Metal distribution and environmental problems related to sulfide oxidationin the Libiola copper mine area (Ligurian Apennines, Italy)

Metal mobility and distribution in water and sediments in the surroundings of the pyrite-chalcopyrite-sphalerite mine of Libiola, in the Gromolo Valle y near Sestri Levante (Genova), are investigated to evaluate the environmen tal hazard in the area. The mineralisation, related to Apennine ophiolites, was already known in the Bronze Age (about 2500 yr BC), but economic explo itation started in the XVII century. Open galleries, waste dumps and acid d rainage testified the past mining activities which ended in 1965. Mine waste material, covering an area of about 0.5 km(2), is reddish-yellow ish, generally coarse-grained and stratified. The waste is a mixture of bas alt, ultramafic-derived and iron-rich phases, with relatively high concentr ations of S (mean 0.3% S) and Cu (mean 0.3% Cu), and significant contents o f Zn, As, Mo and Se. Acid drainage, with pH values as low as 2.5, is quite rich in dissolved Fe, Al, Cu, Zn, Mn, Ni. Repeated sampling revealed marked chemical variations, particularly in the mine waste area, depending on water flow conditions. W here low-pH water mixes with normal (pH 8) surface water, reddish amorphous iron phases (e.g. ferrihydrite, schwertmannite) precipitate, favouring the scavenging of many elements carried by the acid waters and providing a nat ural way of remediation for the stream waters. The rapid flocculation cause s anomalous contents of Fe, Cu, Zn, Co, Sc, Y, La, Ce, and to a lesser exte nt of Cr and Ni, in the sediments. Although the ochreous colloids are impor tant components of the Gromolo River sediments for about 8 km from the mine , preliminary results indicate that, unless natural conditions change, remo bilisation of heavy metals should not be expected. (C) 2001 Elsevier Scienc e B.V. All rights reserved.