Crystallization of a Monosulfide Solid Solution under Diamond Formation Parameters: Experiments in the Fe-Ni-S System

Samples of a monosulfide solid solution (Mss) based on alpha-NiS and FeS have been obtained at P = 7.0 GPa and T = 900-1500 degrees C with presynthesized sulfide compounds using the solid-phase method at T = 400-600 degrees C. The structural and textural characteristics of the samples have been identified. Based on the features discovered and the chemical compositions of sulfide phases, a fragment of the phase diagram in the Fe-Ni-S system has been constructed with the assumed solidus and liquidus lines set. Thus, the obtained results show that in the studied range of compositions a complete series of solid solutions of minerals is formed. The evolution in the composition of the monosulfide solid solution and of the corresponding sulfide melt under diamond formation conditions as a function of temperature change has been traced. We have obtained preliminary estimates for the maximum Ni content in sulfide melts (up to 58 wt %), which may crystallize the minerals found in inclusions in natural diamonds of the peridotite paragenesis.