The effect of unconfined mine tailings on the geochemistry of soils, sediments and surface waters of the lousal area (Iberian Pyrite Belt, Southern Portugal)

• Published in: Land degradation & development 2005-04, Vol.16 (2), p.213-228
• Main Authors: Da Silva, E Ferreira, Fonseca, E Cardoso, Matos, J X, Patinha, C, Reis, P, Oliveira, J M Santos
• Format: Article
• Language: English
• ISSN: 1085-3278; 1099-145X
• DOI: 10.1002/ldr.662

The former Lousal mine, on the SW limb of the Lousal anticline, closed in 1988. Today Lousal is a small village, with much evidence of environmental and landscape disturbance. This is largely the legacy of mining and mine tailings dumped around the site, which, in turn, caused soil contamination and acid mine drainage. Particular attention is being given by the Portuguese Government to this sort of problem, bearing in mind the State's responsibilities for the abandoned mine sites that occur in many parts of the Country. Despite the semiarid climatic conditions of the area, a visual inspection of the mine site indicates that the tailings are affected by considerable water erosion, particularly during large rainfall events. Significant amounts of Cu, Pb, Zn, As, Cd and Hg, occur within the soil collected near the tailing deposits (292-7013mgkg-1Cu, 871-12930mgkg-1Pb, 126-7481mgkg-1Zn, 597-6377mgkg-1 As, 0·2-16·4mgkg-1Cd and 1-130mgkg-1Hg) and in stream sediments downstream of the tailings site (1-1986mgkg-1Cu, 41-5981mgkg-1Pb, 17-1756mgkg-1Zn, 6-1988mgkg-1 As and 0·2-5·7mgkg-1Cd). All the soil samples collected in the tailings deposits exceed the permissible levels. Near the mine site, significant acid mine drainage is associated with the pyritic material and such waters show values of pH ranging from 1·9 to 2·9 and concentrations of 9249 to 20700mgL-1SO, 959 to 4830mgL-1Fe and 136 to 624mgL-1 A1. Meanwhile, the acid effluents and mixed stream waters also carry high contents of SO, Fe, Al, Cu, Pb, Zn, Cd, and As, generally exceeding the Fresh Water Aquatic Life Acute Criteria.