| Summary: | The water-rock interactions under geothermal conditions for metasomatic basalt and rhyolite were studied experimentally and with using geochemical calculations to understand the potential of in situ carbon capture storage in previously altered geothermal rock bodies by analyzing water chemistry, primary and secondary rock mineralogy and chemistry, and saturation indices for select secondary minerals and carbonates. The experiments were conducted at 250°C and 40 bar with altered basalt samples collected from Geitafell (SE Iceland), altered rhyolite samples from Slaufrudalur (SE Iceland), and non-geothermal spring water from Vellankatla (SW Iceland) containing 8.04 ppm CO2. The reaction between the altered rocks and CO2 injected spring water showed no potential for CO2 mineralization instead preferring precipitation of other Alumina-Silicate secondary minerals, particularly smectites, clays, and epidotes according to the saturation indices calculations. The majority of the minerals observed were shown to be stable and undersaturated. Solid rock mineral chemistry was shown to have undergone at most negligible change from their pre-experiment chemistries. Water chemistry has shown decreases in ion concentration for Ca, Na, K, and Mg with CO2 decreasing in the case of the rhyolite experiment while SiO2, Al, F, Cl, SO4, and Fe remained relatively stable. The experiments and calculations showed that metasomatic basalt and rhyolite do not possess the potential for precipitating carbonates for use in CCS technology and that only un-altered rock bodies should be considered.
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