Chemical characteristics and formation mechanism of mineral water in Mianxian county, Shaanxi province

This study systematically investigated the hydrochemical characteristics and formation mechanism of mineral water in Mianxian County, Shaanxi Province. Based on systematic collection and hydrochemical analysis of 56 water samples from the area, integrated application of Self-Organizing Map (SOM) combined with k-means clustering, Piper trilinear diagrams, correlation analysis, mineral Saturation Index (SI) calculations, and ion ratio analysis, the main findings are as follows: (1) The hydrochemical type assemblages and spatial differentiation characteristics of the mineral water in the study area were revealed. The mineral water is predominantly of the HCO₃-Ca type, generally neutral to weakly alkaline, and classified as fresh water with low total dissolved solids. SOM clustering categorized the water samples into six clusters, with their spatial distribution patterns clearly indicating the differential influences of water-rock interactions (Cluster 1, 3, 4), localized evaporation-concentration (Cluster 5, 6), and mixing-dilution processes (Cluster 2). (2) The key mechanisms controlling the hydrochemical evolution were identified by synthesizing multiple lines of evidence. Both mineral saturation indices and ion ratio analyses confirm that the dissolution-precipitation equilibrium of carbonate minerals is the predominant process governing the hydrochemical composition. The weathering of aluminosilicate minerals (particularly feldspars) constitutes a significant source of ion replenishment, with the weathering system having reached an intermediate stage where kaolinite is the stable product. Local evaporation-concentration and mixing with atmospheric precipitation are important secondary processes responsible for the spatial heterogeneity of water quality. This study elucidates the formation mechanism of mineral water in Mianxian, which is centered on natural water-rock interactions and coupled with multiple processes, providing a scientific basis for the evaluation, development, and protection of mineral water resources in the region.