A MINERALOGICAL AND GEOCHEMICAL APPROACH TO ASSESS AND CONTAIN POLLUTION IN ABANDONED MINING AREAS OF SARDINIA

Abandoned mining areas are subject to environmental hazards of different nature; however the most dangerous effect of the cessation of mine activity consists in the chemical contamination of soil and water which demands investigation strategies capable of describing sources and pathways of contaminants and containment strategies devoted to limit the diffusion of toxic components. On the one hand economy and environmental resources of Sardinia have been seriously degraded by the abandonment of a thriving industry lasting approximately longer than one century, on the other hand some parts of the island have acquired great relevance as archaeological industrial sites and test areas for scientific studies on remediation strategies in abandoned mining areas. In the South-western mining districts of Iglesias and Guspini-Arbus Pb-Zn ore processing produced an estimated volume of 8.106 m3 of abandoned flotation mud from settling ponds and wastes from rock dumps. After the dewatering plants were stopped, flooding of mines caused the flow out of contaminated water from adits everywhere. In the South-eastern mining district the As mine at Baccu Locci , abandoned in 1965, is still generating a harmful impact on the downstream coastal plain. The studies undertaken by the mineralogical-geochemical group of the University of Cagliari has revealed: (I) Pb, Cd, and Zn dissolved amounts in the streams draining the South-western area reach up to 1, 1.7, and 1000 mgl-1 respectively; (II) these amounts are slightly influenced by the pH even at values approximating the neutrality; (III) the solubility control of these metals is ruled by the precipitation of silicate or carbonate species (the last ones induced by the presence of microorganisms); (IV) the high dissolved amounts of As, observed in the Baccu Locci catchment even at long distance from the mine, are related to the continuous supply from contaminated materials transported downstream and the high mobility of this element under near neutral-oxidative conditions.