Platinum-group minerals and their host chromitites in Macedonian ophiolites

Abstract

Several ophiolite bodies that have been a significant source of chromium ore are located in the Vardar Zone of Macedonia. Three relatively small (maximum 15 × 4 km) bodies have been studied in detail. In the Radusa and Lojane complexes, the mantle series consisting of harzburgite and rare dunite are well preserved, whereas minor pyroxenite and gabbro occurrences belong to a poorly preserved cumulate series. The Rabrovo massif corresponds to the basal part of the cumulate sequence. In all three complexes, chromitite mineralization occurs as pods and irregular layered bodies and exhibits all the characteristics of typical ophiolite mineralization with nodular, orbicular, net, schlieren or massive texture, and an Mg–Cr-rich composition. Platinum-group minerals (PGM) are associated with the chromitite concentrations. Described for the first time in Macedonia, they are typical of ophiolitic chromitite, dominated by the laurite–erlichmanite solid solution, and rare Ru–Os–Ir alloy, cuprorhodsite and cuproiridsite. One of the characteristics of the Macedonian PGM is a relative Cu enrichment, marked by Cu-PGM, but also by the presence of Cu in solid solution in laurite, and the occurrence of a Cu-sulfide rim around the PGM trapped in chromite crystals, suggesting that Cu was present in the PGE–S system.