Integrated geophysical and remote sensing investigations in hydrothermal mapping for orogenic gold mineralization in parts of Ife–Ilesa schist belt SW Nigeria—a case study

Abstract

This paper presents an integrated approach involving geophysical and remote sensing datasets in the identification of regions that have undergone hydrothermal alteration in the gold-hosted site of the Ife–Ilesa schist belt. Geophysical methods employed include the aeromagnetic and aeroradiometric data, while the remote sensing involved Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data. Derivatives such as analytic signal, total horizontal derivative, tilt derivative of the total horizontal derivative, and 3-D Euler deconvolution were applied on the aeromagnetic data for the mapping and delineation of structures guiding migration of hydrothermal and mineralizing fluids in the study area. Radiometric analyses involving K/eTh, Ideal K anomalies deviation (Kd), and F-parameter, including principal component analyses on ASTER to isolate Potassic, Argillic, Propylitic, and Phyllic alteration zones were performed to delineate hydrothermally altered zones. The lineament map showed that the study area is geodynamically active as evident by the presence of deep-seated intersecting structures with depths ranging from 189 to 899 m, principally trending NE–SW, which is an impression of the Pan–African orogeny. The fuzzy gamma operator 0.9 was thereafter used in the integration of aeroradiometric and ASTER data for the hydrothermal alteration map production. Subsequently, five classes ranging from background to very high alteration anomalies were derived using the concentration–area (C–A) fractal model from the hydrothermal alteration map. These classes reveal the pervasive styles of alteration in the study area. The study further revealed the close association of structures, granitoids, hydrothermal alteration, and orogenic gold deposits. Also, the flurry of mining activities in the southern flank of the study coincides with most of the hydrothermally mapped areas with the Prediction–area (P–A) plot showing 78% occurrence of orogenic gold deposits in 22% of the total area explored. This translates to high potential of orogenic gold mineralization in the study area. The study therefore concluded based on the validation result that hydrothermal alteration mapping is important in the mapping of orogenic gold deposit. Hence, unexplored areas particularly in the western and eastern flank of the study area where there are strong indications of hydrothermal alteration have good prospect for gold mineralization.