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 burden 5.7m
2. Blasthole spacing 6.5m
3. Bench height 15m
4. Subgrade drilling 1.6m
5. Explosive ANFO density 0.85 g/cc
6. Powder Factor 0.57 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:
Shank Life 600 m Cost $130.00
Coupling Life 500 m Cost $85.00
Drill Steel (3.6m length) Life 1000m Cost $230.00
Drill Bit Life 210m Cost $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