湖南仁里5号伟晶岩脉铌钽矿物特征与岩浆热液成因的探讨  

Discussion on mineral characteristics and magmatic hydrothermal fluid genesis of columbite-tantalite from Renli No.5 pegmatite vein in Hunan Province

作　　者：杨晗 陈振宇[1] 李建康[1] 李鹏 王臻 周芳春 YANG Han;CHEN ZhenYu;LI JianKang;LI Peng;WANG Zhen;ZHOU FangChun(Key Laboratory ofMetallogeny andMineral ResourceAssessment,Institute ofMineral Resources,ChineseAcademy of Geological Sciences,Beijing 100037,China;No.311 Brigade of Hunan Nuclear Geology,Changsha 410011,Hunan,China)

机构地区：[1]中国地质科学院矿产资源研究所自然资源部成矿作用与资源评价重点实验室,北京100037 [2]湖南省核工业地质局311大队,湖南长沙410011

出　　处：《矿床地质》2021年第4期706-722,共17页Mineral Deposits

基　　金：国家重点研发计划项目(编号:2019YFC0605203);中央级公益性科研院所基本科研业务费(编号:JYYWF201814);中国地质科学院矿产资源研究所基本科研业务费专项经费资助(编号:IMRKK1927);国家自然科学基金项目(编号:41872096);湖南省国土资源厅科研项目(编号:2018-02);国家社会科学基金重大项目(编号:19ZDA111)联合资助。

摘　　要：湖南仁里5号花岗伟晶岩是1条分异程度很高的伟晶岩脉,其岩相带分为2类:外部带(Ⅰ—Ⅱ)和内部带(Ⅲ—Ⅴ)。文章用电子探针定量分析(EPMA)和背散射电子图像(BSE)研究了5号脉中的铌钽矿物。研究揭示:铌铁矿-钽铁矿存在于大部分结构带中,而铌锰矿和细晶石主要局限于Ⅴ带。Ⅰ—Ⅲ带的铌钽铁矿在结构上表现为中心富集Nb元素,边缘富集Ta元素的韵律环带结构,在Ⅳ带出现富钽细脉交代铌铁矿的复杂结构,Ⅴ带的内部结构不明显,Nb、Ta元素在Ⅴ带发生突变:Nb元素含量升高,Ta元素含量降低,表明伟晶岩浆可能在Ⅳ—Ⅴ带发生了转变。从外部带到内部带钠长石增加而微斜长石减少,Ⅲ带F元素含量不断增高,铌钽矿化主要发生在白云母钠长石带(Ⅲ带)和锂云母石英核中(Ⅴ带),表明挥发分(如F)有效促进了稀有金属元素的迁移和富集(Ⅲ带),同时晚期富钠等碱金属的流体促进了仁里铌钽元素的富集(Ⅴ带)。The No. 5 rare metal pegmatite is a strongly differentiated rare-element granitic pegmatite vein, where the lithofacies are distinguished into two groups: outer zones(Ⅰ-Ⅱ) and inner zones(Ⅲ-Ⅴ). Nb-Ta oxides are investigated in this paper by using quantitative electron-microprobe analysis(EPMA) and backscattered-electron(BSE) imaging. Columbite-tantalite occur in most lithofacies zones, whereas mangancolumbite and microlite are mainly restricted to zone Ⅴ. The columbite-tantalite in lithofacies Ⅰ-Ⅲ have a Nb enrichment core and Ta enrichment edge showing a kind of oscillatory zoning texture, the complex texture of niobite metasomatized by tantalum-rich veinlet appears in the Ⅳ zone, and there is no specific internal texture in zone Ⅴ. There is a sudden change in Nb and Ta contents in zone Ⅴ: the content of Nb increased and the content of Ta decreased, indicating that the pegmatite magma may have a dramatic change in composition in zones Ⅳ-Ⅴ. From outer zone to inner zone, the albite content is increasing while the microcline is decreasing, and the F content increases in zone Ⅲ;Nb-Ta mineralization mainly occur in the muscovite-albite zone(zone Ⅲ) and lepidolite-quartz core(zone Ⅴ), indicating that volatiles(such as F) effectively promotes the migration and enrichment of rare metal elements(such as in zone Ⅲ). At the same time, the fluid rich in sodium and other alkali metals promoted the enrichment of Nb and Ta at Renli(zone Ⅴ).

关 键 词：地球化学 稀有金属伟晶岩 矿物学 化学成分 仁里铌钽矿 

分 类 号：P611.12[天文地球—矿床学] P618.79[天文地球—地质学]