福建连城铜坑钼矿床辉钼矿 Re Os 同位素年龄及燕山期成矿事件

摘要

Located in the southwestern Fujian Province,the Tongkeng ore deposit in Liancheng is a newly discovered molybdenum deposit.The molybdenum mineralization occurs within the contact zone between the granite porphyry stock formed in the first stage of late Yanshanian magmatic event in Tongkeng area and late Paleozoic metamorphic rocks.Ore bodies are charactered by vein,veinlet and disseminated.Re Os dating of six molybdenite samples collected from the major ore body shows that the isochron age is (1 15.7 ±1.1 )Ma and the model ages range from 1 15.1 Ma to 1 1 6.7 Ma,with an average value of (1 15.8±0.8)Ma.It can be considered that both the granite-porphyry and associated molybdenum mineralization were formed in Early Cretaceous,and that both were derived by the late Yanshanian tectonic-magmatic event in the southwestern Fujian depression.Combined with isotopic age data from other adjacent molybdenum deposits,it can be inferred that the early Yanshanian large-scale molybdenum mineralization in the southwestern Fujian depression formed during the transition stage from the Indosinian sustained platform to active continental margin,and accompanied by compressing and uplifting in early Yanshanian (about 1 60 145 Ma);the late Yanshanian tectonic conversion from compressing to tension (about 125 105 Ma)resulted in the magmatism which seemed to be the dominant factor for the late Yanshanian molybdenum deposit.%福建连城铜坑钼矿床是近年来在闽西南地区找到的又一处钼矿床。钼矿化在铜坑燕山晚期第一阶段花岗斑岩岩体与晚古生界变质岩接触带内呈浸染状、脉状、透镜状等形态产出。本次研究过程中,对6件代表性辉钼矿样品进行了 Re Os 同位素年龄测定,Re Os 同位素模式年龄值为115.1~116.7 Ma,等时线年龄为(115.7±1.1)Ma,由此认为铜坑钼矿床与花岗斑岩的形成时间均为早白垩世,属燕山晚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,闽西南坳陷燕山早期大规模钼矿化发生在印支期稳定的台地向活动大陆边缘转变阶段并伴随燕山早期挤压隆升(160~145 Ma),燕山晚期由挤压向拉张机制转换(125~105 Ma)的构造改造阶段所诱发的岩浆活动是导致钼矿床形成的主导因素。