GEOPHYSICAL MAPPING OF LEAD-ZINC METALLOGENIC PROVINCE IN PART OF SOUTHERN BENUE TROUGH, NIGERIA.

Abstract

Interpretation of airborne magnetic, land gravity and airborne radiometric (AR) datasets were carried out in parts of Southern Benue Trough, Nigeria to map lead-zinc deposit in the study area using its geophysical characteristics. Reduction to equator, analytic signal, derivatives filters algorithms were used to enhance magnetic and gravity data while ratio and ternary algorithms are used for radiometric data. AR data was interpreted in conjunction with elevation data to isolate false from real anomalies. Total Magnetic Intensity (TMI) ranges from 21.1 to 95.3 nT after IGRF correction. Residual magnetic anomaly ranges from -10 to 8.1 nT. First vertical derivative ranges from -0.022 to 0.022 nT/m. Magnetic Analytic signal (AS) ranges from 0.001 to 0.047 nT/m. Interpretation revealed that AS enhanced sedimentary magnetic anomalies and is not affected by the direction of magnetization. The probable depth to the top of sedimentary magnetic bodies (mineral) in the study area ranges from 47 to 113 m as revealed by AS depth method. The Bouguer gravity within the study area ranges from 8 to 34 mgal. Residual gravity (RG) ranges from -5.67 to 5.845 mgal. AS of Bouguer gravity data ranges from -5.671 to 318.83 mgal/m. RG map revealed potential zones where high density minerals could be hosted. 40K ranges from 0.2 to 1.2%. eTh ranges from 6.6 to 21.6 %. eU ranges from 1.7 to 5.3 %. It is realized that radiometric anomalies of 40K, eTh, eTh/40K and ternary are limited to alteration zone in the western part of the study area. The type of alteration in the study area is potassic alteration since it coincided with high magnetic zones. Correlation of results shows that Southeastern part is structurally dense than the western part of the study area and of low mineralization potential. The result was validated by posting the existing mining sites on mineralization potential map and the high mineralization zones correlates with the existing mining site