Application of ground magnetic and very low frequency electromagnetic (VLF- EM) surveys for gold and base metal exploration around Ihale in Bunnu – Kabba area of Kogi, North-central Nigeria

Abstract

This study integrates ground magnetic and Very Low Frequency Electromagnetic (VLF-EM) methods of geophysical investigation to probe the subsurface in terms of rock magnetic susceptibility and ground conductivity for the purpose of identifying mineralized pegmatite veins that could serve as host for gold and associated metallic deposits. Twenty five (25) carefully planned ground magnetic and VLF-EM profiles, each, were occupied east and west of a reference profile which was purposively established on an identified mineralized pegmatite vein around Ihale in Bunnu – Kabba area of Kogi, north-central Nigeria. The acquired ground magnetic data were filtered using Guassian, Butterworth and Reduction To Pole at Low Latitude (RTPLL) filters among others to remove regional field effect, cultural noise as well as simplify and focus the peaks of magnetic anomalies over corresponding sources due to the mid latitude effect of magnetic inclination on magnetic anomaly. The measured raw real and raw imaginary components of the EM fields were subjected to Fraser and Karous Hjelt filtering to remove harmonic and non-linear noise, make anomaly amplitudes to directly relate to the causative conductor, focus anomaly peaks as well as generate current density used to characterise the study area. Seven (7) zones of relatively high VLF-EM derived current density with matching high residual positive magnetic anomalies present closely correlate-able signatures with subsurface response obtained around the reference profile established where local mining activities indicate evidence of gold and associated metallic mineralization of the pegmatite vein. The delineated zones constitute targets for gold and associated base metal prospects development.