Hidden Gold Corridors Revealed by Aeromagnetic Scans in Nigeria’s Ancient Basement Rocks

A team of Nigerian geoscientists has used high-resolution airborne magnetic data to peel back the cover of weathered rock and dense vegetation in the Auchi area of Edo State, revealing a network of buried faults, shear zones and lithological contacts that appear to control where gold accumulates in this underexplored corner of the southwestern Nigerian Basement Complex. The study, published in Discover Geoscience, demonstrates that a carefully sequenced suite of magnetic filtering techniques can transform decades-old survey data into a modern exploration roadmap, and its predictions align strikingly well with the locations of active artisanal gold workings on the ground.

The research area sits within the Igarra Schist Belt, a segment of the West African Precambrian terrain dominated by migmatites, gneisses, quartzite mica schists, a psammite-pelite sequence and hornblende granite gneiss. These rocks were forged and deformed during two major orogenic episodes: the Eburnean event roughly two billion years ago and the Pan-African orogeny around 600 million years ago. That long tectonic history left the region riddled with faults, folds and shear zones, the classic plumbing through which hot, metal-bearing fluids migrate and deposit gold in quartz veins. The terrain also hosts limestone, granite, kaolin, feldspar, quartz, lateritic iron ore and pegmatites carrying gemstones such as tourmaline, garnet and zircon, yet the structural controls on its mineral wealth have remained only partially understood.

The dataset underpinning the study came from a nationwide airborne geophysical survey flown between 2005 and 2009 by Fugro Airborne Surveys, funded by the Federal Government of Nigeria and the World Bank and archived by the Nigerian Geological Survey Agency. Flight lines ran north-south at 500 metre spacing with east-west tie lines every 2,000 metres, at an average terrain clearance of just 80 metres. The researchers processed the total magnetic intensity data in Oasis Montaj, removing the International Geomagnetic Reference Field to isolate residual anomalies, applying tie-line and micro-leveling to suppress survey noise, and gridding the measurements at 125 metre resolution using the minimum curvature method.

Because the study area lies at low magnetic latitude, with an inclination of minus 13.91 degrees and a declination of minus 2.15 degrees, raw magnetic anomalies appear asymmetric and shifted away from the rocks that cause them. To correct this distortion, the team applied a Reduction to the Equator transformation, which mathematically repositions anomalies as if measured at the magnetic equator, centering them directly over their sources. The resulting map, with residual intensity values ranging from minus 79.1 to 60.3 nanotesla, showed noticeably realigned anomaly peaks and troughs, particularly in the southeast and along mapped lithological contacts, sharpening the definition of geological boundaries that the uncorrected data blurred.

The raw total magnetic intensity map itself, spanning 32,931.4 to 33,079.9 nanotesla, already told a geological story. Magnetic highs cluster in the northwest, southwest and northeast, while prominent lows occupy the central and southeastern portions around Aiyetoro, Iretutu, Igarra, Somorika, Ojirami Oke and Akuku. When overlaid on the geological map, the lows correspond to the psammite-pelite sequence and weathered hornblende granite gneiss, both depleted in magnetite through composition and leaching. Pockets of high magnetization within the quartzite mica schist terrain suggest either unaltered basement blocks or intrusive magmatic bodies emplaced during later tectonic events, precisely the kind of magnetization contrasts that flag lithological boundaries and potential mineralization zones.

To separate deep crustal architecture from shallow detail, the team decomposed the field into regional and residual components and extended the reduced grid upward to 10 kilometres above the survey plane. The regional map revealed broad northeast-southwest trending anomalies tied to crustal thickness and deep tectonic fabric, while the residual field, spanning minus 72.7 to 68.3 nanotesla, isolated shallow lithological changes and structural discontinuities superimposed on those regional trends. First and second vertical derivative filters then acted as edge detectors: the first derivative exposed north-south trending shallow faults and fractures in the western and eastern parts of the area, and the second derivative refined those boundaries with high precision, delineating shallow fault corridors and fracture networks that define prospective mineralization zones.

