Inverse geochemical modelling demonstrates how weathering and ion surface exchange control groundwater chemistry in the Pra Basin (Ghana)

Effective implementation of sustainable water resources management is one of the daunting tasks in most parts of the world. The Pra Basin has a high economic importance, hosting most of Ghana’s mineral resources, including gold, bauxite, iron, manganese, and diamonds. Currently, the basin is faced with several water resources management issues, especially pollution arising from the discharge of untreated waste into water bodies and illegal artisanal mining. Considering this background, the present study aims to determine the geochemical processes controlling the Pra Basin’s groundwater chemistry and provide the baseline information for groundwater management. A total of 65 groundwater samples sourced from boreholes (depths >30 m) were analysed for their physico-chemical parameters. Hierarchical cluster analysis and inverse geochemical modelling were applied to the hydrochemical data to investigate the sources of variation in groundwater hydrochemistry in the area. Three major geochemical processes were determined as drivers for groundwater chemical evolution: dissolution of carbonates, weathering of silicates and ion exchange. Inverse modelling underlines the dissolution of primary biotite, dolomite, halite, plagioclase, and precipitation of secondary calcite and gypsum as the apparent dominating reactions, reflecting the general groundwater chemistry in the basin. Groundwater evolves, namely from CaHCO3 to NaHCO3, and finally into NaCl water along its flow path. The presented results improve our understanding of the hydrochemical controls of the groundwater resources and support the design and implementation of sustainable water resources management strategies for the Pra Basin.