华南幕阜山花岗伟晶岩的矿物化学特征及指示意义

华南晚中生代幕阜山花岗复式岩基内部及周缘广泛发育花岗伟晶岩脉，部分岩脉富含Li-Nb-Ta等元素，形成大型－超大型稀有金属矿床.本文以幕阜山北缘断峰山地区贫锂伟晶岩类和南缘仁里地区新发现的富锂伟晶岩为主要研究对象，通过详细的岩相学和主要及特征矿物（长石、云母、电气石、石榴子石、绿柱石、铌钽铁矿）的微区原位EPMA和LA-ICP-MS主微量元素地球化学的对比分析，深入探讨了伟晶岩的分类、成因演化及成矿潜力.按照特征矿物组合将伟晶岩划分为断峰山地区电气石伟晶岩、电气石－绿柱石伟晶岩、绿柱石伟晶岩、铌钽铁矿－绿柱石伟晶岩和仁里地区的锂电气石－锂云母伟晶岩5类.5类岩脉中的长石、云母、电气石和/或石榴子石的化学成分记录了不同程度花岗伟晶岩脉的演化阶段，按岩浆演化程度由低至高依次为电气石伟晶岩→电气石－绿柱石伟晶岩→绿柱石伟晶岩→铌钽铁矿－绿柱石伟晶岩→锂电气石－锂云母伟晶岩，并分别对应伟晶岩稀有金属富集程度分类中的无矿→（含Be）→富Be→富Be、Nb、Ta→富Li、Be、Nb、Ta阶段.这一结果表明仁里地区伟晶岩已演化至晚期富集多种稀有金属元素阶段，具有Li-Nb-Ta多金属成矿潜力，而断峰山地区的伟晶岩演化程度相对较低.断峰山电气石－绿柱石伟晶岩中的色带电气石晶体发育强烈成分环带，由内向外可明显分为5环，自核部至边部，Li、Zn、Ga、Ge、Nb、Ta、Sn、Pb等不相容元素和金属元素含量逐渐升高，清晰记录了正常岩浆演化序列及稀有金属富集过程.结合前人有关幕阜山花岗岩类的研究资料，本文认为幕阜山伟晶岩为该地区晚中生代巨量花岗质岩浆经历长期结晶分异作用晚期的分异产物. 

Petrogenesis and Rare-Metal Mineralization of the Mufushan Granitic Pegmatite,South China: Insights from in Situ Mineral Analysis

Granitic pegmatites are widely distributed in the inner and adjacent region of the Late Mesozoic Mufushan granitic complex in South China. Some of them are rich in Li-Nb-Ta and related elements, forming large-ultra-large rare metal deposits. This study focuses on the lithium-poor pegmatites from Duanfengshan area in the northern Mufushan and the newly discovered lithium-rich pegmatite from Renli area in the south. Hereby we provided detailed petrographic and in situ EPMA and LA-ICP-MS geochemical analysis of major and characteristic minerals (feldspar, mica, tourmaline, garnet, beryl, columbite-tantalite) from the Mufushan pegmatites, aiming to constrain the classification, evolution and mineralization of the investigated pegmatites. Based on the combination of the characteristics minerals, the Mufushan pegmatites have been divided into five groups:Tur-pegmatite, Tur-Brl-pegmatite, Brl-pegmatite, Col-Brl-pegmatite in Duanfengshan area and Elb-Lpd-pegmatite in Renli area. Compositional variation of feldspar, mica, tourmaline and garnet from the studied pegmatites display continuous magmatic evolution sequence. From low to high evolution degrees, the Mufushan pegmatites are Tur-pegmatite→Tur-Brl-pegmatite→Brl-pegmatite→Col-Brl-pegmatite→Elb-Lpd-pegmatite, corresponding to the mineralization stages of metal barren→(Be-bearing)→Be-rich→Be, Nb, Ta-rich→Li, Be, Nb, Ta-rich, respectively. This result indicates that the Renli pegmatites have evolved to a relatively late-stage with various rare metal enrichment, which thus has higher potential of Li-Nb-Ta polymetallic mineralization. In contrast, the evolutionary degrees of Duanfengshan pegmatites are relatively low. A strongly zoned tourmaline crystal has been observed in the Tur-Brl-pegmatite from Duanfengshan area, in which five compositional zones from inside to outside can be divided. The content of incompatible elements such as Li, Zn, Ga, Ge, Nb, Ta, Sn, Pb gradually increased from inner to outter, which clearly recording the normal magmatic evolution sequences and the rare metal enrichment processes. Combined with previous studies, our work suggests that the Mufushan pegmatites are generated by extremely prolonged fractional crystallization of the Mufushan massive granitic magma, representing the final-stage product of granitic magma.