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

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。

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

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 stage Ⅱ, the homogenization temperatures range from 231.1 to 294.3 ℃, with salinities of 4.80%-10.49%. And in stage Ⅲ, 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.