Host rock geology and geochemistry of the Zona uranium occurrence, Peta Gulf Syncline (Upper Benue Trough), northeast Nigeria

The Peta Gulf Syncline (Upper Benue Trough, northeast Nigeria) is a fault-bounded pull-apart sub-basin. The boundary faults are mainly northeast-southwest-trending en echelon strike-slip faults, truncated along their lengths by normal and tear faults with stepovers. The eastern marginal faults underwent rotation during sedimentation, whereas the steeply dipping western marginal faults were inactive.The Peta Gulf Sub-basin is filled by the Bima Sandstone Formation (Lower Cretaceous) which has three siliciclastic members: (i) B₁: medial fan coarse-grained to microconglomeratic sandstones; (ii) B₂: full fluvial medium-grained sandstones with minimal fines; and (iii) B₃: lacustrine and flood basin deposits comprising alternating fine-grained sandstones and siltstones/claystones. Sediment supply was from east to west and facies changes show a general fining in this direction. B₃ offers the most favourable environment/lithology for U concentration.The only significant U occurrence in the Peta Gulf Syncline is the Zona U anomaly, which occurs within transitional B₂-B₃ brecciated sandstones with wall rock alterations zones. The mineralised zone has elevated SiO₂, Fe, As, Ba and W levels but is depleted in the alkalis, Zr, Rb and Sr. This chemical zonation supports the epigenetic orgin of this anomaly.