ABSTRACT

Sixteen hot alkaline waters from geothermal drillholes in S. W. Bulgaria have been studied. Nine of them are in approximate equilibrium with chalcedony, albite, adularia, calcite, kaolinite, and low-temperature calcium zeolite at a temperature close to the outflow temperature. The others are in equilibrium with calcite and kaolinite and oversaturated with albite, chalcedony and adularia at the outflow temperature. Calculations of the evolution of chemical species due to the cooling indicate that equilibrium with these minerals is established at a temperature close to the temperature derived from the chemical geothermometers. Na/K, Na-K-Ca (β=4/3) and chalcedony (or quartz) geothermometers give satisfactory results in the low temperature range 40–140°C. Results obtained corroborate the model previously presented by Michard and Fouillac (1980) for alkaline hot waters.