右江盆地北山MVT铅锌矿床黄铁矿Re-Os同位素体系及其对定年的启示  

Pyrite Re-Os isotope system of the Beishan MVT Pb-Zn depsoit in the Youjiang Basin and its significance for dating

作　　者：许晓杰 李超[2] 王庆飞[1] 翁玮俊 陈家浩 曾瑜山 XU XiaoJie;LI Chao;WANG QingFei;WENG WeiJun;CHEN JiaHao;ZENG YuShan(State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;National Research Center of Geoanalysis,Beijing 100037,China)

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]国家地质实验测试中心,北京100037

出　　处：《岩石学报》2022年第6期1727-1740,共14页Acta Petrologica Sinica

基　　金：国家重点研发计划项目(2020YFA0714802);广西壮族自治区地质矿产勘察开发局地质勘察项目(201822)联合资助.

摘　　要：密西西比河谷型(MVT)铅锌矿作为一种重要的矿床类型,其成矿时代的精确厘定一直是该类矿床研究的重点。中国西南右江盆地是我国重要的MVT铅锌成矿带,本次研究选取了右江盆地东部北山铅锌矿作为研究对象,对成矿期内黄铁矿开展了LA-ICP-MS微量元素分布分析和Re-Os同位素定年。8件黄铁矿样品Re-Os等时线年龄为443.2±3.3Ma(MSWD=320),明显早于赋矿的泥盆系碳酸盐岩地层,且数据点具有较高的离散性,表明黄铁矿Re-Os同位素年龄不能够有效约束北山Pb-Zn矿床成矿时代。其中,2件黄铁矿样品具有较高的Re含量,分别是107.1×10^(-9)和260.0×10^(-9),结合对应薄片LA-ICP-MS微量元素面扫描分析结果,表明黄铁矿裂隙有机充填物具有较高的Re含量,对黄铁矿Re-Os测试结果存在显著的干扰。年代学结果显示,裂隙较发育的具有较高Re含量的2件黄铁矿样品模式年龄分别为399.0Ma和402.0Ma,这与富含有机质的泥盆系赋矿地层的年代基本一致,初步表明黄铁矿中高Re含量的充填物质可能来自于围岩地层。基于北山Pb-Zn矿床黄铁矿Re-Os定年及硫化物面微量元素分析结果,本次研究认为复杂的矿石结构及其所影响的样品物质不纯是阻碍MVT矿床高精度定年的重要因素。Since the Mississippi Valley-type(MVT)Pb-Zn deposit is one of the most important types of Pb-Zn deposit,and precise dating on mineralization age has always been the research focus on this type of ore deposit.The Youjiang Basin is an important MVT Pb-Zn metallogenic province in southwestern China.We apply LA-ICP-MS trace element mapping analysis and Re-Os isotope dating on ore pyrite from the Beishan Pb-Zn deposit in the eastern Youjiang Basin to probe the feasibility of high-precision dating.Eight pyrite samples yielded an isochron age of 443.2±3.3Ma with an extraordinary high MSWD of 320,which is obviously older than the host rock of Devonian carbonates.Thus,this age can not represent the mineralization time of the deposit.Two pyrite samples show relatively high Re contents of 107.1×10^(-9) and 260.0×10^(-9).LA-ICP-MS mapping on these two samples showed significant high Re signals of organic matter along the fractures of pyrite,which should contribute as a most predominant factor to the failure of Re-Os dating.In addition,model ages of the two high Re samples are 399.0Ma and 402.0Ma,which are broadly consistent with the time of ore-hosting Devonian strata.It is speculated that high Re matter may be sourced from host rocks.This study showed that the complicated microscopic ore textures and the resultant impurities of the samples are the most important unneglectable barriers for the high-precision dating of MVT ore deposit.

关 键 词：北山铅锌矿 右江盆地 黄铁矿Re-Os定年 LA-ICP-MS面扫描 

分 类 号：P597[天文地球—地球化学] P618.42[天文地球—地质学] R618.43[医药卫生—外科学]