ASSESSMENT OF RARE EARTH ENRICHMENT OF PEGMATITES IN THE BASEMENT COMPLEX OF SOME PARTS OF OSUN STATE, SOUTH WESTERN NIGERIA

Abstract

This study was conducted in Osun State, which included towns like Ede,Awo, Ikire, Wasimi, Odeyinka, Sekona among others. Pegmatites are known to habour solid minerals, ranging from rare metals, gemstones, to some industrial minerals. In this study, interpretation of Landsat imagery was carried out along with detailed mapping of all pegmatite bodies, pitting, trenching and shaft sinking. Channel sampling was carried out on the pits, shafts and trenches, while whole rock sampling was carried out on outcrops. Geochemical analyses were conducted on fifteen representative samples of pegmatite bodies across Awo and Apomu fields, and channel samples of 24m deep test shaft for major, trace and rare earth elements using lithium. metaborate/tetraborate Fusion, Inductively Coupled Atomic Emission Spectrometry (ICP-AES) and Inductively Coupled Plasma-Mass Spectrometry (ICPMS) technique developed by Activation Laboratories Ltd.(ACTLABS), Ontario, Canada. Results obtained for major and trace elements showed that SiO2 in all areas sampled falls between 65-80%. Al2O2 is equally common. Major oxides like N2O and K2O vary in different areas sampled. The content of TiO2, MgO2, CaO and FeO3 are mostly low especially below 1%. The pegmatites sampled are significantly enriched in Rb.Cs, Nb,Ta,Sn,Ba and Ga. The degree of fractionation defined by the K/Rb vs Rb and the K/Rb vs Cs plots revealed that most of the pegmatites of the fields worked upon could be classified as mineralized. Equally, photomicrographs were used in identifying minerals in the pegmatite bodies as a corroborative measure. All the analyses carried out on the samples indicated that the petrogenetic indicator elements (Rb, Cs and Be) increases with depth, correlating positively with increase in Ta, Nb, Na2O and K2O concentrations.