Re-evaluating stope leaching: a critical review of metal extraction strategies for deep low-grade ore under energy transition constraints

• Critical synthesis of non-uranium hard rock stope leaching systems. • Technical feasibility proven but sustained commercial operation remains unrealised.. • Key barriers: solution loss, suboptimal geometry/fragmentation, and slow recovery. • Viable for < 1 % Cu ore bodies if containment and extraction rates are predictable. • Current challenges and future directions for hard rock stope leaching discus. The global energy transition is projected to require a twofold to fivefold increase in transition metal supply by 2050, yet conventional mining faces escalating technical, economic and environmental constraints that threaten significant supply-demand imbalances. Stope leaching (SL), a controlled-volume, post-fragmentation underground mine-to-leach system, offers a potential pathway to recover low-grade ores while reducing surface disturbance, contingent on overcoming key design and operational challenges. This review provides a comprehensive, systems-level synthesis of non-uranium hard-rock SL. It integrates historically fragmented research into a coherent evidence base, drawing on 39 studies conducted between 1938 and 2024 across 16 countries. The analysis characterises SL configurations, traces technological development and identifies limitations that have constrained scale-up and commercial deployment. Findings show that SL in hard rock is not a recent innovation but a recurring experimental practice demonstrated through isolated trials. Although technical feasibility has been repeatedly demonstrated, sustained commercial adoption has not followed. Performance shortfalls stem primarily from methodological limitations: solution losses compromised containment and recovery; retrofitted geometries and fragmentation produced oxidant-limited kinetics, slow recoveries and dip-driven channelling; environmentally compatible lixiviants remain insufficiently validated; and research has emphasised subsystem optimisation over integrated process design. Synthesising results across flow behaviour, leaching efficiency and economic performance shows that SL’s history is best understood as cycles of rediscovery, marked by periodic re-engagement driven by declining ore grades, advancing technology, supply-security concerns and alignment with net-zero targets rather than linear technological maturation. Progress therefore depends on advancing design methodologies within unified quantitative frameworks supported by rigorous field validation.