Application of Integrated Geophysical Methods in Mapping the Location of Basaltic Intrusions in Mambilla Plateau and Environs, Northeast, Nigeria

Abstract

Integrated geophysical investigation on the Mambilla Plateau and its environs was necessary to map the locations of basaltic intrusions  and their patterns of distribution. The Landsat-8 ETM+ false colour composite image (bands 7, 4, 2 in R, G, and B) was used to identify  rocks such as younger basalt (yb), porphyritic granite (pg), granite gneiss (Gn), and migmatite gneiss (Mg). Similarly, rocks like granite gneiss (Mg), porphyritic granite (pg), and migmatite gneiss (Mg) were recognised by the Principal Component Analysis of the Landsat 8  ETM+ picture (PC2, PC1, and PC4 in R, G, and B). The lowest and maximum values for the total magnetic intensity map were 33030.343 nT  and 33172.792 nT, respectively, along with mean of value 31.50nT to 33068.89nT.The primary magnetic field map showed an average  value of 33293.4495 nT, with values ranging from 33228.522nT to 33358.377nT. The crustal magnetic field map resulting from ore bodies  or intrusions had an average value of -159.50 nT, with values ranging from -397.669 nT to -80.699 nT. The RTE values, which range from  -82.382nT to -392.122nT, indicate regional geological intrusions, fractures, and faults. Values were shown on the magnetic equator field  map, which was further upward continued to 15 km, with an average values ranging from -279.141nT to -157.160nT. The pseudo-gravity  map of the region showed two low densities, ranging from -0.11 to -0.01 mGal, depending on the location, and three high densities, indicating moderate to intermediate densities, ranging from 0.25 mGal to 0.01 mGal. RTE anomaly data produced from subsurface rocks  typically has the greatest horizontal gradient along the object's border. This means that the maximum gradient is directly localised to the  map boundaries of the distinct lithologies. By examination of the abrupt changes in rock magnetism in a lateral direction, this led to the  determination of contact limits of the basaltic intrusion, faults, and mineralization of the underlying rocks