The potential of water resources contamination around a large-scale gold mine

Abstract

This study used the hydro-chemical properties and isotopic signatures of water to understand the main sources of deterioration of water quality around the North Mara gold mine in Tarime District, Mara Region. The chemical and isotopic signatures of the surface and groundwater were used in understanding the origin, flow pattern, residence times, and vulnerability to pollution. Most samples that were located downstream, western side of the mine tailings dam were slightly acidic with pH as low as 4.6 and enriched with stable isotopes. Most samples with elevated concentrations of Na+ , Cl- , SO4 2- and NO3 - could not be isotopically linked with the local geochemistry, but the observed water chemistry was controlled by evaporation and anthropogenic effects. The Piper trilinear diagram showed Ca and Mg cations dominance, while bicarbonates and sulfates dominated the anions. The heavy metals, Pb and Hg levels (mean 70.29 and 17.95 µg/L, respectively) were all higher than the levels recommended in both the World Health Organization (WHO) and Tanzanian drinking water guidelines. The low pH values and elevated concentrations of cyanides, heavy metals, and metalloids were probably associated with mining activities. The radioactive isotope results indicated the vulnerability of the water to recent contamination that could be attributed to near-surface anthropogenic activities. Moreover, stable isotopic studies indicated the pollutants-carrying water flow pattern was from the eastern to the western side of the study area. Lowland samples had higher tritium activities than the highland ones. Therefore, the present study concludes that groundwater recharge from recent local precipitation may have an impact on the sources studied and the use of shallow dug out wells should be minimized.