Equilibrium status of some mineral springs in Victoria

Abstract

The chemical composition of 26 mineral springs in the Daylesford district of Victoria was determined at regular intervals over about 2 years, and the possible equilibria examined. All the springs have a similar composition, but a common reservoir is doubtful. A similar mechanism for the origin of the waters appears to operate throughout the region. For the springs on a line approximately east-west and about 1 km north of the Dividing Range, the water compositions are those expected for an equilibrium between kaolinite and montmorillonite (Ca and Na). To the north of this line the composition is appropriate to water in equilibrium with montmorillonite, while to the south the water composition relates to kaolinite. The geographical distribution of the composition shows a rough relationship to the rainfall, with the higher rainfall associated with the equilibrium line. An equilibrium with K = [Na⁺]/[K⁺] = 50 appears to be generally established in the district and may involve the potassium and sodium feldspars. The concentration of CO₂ is about 14% in excess of the calculated equilibrium value for the existing conditions of pH, HCO₃^- and temperature. Evidence is given confirming that the probable source of the CO₂ lies in the vicinity of Babbington's Hill. It is suggested that the main source of the cations in solution is the basalt rather than the altered sediments of the region.