The Fe–S Binary at 6 GPa

The abundance of sulfide inclusions in diamonds, mantle xenoliths, and meteorites determines the importance of studying the Fe–S system at mantle pressures and temperatures. In the present work, the phase relationships in the Fe–S system were studied at 6 GPa in the range of 450–1500°C using a Kawai-type multianvil press. It was found that in the entered temperature range, the iron metal does not dissolve measurable amounts of sulfur and remains solid. Two intermediate compounds are stable in the system: a monosulfide solid solution (Fe1 – xS, where x = 0–0.036, 50–54 mol % S) and iron disulfide (FeS2). In coexistence with iron metal or Fe-rich liquid, monosulfide solid solution contains 50 mol % S. The Fe–FeS eutectic is located at 1000°C and 33 mol % S. Sulfur content in Fe1 – xS, coexisting with FeS2, increases from 52 to 54 mol % as temperature increases from 500 to 1100°C and does not change systematically with further temperature increase. At 1500°C, Fe1 – xS is still crystalline. The Fe1 – xS–FeS2 eutectic is situated at 1350°C and 63 mol % S. FeS2 melts congruently at 1375°C. In the range 450–1200°C, the solubility of Fe in sulfur does not exceed the detection limit (<0.5 mol %). At 1300°C, sulfur melt coexisting with FeS2 contains 10 mol % Fe. At 1400°C in the ranges of 20–43 and 58–100 mol % S, the system undergoes complete melting.