青海省巴斯湖铅锌矿床M9矿体成因探讨——流体包裹体和H-O-S同位素约束

Genesis of M9 Ore Body of Basihu Pb-Zn Deposit in Qinghai Province:Constraints of Fluid Inclusions and H-O-S Isotopic Evidences

巴斯湖铅锌矿床位于三江多金属成矿带北段的青海省沱沱河地区,M9铅锌矿体赋存于下二叠统九十道班组碎裂蚀变灰岩和泥晶灰岩中,主控矿构造为切割地层的NWW向断裂构造。成矿过程分为石英-黄铁矿阶段(Ⅰ)、石英-重晶石-多金属硫化物阶段(Ⅱ)和碳酸盐-石英阶段(Ⅲ)3个阶段。成矿流体包裹体以气液两相为主,成矿Ⅰ阶段均一温度为315.1~365.9℃,盐度(w(NaCl))为8.81%~11.46%;成矿Ⅱ阶段均一温度为231.1~294.3℃,盐度为4.80%~10.49%;成矿Ⅲ阶段均一温度为155.1~233.7℃,盐度为2.41%~6.88%。成矿流体为典型的中温、低盐度流体,均一温度和盐度从成矿早期到晚期逐渐降低。H-O同位素数据显示成矿流体为岩浆水和大气水的混合水,早期主要为岩浆水,晚期有大气降水的混入;S同位素数据显示成矿物质来源与新生代深部钾质岩浆活动有关。巴斯湖铅锌矿床M9矿体成因类型为中温热液脉型,形成于印度-欧亚板块晚碰撞造山作用引起的伸展环境。

Basihu Pb-Zn deposit is located in Tuotuohe area of Qinghai Province in the northern part of Sanjiang polymetallic metallogenic belt.The M9 Pb-Zn ore body is hosted by the cataclastic alterated limestone and micrite of the Lower Permian Jiushidaoban Formation,and the main ore-controlling structure is the NWW trending fault that cuts through the formation.The mineralization process can be divided into three stages:Quartz-pyrite stage(Ⅰ),quartz-barite-polymetallic sulfide stage(Ⅱ),and carbonate-quartz stage(Ⅲ).The ore-forming fluid inclusions are dominated by gas-liquid two-phase fluid inclusions.The homogenization temperatures of fluid inclusions in stage I range from 315.1 to 365.9℃,with salinities(w(NaCl))of 8.81%-11.46%.In stageⅡ,the homogenization temperatures range from 231.1 to 294.3℃,with salinities of 4.80%-10.49%.And in stageⅢ,the homogenization temperatures range from 155.1 to 233.7℃,with salinities of 2.41%-6.88%,indicating a typical medium temperature and low salinity fluid.The temperature and salinity decreased gradually from early to late mineralization.The H-O isotope data show that the mineralizing fluid was a mixture of magmatic water and meteoric water,mainly magmatic water in the early stage and mixed with meteoric water in the later stage.The S isotope data indicate that the ore-forming material source was related to the deep potassium magmatic activity in Cenozoic.The genetic type of M9 ore body in Basihu Pb-Zn deposit was a mesothermal hydrothermal vein type,and was formed in an extensional environment related to the late stage of the intracontinental orogenesis resulting from the India-Asia collision.