CAJ | 학술논문

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SiO_2,Al_2O_3和BeO外还含Na,Cs,Fe,Mg等元素;FeO,MgO,Na_2O和Cs_2O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,Na_2O和Cs_2O的含量逐渐升高,尤其是Cs_2O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Cs_2O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.
복건남평화강위정암시중국중요적희유금속화강위정암지일,기중31호맥시분이정도최고、희유금속성광작용최중요적암맥,록주석시기중최주요적피광물.이용전자탐침화배산사전자성상기술대해암맥중록주석진행료교계통분석.결과표명,남평31호화강위정암중록주석가분위원생록주석화만기록주석.원생록주석형성우조기암장계단,여조암광물석영、백운모、납장석、리휘석공생.만기록주석여원생록주석밀절반생,시부피류체연원생록주석적변연결정이성.혹열액연원생록주석적해리、렬극혹공극도교대부위진행교대적산물.전자탐침성분분석현시,남평31호화강위정암맥중원생록주석제함주요화학성분SiO_2,Al_2O_3화BeO외환함Na,Cs,Fe,Mg등원소;FeO,MgO,Na_2O화Cs_2O적최고함량분별위0.28%,0.89%,1.36%화3.92%.총체상,종Ⅰ대지Ⅳ대,원생록주석적FeO화MgO함량축점강저,Na_2O화Cs_2O적함량축점승고,우기시Cs_2O적함량변화교대.Ⅲ-Ⅳ대중소량원생록주석분포우리휘석중,구유부FeO화MgO적특정.만기록주석적Cs_2O함량교저,가능시유우색비석화남평석(색운모)등색광물적결정,도치만기용체-열액중상대빈색,이열액류체여부색록주석지간가능존재색적화학재평형.
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 pegmatitic 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-rich 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% Cs_2O. Overall,in the primary beryl crystals from zone Ⅰ to zone Ⅳ,the contents of FeO and MgO decrease,but contents of Na_2O and Cs_2O increase. Especially,the contents of Cs_2O 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 Cs_2O are attributed to crystallization of pullucite and nanpingite. There is possibly a re-equilibrium between the late hydrothermal fluids and the Cs-rich beryl.