CHROMITE ORES IN THE GERAKINI-ORMYLIA OPHIOLITES, CHALKIDIKI PENINSULA, NORTHERN GREECE

The Gerakini-Ormylia ophiolites, Chalkidiki peninsula (N. Greece), hos t chromite ore segregations gradational from disseminated to massive t ype. The chromite ores are linked with variably serpentinized dunitic lithologies. Primary mineral constituents are Cr-rich chromite (Cr2O3 = 47 to 58 wt.%, Al2O3 = 11-18 wt.%, Mg/(Mg + Fe2+) = 0.32-0.65 and Cr /(Cr + Al) = 0.65-0.77), olivine (Fo(90-94)), minor orthopyroxene (En( 90-93)Fs(6-8)) and clinopyroxene (En(48-50)Fs(1.5-2.5)Wo(47-50)). Seco ndary minerals include serpentine, talc, carbonates and the chromian s ilicates chlorite (1.6-7.4 wt.% Cr2O3), titanite (1.5-3.6 wt.% Cr2O3), calcic amphibole (0.8-2.6 wt.% Cr2O3) and phlogopite (1.5-1.9 wt.% Cr 2O3). The chromite chemistry of the Gerakini-Ormylia chromite ores is indicative of a supra-subduction zone related environment for the ophi olitic host rocks. Chromian silicates formation is considered concomit ant to the alteration of chromite to ''ferritchromite'' under upper gr eenschist to lower amphibolite facies metamorphic conditions.