Mine planning for responsible resource development: Integrated economic and sustainability-aware block valuation for open-pit to underground transition

Mine planning involves high-stakes decisions under geological, economic, operational, and sustainability-related uncertainties. Conventional optimization frameworks rely on simplified block economic value (BEV) models that omit geomechanical variability, metallurgical responses, multi-element contributions, and environmental and social externalities. This paper introduces the Comprehensive Net Block Value (CNBV) framework, which extends conventional block economic valuation through a comprehensive representation of block value. CNBV extends the conventional BEV formulation through five value-modifying modules: (i) a Rock Cost Index (RCI) for cost scaling based on material properties; (ii) an Extra Substance Impact Coefficient (ESIC) capturing recovery penalties from undesirable material content; (iii) penalty functions for deleterious elements under different mining and processing pathways; (iv) generalized by-product and co-product contributions; and (v) monetized environmental and social costs. The framework is applied to the transition from open-pit to block caving by extending the model of Badakhshan et al. (2024) and demonstrated on a large-scale copper deposit. The CNBV model identifies an optimal transition at 725 m, with a 22-year mine life, extracting 510 Mt at 0.50% grade, a stripping ratio of 1.22, and an NPV of USD 6.80 billion. In contrast, the BEV model suggests a deeper transition at 887.5 m, a higher stripping ratio of 1.64, a lower grade of 0.46%, and a higher NPV of USD 7.51 billion. The 162.5 m difference demonstrates the influence of incorporating additional value-modifying factors into block valuation. Sensitivity analysis shows that cost scaling and multi-element contributions most influence NPV, while environmental and social costs gain importance under stricter regulations.