细微矿物拉曼成像分析技术与方法研究

岩矿鉴定是各类地质工作开展的基础,其鉴定水平和质量直接影响着工作的深入程度和研究程度。传统鉴定方法受人员自身经验水平、光学显微镜分辨率等因素的影响较大,对于现今需要研究的细微稀有矿物、细粒沉积岩矿物等很难准确地识别鉴定。而依托高精密大型仪器的技术方法多数对样品制备有特殊要求,不利于样品的再利用,诸如扫描电镜、电子探针等在高倍数反射光下探寻、观测特定的细微透明矿物也存在一定的不足。本文将激光拉曼高分辨大面积快速成像方法(StreamLineHR)运用于两块标准岩石光薄片的全区域大面积扫谱,准确识别出其中透明矿物有碱性长石、斜长石、石英、普通角闪石、黑云母、方解石、榍石、磷灰石、锆石和绿帘石,不透明矿物有磁铁矿,部分矿物间存在紧密伴生的情况(如石英与长石、榍石与角闪石)和次生蚀变的情况(如长石碳酸盐化蚀变为方解石)。并以此为基础进行了含量统计,将其分别定名为细粒角闪石英二长闪长岩与细粒黑云母斜长角闪岩。实验过程中,荧光效应,类质同象类矿物(长石、角闪石)峰位相似性和蚀变矿物峰位偏移会对矿物识别、谱图解析造成干扰,可结合矿物镜下光性特征来解决。另外,面扫步长设置越小,分析精确度越高,时间成本也会相应增加,应用时需兼顾考虑。该方法实现了对细微矿物便捷、直观、准确的大范围快速识别鉴定,可弥补传统岩矿鉴定和其他技术方法的不足,拓展了拉曼光谱法在地质工作中的应用范围。

Raman Imaging Analysis Method of Fine Minerals in Rock Ore

BACKGROUND: Mineral identification is the basis of all types of geological work, and its appraisal level and quality directly affect the depth and degree of research of a study. Conventional identification methods are significantly influenced by experience level, optical microscope resolution, and other factors. It is difficult to accurately identify fine rare minerals and clay minerals that need to be studied. Additionally, most of the technical methods relying on high-precision large-scale instruments have special requirements for sample preparation, which is not conducive to the reuse of the samples. It is also inconvenient to explore and observe specific fine transparent minerals under high multiple reflected lights, such as scanning electron microscopy and electron microprobe.OBJECTIVES: To develop a more rapid and accurate method for identifying fine minerals.METHODS: The laser Raman high-resolution large-area fast imaging method (StreamLineHR) was applied to the whole-area large-area scanning spectrum of two standard rock slices.RESULTS: The transparent minerals were identified as alkali feldspar, plagioclase, quartz, amphibole, biotite, calcite, sphene, apatite, zircon, and epidote. The opaque mineral was identified as magnetite. Some of the minerals were closely associated (e.g., quartz and feldspar as well as sphene and hornblende), and some minerals showed secondary alterations (e.g., feldspar was transformed to calcite). Based on the content statistics, the two thin sections were named fine-grained amphibolite monzonite and fine-grained biotite plagioclase amphibolite.CONCLUSIONS: Experimental results showed that this method was more accurate than the conventional methods used for the identification of fine minerals with very low content. However, the interference caused by the fluorescence effect, similarity in peak positions of similar minerals (feldspar, amphibole), and shift of the peak position of altered minerals during mineral identification and spectral fitting were solved by combining the optical characteristics under the mineral objective lens when necessary. In addition, the smaller the setting of the surface sweep step size, the more accurate the analysis, and the time cost correspondingly increased. This method realized the rapid identification of fine minerals over a large range, which was convenient, intuitive, and accurate. It compensated for the shortcomings of conventional rock and ore identification and other technical methods and expanded the application scope of Raman spectroscopy in geological studies.