Techno- Economics Viability Assessment of Associate Rocks at Obu- Mines Okpella, Nigeria

Mining and quarrying activities generate significant quantities of associated rocks and other materials that are often treated as waste despite their potential value as construction resources. This study assessed the techno-economic viability of recovering and utilizing associated rocks generated at Obu Mines, Okpella, Edo State, Nigeria, with emphasis on their engineering properties, mineralogical characteristics, resource potential, processing requirements, and economic value. Representative samples were collected from three mining pits, designated Pit 1, Pit 2, and Pit 3, and subjected to physical, mechanical, chemical, and mineralogical analyses. The physical tests included moisture content, water absorption, effective porosity, specific gravity, and particle-size distribution, while mechanical characterization involved Aggregate Impact Value (AIV), Aggregate Crushing Value (ACV), Uniaxial Compressive Strength (UCS), and flexural strength. X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses were also conducted to establish the chemical and mineralogical compositions. Results showed that Pit 1 exhibited the highest engineering quality, with a specific gravity of 3.10, AIV of 6.96%, ACV of 4.10%, and UCS of 107.0 MPa, making it suitable for high-value applications such as concrete and road aggregates. Pit 2 recorded a specific gravity of 2.64, AIV of 10.00%, ACV of 7.52%, and UCS of 79.5 MPa, indicating suitability for road base, asphalt aggregate, and general construction applications. Pit 3 showed comparatively lower strength, with AIV of 31.10%, ACV of 30.50%, and UCS of 50.1 MPa, making it more appropriate for embankment, hardcore, drainage, and other lower-grade applications. XRF and XRD results revealed significant mineralogical variations, with Pit 1 dominated by wollastonite and Pits 2 and 3 predominantly composed of quartz. Preliminary resource estimation based on an active area of approximately 400,000 m², an estimated extraction depth of 180 m, and a mean density of 2.79 t/m³ produced an indicative resource of approximately 201.12 million tonnes. The crushing plant had an installed capacity of 350 t/h but operated at an average rate of 200 t/h, representing 57.14% utilization. Estimated production was approximately 3,200 tonnes/day, with projected gross revenue ranging from ₦38.4 million to ₦44.8 million per day depending on product mix. The study concludes that the associated rocks constitute a technically and economically viable secondary resource. It recommends selective classification, continuous quality control, improved blasting and crushing efficiency, accurate production and cost records, and appropriate allocation of each rock type to suitable construction applications to enhance profitability, resource recovery, and environmental sustainability.

Associated rocks, techno-economic viability, Obu Mines, construction materials, aggregate, resource recovery, Okpella.

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