McArthur River, operated by Glencore, is the world’s second largest deposit of zinc.
Underground mining at McArthur River began in 1995, converting to an open pit operation in 2006. The final length and depth of the pit are expected to be 1.75 km and 420 m, respectively.
Dewatering is mainly achieved by pumping from the old underground workings beneath the pit. A very high instantaneous rate of extraction is required, especially after the pit becomes flooded by tropical cyclones.
To assist with dewatering of the McArthur River deposit to 350 m depth, Rockwater was engaged to design and supervise the drilling of three breakthrough bores into the old underground workings.
The breakthrough bores were drilled conventional-hammer through alternating layers of dolomite and shale, making it difficult to control deviation. Regular down-hole vertically (gyro) surveys and amendments to the bottom hole assembly were required to ensure the underground workings were intersected, and that the bores where straight enough to accommodate 15 m-long submersible pumps. Injection tests were performed in the completed bores to confirm their viability.
