Abstract
This study attempts to show processes controlling the geochemical evolution of Menengai geothermal system using 1-D reactive transport model. The model uses geothermal fluids, modeled from wellhead discharge chemistry to obtain the initial aquifer fluids. The resulting fluid is then injected into the model at the bottom and allowed to ascend through a porous media as the ‘parent’ fluid. Chemical data from a nearby water borehole was used as initial medium fluid while pressure and temperature information taken from well downhole measurements. The reservoir rocks are predominantly peralkaline, silica-oversaturated trachytes, with a few lenses of tuffs, rhyolite, and basalt, thus, the initial mineral assemblage of the model taken to be of the trachytic composition. The simulation was performed using TOUGHREACT v2, and the model was calibrated using field-observed hydrothermal minerals. This study demonstrates the relationship between fluid flow, chemical reactions, and mass transport in a peralkaline salic volcanic complex, a caldera-hosted geothermal system with a view of explaining the occurrence of hydrothermal minerals in up-flow zones in such systems.
