Geochemistry of neutral mine drainage at sulfide deposits ‒ example of the „Grot“ Pb-Zn mine, South-Eastern Serbia

Abstract

This study examines the chemistry of mine waters of the “Grot” Pb– –Zn mine and identifies the hydrogeochemical factors that influence the formation of mine waters chemical composition. Eleven mine water samples were collected at six locations across the area of Kriva Feja in order to determine their chemical composition. Data analysis revealed that the waters belong to the HCO3 -‒SO4 2-‒Ca2+ and SO4 2-‒Ca2+ water types, with neutral pH values. The concentrations of metals in these waters (zinc, lead, barium, copper, chromium) are generally low, and most of the samples meet drinking water quality criteria (USEPA standards). Modelling using the PHREEQC software indicates that the dominant processes in the formation of the chemical composition of these waters are the dissolution of carbonate minerals and the oxidation of sulphide minerals. Carbonate minerals have a scarcer occurrence compared to sulphide minerals, such as galena, sphalerite and pyrite, which are dominantly distributed. The low intensity of sulphide mineral oxidation is interpreted to result from a rapid water exchange and reduced contact time between the water and the rock. The occurrence of this process is localized only in the ore body zone. This study highlights the importance of kinetics (in terms of the chemical reaction rate) as the main factor influencing the oxidation of sulphide minerals and, subsequently the quality of mine waters.

Keywords

• groundwater
• acid mine drainage
• hydrogeochemical factors
• metals
• phreeqc modeling
• saturation index