东昆仑冰沟南铜镍矿锆石SHRIMP U-Pb年龄及构造意义

Zircon SHRIMP U-Pb Age of the Binggounan Magmatic Ni-Cu Deposit in East Kunlun Mountains and Its Tectonic Implications

冰沟南镁铁—超镁铁质岩体位于东昆仑造山带西段祁漫塔格岩浆岩带内,邻近昆北断裂,主要由橄榄辉石岩、辉长岩、闪长岩及辉长辉绿岩脉构成,铜镍矿体仅赋存于橄榄辉石岩中。岩体地质特征、岩石地球化学特征及矿体地质特征表明,成矿岩体为铁质系列的基性-超基性岩,岩性为含长橄榄辉石岩。锆石SHRIMP U-Pb同位素测年获得含长橄榄辉石岩年龄为377.8±3.4Ma,为晚古生代岩浆作用的产物,这也是东昆仑造山带目前发现时代较新的岩浆铜镍矿床。岩石Sr-Nd同位素特征表明,(^(87)Sr/^(86)Sr)_i值在0.7057~0.7105之间,变化范围相对较宽,ε_(Nd)(t)值变化在2.35~3.81之间,均为正值。推测矿床形成过程为幔源岩浆上涌过程中,由于地壳物质的加入,伴随着同化混染作用的发生,岩浆中S达到饱和,进而硫化物发生不混溶作用,富含硫化物的岩浆运移至东昆仑造山带邻近昆北断裂构造薄弱的部位成岩成矿。冰沟南铜镍矿床可能是形成于造山后伸展背景,与夏日哈木超大型铜镍硫化物矿床形成时的构造背景不同,本次研究对东昆仑造山带同类矿床的勘查评价工作具有一定指导意义。

The Binggounan mafic-ultramafic intrusion is located in the East Kunlun orogenic belt that belongs to the southwestern margin of Qaidam basin and adjacent to the Kunbei fault. This intrusion is mainly made up of olivine-pyroxenite, gabbro, diorite and diabase dykes, but the orebodies only occur in the olivine- pyroxenite. Petrologic and geochemical characteristics show that the Binggounan mafic-ultramafic intrusion was a ferruginous series mafic-ultramafic intrusive body and the deposit belongs to magmatic segregation sulfide Cu-Ni deposit. The SHPIMP U-Pb age （377.8±3.4 Ma） of the zircons in the olivine-pyroxenite indicates that it is a relatively young Cu-Ni deposit in the East Kunlun orogenic belt. The rocks in the deposit have positive Na（g） values ranging from 4-2. 35 to 4-3. 81 and （SrSr/86Sr）i from 0. 7057 to 0. 7105, indicating that the magma have experienced some contamination of the surrounding rocks which probably led to the sulfur saturation and then the immiscible of the sulfides. The Binggounnan Cu-Ni deposit perhaps is a product in the post-collision tectonic setting, which is different from the Xiarihamu Cu-Ni deposit. Therefore, the study is of significant implication for the exploration of Cu-Ni deposits in the East Kunlun orogenic belt.