湖南康家湾大型隐伏铅锌矿床成因探讨:流体包裹体、氢氧同位素及硫同位素证据

Genesis of the giant Kangjiawan lead-zinc ore deposit in Hunan Province:Evidences from fluid inclusion,H-O and S isotope

康家湾铅锌矿床位于湖南省水口山矿田,矿体主要产于二叠系当冲组下段泥灰岩、硅质岩与栖霞组灰岩的层间硅化破碎带中。根据矿物组合和穿插关系,可将该矿床的成矿作用过程划分为3个阶段:黄铁矿-石英阶段、闪锌矿-方铅矿(黄铁矿)-石英阶段和方解石-闪锌矿-方铅矿阶段。流体包裹体研究表明,康家湾铅锌矿床黄铁矿-石英阶段的流体主要为中-高温(243~343℃)、中-高盐度(18.4%~33.8%NaCleqv)的流体;闪锌矿-方铅矿(黄铁矿)-石英阶段的流体为中-高温(278~352℃)、中-低盐度(1.1%~20.7%NaCleqv)流体;晚期方解石-闪锌矿-方铅矿阶段的流体为低温(125~191℃)、低盐度(0.2%~6.7%NaCleqv)的流体。其中,闪锌矿-方铅矿(黄铁矿)-石英阶段的流体发生了沸腾作用。激光拉曼分析结果显示,该矿床成矿期的石英和闪锌矿中的液体包裹体气相成分主要为H_(2)O。H-O、S同位素研究显示,康家湾铅锌矿床的成矿流体可能主要来源于岩浆水,并在运移过程中混合了大气水。结合矿床地质、流体包裹体和氢氧、硫同位素特征,流体混合导致温度、盐度降低和沸腾作用可能是导致康家湾铅锌矿床成矿物质发生大规模沉淀的重要因素。

Kangjiawan Pb-Zn deposit is located in the Shuikoushan Pb-Zn-Au ore field of Hunan Province.The orebodies were hosted in the interlayer silicified fracture zone of lower part of Permian Dangchong Formation mudstone,silicalite and Qixia Formation limestone.According to the mineral assemblage and interleaving relationship,the mineralization process of the Kangjiawan Pb-Zn deposit can be divided into three stages:early pyrite-quartz stage,sphalerite-galena(pyrite)-quartz stage and late calcite-sphaleritegalena stage.Microthermometric studies of fluid inclusions show that the fluid in the early pyrite-quartz stage of the Kangjiawan Pb-Zn deposit is mainly medium-high temperature(243~343℃)and medium-high salinity(18.4%~33.8%NaCleqv).The fluid of the sphalerite-galena(pyrite)-quartz stage is medium-low temperature(278~352℃),medium-low salinity(1.1%~20.7%NaCleqv)and has undergone boiling.The fluid in the late calcite-sphalerite-galena stage is low temperature(125~191℃),low salinity(0.2%~6.7%NaCleqv)fliud.Laser Raman spectrum studies of fluid inclusions indicate that components of fluid inclusions in quartz and sphalerite during the mineralization period are mostly H_(2)O.H-O and S isotope geochemistry shows that the ore-forming fluids of the Kangjiawan lead-zinc deposit were mainly derived from magmatic water,which is mixed with atmospheric water during the migration process.Combining the deposit geology,fluid inclusions,and hydrogen,oxygen,sulfur isotopic characteristics,the decrease of temperature,salinity and boiling may be important factors leading to the large-scale precipitation of ore-forming materials in the Kangjiawan Pb-Zn deposit.