西藏则不吓铅锌矿床硫、铅同位素组成及对成矿物质来源的指示

Sulfur and Lead Isotopic Compositions of Zebuxia Pb-Zn Deposit in Tibet:Implications for the Sources of Ore-forming Material

西藏则不吓铅锌矿床位于冈底斯成矿带北缘西部,矿体主要赋存于古近系林子宗群典中组火山碎屑岩中。在分析成矿地质条件的基础上,系统地研究该矿床矿石硫、铅同位素组成特征,探讨其成矿物质来源。结果表明,则不吓铅锌矿床金属硫化物样品的δ^(14)s值变化于-0.6‰~2.7‰之间,变化范围较窄,具有明显的塔式分布特征,显示硫来源较单一,具有岩浆硫的特征,可能与区内花岗斑岩及深部相关的隐伏岩体有关。矿石铅的^(206)Pb/^(204)Pb、^(207)Pb/^(204)Pb和^(208)Pb/^(204)Pb同位素比值十分稳定,变化范围较小,具正常铅特征;根据铅同位素μ值(9.61~10.0)和构造演化模式图投图结果,反映该矿床矿石铅主要来自于上地壳物质。结合区域成岩成矿事件和矿区地质特征,认为该矿床成矿物质很可能来源于印亚大陆主碰撞时期上地壳部分熔融形成的中酸性岩浆。

Zebuxia Pb-Zn deposit in Tibet is located in the western part of the north Gangdean metallogenic belt,and it occurs in the Dianzhong Formation of Paleogene.Based on analysis of the metallogenic geological conditions,this paper studies systematically the composition characteristics of sulfur and lead isotope in the ore minerals and discusses the sources of the ore-forming materials.The results have shown that the composition of sulfur isotope in ore sulfides has a narrow variation range from-0.6‰ to 2.7‰ and a tower distribution fea-tures,which indicates relatively concentrate and presents a characteristic of sulfur from magmatic origin,and may be related to the lots of granite porphyry or concealed granite.The lead isotopic composition of ore sulfides is stable and should belong to ordinary lead.According to theμvalues range from9.61 to 10.0 and the tectonic evolution diagram of lead isotopic,it can be concluded that the ore lead mainly derived from upper crust.Com-bined with regional diagenesis-metallogenic event and geological characteristics of Zebuxia Pb-Zn deposit,the ore-forming materials probably came from the magma formed by partial melting of the upper crust in the period of main collisional setting in Tibetan orogenic belt.