| 西藏谢通门县雄村铜金矿主要地质体形成的时限：锆石U-Pb、辉钼矿Re-Os年龄的证据 |
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| 引用本文：黎风佶,李志军,张丽,唐晓倩,邓起,郎兴海,黄勇,姚晓峰,王友.2010.[J].Mineral Deposits,29(3):461~475 |
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| 基金项目:国家科技支撑项目（2006BAB01A01）、天圆矿业公司项目、青藏专项（1212010818089）、国家基础研究计划“印度_亚洲大陆主碰撞带成矿作用”973项目(2002CB412607) |
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| 中文摘要:雄村超大型铜金矿床的主要成矿作用发生在具眼球状石英斑晶的石英闪长玢岩及其外接触带强蚀变中细粒凝灰岩中，由产于斑岩体内的细脉浸染型矿体和产于凝灰岩中的细脉浸染型矿体、脉状矿体组成。文章在对含矿岩系及其侵位于含矿岩系的浅成岩和穿切矿体的花岗闪长岩等地质体进行详细的地质填图基础上，对雄村Ⅰ号、Ⅱ号矿体含矿围岩（暂定为雄村组J1-2x）、最早侵位的浅成岩-角闪石英闪长玢岩（J2δομ1）、含矿斑岩——具眼球状角闪石英闪长玢岩（J2δομ）、穿插矿体的黑云母花岗闪长岩（E2γδβ）（谢通门大岩基的一部分）、Ⅱ号矿体矿石中的辉钼矿等，开展了系统的成岩成矿年代学研究。锆石的U-Pb同位素测年结果表明，含矿围岩凝灰岩加权平均年龄为（176±5）Ma（MSWD=0.63；n=9）；与成矿有关的含眼球状石英斑晶的石英闪长玢岩加权平均年龄为（173±3）Ma（MSWD=1.16；n=16）；穿插侵吞矿体的谢通门大岩基花岗闪长斑岩加权平均年龄为（46.5±1.1）Ma（MSWD=0.83；n=14）；所有锆石均显示岩浆成因锆石的特点。锆石U-Pb同位素研究显示含矿围岩形成于早中侏罗世，偏中性的含矿岩体侵位于中侏罗世，而侵吞穿插矿体的大岩基形成时代为始新世。雄村铜金矿Ⅱ号矿体4件辉钼矿样品的Re-Os同位素测定结果显示，辉钼矿w(187Re)为1 269～1 354 μg/g，w(187Os)为3 587～3 993 ng/g。辉钼矿的模式年龄为169.5～176.8 Ma，平均模式年龄为 (173.2±4.7) Ma（MSWD=5.6），显示成矿年龄为中侏罗世早期。结合多个岩体和岩脉的Ar-Ar同位素年龄测定结果和其他研究者的成果，认为雄村铜金矿属于岛弧型斑岩铜金矿床，由新特提斯洋的早期俯冲所致。雄村岛弧型斑岩铜金矿的发现和勘探、外围找矿的突破及本次系统年代学研究，提供了特提斯洋俯冲阶段成矿的信息，拓宽了西藏冈底斯成矿带新的找矿方向。 |
| 中文关键词:地质学 雄村铜金矿 锆石U-Pb年龄 Re-Os同位素年龄 俯冲成矿 岛弧型斑岩铜金矿 冈底斯 西藏 |
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| Abstract:Time limit for formation of main geological bodies in Xiongcun copper-gold deposit，Xietongmen County, Tibet: Evidence from zircon U-Pb ages and Re-Os age of molybdenite. The Xiongcun copper-gold deposit is a superlarge copper and gold deposit. The main mineralization occurs in quartz-augen diorite porphyry and exo-contact zone of strongly altered fine-grained tuff and is composed of veinlet disseminations in the porphyry and veinlet-disseminations and veins in the tuff. The genetic types of the ore deposit include porphyry ore type, epithermal ore type, sedex type, fracture-controlled altered rock type, and structure-altered rock type. Much controversy still exists concerning the rock-forming and ore-forming age. Based on zircon dating of ore-bearing rocks, intrusions and penetrating ore bodies as well as detailed geological mapping, the authors carried out chronologic studies of ore-bearing wall rocks of No Ⅰ and Ⅱ ore bodies, the oldest hornblende quartz diorite porphyry (J2δομ1), quartz-augen diorite porphyry (J2δομ),biotite granodiorite (E2γδβ), lamprophyre, and molybdenite of No Ⅱ ore body. According to the results of zircon U-Pb isotopic dating, the weighted average age of 9 analytical data from ore-bearing tuff (ZK5036-68 m) is (175±5) Ma, with MSWD being 0.63; the weighted average age of 16 analytical data from quartz-augen diorite porphyry (ZK5036-303 m) is (173±3) Ma, with MSWD being 1.16; and the weighted average age of 14 analytical data from diorite granodiorite (ZK6187-335 m) is (46.5±1.1) Ma, with MSWD being 0.83. All the zircons have characteristics of magmatic origin. Zircon U-Pb isotopic dating data suggest that the ore-bearing wall rocks were formed in early Middle Jurassic, the mineralized intrusions were formed in Middle Jurassic, and the batholiths were formed in Eocene. The dating results of four molybdenite Re-Os isotope samples from Xiongcun No Ⅱ ore body show that the content of 187Re is 1 269～1 354 (μg/g) and the content of 187Os is 3 587～3 993 (ng/g). Model ages of molybdenite are around (1 695～176 8) Ma, and model ages are consistent with in the error range (MSWD=5.6), implying that mineralization took place in middle Jurassic. Ar-Ar dating of the magmatic body and dyke show that 39Ar/40Ar plateau age of biotite from lamprophyre is (49.59±0.58) Ma, and 39Ar/40Ar plateau age of biotite from biotite granodiorite is (46.96±0.42) Ma. Combined with the results obtained by other researchers,it is thought that retrograde metamorphism is the cause for the Ar-Ar dating of mica minerals around 46～50 Ma. The Xiongcun copper-gold deposit is an island arc porphyry copper-gold deposit, as evidenced by the study of petrologic and geochemical characteristics and the analysis of ore-bearing features, ore mineral assemblage, element assemblages and chronology. The discovery, exploration and chronologic studies of the Xiongcun island arc porphyry copper-gold deposit have provided the information concerning the Tethys subduction ore-forming stage, and also widened the new prospecting direction in the Gangdese metallogenic belt of Tibet. |
| keywords:geology, Xiongcun copper-gold deposit, zircon U-Pb age, Re-Os age, subduction ore-forming process, island-arc porphyry copper-gold deposit, Gangdese belt, Tibet |
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