Elemental and mineral composition of salts from selected natural and mine-affected areas in the Poopó and Uru-Uru lakes (Bolivia)

The environmental effects of extensive mineral extractions have been the focus of recent remediation efforts in the Poopó and Uru-Uru lakes (Bolivia). Our study determined the chemical and mineral composition of salt and water samples collected in mine areas (MA) and natural sites [basin and lakes (BL), Salar de Uyuni (SU)] in the Oruro mining district. The laboratory techniques that we used included X-ray diffraction, scanning electron microscopy and total elemental analysis. Results revealed that salt samples in SU sites were dominated by halite, while thenardite, halite and konyaite were observed in BL. Sites in MA had > 15 species of sulphates, oxides, hydroxides and other minerals. Metals such as Au, Ba, Cd, Co, Cr, Cu, Li, Ni, Pb, Sn, Sc, and Zn were elevated in salt samples in MA sites compared to BL and SU sites. Salts in MA sites had lower pH (3.2) than BL (pH = 9.6) and SU (pH = 8.0). In MA sites, dissolution of minerals during the rainy season may mobilize metals from terrestrial (e.g., tailing deposits) to aquatic environments. We can conclude that mining activities combined with some natural metal mobilization events such as dissolution of salt efflorescence on rainy days and oxidation of pyrites may degrade the quality of water and land in the region.