Geochemical Characterization and Rare-Metals (Ta-Nb) Mineralization Potentials of Pegmatites Around Lokoja, Central Nigeria
Abstract
Pegmatite bodies intruding the basement complex as dykes and large veins around Lokoja were studied geochemically to characterise them and determine their rare metals mineralization potentials. Thin sections studies show they are predominantly made up of quartz, microcline, muscovite, opaque minerals, occasional biotite and some minor/accessory beryl, apatite and zircon. Composite whole-rock samples were analysed for major, trace and rare earth elements using X-Ray Fluorescence Spectrometer (XRF) and Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The results reveal the pegmatites are considerably siliceous with SiO2 values of 69.00% to 74.60%. Al2O3 values are relatively moderate (14.80% to 19.60%). Na2O and K2O abundances are low with ranges of 2.32% – 5.93%, 1.22% – 11.00% respectively. MgO abundances are generally low (0.03 – 0.07%). Fe203 values are also low; ranging from 0.31% to 1.16%. Alumina Saturation Index (A/CNK) computation with values ranging from 1.40 to 3.06 indicates the pegmatites are peraluminous. Trace and rare-earth elements results show Bakunba location pegmatite is mineralised (Nb: 571.86ppm, Ta: 180ppm) and compare favourably with other mineralised pegmatites in Nigeria; while Ganaja-2 location (Nb: 100.37ppm, Ta: 26.6ppm) are moderately mineralised. Nb-Ta values of Shagari location (33.14ppm; 2.7ppm), Ganaja-1 location (12.6ppm; 3.6ppm) and Crusher location (0.91ppm; 0.2ppm) show they are barren. Various variation plot diagrams, such as Kb/Rb vs Cs, K/Rb vs Rb, also show mineralization status of these pegmatite bodies as compared with some local and foreign pegmatites. Plots of Zr vs SiO2, Rb vs Y+Nb and Rb vs Sr indicate the pegmatites are magmatic, from within plate granites and in crustal thickness of more than 30 km during the time of emplacement.
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