Original Contributions to the Theory and Practice of Induced Polarisation Spectroscopy for Detecting Disseminated Sulphide Mineralisation in Nigerian Schist Belts

Spectral or frequency-domain induced polarisation provides textural and mineralogical information about subsurface materials beyond what is available from conventional time-domain IP measurements, yet the theoretical foundations relating IP spectral parameters to sulphide mineral grain size, dissemination pattern, and mineral species have not been systematically validated for the specific ore-forming environments of Nigerian schist belt deposits. This research develops an original theoretical extension of the Cole-Cole relaxation model to account for multi-mineral assemblages typical of Nigerian schist belt disseminated sulphide systems, where pyrite, pyrrhotite, arsenopyrite, and chalcopyrite coexist in varying proportions. Laboratory spectral IP measurements on a suite of 85 synthetic and natural rock samples from three schist belt areas in Kwara, Oyo, and Kaduna states provide the empirical dataset for model development and calibration. The new multi-mineral Cole-Cole model is parameterised by fitting to the laboratory spectra and the derived parameters are interpreted in terms of physically meaningful mineral quantities including effective grain size and volume fraction. Field spectral IP surveys conducted at two gold-mineralised zones validate the laboratory-derived model by predicting mineralogical compositions that are confirmed by drill-core assay and petrographic analysis within 15 percent relative error. The research contributes the first mineralogically grounded spectral IP forward model calibrated to Nigerian ore-forming environments, with direct implications for improving the selectivity of IP surveys in distinguishing economic from barren sulphide zones. Keywords: spectral IP, Cole-Cole model, sulphide mineralisation, schist belt, Nigeria