Phase relations in the metal-rich portions of the phase system Pt-Ir-Fe-S at 1000 degrees C and 1100 degrees C

Phase relations in the S-poor portions of the dry condensed Pt-Ir-Fe-S system were determined at 1000 degrees and 1100 degreesC with a particular emphasis on delineation of the solid solubility fields of the Pt-Ir-Fe alloys. At both temperatures, a broad field of gamma (Ir,Fe,Pt) alloy coexists with gamma-(Pt,Fe), Pt3Fe and PtFe which dissolve respectively at least 5.1, 29.3 and 24.0 at.% Ir at 1100 degreesC (2.2, 23.6 and less than or equal to 17.2 at.% Ir at 1000 degreesC). Gaps between the nearly Ir-free Pt-Fe alloys gamma (Pt,Fe), Pt3Fe s.s., PtFe s.s. and gamma (Fe,Pt) were estimated as 20-23 at.%, 40-42 at.% and 54.2-similar to 57 at.% Fe at 1100 degreesC (18-23, 39.5-42.5 and 59-62 at.% Fe at 1000 degreesC). The first gap agrees with data from natural phases by Cabri et ni. (1996). The Fe-rich sulphide melt dissolves only traces of Pt and Ir; Fe1-xS dissolves up to 5.8 at.% Ir at 1100 degreesC and 3.4 at.% Ir at 1000 degreesC. These solubilities and the compositions of coexisting alloys (before low-temperature exsolution) may serve as geothermometers. The S-rich melt dissolves up to 8.2 at.% Pt and 2.5 at.% Ir (measured on a solidified melt) at 1100 degreesC. The Fe-lr thiospinel dissolves up to 2.2 at.% Pt (for the composition Fe21.6Ir18.9Pt2.2S57.3 at 1100 degreesC). The 25-28 at.% Fe portions of Pt3Fe with