Dumping oversize rock fragments in orepasses: the impact on the production cycle of a sublevel caving operation

Oversize rock fragments are highly undesired in a sublevel caving (SLC) operation as they affect the production cycle, equipment, and infrastructure. In this study, a field test was carried out in Malmberget mine to analyse the impact of oversize fragments on the production cycle and the costs of different procedures for handling such fragments. The tests involved monitoring of dumping oversize fragments in two orepasses, one with a grizzly and the other one without a grizzly, using cameras. The cycle times of load-haul-dump (LHD) machines were determined for both orepasses. The results indicate that the grizzly increased the availability and productivity of the orepass despite increasing the cycle time of the LHD machines. Moreover, installation of a boulder breaker system along with the grizzly can further increase the productivity and the cost of such a system will be paid off in a shorter time in terms of enhanced productivity.