Authors: Campbell, AD

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Campbell, AD 2018, 'Effects of blast ring burden and explosive density on fragmentation and ore recovery in sublevel cave mines', in Y Potvin & J Jakubec (eds), Proceedings of the Fourth International Symposium on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 457-470.

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Abstract:
Numerous studies have proved that blast design impacts gravity flow in sublevel cave mines. However, such designs are yet to be fully optimised owing to the small number of mines with published full-scale experimental studies specifically planned to measure the effect of blast design variables on fragmentation and recovery. This paper details the results of a three-year experimental program undertaken at the Ernest Henry sublevel cave mine. The program consisted of 162 production blast rings conducted over six experimental trials to quantify the impact of ring burden, explosive density and crosscut height on gravity flow and recovery. The results of the research program are split between this paper and another entitled ‘Full-scale experiments to measure the effect of crosscut height on recovery in sublevel cave mines’ (Campbell 2018). The impact of ring burden and explosive density on fragmentation and recovery was quantified using fullscale experiments. Electronic cave markers were used to measure recovery over multiple sublevels and the extraction zone evolution in real time. Fragmentation was measured during loading since the size of the fragmented rock is known to affect gravity flow behaviour and ore recovery in sublevel cave mines. The size distribution of the fragmented rock from blasting was measured using high-resolution 3D laser scanning technology. Results of the experimental programs prove that ring burden and explosive density have a significant impact on ore recovery. Cumulative secondary recovery was between 8 and 10% higher on average for the reduced explosive density and increased ring burden trials compared with the baseline measurements. The effect of blast design variables on fragmentation was found to be less than expected. The experimental outcomes differ from earlier theories and the research hypotheses, which predicted the opposite effect on recovery for changes in ring burden and explosive density. Underground observations and detailed analysis are used to explain the results. Although the results are affected by the mine design and rock mass conditions at the mine and therefore sitespecific, the findings on the relative impact of design variables on fragmentation and recovery are potentially transferable to other sublevel cave (SLC) mines. Additional site-specific testing is required to confirm the impact of design variables in different conditions and is recommended prior to selecting or altering blast design parameters. Keywords: blast design, fragmentation, gravity flow, recovery, sublevel caving

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