Geological Setting, Compositional and Economic Appraisal of Clay-Shale Occurrence in Itu-Mbonuso/Iwere Area, South-Eastern Nigeria

Abstract

The clay-shale bodies of Itu-Mbonuso/Iwere area occur in blankets within the first half of a metre from thesurface in most places. They are medium to dark gray.To assess their potentials as raw materials for industrial usage in the manufacture of Ceramics, Cement,Structural, Refractory bricks and pottery wares, the representative samples were subjected to mineralogical,chemical analyses using Inductive Coupled Plasma Spectrometer and X-Ray Diffraction respectively, whilegeotechnical properties tests were carried out on grain size distribution, sedimentation, Atterberg Limits andfiring tests in the laboratories.Mineralogical analysis revealed that kaolinite is the major clay mineral with a range of 18.17 – 55.09 % and 6.95– 38.76 in the clay and shale respectively.8%; smectites ranges from 10.62 – 12.72% and 4.94 – 10.84% in the clay and shalerespectively. Palygorskite occurs in one sample only at 53.99%. The non-clay mineral is quartz and rangesbetween 34.24 – 81.17% and 51.93 – 55.28% in clays and shale respectively.Chemical analysis showed that the average Si2O content is 53.10% and 49.92%; Al203, 18.81% and 18.15%;Fe203, 8.25% and 6.63%; MgO, 1.59% and 3.72%; TiO2, 1.43% and 1.49% for clay and shale respectively; whileother oxides Na2O, K2O, MnO, and P205 are less than 1% each. The three oxides silica, alumina and iron oxideaccount for 80.16% and 74.70% of the bulk chemical composition of the clay and shale respectively. Theaverage AR is 2.38 and 2.78, while the SR is 1.92 and 2.04 for the clay and shale respectively. The chemicalcompositions of the clay-shale compare favourably with some sedimentary clays and shale within the NigerianSedimentary basins.Results of grain size and sedimentation analyses showed that the fine fraction ranges from 84.40 to 96.40%while the clay-size fraction range from 36 to 76% in the clay- shale.About 76% of the representative samples have clay size fraction between 50 to 76%. Atterberg limits testsindicated that the studied clay-shale have wide range of liquid limits (47.7 to 194.0%), plastic limits (22.2 to77.7%), and plastic indices (15.8 to 116.3%). Plasticity results indicated that the clays and shale are majorlyinorganic clay of medium to high compressibility, a few organic silt of medium plasticity and organic silt or clayof high plasticity and compressibility.Firing test result indicated that the colour change is from greyish through orange to light Brown. Other physicalparameters include water absorption capacity (10.12 – 13.4%); firing shrinkage (4.8 – 9.1%) loss on ignition(9.50-14.98%) and plasticity indices of 15.78%-77.3% and16.7 and 116.3% for the clays and shale respectively.On the basis of the chemical compositions the clay-shale is suitable for use in the manufacture of good qualitycement and structural wares, while 95% of the representative samples having plastic limits between 22.3 and57.5% are suitable for the production of ceramics, pottery and wall bricks. Adequate processing and proportionalmixing in specified ratio with fine sand would reduce the firing shrinkage to an acceptable limit. Improving or upgrading of the alumina content by the addition of pure alumina or blending with clay of high alumina contentcan improve the refractory characteristics of the clay-shale.