Geochemistry, Mineralogy and Petrogenesis of the Vein-Type Barites of Some Portions of the Benue Trough, Nigeria

Abstract

Several barite deposits have been reported to occur in Nigeria within the Benue Trough, one of the West Central African Rift Systems (WCARS) considered variously as an aulacogen, strike-slip or pull-apart basin. In spite of these occurrences and the high local and international demand for barites, Nigerian barite is yet to find a place even in its local market probably due to the poor knowledge of the fundamental properties of the barites. To throw more light on this some deposits that are mined on artisanal basis in the Trough were studied alongside an overview of the evolution of the basin and the geochemistry and petrogenesis of the barite. Barites in the area of study occur as white, reddish-brown and clear varieties with specific gravity varying between 3.3966 and 4.3432 based on pycnometric and immersion methods. They occur as epigenetic veins of between about 0.1 m to more than 1.5 m, which encourages open cast mining. Chemical analysis show that the samples studied contain between 72.61 and 72.12% Ba corresponding to a calculated total BaO of 48.37 and 60.1%. The other relatively significant elements but of less value in the samples include Si, Fe, Sr, Ca, Al, Pb, Mg, Mn, P, and Ni. XRD results also show barite mineralogical association with wenkite and plumbian barite of insignificant quantity. The barites likely formed from intermingling of infiltrating solutions containing barium with soluble sulphates arising within the rocks passing through fractures created during the Late Cretaceous inversion in the basin. The inversion is suggested herein to have resulted from magmatic underplating and consequent peneplanation in the middle Benue Trough.