Structural and hydrothermal alteration mapping related to orogenic gold mineralization in part of Kushaka schist belt, N
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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 Sherif Olumide Sanusi1 · John Olurotimi Amigun1 Received: 23 April 2020 / Accepted: 26 August 2020 © Springer Nature Switzerland AG 2020
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. Keywords Structural framework · Orogenic gold mineralization · Hydrothermal alteration · Aeromagnetics · Aeroradiometrics · Kushaka schist belt
1 Introduction The Gurara area (Fig. 1), situated in the Kushaka schist belt of north-central Nigeria, has been reported to be associated with gold mineralization in stream sediments (alluvial), soil sediments (eluvial), and within geologic structures and quartz veins [1]. Although approximately 90% of Nigeria’s total gold production is from alluvial and eluvial deposits [2], it is equally important to consider the orogenic gold mineralization in the Kushaka schist belt from which both the alluvial and eluvial deposits originated.
One of the critical factors controlling orogenic gold mineralization in the Kushaka schist belt and in some other schist belts in Nigeria (Maru, Anka, Zuru, Zungeru-Birnin Gwari, Karaukarau, Ilesa, Iseyin-Oyan and Egbe-Isanlu schist belts) is the geologic structure. These structures are significantly involved in the migration, remobilization and localization of primary gold deposits [1–4]. Delineation of these crustal-scale structures such as dykes, faults, shear zones, folds, j
