Your company operates an underground nickel mine producing 1.2 million tonnes of ore at a grade of 2.8% nickel. The orebody dips at 70° fairly regularly and is extensive along strike and down dip. Orebody width varies between 14 and 30 metres and averages 25 metres.
Until now the method of stoping has been by the sub-level blasthole stoping method, however due to dilution problems from a weaker than expected dunite hanging wall the decision to change mining method to mechanised transverse cut and fill stoping has been made. The UCS of dunite is 30 to 110 MPa.
The ore consists of a fine pentlandite disseminated in quartz dolerite. The UCS of the ore averages 250 MPA in a small range. The ore tends to be massive with little evidence of jointing or other structural features.
Cut and fill stope widths are to be 8 metres with 4m separating pillars, pillar recovery is to occur at a later date. Mining will be by 3 metre lifts using horizontal benching. Mechanised drilling is to be employed and 3m3 LHD’s are to be used to haul ore to the mill holes. The mill holes are to be equipped with grizzlies with 0.5m apertures.
Occasionally the ground will be wet, but dry conditions are generally experienced.
1) Design the drilling/blasting pattern showing hole diameter, hole depth, burdens, spacings, explosive types, primers and initiation system and indicate the initiation sequence.
2) Select drill types, makes and models and estimate the number of drill units required to maintain production at existing levels. For the purposes of this exercise assume adjacent stopes can be accessed through pillars and that a 2 production shifts per day system is used
3) Calculate average figures for tonnes/round and powder factors in kg/tonne
Submit your findings in a report format.