云南金宝山含铂钯超镁铁质侵入体中铬铁矿的成因研究  

GENETIC RESEARCH ONCHROMITE FROM THE Pt-Pd-BEARING ULTRAMAFIC INTRUSIONS IN JINBAOSHAN,YUNNAN

作　　者：马言胜[1] 陶琰[1] 钟宏[1] 王兴阵[2] 

机构地区：[1]中国科学院地球化学研究所矿床国家重点实验室 [2]安徽理工大学,安徽淮南232001

出　　处：《矿物学报》2007年第3期342-350,共9页Acta Mineralogica Sinica

基　　金：国家自然科学基金(批准号:40573020);中国科学院重要方向项目(KZCX3-SW-125)

摘　　要：位于扬子地台西缘的金宝山岩体赋存我国最大的独立铂族元素矿床,岩体为似层状产出的小型超镁铁岩,在时间和空间上与晚二叠纪(260 Ma)峨眉山大火成岩省相关。该岩体由单辉橄榄岩、辉橄岩及橄辉岩、辉石岩异离体组成。铬铁矿以副矿物形式出现,从形态上可以分为三类:包嵌于橄榄石中的自形铬铁矿、以自形或半自形体存在于辉石中铬铁矿以及环绕结构铬铁矿。其中环绕结构铬铁矿外壁浑圆,内为棱角状,其中心为橄榄石、辉石。本文在薄片观察的基础上,结合电子探针研究,认为包嵌于橄榄石中的自形铬铁矿是在岩浆早期深部岩浆房中结晶形成的;存在于辉石中的铬铁矿则是岩浆进一步结晶演化的结果,主要为就地结晶的产物;在岩体形成的过程中,作为岩体赋存空间的堆晶相与后续岩浆持续反应,使铬铁矿不断聚集和生长,最终形成了环绕橄榄石晶体的形态。铬铁矿的生成模式进一步说明了金宝山侵入体为一岩浆通道,并且经历深部结晶分异演化。The Jinbaoshan Pt-Pd deposit, the largest independent PGE deposit in China, is hosted in an ultramafic intrusion on the westem margin of the Yangtze Block. This intrusion, temporally and spatially associated with the Late Permian Emeishan Large Igneous Province （ELIP）, is a sheet-like body with a thick wehrlite unit in the center and thin pyroxenite units at the margins. Chromites, which are accessory minerals in the ultramafic intrusion, can be classified as three types： occurring as inclusions in olivine; as euhedral or subhedral inclusions in clinopyroxene, and those exhibiting rounding structure. The typical characteristics of chromites with rounding structure are their smooth and rounded appearance, their inner angular shape and the occurrence of olivine or pyroxene in the center. Based on quantitative electron microprobe analysis （EMPA） as well as thin section observation, it is believed that the chromites occurring as inclusions in olivine may be formed in the deep chamber during the early stage of magma evolution; as euhedral or subhedral inclusions in clinopyroxene, mostly the products of crystallization at depth, it may be due to further magma evolution. During the formation of the Jinbaoshan intrusion, cumulus phase which acted as the host space of the intrusion interacted continuously with subsequent magma; this interaction made chromite crystals continuously accumulate and grow and eventually the chromites with rounding structure were then formed. The mechanism of formation the chromites suggested that the Jinbaoshan intrusion is a magma conduit with crystallization differentiation at depth.

关 键 词：铬铁矿 超镁铁岩 橄榄石 结晶作用 金宝山 云南 

分 类 号：P571[天文地球—矿物学] P578.4[天文地球—地质学]