The Argyle diamond mine is located in the East Kimberley area of
Western Australia, some 100 km south of the town of Kununurra. The
diamondiferous Argyle olivine-lamproite diatreme was discovered in
August 1979. Production began in December 1985 at a planned
throughput of 3 Mtpa to recover 25 million carats of diamonds. Presently,
Argyle is the world's largest producer of natural diamonds and produced
over 40 million carats in 1993 from seven million tonnes of lamproite ore
treated. Two phases of evaluation have been carried out. The first in 1981-82
was designed to prove around 60 million tonnes of ore to justify the
establishment of a mine with a minimum life of 20 years. The second
phase, in 1989-90 involved drilling the orebody to greater depths to
provide data on which to plan the final pit design. The final pit contained
120 million tonnes of ore at 5.3 carats per tonne (ct/t) grade. Mining of the planned pit will extend the mine life to around the year
2004, following which it is possible that a further cut-back could be
mined. There is also the potential for future underground mining. A substantial amount of geotechnical work has been undertaken due to
the fact that the pit will be nearly 500 m deep and is located in a mobile
zone causing abnormally high residual stresses to occur in the pit walls.
The occurrence of low strength rocks at depth in the pit walls further
complicated the situation. Hydrogeological investigations were done to determine pit dewatering
requirements and to assess the effect of dewatering on pit wall stability.