湘东北正冲金矿床成因:年代学和硫同位素制约  

Genesis of the Zhengchong Gold Deposit in Northeast Hunan—Constraints from Geochronology and In-situ Sulfur Isotope

作　　者：吴华浩 邵拥军[1,2] 刘清泉[1,2] 王智琳[1,2] 张毓策[1,2] 袁梓焜 WU Huahao;SHAO Yongjun;LIU Qingquan;WANG Zhilin;ZHANG Yuce;YUAN Zikun(Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring,Ministry of Education,Central South University,Changsha 410083,Hunan,China;School of Geosciences and Info-Physics,Central South University,Changsha 410083,Hunan,China)

机构地区：[1]中南大学有色金属成矿预测与地质环境监测教育部重点实验室,湖南长沙410083 [2]中南大学地球科学与信息物理学院,湖南长沙410083

出　　处：《黄金科学技术》2023年第2期190-205,共16页Gold Science and Technology

基　　金：国家自然科学基金项目“基性岩浆对金成矿的作用:以江南造山带醴陵金矿田为例”(编号:42272100);湖南省科技创新计划“关键金属资源勘查创新团队”(编号:2021RC4055);湖南省自然科学基金项目“江南造山带正冲金矿床成矿作用机制及其与造山作用的时空耦合”(编号:2021JJ30809)联合资助。

摘　　要：正冲金矿床是湘东北地区典型的金矿床,其矿体受NNE和NW向2组断裂控制,赋存于低变质程度的冷家溪群中,矿床成矿时代和成矿物质来源尚存在争议。借助LA-(MC)-ICP-MS分析方法,对正冲金矿床中含金石英脉中的绢云母进行原位Rb-Sr定年和黄铁矿原位S同位素分析,以确定其成矿时代和成矿物质来源,进而明确矿床成因。绢云母原位Rb-Sr定年结果显示:正冲金矿床的年龄在(219.1±6.0)~(215.8±7.7)Ma之间,黄铁矿的δ^(34)S值(-3.85‰~1.95‰)接近于0,且具有由负值向正值移动的趋势,表明深部岩浆(或幔源物质)可能是正冲金矿床成矿物质的主要来源,有少量地层物质参与成矿。结合矿床地质特征、成矿年代学和硫同位素地球化学特征,认为正冲金矿床形成于印支期陆内造山环境下,属于与深部岩浆活动有关的金矿床。The Zhengchong gold deposit is a typical gold deposit in northeast Hunan.Its orebodies are controlled by NNE and NW trending faults and occur in Lengjiaxi Group with low metamorphism.The oreforming age and the source of ore-forming materials are still controversial.In this study,by using the LA-(MC)-ICP-MS analysis method,in situ Rb-Sr dating of sericite in gold-bearing quartz vein and in situ S isotope analysis of pyrite were carried out to determine the ore-forming age and source of ore-forming materials,so as to clarify the genesis of the deposit.According to the ore-vein interpenetrating relationship of ore-veins and mineral paragenesis,the mineralization can be divided into three ore-forming stages,namely quartz-pyrite-gold stage,quartz-pyrite-arsenopyrite-polymetallic sulfide stage,quartz-calcite stage.Microscopic observation show that sericite in stage 1 and stage 2 had a close intergrow with pyrite/arsenopyrite.In situ Rb-Sr dating of sericite show that the ore-forming ages of stage 1 and stage 2 were(219.1±6.0)Ma and(215.8±7.7)Ma,respectively.Three kinds of pyrite were identified under the backscattering(BSE)image.The pyrite(Py1)in stage 1 is mainly eudedral and medium-coarse-grained,withδ^(34)S ranging from−3.86‰to 1.03‰.The pyrite(Py2)in stage 2 has an euhedral,mesocoarse-grained structure and an obvious core-rim zonation. The core (Py2a) isuniform in the BSE image withδ^(34)S ranging from −1.43‰ to 1.51‰,while the edge (Py2b) has an obviousoscillation zone and other sulfide (galena) inclusions,with δ^(34)S ranging from −3.21‰ to 1.95‰.The δ^(34)S values(−3.85‰~1.95‰) of the three types of pyrite are close to 0 and the negative value moves to positive value,indicating that deep magmatic (or mantle-derived) materials may be the main source of ore-forming materialsin Zhengchong gold deposit,and a small amount of stratigraphic material is involved in the mineralization.Based on the geological characteristics,metallogenic chronology and sulfur isotope geochemistry,We believeth

关 键 词：绢云母Rb-Sr同位素 硫同位素 成矿物质来源 成矿时代 正冲金矿床 江南造山带 

分 类 号：P618.51[天文地球—矿床学]