TRANSFORMING THE GEOMAGNETIC TRANSFER FUNCTION OF VLF-EM TO CURRENT DENSITY FOR ISHIAGU Pb-Zn DEPOSITS, EBONYI STATE

Abstract

The economic value of mineral deposits today calls for more interest in geophysical exploration over the Ishiagu area of Abakaliki Basin, Nigeria to delineate the Pb-Zn mineralization in the sedimentary bedrock. Recorded as VLF-EM anomalies are the in-phase and quadrature components of the geomagnetic transfer function, tipper due to induction and these reflect the conductivity contrast between the Pb-Zn mineralized veins and the host rock. Results of sharp tipper responses due to strong EM induction were detected in the surveyed area and on the average, the deeper sources responses range from 4.7% to 7.6%, while the shallower sources responses range from 8.8% to 17.1%. Interpretation with the recorded tipper responses was noted to be of much misfit to the dimensionality, trends and geometry of the Pb-Zn mineralization in view at the nearby existing mines. As a geoelectrical conductivity technique, the efficacy and high resolution of the work is revealed by the 2D current density transformation of the tipper responses. Dimensionality analysis of the current density maps bares these prospective Pb-Zn mineralized veins to trend in the NW–SE direction with their subordinates in N–S direction in correlation to the geologic information of the area that describes/indicates the various episodes of deformation with their characteristic structures. The shallow anomaly sources of Pb-Zn mineralized veins as shown by very sharp tipper responses were detected in the central part, while the deeper sources as shown by broad tipper responses were in the northern part of the study area. The dimensions, trends and shallow depth range of the prospective mineralized veins obtained from VLF readings immensely indicate the prominence of Ishiagu Pb-Zn mineralization.