INTEGRATED GEOCHEMICAL AND GEOPHYSICAL CHARACTERISATION OF TOURMALINE-BEARING PEGMATITES FROM IJERO-EKITI, SOUTHWESTERN NIGERIA

Abstract

The Ijero-Ekiti tourmaline-bearing pegmatite was investigated, using geological, geochemical, and geophysical methods to characterize its geological evolution and evaluate its mineralisation potential. Petrographical studies revealed a typical granitic mineralogical composition of quartz, feldspar, and muscovite, with tourmaline as accessory minerals. Geochemical data on whole rock analysis showed high and moderate enrichments in SiO2 (av. 71.65 wt. %) and Al2O3 (av. 14.71 wt. %) respectively, while mean values for the other major oxides ranged between 0.01 and 3.63 wt. %. Results also showed that K2O (av. 3.63 wt. %) and Na2O (av. 3.52 wt. %) concentrations were comparable to average Upper Continental values. The relatively high aluminum and alkaline compositions could be attributed to pneumatolytic crystallization from the pegmatitic melt. Aluminum Saturation Index (ASI) [Al/(Ca+Na+K)] indicated peraluminous character. Ranges of some trace elements (Cs, 1.5 – 705.6 ppm; Be, 0.5 – 12 ppm; Sn, 2.0 – 34 ppm; Ta, 1.0 – 14) support a Lithium-Cesium-Tantalum (LCT) type rare-elements pegmatites for the pegmatites of the study. The spider and K/Rb vs K/ Cs plots portrayed fractionation trends suggestive of potential mineralisation. The vertical electric sounding data showed that pegmatites underlie the lateritic zone and represent the anomalous layer characterized by high resistivity values ranging from 1086 to 9489 Ohm-m with the surface to a maximum depth of 20.8m which is suspected to be a mineralised zone. Some of these pegmatites are highly tourmalinated, suggesting that they emanate from highly mineralised magma and are believed to represent late-stage pneumatolytic fluids derived from acidic magma bodies through magmatogenic processes.