Hydrogen Isotope Fractionation in the Epidote-Hydrogen and Epidote-Water Systems: Theoretical Study and Implications

Experimental data for hydrogen isotope and, in general, stable isotope fractionation between mineral and water often tend to be widely divergent primarily because of solution and reprecipitation of finely ground mineral grains in the experimental charges. With the objective of development of a theoretical methodology for calculation of stable isotope fractionation that may be suitably integrated with experimental data to produce better constraints on the fractionation behavior, we have calculated hydrogen isotope fractionation in the epidote-water and epidote-hydrogen systems, for which reliable experimental data are available. The calculations were carried out using a combination of classical and statistical thermodynamics and quantum chemical methods. The calculated fractionation factors versus temperature in both systems have been found to be in very good agreement with the experimental data and provide a theoretical framework for extrapolation of experimental data as a function of temperature.