Granite-Saline Fluid Interactions in a Dynamic Experimental System at 200 Degrees C and 50 Bars

Abstract

Granite dissolution experiments were performed in a dynamic system at 200 ?C and 50 bars on fresh granite from Soultzsous- Forets (NE of France). Two different saline fluids were used for these experiments: about 1 and 10 g?l-1 for the low salinity (LS) fluid and high salinity (HS) fluid, respectively. SEM observations after the experiments showed that K-spars and plagioclase were the most reactive granite minerals with the LS and the HS fluids, respectively. The precipitation rate was high whatever the salinity of the percolative fluids, but the precipitates were of different types: mainly zeolite for the LS fluid and illite for the HS fluid. Measurements of the outlet fluid concentrations of some relevant elements have helped to identify the main chemical processes that occur between granite and hot saline fluids at such a high temperature and pressure.

The experimental results (morphological observations and chemical monitoring of the outlet fluid) provided constraints for a geochemical model that was used to simulate the reaction pathway of the experiments. In this study, the geochemical code EQ3NR (Wolery, 1992) was used to estimate the saturation state of the outlet fluids with granite minerals and a number of potentially precipitating minerals.