Ore body-specific bulk density versus specific gravity in copper resource estimation at Mopani Copper Mines PLC, Mufulira, Zambia

Accurate bulk density determination is critical in mineral resource estimation, as it is used to convert volumes to tonnages. However, many mining firms, including Mopani Copper Mines PLC (Mufulira mine site), utilize a single tonnage factor for various lithological and mineralogical ore bodies. Therefore, the aim of this study was to assess the importance of accurately determined bulk density in the mineral resource and reserve estimates, essential for effective mine planning and improving operational performance. Using the Snowrex NHV-3 scale, we analyzed 1263 NQ drill core samples from quartzite-hosted A, B, and C ore bodies, obtaining representative bulk density values via the wax-coated water displacement method (Archimedes’ principle). The measured weighted average bulk densities (2.71–2.76 g/cm3) exceeded the historically used specific gravity (SG) value of 2.65, indicating a potential underestimation of tonnage by approximately 2.3% to 4.1%. Our results suggest that discrepancies in bulk density moderately to weakly correlate with copper grades across the ore bodies. Consequently, we recommend more conservative resource classification and further density sampling to enhance predictive accuracy in resource estimation. The findings necessitate a re-evaluation of the resource model at Mufulira.