青海东昆仑阿斯哈金矿Ⅰ号脉成矿流体地球化学特征和矿床成因

Geochemical Features of Ore-Forming Fluids and Metallogenesis of Vein Ⅰ in Asiha Gold Ore Deposit,Eastern Kunlun,Qinghai Province

阿斯哈金矿位于东昆中隆起带东段,是东昆仑重要的金、铁多金属成矿带。金矿的容矿围岩为印支早期闪长岩和黑云母花岗岩,NNE向和NW向断裂为主要的容矿构造,Ⅰ号脉为该金矿主要的矿脉之一,云煌岩与金矿脉空间关系密切。流体包裹体主要有富CO2三相和气液两相2种类型。流体盐度(w(NaCl))为1.83%～8.13%,流体密度为0.69～0.87g/cm3,成矿温度为155.3～425.6℃。成矿Ⅰ阶段流体为低盐度、富CO2的高温流体;成矿Ⅱ阶段富CO2型和气液两相流体包裹体共存,发生了以CO2逸失为特征的不混溶或沸腾,致使残余流体盐度升高;成矿Ⅲ阶段为气液两相包裹体。激光拉曼光谱分析表明,流体气相成分主要有CO2、CH4、N2。结合氢、氧和硫同位素组成分析认为,成矿流体主要为幔源流体,晚期有大气水的加入。通过等容线图解法估算成矿压力为98～132 MPa,估算成矿深度为8.16～9.58km。通过与典型造山型金矿特征对比,阿斯哈金矿为中成造山型金矿,矿床形成于早印支期陆内造山由挤压向伸展转换时期。

The Asiha gold ore deposit is located in the east part of the middle uplifted basement and granitic belt which is one important gold and ferro-polymetallic metallogenic belt in eastern Kunlun.The Early Indosinian diorite and biotite granite are the main ore-hosting rocks,while the NNE and NW-trending faults are major ore-bearing structures in the mine area.Vein Ⅰ is one of the major auriferous veins,and is closely related to the minette spatially.Fluid inclusions in quartz crystals can be classified into aqueous two-phase and CO2-rich three-phase inclusion.Salinities of fluid inclusions contents of NaCl range from 1.83% to 8.13%,densities range from 0.69 to 0.87 g/cm3,and homogenization temperatures range from 155.3 ℃ to 425.6 ℃.In mineralization stage Ⅰ,fluid inclusions are characterized by low salinity,high-temperature,and CO2-rich.In mineralization stage Ⅱ,CO2-rich fluid inclusions and gas-liquid two-phase inclusions coexist,which show the immiscibility or boiling characterized by CO2 escaping,and resulted in salinity increasing of the residual fluid.Fluid inclusions in mineralized stage Ⅲ are the gas-liquid two-phase inclusions.Charteristics of fluid inclusions,accompanied with H,O,S isotopic compositions,indicates that the ore-forming fluid is mainly mantle-derived and additional meteoric water in the late stage.By analyzing of Laser Raman spectrum,the gas-phase in fluid inclusions chiefly make up of CO2,CH4 and N2.According to the diagram of isochore,the ore-forming pressure can be calculated to almost 98-132 MPa,the ore-forming depth ranges from 8.16-9.58 km.By contrast to other typical orogenic gold deposits,A conclusion can be safely darwn that Asiha gold deposit belongs to the mesozonal orogenic gold deposit,and the gold mineralization occured in the transition period from compression to extension tectonic environment during intro-continental orogenic movement in Early Indosinian.