The opening of the Benue Trough as well as the sinistral displacement of the strike slip fault that displaced the whole inlier has been well documented in recent times. Fractures formed are believed to have occurred at the time of the opening of Benue Trough in the Cretaceous. Large sedimentary basins were developed with carbonates and continental platforms that provided ideal conditions for the formation of suits of sandstone hosted, stratiform deposits such as barite, celestine and fluorite of Cretaceous age. Barite is the economic mineral and the shape of the ore bodies is considered massive, the gangue minerals are calcite, traces of celestine and silica. A fluid inclusion and stable isotope analysis (S and O) for barite and fluorite were conducted. The result shows a melting ice temperature between −24 °C and −15 °C (salinities of 13.6 to 24 wt. % NaCl equiv.) and a homogenization temperature ranged between 60 °C to 155 °C. Isotopic analysis of barite showed δ34SVCDT ranges from +18.1‰ to +19.7‰ (average of 19.03‰), fluorite sulphur isotope value gives 17.7‰ to 19.6‰ (average of 18.6‰). Sulfur isotope data for the barite and fluorite from the study area is consistent with a sulfur source formed during the Cretaceous, which coincides with the age of the Bima Formation. The oxygen isotope analysis showed a range between δ18OVSMOW 9.9‰ and 12.3‰ for both minerals. Fluid inclusion microthermometry and isotopic measurements lead us to conclude that brines from the Upper Benue Basin led to the replacement of the evaporite strata (gypsum) by barite and fluorite and its subsequent deposition within the veins and fractures of the Bima Formation.
Keywords: Displacement, barite, basinal brines, microthermometry., paleogeographic, sinistral, stable isotopes
