Deciphering Hydrochemical Characteristics and Formation mechanism of Groundwater in the Pongo Iron Mine Area, Peru

Abstract

Understanding the hydrochemical characteristics and formation processes of groundwater in mining areas is crucial for protecting and utilizing underground water resources. This study analyzed 42 groundwater samples from the Pongo mining area in Peru to determine the spatial-temporal distribution patterns and formation processes of chemical components. Statistical analysis, Gibbs diagrams, ion ratios, and hydrogeochemical modeling techniques were used. The results show that the groundwater in the study area is weakly alkaline (pH = 7.72) and has a total dissolved solids (TDS) range of 253.19 to 17912.82 mg/L, with an average of 2788.31 mg/L. About 55% of the groundwater samples are classified as brackish or saline water. According to the Gibbs diagram, the chemical composition of groundwater is mainly controlled by evaporation and rock weathering. Furthermore, ion ratios indicate the contribution of human activities, oxidation of pyrite, and desulfurization reactions to ionic concentrations in this groundwater system. The dissolution of evaporite minerals such as halite and gypsum contributes to the presence of Na+, Cl−, and SO42−, while Ca2+ and Mg2+ mainly come from the dissolution of minerals like calcite, gypsum, dolomite, and silicate. It is worth noting that approximately 38% groundwater samples have recorded NO3− concentrations levels surpassing the standard limit of 10 mg/L for drinking purpose, which is mainly attributed to agricultural activities. Moreover, the hydrogeochemical modeling indicates a strong dissolution tendency for halite and propensity for dissolution for gypsum, calcite, and dolomite. Additionally, pyrite oxidation and cation exchange processes also occur.