Hydrogeochemical and isotopic investigations in the abandoned Fe-Cu mine of Libiola (northern Italy)

摘要

Hydrogeochemical and isotopic studies carried out over three years (1996-1998) in the abandoned Fe-Cu sulfide mine area of Libiola are reported. The acid drainage, which can be ephemeral or restricted to high water flow conditions in some sites, carries high content of Fe, Al, Cu, Zn, Mn, Ni, Co, Cr and Cd. Gradual mixing of the acidic waters with normal, diluted, alkaline surface waters develops a selective removal of heavy metals from the solution; sudden mixing produces an almost complete purification of the waters, leading to fine-grained ochreous sediments enriched in heavy metals. δ~2H and δ~(18)O values of mine water match those of local rainwater, thus denoting high water to rock ratio during mineral alteration processes. Aqueous sulfate is enriched in ~(34)S with respect to ore sulfide, probably due to oxidation processes mediated by photosynthetic sulfur bacteria.