摘要
金川超镁铁质岩体赋存着仅次于加拿大Sudbury和俄罗斯Noril'sk-Talnakh的世界第三大在采铜镍硫化物矿床,岩体以一系列的NE向断层为界分成四个小岩体,由西至东依次为:Ⅲ、Ⅰ、Ⅱ、Ⅳ岩体。Ⅰ号岩体主要由二辉橄榄岩、含辉橄榄岩和橄榄二辉岩构成,橄榄石在各岩相中均为保存较好的主要造岩矿物。本文研究得到金川Ⅰ号岩体上部二辉橄榄岩和含辉橄榄岩中橄榄石的镁橄榄石Fo值介于83.9～85.7,而其Ni含量为1396×10^(-6)～2043×10^(-6),大多低于从S不饱和玄武岩浆中结晶出采的橄榄石的Ni含量。模拟计算结果表明橄榄石较低的Ni含量是因为橄榄石结晶的同时,发生了强烈的硫化物熔离;橄榄石的Fo-Ni关系还因与晶间硅酸盐熔浆的物质交换而发生改变。模拟计算还证明大约有30%的晶间硅酸盐岩浆与橄榄石发生Fe-Mg物质交换反应,导致早结晶橄榄石的Fo值减少了1～1.5。同时,橄榄石较小的Fo值变化表明,在橄榄石结晶和硫化物熔离过程中,不断有新的岩浆贯入和补充。
The Jinchuan ultramafic intrusion at the southwestern margin of the North China Craton hosts the third largest Ni-Cu-(PGE) deposit in the world. The Jinchuan intrusion is divided by several strike-slip faults into four segments, III, I, IT, and IV from west to east respectively. The Segment I of the Jinchuan intrusion is composed mainly of lherzolite, pyroxene dunite and olivine pyroxenite. Olivine is the dominant rock-forming mineral of these rocks. Chemical composition of olivine of the lherzolite and pyroxene dunite in the upper part of segment I have been measured its this study. The forsterite percentages (Fo) of olivine range from 83. 9 to 85.7 and Ni contents vary from 1396 x 10(-6) to 2043 x 10(-6), which are obviously lower than those fractionated from Ni undepleted basaltic magma. Model calculations indicate that olivine fractional crystallization and sulfide segregation occur at the same time during its magma evolution. The compositional variations of olivine may be resulted from its crystallization, sulfide segregation and reaction with trapped liquid. The Fe-Mg exchange reaction between olivine crystals and the trapped silicate liquid (about 30%) results in the Fo of the early crystallized olivine decreasing 1 similar to 1.5. In addition, relatively small variations of the Fo of olivine indicate a continuous injection of fresh magmas into the deeper chamber during olivine fractional crystallization and sulfide segregation.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2009年第12期3369-3378,共10页
Acta Petrologica Sinica
基金
国家自然科学基金(40730420
40573014)
中国科学院"百人计划"项目联合资助
