Geochemistry of lead at the old mine area of Baccu Locci (South-East Sardinia, Italy)

About a century of exploitation of the galena-arsenopyrite deposit of Baccu Locci in Sardinia (Italy) has caused a severe, persistent arsenic contamination that extends downstream of the mine for several kilometres. Differently from As, the aqueous contamination of lead is only localised in the upper part of the mine despite very high Pb concentrations in geologic materials (waste rocks, tailings, stream sediments, soils) over the whole Baccu Locci stream catchment. The determination of aqueous and solid Pb speciation in various environmental media of the Baccu Locci system has pointed out that the peculiar geochemical behaviour of Pb is mainly due to (i) the short residence time of dissolved Pb in surface and ground water under near-neutral pH conditions and (ii) the low solubility of plumbojarosite that represents the main secondary Pb-bearing mineral in the Baccu Locci environment