34 4. Objective function description – compose time-based models to relate Net Present Value (NPV), Net Recoverable Metal Value (NRMV) or other key performance indicators to the inputs provided from 1 to 3 above over the scheduling horizon. Stage 4 transitioned into scheduling optimisation. In this study the objective was to maximise NPV over the mine life. Using the mathematical programming model created in Stage 3, the simulation allocated stopes to specific extraction routes (CM or ILR), sequenced development levels and scheduled backfilling and IMR to maintain geotechnical stability and enable continuous operation. The outputs from the CM/ILR scheduling step were used as inputs for IMR scheduling, allowing selected lower-grade, fragmented or residual material streams to be assessed for IMR. At this stage, additional economic parameters and recovery assumptions were incorporated, and the model evaluated how IMR would interact with the previously scheduled mining and processing streams. The final step was financial evaluation and analysis. The outputs from the CM, ILR and IMR scheduling steps were combined into a final production and processing profile, which was then used for economic assessment. The financial model evaluated the relative performance of each configuration using NPV and other operating indicators, allowing comparison between the conventional baseline and hybrid IPM scenarios. This model captured not only revenue and cost streams, but also infrastructure, fill and timing constraints, ensuring that mining and processing activities aligned with physical, technical and operational realities. The integrated simulation model offered a powerful framework for strategic mine planning, combining rigorous economic analysis with operational realism. By combining these steps, the framework could evaluate how the integration of ILR and IMR affected mine sequencing, processing capacity, material handling and economic performance under a common modelling structure. 2.3 Model assumptions and limitations To simplify the modelling the following technical assumptions are typically made: • The processing system must be sufficiently robust and capable of treating variable feed grades and rates, while maintaining assumed average recoveries. • Waste generated should be suitable for underground backfill. • Excavation and backfilling processes would be cyclic and incorporated flexibility through alternate surge control and temporary buffer stockpiles where possible. This would be inherently more complex than in conventional underground operations. • Short-term storage of ore, concentrate and waste is critical and would need to be available to manage peak mining rates, processing capacities and transport logistics - in particular, waste/low grade ore storage would be needed until underground voids become available for backfill. • Underground stope voids should be usable temporarily for blending and buffer storage when IMR stopes are not available or until made available.
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