Structural and hydrothermal alteration mapping related to orogenic gold mineralization in part of Kushaka schist belt, North-central Nigeria, using airborne magnetic and gamma-ray spectrometry data

Abstract

This paper presents an interpretation of airborne magnetic and gamma-ray spectrometry data over a part of the Kushaka schist belt of Nigeria with a view to assess the sub-surface structural framework and hydrothermal alteration haloes that are related to orogenic gold mineralization in the study area. The geophysical analyses performed to improve the quality of the aeromagnetic data for better understanding of the subsurface geology were reduction to the equator, upward continuation, total horizontal derivative, analytical signal, source edge detection, tilt-angle derivative of total horizontal derivative. The analyses performed on the airborne gamma-ray spectrometry data were made on K/eTh, F parameter and deviation of ideal K values (Kd). Deep-seated, brittle-ductile shear/fracture zones with characteristic depth of 428.0-607.6 m and area extent of 15.5 km by 6.5 km that were delineated in the area coincide with beehive of artisanal miners exploiting gold deposits. In this study, subsurface geologic structures, specifically dykes/faults, that trend in the ENE-WSW direction constitute a first-order control on orogenic gold mineralization in the study area. The hydrothermally altered zones mapped in the area indicated they are structurally controlled and closely associated with orogenic gold mineralization. Apart from geologic structural evidences that are controlling orogenic gold mineralization, this study has indicated that hydrothermal alteration mapping is equally important for a promising orogenic gold mineralization mapping.

Utilizing remote sensing and aerogeophysical data for spatial decision support system for optimal gold mineralization site identification in North-Central Nigeria

“…The processing of the gamma-ray spectrometry data adopted the methods of Boadi et al, [82]. It has been established that mineralization zones occurring along shear zones and contacts in the Schist belt within the study area have been subject to variable degrees of hydrothermal alteration [83]. Delineation of hydrothermal alteration zones relied on regions exhibiting elevated potassium (K) concentrations extracted from gamma-ray spectrometric data, a method employed by de Quadros et al [84].…”

Detection of Uranium Anomalies and Alteration Zones Using Airborne Gamma-Ray Spectrometry at Gabal Attala and Its Surrounding Area, Eastern Desert, Egypt

“…Thorium is known to be less mobile geochemically than potassium and uranium. Therefore, thorium (eTh) is used as a lithological background monitor to determine ideal eU and K values [29,30]. Therefore, normalization of the radioactive data by eTh values is necessary to overcome the influences of environment, lithology, leaching and weathering on K and eU concentrations.…”

“…The Potassium Ternary Composite Image (Figure 5) of the study area is generated and compared with the (eTh/K map) (Figure 4) and hydrothermal alteration zones such as potassic and phyllic altered areas were detected. As thorium impoverishment often occurs with K enrichment during hydrothermal alteration processes [30]. The F-Parameter technique proposed by Efmov, 1978 [31] was also applied because it involves two significant relationships, the K richness correlated to eTh/eU ratio and eU richness correlated to the eTh/K ratio (equation.…”

Radiometric characteristics of some metallic ores and nonmetallic deposits: an example, Wadi Al-Allaqi, South Eastern Desert, Egypt

“…Unlike potassium and uranium, thorium has lower mobility. Hence, the optimal eU and K values are determined using thorium (eTh) as a lithological background monitor (Thorium normalisation) 50 , 51 . Based on radiometric data, hydrothermal alteration zones can be identified by the observed areas of K enrichment 43 , 45 , 52 – 54 .…”