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

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 gol

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

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 investigations using high precision ground aerial magnetic has been applied in some parts of Ayegunle sheet 226NW, North Central, Nigeria aimed at delineating areas with high magnetic anomalies, magnetic structures and possibly exploration targets for quartz-vein gold mineralization. The geophysical survey resulting in the ground magnetic data was conducted for magnetic element exploration.  The total magnetic intensity was applied to identify regional magnetic anomalies, magnetic structures (faults) and structural trends. Magnetic data was gathered using a GEM system GSM-19T proton precession magnetometer at a nominal station spacing of 10 metres. Grid location information was provided by Garmin system UTM datum WGS 84, Zone 32N coordinates and elevation data as meters above sea level in an excel spreadsheet.  Several areas of total magnetic field was interpreted low as reflecting high magnetic susceptibility bodies and possible quartz vein gold or sulphide mineralization targets. Total Magnetic Intensity data ranging from 33238.5 – 33261.1nT are taken along survey traverses (normally on a regular grid) used to identify metallic mineralization that are related to magnetic materials (normally magnetite and/or pyrrhotite). Two types of magnetic trends are identified. Firstly, there are several NW-SE arcuate lineations that roughly coincide with some of the geologically mapped epithermal/vein trends. These magnetic trends possibly delineates structural breaks or geological contacts related to these exploration targets. Secondly, there are indications of a major structural break trending northerly through the centre of the survey area. While northerly trending magnetic features are not clearly delineated at these low latitudes, they sometimes appear as subtle breaks in easterly trends or as a series of monopole and/or dipole anomalies. Keywords: Granite-gneiss, Mica schist, Leucocratic micro granite and Quartzite, Magnetic anomalies, Quartz-vein gol

Engineering Geophysical Investigation Around Ungwan Doka, Shika Area within the Basement Complex of North-Western Nigeria

Geophysical investigation for engineering or environmental studies was carried out around Ungwan Doka of Shika area which falls within the Basement Complex of North-Western Nigeria. The study is aimed at evaluating the competence of the near surface formation as foundation materials, and to unravel the subsurface profile which in turn determines if there would be any subsurface lithological variation(s) that might lead to structural failure at the site and evaluating the groundwater potential of the site and determining the level of safety of the hydrogeologic system. Vertical Electrical Sounding (VES), using Schlumberger configuration was adopted. A total of 18 VES was conducted. The data obtained were subjected to 1-D inversion algorithm to determine the layer parameters. The geoelectric section revealed two to four lithologic units defined by the topsoil, which comprises clayey-sandy and sandy lateritic hard pan; the weathered basement; partly weathered/fractured basement and the fresh basement. The resistivity values range from 26?m - 373?m; 77?m - 391?m; 473?m - 708?m; and 1161?m - 3600?m in the topsoil, weathered, fractured basement and fresh basement respectively. Layer thicknesses vary from 0.38m – 6.58m in the topsoil, 1.1m – 33.04m in the weathered layer, 5.86m – 34.1m in the fractured basement. Depth from the surface to bedrock/fresh basement generally varied between 2.65m and 37.75m. Based on the resistivity values, it is concluded that the subsurface material up to the depth of 25m is competent and has high load-bearing capacity. However, resistivity values less than 100?m at depths of 10m-15m indicate high porosity, high clayey sand content and high degree of saturation which are indications of soil conditions requiring serious consideration in the design of massive engineering structures. The hydrogeologic system at the site is vulnerable to contamination. Hence, the result reasonably provide a basis for which groundwater potential zones are appraised for safety in case  potential sources of groundwater contamination sites such as septic tanks and sewage channels are planned for the area under study. Key words: VES, Top soil, Weathered Basement, Partly weathered or Fractured Basement, Fresh ,Basemen