TRACING OF THE COPPER SULFATE SOLUTION SPILL IN THE RÍO SONORA BASIN, NORTHWESTERN MEXICO: INSIGHTS FROM PB-ISOTOPE SYSTEMATICS

Mining activity is classified as high risk because of the use, handling, transportation, and storage of chemicals. In fact, mining chemical emergencies cause high costs whose consequences are reflected in material damages, adverse health and environmental effects, and socio-economic problems. The failure of mine tailings is the main cause of release of fluids with metals into the environment. In the last five decades, at least 63 major emergencies related to mine tailings have been recorded globally. In August of 2014, the failure of the Tinaja 2 dam of the Buenavista del Cobre mine in Cananea, Mexico, caused a copper sulfate leachate spill, whose volume was estimated about 40,000 m3 of solution, which was drained into the Río Sonora Basin. In order to trace the copper solution, the systematics of Pb-isotopes was used to determine the isotopic signatures of the lithology and sediments of the Río Sonora Basin. The Pb-isotopic ratios of the studied samples were measured MC-ICP-MS. The lead isotope ratios of the lithology are ²⁰⁶Pb/²⁰⁴Pb = 18.455-19.675, ²⁰⁷Pb/²⁰⁴Pb = 15.587-15.706, ²⁰⁸Pb/²⁰⁴Pb = 38.504-39.089. The Pb-isotope ratios for the sediments are ²⁰⁶Pb/²⁰⁴Pb = 18.559-19.171, ²⁰⁷Pb/²⁰⁴Pb = 15.602-15.666, ²⁰⁸Pb/²⁰⁴Pb = 38.530-39.148. The lead data for the sediments of the tailings dam is ²⁰⁶Pb/²⁰⁴Pb = 18.505, ²⁰⁷Pb/²⁰⁴Pb = 15.606, ²⁰⁸Pb/²⁰⁴Pb = 38.568. The results suggest a linear arrangement from a less radiogenic member characterized by the sediments of the tailings dam, and a more radiogenic member characterized by granitic and altered rocks of the Río Sonora Basin. There is a strong correlation between the Pb-isotope signatures between the sediments and lithology exposed along the basin. The preliminary data suggest that the Pb-isotope signatures in sediments from the dam are not recorded in studied sediments along the Río Sonora.