Olade reported in 2019 that out of more than 20 countries that mine uranium ore worldwide, only five countries account for over half of world’s annual production, and 75% of such production is derived from sediment-hosted and unconformity related deposits. Since the 1970s, Nigeria explored for uranium deposits within its borders, particularly after vast deposits of uranium were discovered to the north in the neighboring country of Niger Republic in the 1960s. Despite Nigeria’s supposed uranium mineralization potential, only a few occurrences have been discovered to date, none of which are economically viable. The known uranium occurrences are classified into four types based on their geological setting and mode of occurrence: (i) magmatic dissemination in peralkaline granites; (ii) epigenetic fissure-filling veins in granites/rhyolites; (iii) sandstone hosted; and (iv) phosphorite uranium.
The sandstone-hosted occurrences are of two subtypes; tectono-lithologic and stratiform. A conceptual framework is proposed utilizing several criteria to develop an exploration model that is focused on targets with substantive mineralization potential. Based on this model, it seems only the stratiform sandstone type uranium is considered as having any future exploration potential in Nigeria. Fortunately, the country is endowed with several Cretaceous riftogenic sedimentary basins, such as the Gongola Basin, Yola Basin, Borno Basin, Lower Benue Trough and Mamfe Embayment that contain several hundred meters thick basal arkosic sandstones and conglomerates of fluvial to deltaic origin and formed in rapidly subsiding depocenters overlying crystalline basement rocks. The formation of sandstone uranium deposits is often dependent, among other factors, on the nature, abundance and the reactivity of the uranium reducing agents which include organic materials, biogenic H2S and hydrocarbons. Several areas that have potential sources for uranium and the conducive environment to precipitate and preserve uranium within the stratigraphic sequence are proposed as potential exploration targets.
The author concluded that Nigeria is a country with considerable potential for the discovery of viable uranium deposits if well-funded systematic exploration is focused on sandstone type uranium deposits within the Lower and Upper Benue Trough and its northern extension in the Borno Basin where crude oil was recently discovered. The close association between uranium deposits and hydrocarbon-bearing basins is well known. The basal sandstones and conglomerates in the Benue Trough and the side basins of Mamfe and Yola are prime targets for uranium exploration involving the use of geophysical and geochemical methods accompanied by geological mapping. The government agencies charged with the responsibility for uranium exploration should provide basic geoscientific information such as up to date topographic and geological maps as well as aerial and ground radiometric survey data that can encourage the private companies and investors to participate in uranium exploration venture by conducting more detailed exploration including subsurface drilling in target areas.
The Nigerian National Petroleum Company exploring for crude oil in the Borno Basin and other basins should be cognizant of the spatial association of uranium with hydrocarbons and include such perspective in its exploration strategy.
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