北祁连浪力克铜矿床锆石U-Pb和辉钼矿Re-Os年龄及其地质意义
Zircon U-Pb and molybdenite Re-Os dating of the Langlike copper deposit in North Qilian Mountain and its geological implications
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摘要: 提要: 浪力克铜矿床是北祁连造山带中段冷龙岭火山岩带内的一个中型铜矿床, 铜矿体主要赋存于火山通道内的石英闪长玢岩及其邻近的安山岩中, 文章在对矿化特征分析的基础上, 对其进行了成岩成矿年代学研究。采用LA-ICP-MS锆石U-Pb测年技术, 得到含矿岩体石英闪长玢岩的成岩年龄为(461.5±7.3) Ma, 通过含辉钼矿矿石中辉钼矿的Re-Os同位素分析, 获得其模式年龄为(467.1±6.3) Ma~(471.3±6.7) Ma, 等时线年龄为(470.5±3.4) Ma, 表明矿床形成于中奥陶世, 成矿与石英闪长玢岩具有密切的时空关系。综合分析表明, 浪力克成岩成矿作用发生在北祁连洋俯冲形成的岛弧环境, 矿床具有斑岩(次火山岩)型矿床的特征, 这对浪力克铜矿床成因类型的进一步查明和指导找矿工作具有重要意义。Abstract: Abstract: Located in the Lenglongling volcanic belt of North Qilian Mountain, the Langlike copper deposit is a medium-sized deposit with mineralization mainly occurring in quartz dioritic porphyrite. Based on an analysis of the mineralization features of the deposit, the authors used the zircon LA-ICP-MS U-Pb and molybdenite ICP-MS Re-Os highly precise dating techniques to study the ore-bearing quartz dioritic porphyrite and five samples of molybdenum collected from the deposit. Zircon U-Pb dating yielded an age of (461.5±7.3) Ma for quartz dioritic porphyrite. The Re-Os model ages of the molybdenite samples vary from (467.1±6.3) Ma to (471.3±6.7) Ma and the Re-Os isochron age is (470.5±3.4) Ma. The similar zircon U-Pb and molybdenite Re-Os isotopic ages suggest that the Langlike copper deposit formed in middle Ordovician and it had a close temporal relationship with the quartz dioritic porphyrite. Combined with the tectonic evolution of the North Qilian, the authors hold that the deposit was produced in an island arc tectonic setting triggered by slab subduction and was similar to the porphyry deposit. These characteristics are of important significance for investigating the genetic type of the Langlike copper deposit and for further prospecting work.