西藏雅拉香波穹窿淡色花岗岩-伟晶岩矿物学特征: 对稀有金属成矿指示意义

近年来提出喜马拉雅新生代淡色花岗岩高分异成因模式使得该带逐渐成为我国极具潜力的稀有金属战略远景区。目前，喜马拉雅北带金属组合类型以铍-铌-钽（锡-钨）组合为主，南带以锂-铍-铌-钽组合为主。本研究聚焦于喜马拉雅北带东段的雅拉香波穹窿内发现的含绿柱石伟晶岩，通过电子探针和激光剥蚀等离子质谱方法获得淡色花岗岩-伟晶岩中长石、云母、电气石和绿柱石的矿物结构和组成，综合判定雅拉香波淡色花岗岩-伟晶岩的岩浆演化分异程度及其稀有金属成矿潜力。研究获得如下结论：1）喜马拉雅东段雅拉香波花岗伟晶岩中稀有金属矿物主要为绿柱石，主要赋存在微斜长石-钠长石伟晶岩中；2）岩浆结晶分异作用控制了雅拉香波穹窿中淡色花岗岩和伟晶岩中矿物组成及其演化，其中白云母替代关系为Al₂□R_-3²⁺和Al₄Si_-3□_-1，电气石替代关系为MgFe_-1和^X□，Al（Na，R²⁺）_-1，绿柱石替代关系为Na（Fe²⁺，Mg）□_-1Al_-1；3）根据长石Cs含量和钾长石K/Rb值，白云母Li-B-Cs含量和K/Rb比值，黑电气石Ge-Pb含量，以及绿柱石Li-Cs含量和Cs/Na比值综合判断雅拉香波含绿柱石伟晶岩为简单铍矿化伟晶岩，其伟晶岩演化程度与典型Be-Nb-Ta矿化伟晶岩和复杂伟晶岩中Be矿化带相类似。

Mineralogical characteristics of the leucogranite-pegmatite in the Yardoi Gneiss Dome,Himalaya, Tibet: Implication to the rare-metal mineralization

In recent years, it has been proposed that the model of the Himalayan highly-differentiated Cenozoic leucogranite makes this belt gradually become a highly-potential strategic prospective area for the rare-metal mineralization in China. At present, the type of metal assemblages in the northern Tethys Himalayan belt is dominated by beryllium-niobium-tantalum (tin-tungsten) assemblage, while the southern Higher Himalayan belt is dominated by lithium-beryllium-niobium-tantalum assemblage. The present study has newly discovered the beryl-bearing pegmatites in the Yardoi Gneiss Dome, and the detailed field observation, internal structures of pegmatites and mineralogical compositions have been analyzed by in-situ microanalysis of EPMA and LA-ICPMS on the feldspar, mica, tourmaline and beryl from the leucogranite-pegmatite. Finally, all the results comprehensively shape the degree of magmatic differentiation of the Yalaxiangbo leucogranite-pegmatite and its rare metal mineralization potential. Based on the detailed field observation and in-situ microanalysis of minerals, the following concluding remarks were obtained: 1) rare-metal minerals in the Yalaxiangbo leucogranite and pegmatite rocks are mainly beryl hosted in the microline-albite pegmatite; 2) compositions of the mica minerals, feldspars, tourmalines and beryl were controlled by the magmatic differentiation, and the elemental substitution includes Al2□R-32+ and Al4Si-3□-1for muscovite, MgFe-1 and X□, Al(Na, R2+)-1 in schorl, and Na(Fe2+, Mg)□-1Al-1 in beryl; 3) according to feldspar Cs content and K-feldspar K/Rb ratio, muscovite Li-B-Cs content and K/Rb ratio, schorl Ge-Pb content, and beryl Li-Cs content and Cs/Na ratio, we suggest the Yalaxiangbo leucogranite-pegmatite evolution is similar to that of typical Be-Nb-Ta mineralized pegmatites and Be-mineralized zones in complex pegmatites.