Back analysis of open stope performance is essential in the dilution control process, as an improved understanding of mechanisms allows one to check the validity of any assumptions and refine geotechnical parameters used in the design process. This paper describe the results of a back analysis of over-break geometries, using non-linear elasto-plastic finite element modelling undertaken at Barrick Gold Australia's Kanowna Belle Gold Mine. The entire sequence of bench and longhole open stopes at the Kanowna Belle mine was modelled. The back analysis study involved analysing hangingwall over-break data from longhole open stopes from a number of key mining blocks. For the numerical modelling exercise, results grids were placed such that various components of velocity and plastic strain could be ascertained into the hangingwall rock mass, with modelling steps calculated at the individual stope's extraction, prior to backfilling. Stochastic analysis of the CMS over-break data, together with the results from the modelling was used to establish global relationships between velocity and plastic strain and marked increases in overbreak. The back analysis results were then used to develop over-break criteria which can be used as a planning tool to estimate probability and volumes of over-break for any future stope design and/or sequencing option.
Open stope performance is generally assessed by the ability to achieve maximum extraction with minimal dilution. Hence, the success of the open stoping method relies on the stability of large (mainly un-reinforced) stope walls and crowns as well as the stability of any exposed fill masses [1]. The performance of an open stope is typically judged on the actual outcome versus the planned outcome, in terms of the final volume, tonnage and grade of material extracted, and the timeliness of extraction, compared to the planned design and schedule. This paper describe the results of a back analysis of overbreak geometries, using non-linear elasto-plastic finite element modeling undertaken at Barrick Gold Australia's Kanowna Belle Gold Mine.
Underground operations at Kanowna Belle Gold Mine (KBGM) are situated beneath the Kanowna Belle Open Pit, with large-scale long hole operations commencing in 1998. Current production stopes at Kanowna Belle are being mined at depths in excess of 1200m in challenging conditions, which will only increase as operations continue to head deeper. The Block A stopes of Kanowna Belle consist of large primary-secondary sub-level open stopes, mined directly beneath an existing open pit to depths of around 400m below surface. Mining was under-taken using transverse longhole open stopes, in an alternate primary/secondary extraction sequence along strike, in conjunction with cemented fill. The stopes are a minimum of two lift heights (2 x 30m), and 20m to 30m along strike, with stope widths up to 35m. Cable reinforcement was mainly restricted to “rib-roc” type patterns, installed from sublevels into the hangingwalls. Block C stopes are generally much smaller than Block A stopes, with stopes heights ranging from 35m to 100m, lengths from 15m to 20m with stope widths generally around 20m.
