Phase equilibria in the KFeS2–Fe–S system at 300–600 °C and bartonite stability

The article deals with phase relations in the KFeS 2 –Fe–S system studied by the dry synthesis method in the range of 300–600 °C and at a pressure of 1 bar. At the temperature below 513 ± 3 °C, pyrite coexists with rasvumite and there are pyrite–rasvumite–KFeS 2 and pyrite–rasvumite–pyrrhotite equilibria established. Above 513 ± 3 °C pyrite and rasvumite react to form KFeS 2 and pyrrhotite, limiting the pyrite–rasvumite association to temperatures below this in nature. The experiments also outline the compositional stability range of the copper-free analog of murunskite (K x Fe 2− y S 2 ) and suggest that mineral called bartonite is not stable in the Cl-free system, at least at atmospheric pressure and the temperature in the experiments. Chlorbartonite could be easily produced after adding KCl in the experiment. Possible parageneses in the quaternary K–Fe–S–Cl system were described based on the data obtained in this research and found in the previous studies. The factors affecting the formation of potassium–iron sulfides in nature were discussed.