Field-scale reactive transport models of CO2 and H2S mineral sequestration are in development, with a focus on Reykjavík Energy’s ongoing gas reinjection tests at Hellisheidi geothermal power plant. A new thermodynamic dataset describing the minerals of interest was developed as a part of this study, since widely used thermodynamic databases did not contain the mineral assemblage needed for the simulations. Simulations predict efficient precipitation of both CO2 and H2S into thermodynamically stable minerals, with calcite and pyrrhotite being the favored carbonate and sulfide sequestering minerals, respectively. Despite only being indicative, we conclude from this study that the capture and sequestration of CO2 and H2S from geothermal power plants is a viable option for reducing their gas emissions, and that basalts may comprise ideal geological CO2 and H2S storage formations.