西天山乌拉根大规模铅锌成矿中H_2S成因:菌生结构和硫同位素组成约束

Origin of H_2S in Uragen large-scale Zn-Pb mineralization,western Tien Shan: bacteriogenic structure and S-isotopic constraints

乌拉根铅锌矿是中国西北地区目前探明金属量最大的铅锌矿床,但大规模成矿所需H2S的成因方式尚不清楚。在野外调查和矿相学观察基础上,论文通过场发射扫描电镜（FESEM）、能谱（EDS）和质谱（MS）观测分析表明,矿石中发育闪锌矿纳米莓球、丝/管状结构,它们由他形闪锌矿微晶集合而成,莓球直径30~700nm,丝/管状结构与莓球密切共生;常见与闪锌矿等矿石矿物共生的方解石纳米莓球结构,由他形方解石微晶集合而成,莓球直径20~800nm;也常见与矿石矿物共生的菱铁矿微米莓球、丝/管状结构,它们由他形菱铁矿微晶集合而成,莓球直径1~3μm,表面毛糙,丝/管状结构常出现在莓球周围并连接着莓球。这些纳/微米莓球在矿石中成群落不均匀分布,属细菌微生物成因,丝/管状结构为胞外聚合物的表现。矿石δ34SCDT变化大且显著偏负值（-27.9‰~15.0‰）。乌拉根大规模铅锌硫化物成矿所需H2S可能主要通过细菌硫酸盐还原（BSR）产生,盆地流体中烃类有机质催化下的细菌微生物硫酸盐还原反应是乌拉根铅锌大规模成矿的重要过程。

The Uragen is the largest Zn-Pb ore deposit proven in northwestern China so far,but the origin of H_2S needed during the large-scale Zn-Pb mineralizations is unclear. Based on the field survey and ore microscopy observations,the further observations,measurements and analysis of the ores by FESEM,EDS and MS have been carried out in the paper. It is often occurrence of sphalerite nano-sized spherical and filamentous / tubular structures constructed by xenomorphic micro-fine grain of sphalerite in the Zn-Pb sulfide ores,the sphalerite spherulite is about 30 ~ 700 nm in diameter,and the filamentous / tubular structures show a close paragenesis relationship with the sphalerite spherulite. The calcite nano-sized spherical structures,which paragenating with the ore minerals such as sphalerite,are often observed in the ore,they are consisted of xenomorphic micro-grain of calcite and about 20 ~ 800 nm in diameter.The siderite micron-sized spherical,filamentous / tubular structures,which paragenating with the ore minerals,are also observed in the ore,constructed by xenomorphic micro-fine grain of siderite,the siderite spherulite is about 1 ~ 3μm with unsmooth surface,the siderite filamentous / tubular structures often occur around and connect the siderite spherulite. These nano / micron-sized spherical caused by the bacteria microorganism,are not evenly distributed as communities in Zn-Pb sulfide ores. The filamentous / tubular structures are the performances of the extracellular polymeric substances（ EPS）. The ore δ34SCDTwidely varied with evident negative value（ ranges from-27. 9‰ to 15. 0‰）. The H_2S needed in the large-scale Zn-Pb mineralization might originate mainly through bacteria sulfate reduction（ BSR）. The reaction of bacteria sulfate reduction under the catalyzing of hydrocarbon organic matter in the basin fluids might be an important process of Uragen large-scale Zn-Pb mineralization.