Mineralogy and Geochemistry of Geophagic Clays from Share Area,Northern Bida Sedimentary Basin,Nigeria

摘要

The Share area occurs within the northern Bida Sedimentary Basin in Nigeria. The focus is on the geological settings, mineralogical and chemical compositions of Share geophagic clays with the aim of inferring their depositional environments, provenance and possible human health implications. The field method include collection of representative samples at appropriate clay stratum and the samples of the geophagic clays were subjected to petrographic, X-Ray fluorescence and X-Ray diffraction analyses. XRD revealed that Geophagic clays are polymineralic and the main reflections of the clay minerals identified were kaolinite, nacrite, gibbsite and dickite. The peaks of other traces are hematite, quartz and pyrite. Geochemical data indicated that geophagic clays composed of SiO2 content ranging from 64.40% to 46.30%, Al2O3 values varies from 36.54% to 20.54%, Fe2O3 values varies from 4.71% to 1.42%, MgO content varies from 0.08% to 0.06%, CaO ranges between 1.30% and 0.03%, TiO2 values varies from 9.17% to 0.20%, and MnO content ranges from 0.631%. to 0.09%. These values indicate that the geophagic clays are essentially siliceous aluminosilicates. The presence of sedimentary structures typical of tidal sedimentation, low abundance of MgO and K2O indicate lack of expandable clays, and the presence of ironstones further attests to abundant oxygen due to sub aerial exposure resulting to the oxidation of Fe2+ to Fe3+. The presence of basal conglomerate, rootlets structures, iron capping, fining upward sequence and abundances of kaolinite indicate a fluvial (continental) sedimentation. Geophagic clays may introduce metals like Fe, Zn, Cu, Ni, Ti, and Zr to the gastro-intestinal system of consumers, causing adverse effects like increase in the gastro-intestinal pH, and the binding of plant toxins and pathogens which create a surfacial coating on the stomach with inferred pharmaceutical implications. Negative impact of ingesting geophagic clays may lead to electrolyte disturbance, intestinal obstruction, constipation, hypertension, peritonitis, eclampsia, iron deficiency, anemia, microbiological infections, helminthiasis and heavy metal poisoning while coarse sandy quartz particles in the clays could affect dental enamel and also lead to the possible rupturing of the Sigmoid colon due to the abrasive nature of the particles.