Geochemistry of water discharges from the Libiola mine, Italy

Abstract

Two distinct groups of mine waters are found at Libiola. They are red acid waters (pH 2.4-2.8) and blue neutral waters (pH 7.0-7.5), based on the color of the precipitating solid phases. Few occurrences have characteristics intermediate between those of red waters and blue waters. The irreversible mass exchanges taking place during interaction of meteoric waters with mine-waste materials and addition of local groundwaters to acid mine waters were simulated by means of the software package EQ3/6. Results of these simulations were compared with the analytical data of mine waters through activity plots, showing the fields of stability of dominant sulfate, hydroxide, and carbonate minerals. The activity plots and the bimodal distribution of pH in mine waters indicate that the main process governing the chemistry of the mine waters of Libiola is variable interaction of meteoric waters with mine-spoil materials. Mixing between local groundwaters and acid mine waters plays a minor role, if any.