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Mining, Crushing and Conveying

Once the caprock layer has been broken by blasting or ripping, the bauxite is ready to be mined.  The average thickness of the bauxite is about 4m (including the caprock and the underlying friable bauxite) but it can be as much as 10m.  An excavator or loader is used to load the bauxite onto haul trucks for transport to the crusher.  The excavator operator uses a GPS screen to indicate where, and how deep to dig.  Several pits are usually mined simultaneously in order to supply the refinery with a constant grade of ore.

Large 190 tonne capacity haul trucks transport the bauxite ore to the central crusher.  The crusher is used to break the ore down to a smaller size suitable for transport along the conveyor belt to the refineries.  The crusher is made up of a number of components that include a vibrating screen, a jaw crusher and sizers.  Fine material drops through the vibrating screen while larger material passes over the screen to the jaw crusher that breaks up the large rocks.  The material that passes through the vibrating screen and jaw crusher is collected and passed through the sizer that further reduces the size of the material before it is passed onto the conveyor belt.  The final size of the crushed bauxite ore is approximately 7.5cm or less in diameter. 
 
Conveyor belts are used to transport the ore to the Wagerup and Pinjarra refineries from the Willowdale and Huntly mines.  The conveyor belt that supplies the Pinjarra Refinery consists of three sections totalling 23.4km in length.  Because the Huntly mine is at a higher elevation than the refinery, two of the conveyor belts run downhill.  The force of gravity pulling the bauxite down the belt generates power that feeds electricity back into the power grid.  The capacity of the conveyor belt system between Huntly and Pinjarra is 5400 tonnes per hour.

The Willowdale conveying system has two belts totalling 18 km in length.  The eastern most conveyor belt at Willowdale is 9km long and unlike most conveyors which need to be dead straight, this one takes a long curve between its start and finish.  Alcoa engineers developed this innovative curved design so that the conveyor would not cross over the waters of the Samson Dam.
 
Ore for the Kwinana Refinery is transported via rail from the Pinjarra Refinery.


Large excavator.

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Large excavator loading a haul truck with bauxite. The average load of bauxite transported to the crusher weighs 190 tonne.

Haul Truck

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The Haul truck empties the load of bauxite into the crusher where it is crushed down into pieces small enough to travel along the conveyor.

Crusher.

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The crusher, with haul truck top left.

Conveyor

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The crushed bauxite travels the length of the conveyor, through the jarrah forest down to the refinery, where it is refined to make Alumina.