1971 At the outset of the project, the mine’s production drilling and blasting practice employed 10 m benches, 4½″ drill holes in ore and 5½″ holes in waste, and bulk emulsion with an in‑hole density of 1.15 g/cm³. Baseline performance indicators were established to anchor the evaluation: powder factor averaged 301 g/t in ore and 220 g/t in waste; measured fragmentation, expressed as P80, was 447 mm in ore and 485 mm in waste; and the EX1200 shovel - selected as main reference, exhibited an average loading time of 4.45 minutes per cycle. The optimization initiative centered on a controlled change in explosive energy. The conventional formulation, Fortis™ Advantage (2.18 MJ/kg; RBS 136%), was replaced by Fortis™ Extra (2.44 MJ/kg; RBS 153%), representing an 11.9% increase in energy per kilogram. The objectives were explicit: to widen drill patterns while maintaining or improving fragmentation, to reduce powder factor and direct drilling‑and‑blasting costs, and to improve productivity and safety by reducing the number of drill holes and exposure time on the bench. Design targets initially contemplated pattern increases up to about 17%, with the understanding that energy‑per‑tonne and quality would be actively monitored and controlled throughout the trial. 3.2.2 Design and Implementation Design development followed a stepwise approach anchored in energy‑per‑tonne control and predictive modeling. Effective energy per tonne (MJ/t) was kept close to baseline in the first scenarios to isolate the influence of explosive energy and spacing changes on fragmentation. Pattern increases from 6% to 17% were simulated in Blast Design Assistant (BDA) using site geotechnical properties and a baseline granulometric curve. The modeling presented in the Figure 126 and the analysis in Table 48 indicates that increases in the range of 6–13% should yield improvements in P80, while a 17% increase could risk a deterioration in fragmentation. Field validation began within a conservative window of 10–13% pattern widening, with blast‑by‑blast reviews to confirm powder factor and fragmentation before any progression. In ore (4½″), burden and spacing moved from approximately 3.30 m × 4.10 m at baseline to configurations such as 3.30 m × 4.50–4.60 m, with effective energy trending from about 0.67 to 0.65 MJ/t as spacing increased. In waste (5½″), burden and spacing evolved from roughly 4.20 m × 6.00 m to 4.40–4.50 m × 6.40–6.60 m, with effective energy near 0.48–0.46 MJ/t. Execution emphasized QA/QC on hole deviation, stemming quality, and charge placement to strengthen energy coupling, and timing schemes remained within established safe practice with minor refinements to inter‑row energy distribution where beneficial. The implementation plan prioritized domain‑aware adjustments, recognizing differences in rock‑mass response between ore and waste and avoiding over‑extension where baselines were already lean. Figure 126 – Fragmentation Modelling
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