The Bauxite Mine
Bauxite is mined and crushed at Worsley Alumina's mine site at Boddington, 123 south east of Perth. Crushed ore is then transported 51km by overland conveyor to the refinery. Mining starts with flora and fauna surveys. Topsoil and overburden is removed and kept for use in rehabilitation.
The bauxite is excavated and taken by truck to primary and secondary crushing stations at the mine site.
Post mining rehabilitation is directed at re-establishing a self-sustaining natural forest.
The 51km conveyor from the Boddington mine site to the refinery at Worsley is the longest of its type in the world.
The mining process
Before mining starts, commercial timber is salvaged by contractors who send it to be milled, or store it to be sold as firewood. Stumps, logs and forest floor litter is set aside to be used later to help reconstruct fauna habitats.
A layer of topsoil and gravel overburden is removed from the bauxite ore by scrapers and loaders. This overburden is directly backfilled into previously mined areas, or stored for later use.
The hardcap layer of bauxite ore is drilled and blasted. Large bulldozers rip into shallow, and softer layers of ore. The bauxite layer varies from two meters to 12 metres deep. In most areas the bauxite is picked up by front-end loaders in a single pass.
The noise from blasting, excavation, transport and crushing operations is minimised to avoid any disruptive impacts when mining operations are close to farming properties.
The primary crusher can take rocks as large as 1.5m in diameter. By the time the ore comes through the other end the biggest rocks are less than 180mm. A secondary crushing plant further reduces the size to less than 30mm. The crushed ore is fed into a stockpile, ready to be carried by conveyor to the refinery.
The Overland Conveyor
Worsley's overland conveyor system is one of the longest of its kind in the world and is a result of a unique engineering approach by Worsley Alumina and UK company Cable Belt during construction in the early 1980s.
The 51km system contains more than 200km of wire rope (drive cable) and approximately 100km of rubber belt.
The decision to use a conveyor to transport bauxite from the Boddington mine to the refinery was made after studies of alternative transport costs, energy use, environmental factors and maintenance.
Construction began in November 1979 and in October 1983 the first delivery of bauxite from Boddington to the refinery took place.
The conveyor consists of two flights - the first is 31km from the bauxite mine to a transfer point and the second is a 20km flight to the refinery. The dog-leg shape avoids an area of forest with a high conservation value.
Both flights follow the natural topography as closely as possible, dipping into valleys and crossing rivers. It is also raised in parts to allow native animals to migrate underneath./
The system operates on a continuous basis with planned breaks for maintenance, and travels at a speed of 26km/h. It carries 2700 tonnes of bauxite per hour and conveys 12 million dry tonnes per annum. The belt rests on two 57mm steel cables and the motors at the end of the conveyors drive the cables. The cables pass over 68,000 polyurethane pulleys.
During operating hours the conveyor is patrolled by teams in 4WD vehicles. Their duties include monitoring and reporting on the condition of all components of the system. When the system is not running, the power is shut down to allow maintenance and repairs.
The conveyor is contained within a 35m wide corridor, along the full length. Also confined in this corridor are a sealed service road, power line, optical fibre communication system, 22 tunnels and 10 bridges.
