The BHP Minerals' Cannington silver-lead-zinc deposit is located
approximately 190 km south-east of Mount Isa. The deposit, is hosted by
Proterozoic rocks beneath a thin cover of younger sediments, and contains
a total estimated resource of 45.3 million tonnes at 11.1 per cent lead, 4.4
per cent zinc and 500 g/t silver. The deposit is separated by faulting to
form a shallow, lower grade Northern Zone and a deeper, higher grade
Southern Zone (Roche, 1994). Contract development of an exploration decline to test mineralisation
in the Southern Zone commenced with the excavation of a boxcut in
August 1993. The complex variably deformed Proterozoic sequence
interpreted from drill core and intersected in the exploration decline has
required a high level of practical rock mechanics input to achieve: appropriate support designs, a high quality of installation, and required development advance schedules. The Norwegian Tunnelling Index (Q System) in conjunction with
regular face mapping is used as an operating tool to assist in decision
making for ground support. Line mapping, discontinuity analysis and
wedge assessments are conducted routinely to optimise ground support
requirements in the decline, intersections and all other underground
excavations. Throughout the project, an emphasis has been placed on developing a
strong working relationship with the contractor to achieve quality
assurance program targets.