Characteristics of multiphase sulfide droplets and their implications for conduit-style mineralization of Tulargen Cu-Ni deposit, eastern Tianshan, Xinjiang
新疆东天山图拉尔根大型铜镍矿床硫化物珠滴构造的特征及其对通道式成矿的指示

An unusual multiphase sulfide droplet structure is found in Tulargen large Cu-Ni sulfide deposit, eastern Tianshan,Xinjiang. These droplets, formed by the crystallization of immiscible sulfide liquid, are approximately 5- to 20-mm-sized, and mainly composed of pyrrhotite, pentlandite and chalcopyrite. Field observations show that the droplets, with various geometrical shapes, only occur between sparsely disseminated sulfide and barren pyroxenite. The analyses of 24 sulfide droplets of the Tulargen complex have revealed that the elongated direction of the droplets corresponds with the extended direction of the orebody, which implies that the droplets were reshaped somehow by the magmas during their emplacement up to the middle-upper crust. Accordingly, the shapes of the droplets may imply the ascending paths of the ore-bearing ultramafic silicate melts. Ore microscopy and mineral chemistry studies suggest that the droplets have a geopetal structure with pyrrhotite and pentlandite at the base, chalcopyrite and other Cu-minerals at the top. This feature of metal element distributions may also be applied to massive sulfideore. Moreover, the sulfide droplets have high contents of Te and Bi compared to early crystallized disseminated sulfides, which indicates that trace element- and volatile-rich magmatic melts tend to crystallize at late stage of magma evolvement.