电子探针技术探究钪在白云鄂博矿床不同矿物中的赋存特征

Application of Electron Probe Microanalyzer in Exploring the Occurrence Characteristics of Scandium in Different Minerals of the Bayan Obo Deposit

随着对钪资源需求的不断增加,世界各国近年陆续开展钪成矿机理研究及找矿工作,核心内容之一是厘清钪的赋存特征。据前人研究,各类钪矿床中钪主要以类质同象、离子吸附形式存在,目前发现的含钪矿物种类已逾800种。对于白云鄂博矿床,钪资源储量较大,无独立钪矿物产出,钪以类质同象形式进入其他矿物,分布分散、含量低。囿于测试技术及取样限制,目前尚无利用精确定量技术系统探究钪在白云鄂博矿床不同矿物中赋存特征,因而主要富钪矿物查明程度不够,难以进一步探讨钪在矿床中富集机制,亦不利于下一步钪资源的利用和勘查找矿。为了解决这一问题,本文利用电子探针技术,对白云鄂博矿床34种矿物进行系统测定。测试结果表明,6种矿物中钪(Sc;O;)平均含量大于0.100%,从高到低为铌钇矿(2.485%)、铌铁矿(1.263%)、铌锰矿(0.251%)、黑紫色萤石(0.181%)、方钍石(0.145%)、富钇易解石(0.124%),其中铌钇矿是各矿物中单点钪含量最高的矿物(3.093%);16种矿物中钪含量介于0.004%~0.067%,分别为褐钇铌矿(0.067%)、碱性角闪石(0.062%)、铁钍石(0.060%)、黄绿石(0.049%)、铌钙矿(0.031%)、氟碳铈矿(0.028%)、磷灰石(0.028%)、铈硅磷灰石(0.025%)、独居石(0.023%)、霓石(0.02%)、黑云母(0.019%)、硅镁石(0.011%)、褐铈铌矿(0.008%)、钾长石(0.007%)、磁铁矿(0.005%)、钠长石(0.004%);12种矿物未检出钪。通过分析发现:(1)本次研究矿区钪含量最高的矿物为铌钇矿,主要6种富钪矿物为铌钇矿、铌铁矿、铌锰矿、黑紫色萤石、方钍石、富钇易解石;(2)34种矿物中,22种矿物钪含量高于电子探针检出限,钪呈稀散分布;(3)钪的赋存与钛、钇及钍有关,钪与钛、钇、钍的相关系数分别为0.869、0.835、0.720。主要分布在铌、铁、钍稀有氧化物、黑紫色萤石、钛铌酸盐的复杂氧化物和链状硅酸盐中,进入矿物时与矿物晶体结构可能有相关性;(4)钪与铌铁矿、铌钙矿、铌锰矿、富钇易解石等铌矿物关系密切,可考虑将钪资源与铌资源同时综合利用。

BACKGROUND: With the increasing demand for scandium resources, countries around the world have carried out scandium metallogenic mechanism research and prospecting in recent years. One of the key research contents is to clarify the occurrence characteristics of scandium. According to previous studies, scandium mainly exists in the form of isomorphism and ion adsorption in various scandium deposits. At present, more than 800 kinds of scandium-bearing minerals have been found. The scandium resource of the Bayan Obo deposit is large, which has the characteristics of dispersed distribution and low content. Scandium enters other minerals in the form of isomorphism and no independent scandium mineral is found. Due to the limitation of testing technology and sampling, there is no accurate quantitative research to systematically explore the occurrence characteristics of scandium in different minerals in the Bayan Obo deposit. Therefore, the identification of the main scandium-bearing minerals is insufficient, which is not conducive to further exploration of the enrichment mechanism of scandium and the utilization of scandium resources in the deposit.OBJECTIVES: To understand the occurrence of Sc in different minerals of the Bayan Obo deposit.METHODS: 34 kinds of minerals in the Bayan Obo deposit were systematically determined by electron probe microanalyzer(EPMA) technology.RESULTS: The test results showed that the average scandium content(Sc;O;) in 6 minerals was more than 0.100%. They were samarskite(with average Sc;O;content of 2.485%), columbite(1.263%), manganocolumbite(0.251%), dark purple fluorite(0.181%), thorianite(0.145%) and Y-rich aeschynite(0.124%) from high to low. Samarskite had the highest scandium content(3.093%). The content of scandium in 16 minerals ranged from 0.004% to 0.067%, which were fergusonite(with average Sc;O;content of 0.067%), alkaline amphibole(0.062%), ferrothorite(0.060%), pyrochlore(0.049%), fersmite(0.031%), bastnaesite(0.028%), apatite(0.028%), britholite(0.025%), monazite(0.023%), aegirine(0.02%), biotite(0.019%), humite(0.011%), fergusonite-(Ce)(0.008%), feldspar(0.007%), magnetite(0.005%), albite(0.004%). Scandium was not detected in the other 12 minerals.CONCLUSIONS: Samarskite has the highest scandium content in the deposit, and the 6 main scandium-bearing minerals are samarskite, columbite, manganocolumbite, dark purple fluorite, thorianite and Y-rich aeschynite. Among the 34 minerals, the content of scandium in 22 minerals is higher than the detection limit of EPMA, and scandium is distributed in a dilute manner. The occurrence of scandium is related to titanium, yttrium and thorium, and the correlation coefficients are 0.869, 0.835 and 0.720, respectively. Scandium is closely related to niobium minerals such as columbite, manganocolumbite, fersmite and Y-rich aeschynite. It can be considered to comprehensively utilize scandium and niobium resources at the same time.