Iron and Sulfur Isotope Factors of Pyrite: Data from Experimental Mössbauer Spectroscopy and Heat Capacity

• Published in: Geochemistry international Vol. 57; no. 4; pp. 369 - 383
• Main Authors: Polyakov, V. B., Osadchii, E. G., Voronin, M. V., Osadchii, V. O., Sipavina, L. V., Chareev, D. A., Tyurin, A. V., Gurevich, V. M., Gavrichev, K. S.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01-04-2019; Springer; Springer Nature B.V
• Subjects: Accuracy; Analysis; Analytical methods; Crystal structure; Crystallinity; Earth and Environmental Science; Earth Sciences; Energy; Experiments; Force and energy; Galena; Geochemistry; Heat exchange; Inelastic scattering; Iron; Iron 57; Iron sulfides; Isotopes; Kinetic energy; Mossbauer spectroscopy; Pyrite; Specific heat; Spectrum analysis; Sphalerite; Sulfur; Sulfur compounds; Sulfur isotopes; Sulphur; Temperature; Temperature dependence; Temperature effects; Vibrations; Zincblende; heat capacity of pyrite; pyrite Mössbauer spectrum; pyrite; iron and sulfur isotope fractionation; β-factors of iron and sulfur for pyrite
• ISSN: 0016-7029; 1556-1968
• DOI: 10.1134/S0016702919040098

Mössbauer spectra of pyrite (FeS
2
) are measured within a temperature range of 90–295 K. The isomer shift is described by the Debye model with a Mössbauer temperature θ
M
= 551.4 K. These results are used to calculate the kinetic energy of thermal vibrations of the iron sublattice of pyrite and the iron β-factor for pyrite: 10
3
= (1.2665 ± 0.0391)
x
– (0.4584 ± 0.0283) × 10
–2
x
2
+ (0.2581 ± 0.0239) × 10
–4
x
3
;
x
= 10
6
/
T 
2
(K
–2
). The calculated iron β-factor in pyrite is in good agreement with results of ab initio calculations,
57
Fe nuclear inelastic X-ray resonant scattering in synchrotron experiments, and direct isotope exchange experiments between pyrite and Fe
2+
dissolved in water. The heat capacity of pyrite is measured within a temperature range of 79–300 K and is described using the Thirring expansion. Based on this expansion, the kinetic energy of thermal vibrations of the total crystalline lattice of pyrite is calculated. The kinetic energy of the thermal vibrations of the sulfur sublattice in pyrite is found by subtracting the kinetic energy of the iron sublattice from the total kinetic energy of pyrite crystalline lattice. The temperature dependence of
34
S/
32
S β-factor for pyrite, which was calculated from the kinetic energy of the sulfur sublattice, is 10
3
= (1.7532 ± 0.0623)
x
– (1.0470 ± 0.0752) × 10
–2
x
2
+ (1.0424 ± 0.1126) × 10
–4
x
3
;
x
= 10
6
/
T
2
(K
–2
). This value of the
34
S/
32
S β-factor is in good agreement with the ab initio calculations and with results of isotope-exchange experiments in the pyrite–sphalerite–galena system.