Compositional trends and rare - metal (ta-nb) mineralization potential of precambrian pegmatites in komu area, south western Nigeria

Petrographic and geochemical evaluation of pegmatite bodies occurring as discontinuous dykes have been studied in Komu area of southwestern Nigeria, with a view to determine the compositional characteristics that may be related to Ta-Nb mineralization potentials. They are found intruding semi discordantly, the older assemblages of granite gneiss, amphibolites and semi pelitic schist. These Precambrian pegmatites bodies are usually coarse grained in texture. Thin section study reveals that they contain mainly quartz, muscovite mica, plagioclase (albite), microcline as the main minerals while tourmaline and beryl occur in subordinate amounts. Opaque minerals, mainly ilmenite, magnetite and tantalite are of accessory constituents. A total of thirty samples comprising whole rock pegmatites and mineral extract of muscovite mica were analyzed for major, trace and rare earth elements using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) geochemical method which show the pegmatite samples to be generally highly siliceous with Sio2 values ranging from (46.14-76.71%) with an average of 62.47% in the whole rock samples, and it also ranges from (45.28-57.50%) with an average of 48.34% in the muscovite extract samples. while Al2 O3 content could be as high as 30.72% in the muscovite extract samples and 21.06% in the whole rock samples depicting the complexity of the pegmatite rock. However, Fe2O3, TiO2, and P2O5 contents are generally low (less than 5%). The samples are fairly enriched in Rb, Ba, Sr, Zr and the rare metals Ta, Li, and Nb. Albitization is indicated by Na/K ratio which are greater than (1.0) in most of the samples and Ti-Sn-Nb-Ta discriminate plot. Variation plots of K/Rb versus Rb, Ta versus Rb, Ta versus Nb, Ta versus K/Cs, Ta versus Cs+Rb and Ta versus Cs discriminant plot indicate the potentials of rare metal mineralization. On most of these diagrams, the samples plot close to those of Tanco deposits which are known to contain appreciable levels of Ta-mineralizaton, it also compares favourably with the pegmatite samples of Noumas, Central claims, Silver leaf and Odd west deposits which are known to contain fairly low level of Ta mineralization endowments.