福建武平十二排钼矿床辉钼矿Re-Os 同位素年龄及其地质意义

福建武平十二排铝矿床是近年来在闽西南地区找到的又一处铝矿床.钼矿化在中细粒黑云母花岗岩岩体与新元古界楼子坝群、晚古生界变质岩接触带内呈浸染状和脉状产出,并且构成透镜状矿体.本次研究过程中,对5件代表性辉钼矿样品进行了Re-Os同位素年龄测定,模式年龄值变化范围为149.7 ～ 152.8Ma,等时线年龄为(151 ±2) Ma,略晚于黑云母花岗岩的成岩年龄,由此认为十二排钼矿床与黑云母花岗岩的形成时间均为晚侏罗世,属燕山早期构造—岩浆活动的产物.结合矿区外围其他钼矿床同位素年龄数据,可以推测闽西南大规模钼矿化发生在印支期台地向活动大陆边缘转变阶段,并伴随燕山早期挤压隆升(约160 ～ 145 Ma)和燕山晚期由挤压向拉张机制转换(约105 ～90 Ma)作用所诱发的岩浆活动是导致钼矿床形成的主导因素.

Re-Os Isotopic Dating of Molybdenite from Shierpai Molybdenum Deposit in Wuping, Fujian, and Its Geological Significance

Located in the southwestern section of the Fujian, the Shierpai ore deposit in Wuping county is a newly discovered molybdenum deposit. Molybdenum mineralization occurs within the biotite granite stock or along its contact zone with Neoproterozoic and Late Paleozoic metamorphic rocks. Ore bodies consist of veins, veinlets and disseminated blocks. Re Os dating of five molybdenite samples collected from the main ore body shows that the isochron age is (151±2) Ma and the model ages range from 149.7 Ma to152.8 Ma with an average value of (150.8±1.3) Ma, a little later than the age of the ore bearing wall rock, the biotite granite. It can thus be considered that the biotite granite and the molybdenum deposit were both formed in Late Jurassic, and that magmatism and mineralization took place in early Yanshanian period in the Southwestern Fujian depression. Combined with other isotopic age data from the molybdenum deposits in adjacent areas, it can be inferred that the large scale molybdenum mineralization in the southwestern Fujian depression occurring during the early Yanshanian. Magmatic activity induced by Indosinian transition from sustained platform to active continental margin accompanied by compressing and uplifting in early Yanshanian(about 160~145Ma) and later Yanshanian tectonic reworking with the conversion from compressing to pulling(about 105~90 Ma) ,seems to have been the dominant factor responsible for the formation of the molybdenum deposit.