The influence of blasting on Kemess hypogene ore milling
Hikita, Daniel Hiroshi
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Traditionally, optimization of drill and blast practices have taken place with sole respect to minimizing mine unit cost (as opposed to the operation as a whole), whilst maintaining fragmentation at a level that is considered “acceptable” to mine operations. Judgments as to “acceptable” are largely based on qualitative measures and the consequences of varying blast practices on subsequent downstream processes are secondary. The objective of this work was to evaluate both the technical and economic consequences of blast practices on comminution processes at the Kemess South Project. Computer modeling indicates that without changes to crusher operating parameters, there does not appear to be much room for improving the performance of the comminution circuit. This indicates that current blasting at the mine is at or near optimal for the mill’s current configuration. Experiments to attempt to detect the effect of blasting on the crushability and grindability of rock were carried out on several different samples, including a copper-gold porphyry ore from Kemess Mine, taconite from Minnesota, granodiorite from the Kingston area, and limestone from the Kingston area. The main focus of this study was the Kemess ore. Examining rock samples from blasted and un-blasted ore, the samples that were blasted showed a significant increase in the density of very small cracks within individual fragments, which would indicate that they should break more easily during crushing and grinding. Drop-weight impact tests investigating the grindability of these samples suggested that there was improved performance with blasting effort, although the difference between some samples was not statistically significant. Preliminary testing of the taconite and the limestone indicated that crushability and grindability may be improved by blasting. Using mineral processing simulation software, the second part of the study investigated the effects of changing the ore size distribution that is fed to the Kemess Primary crusher. It was concluded that the Kemess Semi-Autogenous Grinding (SAG) mill throughput could be increased by increasing fragmentation and making adjustments to the primary crusher closed side set to take advantage of the increased fragmentation. These changes were calculated to be economically advantageous.