甘肃金川铜镍(铂)硫化物矿床中高镁辉绿岩脉的发现及其意义

位于华北板块西缘赋存于超镁铁质岩中的金川矿床,是目前世界第三大镍硫化物矿床.金川铜镍硫化物矿床的原生岩浆问题一直存在着较大的争议,前人通过研究金川铜镍硫化物矿体中的堆晶橄榄岩中橄榄石的成分,从而推导原生岩浆的成分.而作者通过对金川铜镍硫化物矿体内部的基性岩脉深入研究,从另一个角度探究金川铜镍硫化物矿床的原生岩浆成分.通过对岩脉岩相学、主量元素的研究表明金川铜镍硫化物矿体中的岩脉主要是辉绿岩,因其MgO的含量的不同可以划分为高镁辉绿岩和低镁辉绿岩.辉绿岩脉的主量元素和微量元素显示这两类岩脉发生过分离结晶作用.PGE元素特征显示辉绿岩脉和金川矿床是同一期次产物,Pmelts的模拟演化得出本文中辉绿岩脉的液相线矿物橄榄石的牌号为Fo86,与金川矿床发现最高牌号Fo86一致.同时Ol-CATS-Q相图表明JC100925-5样品形成的源区在3GPa以上.多种因素显示这种高镁的岩浆是金川矿区的原生岩浆.

Discovery and significance of high-Mg dolerite in Jinchuan copper-nickel (Pt) sulfide deposits

Located in the western of North China, Jinchuan Cu-Ni sulfide deposits are hosted in the mafic-ultramafic rocks, which is the third largest nickel sulfide deposits in world. The original magma problem of Jinchuan copper-nickel sulfide deposit has been more controversial. Through olivine composition in cumulate peridotite of Jinchuan copper-nickel sulfide, previous studies derive the original magma composition. And author through further research of mafic dikes in Jinchuan ore body, explores original magma of Jinchuan copper-nickel sulfide deposit from another angle. By petrography and major elements study, we find that the dikes mainly are dolerites with different content of MgO. The dolerites can be divided into high magnesium dolerite and low magnesium dolerite. The major and trace elements indicate these two types of dikes occurred fractional crystallization. PGE elements characteristic display dolerites and Jinchuan deposit come from the same period of time. According to the result of the simulation of PMELTS, the liquidus mineral of dolerite JC100925-5 is olivine with Fo86. This is same with olivine (Fo 86) which is the highest Fo fond in Jinchuan deposit. Meanwhile Ol-CATS-Q phase diagram indicates that the sample JC100925-5 formed in 3GPa more. A variety of factors indicate the high MgO magma is original magma of Jinchuan deposit.