青海省曲麻莱县大场金矿床成矿流体演化:来自流体包裹体研究和毒砂地温计的证据

Ore-forming fluid evolution of Dachang gold deposit in Qumalai County, Qinghai Province: Evidence from fluid inclusion study and arsenopyrite geothermometer

通过详尽的野外调研和室内研究,本文简要总结了大场金矿床的矿床地质特征。结合流体包裹体显微测温和毒砂地温计,认为大场金矿成矿阶段由早到晚可划分为贫矿化石英阶段、石英硫化物阶段、石英辉锑矿阶段、含明金石英阶段和石英方解石阶段共五个阶段,其中前四个阶段分别形成贫矿化石英脉(成矿温度350℃左右,均一温度为280~360℃)、金-石英-硫化物碎裂岩型矿石(成矿温度301℃左右,均一温度为220~280℃)、金-石英-辉锑矿型矿石(均一温度为160~220℃)和明金-石英脉型矿石(均一温度为160~220℃),最晚的石英方解石阶段则使先前形成的四类岩/矿石发生轻微硅化和方解石化蚀变(均一温度小于160℃)。结合流体包裹体激光拉曼光谱分析,认为大场金矿成矿流体经历了早阶段静岩压力系统(成矿压力为215MPa,成矿深度8.1km)下的低盐度H2O-CO2-NaCl体系,中阶段静岩向静水压力过度系统(成矿压力为49~108MPa,成矿深度5.5~8.6km)下的低盐度H2O-NaCl体系,以及晚阶段静水压力系统(估计成矿压力小于40MPa)下的低盐度H2O-NaCl体系。最后认为,大场金矿床的成因类型属于中浅成造山型金矿床。

Local geology of Dachang gold deposit was summarized simply according to detailed fieldworks and indoor researches Based on microthermometic analyses of fluid inclusion, it was considered that metallogenic stages could be divided into poor mineralized quartz, quartz sulfide, quartz stibnite, visible-gold-bearing quartz and quartz calcite ones early and late Poor mineralized quartz veins (metallogenic temperatures are about 350℃, and homogenization temperatures are 280~360℃), native-gold-quartz-sulfide cataclastic ores (metallogenic temperatures are about 301℃, and homogenization temperatures are 220~280℃), gold-quartz-stibnite ores (homogenization temperatures are 160~220℃), and native-gold-quartz veins (homogenization temperatures are 160~220℃), formed respectively in the former four stages, and little silicification and carbonification (homogenization temperature is lower than 160℃) could happen in the above four types of rocks or ores during the latest quartz calcite stage Accompany with Laser Raman spectrum analyses, it was concluded that the metallogenic fluids underwent low salinity H2O-CO2-NaCl fluid system in lithostatic pressure system (metallogenic pressure is 215MPa, metallogenic depth is 81km) in the early stage, low salinity H2O-NaCl fluid system in lithostatic to hydrostatic pressure system (metallogenic pressures are 49~108MPa, metallogenic depths are 55~86km) in the middle stage and low salinity H2O-NaCl fluid system under hydrostatic pressure system (metallogenic pressures may be low than 40MPa) in the latest stage, respectively Finally, the author thought the genetic type of Dachang gold deposit belongs to epizonal to mesozonal orogenic gold deposit