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    滇西北安乐铅锌矿床成因：来自闪锌矿原位主微量元素和硫同位素的证据

    Genesis of the Anle lead−zinc deposit in northwestern Yunnan Province: Evidence from in-situ sulfur isotopic and trace elements of sphalerite

      摘要
    • 摘要:
      研究目的 滇西北香格里拉安乐铅锌矿床赋存于上寒武统碳酸盐岩夹碎屑岩建造中，目前对其矿床成因认识不清。
      研究方法 结合地质调查及显微组构特征分析，利用闪锌矿原位硫同位素、主量和微量元素组成特征来示踪其成矿流体来源，探讨矿床成因。
      研究结果 结果表明，安乐铅锌矿床具有上部层状、下部（网）脉状矿体和多层叠置的矿化分布特征，矿石具有块状、角砾状、条带状、浸染状和（网）脉状构造，并表现出喷口相、近端相和远端相的空间分带性，热水喷流沉积成矿特点明显；角砾状、块状和条带状矿石中闪锌矿呈他形产出，以富集Mn、In、Cd、Fe和贫Co、Ni、Cu为特征；其δ34SV-CDT值在−0.8‰~10.57‰之间，结合Cd/Fe、Cd/Mn值及Ge含量变化，成矿流体硫来自海水硫酸盐的还原作用，可能有岩浆热液的参与；闪锌矿的Fe、Zn含量，Ge/In、Ga/In、Ga/Ge值，以及lg(Ga/Ge)–T图解指示，其形成于160~220℃的中低温条件。
      结论 安乐铅锌矿床应属SEDEX型矿床，不排除岩浆热液的成矿贡献。该研究结果大大拓展了本矿区及邻区的勘查找矿空间，也为区域地质演化研究提供了新的信息。

       

      Abstract:
      Objective The Anle lead−zinc deposit in Shangri−La County, northwestern Yunnan Province, SW China, occures in the Upper Cambrian carbonate rock formation interbedded with clastic rocks, and the genesis of this deposit remains unclear.
      Methods  Based on geological investigation and microfabric analysis, the origin of ore-forming fluid is traced by in-situ sulfur isotopic, major and trace elemental compositions of sphalerites, and the ore genesis was discussed.
      Results The results show that the Anle lead−zinc deposit Based on geological investigation and microfabric analysis, the origin of ore-forming fluid is traced by in-situ sulfur isotopic, major and trace elemental compositions of sphalerites, and the ore genesis was discussed. The orebodies show the ore textures of massive, brecciated, banded, disseminated, and veinlet in shape, respectively, and present obvious spatial zonation of vent facies, proximal facies and distal facies ores, which is typical of a subseafloor sedimentary exhalative deposit. Sphalerites in brecciated, massive and banded ores are all anhedral, characterized by enrichment in Mn, In, Cd, and Fe, and depletion of Co, Ni, and Cu. The δ34SV−CDT values of the sphalerite range from −0.8‰ to 10.57‰. Combined with the variations in the ratios of Cd/Fe, Cd/Mn, along with Ge content, the sulfur in the ore−forming fluids may originates from the reduction of sulfate in paleo−seawater, and involved influx of a magmatic−related hydrothermal solution. The Fe and Zn content, Ge/In, Ga/In, and Ga/Ge ratios, along with lg(Ga/Ge) −T diagram plot of sphalerites indicate that it is formed under the medium and low temperature condition of 160~220℃.
      Conclusions Therefore, the Anle lead−zinc deposit is inferred to be a sedimentary exhalative (SEDEX) -type deposit, and the mineralization contribution of magmatic hydrothermal fluids cannot be excluded. This result significantly expands the exploration space of this orefield and its adjacent areas, and also provides a new insight into understanding the regional geological evolution.

       

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