东昆仑石头坑德镁铁-超镁铁质岩体矿物学特征及成矿潜力分析

Mineralogical characteristics of Shitoukengde mafic_ultramafic intrusion and analysis of its metallogenic potential, East Kunlun

位于东昆仑造山带之昆中带内部的石头坑德镁铁-超镁铁质岩体,分别由辉长岩相、辉石岩相和橄榄岩相的多种岩石类型组成。野外地质资料表明各岩相间的先后侵位顺序为辉长岩相→辉石岩相→橄榄岩相。本次研究表明石头坑德岩体尖晶石Ni的平均含量为258×10^(-6);橄榄石Fo=81~86,为贵橄榄石,Ni含量471×10^(-6)~2 279×10^(-6),平均为1 153×10^(-6);斜方辉石的En=80.35~83.89,平均82.51。根据Mg-Fe在结晶相橄榄石和熔体之间的分配系数,利用Fo值最高的橄榄石,得到其原生岩浆MgO=10.5%,属高镁玄武质岩浆。该岩体由上地幔橄榄岩11.2%~14.0%的部分熔融作用形成的。通过对石头坑德岩体的部分熔融程度、原生岩浆、构造标志、岩石组合、直接矿化标志及矿物组合、橄榄石Ni含量及Fo的研究表明,石头坑德镁铁-超镁铁质岩体具有形成铜镍硫化物矿床的有利条件,东昆仑造山带是重要的成镍远景区。

Located in the inner zone of the middle part of the eastern Kunlun orogenic belt, the Shitoukengde mafic-uhramafic intrusion is composed of gabbro-lithofacie, pyroxenite-lithofacie and peridotite-lithofacie. Geological data of field indicate that the emplacement order of each lithofacie is gabbro-lithofacie→pyroxenite-litho- facie-→peridotite-lithofacie. This study shows the average content of Ni in spinel is 258 × 10^-6; the olivine crystals are chrysolite with the forsterite content （Fo） ranging from 81 to 86, the content of Ni in olivine is from 471 × 10^-6 to 2 279 × 10^- 6 and the average is 1 153 × 10- 6 ; En of Orthopyroxene is from 80.35 to 83.89, and the average is 82.51. Based on distribution coefficient of Mg-Fe between olivine and melts, the most Fo-rich olivines indicate that the primary magma of Shitoukengde intrusion belongs to high MgO basaltic magma contain- ing about 10.5 % MgO. This intrusion is derived from 11.2 % - 14.0 % partial melting of mantle. The study of partial melting, primary magma, structural sign, rock assemblage, direct mineralized markers and mineral assemblage, Ni-content and Fo of olivine shows that the Shitoukengde intrusion has favorable conditions for the formation of copper-nickel deposit and the eastern Kunlun orogenic belt can be important nickel prospective region.