Mineralization of sulfidic minerals including realgar, orpiment and pyrite occurs in argillic alteration zones in northeastern Iran, which affects water quality and health in these semi-arid localities. Geochemical source of ions in surface and ground waters was examined to evaluate potential effects of sulfidic mineralization on water quality. The surface and groundwater samples were analyzed to determine the major ions (Na+, Ca2+, Mg2+, K+, HCO3−, SO4 2−, Cl−) and trace elements (such as As, B, Br). Water-rock interactions and evaporation defined as the key phenomena on groundwater chemistry using Gibbs diagram. Concentrations of arsenic (As) varied from 16 to 606 μg/L,whichwas higher than theWHO (2011). Calculated ionic ratios revealed that anions and cations in surface and ground waters originated from partial leaching through ion exchange in alteration zones. We postulate that the primary source of As resulted from oxidation of As-bearing sulfide minerals such as orpiment,realgar and arsenopyrite in argillic-pyrite alteration zone. High pH (N8) could provide the alkalinity to increase sulfide oxidation and release As into thewater. The stable isotope data (δ18Oandδ2H) indicated the origin of the waters, which is mainly meteoric precipitation with partial effects from evaporation processes and exchanging ions with surrounding rocks. This confirms the notion that the source of all analyzed ions including the toxic As is geogenic. Hydrogeochemical process, which affected thewater chemistry and thus environmental public health are likely to be water-rock interactions and evaporation.

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