兰坪盆地连城脉状铜矿床辉钼矿Re-Os定年及其地质意义

Re-Os dating of molybdenite from Liancheng vein copper deposit in Lanping basin and its geological significance

兰坪盆地贱金属矿床是一套独特的受逆冲推覆构造系统控制的矿床类型,连城脉状铜矿床是其重要组成之一。以往研究采用多种测年手段限定脉状铜矿成矿年龄,但结果分歧较大。本文采用辉钼矿Re-Os同位素定年方法,获得连城矿床辉钼矿的Re-Os同位素模式年龄为(48.14±0.87)Ma,等时线年龄为(49.0±1.3)Ma,初步厘定兰坪盆地热液脉型铜矿床形成于48～49Ma。结合区域地质与控矿构造分析,该矿床应为盆地西部逆冲带逆冲变形过程中的产物,由此限定兰坪盆地西部逆冲推覆的起始时间至少早于49Ma,同时佐证了兰坪盆地西部逆冲带内以Cu(-Ag)为主的成矿系统的形成发育可能早于东部逆冲推覆带内以Pb-Zn为主的成矿系统。

The sediments-hosted base metal deposits controlled by Cenozoic thrust-nappe structural system in Lanping basin,southwest China,apparently differ from the sediments-hosted base metal deposits in other parts of the world.The Liancheng vein-type copper deposit is one of these deposits in Lanping basin.Lots of dating methods had been employed to define the ages of this type of ore deposits,but the results were obscure due to the flaws of the methods themselves.In this study,the Re-Os isotopic dating method was used to measure 6 molybdenite samples collected from the Liancheng copper deposit.The isotopic model age is（48.14±0.87）Ma and the isochronic age is（49.0±1.3） Ma,indicating that the deposit was formed at 48～49 Ma.The age in combination with the regional geological setting and the ore-controlling characteristics supports the viewpoint that the vein-type copper deposits similar to the Liancheng ore deposit must have resulted from the thrust deformation in western Lanping basin,and the initial thrust-napping took place at least earlier than 49 Ma.This result also suggests that the copper-silver ore-forming system in western Lanping basin was formed earlier than the lead-zinc ore-forming system in eastern Lanping basin.