内蒙古查木罕钨钼多金属矿床辉钼矿Re-Os同位素年龄及其地质意义

内蒙古克什克腾旗查木罕钨钼矿床是近年新发现的矿床。本文通过5件辉钼矿样品的Re-Os同位素测定与分析,获得模式年龄137.8～139.3Ma,加权平均值为138.8±2.8Ma,对应的等时线年龄为139.3±1.5Ma,表明查木罕钨钼矿床形成于早白垩世,与中国东部燕山期大规模钨钼成矿期一致。查木罕钨钼矿床辉钼矿的铼含量介于0.127～2.317μg/g之间,平均0.875μg/g,表明查木罕矿床成矿物质主要来源于上地壳。结合区域上已有研究成果,早白垩世是西拉木伦钼成矿带一期重要的成矿作用,并与中国东部大规模成矿时限相一致,该期成矿作用发生于中国东部岩石圈减薄构造背景。

Re-Os Dating of Molybdenites from Chamuhan W-Mo Deposit, Inner Mongolia and its Geological Implications

The newly discovered Chamuhan W-Mo deposit is located in the northwest of Keshiketeng county, Inner Mongonia. The Re-Os dating for five molybdenite samples constrains the age of the vein-type Mo mineralization to be 139.3±1.5 Ma (2σ, MSWD=3.3). Given the isotope model ages of between 137.8±2.3 and 139.4±2.1 Ma, averaging 138.8±2.8 Ma (2σ, MSWD=0.044), a perfect isochron line is created at 139.3 Ma. The data indicate that the mineralization in Chamuhan W-Mo deposit occurred in Late Jurassic, and is one of the massive Mo mineralization in East China. Comparing with other Mo or Mo-bearing deposits in the regional, it is believed that the Chamuhan W-Mo deposit is the result of the tectonic transaction in East China. The Re contents of molybdenites in Chamuhan vary in range of 0.127 μg/g to 2.317 μg/g, averaging 0.875 μg/g. As Re content in molybdenite can be used as an important indicator on source of ore-forming material, it is likely that the ore-forming material in the Chamuhan W-Mo deposit was derived from the upper crust.