江西相山矿田西部牛头山铅锌矿化体硫化物地球化学特征及其地质意义

Geochemical Characteristics of Sulfides from the Niutoushan Pb-Zn Ore Occurrence in the Western Xiangshan Orefield, Jiangxi Province and Their Geological Significances

为探讨江西相山矿田西部牛头山铅锌矿化体的成矿流体性质及矿床成因,采用电子探针(EPMA)及电感耦合等离子质谱(ICP-MS)技术对不同矿化阶段的黄铁矿和闪锌矿进行了微量及稀土元素分析。结果显示,牛头山铅锌矿化体中黄铁矿的Nb/Ta<1,Th/La<1,指示该铅锌矿化溶液相对富Cl;黄铁矿与闪锌矿的Y/Ho、Zr/Hf和Nb/Ta值相差较大,表明从矿化早阶段到晚阶段,矿化流体中有大气降水混入。通过对比区内硫化物与基底变质沉积岩及各类岩浆岩(岩脉)的稀土元素配分型式,结合已发表的岩浆岩(岩脉)年龄数据,推测该铅锌矿化体的成矿物质与区内晚阶段次英安斑岩岩浆密切相关。通过对黄铁矿及闪锌矿的微量元素分析,认为其矿化成因与岩浆热液密切相关,结合矿化物质来源特征,确定该铅锌矿化体成因类型为次火山岩型。

Geochemical characteristics of REE and trace elements of pyrites and sphalerites from different mineralization stages of the Niutoushan Pb-Zn ore occurrence in the western Xiangshan orefield of Jiangxi Province have been studied in this paper by applying EPMA and ICP-MS methods in order to discuss properties of its ore-forming fluid and its genetic type. The results show that Th/La and Nb/La values of pyrites from the Niutoushan Pb-Zn ore occurrence are all lower than 1, suggesting that the Pb-Zn ore-forming hydrothermal fluid is relatively rich in Cl. The relatively large differences between Y/Ho, Zr/Hf and Nb/Ta ratios of pyrites and those of sphalerites indicate that the meteoric water was mixed in the ore-forming fluid from the early stage to the late stage of the Pb-Zn mineralization. By comparative study of REE distribution patterns of sulfides, metamorphic sedimentary rock of the basement, and various types of magmatic rocks(dykes) in the Xiangshan orefield and combination of published dating data of magmatic rocks(dykes) in the Xiangshan orefield, it is inferred that the ore-forming material of the Niutoushan Pb-Zn ore occurrence was closely related to the magma of late stage dacite porphyry in the Xiangshan orefield. Based on the analyses of trace elements of pyrites and sphalerites, it is believed that the genesis of Pb-Zn mineralization of the Niutoushan Pb-Zn ore occurrence is closely related to the magmatic hydrothermal fluid. Combining with characteristics of the ore-forming material source, it is confirmed that the Niutoushan Pb-Zn ore occurrence belongs to the subvolcanic hydrothermal type deposit.