Geological and Induced Polarization Geophysical Investigations of the Quartz-Vein Gold Mineralization in Some Parts of Ayegunle Sheet 226nw, North Central, Nigeria

Abstract

The study area is predominated by granite-gneiss, mica schist, leucocratic micro granite and quartzites.  The Pan African orogeny left an imprint of structural similarity upon the rock units. The granite-gneisses are found as small belts within the study area, and hosting the quartz-veins. The metasediments are fractured and folded in places. The dominant fold axes and quartz vein intrusions trend NNE-SSW parallel to the regional foliation of the rocks. The emplacement of the quartz vein is associated with the generalized strike direction of quartz vein and host rocks. The structural settings suggest that the emplacement of gold mineralization occurred during Late Pan African orogeny. Geophysical method using the Electrical Resistivity Tomography (ERT) has been applied in some parts of Ayegunle sheet 226NW, North Central, Nigeria aimed at investigating the electrical properties and probable exploration targets for quartz-vein gold mineralization. Electrical Resistivity Tomography (ERT), using the measuring unit ‘MER124’ and generator unit ‘ASTRA’ Imaging System was adopted to map the electrical properties as an aid to characterizing the subsurface conditions of the study area. Nine (9) profile lines were marked out for ERT investigations. For each profile, the layout for the electrical imaging was such that two reels of cables were used with 5m intervals between the takeout electrodes. However, the two innermost electrodes adjoining the two reels of cables were connected together thus yielding a total of 41 electrodes and a spread length of 200m. The data obtained using MER124 measuring unit were processed using Zond2dinv and Oasis Montaj 8.2 software.  Chargeability and resistivity values varies due to the inhomogeneity of the subsurface rock hence, chargeability values in percentage (%) ranges from 0.17% around the alteration zones and relatively low sulphide mineralization to 6.22% with high sulphide mineralization and resistivities in ohms-meter ranges from as low as 5ohm-m along the alteration zones to >10,000 ohms-meter around the competent bedrock and probable zones of quartz-veins gold mineralization.

Keywords: Granite-gneiss, Mica schist, Leucocratic micro granite and Quartzite, Electrical Resistivity Tomography, Quartz-vein gold