RFID Helps Miners Strike Gold

With the Oretrak system, says John McMurray, RF Tags' engineering manager, 915 MHz semi-active, disposable RFID tags complying with ISO 18000-6C are utilized instead of metal washers or balls. The tube-shaped tags measure about 8 inches in length. In such a scenario, the official identifies an area for blasting and uses a pen and paper to record the location.

When the official returns to the surface, an Oretrak RFID tag is interrogated and its ID number is entered into a database containing that individual's name, the location and type of ore or material, and the time and date. The mine location number is hand-written onto the tag's black surface using a white pen, and the tag is then taken into the mine and placed at the blasting site indicated by the location number. According to McMurray, the system does not yet employ handheld readers for inputting mine wall locations because the dark, cramped and dusty conditions in the mine do not lend themselves to carrying and operating handheld devices.

Interrogators and antennas installed above conveyor belts in the mine shafts, as well as at the surface, can capture the unique ID number on the RFID tag as it is transported with mining material back to the surface, then transmit that data to a back-end system, notifying the company where specific material has gone. Information from the reader can be sent to the back-end system via a cabled or wireless connection using Wi-Fi, ZigBee or GSM/GPRS. If the tag data indicates an instance of cross-tramming—either in the shaft or at the mine's surface—the system can alert the office staff, informing them that material has been transported in the wrong direction.

Each interrogator can store up to several months' worth of data if necessary, McMurray says, to be retrieved at a later date. This ensures that should communications be lost, for example, due to a rock fall damaging cables leading to the surface, no data would be lost. The Oretrak system software also enables self-diagnosis, allowing a user to display a map of every reader on the installed Oretrak system and its status. In the case of large mines with multiple wireless readers, one interrogator can act as the mesh network node to host a large number of readers communicating with it.

Data from the Oretrak system is stored in the mine company's back-end database (usually SQL), including the data inputted when the tag was first read, as well as the time, date and location for every instance the tag was interrogated, the belt it was read on, the type of material being transported and the belt it should travel on.

"Our first mine—Masimong Mine—claimed a saving of 1,000,000 rands ($138,000) in a month against a capital cost [of the system] of under 100,000 rands ($13,800)," McMurray says. Masimong Mine, part of the Harmony Group, has been using the Oretrak system since February 2006. Amplats intends to go live with a similar system at the end of May.

Mines use between two and eight interrogators, some mounted at shaft openings, others at waste belts, and others for issuing tags.