Integrated Geological Mineralogical and Geophysical Characterisation of the Efon Alaaye Basement Terrain in Southwestern Nigeria for Slope Stability and Infrastructure Development

Abstract Efon Alaaye, Ekiti State in southwestern Nigeria, is located within the Precambrian Basement Complex with features of rugged topography, heterogeneous crystalline rocks with variable weathering profiles. This study combines geological mapping, structural measurements, slope assessment, natural-electric-field/electromagnetic reconnaissance survey, X-ray fluorescence (XRF) and X-ray diffraction (XRD) to define the geology of the materials and its implications for slope stability, groundwater occurrence and infrastructure development. Based on field observations granite, quartzite, schist, laterite and minor pegmatite were picked out; and the discontinuities were mainly NW-SE and NE-SW. Five slope traverses were recorded on an inclination range of 25–42°, the maximum slope inclination is 42° and this slope inclination is the greatest recon level concern due to steepness, fracturing and erosion susceptibility. The results of XRF analyses are extremely silica-rich, from 97.12 to 98.44 wt. % SiO₂, with the other major oxides present at very low levels. The diffractograms shown here indicate that quartz reflections are significant in all three samples. Reconnaissance geophysical interpretation delineates surficial material, clayey/weathered horizons, partly fractured basement and deeper basement crystalline, it can be seen that engineering behaviour is controlled by combined effects of lithology, discontinuity geometry, weathering, groundwater and slope morphology. Steep, fractured, deeply weathered and seepage prone areas should be assessed geotechnically and properly drained, and development should be avoided on these areas.Gently sloping ground with a good drainage capacity underlain by verified competent material is preferable for development, while the steep, fractured, deeply weathered and seepage prone areas require detailed geotechnical assessment and drainage control.