ENVIRONMENTAL ASSESSMENT OF ABANDONED MINE TAILINGS FROM NACOZARI DE GARCÍA, NORTHWESTERN MEXICO: INSIGHTS FROM GEOCHEMISTRY AND UNMANNED AERIAL VEHICLES

Mining is known as one of the primary economic activities where exploitation of minerals and other materials of the earth’s crust have become essential for human development. However, this activity represents a risk for the environment, starting from deforestation and ending with the production of a mineral residue that may contain potentially toxic elements. Mine tailings are an example of mining residues that may represent an environmental passive when abandoned and exposed to environmental conditions. Therefore, characterization of abandoned mine tailings is of great concern in order to assess risk of population and environment. Nacozari de García city, Sonora, in northwestern Mexico, is characterized by three abandoned mine tailings within the urban area, and represent important sources of dust and pollutants. In the present study, unmanned aerial vehicles (UAV) in conjunction with geochemical studies are used in order to have a geographical and geochemical perspective to assess the environmental impact. Digital elevation models of the abandoned mine tailings (I, II, and III) were obtained using the photogrammetry with UAV. A total of 47 surficial samples were collected from the three mine tailings to obtain the metal concentrations using a portable X-ray fluorescence (PXRF). The obtained surfaces of mine tailing I, II, and III, are 167336, 70569, and 404075 m², respectively, which accounts for a total of 641980 m² and represent around 11% of the urbanized area. The calculation of actual and loss of volume of the mine tailings will be determined from the digital elevation models. According to the metal concentrations, the contamination indexes for the mine tailings I II, and III, are 48.046, 42.333, and 17.104, respectively. These values are considered very high in toxicity and may be representing a risk to the surrounding population and environment.