东天山图拉尔根大型铜镍硫化物矿床的斜长石主量成分特征：对矿床成因的指示

图拉尔根镍铜矿床产于康古尔塔格-黄山韧性剪切带NEE向的次级挤压破碎带上,位于黄山-镜儿泉岩浆铜镍成矿带的东段。矿田范围内有I、II、III号3个镁铁质-超镁铁质杂岩体,主要铜镍矿体就位于I号基性-超基性杂岩体内。该杂岩体主要包括辉长岩、角闪橄榄岩、二辉橄榄岩、角闪辉橄岩等岩相,其中角闪橄榄岩为主要的赋矿岩相。本文通过对矿物颗粒镜下形态、结构、构造的观察,对钻孔中赋矿岩相、不含矿岩相的斜长石进行系统的成分分析和对比,来进一步限定岩浆的演化及矿床成因。图拉尔根矿床中主要造岩矿物的结晶次序为:橄榄石-辉石(角闪石)-角闪石。仅见极少数斜长石颗粒包裹橄榄石,而与辉石和角闪石没有明显的包裹关系,可能是略晚于橄榄石结晶的另一单独结晶序列的矿物。赋矿的角闪橄榄岩中斜长石与硫化物含量呈负相关性。斜长石中SiO2和Al2O3含量相对集中,CaO、Na2O、K2O含量变化范围大。SiO2含量从深部到浅部,表现出含量从低到高变化的趋势,说明岩体中斜长石受同源岩浆结晶分异作用的控制。越靠近富硫化物的角闪橄榄岩,斜长石中CaO和Al2O3含量越高,SiO2、Al2O3、CaO、Na2O、K2O等主量元素的含量变化范围较大。因此,斜长石的主量成分可以作为接近硫化物富矿体的指示。

Mineral characteristics and mineralization of the Tulaergen magmatic Ni-Cu sulfide deposit, Eastern Tianshan: Constraints from major oxides compositions of plagioclase

Abstract: The Tulaergen magmatic Ni-Cu sulfide deposit, located in the east part of the Huangshan-Jingerquan Cu-Ni mineralization belt, is controlled by the NEE-trending secondary crushing squeeze belt of the Kangguertage-Huangshan ductile shear zone. There are three mafic-ultramafic intrusions which are named No. I, II, and III complexes in the Tulaergen ore field, respectively. Orebody No. I, distributed in the No. I mafic-ultramafic intrusion, is the primary orebody of the Tulaergen deposit. Gabbro, hornblende peridotite, lherzolite and hornblende lherzolite are major rock units in the intrusion. Hornblende peridotite is the main host rock of orebody. The alteration of ultramafic rocks is intensive on the surface, and crustal contamination of the rocks from boreholes is common. In this paper, we observe the shape, structure and texture of silicate minerals, compare the component of plagioclase from sulfide-bearing and sulfide-poor ultramafic rocks, in order to reveal the magma evolution and mineralization. The results show that the crystallization order of major silicate minerals is olivine-pyroxene/hornblende- hornblende. Olivine is anhedral to subhedral and commonly enclosed in large clinopyroxene, orthopyroxene and hornblende crystal, while barely enclosed in plagioclase. So we consider that plagioclase may be the mineral crystallized alone, which is slightly later than olivine. Plagioclase content increases with decreasing sulfide content in sulfide-bearing hornblende peridotite. Increasing plagioclase SiO2 content of sulfide-bearing hornblende peridotite from deep to shallow implies that they are crystal fractionation from the similar magma. The major oxides components of plagioclase can be used as the indicator of the sulfide ore. The SiO2, Al2O3, CaO, Na2O and K2O components of plagioclase are highly variable in the sulfide-rich rocks.