Assessment of gold mineralisation in Osu–Amuta–Itagunmodi areas, Southwestern Nigeria

Abstract

Gold is artisanally mined from eluvial deposits within Osu–Amuta–Itagunmodi areas of Ilesa Schist Belt, southwestern Nigeria. Mine site selection and mining operations are done without any understanding of mode of occurrence, compositional characteristics and extent of gold mineralisation. The present study was aimed at determining the host lithologies, extent and associated geochemical features of the gold mineralisation. Fifty rock samples were cut into thin section for examination and analysed using inductively coupled plasma–mass spectrometry (ICP-MS). Forty-eight soil samples collected from Artisanal Gold Mine (AGM) pits to a depth of 5 m (n = 9), and along defined horizontal profile lines from the mine pits (n = 39) were analysed for elemental constituents, and mineralogical compositions in vertical profile samples using ICPMS and X-ray diffraction (XRD) techniques, respectively. The quartz-biotite schist, quartzite, talc-chlorite schist and amphibolite had Au concentration (ppb) that ranged from 1.3 to 14.4 (average 3.95), BDL–0.9 (average 0.63), 0.9–4.6 (average 2.18) and 0.5–2.7 (average 1.56), respectively. Vertical and lateral profile soil samples were Osu: 4.5–7.6 (average 6.17) and 0.9–78.8 (average 8.54); Amuta: 4.1–6.8 (average 5.2) and 2.8–19.8 (average 7.40); and Itagunmodi 3.9–13.2 (average 7.43) and 0.5–14.8 (average 4.33). Evaluation of the horizontal profile soils revealed higher Au concentrations than the artisanal mine workings, indicating additional mineralisation potentials in the study area. Au concentrations were in the order of quartz-biotite schist > talc-chlorite schist > amphibolite >> quartzite, with anomalous concentrations detected in quartz-biotite and talc-chlorite schists. Elevated concentrations also occurred in residual soils overlying quartzite and amphibolite lithologies. Mineralisation is hydrothermal in nature, extends beyond current artisanal mine workings and has potential for further exploration.