Modeling of the impact of dolomite and biotite dissolution on vermiculite composition in a gneissic shallow aquifer of the Sila Massif (Calabria, Italy)

Reaction path modeling of water–rock interaction in a gneissic shallow aquifer of the Sila Massif was performed in kinetic (time) mode, under conditions of closed-system with secondary minerals and closed-system with CO2, to investigate the influence of both dolomite dissolution and biotite dissolution on the chemical characteristics of secondary vermiculites. Magnesium–Al- and calcium–Al-vermiculites are the major components of the vermiculite solid solution precipitated in the early stages of the process, which is dominated by dolomite dissolution. In contrast, Mg–Mg–Fe- and Ca–Mg–Fe vermiculites are important components of the vermiculite solid solution produced in the late stages of the process, where biotite dissolution prevails. Outcomes of this reaction-path-modeling exercise on vermiculite chemistry are fully consistent with the results obtained by Apollaro et al. (in press) through speciation–saturation calculations. In particular, Apollaro et al. (in press) showed that the pH of Mg–Al-vermiculite/Mg–Mg–Fe-vermiculite coexistence is 7.3. This value is virtually equal to the pH of Mg–Al-vermiculite/Mg–Mg–Fe-vermiculite iso-activity, 7.35, which is obtained from the results of reaction-path-modeling runs 3 and 4 carried out in this work.