Initial behavior of granite in response to injection of CO2-saturated fluid

To understand the initial reactions of granite in a CO2-saturated hydrothermal system, experiments were conducted using a batch-type autoclave over a temperature range of 100–350 °C at up to 250 bar and numerical computations of phase equilibria based on the experimental results were carried out. The experiments showed that the dissolution of granite and the deposition of secondary minerals were encouraged by the addition of CO2. Solution chemistry and examination of the granite’s surface texture suggested that its initial dissolution is characterized by the release of Na and Ca (from the dissolution of plagioclase) and that initial precipitation occurs by deposition of some secondary minerals on to plagioclase and/or biotite in the CO2-saturated system. However, the effect of CO2 was small at 350 °C owing to the low activity of H2CO3. According to EDX analysis and numerical phase equilibrium calculations, the secondary minerals formed might be kaolinite, muscovite, smectite and calcite. That is, the granite as a whole might have the potential to take-up dissolved CO2. The results suggest that the alteration of granite under CO2-saturated hydrothermal conditions has the potential to capture CO2 when it is injected at moderate temperatures (150–250 °C) into granite-hosted rock masses.