卤 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 卤 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.