基于TIMA全扫描技术分析白云鄂博矿床板岩特征

Analysis of slate characteristics of the Bayan Obo deposit based on the TIMA full scan technology

内蒙古白云鄂博矿床是世界最大的稀土矿之一,其矿床内部及周边出露有大量板岩并且板岩具多种颜色(黑色、黄绿色、深绿色等),板岩的研究程度相对较低。为了厘定板岩的矿物组成,本次研究应用玻片全扫描、TIMA(TESCAN Intergrated Mineral Analyzer)全扫描、电子探针、LA-ICP-MS(激光剥蚀电感耦合等离子体质谱仪)对其矿物组合特征和成分特征进行分析。玻片全扫描和TIMA全扫描比对表明板岩虽颜色各异,但主要由正长石组成,正长石体积比可达86.37%;在白云鄂博矿床范围内正长石有隐晶质、单晶集合体和单晶三种赋存形态。电子探针分析表明正长石中SiO_(2)为59.44%~64.76%、Al_(2)O_(3)为16.89%~19.73%、K_(2)O为13.96%~17.90%,K_(2)O/Na_(2)O为15.86~45.71;环带结构正长石K_(2)O的含量较其它正长石较低,K_(2)O/Na_(2)O为15.86~20.85。LA-ICP-MS分析表明正长石中Ba含量为700.08×10^(-6)~47 606.91×10^(-6),其它微量元素和稀土元素含量很少且差异不大。板岩整体颜色和正长石色带均具有随着Ba含量增多而颜色变深的现象,因此正长石的颜色深浅与Ba含量多少呈正相关关系。

The Bayan Obo deposit in Inner Mongolia is one of the largest rare earth deposits in the world.There is a large amount of various colored(black,yellow green,dark green,etc.)slates exposed inside and around the deposit.However,the research level of slate is relatively low.In order to determine mineral compositions of the slates,we have analyzed their mineral assemblage characteristics and compositional features by applying the slide full scan,TIMA(TESCAN Intergrated Mineral Analyzer)full scan,electron probe,and LA-ICP-MS.The slide full-scan and TIMA full-scan comparison show that the colored slates are mainly composed of orthoclase with the mximum volume ratio of 86.37%.Within the Bayan Obo deposit,the orthoclase has three types of occurrence forms including cryptocrystalline,single crystal aggregate and single crystal particles.Electron probe microanalyses show that orthoclase particles have SiO_(2),Al_(2)O_(3) and K_(2)O contents of 59.44%-64.76%,16.89%-19.73%,and 13.96%-17.90%,respectively;with K_(2)O/Na_(2)O ratios of 15.86-45.71.Comparing to other orthoclase particles,the orthoclase particles with zonal texture have relatively low K_(2)O contents,with K_(2)O/Na_(2)O ratios of 15.86-20.85.The LA-ICP-MS analyses show that orthoclase particles contain Ba contents of 700.08×10^(-6)-47606.91×10^(-6) and very low contents of other trace elements and rare earth elements which are very limitedly different among various orthoclase particles.With the increase of Ba contents,both overall colors of slates and orthoclases become darker.Therefore,the color darkness of orthoclase is positively correlated with the high Ba content.