Weathering of granodiorite and micaschists, and soil pollution at Mt. Mottarone (northern Italy)

At the top of Mt. Mottarone a thin level of micaschist, covered by soil, rests on granodioritic rocks. Both rock types underwent weathering with generation of new minerals and variation of the original chemical composition. The weathering produced phyllosilicates and Fe- and Al-hydroxides. Mass balance calculations on the basis of Zr immobility indicate that at least As, Bi, Cd, Mo and Sb were added to the micaschist, whereas the other elements were removed; the soil was also enriched in As, Bi, Cd, Mo and Sb during weathering. Dry and wet pollution was responsible for the addition of the elements listed above. On the other hand, Ca, Na, Mo and Sr were surely removed from the granodiorite during weathering, whereas Bi and Cu were added by percolation from the overlying micaschist. The chemical features of a spring issuing from granodiorite agree well with the element budget as deduced from the rock transformation. This is not the case, however, for a spring issuing from the micaschist.