新疆东昆仑达拉库岸镁铁-超镁铁质岩体年代学、地球化学及成矿条件

Geochronology,geochemical characteristics and ore-forming conditions of the Dalakuan mafic-ultramafic intrusion,East Kunlun,Xinjiang

达拉库岸镁铁-超镁铁质岩体位于东昆仑造山带南带之喀拉米兰晚古生代沟弧系,主要由二辉橄榄岩、单辉橄榄岩、橄榄二辉岩、单辉辉石岩和辉长岩组成。辉长岩的锆石U-Pb谐和年龄为244.4±1.5Ma,属于中三叠世。岩石普遍弱富集稀土元素和大离子亲石元素(Rb、Ba、Sr),亏损不相容元素(Nb、Ta)。岩体原生岩浆为高镁拉斑玄武质岩浆(Mg O 11.4%,Fe O10.8%)。元素地球化学和Nd、Sr同位素组成特征表明岩浆源区为富集岩石圈地幔,岩浆运移和侵位过程中遭受不同程度地壳物质的同化混染作用。依据橄榄石组分模拟获得橄榄石结晶过程中母岩浆达到硫饱和,并发生硫化物的熔离作用。从岩体特征、矿石结构、原生岩浆性质、深部硫化物熔离和物探信息等方面综合分析,岩体具有形成岩浆型铜镍硫化物矿床的良好条件。

The Dalaku＇an mafic-ultramafic intrusion is located in the Late Paleozoic Karamilan arc zone,the southern active zone of the East Kunlun. It consists of lherzolite,wehrlite,olivine websterite,clinopyroxenite and gabbro. U-Pb zircon analysis yield an age of244. 4 ± 1. 5 Ma from gabbro,indicates the intrusion emplaced in Anisian of Middle Triassic. Most of the samples are slightly enriched in LREE,moderately depleted in HFSE（ Nb,Ta）. The estimated primary magma for ultramafic rocks is tholeiitic and contains 11. 4%Mg O and 10. 8% Fe O. The characteristics of trace elements geochemical and Nd-Sr isotope indicate the magmatic source is enriched lithosphere mantle,and contamination at different levels is involved as magma migration and emplacement. The sulfide segregation and olivine fractional crystallization occurred almost at the same time during the magma evolution. Comprehensive analysis based on detailed fieldwork,ore texture/structures and sulfide segregation in the deep demonstrates the intrusion is conductive to form magmatic Cu-Ni sulfide deposits.