Evaluation of the influence of mineralogical attributes on the economic potentials of some carbonate rocks from Abakaliki Fold Belt, south-eastern Nigeria

The mineralogy of some carbonate rocks from the Abakaliki Basin has been investigated to determine the depositional environment classification and assess the suitability of the rocks for application in geotechnical construction and industrial process systems. The method of investigation included field mapping and petrographic and geochemical techniques to characterize their field characteristics, mineral types and texture and chemical contents. Mapping revealed two lithologic units of sandstone and shale that associate with the carbonates in a similar sequence. The carbonates contain fossils and are composed of calcite, quartz and rockclasts. The grains have angular to sub-rounded sphericity and are dispersed in hetereolithic groundmass. The major oxide composition shows average value of 32.30wt% SiO₂, 26.37wt% CaO, 7.23wt% MgO, 6.56wt% Fe₂O₃, 4.38wt% Al₂O₃, and 3.23wt% K₂O + Na₂O in decreasing order of abundance. Concentrations of trace elements are significantly higher (> 100 ppm) for V, Cr, Sr, Zr, Cu, Ba, Pb and Zn and comparatively lower for Sb, Ge, Ce, Y, As, Hg, Tiand Au. The studied rocks qualify as biomicrite or wackestone and range from dolomitic, through carbonaceous to siliceous limestone deposited in a wide spectrum of environment from shallow marine to transitional setting. The rocks are marginally suitable for use as aggregates due to the presence of deleterious contents of quartz and organics. For cement production, their low content of CaO, relatively high SiO₂, comparatively high LOI and elevated abundances of contaminant heavy elements are major limitations. Similarly, in paper, plastic, paint, metallurgy and pharmaceutics, the rocks are unsuitable due to the constituent minerals.