河南老湾金矿床上上河矿段矿床地质和成矿流体地球化学  

Geology and ore-forming fluid geochemistry of Laowan gold deposit in Tongbai County, Henan Province

作　　者：寇少磊 杜杨松[1] 曹毅[1] 陈建立[2] 史革武 陈金铎[2] 王丽红[1] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]河南省地质矿产勘查开发局第一地质勘查院,河南郑州450001 [3]河南省南阳市桐柏兴源矿业有限公司,河南南阳474700

出　　处：《矿床地质》2016年第2期245-260,共16页Mineral Deposits

基　　金：中国地质调查"河南省桐柏县老湾金矿接替资源勘查(编码:1212011220697)"项目资助

摘　　要：河南桐柏老湾金矿床是桐柏-大别山(北坡)金银成矿带内大型造山带型金矿床之一。文章对该矿床的上上河矿段进行了矿床地质和成矿流体地球化学研究,旨在查明该矿段的流体成矿过程。根据矿脉穿插关系、矿石结构构造、矿物共生组合以及黄铁矿的粒度和晶形,将老湾金矿上上河矿段成矿过程划分为:石英粗粒自形黄铁矿(Ⅰ)、石英细粒半自形-他形黄铁矿(Ⅱ)、石英多金属硫化物(Ⅲ)及石英碳酸盐(Ⅳ)4个阶段。镜下观察显示,矿床中的包裹体类型有含CO_2包裹体(LH_2O+LCO_2+VCO_2)、纯CO_2包裹体(LCO_2+VCO_2)、液相包裹体(LH_2O+VH_2O)及少量含子晶包裹体(LH_2O+VH_2O+S)。第Ⅰ阶段、第Ⅱ阶段和第Ⅲ阶段均可见含CO_2包裹体、纯CO_2包裹体和液相包裹体,有时可见含CO_2包裹体与液相包裹体共存。流体包裹体显微测温结果表明,成矿流体可近似看做中温、低盐度、富CO_2的NaCl-H_2O-CO_2体系,纯CO_2包裹体和液相包裹体所代表的流体可能是由含CO_2包裹体所代表的Na Cl-H_2O-CO_2流体经不混溶形成的,三者在寄主矿物沉淀时,被同时捕获而共存。从第Ⅰ阶段到第Ⅳ阶段,成矿流体温度从303~379℃逐渐降低到138~195℃,盐度w(Na Cleq)从4.07%~9.59%逐渐降低到1.06%~2.74%。在成矿的第Ⅰ阶段成矿流体发生了不混溶作用,而在第Ⅱ阶段和第Ⅲ阶段流体中的CO_2起泡分离再次引发了不混溶作用。从第Ⅰ阶段到第Ⅲ阶段,成矿流体的δ18OH_2O从6.56‰~9.71‰经1.89‰~4.01‰变化到0.08‰,δDH_2O从-78.1‰^-64.2‰经-79.5‰^-76.3‰变化到-72.6‰,表明老湾金矿第Ⅰ阶段成矿流体主要为岩浆热液,第Ⅱ阶段成矿流体中有少量大气降水加入,第Ⅲ阶段成矿流体中大气降水的比例明显加大。The Laowan gold deposit, located in Tongbai County of Henan Province, is one of the large orogenic gold deposits on the northern slope of Tongbai-Dabie Mountain gold and silver metallogenic belt. Ore deposit geology and ore-forming fluids geochemistry studies of this deposit were carried out with the purpose of ascertaining its fluid mineralization process. Based on veins cutting relation, ore texture and structure, mineral assemblage, and pyrite size and crystal form, the authors divided fluid mineralization process of the Shangshanghe segment of the Laowan gold deposit into four stages, i. e., stage Ⅰ of quartz with coarse grained euhedral pyrite, stage Ⅱ of quartz with fine grained subhedral-anhedron pyrite, stage Ⅲ of quartz with polymetallic sulfide, and stage Ⅳ of quartz with carbonate. H_2O-CO_2, pure CO_2, and aqueous inclusions were observed under microscopy, with a few aqueous inclusions that contain daughter salt crystals. The H_2O-CO_2, pure CO_2, and aqueous inclusions were always seen in the first, second, and third stages. Coexisting of the H_2O-CO_2 and the aqueous inclusions could be observed sometimes. Microthermometric data of fluid inclusions indicate that ore-forming fluids were of the Na Cl-H_2O-CO_2 system characterized by middle temperature, low salinity, and CO_2 content. The fluids represented by the pure CO_2 and aqueous inclusions resulted from an immiscible process of NaCl-H_2O-CO_2 fluids represented by the H_2O-CO_2 inclusions. The three types of inclusions were captured at the same time during the host mineral precipitation. Homogenization temperature and salinity of fluid inclusions decreased from 303 ~ 379℃ and 4. 07% ~ 9. 59%Na Cl. eq in the first stage to 138 ~ 195℃ and 1. 06% ~ 2. 74% Na Cl. eq in the fourth stage, respectively. The first fluid immiscible process occurred in the first stage of the mineralization and the second fluid immiscible process occurred in the second and third stages of mineralization owing to CO_2 effervescence of fluids. The values of δ18

关 键 词：地球化学 矿床地质 成矿流体 流体包裹体 不混溶 河南老湾金矿床 

分 类 号：P618.51[天文地球—矿床学]