The Role of Rhyolites Melts in the Petrogenesis of Tabenken Coal Seam, Northwest Region, Cameroon
Abstract:
In Cameroon, coal has been identified in Bali, Dschang, Fundong, Mamfe and Tabenken. Though its occurrence has been identified, detailed geologic studies in the areas of geochemistry and petrographic have not been done to qualify these coal seams, which knowledge will afford geologists to have a holistic view of coal. The objective of this research thus was carry petrographic and geochemical analyses of the coal samples in other to have an insight about its quality and afford Government and potential investors take informed decisions when considering exploitation and use of the resource. In other to achieve these ten coal samples collected during field studies were subjected to petrographic studies and two samples for geochemical analyses following standard procedures. Re sults from field description and petrography show that, coal ranks within the seams range from peat to anthracite, some occurring singly, while most were mixed with shale, sandstone and rhyolites. Thin sections show that the coal intercalated with rhyolites has high quartz content The presence of high quartz percentage may suggest two origins; coal formed from detrital origin and intrusion of silica from rhyolitic tuffs, since rhyolites contain high percentages of silica (˃70 %). The presence of hydrocarbon veins observed in the thin sections are interpreted as resulting from the presence of the rhyolitc fluids, whose outpours were caused by diapiric movement, of the coal into the viscous rhyolite. These temperatures thus were sufficiently high to melt the coal into liquids. Results obtained for major elements geochemistry reveal that the percentage composition of the elements SiO2, Al2O3 and Fe2O3 are dominant constituents and account for over 57.46 % average weight composition. Other major elements such as K2O, TiO2, MgO, Na2O and MnO are present in low concentrations (average of 3.97 wt %). The high concentration of SiO2 and Al2O3 indicate high detrital quartz and clay mineral content in the coal measures. This is in general agreement with results obtained with work done in the nearby Anambra basin, Nigeria. The high concentrations of SiO2 (57.46 average wt %), (as observed in thin sections as well) for the samples TBN04, TBN08 and Al2O3 content (19.58 average wt %) compared with the concentrations of other major elements in the analyzed samples, suggest a high detrital input from the surrounding of the basin during peat formation. The presence of TiO2 and P2O5 is indicative of basaltic rocks of oceanic environment. These elements also reveal that Si, Al, Ti and K originate mostly from a mixed clay assemblage, which is a constituent of kaolinite and illite. The XRD analytical results show that the TCS is mainly composed of siliceous mineral such as quartz (SiO2), kaolinite [Al2 (SiO2O5)(OH)4)]. The mineral suites in the TCS coal samples used are similar with the South African coals. Kaolinite is uniformly distributed in the coal samples.
