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Step 1. Designing the mining layout and blasts
Before any hole is drilled or rock mined, much planning goes into making sure the mining sequence runs smoothly and safely as possible. The mine planning engineers, in conjunction with geologists, drill and blast engineers and voids officers, design the size and shape of the blasts. This takes into account:
- location of the ore on the bench
- presence and intensity of old workings
- ore requirements of the Fimiston Mill.
Plans and schedules are checked by all relevant parties and, when agreed upon, mining begins.
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Step 2. Marking out old underground workings.
The location of old workings in the pit are known through plans obtained from the original companies, and drilling information from the resource definition stage. Voids officers are responsible for determining where these old workings are and designing safety zones around them to warn employees of the danger.
These zones are flagged with red and white, or black and white striped tapes, depending on whether the old working is considered a real threat or only a potential one. Points for these zones are given to the surveyors who mark them up on the ground. Once marked, the bench is released for general operations personnel to enter although they must stay outside of these zones, unless precautions are taken.
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Step 3. Probe Drilling
Once the old workings have been marked, probe drills are sent in to confirm their locations. These are special drills designed to reach into potentially unstable ground, while remaining on solid ground. This minimises the risk of damage or injury as a result of an old working opening up under a machine. Void officers design a series of probe holes, generally ranging from 16 to 25m deep. These are pegged by surveyors. Probe drills then work along the zones, drilling these holes until they reach the old workings. By knowing where a hole was drilled; what angle it was drilled at and what depth it hit the old workings, void officers can adjust the danger zones, either shrinking them where the old workings have been satisfactorily filled or by expanding them where the old workings have expanded through self mining. This process may be repeated until the exact locations of the old workings are known.
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Step 4. Reverse Circulation Grade Control Drilling
Once probe drilling is complete, geologists begin work to finalise the location of ore blocks on the bench, by drilling grade control holes with reverse circulation (RC) drill rigs. These holes are on an 8m by 10m grid around the ore zones and range from 38 to 80m deep. A sample is taken every 2m down the hole and sent to the laboratory for assaying, the results of which tell geologists how much gold is in each sample. From this they can model the ore body and design ore blocks. The foremen and shovel operators know that material inside the ore blocks should go to the mill, while material outside should go to the waste or marginal dumps. One benefit of RC drilling is the extra void information gained. As the holes are drilled much deeper than the current 10m bench, it is possible to get further warning of any voids which may be deeper then the level of the probe holes. Once RC drilling is complete and all samples have been collected, the area is cleaned to an even surface for the next stage.
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Step 5. Production Drilling
At July 2002, the working depth of the pit is over 300m below surface. At this depth the rock is very hard, much harder than on the surface, so blasting is required. Blasting breaks the rock into loose material that mining equipment can dig and carry. Before blasting, it is necessary to drill holes in the rock to insert explosives. These holes are drilled by a fleet of production drill rigs and drilled in a “pattern” in an area of the bench identified for blasting. The pattern comprises evenly-spaced rows of drill holes about 5m apart. The holes themselves are about 6m apart along each row, measure 165mm in diameter and go about 11.5m deep.
KCGM has a safety procedure in place that for a rig to be allowed to drill, it must be on solid ground. Drilling action vibrates the ground and, if a drill rig was sitting over an old working, vibrations may cause this area to collapse. Traditionally we have used the long-reach drills to drill inside the old workings. However, this is time consuming and occasionally impossible, due to the size of some zones. KCGM has developed a remote control drill rig that can be operated from a trailer-mounted control room up to 1km away. The operator is then safe on solid ground and the rig can drill in somewhat unstable ground. Each zone is still assessed for stability but the remote control rig allows drilling in dangerous areas without risking personnel.
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Step 6. Charging
Once the pattern has been drilled, its holes are checked for depth and the presence of water. This “quality control” ensures that blasts are as effective as possible and reduces poor blasting practices that may result in toe or oversize in the blast. The holes are then charged – loaded with explosives. A detonator (det) and primer are lowered down the hole to hang about 1m from the bottom. ANFO (Ammonium Nitrate and diesel) is then pumped down the hole around the det and primer. The hole is filled to within 3m of the surface and the last 3m are filled with stemming – gravel, screened to a certain size range. The stemming acts as a plug and forces the explosive energy to go into the surrounding rock, rather than back out the hole. Once all holes have been charged, they are tied in – connected together to explode in a certain sequence. Then the blast is ready for firing.
The old workings are a problem again because the blast crew cannot simply walk into many areas of the pit for fear of an old working opening up under them. However, KCGM has developed several methods to safely enter these zones on foot. These include using harnesses and retractable wire ropes suspended to cherry pickers, allowing a person to walk on possibly unsafe ground. Should an old working open up under them, the harness and cable lock in place to prevent them from falling.
