东昆仑夏日哈木岩浆铜镍硫化物矿床铬尖晶石特征及其指示意义

Characteristics of Chromian Spinels from the Xiarihamu Magmatic Ni-Cu Sulfide Ore Deposit in the Eastern Kunlun Orogenic Belt,Northwest China and Their Implication

为给夏日哈木矿床成因研究提供新的依据,本文在系统岩心编录的基础上,对该矿床的铬尖晶石进行了研究。薄片鉴定表明,铬尖晶石与橄榄石紧密共生,呈粒状或浑圆状分布于橄榄石和辉石晶体内部。电子探针分析表明,铬尖晶石的Ti O2及Fe2O3含量较低,Cr#值与Mg#值变化范围较大且二者呈负相关关系,包裹于橄榄石中的铬尖晶石具有较高的Cr2O3含量。由铬尖晶石成分推测该矿床母岩浆属于低Ti、高Mg拉斑玄武质岩浆,起源于软流圈地幔。铬尖晶石Fe3+-Cr-Al、Mg#-Cr#图解和矿物岩石组合表明,夏日哈木矿床可能不是形成于岛弧环境,而可能形成于碰撞后的伸展环境。

On the basis of systematic cataloging of boreholes of the Xiarihamu deposit,chromian spinels have been studied in this paper in order to provide new evidences for studying metallogenesis of the deposit.Thin section identification sug-gests that chromian spinels are closely intergrown with olivines,or distributed as grain or rounded crystal within the olivine and pyroxene crystals.Electron microprobe studies show that chromian spinels of the Xiarihamu deposit contain low con-tents of TiO2 and Fe2O3,have largely variable Cr#（22 to 62）and Mg#values（22 to 60）,with generally negative correla-tion between Cr#and Mg#values.Especially,the chromian spinels included in olivine crystals often contain relatively high Cr2 O3 contents.On the basis of compositions of the chromian spinels,it is inferred that the parental magma of the Xiari-hamu deposit could be low Ti,high Mg tholeiitic magma which was derived from the ashospheric mantle.Based on the Fe3＋-Cr-Al diagram and Mg#-Cr#diagram of spinel and the mineral assemblage and lithological association of the Xiarihamu deposit,it is believed that the deposit could be formed post-collisional extension environment rather than in island arc or active continental margin settings.