PLATINUM-IRON ALLOYS, THEIR STRUCTURAL AND MAGNETIC CHARACTERISTICS IN RELATION TO HYDROTHERMAL AND LOW-TEMPERATURE GENESIS

Abstract

The structural and magnetic data for the Pt-Fe and Pt-Fe-Cu systems are reviewed in the light of recent advances. Tetraferroplatinum (PtFe) and tulameenite (Pt2FeCu) are both tetragonal with similar cell size. Studies of synthetic phases indicate that a solid solution may exist between them and the composition of natural specimens suggests that this is correct. Tetraferroplatinum and tulameenite are both ferromagnetic and tetraferroplatinum has a Curie temperature which varies with composition between 300 and 480°C. The phase diagram for isoferroplatinum (Pt3 Fe) has recently been completed and the magnetic properties of this phase are now known in outline. At high Fe compositions, isoferroplatinum is ferromagnetic at temperatures above room temperature but at the stoichiometric composition and more Pt-rich compositions the phase is antiferromagnetic with a transition temperature (Curie temperature) at -100 °C. This suggests the possibility of using measurements of the magnetic properties of tetraferroplatinum in relation to the Curie temperature (300 to 480°C.) to determine whether the mineral has a hydrothermal or a magmatic origin. It should also be possible to examine iron-rich isoferroplatinum in the same way to distinguish isoferroplatinum formed at room temperature in lateritic soils from that formed at more elevated temperatures.