Equilibrium Versus Kinetics in CO2 Dominated Hydrothermal Alteration

Abstract

Compositional differences between unaltered protoliths and altered rocks fiom mineral water wells can be related to the compositional variations between groundwater and highly concentrated bicarbonate waters in order to reveal the alteration reactions. One basic process is sufficient to explain the range of bicarbonate waters occurring in the Rhenish Massif: Carbonic acid, produced by the dissolution of magmatic CO, in groundwater, gradually dissolves unstable primary minerals of the wallrock, exposed on fiesh fracture surfaces along the flow path, while the successive formation of stable alumosilicates and carbonates precipitates the surplus of dissolved species. Thermodynamic reaction progress simulations including in-eversible and equilibrium steps are suitable to quanti@ water rock ratios as well as the amounts of reaction products.