东昆仑夏日哈木超大型岩浆镍钴硫化物矿床成矿特征

超大型岩浆镍钴硫化物矿床的形成多与大陆裂谷或地幔柱活动密切相关,是何种机制促使深部幔源金属元素超常富集于东昆仑造山带而形成超大型岩浆镍钴硫化物矿床呢?文章通过剖析夏日哈木岩体及矿体基本特征,发现赋矿岩体整体呈东宽西窄的楔状体,以富集轻稀土元素、贫重稀土元素以及Nb、Ta、Zr、Hf等高场强元素的亏损为特征,镍钴矿体主要富集于辉石岩和橄榄岩中,西段矿石富,东段矿石贫,矿石品位与橄榄石含量呈正相关关系.精细矿物学研究发现,寄主矿物"巨型"斜方辉石所包裹的橄榄石Fo值及Ni含量从核部到边部均增高,揭示含矿岩相侵入过程中可能存在至少2次岩浆活动.由橄榄石和铬尖晶石成分分析,推测夏日哈木母岩浆为低Ti、高Mg的拉斑玄武质岩浆,可能起源于软流圈地幔.结合区域构造演化和岩体形成时代,认为东昆仑夏日哈木镁铁-超镁铁质岩体形成于伸展环境,深部部分熔融形成的岩浆多次脉冲上涌叠加,地壳混染对硫化物达到饱和具有关键作用,于柴达木盆地南缘东昆仑造山带中构造薄弱部位成岩成矿,可能是伴随古特提斯洋演化开始大陆裂解岩浆镍钴成矿响应的表现.该认识对丰富造山带中的岩浆镍钴硫化物矿床成矿理论研究、拓宽岩浆镍钴矿床找矿空间与潜力、支撑并指导区域找矿新突破,具有重要作用.

Metallogenic characteristics of Xiarihamu super-large magmatic nickel-cobalt sulfide deposit in eastern Kunlun Orogenic Belt

The giant magmatic nickel-cobalt sulfides are mostly closely related to the continental rifts or mantle plume.What mechanism promotes the extraordinary enrichment of mantle-derived metal elements in the Eastern Kunlun Orogenic Belt to form the giant Xiarihamu magmatic nickel-cobalt sulfide deposit? We found that ore-bearing Xiarihamu intrusion is a wedge-shaped body that is wide in the East and narrow in the West. The intrusion is characterized by the enrichment of LREE(light rare earth elements) and depletion of HREE(heavy rare earth elements) and HFSE(high-field-strength elements) such as Nb, Ta, Zr and Hf. The nickel-cobalt ore bodies are concentrated mainly in pyroxenite and peridotite. The ore grade in the western section is much richer than that of eastern section. The Ni grade is positively correlated with the olivine content. The Fo value and Ni content of the olivine inclusions within the coarse orthopyroxene increased from both the core and the edge, indicating that at least two magmatic intrusive events occurred. Based on the olivine and chromium-spinel composition, it is speculated that the parent magma of the Xiarihamu is a low Ti and high Mg Tholeiitic magma, which may be derived from the asthenospheric mantle. Combining the regional tectonic evolution and the formation age of the intrusion,it is believed that the Xiarihamu mafic-ultramafic intrusion formed in a post collision extensional environment.The magma formed from mantle partial melting intruded into the crust with multiple pulses and overprint, and the crustal contamination played a critical role during the sulfide saturation process. At last, the giant Ni-Co deposit formed in the weak structural part of the Eastern Kunlun Orogenic Belt on the southern margin of the Qaidam Basin, this may be a response of continental break-up during the opening of the Paleo-Tethys Ocean. This understanding can enrich the theoretical study of magmatic nickel-cobalt sulfide deposits in orogenic belts, broaden the prospecting space and potential of magmatic nickel-cobalt deposits.