This paper reports the results of hydrogeochemical surveys carried out in Sardinia, a Mediterranean region with a mining history dating back to pre-Roman times. Among different ore deposits occurring in the region, the largest basemetal deposits were located in the Arburese-Fluminese-Iglesiente districts (SW Sardinia), with galena and sphalerite being the prominent exploited minerals. At some locations, pyrite, chalcopyrite, antimonite, barite and fluorite were also exploited intensively. Peaks in Pb-Zn production were reached in the 1950-1960 decades. The decline of mining industry led to the closure of most mines over the 1970-1990 period. This resulted in estimated 170 abandoned mines and 200 million tons of mining-related wastes. Because environmental regulation of mining activities has been introduced relatively recently, the Regional and National Authorities did not plan any action for limiting the potential adverse effects of mine closure on the water systems. Nowadays, several drainages from flooded mines (flow range: <0.1 to 30 L/s) and diffused seeps from the mining residues left on the ground are the main mining-related sources of contamination in Sardinia. At specific sites, mine drainages show different physical-chemical characteristics (acid and near-neutral pH) and dissolved concentrations of contaminants (e.g. Zn, Cd, Pb, Ni, As, Sb) that span over several orders of magnitude, mainly depending on the composition of ore and hosting rocks. Due to the proximity of mining sites to water resources, and land that is within reach of animals and humans, the major risks to human health are associated with the direct discharge of contaminated waters into the aquatic recipients and soils located downstream of the abandoned mines. The contamination level increases during the rain season, especially under storm events that have been occurring more frequently since the past decade. In fact, high runoff promotes erosion and increases the weathering of mining residues. These processes result in a higher dispersion of toxic and harmful elements that pose serious environmental hazards, especially to the aquatic system. These results should help the Regional and National Authorities to address the increasing public awareness of health related environmental issues and present regulations on the quality of water resources. Also, they might be useful elsewhere for planning remediation actions at abandoned mining sites. Lessons learnt by past mining in Sardinia indicate that a correct disposal and management of the mining residues should be mandatory since the beginning of exploitation and processing at each mine. This would allow to reduce the environmental hazards during mining as well as the cost of rehabilitation after mine closure.
Effects of past mining on the quality of water resources in Sardinia
CIDU, ROSA;FRAU, FRANCO
2009-01-01
Abstract
This paper reports the results of hydrogeochemical surveys carried out in Sardinia, a Mediterranean region with a mining history dating back to pre-Roman times. Among different ore deposits occurring in the region, the largest basemetal deposits were located in the Arburese-Fluminese-Iglesiente districts (SW Sardinia), with galena and sphalerite being the prominent exploited minerals. At some locations, pyrite, chalcopyrite, antimonite, barite and fluorite were also exploited intensively. Peaks in Pb-Zn production were reached in the 1950-1960 decades. The decline of mining industry led to the closure of most mines over the 1970-1990 period. This resulted in estimated 170 abandoned mines and 200 million tons of mining-related wastes. Because environmental regulation of mining activities has been introduced relatively recently, the Regional and National Authorities did not plan any action for limiting the potential adverse effects of mine closure on the water systems. Nowadays, several drainages from flooded mines (flow range: <0.1 to 30 L/s) and diffused seeps from the mining residues left on the ground are the main mining-related sources of contamination in Sardinia. At specific sites, mine drainages show different physical-chemical characteristics (acid and near-neutral pH) and dissolved concentrations of contaminants (e.g. Zn, Cd, Pb, Ni, As, Sb) that span over several orders of magnitude, mainly depending on the composition of ore and hosting rocks. Due to the proximity of mining sites to water resources, and land that is within reach of animals and humans, the major risks to human health are associated with the direct discharge of contaminated waters into the aquatic recipients and soils located downstream of the abandoned mines. The contamination level increases during the rain season, especially under storm events that have been occurring more frequently since the past decade. In fact, high runoff promotes erosion and increases the weathering of mining residues. These processes result in a higher dispersion of toxic and harmful elements that pose serious environmental hazards, especially to the aquatic system. These results should help the Regional and National Authorities to address the increasing public awareness of health related environmental issues and present regulations on the quality of water resources. Also, they might be useful elsewhere for planning remediation actions at abandoned mining sites. Lessons learnt by past mining in Sardinia indicate that a correct disposal and management of the mining residues should be mandatory since the beginning of exploitation and processing at each mine. This would allow to reduce the environmental hazards during mining as well as the cost of rehabilitation after mine closure.
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