CAJ | 학술논문

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F_o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来的橄榄石的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.
금천초미철질암체부존착부차우가나대Sudbury화아라사Noril'sk-Talnakh적세계제삼대재채동얼류화물광상,암체이일계렬적NE향단층위계분성사개소암체,유서지동의차위:Ⅲ、Ⅰ、Ⅱ、Ⅳ암체.Ⅰ호암체주요유이휘감람암、함휘감람암화감람이휘암구성,감람석재각암상중균위보존교호적주요조암광물.본문연구득도금천Ⅰ호암체상부이휘감람암화함휘감람암중감람석적미감람석F_o치개우83.9～85.7,이기Ni함량위1396×10~(-6)～2043×10~(-6),대다저우종S불포화현무암장중결정출래적감람석적Ni함량.모의계산결과표명감람석교저적Ni함량시인위감람석결정적동시,발생료강렬적류화물용리;감람석적Fo-Ni관계환인여정간규산염용장적물질교환이발생개변.모의계산환증명대약유30%적정간규산염암장여감람석발생Fe-Mg물질교환반응,도치조결정감람석적Fo치감소료1～1.5.동시,감람석교소적Fo치변화표명,재감람석결정화류화물용리과정중,불단유신적암장관입화보충.
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 , Ⅱ, 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 in this study. The forsterite percentages (Fo) of olivine range from 83.9 to 85. 7 and Ni contents vary from 1396×10~(-6) to 2043×10~(-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 ～ 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.