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RFID Helps Miners Strike Gold

Several South African mines are using semi-active UHF RFID tags to identify gold and waste rock as material leaves blasting sites.
By Claire Swedberg
May 27, 2008A number of South African gold mines are employing an RFID-based tracking system known as Oretrak, provided by RF Tags SA, to ensure that extracted material is not misrouted during the mining process. Goldfields, Harmony Gold Mining Co. and AngloGold Ashanti are all utilizing the system, while the Amplats Group is currently installing it.

Tracking gold ore (also known as reef) can be a monumental task in large mining operations. Goldfields' Driefontein mine, in Gauteng, South Africa, for instance, produced 1.1 million ounces of gold from 6.8 million tons of ore in the 2005-2006 financial year—with approximately 13 tons of ore per minute hauled from a number of shafts. In smaller mines, the tunnel network can extend to 17 miles in length, while larger mines may have a total of almost 300 miles in tunnels, along with thousands of workers.

Then Oretrak system helps ensure that extracted material is not misrouted during the mining process.
When material is blasted at a mine and removed from a shaft, it typically travels through a complex transport system comprised of "ore passes" (underground trains), belts and trucks. A skip—a bucket that carries tons of material—is usually employed to transport the rock to the surface, where the ore is sent to one location for processing, while the rest of the material (rock containing no ore) is diverted to another location as refuse.

With such a large volume of material coming from the mine at any particular time on belts moving continuously at a rate of 3 miles per hour, however, it is impossible for a worker at the mine's surface to visually determine what is gold ore and what is waste—and to direct the material to its appropriate destination. As a result, it's common for large mining operations to erroneously identify some ore as refuse to be discarded, while sending some waste to be processed as ore. Such mistakes, known as "cross-tramming," can be costly.

Traditionally, mining officials have used a system involving metal washers or balls imprinted with ID numbers and thrown in with material they wish to monitor—either ore or waste. When an official identifies a vein of gold, for example, its footwall is prepared for blasting and a washer or ball is placed at the site. After blasting, the broken rock, along with the ball or washer, is removed. As the material moves up the mine shaft, it passes a large magnet that pulls the washer or ball from the rubble, alerting employees that the material they wish to monitor has arrived at the surface.

To identify the material, however, a worker must read each washer's ID number and check it by comparing it with a printed list of all the washer IDs, or by entering each number into a computer system. What's more, the rate at which the washers or balls are actually retrieved and identified can be as low as 3 percent, either because they simply don't get captured by the magnets, or because the numbers written on them are illegible.

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