硫化物矿物LA-ICP-MS微区定量分析及其在水银洞载金黄铁矿中的应用研究

Measurement of the content and distribution characteristic of trace elements in sulfide minerals is of great significance because of these elements in studying of ore genesis, economic geology and environmental geochemistry. LA-ICP-MS (Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry) is a promising tool for microanalysis of trace elements in sulfide minerals. However, development of analysis of sulfide minerals using LA-ICP-MS has been limited by extensive melting of sulfide minerals occurred during laser ablation, serious interferences and a lack of reference materials for microanalysis of sulfide minerals. The problem of a lack of reference materials for sulfide minerals will be preliminarily overcame by this foundation project. At first, the project will intend to investigate the differences of matrix effect between silicate glass, synthetic sulfide minerals and EMPA(Electron Microprobe Analysis) reference materials. At the same time, the interferences and element fractionation effect of common elements enriched in sulfide minerals will be studied. Then, a comparison of the influence of different melting phenomena during ablation on the analytical results will be studied in detail. A novel quantitative calibration strategy for microanalysis of sulfide minerals by LA-ICP-MS will be established using glass reference materials and matrix-matched sulfide mineral reference materials for EMPA as external standards plus internal standardization calibration, without prior quantitative knowledge of an internal standard element analyzed by EMPA. Ultrafine powders of sulfide mineral calibration materials are prepared to quantitative analysis of matrix-matched sulfide minerals, which directly using the sulfide mineral powder reference materials (GBW07267-GBW07270). Gold-bearing pyrite contained zoning in Shuiyindong gold deposit, Guizhou province is planned to study by LA-ICP-MS. Microanalysis data about zoning features of the ore-forming elements, distribution of elements of interest and REE distribution pattern will provide the genesis of deposit with new useful information. This foundation project aims to solve the problems of quantitative analysis of sulfide minerals by LA-ICP-MS and lay a theoretical and technical foundation for microanalysis of sulfide minerals using LA-ICP-MS.

硫化物矿物痕量金属元素含量及其分布特征在矿石成因、经济地质及环境地球化学等领域具有重要意义，LA-ICP-MS是分析硫化物痕量元素最有应用前景的微区分析技术。由于硫化物矿物在激光剥蚀时产生较严重的熔融现象与干扰，尤其是缺乏微区分析标准物质，阻碍了LA-ICP-MS在硫化物分析中的广泛应用。本项目在详细研究基体效应、干扰及其校正、元素分馏效应及不同熔融程度对分析结果影响的基础上，建立以玻璃标准物质结合电子探针矿物标准物质为外标、内标归一定量技术分析基体匹配硫化物矿物多元素的新方法；制备硫化物矿物超细粉末校准物质，用于基体匹配硫化物定量分析；利用LA-ICP-MS微区分析技术研究贵州水银洞金矿区载金环带黄铁矿，研究成矿元素分带特征、赋存状态及REE分配模式等，为矿床成因等提供新的科学信息。本项目旨在解决硫化物矿物LA-ICP-MS定量分析存在的问题及为应用研究奠定理论和技术基础。

硫化物是矿物学上的一大类，也是地球科学领域研究的重点矿物之一。一方面由于亲铜元素及亲铁元素高度富集在硫化物矿物中，并且常形成具有工业开采价值的大型矿床，因而硫化物矿物具有重大的经济价值；另一方面，硫化物中痕量金属元素的含量及其变化特征在硫化物矿石矿物及矿床形成过程中具有指示剂的作用，可为成矿预测和找矿勘探提供有关的科学信息，在地质学上、环境地球化学上具有重大的应用价值。LA-ICP-MS是硫化物矿物痕量元素分析最有应用前景的一种微区分析技术。然而，由于硫化物矿物在激光剥蚀时产生较严重的熔融现象，受到的干扰也比氧化物复杂，尤其是缺乏基体匹配的微区分析标准物质，阻碍了LA-ICP-MS 在硫化物分析中的广泛应用。. 基体效应是影响LA-ICP-MS分析结果准确性的主要因素之一，但目前并没有一种量化基体效应研究的方法。本研究提出了一种以分析元素与内标元素的强度比(Ii/Iis)为纵坐标、浓度比(Ci/Cis)为横坐标绘制Ii/Iis-Ci/Cis图，以元素对Ii/Iis-Ci/Cis图的线性相关系数R量化基体效应的思路。研究表明，玻璃标准与硫化物矿物标准、硫化物矿物存在较为显著的基体效应，硫化物矿物标准与天然硫化物矿物也存在显著的基体效应，采用玻璃标准及硫化物矿物标准分析硫化物矿物会造成大于10%的分析误差。. 以Fe为内标，利用具有宽范围痕量元素的玄武岩地质玻璃标准GSD-1G及GSE-1G结合黄铁矿电子探针标样用于分析载金黄铁矿的主量元素不具有可行性，无法克服基体效应，会引入大于20%的分析误差，但分析载金黄铁矿的痕量元素可以获得较为满意的结果。因此，LA-ICP-MS可用于分析硫化物矿物中的痕量元素，为矿床成因等地质问题提供新的研究手段。