白云鄂博稀土氟碳酸盐矿物的LA-ICP-MS多元素基体归一定量分析方法研究

研究稀土氟碳酸盐矿物的激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)成分分析方法能为认识稀土矿床成因提供新的、简便的技术手段。本文选取白云鄂博产的氟碳铈矿和黄河矿,通过对常规基体归一定量法改进,按照稀土氟碳酸盐矿物的晶格配位模式对Ba、Ca元素以(Ba,Ca)CO_3的形式、轻稀土以REECO_3F的形式进行加和归一计算,获得的成分数据结果与电子探针和内标法结果基本吻合。该方法可在ICP-MS因电离能过高、不能准确测量C、F元素的情况下通过基体归一法实现稀土氟碳酸盐矿物多元素的定量分析,并且可替代繁琐的内标法,简化了LA-ICP-MS测试流程。多尺寸束斑条件数据比对结果表明,5μm小束斑条件下数据质量差,但10μm束斑条件下获得的氟碳铈矿成分与其他大束斑条件下的结果较为接近,基本能够满足小颗粒稀土氟碳酸盐矿物元素成分的测定。

Multi-element Content Analysis of Rare Earth Fluorocarbonates from Bayan Obo Deposit by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry(LA-ICP-MS) can provide a new and simple technique to analyze the chemical compositions of fluorocarbonates for understanding the genesis of rare earth deposits. Bastn site and huanghoite from Bayan Obo in polished thin sections are directly examined. According to the lattice coordination mode and the characteristics of light rare earth-rich in Bayan Obo fluorocarbonates, the major element Ba,Ca in forms of(Ba,Ca)CO₃ and light rare earth in forms of REECO₃F are calculated in the matrix-normalization methods. These results agree with the data of electron microprobe and internal standard method analyses. This improved method solves the problem of quantitative analysis by matrix-normalization when carbon and fluorine elements cannot be measured accurately in ICP-MS and simplifies the test process. The composition comparison results of bastnäsite under multi-beam spot size conditions show large data errors in 5 microns. However, more consistent data are obtained in 10 microns with larger spot size conditions, which satisfy the analysis requirements of small fluorocarbonate grains.