Part-1
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
Part-2
A gold mine has just completed mining waste pre-strip prior to commencing grade control mining. The waste rock was drilled and blasted for the pre-strip using 200mm diameter blast holes using a rotary blasthole drill and achieved a mining rate of 15,000 m3 per day. Blast parameters for the pre-strip were:
1.Blasthole burden5.7m
2.Blasthole spacing6.5m
3.Bench height15m
4.Subgrade drilling1.6m
5.ExplosiveANFOdensity 0.85 g/cc
6.Powder Factor0.57 kg/m3
Fragmentation in the waste was acceptable for the excavators; these will be used for grade control mining as well as bulk waste mining. Grade control mining is to be undertaken using 115mm diameter holes to achieve sampling control; these will be drilled using a tophammer hydraulic drill. Bench height for grade control mining is to be 5m.
The waste rock has a density of 2,600 kg/m3, ore has a density of 3,200 kg/m3 due to sulphides and alteration minerals.
1.Scale down the waste blast parameters from 200mm to 115 mm diameter blastholes and determine explosive consumption in the waste and ore rocks.
Note: in addition to ANFO the full range of Heavy ANFO's is available from the supplier.
2. Determine the drill metres required to achieve a production rate from grade control blasting of 6,000 m3/day
3. The penetration rate for the hydraulic drill is estimated to be 50m/hr. Determine the drill productivity based on one rod change that takes 30 seconds going down the hole and 45 seconds withdrawing it from the hole. In addition two samples are collected, this stops the drill for 30 seconds per sample and tramming between holes takes 1 minute 30 seconds.
4. Based on two 12 hour shifts per day, giving an effective 10.5 hours of drilling (assuming two 30 minute crib breaks and a 30 minute service period at the end of each shift) will one hydraulic drill be capable of the required production?
5.Based on the following accessory life calculate the accessory requirements and cost:
ShankLife 600 mCost $130.00
CouplingLife 500 mCost $85.00
Drill Steel (3.6m length)Life 1000mCost $230.00
Drill BitLife 210mCost $165.00
6. Calculate the total drilling cost per m3 based on the following:
Drill fuel $9.50 per drill operating hour
Drill labour cost $22.00/shift hour
Drill maintenance $11.50/drill shift hour
Ownership cost $11.50/drill shift hour based on 20,000 hours working life
7. Calculate the total drill and blast cost based on the following blasting costs:
Explosives $550.00/tonne
Blast initiation $11.30/blasthole
Blast labour $80.00/tonne of explosive