Gravity flow of blasted rock within tall stopes

Authors: Lapcevic, V; Latta, T-O; Saiang, D Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2645_102

Cite As:
Lapcevic, V, Latta, T-O & Saiang, D 2026, 'Gravity flow of blasted rock within tall stopes', in A van As, D Cumming-Potvin & J Wesseloo (eds), Caving 2026: Proceedings of the Sixth International Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 1-12, https://doi.org/10.36487/ACG_repo/2645_102



Abstract:
The Alternative Mining Methods Project, conducted in collaboration between Luleå University of Technology and Boliden, investigates the feasibility of a hybrid mining concept aimed at improving productivity and reducing development requirements in Boliden’s underground operations, with Garpenberg mine selected as the initial test site. The proposed concept is constrained by the need to maintain the existing mass balance between ore production, waste rock development, paste filling capacity, and tailings storage facility capacity. As a result, a hybrid stoping approach has been developed in which primary stope heights are increased, while secondary stopes are extracted using deck blasting and shrinkage-like retention of blasted ore within the stope. In this concept, blasted ore remains stored in the secondary stope until the full stope height has been reached. Final extraction is then carried out from the production level while rockfill is continuously introduced from the top. This creates a constrained gravity-flow system in which ore recovery and dilution are strongly influenced by stope height, production-level layout, drawpoint geometry, fragmentation, and fines migration. To evaluate these effects, a series of discrete element method models were developed using the YADE framework. The models examined several design variants, including 100 and 50 m secondary stopes, different production-level layouts, drawpoint widths, and the use of drawbells. The modelling results show that taller stopes generally promote more favourable gravity-flow development and improved recovery. In the 100 m stope cases, dilution typically entered the draw column at approximately 80% extraction, whereas reducing the stope height to 50 m caused dilution entry to occur as early as 50% extraction. Wider drawpoints improved recovery in the 50 m case, but did not fully compensate for the reduced stope height. The most significant improvement was obtained by incorporating drawbells, which promoted faster development of the gravity-flow and shifted dilution entry to approximately 75% extraction in the reduced-height configuration. Overall, the study indicates that dilution entry point, rather than cumulative dilution alone, should be considered the key operational limit for evaluating the proposed method. The results also highlight drilling accuracy, fragmentation control, fines migration, and drawbells as critical factors that must be addressed before the concept can be advanced toward full-scale implementation.

Keywords: gravity flow, blasting, hybrid mining methods

References: