Metamorphic redistribution of Cr within chromitites and its influence on chromite ore enrichment

Mineralogical and chemical characters of ore strongly affect the efficiency of chromite sand physical concentration. Usually chromite ore enrichment is based on the assumption that all Cr in the rock is hosted within chromite, but alteration in metamorphic conditions can lead to partial redistribution of Cr from chromite to silicates. Such redistribution was studied on the Vavdos chromite deposit (Greece) where more than 3% of whole rock Cr2O3 can be found in silicates. The effect of Cr2O3 redistribution is to lower the efficiency of gravity plants as Cr2O3 contained in silicate phases will be preferentially discharged into the tailing during enrichment. Tests confirm the effect of Cr redistribution on enrichment and show that preferential separation of different silicates does not occur or is negligible. As the redistribution of Cr within the rock is not indicated by any change in whole-rock chemistry only the study of mineralogy, texture and mineral chemistry of the ore can provide a reliable basis for final product quality and Cr2O3 recovery prediction.