The Petrographic Composition of Coal in the Gongola and Yola Arms, Upper Benue Trough Nigeria and a Consideration of the Paleodepositional Environment

Abstract

This study presents the petrographic and chemical analyses of the coal within the Upper Benue
Trough to determine the paleodepositional setting of the coal deposits. The Upper Benue
Trough (UBT) is a basin that extends in a NEE-SSW direction from the Gulf of Guinea to the
South of Chad basin. The UBT is divided into two namely Yola Arm and the Gongola Arm where
the coal was hosted in the Gombe and Lamza Formation. A total of seven (7) samples were
examined from 4 coal localities in the studied area.Chemical analyses were conducted at the
University of Witwatersrand, Coal Laboratory in the School of Chemical and Metallurgy
Engineering (SCHME) The equipment used is the Perkin Elmer thermogravimetric analyzer
(TGA) while the Dry-Cal bomb calorimeter is for gross calorific value (GCV). The procedure for
operating the bomb calorimeter is adopted after SANS 1928:2009/ ISO 1928:2009, and the
ultimate analysis was adoptedafterSANS17247:2006/ISO 17247:2005. The petrographic blocks
were subjected to grinding and polishing using SANS /ISO7404-2 (2009). Vitrinite reflectance
measurement was carried out largely based on SANS /ISO 7404 part 5 (1994). The proximate
analysis revealed the moisture content (MCareal aver.6.8Wt.%), volatile matter (VM areal
aver.27.7wt.%), fixed carbon (FC areal aver.48.4wt.%) with the ash yield (areal aver.17.6 wt.%)
calculated by difference. The gross calorific value areal average. 23.01 MJ/Kg with a low
sulphur content (areal aver. 0.85% daf). The average data for C and H values are 74.30 wt.%,
and 5.88 wt.% respectively, while that of N, S, and O are 1.72 wt.%, 0.85 wt.%, and 16.46wt.%
respectively. The distribution of the maceral groups with vitrinite as the dominant maceral,
followed by varied inertinite, mineral matter and liptinite. The mean random reflectance
measurement value of the coals (0.53 % RoV) points to low-rank-lignite-bituminous rank coal.
The chemical analyses display a y low ash, low sulphur and high moisture content in the coal
samples within the three sub-regions of the Benue Trough typical of the Cretaceous coals.
Given the modified equations and the plots used, understanding the depositional environment
accurately from just a single model is quite challenging