THE IMPACT OF THE TAILINGS STORAGE FACILITIES OF THE MORRO DO OURO MINE ON DOWNSTREAM WATER QUALITY, MINAS GERAIS, BRAZIL

The Morro do Ouro Mine located near Paracatu, Minas Gerais, and owned by Kinross Gold, is the largest gold mine in Brazil. The mine tailings are stored behind two dams, the Santo Antônio Dam and the Eustáquio Dam, with current storage volumes of 399 million m³ and 148 million m³, respectively. Acid mine drainage is suggested by the strong reddish-brown color of the flow from the dam drainage pipes even after treatment with crushed limestone. The same reddish-brown color is found in shallow, hand-dug wells downstream from the tailings dams. The affected downstream population consists of a quilombola community (descendants of escaped slaves) and a major expansion of the mine involved the displacement of two quilombola communities. Two previous studies funded by the City Hall of Paracatu and by Kinross Gold of As in groundwater and surface water were inconclusive due to flawed methodologies and reporting. The city-funded study reported on groundwater and surface water upstream from the dams, but only on surface water downstream from the dams, and measured only filtered samples, while the company-funded study did not report the methodology, sample locations, or individual As values. The objectives of this study are (1) to assess the quality of drinking water and environmental water downstream of the tailings dams (2) to determine whether any degradation of water quality results from flow or seepage from the tailings dams. In May 2019 both filtered and unfiltered water samples were collected in triplicate downstream from the dams from nine hand-dug wells, eight streams, five boreholes, two dam drainage pipes, and one spring. Filtered and unfiltered water samples were also collected in triplicate upstream of the dams from four boreholes, two springs and one stream. Measurement of on-site parameters included temperature, pH, electrical conductivity, dissolved oxygen, and oxidation-reduction potential. Stable isotopes of water are being measured in order to determine whether water samples have the isotopic signature of precipitation or of a tailings pond. Water samples are being analyzed using the Perkin-Elmer Optima 8000 ICP-OES for the contaminants and other elements typically associated with hardock gold mining, including Ag, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sn, Ti, and Zn. Results will be reported at the meeting.