TRANSFORMING THE GEOMAGNETIC TRANSFER FUNCTION OF VLF-EM TO CURRENT DENSITY FOR ISHIAGU Pb-Zn DEPOSITS, EBONYI STATE
Keywords:VLF-EM, Tipper, Current Density Transformation, Mineralized Veins, Conductivity.
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.