Evaluation of the environmental contamination at an abandoned mining site

Abstract

This paper reports the preliminary findings of an environmental survey carried out at an abandoned mining site. The wastes were stored in dumps with poor release control. The mining site had been active for over a century and was mostly exploited for its stibnite mineral. Quantitative analyses were performed on wastes, groundwater, surface water and air. Elements of concern were As, Cd, Hg, Pb, Sb, Sn and Zn. The results of tailing determinations indicated that Pb concentration remains almost constant in samples taken at various depths and that As and Hg levels are quite similar. Leaching tests demonstrated that element release was fairly low. With regard to element concentrations in surface water, particular attention should be given to As and Sb levels in the river and As concentrations in the pond. The high levels of As, Hg, Pb and Sb reported in tailings and groundwater may depend on both the presence of a geochemical aureole with elevated average background levels, and on the enrichment of metals in the stored tailings, due to processing. Among the airborne metal levels, the Hg concentration deserves attention. When considering element levels reported in solid and liquid matrices, particular emphasis should be given to As, Hg, Pb and Sb, since these are known to be long-lasting environmental pollutants that are toxic to most forms of life. They are also worth nothing as the disused mine is only a few km from the nearest town and close to areas used for agriculture and animal breeding. Exposure to the toxic agents can also occur for those workers still employed in the area near the mining site; this risk needs an adequate assessment.