Cannington is the world's largest single mine producer of silver and lead, representing about 6% of the world's primary silver production, while its lead production represents about 7% of the world's primary lead output. The lead concentrate contains 70% lead and over 3,000g/t silver with low levels of impurities.
It is an underground mine with access via a decline ramp from the surface. The hoisting shaft allows for a planned production rate of 1.8 million tonnes of ore a year. In 2008 Cannington mined 3.1Mt of ore. Total metal production in concentrate was over 31Moz of silver. Approximately 404,000 wet metric tonnes of lead and 163,000 wet metric tonnes of zinc were processed. The lead concentrate contains 70% lead and over 3 kg/t of silver. It is recognised as a clean concentrate with low levels of impurities. The zinc concentrate contains 50% zinc and 250 g of silver.
The stoping method used for the extraction of the main, thicker, hangingwall orebodies of the deposit is transverse, long-hole open stoping. Broken ore from the stopes is loaded from draw points at the bottom of each stope and currently hauled to the surface via the decline by trucks. The ore is hauled along the level and tipped into one of several ore passes.
The decline ramp has a cross section of 5.2 metres high by 5.5 metres wide and descends at a gradient of one in eight to the 450-metre level and thereafter one in seven. The main functions of the decline are to provide an access for mobile equipment and personnel to enter the mine and to act as one of the main intakes for fresh air into the mine. The decline has a total length of 5,250 metres.
Excavation involves stripping out a 1.8m-diameter raise-drilled pilot hole and lining with concrete from the surface. The hoisting shaft has a finished internal diametre of 5.6 metres and extends to a depth of 650 metres. The shaft is equipped with a tower-mounted friction winder and two 9t skips in counter balance running on rope guides. The skips are hoisted from a loading station on the 610-metre level and reach a final hoisting speed of 12 metres per second. On the surface, tipping scrolls in the shaft headframe tip the skips into a surface bin for transfer to the processing plant's stockpile area.
Because the site is prone to flooding after heavy rains, the decline, shafts and surface infrastructure at the site have been elevated above known and predicted flood levels.
After completion of the ore extraction from each stope, paste backfill is used to fill the open void to stabilise the area and allow for mining of adjacent stopes.
Paste backfill is a high solid density material, around 80% solids and mixed from tailings produced from the processing plant with the addition of approximately 5% cement. The paste backfill is gravity fed underground via boreholes from the surface and pipe work into the open stopes.