The Australian-developed Cave Tracker provides valuable information and insight into the previously, almost invisible process, of block cave mining. DAVID SIMPSON reports
Cave Tracker technology improving block cave mining
The scale of block caving operations ranges from large to enormous – stretching hundreds of metres to kilometres in length, as well as depths of up to thousands of metres.
The risks and uncertainties of dealing with substantial amounts of material collapsing, in often unpredictable fashions, can lead to inefficient processes and hazardous situations.
This is where the Cave Tracker is delivering significant improvements to conventional block caving. The technology has been developed by Mining3, Newcrest Mining, Rio Tinto and Elexon.
Typically used to mine large, low grade orebodies, block caving involves the creation of an undercut level and haulage access, known as drawpoints.
Caving has two distinct phases: cave initiation/propagation and cave flow or steady-state production. Caves are initiated with blasting and extraction of the orebody immediately above the drawpoints, so that the now unsupported rock above the undercut breaks gradually (caves), while more rock is being removed at drawpoints.
This caving process continues until the zone of broken rock typically extends to surface. It effectively produces a large-scale bin of broken rock that is available for extraction at drawpoints during the steady state production phase. The advantages of this method include that most of the rock doesn’t need blasting for fragmentation and that, once ramped up, mining processes are highly efficient and standardised.
Monitoring cave propagation
During this phase, techniques known as cave engineering are used to control the caving process. The volumes of caved material can be massive and the rock sizes range from dust to very large boulders during production.
During the process, it’s difficult for operators to assess how the caving process is progressing and where the ore originated from. Besides the ability to exert control over the recovery of ore, monitoring cave propagation is critical for managing safety risks such as air-blasts.
Cave Tracker provides a more precise understanding of movement during the caving process, such as how the ore moves towards drawpoints, to enable faster decision-making. Meanwhile, more accurate knowledge of the location and size of voids (air-gaps) can decrease the likelihood of a collapse, followed by a catastrophic rapid displacement of air (air-blast) that may spread air-pressure waves throughout the mine.
Before Cave Tracker, monitoring the flow of caved ore was only possible using markers. Embedded in the orebody, these markers are detected at drawpoints. This method was limited as movement could only be identified retrospectively. Also, the exact path of the ore could not be tracked as it moved inside the cave.
The Cave Tracker uses extremely rugged devices (beacons) containing strong permanent magnets embedded in the orebody, which are spun to generate a magnetic field.
Magnetic beacon signals detectable though solid rock
These magnetic signals are measured by detectors through up to 200 metres of rock. The signal is used to determine the 3D location of beacons and when combined with the locations of other Cave Tracker beacons, can enable 3D modelling of the cave and an indication of how the material within it is breaking up and flowing.
“Being able to measure ore flow and modifying draw strategy in real-time substantially reduces waste and avoids significant loss of value,” Mining3 chief executive officer, Paul Lever, says.
Available for commercial purchase through Elexon Mining, the Cave Tracker advantages include: real-time material movement mapping, improved process control and mine planning, maximised recovery, reduced risks and uncertainties, minimised dilution and increased safety.