SOILS AFFECTED BY ACID-MINE WATERS IN GALICIA (NW SPAIN)

Contaminated soils and surface waters, from copper mining in Galicia, are acidic, high in sulphate and increase appreciably in the concentra tion of elements such as Al, Fe, Ca, Mg, K, Mn, Cu and Zn by contact w ith soils and fragments of rock of an amphibolic composition. Applicat ion of activity data to mineral equilibrium diagrams illustrates the i nstability of Al-hydroxides and aluminosilicates compared to Al-sulpha tes of the alunite and jurbanite type, in the waters which are most ac id and display sulphate activities close to 10(-2) M. The solution ext racted from soils around the spoil heaps reflects the strong influence of the most heavily contaminated run-off waters, with little or no bu ffering by the solid phase. This aspect may be accounted for by both a brief time of residence and a real decrease of the acid buffering pow er of these soils, whose primary minerals undergo strong acidolysis. N eoformation of Al-sulphate (and Fe-sulphate) is observed both in soils and in the channels of the contaminated streams, above all the points of contact with non-acid or slightly acid waters.