2.7 Simulation and blast pattern design A specialized design scheme is employed for radial (fan-shaped) drilling patterns. The number of drill holes per ring can reach 18 (depending of the level of the section), with their lengths varying according to hole position and the geometry of the ore block to be blasted. The parameters considered to simulate the blast pattern design are: SD-IIIA, drill holes (64mm), Anfo explosive for charge column, explosive density (0.85cartridge emulsion for primer, initiation with electronic detonators, rock density (2.93 gr/cm3), burden 1.53m and spacing 1.45m (Figure 7). Figure 7. Simulation of drilling and blasting for pillar recovery in secondary pits. Blast timing sequences incorporated a 7 ms inter-hole delay within each radial ring, with progressive alternation to control vibration superposition. This delay was calibrated through onsite vibration monitoring (near- and far-field PPV measurements) and post-blast fragmentation assessment (Figure 8). Measured data were iteratively compared against blast simulation software predictions to refine and confirm the timing parameters, ensuring minimal overbreak while maintaining high recovery efficiency. As result an average P80 equal to 7.64in was obtained which satisfy the desired size for the milling plant. Figure 8. P80 determination via image analysis. 2.8 Volumetric surveys of mined stopes Post-blast 3D volumetric surveys were conducted to reconcile the actual mined volume
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