西昆仑沃克金矿床地质特征、金的赋存状态及矿床成因探讨

Geological characteristics,gold occurrence state and genesis of Woke gold deposit in West Kunlun

沃克金矿床是西昆仑西段金铜矿带近期发现的一处具有大型远景的金矿床。金矿体主要产于近东西向展布的韧-脆性剪切带中,赋矿岩石为穿切于绢云千枚岩中的石英脉。主要矿化类型为毒砂矿化、黄铁矿化、黄铜矿化,热液蚀变为绢云母化、硬绿泥石化和碳酸盐化。在野外地质勘查与研究的基础上,笔者结合镜下显微观察,将成矿阶段划分为早(S1)、主(S2)和晚(S3)阶段,主阶段形成大量硫化物及方解石石英脉。载金硫化物主要为毒砂,次为黄铜矿、方铅矿。利用电子探针(EPMA)对载金硫化物进行分析,结合单元素面扫描成像,笔者认为金矿石主要以细粒金和中粒金形式存在。流体包裹体显示温度变化范围230~493℃,w(NaCl)_(eq)为1.56%~18.19%,成矿流体具有中高温、中低盐度的特征,表现为NaCl-H_(2)O-CO_(2)体系。石英δ^(18)O值为8.6‰~14.0‰,流体的δD值在−83.7‰~−103.6‰,显示出变质水和大气降水的混合流体来源特征;硫同位素组成显示成矿物质源自中浅变质岩。笔者认为,沃克金矿床为与韧-脆性剪切带有关的中成造山型金矿床。

The Woke gold deposit is found in recent years in the gold-copper belt in the western section of West Kunlun with large-scale resource potential.The gold ore-bodies mainly occur within the nearly East-West trending brittle ductile shear zone.The host rock is quartz vein cutting through sericite phyllite.The mineralization is represented by an assemblage of minerals in quartz vein including arsenopyrite,pyrite and chalcopyrite,with alterations of sericite,chloritoid and carbonates at different stages.On the basis of field geological mapping,systematic optical microscopic observations and EPMA study,the mineralization history of the deposit is simplified into three para‐genetic stages:early stage(S1),main stage(S2)and late stage(S3).In the main stage,a large number of sulfide minerals,quartz and calcite are formed occurring as veins,and gold is mainly hosted in sulfide minerals;the gold bearing minerals are mainly arsenopyrite,and secondly chalcopyrite and galena.Using electron probe microanaly‐sis(EPMA)to analyze gold bearing sulfides,combined with element plane scanning image,it is considered that the gold in the gold ores occurs as micro gold grains distributed in pyrite,arsenopyrite and other sulfides.Fluid in‐clusion study shows a temperature range of 230~493℃and a salinity range of 1.56%~18.19%w(NaCl)_(eq),the ore-forming fluid has the characteristics of medium-high temperature and medium-low salinity,which is repre‐sented by a NaCl-H_(2)O-CO_(2)system.Quartzδ^(18)O value is 8.6‰~14.0‰,and the fluidδD value ranges from−83.7‰~−103.6‰,indicating the source characteristics of mixed fluid of metamorphic water and atmospheric precipitation;The sulfur isotopic composition shows that the ore-forming material comes from medium and low grade metamorphic rocks.The authors believe that the Woke gold deposit is a mesothermal orogenic gold deposit related to the brittle-ductile shear zone.