东天山红石岗镁铁—超镁铁质岩体成因及铜镍成矿潜力

红石岗岩体是新疆东天山铜镍成矿带东段近年来新发现的含铜镍矿化的镁铁—超镁铁质岩体。红石岗岩体由橄榄岩相、辉长岩相和闪长岩相组成,铜镍硫化物主要赋存于辉长岩相和橄榄岩相中。辉长岩中锆石U-Pb定年表明红石岗镁铁—超镁铁质岩体的形成年龄为(280±1)Ma,与东天山其他主要含铜镍矿岩体形成年龄一致。红石岗岩体中橄榄石Fo牌号为82.2～87.3,Ni含量为(1 240～3 470)×10^-6,橄榄石Fo牌号与Ni含量的关系表明岩浆在橄榄石结晶过程存在硫化物熔离,但是模拟计算表明仅橄榄石分离结晶不能使岩浆中硫化物达到饱和。红石岗岩体全岩微量元素特征为轻稀土元素富集,具明显的Nb、Ta负异常,Nb/Yb-Th/Yb图解表明其母岩浆侵位过程中曾经历了10%～20%的地壳物质混染,这可能促使母岩浆中发生硫化物熔离。红石岗镁铁—超镁铁质岩体具有与东天山铜镍成矿带内其他含矿岩体相似的成岩成矿时代、母岩浆特征及硫化物饱和机制,表明红石岗岩体具有形成铜镍硫化物矿床的潜力。

Genesis and Cu-Ni Metallogenetic Potential of Hongshigang Mafic-ultramafic Intrusion in East Tianshan,China

The Hongshigang mafic-ultramafic intrusion, a newly discovered Permian Cu-Ni sulfide-bearing intrusion, is located in the eastern margin of East Tianshan Cu-Ni metallogenic belt, the northern Xinjiang, China. The intrusion is consist of peridotite phase, gabbro phase and diorite phase. The Cu-Ni sulfide is mainly hosted in gabbro phase and peridotite phase. Zircons separated from gabbro yield a concordia age of(280±1)Ma, similar to the ages of other magmatic Cu-Ni sulfide-bearing mafic-ultramafic intrusions in East Tianshan Cu-Ni metallogenic belt. The Fo and Ni contents of olivine crystals from the sulfide-barren samples vary from 82.2 to 87.3 and from 1 240×10^-6 to 3 470×10^-6 respectively, exhibiting a positive Fo-Ni correlation that is consistent with the fractional crystallization of olivine plus removal of small amounts of immiscible sulfide liquid. The Hongshigang intrusive rocks are characterized by light REE enrichment and negative Nb-Ta anomalies. The Nb/Yb-Th/Yb diagram indicates that the parental magmas for Hongshigang intrusion experiences 10%-20% crustal contamination, which should play a major role in triggering sulfide saturation in Hongshigang magma. In addition, the similarities in formation age, parental magma characteristic and sulfide saturation mechanism between Hongshishan intrusion and other known magmatic Cu-Ni sulfide ore deposits in East Tianshan Cu-Ni metallogenic belt, indicate that Hongshigang intrusion has potential to host a sulfide deposit.