Fine-grained weathering products in waste disposal from two sulphide mines of the Northern Apennines, Italy

From mineralogical and chemical characterization of two waste-rock piles from Vigonzano and Libiola sulphide mines in the northern Apennines, two types of fine-grained weathering products were recognized. One, from the Vigonzano mine, has a typical blue colour and consists of the Cu-Al sulphate of the woodwardite group. Its formation is related to an alkaline geochemical barrier, it is rather stable in acidic solution, and it controls Cu and Zn dispersion in the surrounding environment. The other group of sediments has a typical ochreous colour. Vigonzano samples consist mostly of goethite, whereas ferrihydrite is abundant in the Libiola sample. The ochreous sediments are enriched in Co, As, Mo, Se and Mn, thus significantly reducing the potential environmental hazard of the site, whereas solubility tests indicated possible problems due to Al dissolution at Libiola.