西藏罗布莎铬铁矿中的原位铂族矿物研究:铬铁矿结晶环境的指示  

In situ research on PGM in Luobusa ophiolitic chromitites,Tibet:Implications for the crystallization of the chromite

作　　者：郭国林[1,2,3] 杨经绥[2] 刘晓东[1,3] 徐向珍[2] 武勇[2] 

机构地区：[1]东华理工大学放射性地质与勘探技术国防重点学科实验室,南昌330013 [2]中国地质科学院地质研究所,中国地质调查局大陆构造与动力学创新研究中心,地幔研究中心,北京100037 [3]东华理工大学地球科学学院,南昌330013

出　　处：《岩石学报》2016年第12期3673-3684,共12页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41262002;41202036;41302053);国家行业专项(Sino Probe-05-02);中国地质调查局工作项目(DD20160023-01);IGCP-649项目联合资助

摘　　要：本文对罗布莎三个矿区的铬铁矿进行了详细的原位PGM研究,发现罗布莎各个矿区的铬铁矿中PGM组合和显微结构不同,暗示PGM能够记录铬铁矿形成与演化过程。罗布莎矿区的PGM显微特征显示铬铁矿结晶于高温、低硫逸度的环境中,可能系岩石/熔体反应和结晶分异双重作用下的产物;康金拉矿区的原位PGM主要为组合型包裹体,有少量产于铬铁矿裂隙之间的贱金属硫化物和合金矿物,为不同来源的熔体混合作用的结果,并暗示铬铁矿成矿后还受到热液流体的改造;香卡山矿区的PGM表明铬铁矿成矿之后遭受到还原性流体的交代作用,铬铁矿中早期结晶出来的硫化物或者铂族矿物被还原改造,形成铁镍矿等次生矿物,保存于铬铁矿粒间或者铬铁矿的裂隙中,这个过程可能与蛇纹石化或者晚期构造流体改造作用有关。罗布莎原位PGM研究表明,PGM矿物贯穿于铬铁矿结晶成矿过程的始终,PGM的矿物及其组合能够记录铬铁矿结晶时母熔体的物理化学条件,甚至还能反映铬铁矿成矿后所经历的后期构造热液事件。因此,结合单矿物分选和原位调查两种方法,查明铬铁矿中PGM的赋存类型及微观结构,对全面理解铬铁矿的成矿过程有重要意义。This paper study on the in-situ distribution of PGM in three mining areas in the Luobusa deposit, various PGMs and its microstructure obtained so far from each mining area suggesting that PGM can record the evolutions of the host chromitites. In situ PGMs results from Luobusa mining area show that the parental melts in Luobusa chromitite have a condition with high temperature and low sulfur fugacity, suggesting the chromite forms during the process of melting rock reaction and/or crystallization differentiation. The PGM occurrence in Kangjinla mining area are mainly composite phase inclusions in chromitites, also a few single phase PGM host in the fracture, which implying the parental melts of Kangjinla chromite origin from the melt mingling process, and modified by hydrothermal fluid at the later stage. The PGM obtained from Xiangkashan chromitites sample mostly are awaruites, which occurred in the fracture or intercrystalline in chromitites. Maybe subjected to the process of serpentinisation and/or hydrothermal metamorphism after the chromite crystallization. Mineral associations and microstructure of platinum-group minerals （PGM） can provide an efficacious clue to understand the physical and chemical conditions during the crystallization of chromitite. Therefore, PGMs in situ study is significant for us to understand the formation of unusual mineral preserved in chromitite and the crystallization of chromitite, and the study on PGMs combining in-situ examination and mechanical separation can obtain both their abundance and textural information.

关 键 词：罗布莎蛇绿岩 铂族矿物 铬铁矿 原位 

分 类 号：P578.12[天文地球—矿物学]