GEOCHEMISTRY OF ABANDONED MINE TAILINGS AND RURAL DUST FROM A NEARBY TOWN: A CASE OF IGNORED POLLUTION IN SEMI-ARID ZONES OF NORTHWESTERN MEXICO

Abandoned mine tailings are considered as one of the main sources of potentially toxic elements. Because of the lack of control of abandoned mine tailings from small-scale or artisanal mining, the tailings have become part of the natural landscape for decades, especially in rural areas from developing countries. Abandoned mine tailings represent a latent problem in terms of the possible affectations to human health and environment. An example of this is the small-sized (~200 x ~300 m) abandoned mine tailings located ~500 m from the San Felipe de Jesús town, Sonora, in northwestern Mexico. In order to determine the possible impact of the tailings, concentrations of potentially toxic elements were measured using a portable X-ray fluorescence in samples from mine tailings, unpaved roads soils, and road dust from San Felipe de Jesús. Enrichment Factor, Geoaccumulation (Igeo), Contamination Index (CI) and Hazard Average Quotient (HAQ) were calculated in order to assess contamination and risk. The Igeo values for road soil samples indicate no pollution to moderately contamination in order of importance as follows As> Pb> Cu> Zn> Sb, while moderately contamination in order of importance (Pb> As> Zn> Cu> Sb) for road dust samples. In general, EF values suggest minor enrichment of As, moderate enrichment for Pb and Zn, lower enrichment for Cu, and finally no enrichment for Sb. The CI values suggest that mine tailing materials have the highest probability of emitting contaminants into soils/sediments in the following order: Efflorescence minerals (CI=285), non-oxidized tailing (CI=251), oxidized tailing (CI=106), road soil (CI=23), and road dust (CI=3). These contaminants can be transported due to the semi-arid conditions in the region, and potentially can have a negative impact on the surrounding agricultural fields and population. The HAQ values (for soluble elements) from efflorescence minerals (5169-38100) and mine tailings (143-2891), indicate that the potential of toxicity is very high, and can potentially affect the quality of groundwater and drinking in the region.