广东锡坪钼铜多金属矿床辉钼矿Re-Os同位素定年及其地质意义

摘要

广东锡坪钼铜多金属矿床位于钦杭成矿带的西南端,为一大型的斑岩型矿床.本文利用辉钼矿Re-Os同位素定年方法对锡坪钼铜多金属矿床4件辉钼矿样品进行了成矿年代学测定,获得的模式年龄为85.15～88.34Ma,加权平均值为86.1±2.3Ma,对应的等时线年龄为89.9±3.4Ma,模式年龄和等时线年龄结果在误差范围内基本一致,指示锡坪钼铜多金属矿床的成矿时限为晚白垩世.锡坪钼铜多金属矿辉钼矿样品的Re含量较低,表明其成矿物质可能主要来自于壳源.钦杭成矿带成岩成矿作用以中生代燕山期为主,存在180 ～ 150Ma、110 ～ 80Ma两个爆发期,两期成岩成矿作用可能均与太平洋板块的俯冲有一定的关系.锡坪钼铜多金属矿床是在岩石圈伸展减薄环境下发生的大规模成矿作用的产物.%The Xiping Mo-Cu polymetallic deposit is a large porphyry deposit located in the southwestern of the Qin-Hang metallogenic belt.Four molybdenite samples from the Xiping Mo-Cu polymetallic deposit were collected to perform the Re-Os dating.The Re-Os dating yield model ages ranging from 85.15Ma to 88.34Ma,with a weighted mean age of 86.1 ± 2.3Ma,and obtain an isochron age of 89.9 ± 3.4Ma.Evidently,model ages are consistent with isochron age within the error ranges,so we can constrain the ore-forming age of Xiping Mo-Cu polymetallic deposit at the Late Cretaceous.The molybdenites from the Xiping deposit have a very low content of Re,probably showing a crustal source for the ore-forming materials.The granitic magmatism and mineralization in the QinHang metallogenic belt occur mainly in the Mesozoic,especially Yanshanian-aged,and can be divided into two groups:The first group in the Mid-Late Jurassic (180 ～150Ma),and the second group in the Cretaceous (110 ～80Ma).Combining the tectonic geological evolution,it is proposed that the large-scale magmatism and mineralization in the two stages is probably related to subduction of the Pacific plate.The Xiping Mo-Cu polymetallic deposit formed in the Late Yanshanian lithospheric extensional and thinning environment.