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Abstract Strain rate has drawn great research attention in the area of material mechanics. However, thus far the effects of strain rate on the breakage characteristics of rocks or mineral particles were seldom studied. The applied strain rate is one of the key factors causing the variation in breakage environment, and hence the understanding of strain rate's effect on particle breakage is important to the development of a generic breakage model that isolates the rock properties from the breakage environment. This study systematically investigated the characteristics of single particle breakage at different strain rates. The rock samples from four narrow size fractions were used for carrying out impact and compression tests at variable energy input levels. The energy-size reduction relationships for impact and compression breakage were developed, respectively, and the appearance functions for these two breakage mechanisms were also developed based on previous and current work. The results suggest that the sample breaks easier at lower strain rates and the significance of the particle size effect strongly depends on the strain rate. It is demonstrated that the strain rate has an important influence on the progeny size distribution, but the significance of this influence reduces as the energy input increases. It is also found that the sample breaks with a higher energy efficiency at lower strain rates. The strain rate may affect the initiation and propagation of the cracks originate from small flaws and hence results in the difference in the breakage characteristics. Graphical abstract Unlabelled Image Highlights • The sampled ore breaks easier and more energy efficiently at low strain rates • The significance of particle size effect strongly depends on strain rate • Strain rate has a considerable influence on the progeny size distribution • Strain rate is likely to affect the propagation of cracks from small flaws [ABSTRACT FROM AUTHOR]

The productivity of milling circuits is sensitive to the size of mill feed. Uncertainty about the size of caved ore presents unique challenges to forecasting and controlling mill throughput rates. Part I of this paper showed how fragmentation size and hang-up frequency relate to geology, proximity of drawpoints to the cave boundary and the height of draw at the New Afton mine. The second part, presented here, investigates the impact of varying caved fragment size on mill performance. Analysis of historical mine and mill data showed that mill feed size and subsequently mill throughput are sensitive to the areas being mucked within the cave. Fragmentation measurements of drawpoint muck, comminution tests and calibrated mill models were used to assess the impact of variations in feed size and hardness on New Afton mill performance. Image-based size analyses of drawpoint muck and comminution tests showed that coarser material generally contained harder rock. [ABSTRACT FROM AUTHOR]

Block and panel caving mines are increasingly being proposed for the excavation of massive ore-bodies located at depth. The lack of selectivity associated with the mining methods results in both ore and waste being caved and transported through material handling systems to the surface for processing and waste rock disposal. Sensor-based sorting systems provide an opportunity to automate the discrimination between ore grades and rock types, providing an enhanced level of selectivity for ore control and thereby improving mine productivity. To evaluate the potential to add value to a caving operation, a sensor-based ore sorting study, incorporating bulk and particle sorting systems, was carried out for the New Afton block cave mine. Results showed that rock from the copper-gold porphyry deposit is amenable to prompt gamma neutron activation analysis, and to X-ray fluorescence sensors. A conceptual flowsheet, where both technologies are used as separate unit operations, was evaluated. Test samples of varying copper head grades allowed an ore value calculation method to be developed based on the integration of continuous bulk sorting and particle sorting. The calculation method can be applied to block models of a future cave at New Afton and used to evaluate the change in the economic footprint. It was found that the concept demonstrated an improvement in the net smelter return of excavated material. [ABSTRACT FROM AUTHOR]

A method for determining the minimum practical energy for comminution was developed and is presented in this paper. An objective of the method was to determine experimentally the energy-breakage relationship for a wide size range in order to evaluate the energy performance of both crushing and grinding processes using one energy benchmarking value. Single-particle compression breakage, referred to in the field of comminution as one of the more efficient forms of mechanical comminution, was the basis for a test regimen to characterize the energy-breakage properties of ores. Existing models for impact breakage were found to be valid for single-particle compression breakage when used in a modified form. A key parameter of the adopted model, the threshold energy, was also investigated for three ore types and a range of particle sizes. The energy performance of comminution processes at a Canadian mining operation was determined by comparing the determined minimum practical energy, using the new method, with actual site specific energy requirements. In order to evaluate the energy performance of different crushing and grinding technologies, the proposed energy benchmarking method was used to compare the energy performance of alternative comminution flowsheets. [ABSTRACT FROM AUTHOR]