东昆仑夏日哈木镍矿床地质特征与成因

Geological characteristics and genesis of Xiarihamu nickel deposit in East Kunlun

夏日哈木超大型镍矿床位于东昆仑造山带昆中岛弧带内.Ⅰ号含矿岩体主要由橄榄岩相、辉石岩相、辉长苏长岩相等多种岩石类型组成.其中,含矿岩石主要为橄榄岩相、辉石岩相和苏长岩相.矿石构造以准块状-块状、海绵陨铁状和浸染状为主,斑杂状次之,细脉状较少.岩石和矿石的铂族元素（PGE）丰度较低,岩石平均6.45×10^-9,矿石平均456.91×10^-9.岩石和矿石具有相似的PGE配分模式.矿石样品具有高的Ir丰度（0.284×10^-9～1.198×10^-9）,低的Pd/Ir比值（9.12～22.34,平均值16.41）,显示了岩浆型成矿作用特点.铂族元素（PGE）地球化学特征及岩石Ni/Cu-Pd/Ir关系表明,原生岩浆为高镁玄武质岩浆.母岩浆明显亏损PGE,而硫化物的深部熔离可能是导致母岩浆PGE亏损的主要原因.硫同位素特征显示有明显地壳硫的加入.根据铂族元素特征及矿相学、硫同位素特征分析,成矿母岩浆在深部岩浆房分异,为含少量硫化物的岩浆、含较多硫化物的岩浆和矿浆,分阶段脉动式上侵,在上侵过程中和进入终端岩浆房后硫化物继续熔离,是形成夏日哈木镍矿床的主导机制.

The Xiarihamu superlarge nickel deposit is located in the island arc zone in the middle part of the western segment of the East Kunlun orogenic belt. The No. I intrusion is mainly composed of peridotite, pyroxenite and gabbro-norite. The sulfides occur in the peridotite, pyroxenite and norite. Submassive-massive, sideronitic and disseminated sulfide ores are dominant in the orebody besides a little taxitic and veinlet ores. The total con- centrations of platinum-group elements （PGE） in rocks and ores are very low, with their average values being 6.45 ×10^-9 and 456.91 ×10^-9 respectively. Rocks and ores have similar mantle-normalized PGE patterns. The lower Pd/Ir ratios （9.12 -- 22.34, 16.41 on average） and higher Ir content （0.284 ×10^-9 -- 1. 198×10^-9） in ores suggest the magmatic mineralization characteristics. The geochemical characteristics of platinum group elements and the diagram of Ni/Cu versus Pd/Ir indicate that the primary magma was high-MgO basaltic magma. Assuming the primary magma was similar to the continental tholeiite, the simulation result reveals that the parental magma was depleted in PGE obviously. Sulfur isotopic features indicate the obvious addition of the crust sulfur. The characteristics of PGE and ore microscopy as well as features of sulfur isotopes have led the au- thors to believe that the ore-forming parental magma differentiated into magma containing a small amount of sul- fides and magma containing a higher amount of sulfides as well as ore pulp at the deep chamber. After pulsatory invasion and entering the terminal magma chamber, the sulfides continued liquation, which seems to have been the dominant mechanism of the nickel deposit.