Field measurements of brow break and misfires at sublevel caving in Kemi mine

Abstract. Blasting is one of the most important operations in mining, unfortunately this is often ignored. In reality, rock blasting has a strong impact on overall economical results of a mine. Brow break and misfires affect negatively ore extraction. Detonator position can influence both. For example, if brow break and misfires decrease, the impact of blasting on the environmental can be reduced. The scope of this thesis was to investigate how detonator position affects brow break and misfires in sublevel-caving (SLC) -ring blasts at Kemi mine. Detonator position was changed to ¼ & ¾ of charged length in three middle holes of SLC-ring blast. Research-based study point out that detonator position reduces brow break and misfires. The effect of detonator position was investigated by field blast tests. Top and bottom detonator system i.e., ordinary detonator position was compared with the new middle detonator position. Brow break was surveyed by tacheometer after the rings had blasted and mucked. Brow break was set in proportion to burden. Misfired blastholes were inspected visually by comparing designed blast delays to actual particle velocity data from geophone. Research-based studies found that detonator position affect the brow break and misfires. The blast field tests pointed out that the middle detonator system can reduce both brow break and misfires, compared with ordinary detonator system. Still, it is important to understand that there are non-controllable parameters as geological factors which may affect the result of the ring blast. The result of the thesis is one application to use in all SLC-mines