GROUND ELECTROMAGNETIC AND ELECTRICAL RESISTIVITY PROSPECTING FOR ORE MINERALISATION ZONES IN TSOHON-GURUSU NIGER STATE, NORTH-CENTRAL NIGERIA

Abstract

To accurately explore and develop prospective mineral deposits, systematic geophysical approaches becomes a useful tool to establish areas of economically viable zones for exploration activities. This study integrates very low frequency electromagnetic (VLF-EM) and vertical electrical sounding (VES) methods of geophysical investigation to probe the subsurface in terms of its electrical conductivity characteristic to identify mineralised zones that could serve as possible host for conductive minerals and associated conductive metallic deposits in Tsohon Gurusu Area of Minna, North-Central Nigeria lying on latitude 9.621oN to 9.625oN and longitude 6.604oE to 6.608oE with an area extent of 250,000 m2. A total of six profiles were investigated, each with length of 500 metres, 100 m inter-profile spacing and 20 m inter-station distance. The VLF-EM data were collected using Scintrex Envi VLF instrument. The acquired data sets were subjected to analysis and interpretation using MICROSOFT EXCEL, KHFFILT and OASIS MONTAJ software. Twelve points of significantly high and low conductivity were mapped out and sounded, adopting the Schlumberger array method with the help of ABEM Tarrameter SAS 4000 instrument and the data analysed using WinResist software. The result of the study indicated a general structural trend of NE-SW direction with significant conductivity responses due to inferred fracturing units containing conductive minerals as indicated by the peak responses of the current distributions and the surface and subsurface geologic features in the investigated profiles. Areas of high conductivity were observed in all the six profiles corresponding to fracture zones of interest as indicated in the current density sections, with profile 5 having the highest conductivity response of 135.5 mS/m and profile 6 with the least conductivity response of -136.7 mS/m. A general H-type curve were observed at VES 01, 02, 03, 04, 05, 06, 07, 10 and 12, VES 08 and 09 gave rise to an A-type curve indicative of majorly basement rock of granitic nature, however, VES 11 had a HK-type curve with five major layers with possible presence of conductive and non-conductive minerals. With reference to the obtained results from the study area, mineralisation is eminent and occurs within near surface fracture zones at estimated depth of 9 m.