Multitechnique Mineral Exploration in a Part of Igarra North Basement Complex of Southwestern Nigeria

A Multitechnique approach have been employed for mineral deposit exploration in a part of Igarra North Basement complex of Southwestern Nigeria, which is known to have undergone polyphase episodes of deformation, based on earlier structural geological studies reported in the area. Ground geophysical surveys involving 2D resistivity and IP-chargeability tomography, and Magnetic method were employed for locating mineralized zones within the study area. Seven (7) 2D resistivity tomography profiles LI to L7 were occupied in the area. Induced polarization (IP)-chargeability data was acquired alongside 2D ERT along profile seven (L7) which was close to the centre of the survey outlay. In both cases, ground resistivity measurement was made using SAS-1000 Terrameter and the Wenner array was employed with array length limited by space constraint of 200m. Ground magnetic data was also acquired in the area along five (5) profiles (L1 to L5) to supplement the resistivity survey using a high precision fluxgate magnetometer which measures vertical component (ZnT) of the Earth’s field. Landsat 8 OLI remote sensed data was employed for interpretation of geological structures in the area. 2D Resistivity inversion showed anomalous zones with relatively low and high resistivity variation compared with the background trend. In Profile L1, a low resistivity range of 85-243 Ωm was observed disseminated at 8.6m and at 34.3m and interpreted as metallic sulphide/oxide deposit. In Profiles L2 and L3, similar trends in resistivity variations were observed between 8.6 to 17.1m and were both interpreted as quartz veins due to their high resistivity. In Profile L4, a low resistivity value ranging from 85-105 Ωm was observed at 17.1 to 34.3m and interpreted as metallic sulphide/oxide deposits. In Profile L5, a resistivity value ranging from 87-120 Ωm was observed in layers at 17.1 to 34.3m and interpreted as metallic sulphide/oxide deposit. In Profile L6, a resistivity range of 115-315 Ωm was observed at depth of 15 to 17m and interpreted as quartz veins deposits surrounded by metasediments found in the area. In Profile L7, it was observed that both electrical resistivity and IP-chargeability tomography showed similar trends of low resistivity and high chargeability anomalies. A low resistivity value ranging from 31.9-86.6 Ωm corresponded with high chargeability value of 49.5 msec (>20 msec) observed at about 13.5 to 26.9m for both methods. This trend in resistivity and IP-chargeability anomalies is indicative to presence of clay minerals which are derived from weathering of micaschist which is prevalent within the Igarra schist belt as well as presence of segregated sulphide-bearing quartz veins. Total Horizontal Derivative (THD) map computed from Relative magnetic intensity (RMI), estimated the locations of geological contacts (lineaments) and the lineaments were manually digitized as zones of maximum gradient values with amplitude range of 0.00073 nT/m to 0.03668 nT/m. 1661 lineaments where manually digitized from the remote sensed data ranging from 0.103 km to 0.955 km in length. The dominant lineament trend had orientation in the NE – SW direction. Magnetic lineaments picked from the THD map also showed a NE – SW orientation and correlates with remote sensed lineaments. 1718 composite lineaments were digitized using magnetic and remote sensed data and when plotted on rose diagram showed prevalent NE – SW trend.