Auriferous Showings in the Bedrocks and Stream Sediments of Okemesi-Ijero Area, Southwestern Nigeria
The bedrocks and gold mineralization have been widely studied especially, in the southern extension of the Ilesha schist belt, but information regarding stream sediments in the area is rarely available in literature. The present study therefore, focused on bedrock and stream sediments geochemical survey of Okemesi/Ijero area within the northern extension of Ilesha schist belt using an integrated approach to elucidate the gold and other associated mineral potentials. Detailed geological survey involved lithological, structural and geochemical assessment of the bedrocks. Thirty five rocks and stream sediment samples were used for this study in a grid-controlled sampling method. X-ray diffraction (XRD) using Empyrean diffractometer DY (2010) model, and X-ray fluorescence (XRF) analyses in ray flux (66.0% Lithium Tetraborate and 34.0% Lithium Metaborate) to identify the major elements, and pathfinder elements of gold. Major oxides of the bedrocks and stream sediments for major elements were determined using atomic emission spectroscopy (AES). Trace and rare earth elemental analysis was done using inductively coupled plasma mass spectrometry (ICP-MS). Data evaluation was carried out using statistical packages for software simulation. Results showed that bedrock types are quartz-biotite-schists, banded-gneiss, granite-gneiss, biotite-gneiss, calc-gneiss, porphyritic granites, charnockites, massive and schistose quartzites, mica-schists. Structural assessment of the bedrocks revealed folds, fractures and veins as products of Precambrian deformations. XRD peaks revealed quartz, (>70%), albite (22%), microcline (30%), muscovite (26%), fluorite (68%-47%), ulvospinel (61.5%). Geochemical analytical results using XRF analysis also revealed both major elements with the highest concentration in the studied samples such as SiO2 (98.70%-70.59%) and Al2O3 (0.71%-19.01%) respectively and pathfinder elements of gold such as As, Pb, Ir, Pt, Os and Ag which was an indication of gold in the rock samples and their concentration values (10-0.05 mg/kg). The result of sequential analysis also confirmed gold potentials and other associated mineralization such as Cd, Cu, Zn, Fe, Pb and Ni at different extractive phases. Au is found at the lithogenic phase and in the residual fraction of the sediments, while other metals are from anthropogenic sources. However, the folds, fractures and veins provided the structural framework for the type of mineralization in the studied area.
Okemesi, Ijero, Bedrocks, Sediments, Mineralization, Sequential Extraction
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