中文摘要：

福建南平花岗伟晶岩是中国重要的稀有金属花岗伟晶岩之一,其中31号脉是分异程度最高、稀有金属成矿作用最重要的岩脉,绿柱石是其中最主要的铍矿物。利用电子探针和背散射电子成像技术对该岩脉中绿柱石进行了较系统分析。结果表明,南平31号花岗伟晶岩中绿柱石可分为原生绿柱石和晚期绿柱石。原生绿柱石形成于早期岩浆阶段,与造岩矿物石英、白云母、钠长石、锂辉石共生。晚期绿柱石与原生绿柱石密切伴生,是富铍流体沿原生绿柱石的边缘结晶而成,或热液沿原生绿柱石的解理、裂隙或孔隙度较大部位进行交代的产物。电子探针成分分析显示,南平31号花岗伟晶岩脉中原生绿柱石除含主要化学成分SiO2,Al2O3和BeO外还含Na,Cs,Fe,Mg等元素;FeO,MgO,Na2O和Cs2O的最高含量分别为0.28%,0.89%,1.36%和3.92%。总体上,从Ⅰ带至Ⅳ带,原生绿柱石的FeO和MgO含量逐渐降低,Na2O和Cs2O的含量逐渐升高,尤其是Cs2O的含量变化较大。Ⅲ—Ⅳ带中少量原生绿柱石分布于锂辉石中,具有富FeO和MgO的特征。晚期绿柱石的Cs2O含量较低,可能是由于铯沸石和南平石（铯云母）等铯矿物的结晶,导致晚期熔体-热液中相对贫铯,而热液流体与富铯绿柱石之间可能存在铯的化学再平衡。

英文摘要：

The Nanping granitic pegmatite is one of the most important rare-metal deposits in China. In this pegmatite field the No. 31 granitic pegmatite is the most highly evolved and well mineralized one, where beryl is the most important beryllium mineral. The beryls were studied in this paper by using the electron microprobe analyses and back scattered-electron imaging. The results show that the beryls in this pegmatite can be distinguished into primary beryl and late beryl. The primary beryl crystals were crystallized early from the pegmatitie magma in association with rock forming minerals such as quartz, muscovite, albite and spodumene. The late beryl is typically associated with the primary beryl, and was either crystallized from the Be-rich hydrothermal fluids, or the replacement product of Cs-rieh primary beryl by hydrothermal fluids along its cleavages, fissures or porosities. The electronmicroprobe results reveal that the primary beryl is also enriched in Fe, Mg, Na, Cs, and contains up to 0.28% FeO, 0.89% MgO, 1.36% Na2O and 3.92% Cs2O. Overall, in the primary beryl crystals from zone Ⅰ to zone Ⅳ, the contents of FeO and MgO decrease, but contents of Na2O and Cs2O increase. Especially, the contents of Cs2O in the primary beryl show wide variations. Some primary beryl crystals are found in spodumene in zones Ⅲ and Ⅳ, and are enriched in Fe and Mg. The late secondary beryls with low contents of Cs2O are attributed to crystallization of pullucite and nanpingite. There is possibly a re-equilibrium between the late hydrothermal fluids and the Cs-rich beryl.