Aspects of hydrothermal alteration assemblages around Bakwani-Bagwa, Northwestern Nigeria: Insights from multifractal analysis of measured thresholds for mineral exploration

Abstract

This study is aimed at identifying highly altered zones by applying the concentration area 
(C-A) fractal model technique on Landsat ETM+ image of the area around Bakwani-Bagwa, 
Northwestern Nigeria. The multifractal analysis was used to quantify the degree of alter
ation on satellite images processed using the Crosta technique. A log–log plot was used to 
display the multifractal characteristics of clay and iron altered images and identify thresh
old values. Maximum and minimum threshold values obtained from the fractal analysis 
are 1.74 and 4.01 for clay altered images and 0.607 and 3.04 for iron altered images. High 
clay and iron alteration zones account for 5.89% and 7.84%, covering an area of 22.28km2 
and 29.65km2, respectively. Delineating highly altered zones from these images reveals 
higher alteration largely within silicified sheared rocks and areas around faults. The cur
rent study proved that the multifractal processing techniques are valuable mapping tools 
for geological reconnaissance which can be extended to a large area of the Nigerian base
ment and provide preliminary hydrothermal alteration maps that are accurate as well as 
cost-effective and time-saving.