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

The Rietveld phase quantitative analysis (RQPA) method has been widely applied in geology. In the analysis of evaporite, the evaluation and error control of precision are important factors to improve the quality. The RQPA method was applied to 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 show that the absolute errors between theoretical and calculated values are 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 the chemical analysis. The standard deviation of binary mixtures is 0.702 for 10 calculated results. The relative standard deviation of the same samples are 1.74%(KCl) and 1.17%(NaCl), respectively. The study indicates that the RQPA method is accurate in the quantitative analysis of mineral contents of evaporite rocks. The error sources arose mainly from the nature of the samples, sample preparation, measuring conditions, and refinement process. Due to the advantages of reducing the preferred orientation, not requiring pure samples, and high utilization of data, the RQPA method has a potentially extensive application in mineral exploration analysis, reserve evaluation, and industries of evaporites, when coupled with the chemical analysis method.