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Geochemical modelling and seasonal hydrogeochemical processes of the open-pit groundwater at O’Kiep, Namaqualand, South Africa

To assess dissolution, precipitation processes and saturation indices (SI) of some mineral phases, PHREEQC modelling software was used to assess these different geochemical processes and to elucidate reactive minerals of the open-pit groundwater (OPGW) in O’Kiep, Namaqualand, South Africa. Equilibrium constants were not fixed into the coding of the software PHREEQC, to accommodate equilibrium constant changes, and PHREEQC user input file manipulation. The SI of less than zero implied that the OPGW was undersaturated and that mineral dissolution was required to reach equilibrium. The data of the hydrogeochemical analysis indicated that the sources of ions into the OPGW are largely from the dissolution and leaching of mine waste and tailings including runoffs during the wet season, with the underlying fracturing of rocks, cation exchanges and other anthropogenic activities making a contribution. Additionally, climatic seasonality significantly influenced the OPGW hydrogeochemistry, indicating that the hydrological processes which control changes were dilution and mobilization of potentially toxic elements (PTEs). The data set generated showed that the OPGW chemistry was mainly influenced by evaporation, ion exchange, silicate weathering and dissolution of minerals including precipitation. Overall, this dataset details hydrogeochemical processes that are responsible for seasonal variations in the OPGW chemistry.