Rock Mechanics Evaluation for Underground Mining Feasibility in Ilesha Gold Belt, Osun State

The Ilesha gold belt in Osun State, South West Nigeria, has been exploited by artisanal miners through shallow underground workings for decades, but the transition to mechanised underground mining requires a comprehensive rock mechanics evaluation to ensure safe and economically viable operations. This study evaluates the rock mechanical properties and ground conditions of the dominant rock types in the Ilesha gold belt, providing data for underground mine design. Rock core samples recovered during exploration drilling were subjected to uniaxial compressive strength, Brazilian tensile strength, triaxial compressive strength, and point load strength tests. The Schmidt hammer rebound value was measured on accessible outcrops as an index of surface hardness. Geomechanical classification using the Rock Mass Rating and Q-system was conducted using discontinuity data from oriented core logging and scanline surveys in existing underground workings. Numerical modelling using the finite element method was applied to assess roof and pillar stability for proposed stope geometries at depths of two hundred to four hundred metres. Results indicate that the dominant schistose host rocks exhibit moderate rock mass quality but significant anisotropy that must be considered in excavation orientation planning. Recommendations for support design, acceptable stope dimensions, and pillar recovery ratios are presented. Keywords: rock mechanics, underground mining, Ilesha gold belt, Rock Mass Rating, mine design.