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金川铜镍硫化物矿床是仅次于加拿大Sudbury和俄罗斯Noril’sk-Talnakh的世界第三大在采镍矿床。金川岩体主要由含二辉橄榄岩、二辉橄榄岩、斜长二辉橄榄岩和橄榄辉石岩组成,岩相学观察表明主要造岩矿物的结晶顺序为:橄榄石→斜方辉石→单斜辉石→斜长石。为了进一步探讨金川岩体母岩浆成分及其分离结晶过程,本文在前人工作基础上根据主要造岩矿物结晶顺序及其电子探针成分,借助熔浆热力学软件“MELTS”的计算,获得金川岩体更为准确的母岩浆成分为:SiO248.2%,TiO21.00%,Al2O311.3%,FeO12.9%,Fe2O31.30%,MgO12.6%,CaO10.1%,Na2O1.51%,K2O0.72%,NiO0.04%。MELTS模拟计算表明金川岩体母岩浆的分离结晶经历了两个阶段,在深度约为10.9～12.5km的深部岩浆房经历了约5%的橄榄石以及约4%的斜方辉石分离结晶,并伴随硫化物熔离。在重力作用的影响下,橄榄石、斜方辉石和硫化物向下沉降,形成由下至上的分层:橄榄石-斜方辉石-硫化物-硅酸盐熔浆层,橄榄石-斜方辉石-硅酸盐熔浆层和硅酸盐熔浆层。硅酸盐熔浆首先挤出形成贫硫化物的岩体或喷出地表,之后橄榄石-斜方辉石-硅酸盐熔浆被挤入到7.6～9.2km的浅部岩浆房,经重力分异形成金川I号岩体的上部岩相带和II号岩体顶部的含辉橄榄岩。橄榄石-斜方辉石-硫化物-硅酸盐熔浆层最后被挤入金川岩体,并再次结晶出橄榄石、单斜辉石、斜长石,形成金川岩体的主要岩相和硫化物矿体。这些计算结果不仅与野外和室内岩相学观察吻合,也与硫化物熔离过程的最新研究结果相一致。
The Jinchuan copper-nickel sulfide deposit is the third largest nickel-mining deposit in the world after Sudbury in Canada and Noril’sk-Talnakh in Russia. The Jinchuan pluton mainly consists of lherzolite, lherzolite, plagioclase peridotite and olivine pyroxene. The petrographic observation shows that the crystallization order of the main rocks is olivine → orthopyroxene → clinopyroxene → plagioclase. In order to further explore the parent magma component and its crystallization process of Jinchuan granitoid, based on the predecessors’ work, based on the crystallization order of the main rock-forming minerals and their electronic probe components, the calculation of the melt thermodynamic software "MELTS The more accurate parent magmatic components of Jinchuan granulometry are: SiO248.2%, TiO21.00%, Al2O311.3%, FeO12.9%, Fe2O31.30%, MgO12.6%, CaO10.1%, Na2O1.51 %, K2O 0.72%, NiO 0.04%. The MELTS simulation shows that the separation and crystallization of the parent magma in Jinchuan pluton have gone through two stages. In the deep magma chamber with a depth of about 10.9 ~ 12.5km, it experiences about 5% olivine and about 4% separation of orthopyroxene, With sulfide melting. Under the influence of gravity, olivine, orthopyroxene and sulfide subsidence, forming a bottom-up stratification: olivine-orthopyroxene-sulfide-silicate melt layer, olivine-skew Silicate Slurry and Silicate Slurry. Silicate slurries are first extruded to form sulfide-poor rocks or spouted from the earth’s surface. Olivine-orthopyroxene-silicate slurries are then extruded into shallow magma chambers of 7.6-9.2 km and gravitationally Differentially formed the upper lithofacies belt of the Jinchuan I rock mass and the karst peridotite on the top of the No.2 rock mass. The olivine-orthopyroxene-sulfide-silicate melt layer was finally pushed into the Jinchuan massif and olivine, clinopyroxene and plagioclase again crystallized to form the main lithofacies of the Jinchuan massif Sulfide ore body. These calculations are consistent not only with field and indoor petrographic observations but also with recent studies of sulfide flotation processes.