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.
