西藏雄村斑岩铜矿床辉钼矿Re-Os同位素体系

The Re-Os isotope system of the Xiongcun porphyry copper-gold deposit, Tibet

辉钼矿Re—os同位素测年是现今研究斑岩铜矿成矿时限最有效的手段。本文通过开展冈底斯成矿带雄村斑岩铜金矿辉钼矿Re—Os同位素年代学研究．并结合前人已发表的数据．认为雄村斑岩铜金矿床成矿时限为171～175Ma。I号矿体可能受到始新世大规模的岩浆活动扰动。辉钼矿在经历过后期热事件影响，在辉钼矿中形成有极微量富Re的K一硅酸盐矿物．I号矿体辉钼矿Re含量比Ⅱ号矿体以及Ⅲ号矿体中辉钼矿Re含量高出1～4倍。其Re一0s同位素年龄比真实年龄偏低．不能完全代表成矿年龄。同时通过与冈底斯成矿带斑岩一矽卡岩铜钼矿床，钼／钼铜矿床的对比研究后发现．雄村斑岩铜金矿中辉镅矿Re含量比同一成矿带上中新世斑岩铜铝矿床中辉钼矿Re含量高出一个数量级．比古新世一始新世斑岩钼矿／钼铜矿床中辉钼矿Re含量高出两个数量级。辉钼矿Re含量变化特征与成矿物质的来源、钼的浓度、成矿母岩组分以及成矿期间的物理／化学条件有关。

Re-Os dating of molybdenite is an efficient means to restrict the time of mineralization. The age of mineralization of the Xiongcun porphyry copper-gold deposit is confined between 171 Ma and 175 Ma based on this study and other data available. No. I ore body of the Xiongcun deposit was affected by later magmtic thermal event. Molybdenite contains trace K-Si silicate enriched in Re. As a result of this event, the Re content of molybdenite is one to four times higher than that of molybdenite in No. Ⅱ ore body and No. Ⅲ ore body, and the age of molybdenite in No. I ore body is younger than the real age. The authors also compared the Re content of molybdenite between this deposit and other porphyry-skam deposits within this bek and found that the content of Re shows systematic variation. The Re content of the Xiongcun porphyry copper-gold deposit is one order of magnitude high than that of Miocene porphyry deposits and two order of magnitude higher than Paleocene to Eocene porphyry-skarn deposits. The Re variation is related to the source of metal, the content of molybdenum, the composition of magma and the physical/chemical condition of magmatic-hydrothermal solution.