延边地区沙金沟金矿床流体地球化学特征及矿床成因研究

沙金沟金矿床成矿过程由早至晚主要分为4个成矿阶段,磁铁矿-石英-钾长石阶段(Ⅰ)、石英-黄铁矿-磁黄铁矿阶段(Ⅱ)、多金属硫化物阶段(Ⅲ)和石英-碳酸盐阶段(Ⅳ),其中Ⅱ阶段和Ⅲ阶段为主成矿阶段。成矿流体类型复杂,主要有含子矿物三相、富CO_2三相和气液二相包裹体。流体均一温度为224℃～478℃,显示为中高温特点;流体盐度为0.62%～53.81%,流体密度为0.61～1.14 g/cm~3,既存在高盐度和中高密度的流体,也存在低盐度和低密度的流体。结合氢氧同位素组成分析,流体以岩浆水为主,晚阶段有大气水加入。Ⅱ阶段流体不混溶和Ⅲ阶段大气水与岩浆水混合是Au沉淀的主要原因。流体性质早阶段为氧化性流体,主成矿阶段为中性和还原流体,晚阶段为弱碱性和弱氧化的流体。估算出沙金沟金矿床成矿深度为5.9～9.7 km,矿床成因类型为中(高)温热液脉型金矿床,按照成矿动力学背景,属中成造山型金矿床。

Study on geochemical characteristics of fluids in Shajingou Gold Deposit in Yanbian Region,and the deposit genesis

The ore-forming process of Shajingou Gold Deposit is mainly divided into four mineralization stages:magnetite-quartz-orthoclase stage (stageⅠ),quartz-pyrite-pyrrhotite stage (stageⅡ),polymetallic sulfide stage (stage Ⅲ) and quartz-carbonate stage (stage Ⅳ),out of which stage Ⅱ and Ⅲ are the main metallogenic stages.The types of ore-forming fluids are complex,mainly composed of daughter mineral-bearing three-phase,CO2-rich three-phase,aqueous and gas two-phase inclusions.The homogeneous temperature of the fluids ranges 224 ℃~478 ℃,indicative of characteristics of medium-high temperature.The salinity of the fluids ranges 0.62 %~53.81 % and the density ranges 0.61~1.14 g/cm3,showing that there are fluids with high salinity and medium-high density and there are also fluids with low salinity and low density.The analysis of H-O isotopic data suggests that the fluids are mainly composed of magmatic water,with atmospheric water mixing in the later stage,and that the unmixing stage Ⅱ fluids and the mixing stage Ⅲ fluids of atmospheric water and magmatic water are the key factor in Au precipitation.It is also concluded that the fluid system is oxidizing in early stage,and is neutral and reductive during the main ore-forming stages,while is weakly alkaline and weakly oxidizing in later stage.The ore-forming depths of the Shajingou Gold Deposit are estimated to be 5.9~9.7 km.Finally,it is determined that the genesis of the Shajingou Gold Deposit is mesothermal(hypothermal) vein-type gold deposit,which belongs to mesozonal orogenic gold deposit according to the metallogenic dynamics background.