Mossbauer study of the lattice dynamics of pyrite

Comment on “New data on equilibrium iron isotope fractionation among sulfides: Constraints on mechanisms of sulfide formation in hydrothermal and igneous systems” by V.B. Polyakov and D.M. Soultanov

“…The best fit to the whole data set is obtained with h M = 557 K and Cst = 0.564 mm/s. The characteristic Mossbauer temperature h M = 557 K is within the h M error bar determined by Kansy et al (1984). Fig.…”

“…1). One can note that the data of Nishihara and Ogawa (1979) (Nishihara and Ogawa, 1979;Kansy et al, 1984). inconsistent with their own reported characteristic Mö ssbauer temperature.…”

“…However, this value must be considered with caution since the sample contains several sulfide minerals (Permyakov et al, 2004). An additional study (Kansy et al, 1984), not used until now, investigated the temperature dependence of the Mö ssbauer spectra of a natural pyrite between 290 and 430 K, and proposed a Mö ssbauer temperature of 568 ± 20 K, i.e. lower than the one previously used.…”

“…In this context, it is important to remark that the relative isotopic fractionation factors (e.g., between two different minerals) are much more important for geochemical applications than absolute b-factors. Only b-factors obtained within exactly the same framework should be combined to obtain (Nishihara and Ogawa, 1979;Kansy et al, 1984) along with the best fit corresponding to h M = 557 K, are compared with b-factors obtained from the DFT frequencies (Blanchard et al, 2009) and from h M = 610 ± 15 K (Polyakov and Soultanov, 2011). Error bars on experimental data were determined by propagating the measurement accuracy while error bars on DFT results were determined by propagating the standard deviation found on the scaling factors applied to theoretical frequencies.…”

Response to the comment by M. Blanchard, F. Poitrasson, M. Méheut, M. Lazzeri, F. Mauri, E. Balan on “New data on equilibrium iron isotope fractionation among sulfides: Constraints on mechanisms of sulfide formation in hydrothermal and igneous systems” published in Geochim. Cosmochim. Acta 75 (2011) 1957–1974

“…They calculated the Fe reduced isotopic partition function ratio (b-factor) for pyrite based on corrected Mö ssbauer results by Nishihara and Ogawa (1979) and Mö ssbauer data by Kansy et al (1984), which were not used for the b-factor calculations before, and concluded that the Mö ssbauer-derived b-factor for pyrite is in a good agreement with their previous calculation by the density functional theory (DFT) approach (Blanchard et al, 2009). Blanchard et al (2012 also claimed that all properties of pyrite (including isotopic ones), they calculated by the DFT approach, are in an excellent agreement with all existent experimental data.…”