ENRICHMENT PROCESS OF CHROMIUM AND PLATINUM GROUP ELEMENTS IN THE OMAN OPHIOLITE

Chromitite deposits in the mantle peridotite of the ophiolite suites in the Northern Oman Mountains provide insights into the geochemistry of the PGEs. Potential chromitite occurrence was found in the Samad Maqsad area 80 km south of the capital Muscat. Chromitite deposits were divided into two types, podiform and stratiform. Five stratiform chromitite layers were found within a 30-m-wide outcrop with thickness of 10 cm to tens of meters, and in total length of about 10 m enclosed by dunite or its serpentinized equivalent. The shape of podiform chromitite is like a lens and is discontinuous with tens of meters in thickness compared to the stratiform chromitite, which makes an antinodular form complex. They exhibit orbicular and antinodular magmatic textures. The majority of the chromitite samples examined in this study utilizing XRF bulk analysis show high Cr₂O₃ content around 44%, while it ranges from 22% to 32% in the layered chromitite. Al₂O₃ was high in the most chromitites, a typical characteristic in the Oman ophiolite. SiO₂, MgO and FeO contents were higher in the dunite and harzburgite samples than in the chromitite due to high olivine content. Ni content was around 2700 ppm in the dunite compared to the chromitite samples, which are around 1000 ppm. Ni is often associated with the sulfides as iron-nickel sulfide, pentlandite (Fe,Ni)₉S₈ found as interstitial grains. V on the other hand was higher in the chromitite than dunite and harzburgite samples. The positive correlation of V with Cr₂O₃, indicates that V is mainly accommodated in the chromitite. The bulk chemistry analysis have typical ophiolitic PGE chondrite patterns. Chromitites have high Os, Ir, Ru and Rh contents relative to Pt and Pd contents with negatively sloping pattern that defines IPGE group. Dunite and harzburgite are identified by positive sloping patterns with variable positive Ru and negative Pt anomalies defines PPGE group. Therefore, the PGE distribution patterns of the selected samples from the Oman ophiolite belong to IPGE group as other equivalents podiform chromitite deposits around the world.