Advancing the Theory of Electromagnetic Induction in Heterogeneous Nigerian Geological Formations for Mineral Prospecting

The theory of electromagnetic induction in heterogeneous geological formations underpins the interpretation of frequency-domain and time-domain EM surveys used for mineral prospecting and groundwater exploration across Nigeria's geologically diverse terrain. Standard EM interpretation models assume simplified horizontal layer geometries that inadequately represent the complex 3D structures of Nigerian basement complex and sedimentary basin environments. This study advances the theory of electromagnetic induction in heterogeneous Nigerian geological formations by developing a 3D finite element forward modelling and inversion framework adapted to the anisotropic, deeply weathered basement complex of North West and North Central Nigeria. The finite element discretisation employs tetrahedral elements with node-based Nedelec basis functions that correctly handle conductivity discontinuities at geological boundaries. A sensitivity-regularised gradient descent inversion algorithm is implemented and parallelised using MPI. The forward model is validated against analytical solutions for spherical and layered earth models and against synthetic data from known basement complex conductivity distributions. The inversion framework is applied to field data from a dual-frequency EM-34 survey over known columbite and tantalite mineralisation in Bauchi State. Results demonstrate resolution of conductive mineralised zones at depths of 30 to 80 metres undetectable by previous 1D layer inversion. Keywords: electromagnetic induction, finite element, mineral prospecting, basement complex, Nigeria