THE MINERALOGY AND GEOCHEMISTRY OF SOME CASSITERITE FROM THE YOUNGER GRANITE PROVINCE OF THE JOS PLATEAU, NIGERIA

Cassiterite from four different alluvial mining localities on the Jos Plateau were investigated from the point of view of their mineralogy, colour variety and chemistry. The optical properties of each of the colour varieties as revealed by the incident light microscopic studies coupled with the variation in their chemical composition as revealed by the electron microprobe analyses indicate that the cassiterites crystallized under different physicochemical conditions. Some (black varieties) are high temperature forms, whereas others, i.e., the red and white varieties are low temperature forms. Furthermore, the chemistry of these cassiterites tends to support the age migration of the Younger Granites whereby the northern cassiterites tend to be older, richer in SnO2 and poorer in the elements Fe, Nb arid Ta than the southern cassiterites.