GROUND MAGNETIC AND GEOELECTRICAL PROSPECTING FOR GOLD MINERALISATION WITHIN TSOHO- GURUSU AREA OF MINNA, NIGER STATE, NIGERIA

Abstract

Ground magnetic and geoelectrical resistivity methods were used to prospect for gold mineralisation within Tsoho-Gurusu area of Minna, Niger state. The study area is bounded with latitudes 09o 37׳ 13״N to 09o37׳28.6״ N and longitudes 006o 36׳ 29.4״ E to 006o 36׳ 13.1״E, with a total area of 250,000 m2. Magnetic was collected using Geometric 857AX proton precession magnetometer. Prior to the geophysical survey, geological mapping was conducted to map out the surface structural features. Eleven traverses were occupied and aligned in North-South direction. Each traverse is 500 m long and uniformly spaced 50 m apart. The measurement stations were position East-West, across the traverses at 10 m apart in the mineral foliation direction. The magnetic data acquired were subjected to International Geomagnetic Referenced Field to obtained the residual field. The residual field was then processed and analysed using Euler and Analytical signal methods. The Electrical Resistivity Tomography (ERT) data was collected along two profile of anomalously high residual values (-99 to 82 nT) and low TMI value. The result from the analytical signal shows both high and low amplitude anomalies with the high amplitude anomalies dominates the entire study area. The result from Euler deconvolution shows a variation of depths between 8.0 to 25.0 m. The results from the electrical resistivity method shows a depth variation between 5 – 13.4 m. Low electrical resistivity values were found to associate with the high TMI values in an East-West pattern. This anomaly pattern agreed with the major East-West and Northeast-Southwest fracture pattern captured in the rose diagram and the lineament map. These indicates that fractures are potential mineralization zones for conductive minerals. Two possible mineralised zones were identified from the study area based on 2D electrical resistivity and magnetic data. The South Eastern part along the ERT profile shows eluvial and primary gold veins. The primary veins are trending in the NE-SW in consistent with the general trend of the geological formation likewise as revealed in the ERT profile in the North Eastern part of the study area. The surface structure pattern, magnetic anomaly pattern and electrical anomaly pattern are indicative of quartz vein and eluvial deposits. Both the quartz vein and the eluvial gold deposits could be found within 5 m and 13.4 m depths.