Acid drainage from Pan de Azúcar Mine, and possible arsenic input in Pozuelos Lagoon basin, Argentina

MURRAY, J.; ALICIA MATILDE KIRSCHBAUM; DOLD, BERNHARD

Proceedings of the First International Conference on Mine Water Solutions in Extreme Environments ? Mine Water Solutions 2013

Peperback

Lugar: Lima; Año: 2013; p. 342 - 350

Sulfide oxidation in tailings impoundments, especially pyrite, produces acid mine drainage (AMD), which is one of the most serious environmental problems caused by mining. Pan de Azúcar Mine is located in the Altiplano Region of Northwest Argentina. The mine is situated at an altitude of 3,300 m and the annual precipitation is 350 mm. Mining operations ceased in 1990 without setting any closure plan. Pb-Zn-Ag metals were recovered after a benefaction process that included milling and flotation. The tailings deposits are about 1 m thick and cover an area of 70 ha. A high grade of sulfide oxidation process, secondary minerals formation and acid conditions were identified. Acid waters, with high sulfate (139 g/l SO42) and heavy metals content (44 ? 0.7 mg/l As, 99.7 ? 3.2 mg/l Cd, 1.7 ? 0.4 mg/l Cr, 21.3 ? 10 mg/l Cu, 47 ? 1.3 mg/l Fe, 1.4 ? 0.1 mg/l Pb, 8,960 ? 388 mg/l Zn) drain from the tailings. Pan de Azúcar is situated 25 km upstream from the Pozuelos Lagoon (UNESCO Biosfere Reserve); Cincel River, the main lagoon tributary, drains near the mine and receives acid drainage from the tailings impoundments. In order to evaluate the possible influence of heavy metals in the Cincel River, in the aquifer and finally in the Pozuelos Lagoon, water samples were taken in the rainy season and analyzed by ICP-MS and ICP-OES. The pH values increase rapidly from the acid mine drainage (pH = 2.1 to 3.44) source to the downstream river and aquifer sampling points (pH = 7.3 to 7.9). All water samples show a diminution in metals concentration downstream due to the increasing pH values and metals co-precipitation and sorption in secondary minerals. Nevertheless, the concentration of arsenic still represents a risk for human consumption for all samples from the aquifer (values above 0.01 mg/l (OMS)). Reducing condition and near neutral pH values for underground water favors the presence of As(III) as H3AsO3 and its migration in the aquifer. The source for the As detected in water samples could be directly related to the mine wastes and sulfide oxidation. However, another source for As could be the presence of effusive volcanic rocks in the surrounding area.