Pyrrhotite Fe 1-x S is the main sulphide component of platinum group elements (PGEs) ores where it commonly contains from a few tenths to a few dozen ppm of disseminated Pt. Here we report an investigation of the state of Pt in synthetic pyrrhotite performed by X-ray absorption spectroscopy (XAS) in combination with theoretical spectra modelling. The pyrrhotite crystals were obtained by means of salt flux technique, using an eutectic mixture of alkali metal halides as a transport media.

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... of the chemical composition of synthesized crystals showed that an increase of the temperature and sulphur fugacity yields higher concentrations of Pt in pyrrhotite. The Pt content reaches 0.6 wt% at the maximum achieved temperature and sulphur fugacity (t = 720°C, log f(S 2 ) = -0.1) in Pt-saturated system. Analysis of Pt L 3 -edge XANES spectra revealed that Pt presents in pyrrhotite in the 4+ and 2+ "formal" oxidation states. Theoretical modelling of XANES and interpretation of EXAFS spectra showed that Pt 4+ substitutes for Fe in the crystal lattice of pyrrhotite, whereas Pt 2+ forms PtS-like clusters disseminated in the pyrrhotite matrix. Atoms of isomorphous Pt 4+ are surrounded by 6 S atoms at a distance of 2.39±0.02 Å. According to theoretical FDMNES simulations, the 2 nd coordination sphere of the solid solution Pt contains one vacancy in the Fe sublattice within the Fe-layer. The Pt 2+ S-like clusters can be considered as a quench product. High sulphur fugacity stabilizes the solid solution Pt and prevents the formation of the PtS-like clusters during cooling. The maximum content of the solid solution Pt in pyrrhotite is ca. 50 times lower than in pyrite and can be approximated by a straight line in the log C(Pt) vs. 1/T coordinates, it increases from 1 ppm at 350°C to 3 wt% at 900°C.