海南金昌金矿成矿流体特征及其对矿床成因的制约

Ore-Forming Fluid Characteristics of the Jinchang Gold Deposit in Hainan Island of China and Its Constraint on Ore Genesis

金昌金矿位于海南岛西部戈枕韧性剪切带北东段,属碎裂蚀变岩型金矿。据矿石结构和构造特征及矿物共生组合将热液成矿期划分为早、中、晚三个阶段,且中阶段为金成矿的主要阶段。包裹体岩相学观察显示,早、中阶段原生包裹体以含CO2包裹体为主,晚阶段发育水溶液包裹体。上述三个阶段包裹体均一温度范围分别为280-324℃、211-303℃和147-259℃,盐度范围分别为6.20%-9.98%NaCleq、1.74%-10.73%NaCleq和0.18%-10.11%NaCleq,指示成矿流体以中低温、低盐度为特征。结合包裹体激光拉曼光谱分析,成矿流体属于典型H2O-CO2-NaCl流体体系。利用不混溶包裹体显微测温数据计算得到主成矿阶段包裹体捕获温度为330-360℃,捕获压力为130-150 MPa。综合研究表明主成矿阶段发生的流体沸腾与相分离为金沉淀的主要机制。

Jinchang gold deposit, located at the northeastern end of Gezhen shear zone of western Hainan, is a eataclastic altered rock-host gold deposit. The mineralization in Jinchang can be divided into three stages, based on ore structure and mineral symbiotic combination, with the middle stage Beijing the main stage for Au precipitation.. Petrography study of fluid inclusions shows that the early and middle stages were rich in CO2 fluid inclusions and the late stage was dominated by aqueous fluid inclusions. The homogenization temperature of each stage was 280-324℃, 211-303℃, 147-259℃ while the salinity ranges from 6.20% -9.98% NaCl eqv, 1.74%-10.73% NaCl eqv, 0.18%-10.11% NaCl eqv, respectively. The ore-forming fluid is characterized by medium to low temperature and low salinity. Combined with Laser Raman spectrum analysis, the ore-forming fluid belongs to H2O-CO2-NaCl type. Using isoehore intersection method of immiscible fluid the trapping temperature of the main stage is 330-360℃ while the trapping pressure is 130-150 MPa. Comprehensive research shows that fluid boiling and phase separation due to pressure reducing is the main reason for Au precipitation.