Numerical modelling of an aqueous F-Cl-Na-K-Al bearing fluid in local equilibrium with granitic rocks with relevance to enhanced geothermal systems and ore deposit formation.

We investigate infiltration of an aqueous fluid into granitic rocks by means of numerical models at the field scale. Our methodology is based on a finite difference approach for solving the transport problem in combination with lookup tables generated from precomputed thermodynamic equilibria covering the compositional space. We also compare results to an approach involving on-the-fly calculation of local equilibrium between fluid and rock. Porosity and density evolution is predicted based on mass conservation. The ability to predict porosity evolution is valuable to better understand applications such as enhanced geothermal systems (EGS). The prediction of reaction zone sequences is also helpful in the understanding of ore deposit formation. We demonstrate how sensitive the metasomatic zoning sequences are to varying rock and fluid composition. As an example, we model metasomatic zone sequences observed in topaz-greisen to show how metasomatic sequences comprising multiple lithologies can be formed in one event with constant incoming fluid composition as boundary condition. Lithological zones formed along fractures do not necessarily imply temporal changes in the fluid composition of the source.