ABSTRACT

The chemical analyses of the mineral waters issuing in the basin of Vichy St Yorre provide the means to decipher different subsuperficial modifications superposed on the fluid originating at great depths: (1) Increasing amounts of dissolved Ca, Sr, Mg and sometimes K, by gradual attack of shallow host rocks. (2) Precipitation of silica and associated aluminium. (3) Mixing with fresh surface waters. The comprehensive study of these alterations allows to shed light on the initial composition of deep water. From the silica content, the Na/K ratio and the calcite saturation, a temperature of 135°C is inferred for this water.