Micro paste: producing paste backfill utilising ultra-fine copper tailings

The new generation of copper mines in central and southern Africa are characterised by finely disseminated ore requiring ultra-fine grinding to liberate the copper. As a result, the tailings produced from these operations are significantly finer than those typically used in backfill applications. In this context, the conventional rules-of-thumb for paste backfill design are no longer applicable, as the cement addition effectively serves as the coarse fraction of the mixture and these mixtures demand significantly higher binder additions to attain comparable unconfined compressive strength (UCS) results. Producing paste backfill from these ultra-fine tailings requires extensive testwork to assess both particle and paste properties. Key factors such as dewatering characteristics, optimal dewatering technology selection, rheology testwork and strength testing are crucial for ensuring that backfill plants can process these tailings and meet the required strength specifications. This paper presents and compares three case studies that explore testwork on ultra-fine copper tailings with a significant micro-sized fraction, providing insights into the challenges and solutions for achieving effective paste backfill in these new mining environments. The findings emphasise the importance of tailored testwork to inform the backfill plant design as well as the underground reticulation design.