An Integrated Aeromagnetic, Source-Depth, and Radiometric Geophysical Framework for the Pan-African Basement Complex of the Oban Massif and Obudu Plateau

Abstract

The Precambrian basement of southeastern Nigeria, encompassing the Oban Massif and Obudu Plateau, is closely linked to the Cameroon Mobile Belt and is rich in gold, rare metals, and radioactive elements. This study employs an integrated aeromagnetic–radiometric approach for both qualitative and quantitative analyses to explore the tectonic structures of these basement terranes. High-resolution aeromagnetic and radiometric datasets were processed using seven enhancement filters, Centre for Exploration Targeting (CET) lineament analysis, Source Parameter Imaging (SPI), Standard Euler Deconvolution (SED), two-dimensional forward magnetic modelling, and K–Th–U radiometric mapping. The aeromagnetic datasets reveal fundamentally contrasting structural fabrics: the Obudu Plateau is characterized by dominant NE–SW lineaments (35–55° azimuth), whereas NW dominates the Oban Massif–SE structural trends (130–150° azimuth), indicating contrasting deformation histories within the Pan-African orogenic belt. Reduced-to-pole magnetic anomalies range from −131.8 to +113.0 nT in the Obudu Plateau and from −34.2 to +75.4 nT in the Oban Massif. At the same time, analytic signal amplitudes vary between 0.003 and 0.187 nT m⁻² and 0.0032 and 0.1836 nT m⁻², respectively, delineating structurally controlled shallow intrusive bodies and major lithological contacts. Source-depth modelling identifies a systematic four-tier basement architecture comprising shallow (<500 m), intermediate (500–1200 m), deep (1200–1750 m), and very deep (>1750 m; locally exceeding 2580 m) magnetic sources. SPI-derived depths (~100–2580 m) exhibit close agreement with Standard Euler Deconvolution solutions, with discrepancies generally less than 15%. Two-dimensional forward magnetic modelling resolves six basement blocks beneath the Oban Massif with magnetic susceptibilities ranging from 0.00130 to 0.00475 SI, corresponding to variably magnetized granitoids, gneisses, migmatites, and localized mafic intrusive bodies. Airborne radiometric mapping records maximum concentrations of K = 2.06%, Th = 33.89 ppm, and U = 5.81 ppm, with radioelement-enriched domains spatially coincident with the dominant structural fabrics, indicating that Pan-African shear systems strongly controlled granitoid emplacement, pegmatitic intrusion, and hydrothermal fluid migration. Integration of various datasets reveals the central-southwestern Oban Massif as the prime area for structurally controlled gold and Sn–Ta–Nb pegmatite mineralization. The southwestern and central Obudu Plateau are also promising for shear-hosted gold and U–Th-enriched granitoid systems. The study highlights that combining aeromagnetic and radiometric datasets reduces interpretational ambiguity and offers a reproducible exploration methodology suitable for similar Pan-African crystalline basement regions in West and Central Africa.