GEOCHEMICAL CHARACTERIZATION, RARE-METALS MINERALIZATION AND INDUSTRIAL POTENTIALS OF PEGMATITES

ABSTRACT

Pegmatites dykes and large veins of various width occurring sparingly and sparsely intrude basement rocks around Ibillo, Dagbala, Ososo and Ukpilla, all parts of the Igarra Schist Belt located within “AUCHI” Topography Sheet 266 southwest Nigeria are evaluated using petrography and geochemistry with a view to understanding their mineralogy, chemical composition, geochemical characteristics, rare-metals mineralization potentials and petrogenesis. Field observation show the pegmatite bodies are made up largely of pink feldspar (microcline) which is being quarried at six locations (one in Ibillo, five at Dagballa). Exposures at the quarry sites provided good opportunity to obtain clean, fresh unweathered samples for petrographic and geochemical analyses. Thin section petrographic studies show the pegmatites are predominantly composed of feldspar with quartz large subsumed by the feldspar, mica (microcline and biotite) sparsely present, with accessory zircon and opaques Major elements compositional values obtained from X-ray fluorescence spectrometry analysis indicate that pegmatites are highly siliceous with SiO2 value range of 70.04% - 74.98%; Al2O3 values are high 15.02% - 17.30%. K2O 3.50% - 8.43%, Na2O 2.73% - 5.56% are moderate. Alumina Saturation Index computation put the pegmatite as Peraluminous. Inductively Coupled Plasma Mass spectrometer (ICP-MS) was used to evaluate the minor and trace elements (including the Rare Earth Elements) abundance values. Spider web diagram plot of Chondrite-normalized values of the REE show a pronounced Eu negative anomaly that is characteristic of granitic rocks. Various bivariate and ternary plots are used for characterization and rare metals mineralization potentials/status determination. The pegmatites are mildly rare metals mineralized and rich in feldspar.