Potential environmental hazard in the mining district of southern Iglesiente (SW Sardinia, Italy)

A stream sediment survey carried out in southern Iglesiente, southwestern Sardinia, comprised 249 samples which were analysed for 35 elements. The data from 83 samples derived from a previous survey by Ente Minerario Sardo were also used. Maps showing element distribution were created using the GIS program Arc View 3.1. For the compilation of potential risk maps, the regional distribution of the elements has been reclassified using as thresholds the Italian intervention criteria for residential/recreational and commercial/industrial land use. The main concentrations of heavy elements mainly follow the carbonate lithologies, hosting most of the ore deposits of Mississippi Valley and Sedimentary Exhalative types. Fairly high contents of Pb, Zn, Cd, and As are reflected in the stream sediments sampled along the carbonate ridges bordering the mining district along the Iglesias syncline. Treatment plants, tailings and dumps are also located in this area. Another area with high metal values is the swampy river mouth of Rio Sa Masa, near Gonnesa, draining not only the main mining sites of the Iglesias syncline, but also the small industrial areas around the town of Iglesias and a few villages. Potential risk maps have been compiled for four elements: Zn, Pb, Cd and As. Among those, the state of geochemical pollution is very serious for Cd, Pb, and Zn, which are the main elements contained in the stratabound orebodies, but less so for As. If even only partly transfered to the soils, the concentration in these elements should limit any further development in this area, unless remediation is carried out