甘肃金川Ⅱ号岩体橄榄石成因探讨  

Petrogenesis of olivine from the Segment Ⅱ of the Jinchuan intrusion in the Jinchuan mine in Gansu Province, NW China

作　　者：索文德 康健[2,3] 艾启兴 宋谢炎 SUO Wen-de;KANG Jian;AI Qi-xing;SONG Xie-yan(Jinchuan Group Co.Ltd.,Jinchang 737102,China;State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550081,China;University of Chinese Academy of Science,Beijing 100049,China)

机构地区：[1]金川集团股份有限责任公司,甘肃金昌737102 [2]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵州贵阳550081 [3]中国科学院大学,北京100049

出　　处：《矿物学报》2022年第3期376-386,共11页Acta Mineralogica Sinica

基　　金：国家自然科学基金项目(编号:41630316,41772067)。

摘　　要：金川是世界第三大在采岩浆铜镍硫化物矿床,其成因备受中外地质学家的关注。金川岩体被一系列北东-东向左行平移断层自西向东依次划分为Ⅲ、Ⅰ、Ⅱ、Ⅳ等4个岩体。金川岩体主要由硫化物纯橄岩、二辉橄榄岩、橄榄辉石岩组成,边缘断续分布少量斜长石二辉橄榄岩和辉石岩。金川最大的1号矿体产于Ⅱ号岩体的中心,呈现出由中间硫化物纯橄岩向两侧浸染状的二辉橄榄岩和橄榄辉石岩过渡的对称式岩相分布。电子探针分析结果显示,金川Ⅱ号岩体橄榄石Fo值在79.7%~83.9%之间变化,w(Ni)为959×10^(-6)~2060×10^(-6),大多低于从硫不饱和玄武岩浆中结晶出的橄榄石Ni含量。模拟计算表明金川岩体母岩浆为高MgO玄武岩浆(w(MgO)=10%~13%,w(FeO)=11.5%~12.5%)。橄榄石Ni含量偏低的原因是橄榄石结晶的同时发生了硫化物熔离,橄榄石与硫化物的质量比值约为40﹕1。硫化物纯橄岩和二辉橄榄岩中橄榄石的Ni含量及其与Fo值的相关性都存在显著的区别,暗示它们可能是从Ni含量不同的母岩浆中结晶出来的。同时,硫化物纯橄岩中橄榄岩经历了与硫化物熔体的Fe-Ni交换,而二辉橄榄岩中的橄榄石经历了与硅酸盐熔体的Mg-Fe交换。The giant Jinchuan magmatic sulfide deposit in China is the third largest mining deposit in the world. Its genesis has attracted the attention of many geologists. The Jinchuan intrusion was divided into four segments, named Segment Ⅲ,Ⅰ, Ⅱ and Ⅳ from west to east, by a series of NEE-trending left-lateral strike-slip faults. It consists mainly of sulfide-bearing dunite, lherzolite, and olivine pyroxenite, with a small amount of plagioclase lherzolite and pyroxenite discontinuously distributed in its margin. The largest No.1 orebody of the Jinchuan deposit is hosted in the center of the Segment Ⅱ. From center to margin of the Segment Ⅱ, rock types are systematically transitioned from sulfide-mineralized dunite, to lherzolite,and olivine pyroxenite. The EPMA analytical results display that Fo values and Ni contents of olivines of the Segment Ⅱare changed from 79.7 to 83.9 and from 959 ppm to 2060 ppm, respectively. Ni contents of olivines of the Segment Ⅱ are mostly lower than those of olivines crystallized from the sulfur-unsaturated basaltic magma. Model calculation results indicate that the parental magma of the Jinchuan intrusion was a high-MgO basaltic magma which containing about 10%-13% of MgO and 11.5%-12.5% of FeO. The relatively low Ni contents of olivine crystals could be caused by the sulfide segregation at the time of olivine crystallization from the basaltic magma with about 40:1 for the mass ratio of olivine to sulfide. The Ni contents and their correlations with Fo values of olivines in sulfide-bearing dunite and lherzolite are significantly different, suggesting that olivines of the sulfide-bearing dunite and lherzolite could be crystallized from different parental magmas with different Ni contents. Meanwhile, olivines in the sulfide-bearing dunite had experienced the Fe-Ni exchange reaction with sulfide melt, while olivines in the lherzolite had experienced the Mg-Fe exchange reaction with silicate melt.

关 键 词：金川超镁铁质岩体 岩浆铜镍矿床 橄榄石 母岩浆 硫化物熔离 

分 类 号：P611[天文地球—矿床学] P595[天文地球—地质学]