Petrographic and mineralogical study of extended outcrops of lignite layers in Agbor area, southern Nigeria

Abstract

Coal layers up to 1 m thick, exposed mainly on river banks in the vicinity of Agbor, Okhuokhuo and Ubiaja, Southern Nigeria, were examined by means of organic petrology, mineralogy and geochemistry, in order to gain coal quality data and understand the palaeoenvironmental conditions during peat accumulation in the broad area of the Ogwashi-Asaba Formation. The obtained results show that coal is of low-rank C; it overlies mainly claystone derived from flooding of branches of the palaeo-Niger River. The precursor peat was accumulating in mires under mesotrophic to ombrotrophic, anoxic conditions. The peat-forming vegetation represented mainly herbaceous plants with minor tree contribution. Though the number of studied samples is low, the distribution of the lignite layers extends further towards N.NW of the known lignite-bearing area. Taking into consideration the low ash yields of some samples, there are encouraging indications for notable lignite deposits of high quality. The mineralogical composition and the activity concentrations of 238U, 226Ra, 232Th and 40K exclude any severe environmental effect from coal exploitation. Due to all these promising evidences, a detailed exploration in these and between these outcrops is recommended in order to estimate the lignite potential hosted in this area.