The Geochemistry of podiform chromite deposits from two ophiolite complexes, Chalkidiki peninsula, Northern Greece

Abstract

The geochemistry of various petrological units from two mafic-ultramafic complexes, from the Chalkidiki peninsula have been studied. These complexes have been tectonically incorporated into the metamorphic country rocks, forming allochtonous bodies bounded by thrust zones. Chromite deposits occur in both complexes. They are highly sheared in the Gomati complex but grade to host dunite in the Vavdos complex. Major oxide contents and trace element abundances have been determined by X-ray fluorescence spectrometry, mineral analyses have been made by electron microprobe. Data on chromite from both complexes reveal that the chromite ores are of metallurgical type in the Wades complex and of refractory type at Gomati. The genetic model proposed relates to extraction of basaltic melt from depleted upper mantle material and its subsequent fractional crystallization. Podiform chromites are an early product of the crystallization of such a basaltic melt. They are intimately associated with a dunite host rock. The structures of the petrological1y different rock units, suggest formation through processes involving an original magmatic environment. This is reinforced by trends for particular minerals in the Vavdos complex. In the Gomati complex, the rocks are extensively serpentinized although various rock types can still be recognized. Amphibolites, at the contacts to the country rocks, show similarities to ocean floor basaltic extrusives. The two mafic-ultramafic have been interpreted as ophiolitic complexes, generated in small ocean basins or maginal seas, and emplaced inot the crust during the Mesozoic.