甘肃金川II号岩体岩浆演化及铜镍硫化物成矿过程探讨

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	甘肃金川II号岩体岩浆演化及铜镍硫化物成矿过程探讨
其他题名	Magmatic evolution and the formation of Ni-Cu sulfide ore bodies in Segment II of the Jinchuan intrusion
	李士彬
	2008-09-07
学位授予单位	中国科学院地球化学研究所
学位授予地点	地球化学研究所
学位名称	博士
关键词	岩浆ni-cu-pge硫化物矿床金川矿床 (1)、(2)号矿体岩浆演化过程硫化物熔离 S的饱和机制二次硫化物熔离
摘要	金川矿床是超大型岩浆 Ni-Cu-PGE 硫化物矿床，它赋存有世界第三的镍储量（5.45×106 t，Ni 的平均品位为 1.2%）。该矿床位于华北板块西侧阿拉善地块西南边缘龙首山隆起中。本论文以金川矿区的 II 号岩体为研究对象，在系统整理前人工作的基础上，通过深入细致的野外地质考察和系统采样，选取有代表性的样品，进行详细的显微镜鉴定，并运用元素地球化学等手段，对 II 号岩体的源区特征、岩浆演化过程及其赋存的⑴、⑵号矿体的成矿机制等主要矿床学问题进行了系统成因研究，并尝试提出了二次硫化物熔离成矿模式。本论文主要取得以下几点结论性成果： 1）岩浆起源：起源于上地幔尖晶石－石榴石二辉橄榄岩过渡地带的下部。通过上地幔源岩的柱状部分熔融模式（≥25%）或三角部分熔融模式（10～15%），形成富PGE的S不饱和原始岩浆。 2）地壳同化混染：地壳物质的同化混染主要是由早期下地壳物质的同化混染和晚期上地壳物质的同化混染组成的多阶段同化混染，并且其成分为富钙质围岩。 3）结晶分异演化：金川II号岩体作为橄榄石堆积相，其橄榄石的结晶主要发生在上地壳深部岩浆房，而橄榄石与熔浆的反应及辉石和斜长石的结晶则主要发生在浅部岩浆房，既现今岩体所在位置。 4）S 的饱和机制：岩浆通道内下地壳物质的同化混染，导致岩浆硫饱和，并于岩浆通道中发生了第一次硫化物熔离；上地壳深部岩浆房中地壳物质的同化混染和橄榄石的分离结晶，促使硫饱和的母岩浆发生了第二次硫化物熔离。 5）深部岩浆房的演化：上地壳深部岩浆房中橄榄石分离结晶与硫化物熔离之后，在重力分异作用下，形成了自上而下的硅酸盐岩浆、橄榄石“晶粥”、含硫化物熔体的橄榄石“晶粥”以及矿浆的四层分层格局。同时，底部部分硫化物熔体发生了Pt合金（Pt-Fe）的脱离。 6）侵入期次：上地壳深部岩浆房中，母岩浆分异演化早期，其顶部含有尚未完全成长橄榄石颗粒的“晶粥”在构造应力挤压下首先上侵、成岩形成金川II号岩体顶部、呈“上悬体”的中细粒含辉橄榄岩；分层格局形成之后，橄榄石“晶 VI 粥”、含硫化物熔体的橄榄石“晶粥”以及矿浆依次上侵成岩、成矿，分别形成金川 II 号岩体上部的二辉橄榄岩相、⑴、⑵号矿体的主体以及⑵号矿体底部的块状矿石。
其他摘要	The Jinchuan deposit is one of the largest Ni-Cu-PGE sulfide deposit in the world，and it contains more than 5.45 million metric tons Ni with an average grade of ore 1.2%. It is located in Longshoushan uplift on the southwest margin of the Sino-Korea platform. Based on previous studies, the systematic field investigation and sampling, we have chosen typical samples and carried out the systematic microscopic observation. Meanwhile, applied with the tool of geochemistry, the dissertation has systematically discussed on the origin of primary magma, magmatic evolvement and the mechanism of mineralization of orebody ⑴ and ⑵. Finally, a genetic model for the second sulfide segregation of the deposit was proposed. Some important conclusions are obtained in the dissertation as follows: 1) The origin of primary magma. Studies have indicated the primary magma of the Jinchuan deposit is S-undersaturated and PGE-rich silicate magma, and was generated by partial melting in columnar melting regime (≥25% ) or triangular melting regime (10～15%) in the spinel-garnet lherzolite transition zone in the upper mantle. 2) Crustal contamination. The crustal contamination is multiple-stage contamination, including contamination of the lower and upper crusts. 3) Fractional crystallization. The fractional crystallization of olivine happened in the staging chamber in the upper crust, and the reaction of olivine with silicate magma, the pyroxene and plagioclase crystallization occurred in the shallower chamber in the upper crust. 4) S saturation mechanism. The contamination of the lower crust in magma conduits induced S saturation of silicate magma and subsequently occurred the sulfide segregation in magma conduits. Moreover, the crustal contamination and the fractional crystallization of olivine in the staging chamber in the upper crust resulted in further extensive sulfide segregation. 5) Evolution in the staging chamber. After sulfide segregation and the fractional crystallization of olivine, the gravity settling of sulfide droplets and olivine VIII crystals gave rise to sulfide-olivine-magma stratification. There formed silicate magma, olivine mushes, sulfide-bearing olivine mushes and pure sulfide liquid from top to bottom in the staging chamber. Meanwhile, Pt alloy (Pt-Fe) separated from sulfide melts in the base of staging chamber. 6) Injection of the mushes. In the early evolution stage of parental magma, sulfide-barren mushes bearing undergrown olivine crystals from the upper parts of the staging chamber in the upper crust were injected into Jinchuan planar fractures. After forming stratified structure, the olivine mushes, sulfide-bearing olivine mushes and pure sulfide liquid in the staging chamber were respectively extracted sequentially from top to bottom and emplaced to form the Jinchuan deposit.
页数	171
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/3406
专题	研究生_研究生_学位论文
推荐引用方式 GB/T 7714	李士彬. 甘肃金川II号岩体岩浆演化及铜镍硫化物成矿过程探讨[D]. 地球化学研究所. 中国科学院地球化学研究所,2008.

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