The reactive surface areas of the most abundant reacting minerals have been estimated in the granite hydrothermal field of Jiangxi Province in South-East China. The chemical composition of the sampled fluids was used as input data and the continuous equilibrium approach was assumed for the kinetic calculations. Dissolution rates and the reactive surface areas of different minerals were obtained by reconstructing the chemical evolution of the interacting fluids in a reaction process schema defined by a fractional degree of advance of the irreversible mass-transfer process. We found that the reactive surface area ratio of albite/K-feldspar varies by 23 orders of magnitude while that of biotite/K-feldspar ratio by 4 orders of magnitude. The obtained results indicate that mineral reactive surface areas are not constant during the fluid-granite interaction: higher reactive surface areas were obtained at higher pCO2 partial pressure (lower pH) compared to water with lower pCO2 partial pressure (higher pH). The eventual formation of secondary clay-minerals overlaying the primary ones may be responsible for decreasing the contact area of the rock-forming mineral in thermal waters having higher pH. The results of our investigation indicate that the reactive surface area of biotite play an important role in the CO2-neutralizing process of this area that in turn, controls the natural releasing of CO2 to the atmosphere in this area.