东天山似斑状角闪辉长岩类与铁钛氧化物矿床的关系

Relationship between amphibole-porphyric gabbroic rocks and Fe-Ti oxide ore deposits of the East Tianshan

似斑状角闪辉长岩类是东天山镁铁-超镁铁杂岩的一部分,以含有嵌晶角闪石为特征,其中部分岩体的似斑状角闪辉长岩赋存铁钛氧化物矿床。为探讨东天山似斑状角闪辉长岩类和铁钛氧化物矿床形成的内在成因关系,本次研究对二红洼、牛毛泉和香山西似斑状角闪辉长岩类的斜长石、单斜辉石、斜方辉石以及嵌晶角闪石进行了系统的电子探针成分分析,并对其形成物理化学条件进行了探讨。结果表明,东天山似斑状角闪辉长岩类的母岩浆氧逸度变化范围为NNO-0.37~NNO+1.15,和攀西地区最大的红格岩体的氧逸度一致,侵入于中下地壳,深度介于8.9~15.7km,结晶温度大于914℃。东天山似斑状角闪辉长岩中铁钛氧化物矿床的富集得益于母岩浆的高氧逸度,但铁钛氧化物矿床的形成和规模则受控于各个岩体的岩浆演化程度。二红洼、牛毛泉和香山西的岩浆的演化程度系统增高,演化程度最低的二红洼岩体并未形成铁钛氧化物矿床,而分异演化程度逐渐增高的牛毛泉和香山西似斑状角闪辉长岩类则分别形成了本区一个小型的和一个大型的铁钛氧化物矿床。

Amphibole-porphyritic gabbroic rocks characterized by poikilitic amphibole is a part of the mafic- ultramafic complexes, East Tianshan, and some of them host the Fe-Ti oxide ore in this district. In order to better understand the genesis relationship between the gabbroic rocks and the Fe-Ti oxide deposits of the East Tianshan, this study used EMPA to analyze the chemical composition of silicate minerals, including plagioclase, clinopyroxene, orthopyroxene and poikilitic amphibole of the amphibole-porphyritic gabbroic rocks, and discussed the physic-chemical parameter of their parental magma. The results show that amphiboleporphiritic gabbroic rocks formed in middle-lower crust, within a depth of 8. 9 to 15. 7 kin, a temperature higher than 914 ℃. The oxygen fugacity of amphibole-porphyric gabbroic rocks of the East Tianshan varies from NNO-0. 37 to NNO--1. 15, and show similar ranges with the Hongge layered gabbroic intrusion, which hosts the largest Fe-Ti oxide ore in Panxi district. The enrichment of Fe-Ti oxide in amphibole-porphyric gabbroic rocks of the East Tianshan benefited from high oxygen fugacity, however, the formation and scale of Fe-Ti oxide ore deposits associated with amphibole-porphyric gabbroic rocks is strongly controlled by the evolution degree of their parental magma. The least differentiated Erhongwa amphibole-porphyric gabbroic intrusion hosts no Fe-Ti oxide ore. The parental magma of the Niumaoquan and Xiangshanxi amphibole~ porphyric gabbroic intrusion becomes more and more differentiated, and the elevated evolution degree contributed to one small scale and one large scale Fe-Ti oxide ore deposit in this district.