丫他金矿床流体来源及演化:流体包裹体和稳定同位素证据

Source and Evolution of the Ore-forming Fluid of the Yata Gold Deposit:Evidences from Fluid Inclusions and Stable Isotopes

为探讨丫他金矿床成矿流体的特征和矿床成因,对热液成矿阶段中石英中的流体包裹体进行了岩相学、显微测温、激光拉曼分析以及H、O同位素研究。结果表明,丫他金矿床中存在H_2O包裹体、CO_2-H_2O包裹体和CO_2包裹体三类流体包裹体;其中同一阶段同一视域中富H_2O相CO_2-H_2O包裹体在加热中完全均一到H_2O相,以及富CO_2相CO_2-H_2O包裹体完全均一到CO_2相,它们的均一温度和形成压力基本一致,说明同时捕获了富CO_2和富H_2O两种流体;流体包裹体的H、O同位素组成特征显示,成矿流体主要来源为大气降水或与大气降水有关的盆地流体;热液成矿阶段流体发生相分离,CO_2-H_2O不混溶作用导致热液中Au的溶解度迅速降低并沉淀形成矿床。

In order to discuss characteristics of the ore-forming fluids and metallogenesis of the Yata gold deposit,studies on fluid inclusions in the mineral stage quartz through petrography,micro-thermometry,and Laser Raman Spectra,and hydrogen and oxygen isotopes of the inclusion fluids have been carried out in this paper. Results show that there are three types of fluid inclusions,including H2O inclusions,CO2-H2O inclusions and CO2 inclusions. It is observed that the H2O rich CO2-H2O inclusions was homogenized to the H2O phase,while the coexisted CO2- rich CO2-H2O inclusions was homogenized to the CO2 phase during heating process,with basically similar homogenization temperatures and pressures.This suggests that these CO2- rich and H2O-rich fluids were captured at the same time. The hydrogen and oxygen isotopes of fluid in inclusions indicate that the ore-forming fluid was mainly from meteoric water or basin fluid associated with meteoric water. The unmixing of CO2- rich and H2O-rich phases of the ore-forming fluid resulted in the rapid decrease of solubility of Au complex in hydrothermal fluid and the precipitation of Au-bearing sulfides to form the deposit.