TY - JOUR
T1 - Equilibrium iron isotope fractionation factors of minerals
T2 - Reevaluation from the data of nuclear inelastic resonant X-ray scattering and Mössbauer spectroscopy
AU - Polyakov, V. B.
AU - Clayton, R. N.
AU - Horita, J.
AU - Mineev, S. D.
N1 - Funding Information:
Valuable comments by AE T. Chacko and constructive reviews by C.M.Johnson and E.A.Shauble promoted significant improvements of the paper, especially, the discussion chapter. We are particularly grateful to Dr. J.F. Lin for numerical data on Fe 3 S PDOS. V.B.Polyakov and S.D.Mineev acknowledge support of Scientific Program # 7 of the Geoscience Department of Russian Academy of Sciences. Research was supported in part by an appointment to the Higher Education Research Experience at the Oak Ridge National Laboratory for Faculty, sponsored by U.S. DOE and administered by the Oak Ridge Institute for Science and Education. J. Horita was sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy, under contract DE-AC05-00OR22725, Oak Ridge National Laboratory, managed by UT-Battelle, LLC. R.N.Clayton acknowledges support of the NSF through grant EAR-0439925.
PY - 2007/8/1
Y1 - 2007/8/1
N2 - We have critically reevaluated equilibrium iron isotope fractionation factors for oxide and sulfide minerals using recently acquired data obtained by Mössbauer spectroscopy and inelastic nuclear resonant X-ray scattering (INRXS) synchrotron radiation. Good agreement was observed in the iron β-factors of metallic iron (α-Fe) and hematite calculated using both Mössbauer- and INRXS-derived data, which supports the validity and reliability of the calculations. Based on this excellent agreement, we suggest the use of the present data on the iron β-factors of hematite as a reference. The previous Mössbauer-derived iron β-factor for magnetite has been modified significantly based on the Fe-sublattice density of states obtained from the INRXS experiments. This resolves the disagreement between naturally observed iron isotope fractionation factors for mineral pairs involving magnetite and those obtained from the calculated β-factors. The correctness of iron β-factor for pyrite has been corroborated by the good agreement with experimental data of sulfur isotope geothermometers of pyrite-galena and pyrite-sphalerite. A good correlation between the potential energy of the cation site, the oxidation state of iron and the iron β-factor value has been established. Specifically, ferric compounds, which have a higher potential energy of iron than ferrous compounds, have higher β-factors. A similar dependence of β-factors on the oxidation state and potential energy could be extended to other transition metals. Extremely low values of INRXS-derived iron β-factors for troilite and Fe3S significantly widen the range of iron β-factors for covalently bonded compounds.
AB - We have critically reevaluated equilibrium iron isotope fractionation factors for oxide and sulfide minerals using recently acquired data obtained by Mössbauer spectroscopy and inelastic nuclear resonant X-ray scattering (INRXS) synchrotron radiation. Good agreement was observed in the iron β-factors of metallic iron (α-Fe) and hematite calculated using both Mössbauer- and INRXS-derived data, which supports the validity and reliability of the calculations. Based on this excellent agreement, we suggest the use of the present data on the iron β-factors of hematite as a reference. The previous Mössbauer-derived iron β-factor for magnetite has been modified significantly based on the Fe-sublattice density of states obtained from the INRXS experiments. This resolves the disagreement between naturally observed iron isotope fractionation factors for mineral pairs involving magnetite and those obtained from the calculated β-factors. The correctness of iron β-factor for pyrite has been corroborated by the good agreement with experimental data of sulfur isotope geothermometers of pyrite-galena and pyrite-sphalerite. A good correlation between the potential energy of the cation site, the oxidation state of iron and the iron β-factor value has been established. Specifically, ferric compounds, which have a higher potential energy of iron than ferrous compounds, have higher β-factors. A similar dependence of β-factors on the oxidation state and potential energy could be extended to other transition metals. Extremely low values of INRXS-derived iron β-factors for troilite and Fe3S significantly widen the range of iron β-factors for covalently bonded compounds.
UR - http://www.scopus.com/inward/record.url?scp=34447550339&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2007.05.019
DO - 10.1016/j.gca.2007.05.019
M3 - Article
AN - SCOPUS:34447550339
SN - 0016-7037
VL - 71
SP - 3833
EP - 3846
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 15
ER -