Abstract

The Bima sandstone is the oldest, thickest, and most extensive formation in the Upper Benue Trough, located in north-eastern Nigeria, and it is included in a region known for its Uranium mineralisation. The sandstone has been subdivided into three siliciclastic members: B1, B2, and B3. Sedimentological and structural factors necessary for uranium precipitation are recognised within the members. B1 consists of basement-derived conglomerates supported in a gravelly or sandy matrix. B2 is coarse- to medium- and fine grained sandstone with good lateral continuity. B3 consists of well-sorted, uniformly fine grained ferruginised sandstone interbedded with more clayey to shaly carbonaceous beds. The Benue Trough represents a rift-related basin formed in horst and graben structures, and is characterised by numerous post-depositional structures such as fracture/fault zones. The sedimentological and structural factors may reduce permeability of sediments and prolong regional scale fluids circulation. We anticipate that, Uranium that is leached from sub adjacent basement granites and disseminated in the sandstone may be concentrated in the fracture/fault zones within B3 and B2/B3 transitional sequences that form sandstone-hosted Uranium deposits.

Key words: Geology, Bima sandstone, Uranium, Upper Benue Trough.