A Step back in time to Hand-Held Mining for Profitability
2nd Int'l Symposium on Mining Techniques of Narrow-Vein Deposits
Mike Turner, Peter Teasdale, Tim Green,
The Otter-Juan mine was closed by WMC-KNO in 1999 due to the combined effects of low Nickel prices and high mining costs. GBF Mining Pty Ltd purchased Otter-Juan Mine from WMC in early 2001 as part of WMC’s disinvestment from the nickel mines in the Kambalda area. Goldfield Mine Management (GMM), (a wholly owned subsidiary of GBF Pty Ltd) re-opened Otter –Juan in May 2001.
The Otter-Juan mine is one of the oldest mines in the Kambalda region and is now mining at depths below 1160mbs. Stresses are very high, rock mass deformation considerable, and the mine has a history of serious seismic activity. Orebody widths in the current mining area range from 2 to 2.5m, with dips ranging from 25 to 40°.
On taking over the operation, GMM converted the mining method from the previous mechanised drift and fill method to a slot-rise and strip method using hand held airlegs. During the latter years of production under the control of WMC production averaged around 12000 tonnes per month, with grades of 2.7% and orebody extraction of only 55 to 60%.
In the last three years of operation under the control of GMM the mine has produced an average of 12000 tonnes per month of ore at an average grade of 4.2% and with an orebody extraction of 70 to 75%. The mine is now highly profitable with at least another 3 years of reserves remaining at depth. The main benefits of the current method include reduced dilution and increased extraction. In the relatively poor ground conditions experienced this has only been possible using airleg mining, with excavations designed to suit conditions, support to suit rockmass deformations, and with improved extraction sequencing.
Other benefits have included improved conditions, reduced falls of ground incidents, and a dramatic reduction in seismic activity. These achievements have only been possible by stepping back in time and using traditional airleg stoping methods to extract the maximum amount of the orebody with minimum dilution.
This paper includes details of the mine history, geology, mining method, seismicity, and support.