Rietveld定量方法在蒸发岩矿物组分分析中的精确度评价和误差来源

Rietveld物相定量分析(RQPA)方法在地质学中已有大量应用,在蒸发岩定量分析中,对精确度的评价和误差控制是提高分析质量的重要因素。本文对人工配制和野外采集的样品(石膏和钾盐)进行RQPA分析,并与化学分析结果对比,评价其精确度并分析其主要的误差来源。结果表明:人工配制的氯化钠-氯化钾二元物相的绝对误差为0.4%~0.9%;氯化钠-氯化钾-碳酸钙三元物相的绝对误差为0.1%~1.2%;二元物相样品10次分析的标准偏差为0.702%,相对标准偏差为1.74%(氯化钾)和1.17%(氯化钠);野外采集的石膏和钾盐样品的RQPA分析结果与化学分析结果具有很好的一致性。表明RQPA方法在蒸发岩矿物组分定量分析中具有较高的精确度,其误差主要来源于样品性质、样品制备、测试条件和精修过程等。RQPA方法具有减弱择优取向效应、无需纯样以及提高数据利用率等优点,与化学分析技术联用在蒸发岩矿产勘探、储量评价以及工业应用中具有广泛的前景。

Assessment of Accuracy and Error Sources of the Rietveld Quantitative Phase Analysis Method in Mineral Contents of Evaporites

Rietveld phase quantitative analysis (RQPA) method has been widely applied in geology. In the quantitative analysis of evaporite, the evaluation and error control of precision are important factors to improve the analysis quality. In this paper, RQPA method was applied to the simulated binary mixtures (halite and sylvite), ternary mixtures (halite, sylvite, and calcite), and geological samples (i.e., gypsum and sylvite samples). The contents of each mineral calculated by RQPA were compared with the results of chemical analytical data to evaluate the RQPA''s accuracy and the main error sources were analyzed. The results showed that the absolute errors between theoretical and calculated values were in the range of 0.4%-0.9% and 0.1%-1.2% for the binary and ternary mixtures, respectively. The mineral contents of geological samples matched very well with the results of chemical analysis. The standard deviation of binary mixtures is 0.702 for 10 calculated results. The relative standard deviation of the same sample are 1.74% (KCl) and 1.17% (NaCl), respectively. The presented study indicated that RQPA method got high accuracy in the quantitative analysis of the mineral contents of evaporite rocks. The error sources mainly came from the nature of samples, sample preparation, measure conditions, and refinement process. Due to advantages of reducing preferred orientation, no need of pure samples, and high utilization of data, the RQPA method has a potentially extensive application in the mineral exploration, reserve evaluation, and industries of evaporites, when coupled with chemical analysis method.