In looking to develop a mineral prospect, a number of factors need to be determined and weighed in balance, including geology and mineralogy at the time, and ore valuation forecasts over the various horizons for possible life-time periods of the potential mine. Into the planning investigations also goes potential mining methods and sizing for mine production, the openings, productivity and costs.
The massive iron ore mines of the famous Pilbara region in Western Australia nowadays use largely automated drill rigs and driverless trucks to speed production; the ground level equivalent of ‘drones’, it might be said. Via GPS and satellite control systems many are remotely operated from command centres hundreds of kilometres away in the state’s capital, Perth.
But the many deep metal mines found more frequently in the gold fields to the south of the state, have traditionally follow their own tried and tested ways, relying on skilled operators and manual mark-up for boring access tunnels and the production drilling of adits and stopes into the ore body.
"The tape measure and the can of spray paint is very much the usual means to mark up the face," says one local mine engineer. Anything more than that is viewed as an unnecessary expense. The economies count, particularly in small and medium size mines with constrained capital investment and requiring twisting and turning short runs of small tunnels to reach and then haul out the ore.
For boring these rough and ready mine tunnels, robustness and flexibility of machines is valued firstly. They are used as all-purpose tools, for basic drilling, anchor installation, for scaling back underbreak and cleaning. They also pin mesh to the walls and very often the tunnel face for safety. Precision needed in construction work for long life tunnels is not so important and even basic computerisation of rig is rarely used.
That might be beginning to change and at least two or three mines are testing out some of the modern automated equipment to assess cost effectiveness and productivity. If the trials go well that could see much more automation within deep mines, using handheld remote controls and perhaps operation from surface control centres eventually.
One of the most significant trials is at a medium size mine in the Kalgoorlie region owned and run by the Barrick mining group. It lies about four-hours drive in the wide flung outback region around the once boom city of Kalgoorlie, a centre of a great 19th century gold rush.
The town and hinterland is still a major producer of gold and other metals like nickel and lead. Open pit mines are dotted around the flat open scrubland, and many of these have associated deep mine works which continue extraction further downwards with deep mine methods.
The Granny Smith mine is currently trying out a newer machine in an underground mine extending extraction onwards from the bottom of one of its several open cut pits. An unusual shape to the mine’s ore body has made it particularly suitable for testing out a drilling jumbo from Atlas Copco fitted with a rig control system (RCS).
Unlike the majority of the mines in the Kalgoorlie area, which often have rich but narrow vertical seams chased with spiralling ramps from level to level, the Granny Smith has big flat ore bodies, explains Kim Gunderson a production engineer at the mine.
"The geological formation seems to have seen an upwelling into ground with relatively porous lenses of rock every 120m or so," he says. "That leaves us with quite large bodies of ore about 6m to 7m deep and quite long.
"Most mines would use fairly short drives to the ore and then push out quite long production holes to extract the ore itself," he explains. But the Granny Smith requires much more "development" work, the miners’ shorthand for the slightly larger tunnels used to get into the ground and access the ore in the first place.
"We drive maybe 1,200m of development a month and then relatively short production tunnels. Other mines might do 200m only of development drives."
The necessity for longer tunnels made it worthwhile to see if the mine could improve drilling efficiency, he says, and would give an RCS rig a chance to show its benefits. These include savings and efficiencies in the drilling work. The on board computers, which direct the booms and drilling operations, positioning the booms accurately for the drill pattern and then operating the drilling. The machine is able to control its movements and drill rates in an optimised manner for the engine, the hydraulics and the bearings, which reduces wear and increases accuracy. It also uses the most efficient path from drill hole to drill hole to minimise movements.
But the computer control was only a secondary reason for selecting the rig, an Atlas Copco two-boom M2C .
The primary concern was to use a rig with longer drill mountings allowing it to drive deeper rounds for blasting, says Andrew Cooper, the mine manager is charge of operations overall at Granny Smith. "We are using a long feed mount for the drills on these booms, which allow drilling rounds up to 4.6m deep on average," he says.
This configuration is different to the three other twin boom tunnelling rigs used on Granny Smith and in fact those used in most other mines.
"Normally we use a split feed," explains Gunderson, who has been working closely with the machine. The telescopic mount of a split feed allows it to be shorter when withdrawn, he says, which gives a machine flexibility in the relatively small diameter tunnels used in the mines.
Development tunnels are usually 4.6m square for the ore drives and 5.2m by 5.7m for the main haul and access tunnels for the trucks.
