新疆望峰金矿床流体包裹体地球化学及矿床成因类型

The fluid inclusion geochemistry and mineragenetic type of the Wangfeng gold deposit, Xinjiang, China

西天山东缘的望峰金矿床受胜利达坂韧性剪切带的控制,成矿过程包括早、中、晚3个阶段,自然金和矿石矿物主要形成于中阶段。岩相学、显微测温及单个包裹体成分激光拉曼光谱研究表明,望峰金矿床石英中的流体包裹体有CO_2-H_2O型、纯CO_2型、NaCl-H_2O溶液型和含子晶多相等4种类型。早阶段石英中原生包裹体主要是CO_2-H_2O型,其盐度1.62%～8.03%NaCl eqv.,流体密度0.73～0.89g/cm^3,均一温度为250～390℃,气相成分为CO_2。中阶段石英中的原生包裹体包括了所有4种类.型,其CO_2-H_2O型和NaCl-H_2O溶液型包裹体的均一温度分别为210～340℃和230～300℃,显示了流体沸腾现象的存在。CO_2-H_2O型包裹体的盐度0.83%～9.59%NaCl eqv.,密度0.77～0.95g/cm^3,气相成分为CO_2±CH_4±N_2。晚阶段石英只发育水溶液包裹体,具有较低的盐度(0.35%～3.87%NaCl eqv.)和均一温度(120～214℃)。根据CO_2-H_2O型包裹体估算早、中阶段流体包裹体捕获压力分别为110～300PMa和90～250MPa,成矿深度为9～11km。总体而言,望峰金矿床由低盐度、低密度、富CO_2的变质流体系统形成,流体减压沸腾导致矿质沉淀,属于中深带的造山型金矿系统。

The Wangfeng gold deposit, Xinjiang Uygur Autonomous Region, is controlled by the Bingdaban ductile shear zone in the western end of the western Tianshan Mountain. Its mineralization process is divided into the early, middle and late stages. Ore minerals and native gold are revealed to have mainly formed in the middle stage. Petrographic, microthermometric and laser Raman spectroscopic: studies show that the fluid inclusions in quartz veins include compositional types of CO(2)-H(2)O, pure liquid CO,, NaCl-H(2)O solution, and daughter crystal-bearing. The early-stage quartz only contains primary CO(2)-H(2)O fluid inclusions with salinities of 1.62% similar to 8.03% NaCl equiv., bulk densities of 0.73 similar to 0.89g/cm(3), and homogenization temperatures of 256 similar to 390 degrees C,. Vapor bubbles are composed of CO(2). The middle-stage quartz contains all the four types Of fluid inclusions, of which the CO(2)-H(2)O and NaCl-H(2)O types yielding homogenization temperatures of 210 similar to 340 degrees C and 230 similar to 300 degrees C, respectively, and thus implying that fluid boiling occurred in the middle-stage mineralization. The CO(2)-H(2)O fluid inclusions have salinities of 0.83% to 9.59% NaCl equiv. and bulk densities of 0.77 to 0.95g/cm(3), with vapor bubbles composed of CO +/- CH(4) +/- N(2). Fluid inclusions in late-stage quartz are NaCl-H(2)O solution with low salinities and low homogenization temperatures. Trapping pressures estimated from CO(2)-H(2)O inclusions are 110 similar to 300 MPa and 90 similar to 250 MPa for the early and middle stages, respectively, suggesting that gold mineralization mainly occurred at the depths of 9 similar to 11 km. In general, the Wangfeng gold deposit was originated from a metamorphic fluid-system characterized by low salinity, low density and enrichment in CO(2); and depressurized fluid-boiling caused gold precipitation. Hence the Wangfeng gold deposit is a meso-hypozonal orogenic-type gold system.