A cut-and-fill stope technique for mining ores involves cutting the ore in layers horizontally while filling up the cavities with waste rocks called backfilling. Dilution occurs due to the accidental mingling of poor grade or worthless waste rocks or backfilling material within the mined ore. This process tends to lower the quality of the ore and increase the cost of processing the material (Zhang et al., 2021).
Primary sources of dilution
Dilution occurring in a cut and fill stope is largely due to:
Geomechanical instability: this is a function of the characteristics of the surrounding rock mass itself. Naturally occurring discontinuities in the form of rock joints, faults, and thin hanging walls create the risk of instability and rockfall, thereby causing ore dilution (Rinne et al., 2024). Moreover, small-sized pillars will increase the concentration of stresses, which causes side-wall failure that mixes waste rock with the ore (Mehra & Budi, 2024).
Blasting faults: one of the most significant operational causes of dilution is improper blasting operations. Overenergizing the blast holes leads to an overbreak condition where the blast shatters the waste rock material beyond the designed boundaries of the stope (Zhang et al., 2021).
Mucking errors: when extracting minerals, there may be some operational errors in terms of mucking using LHD equipment. This may happen where the machine digs into the backfill material on the mine floor during extraction from the upper slices.
Engineering controls for limiting overbreak
Engineers use the following targeted engineering controls to achieve acceptable overbreak limits:
Controlled blasting: changing the parameters such as burden, spacing, stemming, and explosives will reduce blast damage to the host rock (Zhang et al., 2021). Smooth blasting technique is often used for limiting blasting damages.
Optimized stope size and rock support: thanks to advanced geological and geomechanical modeling technologies, stope size can be optimized, and ground supports can be put in place before any wall collapse occurs (Rinne et al., 2024).
Improved backfilling technologies: cemented backfill with certain mechanical properties will provide stability to the stope and also create a stable platform for the mechanized equipment. Sometimes, in the case of multi-layer filling system, an additional top layer can be applied made of paste or some visual marker that would prevent the LHD from reaching the waste material in the stope (Li et al., 2024).
Through application of the above engineering controls, overbreak problems will be successfully managed and the economic feasibility of the cut-and-fill method will be achieved.
Dilution in cut and fill stoping is a major obstacle that poses a direct threat to the economic feasibility of a mine through false reduction in grades of ore and increased cost of processing and handling. It is important to note that major factors leading to dilution range from geomechanical instability to ineffective drilling and blasting.
References
Li, S., Yu, L., Dan, Z., Yin, T., & Chen, J. (2024). The Recent Progress China Has Made in Mining Method Transformation, Part I: Shrinkage Method Transformed into Backfilling Method. Applied Sciences, 14(21), 10033. https://doi.org/10.3390/app142110033
Mehra, A., & Budi, G. (2024). 3D Modelling approach to identify parametric configurations for pillar stability in underground metal mine: a case study. Geomatics, Natural Hazards and Risk, 15. https://doi.org/10.1080/19475705.2024.2367630
Rinne, M., Janiszewski, M., Pontow, S., Uotinen, L., Kiuru, R., Kangas, L., Laine, I., & Leveinen, J. (2024). Improvements in Rock Mass Description for Stope Design by Geophysical and Geochemical Methods. Applied Sciences, 14(3), 957. https://doi.org/10.3390/app14030957
Zhang, Z.-X., Hou, D.-F., Aladejare, A., Ozoji, T., & Qiao, Y. (2021). World mineral loss and possibility to increase ore recovery ratio in mining production. International Journal of Mining, Reclamation and Environment, 35, 670–691. https://doi.org/10.1080/17480930.2021.1949878
