The Ikom-Mamfe basin, Nigeria: A study of fracture and mineral vein lineament trends and Cretaceous deformations

• Mineral veins are loaded in “ac” extension fractures in the Ikom-Mamfe basin.
• Veins in this basin can separate U. Cretaceous sequence from the L. Cretaceous.
• Majority of barite samples in the Ikom-Mamfe basin have specific gravity above 4.2.
• In terms of mineralization, the Ikom-Mamfe basin is a baritogenic environment.

The Ikom-Mamfe basin is approximately a 130 km long, east–west abutment onto the eastern flank of the lower Benue trough of Nigeria and extends westwards into Cameroon. Two hundred and six fracture lineaments were analyzed in the Nigerian sector of this basin. They vary in length from 0.5 to 23.75 km, with the most frequently occurring fracture length being about 2.25 km. The most prominent fracture sets have NE-SW and NW-SE orientations, while less prominent patterns are in the NNE-SSW and ESE-WNW directions. NW-SE and NNE-SSW fracture sets are interpreted as “ac” extension fractures from two different deformation episodes, while NE-SW and ESE-WNW sets are “bc” tensile fractures parallel to the axes of F1 and F2 folds, respectively. This implies two deformation episodes in this basin, with the earlier one producing the NE-SW (F1) fold axes, exactly as in the Benue trough. Two prominent mineral vein trends in the basin are the NW-SE and NNE-SSW sets, in which minerals are loaded in “ac” extension fractures. The orientations, lengths and frequency of these lineaments should help in differentiating their ages. The less prominent veins are in the NE-SW and ESE-WNW directions, which are in the “bc” tensile fractures. Early Cretaceous sediments are characterized by NW-SE major and NE-SW minor sets of veins, while the late Cretaceous sequence is characterized by NNE-SSW major and ESE-WNW minor, mainly barite, veins. More than 70% of the barite samples tested gave specific gravity values of 4.2 and above, which is the range specified by the American Petroleum Institution (API) as drilling mud additive or weighting agent. Other vein-filling minerals in this basin are lead ore (galena), zinc ore (sphalerite), pyrite and amethyst, which are altogether subsidiary to barite mineralization.