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MEI Online: Plant Operation News: Australasia: July 5th 2007


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:: Tasmania's Beaconsfield Gold Mine Resumes Production

Quick re-start shows robustness of BacoxTM technology

Gold production from the bacterial oxidation circuit at the Beaconsfield Gold Mine in Tasmania, Australia, has resumed after a hiatus of almost a year, during which mining was suspended following a seismic incident and rockfall.

Limited underground operations began in April, and all sections of the ore processing plant have now been successfully re-commissioned. The mine is returning to full commercial production with stoping in all areas of the mine expected during the September 2007 quarter.

Beaconsfield was the focus of world-wide media attention in April and May 2006, while a bid to rescue two miners trapped underground by the rockfall was undertaken. Sadly, a miner was killed during the incident, but after two weeks underground, the two trapped men were freed and reunited with their families.

Following the incident, all mining and ore-processing operations at Beaconsfield were stopped. As a result, the bacterial oxidation circuit, which uses Bacox™ technology supplied by Mintek and its joint-venture partner BacTech, had to be shut down at very short notice. At the time, the processing plant's personnel consulted with specialists at Mintek and BacTech regarding the best way to preserve the bacterial culture during an extended shut-down.

"Based on our advice and their own extensive experience, the operational staff at Beaconsfield devised a shut-down plan", explained John Neale, specialist engineer in Mintek's Biotechnology division. "We were always confident that the bacterial culture could be revived after a lengthy period of dormancy, as and when operations at the mine were resumed. Nevertheless, there were some concerns over how long this might take."

The mine remained closed for nearly a year, while an independent investigation was undertaken into the circumstances surrounding the tragic mishap. When the go-ahead was given to resume operations, the dormant bacterial culture had to be revived.

As Richard Holder, acting resident manager of the Beaconsfield Mine Joint venture, explained, this was achieved very successfully: "The re-start of the primary bioleach reactors took a similar time to what we would have expected if the power had been off for only four hours. The bacteria are certainly resilient, and our experiences in re-starting the plant should dispel perceptions of them being incredibly sensitive."

At the time of the shutdown, the contents of two of the six 385m3 bioleach reactors at Beaconsfield were retained for the future start-up, while the others were drained to recover the remaining gold. During the year-long shutdown, the resilience of the bacteria was checked periodically by removing a portion of the contents of one of the reactors, and simulating the early stages of the start-up procedure. "We tested the inoculum in a small 30m3 heated tank on a month-by-month basis, and had no problem in recovering bacterial activity", said Holder. "After seven months, we revived the contents of one of the two dormant reactors by following a simple start-up procedure. We were able to heat the reactor to operating temperature within two days, and three days later the first signs of bacterial activity were measured. After just seven days, the process was self-sustaining. At that stage, we shut the reactor down again, but when the plant was re-commissioned several months later, we were able to re-start it in the same way and achieve continuous operation without experiencing any problems."




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