关于高纯石英原料矿石地质学评价方法的探讨

Discussion on the geological evaluation for high purity quartz raw material

高纯石英资源是一种重要的战略性资源。本文结合高纯石英成矿地质特征及其对后期选矿提纯、材料加工等的影响,系统总结了高纯石英原料中杂质的赋存状态、形成机理以及评价方法等,得出:(1)可以作为高纯石英原料的潜在岩石类型有花岗伟晶岩(包括不含暗色矿物的伟晶状花岗岩)、脉石英以及水晶,岩浆演化晚期的伟晶状花岗岩-伟晶岩早期阶段的NYF型花岗伟晶岩结晶形成的石英纯度更高,后期适当的变形变质作用更有利于高纯石英矿床的形成。高纯石英原料矿石中石英矿物呈现无色透明至半透明,矿物构造裂隙少,伟晶岩型矿石矿物组成通常为石英、钠长石、条纹长石、白云母等,黑云母等暗色矿物含量极少,基本不见锂辉石、独居石等稀有金属矿物和电气石、萤石等含挥发分矿物。(2)影响高纯石英的主要地质因素包括脉石矿物及晶界杂质、包裹体、晶格杂质等。其中包裹体类型、数量和尺寸是包裹体评价的关键指标,天然石英矿物中的气液两相包裹体、矿物包裹体和<10μm包裹体应尽量少;Al和Ti是晶格杂质元素评价标志性元素,通常要求天然石英矿物中Al<50×10-6和Ti<10×10-6。(3)建议按照手标本特征-石英矿物特征-石英中包裹体特征-晶格元素赋存状态及含量的顺序,从宏观到微观,综合借助光学显微镜、扫描电子显微镜(SEM)、阴极荧光光谱分析系统(SEM-CL)、激光剥蚀电感耦合等离子质谱仪(LA-ICP-MS)等开展地质学评价和研究工作。

High purity quartz is an important strategic resource. This paper systematically summarizes the petrographic characteristics, impurities' existing state and formation and evaluation methods for high purity quartz. The results suggested that: (1) Potential rocks that can be used as raw materials for high purity quartz include granite pegmatite, quartz vein, and crystal. The quartz that crystallized in late stage of magma evolution-early stage of the pegmatitic granite (NYF) may be more possible to form high-purity quartz;Moderate metamorphism and deformation in the later stage is beneficial for the formation of high purity quartz. The quartz mineral is transparent to semi-transparent, with minimal mineral structural fractures. The mineral composition of pegmatite type ores is usually composed of quartz, albite, perthite, muscovite, etc., minimal content of mafic minerals, without rare metal minerals and volatile minerals. (2) The main factors affecting quartz purity include: gangue minerals and grain boundary impurities, inclusions, lattice-bound elements, etc. The type, quantity and size of inclusions are the most critical indicators for inclusions evaluation. The quantity of mineral inclusions, gas-liquid inclusions, and < 10μm inclusions in quartz minerals should be as low as possible. Al and Ti are the most important elements for lattice-bound elements evaluation, and typically require Al < 50×10-6 and Ti < 10×10-6. (3) It is recommended to conduct evaluation and research work from macro to micro levels, and the order can be: Geological occurrence characteristics-the inclusion characteristics, configuration and content of lattice-bound elements in quartz. We can use optical microscopy, scanning electron microscopy (SEM), cathode fluorescence (SEM-CL), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), to conduct research work.