FIRST REPORT ON PLATINUM-GROUP MINERALS IN CHROMITITES J%OM NORTHWESTERN NEYRIZ OPHIOLITE, IRAN

Electron-probe microanalyses and scanning electron microscopy of chrornitites from some ultramafic members of Neyriz ophiolite indicate that sulifides of platinum- group minerals (PGMs) occur as solid inclusions in chromite grains. Laurite with the general formula of (Ru ,Os ,lr ) S , and erlichmanite are the main identified sulfide phases. The PGMs occur as 4 to 20 microns euhedral to rectangular inclusions, and seem to be confined to massive chrornitite deposits. The PGMs do not seem to have exsolved from chromite, it is believed that their crystallization has taken place prior and/or during the crystallization of this mineral. Some secondary minerals of rare earth elements (REEs) were also found to fill the micro cracks and fractures in chromite grains. Semiquantitative analyses reveal the presence of appreciable amounts of Ce and La along with some minor quantities of Gd, Eu, Pr, and Nd. These secondary minerals are extremely small and none were found to be larger then 10 microns in diameter. Some base metal alloys (largely made of Ni-Fe), along with magnetite, ferritechromite, and some olivine and pyroxene silicate inclusions are also reported.