江西萍乡富铷花岗细晶岩脉的地质特征及成因分析

Geological Characteristics and Genesis of Rb Rich Granitic Aplite in the Pingxiang Area,Jiangxi Province

江西萍乡地区出露的花岗细晶岩富含铷,相关研究较少.为了解铷矿床的地质特征及其成因,在野外调查的基础上,采用偏光显微镜、XRF、LA-ICPMS等测试手段,对矿区的花岗细晶岩和二云母花岗岩的主微量元素、锆石年龄等进行综合分析研究.经研究表明:矿区的花岗细晶岩以岩脉的形式产出,宽几米到几十米,长数百米到数千米;花岗细晶岩主要由长石、云母和石英组成,具有富硅(SiO_(2)平均质量分数74.71%)的特征,里特曼指数为1.21,铝饱和指数为2.15,属于过铝质钙碱性花岗岩;花岗细晶岩中铷的平均质量分数为543×10^(-6),Zr/Hf较高(25.36~35.31),Nb/Ta较低(3.13~4.18),显示出高分异花岗岩的特点.综上所述,萍乡地区花岗细晶岩中的Rb和Sr的含量呈互补关系,Zr/Hf<36.70,Nb/Ta<5.00,且矿区附近出露的二云母花岗岩同样具有较高的铷含量(平均质量分数为319.6×10^(-6)),高分异的花岗岩可能造成铷等不相容元素的富集.

Granitic aplite in the Pingxiang area,Jiangxi Province is enriched in rubidium(Rb),but no studies have been reported.In order to understand the geological characteristics and genesis of rubidium deposit,this paper studies the major and trace elements and zircon U-Pb dating of the granitic aplite and mica granite in the mining area by polarizing microscope,XRF,and LA-ICPMS after field investigation.The granitic aplite rocks occur as dikes ranging from several meters to tens of meters in width and hundreds of meters to thousands of meters in length.They are mainly composed of feldspar,mica,and quartz,and are rich in SiO_(2)(average 74.71%),withδ=1.21 and A/CNK=2.15,belonging to peraluminous calc-alkaline granite.The average concentration of Rb is 543×10^(-6),and the Zr/Hf ratio is higher(25.36~35.31),while the Nb/Ta ratio is lower(3.13~4.18),indicating the characteristics of highly differentiated granite.The contents of Rb and Sr in the granitic fine-grained rocks in Pingxiang area are complementary,Zr/Hf<36.70 and Nb/Ta<5.00.The bimica granites exposed near the mining area also have high rubidium content(average 319.6×10^(-6)),indicating that the highly differentiated granites may cause the enrichment of rubidium and other incompatible elements.