• Uncontrolled drill hole deviation can increase operating costs by 5–15% per tonne mined, primarily due to additional mucking, backfilling, and remedial blasting requirements. This challenge is particularly pronounced in secondary stope recovery under sublevel stoping, where retreating sequences across multiple levels expose tall (up to 60 m) and narrow (12– 15 m) openings, necessitating precise geomechanical stability to prevent instability and excessive dilution. • Given the demonstrated effects of drill hole deviation on overbreak, dilution, and overall recovery efficiency, this factor can significantly influence operating costs. Incorporating the quantified cost of percentage deviation per tonne into cost models enables more accurate economic evaluations and supports scalable improvements in drill-and-blast practices. 4. ACKNOWLEDGEMENTS This work would not have been possible without the strong collaboration of Minera Colquisiri at the María Teresa underground operation. The authors sincerely thank the mine management and operational teams for granting operational access to the site, facilitating safe implementation of the sequential recovery strategy, and providing essential support for the extensive field monitoring required for this work. Special thanks are given to the underground crews - drilling, blasting, planning, geotechnical, and survey personnel - for their precise execution and consistent data collection efforts. As Orica Mining Services Peru engineers responsible for the technical development of this paper, the authors also acknowledge the valuable contributions of their colleagues within Orica in blast design development, drill deviation analysis, vibration monitoring and control strategies, and post-blast performance analysis.
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