Mineralogy, Geochemistry and Economic Potentials of Pegmatites around Egbe-Ejiba-Isanlu, Isanlu Sheet 225, Southwestern, Nigeria

This study focused on the geochemistry and economic potential of the rare metal mineralization within the pegmatites of the Egbe-Ejiba-Isanlu areas using geological, geophysical, and geochemical techniques. From a total of 92 fresh rock samples collected, 40 were cut into thin sections for petrographic studies, 20 were cut and polished for ore microscopic studies, while 30 were analysed for elemental composition of major oxides and trace elements, using XRF and ICPMS techniques, respectively. Petrographic study shows that the area is underlain by Biotite Gneiss, Migmatitic Gneiss, Augen Gneiss, Banded Iron Formation (BIF), Quartzite, Quartz-mica Schist, Porphyritic Granites, Coarse-grained Granite, Quartz Diorite and Pegmatite. Structural data shows a dominant NNE-SSW trending lineament with minor complementary NNW-SSE trends. The Total Magnetic Intensity and Reduced to Equator images from aeromagnetic anomaly data were used to enhance existing inferred geological boundaries of adjoining lithological units. The Total Magnetic Intensity map (TMI) depicts magnetic anomaly values that range between 52.5- 85.2. The map also shows a prominent high magnetic anomaly (71.5nT- 84.0nT) in rocks of the eastern part of the area. The molecular plot of Al O /CaO+Na O +K O versus SiO reveals that the pegmatites have I-type 3 2 2 3 2 2 characteristics. The K/Rb vs Cs discrimination diagram indicates that the pegmatites of the Egbe, Omi, Takete and Idofin areas are of the mineralized type. The geochemistry of some selected pegmatite samples shows enriched concentration values in ppm of 716.10, 19.68, 37.40, 92.00 and 481.70 for Rb, Cs, Ta, Sn and Nb, respectively. These suggest that the pegmatites are rare metal type with enrichment trend of Rb>Nb>Sn>Ta>Cs, exhibiting strong negative Eu anomalies, which suggests that the pegmatites are of the LCT-type. Ore microscopic studies show that the pegmatites are associated with tantalite, pyrite, chalcopyrite, tourmaline, and galena ores of economic value, as evidenced in the high level of artisanal mining activities in the areas.