Compositional Features and Ta-Sn-Nb Rare Metal Mineralization Potential of Ogodo-Odobola Pegmatite, Central Nigeria

Abstract

Large pegmatite bodies are abundant in Ogodo-Odobola area. They occur in tabular forms and concordant to discordantly intruding the host rocks of migmatitic gneiss, schist and granite. This research is aimed at assessing the geochemical characteristics of pegmatite in the Ogodo-Odobola area to evaluate their rare metal potential. Field investigation was undertaken to determine the occurrences and relationships of the pegmatites with the host rocks. Thirty-three (33) fresh pegmatite samples were analysed using X-Ray Fluorescence (XRF), Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) and Inductively Coupled Plasma Mass Spectrometry (ICPMS) techniques at the National Geoscience Research Laboratory, Kaduna and the Activation Laboratories Ltd. (Actlab), Ontario, Canada respectively. Major oxides in the whole rock pegmatite show that they are of siliceous (SiO ; 72.82 wt.% average) and peraluminous (Al O ; 16.78 wt.% average) composition. The K O, Na O and Fe O contents average 4.81 wt.%, 3.13 wt.% and 1.27 wt.% respectively while CaO, MnO, MgO, TiO and P O are each less than 1.0 wt.%. Average values of trace elements in the pegmatite are Ta (12.40 ppm), Sn (18.36 ppm), Nb (94.51 ppm), Be (16.14 ppm), Rb (480.23 ppm), U (12.47 ppm), Cs (17.14 ppm), Ga (39.91 ppm), Ge (3.91 ppm), W (4.81 ppm), Li (40.98 ppm), Mn (890 ppm) and B (18.96 ppm). Ratios of diagnostic elements of K/Rb (75.21 ppm), K/Cs (3348.39 ppm), Rb/Sr (25.55 ppm), Rb/Cs (37.18 ppm), Ta/W (2.78 ppm), Nb/Ta (8.81 ppm), Ba/Rb (0.07 ppm) indicate a moderate index of fractionation. A/CNK >1 and Al O>CaO+NaO+KO with enrichment of SiO , Al O , Na O, K O and depletion of Fe O , MnO and MgO suggests that Ogodo-Odobola pegmatite is of peraluminous bulk composition and plots of A/NK versus A/CNK and Rb versus (Y+Nb) discriminates the pegmatite in the peraluminous Lithium-Caesium-Tantalum (Li, Rb, Cs, Be, Ga, Nb Ta, Sn, B, Ge, U, W) of syn-collisional to within plate granitic family. The plots of Ta versus Cs, Ta versus Ga, Ta versus (Cs+Rb) and Be versus K/Nb, with over 70 % of the samples plotting below the Beus line and 100 % below the Gordiyenko line reveal that the pegmatites from the study area are barren to marginally mineralized in rare metals (Ta>Sn>Nb).