Engineering & Mining Journal

AUG 2017

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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MINE DEVELOPMENT 32 E&MJ • AUGUST 2017 Technological advances are increasing the real-time data available to block cave operations. A system of magnet- ic beacons and readers first tested in 2007 and trialed in a diamond mine in 2014 have reportedly proven capable of tracking cave propagation and ore flow in real time. Separately, a system of RFID chips and readers that was upgraded in 2015 enables heightened draw con- trol and material movement monitoring. Both are claimed to nix costs by enabling tight planning, controlling dilution and reducing operator error. And both are now being pitched as proven technology available today. Tracking Cave Propagation Developed by CRCMining, Elexon Mining and Rio Tinto, Cave Tracker places rug- ged magnetic beacons into holes drilled into rock of strategic interest, usually above the extraction level. The beacons travel with the caved muck toward the ex- traction level. That movement is tracked with detectors located in and around the mine. Thus, cave propagation can be cap- tured in real time, empowering miners with critical data. The proof of concept was conducted at Northparkes copper and gold mine, then owned by Rio Tinto. A prototype system was then trialed at Rio Tinto's Argyle un- derground diamond mine in Australia in 2014. As of last year, it was slated for de- ployment to Rio's Oyu Tolgoi copper mine in Mongolia. Also last year it nabbed El- exon a semifinalist slot in the Australian Technologies Competition. It is currently being deployed to Newcrest's Cadia East gold mine in New South Wales. After three years of trials and tests, the system, which is intended to work in conjunction with other in-situ Elexon products, gives miners a glimpse of what was previously invisible: real-time ore flow, Simon Stef- fen, business manager, Elexon Mining, said. "The data captured so far has shown effects that were never actually 'seen' be- fore," he said. "For example, rat holing was clearly identifiable." Seeing into rock presents a formidable challenge as Wi-Fi and most radio waves will not penetrate through deep rock. Low frequency magnetic signals, however, will. Cave Tracker's beacons employ bat- tery-powered spinning magnets that generate a magnetic field. The batteries have an up to 10-year operating life, depending on how often the magnet is spun. At Argyle, for example, the bea- cons are set to transmit every three days. "The background magnetic field of the Earth has no effect on the system's operation," Steffen said. "For calculat- ing the Beacon's distance, only magnet- ic signals very close to the beacon's fre- quency will be considered. Other signals are ignored. Magnetic noise in the bea- con's frequency spectrum can affect the reading, but most of the noise is filtered out by algorithms." Larger beacons allow bigger magnets to be used, generating stronger signals. A 135-millimeter (mm)-diameter beacon has a proven transmission range of 200 meters (m). The 76-mm beacon can talk to a receiver 150 m away. "We are cur- rently working on increasing the range by improving our signal processing algo- rithms," Steffen said. "Testing thus far has yielded promising results." Placement of the beacons is deter- mined by the type of flow effect that is desired to be monitored, as well as the access constraints. For example, bea- cons placed at the mine boundaries can reveal if the cave is propagating into un- desired areas. Beacons placed around fault boundaries can detect if the cave has propagated through the fault, and Block Cave Ops Benefit From Real-time Data Proven monitoring systems help underground miners envision the previously unforeseeable, forge plans, streamline processes and cut costs By Jesse Morton, Technical Writer Rio Tinto's Oyu Tolgoi copper mine was slated to deploy Cave Tracker after the system was tested at two of the company's other mines. Above, drilling before concreting at Oyu Tolgoi. (Photo: Rio Tinto)

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