GEOLOGICAL AND INTEGRATED GEOPHYSICAL INVESTIGATION OF ASSOCIATED SULPHIDE MINERALISATION AROUND BABAN-TSAUNI AREA, NORTH CENTRAL NIGERIA

Abstract

The associated sulphide mineralisation provinces comprising lead-zinc ore in Nigeria have always been associated with the sedimentary Benue trough. However, there had been reports of associated sulphide mineralisation within the basement complex, which are not fully understood in terms of the controlling structures and geometry. Thus, this study focused on the evaluation of structural setting, lithological association and ore body geometry of the sulphide ores around Baban-Tsauni, Northcentral Nigeria. Aeromagnetic and airborne radiometric datasets were obtained from Nigerian Geological Survey Agency acquired at 500m inter-profile spacing and 80m terrain clearance. The data were processed using Fast Fourier Transform filters and grid rationing, respectively for enhanced interpretation of structural settings and lithological delineations. Geological ground truthing and petrographic study were carried out over prospective areas delineated from the interpreted airborne data. Ground magnetic survey was conducted over the delineated areas with 50 profiles, each measuring 5 km at 100 m inter-profile spacing. Interpreted structures were then characterised using electrical resistivity and induced polarisation responses in time domain, acquired with a 5000-Watt transmitter and 8-channel receiver. Profile running across an open mineralised pit was used as control profile. Electrode configuration was dipole-dipole, with 50m dipole spacing and 25m station interval. Three-dimensional model was generated from the stack plot of the resistivity and chargeability pseudo-sections, to configure the associated sulphide ore body geometry and volume estimation, using voxel mathematical algorithm. Primary NE-SW structural setting and secondary NNE-SSW, NW-SE and WNW-ESE geological structures were delineated. Granitic intrusives suspected to be co-genetic but occurred at different depths as reflected in the variations of their signature intensities. Sulphide mineralisations were related to regions of high thorium concentration with quartzo-feldspathic and quartz veins lithology. The area is underlain by basement rock comprising gneisses, quartzite, granitic intrusions and pegmatite. Ground magnetic data isolated more of the NW-SE and NNE-SSW trending secondary structures indicating that the mineralisations were structurally controlled and epigenetic. Induced polarisation and resistivity structures delineated regions of relatively high chargeability with corresponding high resistivity signatures, which correlated with the mapped structures from the ground magnetic interpretation confirming disseminated mineralisations. The estimated depths to the interpreted ore bodies were between 5 m to 30 m from the surface. The signature extended in a disseminated pattern down to depth of approximately 167 m, which was the maximum depth for the survey. Resistivity and chargeability anomalies with values higher than 1000 Ωm and 30 mV/V, respectively were set as threshold as obtained from the control profile and a 3-dimensional model of the ore body geometry gave a volumetric value of 23,328,000 m3 with a mean chargeability value of 54.98 mV/V. The NW-SE and NNE-SSW structures controlled the emplacement of the associated sulphide mineralisation in Baban-Tsauni area corresponding to regions of high thorium enrichment. A 3- dimensional model was successfully configured for the ore body geometry.