The bauxites have developed on the exposed Achaean basement of the Western Gneiss Terrane, which is located on the western edge of the Yilgarn Block. In the project area, the Western Gneiss Terrane is predominantly composed of granitic gneisses and migmatites, as well as the greenstones of the Saddleback Greenstone Belt. The northerly trending greenstone belt is approximately 43 km long and 5 - 12 km wide, and consists of sequences of mafic to felsic volcanics, pyroclastics, and sediments that have undergone greenschist facies metamorphism. The gneisses and greenstones have been intruded by relatively undeformed granites, and subsequently by numerous northerly trending doleritic dykes that range in thickness from 1 to 200 m. The dominant structural feature in the region is the Darling Fault, which forms the western boundary of the Western Gneiss Terrane.

The bauxites are thought to have formed from the lateritisation of the peneplained surface of the Western Gneiss Terrane rocks. Lateritisation is thought to have commenced during the Cretaceous and continued through to the Eocene.

In the project area, bauxite exists as irregular lenses, locally referred to as pods, within the remnant laterite. The pods are generally elongated in the NNW-SSE direction and vary in size from 1 to 200 ha. The majority of the pods contain approximately 2 million tonnes (Mt) of bauxite. The pods are generally confined to slopes where the gradient is between 5° and 10°. In ste ........

The mining of bauxite by Worsley at Boddington Bauxite Mine (BBM) is a continuous process of mining and rehabilitation. Bauxite ore mined at BBM is transported to crushing facilities and crushed ore is then transported via conveyors to the Refinery.

BBM mines the bauxite by shallow open pit mining methods from a number of open pits. The bauxite occurs in pods, close to the surface, with an ore thickness of up to 5 m.

There are two mining areas at Boddington Bauxite Mine, the Saddleback Mining Envelope and the Marradong Mining Envelope. The crushed bauxite product, after primary crushing (at Marradong or Saddleback) and secondary crushing at the Saddleback area, is transported to the Worsley Refinery near Collie, via a 2-flight cable belt overland bauxite conveyor with a total length of 51 km. The bauxite is stockpiled at the refinery.

The majority of the open pits at Boddington Bauxite Mine are shallow to very shallow, typically less than 10 to 15 m deep. Mining of around 18 Mtpa of (wet) bauxite feed to the Alumina refinery requires large areas to be mined on an annual basis, given the limited thickness (between 1 m and 10 m thick) of the bauxite mineralisation. Typically, an area of around 200 ha is mined on an annual basis.

Initial overburden is removed by scrapers and secondary overburden is removed by small 30 t backhoe excavators, when it is impractical for the scrapers to remove the remaining overburden.

Drilling ........

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The bauxite is transported to the alumina refinery via an overland conveyor system that stretches more than 50 kilometres. The refinery extracts alumina using a four-stage Bayer process. This process turns the red bauxite rock into white alumina powder. The alumina is then transported 55 kilometres by rail to the Bunbury Port for export to aluminium smelters worldwide, including South32’s Hillside and Mozal aluminium smelters in Southern Africa.

Worsley Refinery has been operating since 1984. In the 30 years since operations commenced, the capacity has increased from the original 1 million tonnes per annum (Mtpa) of alumina production to the nameplate capacity of 4.6 Mtpa through a series of expansions. The most recent expansion in 2012 makes it one of the largest bauxite mining and alumina refinery operations in the world.

This process relies on the principal that aluminium is an element with a high solubility in alkaline solution, whereas most of the other eleme ........