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Step 7. Blasting
One of the more exciting stages of the process is the blasting of a pattern. Once all holes have been charged and the blast tied in, it is ready for blasting. At KCGM, firing times are at 1pm and 5pm each day. Blasting is actually limited to three or four times a week, depending on production requirements, reducing disruption to the operation and production cycles. Whenever there is going to be a blast, a number of agencies in Kalgoorlie-Boulder are notified, including the Tourist Bureau, who pass this information to the public. A public viewing platform provides a very good view of the operation and is open to the public during blasting times. The Superpit is one of the few mines in Australia where the general public can observe blasting in action.
Blasting at KCGM is not as simple as at many other mines due to the fact that the mine is close to the city. Weather conditions are monitored very closely up to a blast and, if the wind is blowing towards the city, the blast may be delayed. This reduces the risk of creating a dusty environment for the town. KCGM is also very conscious of noise and vibration from blasting and have monitors for these throughout the town.
Blasting is done on a hole-by-hole basis – no two holes are blasted at exactly the same time. This also helps reduce noise and vibration. The blast is initiated by remote control from one of several control rooms spread around the surface of the open pit. Whenever a blast is scheduled, the area must be cleared of personnel within 400m of the blast. Despite this fact it is possible for KCGM to blast in one part of the pit while still mining in another, due to the size of the operation.
Every blast is filmed and analysed for any problems that may occur. The videos are downloaded onto computer and kept for future reference.
You can view some of these videos by clicking here.
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Step 8. Clearing the blast, marking up old workings
Due to the presence of the old workings, KCGM’s does not allow personnel or equipment on a blast for at least 12 hours. This gives the blast time to settle and, if there are any old workings under the surface, they will open up within that time. Once a hole is opened to surface, it is much easier to manage as its location and extents are easily determined. The blast has settled, surveyors will onto the shot (another term for the blast) and peg out the positions of all of the known old workings. This makes it safe for other people to come onto the top of the broken shot. Then the shot firer, who is responsible for charging and firing the blast, inspects the blast for any explosives which may not have detonated. If any are found they are dealt with before anything further is done. When the shot firer is satisfied that the blast is safe, he will release it for the geologists and production crew.
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Step 9. Marking up ore.
Before the shot can be dug, any ore blocks need to be identified. Geologists do this by pegging out the blocks with wooden pegs and coloured flagging tape, providing a visual aid to shovel operators and other production personnel to identify the location of the ore blocks. Once the shot is marked out, geologists produce a plan showing the ore blocks, old workings and any other important feature. This is referred to as a “dig plan”. An electronic copy of this is also sent to the on board navigation system (CAES: short for Computer Aided Earthmoving System) of the shovels and other loading tools. Once the shovel operators have a copy of this dig plan they are permitted to dig the shot.
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Step 10. Digging the blast.
Finally, the blast is ready to be dug. The primary loading machines for the Fimiston Pit operations are Komatsu PC 8000 hydraulic shovels. These are 650 tonne machines capable of moving 60 tonnes of material in their bucket in one pass. They generally load Caterpillar 793 haul trucks, which carry 225 tonnes. KCGM currently has a fleet of three PC 8000s and 24 CAT 793s in operation. See the fleet statistics section for more information.
While digging is occurring, other equipment associated with production are around the area. CAT D10R dozers are used to keep the floor level and clean up any spillage. This helps care for the trucks tyres, which are worth $25,000 each. Water trucks are constantly spraying down the blasts and the floor, in order to keep the dust down and allow operators to see what they are doing. This also reduces the overall dust levels emitted from the operation.
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Step 10. Digging the blast (continued...)
As the shovel digs the shot, the display in the cab, in conjunction with the tapes on the top of the shot, tell the shovel operator what material (ore, marginal sub-grade, or waste) the shovel is mining. The shovel operator notifies the dispatch operator who is overseeing the entire pit operations and they enter this information into their computer, along with the destination for the material. When a truck pulls up to the shovel, the computer system on the truck uses a GPS receiver to determine at which shovel the truck has stopped. It then sends a message to the dispatch computer asking what material is being loaded. The dispatch computer replies with the material type and its destination. When the truck’s on-board computer receives this information, it notifies the truck driver through a display screen in their cab.
Once the truck is full, it leaves the shovel and takes its load to the specified destination. This may be the primary crusher, a blend finger (which is a stockpile for ore), a waste dump, or some other specific location. The truck knows the planned route it should be taking so if its GPS unit detects that the driver has taken a wrong turn it sounds a warning. This prevents ore being taken to a waste dump or waste being taken to the crusher
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Step 10. Digging the blast (continued...)
The truck dumps its load and returns to the shovel to collect another one. Depending on where the shovels are and where the material has to go, a round trip for the truck may take between 20 and 40 minutes.
This cycle continues 24 hours a day, 365 days a year. Currently the mining fleet at the Fimiston pit is moving around 240,000 tonnes per day.
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Step 11. Clean up and bench preparation
Once the shovels and trucks have cleaned off the blast, it is time to send in the clean up equipment. This consists of Hitachi EX1200 excavators, CAT D10R dozers and CAT 16H graders. These machines clean up the walls, pull out any material from the old workings that the shovels couldn’t reach and generally tidy up the bench for general use. Once this is done, surveyors mark up the old workings and the process starts all over again.
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