In long hole stoping, dilution commonly arises from overbreak and wall sloughage, often caused by blast damage, drilling inaccuracies, and suboptimal blast design. For example, imprecise drilling near the footwall and hangingwall can lead to holes breaking beyond the ore boundaries, allowing waste rock to enter the stope and increase dilution. Specifically, incorrect hole placement and deviation such as from the absence of guide rods or improper rig setup can result in increased burdens at the toe and ring. This leads to the release of excessive explosive energy, which damages the stope walls and contributes to unplanned dilution(Jang et al., 2015).
One method frequently used to reduce this type of dilution is the intentional preservation of an ore skin along the hangingwall, which is left undrilled to act as a buffer against waste entry. However, this strategy is often compromised by inadequate charge control and poor blast timing, which can still damage the skin and lead to dilution. Moreover, secondary stopes that are mined adjacent to previously backfilled areas often suffer higher dilution due to hangingwall overbreak compared to primary stopes(Narrow Vein Minimum Dilution Case Study | Geotechnical Design, 2018).
Effective dilution control requires careful blast design, accurate drilling, detailed survey verification, and strict quality control. It also depends on strong collaboration between geology, mining, and rock mechanics teams. Case studies, such as those from Konkola Mine in Zambia, highlight how poor drilling and blasting practices can lead to significant unplanned dilution. These examples emphasize the importance of integrated planning and execution in minimizing dilution in longhole stoping(“Factors Influencing Ore Recovery and Unplanned Dilution in Sublevel Open Stopes. Case Study of Shaft No.4 at Konkola Mine, Zambia,” n.d.).
Long hole stoping is highly productive, but susceptible to dilution. What’s a practical, real-world example of unplanned dilution caused by over-blasting or weak ground during a typical long hole stope cycle? Share your operational insights!
Reference:
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Factors Influencing Ore Recovery and Unplanned Dilution in Sublevel Open Stopes. Case study of Shaft No.4 at Konkola Mine, Zambia. (n.d.). Current World Environment, Special Issue 2019-20(Special Issue: Sustainable Mining). Retrieved October 15, 2025, from https://www.cwejournal.org/volSpecial%20Issue%202019-20no2020/factors-influencing-ore-recovery-and-unplanned-dilution-in-sublevel-open-stopes–case-study-of-shaft-no-4-at-konkola-mine–zambia
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Jang, H., Topal, E., & Kawamura, Y. (2015). Unplanned dilution and ore loss prediction in longhole stoping mines via multiple regression and artificial neural network analyses. Journal of the Southern African Institute of Mining and Metallurgy, 115(5), 449–456.
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Narrow Vein Minimum Dilution Case Study | Geotechnical Design. (2018, February 21). https://www.amcconsultants.com/narrow-vein-minimum-dilution-case-study
