东天山香山中镁铁-超镁铁质岩体岩石学与矿物学特征:对成岩成矿过程的约束

摘要

香山中镁铁?超镁铁岩体产出于新疆东天山地区的黄山—镜儿泉镁铁?超镁铁岩带.主要的岩石类型为二辉橄榄岩、(含长)单辉橄榄岩、橄榄辉石岩及角闪辉长岩.矿物学特征显示,岩体造岩矿物的结晶顺序为铬尖晶石→橄榄石→斜方辉石→单斜辉石→斜长石→角闪石.电子探针分析显示,同一侵入期次中各岩相具有良好的过渡渐变关系,钻孔剖面上橄榄石含量与颗粒大小、单斜辉石的成分有随深度连续变化的特征,铬尖晶石则具有良好的Cr→Fe3+、Ti的演化趋势,由此反映岩体的形成主要受结晶分异作用的控制;含长单辉橄榄岩中橄榄石和单斜辉石成分的突然变化显示岩浆结晶过程中受到了地壳物质阶段性的混染;模拟计算表明,橄榄石分离结晶伴随着硫化物的熔离;钻孔ZK3693深度为295~325 m,含长单辉橄榄岩中橄榄石、斜长石、单颗粒单斜辉石成分突然性的变化指示在区间内有新鲜的基性程度更高的岩浆注入,而此区间内矿石的Cu、Ni品位明显高于区间外同一岩相岩体,说明新鲜岩浆的注入是香山中岩体硫化物富集的重要原因.%Mafic-ultramafic rocks in Xiangshan are located in Huangshan-Jingerquan mafic-ultramafic rock zone in east Tianshan Mountains, Xinjiang. The main rock types are iherzolite, (containing feldspar) clinopyroxene peridotite, olivine pyroxenite and hornblende gabbro. According to the mineralogical characteristics, the rock mineral crystallization sequence is in order of chrome spinel, olivine, orthopyroxene, clinopyroxene, plagioclase, and angle amphibole. In the same period, the transition of the lithofacies in each stage of the invasion period has a good transition. The content of olivine in the drilling section and the composition of the particles and the composition of the particles in the drilling section vary with depth. The evolution of Cr→Fe3+, Ti in picotite is good. According to these features, the formation of the rock mass is mainly controlled by the crystallization differentiation. Abrupt change of olivine and the composition of the olivine in the (feldspar-bearing) clinopyroxene show the existence of crustal mixture in the process of magma crystallization. The simulation results show that the crystallization of olivine was accompanied by the melting of the sulfide. At the depths of 295-325 m in ZK3693 borehole, abrupt change of the composition of (feldspar-bearing) clinopyroxene in the olivine, plagioclase, single grain clino-feldspar and the Al→Cr evolution of the Cr spinel indicates that there is a higher basic level of magma injection in the interval. The Cu and Ni grades of the ore in this area are obviously higher than those of the same rock mass which is not in the interval. That injection of fresh magma is an important cause of the sulfide enrichment in Xiangshan.