Open pit mining
The history of the mine began with a period of exploration from 1976. Several small diamonds found in 1979 led to the discovery of the diamond-bearing ’pipe’ that is the source of the mine's open pit. A lease for the land was secured and alluvial mining in the area commenced in 1983 while the mine was under construction. It was commissioned in December 1985.
Argyle's open pit was mistakenly named Argyle kimberlite 1 (referred to as AK1) by the geologists who initially thought the diamond bearing rock was kimberlite. Although it was soon discovered to be lamproite, the diamond-bearing pipes of ore in the area had already been identified and numbered sequentially. The AK1 pipe, being the most viable, became the source of the mine's open pit.
Argyle currently operates an open pit mine and a processing plant 24 hours a day, 365 days a year. The AK1 open pit is 2 kilometres long, 1 kilometre wide and covers an area of almost 300 hectares. The principal activity in the pit is the removal of overburden and collection of diamondiferous ore. Ore in the pit is broken by the use of explosives with each blast hole liberating about 3000 tonnes of rock.
Excavators capable of holding 45 tonnes load rock into haul trucks with an average 200 tonne capacity. These trucks transport diamond-bearing ore approximately 2.5 kilometres to a primary crusher to commence the diamond extraction process in the main recovery plant. The unwanted overburden is deposited on the perimeter of the pit and represents around six times the volume of the diamondiferous ore.
In the past Argyle has also conducted alluvial mining of ancient creek beds where diamonds were washed down from the AK1 pipe over millions of years. An excavator dumped gravel directly into a mobile screening unit. The reduced volume was then hauled to the alluvial processing plant for additional treatment. The remainder (about 60 per cent of the volume excavated) was returned immediately to the area being mined.
Rehabilitation is an important component of alluvial mining, and Argyle's Health Safety and Environment department undertakes a range of rehabilitation activities.