Application of VLF-EM method for base metal exploration in Gwani area (Misau 107), Jigawa state, Nigeria

Abstract

The Very Low Frequency (VLF) electromagnetic (EM) survey is a reliable technique for identifying network of fractures usually hidden by overburden materials that overlie the crystalline basement. The Gwaram area, Jigawa state of Nigeria is underlain by Older Granite of the basement complex of Nigeria, with predominant rock type being coarsely porphyritic biotite granite. The project is aimed at confirming the occurrence of sulphide mineralization within the study area, using both the geological information and VLF techniques. Measurements involving 10 profiles spaced 50 m interval were collected within the study area, using the transmitter of Le Blanc in France whose radio frequency is 18.3 kHz. Profiles 1-10 show the respective cross-over points (points of intersection) at 430, 460, 430, 470, 480, 500, 550, 560, 610, and 620 m with a positive in-phase response of 11.1, 7.3, 22.1, 23.7, 30.8, 36.2, 29.5, 17.6 and 20.8% respectively, the suspected fault occurred at respective depth of 45, 130, 150, 135, 150, 135, 140, 145, 145 and 125 m. The ratios of primary to secondary electromagnetic anomalies on the ten profiles are not constant and their profile shapes are never identical or consistent. Such anomalies at cross-over points have been used to infer the presence of fracture. All the profiles show one identical anomaly which is suspected to be a hydrothermal zone or mineralized fault. VLF-EM contour and 3D map were produced and indicate that there is high conductivity toward the southwest of the map. The results obtained in the survey inferred that the deposit is expected to be economically viable.