With the split feed, booms can be turned and angled in all directions, allowing installation of anchors into the tunnel roof and change of direction when using the rigs for scaling work. Skilled operators can twist and turn the booms rapidly as they chip away at protrusions.
The long feed mounts on the new rig are better suited to making long straight drives. Allowing for longer blast rounds can reduce the number of cycles needed to blast and excavate the tunnels.
Three cycles can replace four or five, which gives significant time savings, particularly for loading, and for installing the necessary support. Combined with the enhanced accuracy of the RCS this adds up significantly.
"There is less set-up time overall and less travel time for the rig. It adds up over time to a lot of material we don’t have to move about in the mine or dispose of outside," says Cooper "especially on longer development drives." That counts on the Granny Smith’s very particular ore deposits.
Once the long-feed was chosen it then made sense to chose an RCS rig since with a longer bore, reducing deviation during drilling would have a bigger impact than with shorter drill holes. Keeping overbreak to a minimum on drives is more easily achievable with the computerised controls.
Cooper says, an eight per cent gain has been made, though on some rounds a 50 per cent reduction is achieved, which implies a better performance will come with experience.
Atlas Copco itself has been to see the rig tested, too, and offered the mine a full backup and training, according to local manager Dave White at the company’s Kalgoorlie supply and maintenance base. x The company already has a good working relationship with the Granny Smith mine, which uses a significant range of Atlas Copco equipment including five of its well regarded 60t MT6020 mine haul trucks as well as the other twin-boom jumbos, another Boomer M2C and two Boomer M2D machines, all manually operated. Long bore Simba drills, also from Atlas are used for extracting the ore itself.
In its overall look and feel the new RCS rig is similar to an existing hydraulic control rig. The difference with the new machine is the on board computers that direct the booms and drilling operations, positioning the booms accurately for the drill pattern and then operating the drilling, he says.
Drilling patterns are not marked up by hand but calculated above ground by a mine engineer, using the survey and core drill data from the geophysicists, which is constantly being updated, refined and extended to give the best precision possible in reaching and extracting the ore. Perhaps more than on most mines the sheer value of gold makes it important to be as precise as possible in avoiding any dilution with non-bearing or low content rock when blasting out the ore itself.
The output from the software feeds into the machine and either controls it directly or is displayed on a screen for the machine operator to follow.
The rig operators at Granny Smith declare that the machine is much easier to use and for much of the drill pattern they can usually simply load the engineer’s design and go straight ahead. There is still some manual work to do since the machine does not drill the outer perimeter of the drill hole pattern. "It brings the boom close to the wall of the tunnel and there are automatic cutouts that operate," one of the operators explains.
"There are interlocks and cutouts," agrees Cooper, who has been tracking the progress of the machine carefully since it was brought into use about two years ago. "They just prevent any damage if it gets too close."
Atlas Copco is working to reduce the cutout envelope for its latest machines.
The operators seem to have embraced the new rig, reports Cooper. Overall he says the machine can help the operator achieve a good result more consistently, even when he might not be as experienced as some of the most highly skilled operators. "He is less reliant on skill and judgement and positioning the booms by eye" he says "even though he still needs to know what he is doing."
That means there is potential to keep production going even when there is a shortage of the most highly-skilled rig operators, which in the current high levels of output in Western Australia, is a major issue. Labour and especially skilled workers are at a premium, and wages high, for both iron and high value metal mines.
There are some counterpoints, however, says Cooper. The machine needs to be backed up with one of the other drills for mesh and scaling, though admittedly there is less of that to do. The ground is relatively good, too, he says, which means there is less anchoring and support needed than might be the case elsewhere.
That perhaps means a smaller mine might have second thoughts, though his has enough work going on to be able to shift the machines easily from section to section and make good use of them.
Granny Smith mine is still reviewing its assessment of the rig at present, says Cooper. The decision to use it put Barrick out on a limb in the Australian industry, which has been biding its time on these advances.
"Being first is never easy," says Cooper, though he says the decision to try the machine was carefully thought through in consultation with senior management.
But the continuing improvements needed in safety in mines, and the growing capacities of computers, data transmission and satellites, are factors likely to push the industry in the direction of more automation and remote control.
Atlas Copco is certainly keen to see the technology advance. For the moment this trial is still a long way from robotic control systems like those on the big surface mines because, not least, telecommunication and radio telemetry signals cannot reach through the ground from GPS and other satellites.
But various possibilities are opening up including remote machine operation with local umbilical cables to an operator standing in a safer position along the tunnel and perhaps at the surface via the fibre optic networks increasingly installed for mine communication
