- By Stephanie McDonald
Mining projects can be dangerous jobs that are difficult to manage, and when things go wrong, the consequences can cost millions.
But a new system is tackling both safety and productivity, which could have gains both in Australia and overseas.
The Cave Tracker has been developed by Elexon Mining in conjunction with CRC Mining, Rio Tinto and Newcrest, to enhance critical monitoring in block caving projects where miners go beneath an ore body and undercut it.
This requires blasting a segment out from under the ore body, which removes the support for the rock that’s above it. As ore is removed, gravity pushes down fragments to the undercut area where it can be collected.
As miners are unable to see into the ore body, it is hard to predict ore flows and manage the mine.
But the Cave Tracker system is looking to change that through the use of beacons that are installed into the ore body. These wireless beacons can then be tracked in 3D by detectors as they move through the mine as the ore is drawn to the bottom.
Beacon prototype
The cylindrical beacons measure 76 mm wide and about 33 cm long and are made of fibreglass to withstand the harsh environment of underground mines.
But the first beacon prototype was not designed to survive the force of a cave but to test the locating technology. Instead, Elexon Mining had access to holes in a mine where it lowered the first prototypes down on rope and recovered them again.
“They weren’t exposed to massive forces like the ones we have now. The prototype was pretty simple and probably quite far away from what we've got now,” said Simon Steffen, product manager at Elexon Mining.
The initial beacons measured much wider at 135 mm in diameter, but due to constraints on mine sites and the cost of drilling holes of that size, the beacons were downsized to its current 76 mm.
The newest generation beacons comprise a spinning magnet, electronics for controlling the motor and a battery pack, which has a lifespan of up to 10 years.
“We had to make sure the forces of the rock in the cave didn’t destroy the beacon, its housing, the electronics and the spinning element. From a mechanical point-of-view, this was very challenging,” Steffen said.
Elsewhere in the mine, detectors are installed deep around the mine and can detect signals between 160 m and 210 m away. It then collects this information via a cable to a central system where the data can be stored and analysed.
The system also works in near real time, which enables operators to analyse if material is traveling down according to plan, is moving in an accelerated fashion or whether there are areas that aren’t moving. This insight allows them to optimise ore recovery and minimise waste.
The system also has flow-on effects that improve safety by detecting areas that aren’t moving.
“If [the mine is] not propagating to plan and the cave stalls … it can create what’s called an air gap, which means they extract material that’s broken but no new material is flowing down from above, which creates a void,” Steffen said.
“If the rock above the void collapses at some point, it can displace a huge amount of air, which can have critical safety implications.”
Software prediction
The system has undergone two trials – the first at Newcrest’s Ridgeway underground mine and the second at Rio Tinto’s Argyle diamond mine.
In the first trial, Elexon deployed a small number of beacons. A small number of issues were identified and resolved, while the second trial deployed a larger number of beacons.
“It was really interesting … to actually compare measured locations of devices in the cave with modeling software prediction. To get these lined up was really good,” Steffen said.
“Also, from a technology point-of-view, we were happy that the beacons performed really well. There were a few beacons that failed, which we expected as a first-generation prototype.
“The number of failed beacons was relatively small and we investigated potential causes, which we followed up. Now with the next generation, we'll hopefully have resolved most of these issues.”
Some of those potential issues included a software bug, but Steffen said as the beacons can’t be recovered once they’re in the ground, it can be diffciult to see what actually happened.
Elexon Mining is now a semi-finalist in the Australian Technologies Competition, and the system is still currently running at the Argyle mine. Another a system is also scheduled to be delivered to Newcrest. Rio Tinto also plans to use it in its cave mining operations at Oyu Tolgoi in Mongolia.
“In the scale of the mining projects we are looking at, where costs and revenue are in the multiples of billion dollars, the economic value of [this system] is potentially huge,” Steffen said. “Even small improvements can have a big effect on the bottom line.”
[Image: Screengrab from the Cave Tracker video courtesy Rio Tinto, Elexon and CRC Mining]