Sediment Characteristics and Geochemistry of Ogwashi Asaba Formation at Oraifite and Environs, South Eastern Nigeria

                                ABSTRACT

Geochemical characterization and lithostrtigraphic description of the Neogene strata in the Orafite-Nnewi area of Southeastern  Nigeria are carried out based on detailed field measurments and laboratory studies. The Ogwashi-Asaba formation consists of multi storey channelized sandstone, pebbly at the base and fining upward. Lignite seams occurs at various levels. Some geochemical properties of Enem, Olulu and Ejighioku lignites deposits in Oraifite area of Anambra state, Southeastern Nigeria were investigated using both proximate and ultimate analytical procedures. The analytical evaluation of properties such as moisture, volatile matter, fixed carbon, and ash forms the proximate analysis. The average fixed carbon contents of the lignite deposits in Olulu, Ejighioku and Enem were 30.40, 1.60 and 23.21 respectively, indicating a low quality coal while the average ash values (in dry base) were 9.40, 70.75, and 12.40 respectively. The average volatile matter contents (in ash free base) of the lignite in Olulu, Ejighioku and Enem were 39.92, 15.55, and 33.63 respectively while the average moisture contents of the deposits were 20.20, 12.10 and 30.70% respectively. The volatile matter of the Lignite samples in the three locations increased with decrease in moisture content. These results revealed that the Lignite in these locations are of low economic value as the cannot be efficiently used for power generation, coal gasification by- products and other industrial uses. The results of ultimate analysis of each elements are discussed in details: the concentration of Carbon content ranges between 11.59 and 50.05 wt%, Oxygen content ranges between 3.598 and 14.52wt%, the Hydrogen ranges between 0.13wt and 4.44wt%, Sulphur ranges between 0.04 and 0.08wt% and Nitrogen ranges between 1.30 and 1.79wt%.  The statistical analysis of the results show Sulphur as 0.06, and Oxygen as 10.66wt%. Carbon and Oxygen increases with decreases in Sulphur content. The increase Carbon and Oxygen content is an indication of high volatility or combustibility while the decreased sulphur contents adds preference and value to the Lignite deposits, since sulphur burns with suffocating and irritating odour. The proximate and ultimate compositions of the samples show that it is of low quality Coal, the analytical results suggest the existing Coal with varying thickness spread all over the region is of Lignite rank. Based on sediment characteristics and textural attributes, fluvial influenced shallow marine environment and beach process adjacent to near shore whirl pool agitating turbidity conditions are indicated for the Ogwashi-Asaba Formation within the study area. Textural analysis shows that the sand facies of the formations are generally moderately- well sorted and potentially aquiferous