新疆东天山土墩铜镍硫化物矿床岩石地球化学和铂族元素特征及其对成矿的指示意义

Rock geochemistry and platinum group elements characteristics of Tudun CuNi sulfide deposit in East Tianshan Mountains of Xinjiang and their metallogenic implications

为了探讨土墩铜镍硫化物矿床的成矿岩浆来源、岩浆演化过程以及硫化物熔离成矿作用,文章对土墩矿区内不同类型的岩石进行了岩石地球化学特征的研究,认为该矿床的成矿岩浆属于拉斑玄武岩浆系列。岩浆在岩浆房和/或侵位过程中存在着分离结晶作用,并且,在其上升演化过程中可能经历了同化混染作用。首次对该矿区内岩石和矿石的铂族元素地球化学特征开展了研究,发现其岩石及矿石具有一致的物质来源;岩石及矿石的PGE总量都较低,配分模式都为左倾富集PPGE的Pt-Pd型。根据Ni/Cu-Pd/Ir图解和地球化学特征,认为土墩岩体的原始岩浆应是低程度地幔部分熔融岩浆,是MgO含量较高的PGE不亏损的玄武质岩浆。根据Cu/Pd值较高,可以推断土墩矿床的成矿母岩浆在演化过程中经历了深部硫化物部分熔离的过程,这可能是导致该矿床PGE明显亏损的原因之一。同时,根据Cr与PGE和Ni的相关关系,认为其母岩浆可能经历了铬铁矿的分离结晶作用,这也许是导致该矿床硫化物发生熔离作用的重要因素。结合Ti/Y-Zr/Y相关图解及东天山区域地质演化史,笔者认为,土墩矿区的成矿镁铁质-超镁铁质岩体是形成于碰撞后的拉张环境。

In this paper, the origin, the evolutionary process of metallogenic magma, the segregation of sulfides and the ore-forming process were studied. Based on geochemical characteristics of different rocks in the Tudun Cu-Ni deposit, the authors infer that the magma belonged to tholeiitic magma series, fractional crystallization occurred in magma chamber and/or during the emplacement process, and there might have occurred assimilation and hy-bridization during the evolution of the ascending magma. In addition, the authors studied geochemistry of platinum group elements in rocks and ores of the Tudun Cu-Ni deposit and wrote the first report. The total con- centrations of PGE in rock and ore samples are low. Rock and ore samples have similar mantle-normalized PGE distribution patterns, suggesting the Pt-Pd type. The diagram of Ni/Cu against Pd/Ir and geochemistry of rocks reveal that the primary magma of Tudun was basaltic magma with high MgO content, without depletion of platinum group elements. The relatively high Cu/Pd ratios imply that partial segregation of sulfides occurred in the initial magmatic evolution process, resulting in the depletion of parental magma in PGE. According to the relationship between Cr, PGE and Ni, the fractionation of chromite was likely the main factor leading to sulfide segregation. The diagram of Ti/Y against Zr/Y and the regional geological revolution show that Tudun orebearing mafic-ultramafic rocks occurred in an erosion environment after collision.