应用电子探针技术研究北京密云放马峪铬铁矿床成因--来自含铬尖晶石矿物化学的证据  

Origin of the Fangmayu Chromite Deposit,Miyun,Beijing: Constraints from Electron Microprobe Analyses of Cr-Spinel

作　　者：李立兴[1] 朱明玉[1] 方同明[2] 李厚民[1] 

机构地区：[1]国土资源部成矿作用与资源评价重点实验室,中国地质科学院矿产资源研究所,北京100037 [2]北京市地质调查研究院,北京100195

出　　处：《岩矿测试》2015年第5期600-608,共9页Rock and Mineral Analysis

基　　金：国家自然科学基金资助项目(41402067);中国地质科学院矿产资源研究所基本科研业务费项目(K1410)

摘　　要：似层状铬铁矿床长期以来被认为是岩浆分异成因,但近年来有学者提出其中个别产在蛇绿岩中。本文选择北京放马峪似层状铬铁矿床中纯橄岩、辉橄岩和辉石岩中不同类型的含铬尖晶石进行了电子探针分析。研究表明,岩浆早期的纯橄岩和辉橄岩中的铬尖晶石富铬(Cr2O3平均43.32%),而岩浆晚期辉石的结晶消耗了大量Cr3+,由于氧逸度的升高,在辉石岩的单斜辉石中出溶贫铬的铬磁铁矿(Cr2O3平均10.32%)和富铝尖晶石(Cr2O3平均15.77%)。与世界上不同类型铬尖晶石的矿物化学特征进行对比,可以认为放马峪铬铁矿床是产在阿拉斯加型岩体中的早期岩浆矿床,而与蛇绿岩无关。本文对放马峪铬铁矿床成因和成矿专属性的限定,为这类镁铁-超镁铁岩体的铬、铜镍、铂族元素的找矿勘查提供了依据。Stratiform chromite deposits in China have long been considered to form by fractional crystallization of mafic magma. However,some researchers recently proposed that some chromite deposits are also hosted in ophiolite. In this study,Cr-spinels of the dunites,wehrlites and clinopyroxenites from the Fangmayu chromite deposit in Beijing are analyzed by EPMA. Results show that Cr-spinels of dunites and wehrlites at the early stage of magma differentiation are rich in Cr with an average Cr2O3 content of 43. 32%. At the late stage of magma differentiation,the crystallization of clinopyroxenites consumed large amounts of Cr3 ＋and elevated the oxygen fugacity,leading to the Cr-rich magnetite and Al-rich spinel with average Cr2O3 contents of 10. 32% and 15. 77%,respectively. By comparing with the chemical composition of different types of Cr-spinels from the world,the suggestion is that Fangmayu chromite deposit was a magmatic deposit hosted in Alaskan-type intrusion,and was not related to ophiolite. The constraints on the genesis and metallogenic specialization provide evidence for mineral prospecting of Cr,Cu-Ni and PGE deposits hosted in mafic-ultramafic intrusions.

关 键 词：放马峪 铬铁矿床 铬尖晶石 超镁铁岩 阿拉斯加型岩体 电子探针 

分 类 号：P597.3[天文地球—地球化学] P618.4[天文地球—地质学]