Gravity Modeling of the Au–U Mineralized Crust at the North-Central Cameroon Illustrating Crustal Permeability

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The north-central Cameroon is located at the northern edge of Archean Congo–Sao Francisco craton and at the east of the West African craton. This area includes various Neoproterozoic to Holocene geological litho-structural units. It corresponds to a juvenile crust resulting from the collision of the above cratons. Geological features associated with the Poli–Ounianga–Kebir heavy gravity line trending NE–SW crosscuts the study area and hosts several deposits, chiefly auriferous and uraniferous ore deposits. Uraniferous bodies are described at the SW and NE sides of the Benue Trough and are related to hydrothermal processes and structural events in Neoproterozoic granitoids of Poli (Cameroon) and Zabili (Chad). Gold ore deposits are found around faulted zones mostly in the Tchollire shear zone. Gravity data derived from the Earth Gravitational Model EGM2008, combining terrestrial, maritime and satellite-derived data, were used to model the crust of the north-central Cameroon. The geophysical filtering enabled to highlight that the most fractured areas with the deepest faults are situated on the positive anomalies of the mineralized volcano-sedimentary belts of Poli and Bibemi. The Benue Trough that crosscuts the volcano-sedimentary belts exposes few structural features due to the weak gravity signal of Cretaceous sedimentary cover. The radially averaged power spectrum analysis brought out the density contrast depths of some geological belts and revealed the Moho discontinuity of the study area at about 24 km depth. This Moho depth is in accordance with the assumption of a thin crust and a mantle upwelling in the study area proposed by previous works. Thus, the presence of geological formations of mantle, crustal and mixed crustal-mantle origin such as mafic rocks as well as calc-alkaline to alkaline granitoid outcropping in the study area may be the consequence of the proximity of the upper mantle to the surface. Moreover, fractures highlighted in this work brought out the crustal permeability in the study area illustrating migratory passages for mantle formations found at the surface. Based on the gravity field analysis, the proposed models of basement in this study provide geological architecture highlighting the presence of more or less dense rocks and hydrothermal fluids migration along faults as key elements for ore deposits formation.