Major ion chemistry and weathering processes in the Midyan Basin, northwestern Saudi Arabia.

Chemical characteristics of 72 groundwater samples collected from Midyan Basin have been studied to evaluate major ion chemistry together with the geochemical and weathering processes controlling the water composition. Water chemistry of the study area is mainly dominated by Na, Ca, SO4, and Cl. The molar ratios of (Ca + Mg)/total cations, (Na + K)/total cations, (Ca + Mg)/(Na + K), (Ca + Mg)/(HCO3 + SO4), (Ca + Mg)/HCO3, and Na/Cl reveal that water chemistry of the Midyan Basin is controlled by evaporite dissolution (gypsum and/or anhydrite, and halite), silicate weathering, and minor contribution of carbonate weathering. The studied groundwater samples are largely undersaturated with respect to dolomite, gypsum, and anhydrite. These waters are capable of dissolving more of these minerals under suitable physicochemical conditions.