The most diagnostic tool proved to be the Analytic Signal Amplitude, which is independent of both the Earth’s field direction and the magnetization of the source, making it especially robust at low latitudes. Its peaks fall directly over the edges of magnetized bodies, and in this survey its values ranged from 0.01 to 0.294 nanotesla per metre, sorting the terrain into three magnetic domains. Low amplitudes of 0.01 to 0.045 nanotesla per metre mark quartz-rich metasediments and weathered granites; moderate values of 0.045 to 0.101 reflect the granite-gneiss complex; and high amplitudes above 0.294 concentrate along the western margin and parts of the southeast, coinciding with migmatite and the psammite-pelite sequence. Critically, the high-amplitude zones align with lithological boundaries and structural intersections, the very settings where hydrothermal fluids are channeled and gold is deposited.

Lineaments digitized from the derivative and analytic signal maps and plotted in rose diagrams revealed a dominant east-northeast to west-southwest structural grain, followed by west-northwest to east-southeast trends, with minor northeast-southwest and northwest-southeast orientations. This fabric matches the Pan-African tectonic trends documented across the Nigerian Basement Complex and the Benue Trough in earlier studies, indicating that regional deformation, not local accident, dictated where mineralizing fluids could travel. The synthesis yields a hierarchical framework: crustal-scale northeast-southwest basement grain overlain by east-northeast and west-northwest fault corridors where edge-detection anomalies, derivative lineaments and mapped geology converge.

The decisive test came from the ground. Nine known artisanal gold mining sites were overlaid on the analytic signal map, and most sit directly on or adjacent to high-amplitude anomalies and major structural intersections. The northeastern workings in particular follow the contact between the schist and porphyritic granite, close to a major mapped structure. This spatial correlation validates the geophysical interpretation and confirms that gold emplacement here reflects the combined influence of favourable lithologies, including biotite granite, granite gneiss, quartzite-mica schist and migmatites, and tectonic deformation rather than lithology alone. Areas around Ojirami, Akuku, Somorika, Ogbe and the northeastern sector of the study area emerge as priority exploration targets where structural complexity, magnetic signatures and known occurrences converge.

Beyond its immediate findings, the study makes a case for aeromagnetic interpretation as a cost-efficient, non-invasive first step in exploring crystalline basement terrains where surface exposure is poor and conventional mapping struggles. The authors position their structural framework as the essential foundation for future three-dimensional magnetic inversion and magnetization vector inversion modelling, and for integration with aeroradiometric, gravity, remote sensing and geochemical datasets within a GIS-based prospectivity model. For a nation seeking to grow its solid mineral reserves, the message is that the gold-bearing architecture of the Igarra Schist Belt was already recorded in the airborne data; it simply needed the right filters to be seen.

Subject of Research: Aeromagnetic delineation of structurally controlled gold mineralization zones in the Igarra Schist Belt, southwestern Nigerian Basement Complex

Article Title: Preliminary assessment for delineation of mineralized structures and potential gold alteration zones in Igarra Schist Belt southwestern Nigerian Basement Complex

Article References: Ogbamikhumi, A., Salami, S. A., Ehinlaiye, A. O., Worenwu, W. E., Aigbadon, G. O., Ojeaga, K., Igbinigie, N. S., & Tawey, M. D. (2026). Preliminary assessment for delineation of mineralized structures and potential gold alteration zones in Igarra Schist Belt southwestern Nigerian Basement Complex. Discover Geoscience, 4(1), Article 321. https://doi.org/10.1007/s44288-026-00695-z

Image Credits: AI Generated

DOI: 10.1007/s44288-026-00695-z

Keywords: aeromagnetic data, gold mineralization, Igarra Schist Belt, Nigerian Basement Complex, analytic signal, vertical derivatives, Reduction to the Equator, structural geology, Pan-African orogeny, mineral exploration, shear zones, hydrothermal fluids