Underground metalliferous mining involves extraction of minerals from a relatively thin, inclined orebody (also known as veins), ranging from 0.5 to 3.0 meters wide and with a dip more than 50 degrees (Hustrulid & Bullock, 2001). Two main techniques that have been developed for extraction include longhole stoping (LHS) and cut-and-fill (CAF) mining. The former involves a bulk technique where huge quantities of ore are blasted and excavated at lower drawpoints, whereas the latter is a cyclic, selective technique involving mining of ore in horizontal layers with backfill immediately after ore removal.
The geometry of the veins determines whether these techniques are practical or not. In order for LHS technique to work, the dips of the veins have to be above 55 degrees such that broken ore moves down through gravity (Villaescusa, 2014). This technique also needs a constant strike, and therefore, geometrical anomalies in veins, such as pinch and swell, make it impossible because of fixed blastholes. On the other hand, CAF technique is very flexible since miners can adapt to changes in the geometry of the veins by adjusting the boundaries of the extraction face during breasting.
Geotechnical factors significantly affect the selection of the mining method. LHS leaves large unsupported spans of the hanging wall and footwall during extraction. In case of a weak host rock, stress release around these open stopes can lead to sloughing and wall failures (Guggari, Mohanto, & Deb, 2023). CAF is required for low wall rock competency. The introduction of engineered backfill creates active confinement of the host rock and limits wall closure while reducing the hydraulic radius of the exposed rock mass.
Narrow veins often contain high grades of precious metals, which makes the management of dilution crucial for the economic feasibility of the mining project. LHS is less selective; blasting results in the creation of a stoping span that exceeds the actual size of the vein and includes waste rock in it (Stewart, Trueman, & Lyman, 2001). Although a modern decoupled blasting technique can alleviate the problem, LHS cannot avoid the inclusion of internal waste rock. CAF method allows for precise mapping of the face before blasting, ore extraction and preserving high-grade material.
Factors of productivity and equipment capacity determine the tradeoff between these two methods. LHS uses heavy machinery such as longhole drill rig and load haul dump machines in order to attain high production rate. It has low operating costs per unit but entails high cost of development. CAF is a less productive method that is constrained by the long drilling, mucking and backfilling cycle time. CAF is relatively labor intensive, hence having higher operating cost which is balanced by the high value of the un-diluted ore.
In conclusion, the decision-making process takes into account engineering facts in order to meet the economic objectives. LHS is recommended when orebody is continuous, steep and competent in which the productivity becomes an advantage even if it means accepting some amount of dilution. CAF is a must-have in situations where rock mass is weak or orebody is very erratic. In either case, the safety of personnel is the top priority. Engineering keeps developing ways of eliminating personnel from unsupported space; hence, the trend in the industry is the use of remote-controlled machinery in longhole mining and efficient backfill system in cut and fill mining.
References
Guggari, V. B., Mohanto, S., & Deb, D. (2023). Stability analysis of crown pillar under the zone of relaxation around sub-level open stopes using numerical modelling. Geomatics, Natural Hazards and Risk, 14(1).
Hustrulid, W. A., & Bullock, R. L. (2001). Underground Mining Methods: Engineering Fundamentals and International Case Studies. Society for Mining, Metallurgy, and Exploration.
Soto-Juscamayta, L. M., Perales-Rivas, R. Y., Berrocal-Argumedo, K., Flores-Nuñez, J. F., Jorge-Berrocal, R. R., Quispe-Arones, L. F., Berrocal-Argumedo, G., & Sulca-Ñaupas, G. S. (2025). Optimizing blasting in narrow veins: Using DECKs to reduce dilution and improve recovery in underground mining. Mathematical Modelling of Engineering Problems, 12(10), 3119-3125.
Stewart, P., Trueman, R., & Lyman, G. (2001). Development of benchmark stoping widths for longhole narrow-vein stoping. Mining Technology, 110(3), 168-175.
Villaescusa, E. (2014). Geotechnical Design for Sublevel Open Stoping. CRC Press.
