新疆中天山东部彩霞山铅锌矿床稳定同位素特征及成因探讨

Stable isotope geochemistry and ore genesis of Caixiashan Pb-Zn deposit at eastern Middle Tianshan, Xinjiang

彩霞山铅锌矿床是卡瓦布拉克—星星峡中天山地块铅锌成矿带中发育的唯一大型矿床。矿体赋存于青白口纪卡瓦布拉克组第一岩性段的碎屑岩—碳酸盐岩建造中,受构造控制,呈似层状、透镜状产于顺层破碎带及糜棱岩中,近东西向展布,南倾,倾角为65°-80°,与矿区断裂及地层产状一致。通过碳、氢、氧、硫和铅同位素分析可知：成矿热液及挥发分主要来源于岩浆热液,在与围岩碳酸盐岩发生反应时,交代溶解碳酸盐岩并在成矿过程中形成新生方解石和石英;成矿所需的硫主要来自海水硫酸盐的有机还原及细菌还原作用;铅同位素显示成矿物质主要来自岩浆源,与海西期岩浆活动关系密切,并同化了围岩中的铅。其成矿机理为岩浆热液携带了大量的挥发分和成矿物质,构造导通岩浆热液,使之在构造破碎带中与围岩发生反应,溶解围岩碳酸盐岩并与围岩中的硫结合,形成铅锌矿化;彩霞山铅锌矿床为一受构造控制的中温岩浆热液型矿床。

Caixiashan is the largest Pb-Zn deposit in the Kawabulake-Xinxinxia Middle Tianshan massif. Ore bodies are hosted in the first member of early Neoproterozoic Kawabulake group, which comprises elastic rocks and carbonatites. The deposit is well controlled by the near EW structures with stratoid and lenticular ore bodies dipping 65°-80°to the south. The ore bodies are distributed in the faults and mylonites. C--O--H isotopes indicate that the fluid and volatile are mainly from magrnatic source, then react with carbonatites and dissolve the carbonates, and at last form new calcite and quartz. Sulfur isotope displays that sulfur mainly originate from sulfate-reduction of sea water. Lead isotope reveals thatit is mainly provided by magmatic fluid and contaminated by the wall-rock lead. The ore-forming mechanism describes that magmatic fluid carries considerable volatile matter and metals; when it travels trough fault-induced channel and encounters with the carbonate-rich wall rock, the metals combine with the sulfur from the wall rock and precipitate. Based on the characteristics of ore deposit geology and isotope geochemistry. Caixiashan Pb-Zn deposit is a structure-controlled magmatic hydrothermal deposit.