CHROMIAN DRAVITE FROM THE CHROMITE ORES OF VAVDOS AREA, CHALKIDIKI PENINSULA, NORTHERN GREECE

Emerald green chromian tourmaline of dravitic composition (1.1-13.9 wt % Cr2O3, 8.4 - 10.6 wt % MgO) is found locally in the chromite ores of the Vavdos area, in Chalkidiki peninsula, Northern Greece. The minera l is restricted within shear zones at lithological boundaries between the chromitiferous ultramafics and the metamorphic rocks of the baseme nt. Tourmaline is found with chromian pargasitic-edenitic hornblende, as fracture-fillings in chromite, as the matrix of chromite clasts, or as epitactically grown crystals on chromite grains. Step-scanning ele ctron microprobe analyses revealed that the crystals are compositional ly zoned, showing depletion in Cr, and enrichment in Al, Fe and Ca, fr om core to rim. Tourmaline was formed by the metasomatic action of bor on rich fluids on the initial mineral constituents of the chromite ore . These fluids were released from the tourmaline rich pegmatitic veins outcropping close by and cross-cutting the ultramafic rocks of the Va vdos area.