THE FORGOTTEN ENVIRONMENTAL PASSIVES: IMPLICATIONS AND NEED OF AN INVENTORY OF ABANDONED MINE TAILINGS IN SONORA, MEXICO

Abandoned mine tailing represent environmental passives that act as important sources of pollutants into the environment. Abandoned mine tailings can be the result of large- or small scale historical mining, or can actually be the result of recent or artisanal mining in developing countries such as Mexico. Sonora, located in northwestern Mexico, is characterized by three metallogenetic belts, which consist of orogenic gold, porphyry Cu, and epithermal (Au-Ag) deposits. Several abandoned mine tailings can be found along these belts. Although the Mexican regulations are severe for active mining, the abandoned mine tailings are mostly ignored in terms of pollutants emissions. The lack of a georeferenced inventory in Sonora, including the geochemical features and health risk is essential know the environmental risks and to establish mitigation programs. Two contrasting cases of abandoned tailings are shown in this investigation: 1) The historical large-scale mine tailing situated within the urban area of Nacozari de García town; and 2) The relatively recent small-scale mine tailing situated 0.5 km of the San Felipe de Jesús. The first tailing has relatively low metal concentrations, exposed over a huge area (~640,000 m²), but more importantly located within the urban zone. In contrast, the second tailing is enriched in metals (Zn = ~18%, and Pb = 1.5%), and is covering an area of ~40,000 m², located outside the town, but next to agricultural fields and the river of Rio Sonora. The contrasting features suggest different pollution and human health risks. The preliminary data highlight the need of a geographically controlled and categorized inventory of mine tailings in Sonora, for the analysis of geoinformation and geochemical features, to determine potential pollution and health risk.