滇西北卓玛Cu--Pb--Zn矿床成矿流体特征

卓玛矿床位于云南香格里拉格咱弧东北部,属斑岩-热液脉型铜多金属矿床。矿体主要赋存于矿区石英二长斑岩内及附近,严格受NW向断裂控制。卓玛矿床的形成经历了黄铁矿-石英(Ⅰ)、黄铁矿±黄铜矿--石英(Ⅱ)、黄铁矿±黄铜矿±方铅矿±闪锌矿-石英(Ⅲ)及贫硫化物-石英-碳酸盐(Ⅳ)四个成矿阶段。通过对各成矿阶段研究样品石英颗粒中的原生流体包裹体进行岩相学、显微测温学及激光拉曼光谱研究,探讨卓玛铜多金属矿床成矿流体特征,结果表明:Ⅰ阶段石英中主要发育富CO_2及气液两相型包裹体;Ⅱ阶段石英中主要发育碳质、富CO_2、含CO_2及气液两相4种类型包裹体;Ⅲ阶段石英中主要发育含CO_2及气液两相型包裹体;Ⅳ阶段石英中主要发育富CO_2、含CO_2及气液两相3种类型包裹体。激光拉曼光谱显示碳质包裹体主要成分为CO_2和CH_4,而CO_2包裹体中除CO_2和CH_4气相成分外,还有部分H_2O。因此,综合研究结果显示卓玛铜多金属矿床成矿流体为中温、低盐度的CO_2--CH_4-Na Cl--H_2O体系热液。成矿过程中,流体温度和盐度数值略有降低趋势,成矿流体的不混溶作用是导致成矿物质大量卸载的关键因素。

Characteristics of fluid inclusions of Zhuoma Cu-Pb-Zn deposit,northwestern Yunnan

Zhuoma Cu-Pb-Zn deposit, located in northeastern Garze arc,Shangrila,Yunnan Province, is a porphyry-hydrothermal vein-type deposit. Ore bodies are mainly hosted in quartz monzonite porphyry and controlled by NW-trending faults. Cu polymetallic mineralization in this deposit consists of four stages of paragenesis, namely (Ⅰ) pyrite-quart, (Ⅱ) pyrite ±chalcopyrite-quartz, (Ⅲ) pyrite ±chalcopyrite ±galena ±sphalerite-quartz and (Ⅳ) barren sulfide-quartz-carbonate. The comprehensive study on petrography, microthermometry and laser Raman of fluid inclusions showed that:CO2-rich and liquid-rich fluid inclusions were observed in stage Ⅰ; C-type, CO2-rich, CO2-bearing and liquid-rich fluid inclusions were observed in stage Ⅱ; only CO2-bearing and liquid-rich fluid inclusions were observed in stage Ⅲ; CO2-rich, CO2-bearing and liquid-rich fluid inclusions were observed in stage Ⅳ. Laser Raman spectrum suggest that the main components of C-type inclusions are CO2 and CH4, while in CO2 inclusions, there are some H2O in addition to CO2 and CH4 in gas phase. Comprehensive research indicates that the ore-forming fluids in Zhuoma deposit are characterized by a medium temperature, low salinity CO2-CH4-NaCl-H2O system of hydrothermal fluids, and the immiscibility of fluids is a key factor leading to the discharging of minerals in mineralization.