Bauxite Deposits Lateritic bauxite deposits such as those in the Darling Range of WA generally formed in tropical (hot and humid) environments through chemical weathering. As a result, lateritic bauxite deposits are known to exist across Central and South America, West Africa, Central Asia, and Australia. Bauxite deposits have been identified throughout the Darling Range and generally occur as erratically distributed alumina-rich lenses within the eroded laterites that mantle the granites to the east of the scarp line. The bauxites are thought to have formed from the lateritization of the peneplained surface of the Western Gneiss Terrane rocks. Lateritization is thought to have commenced during the Cretaceous and continued through to the Eocene, with the subsequent periodic activity of the Darling Fault resulting in the current landform of scarps and deeply incised valleys on the western edge of the Darling Range. Mineralization Weathering, alteration and leaching of the granite bedrock has developed the bauxite mineralization which principally occurs as 65% microcrystalline gibbsite Al(OH)3 with minor to rare boehmite ALO(OH), and accessory minerals of 18% goethite FeO(OH), 7% hematite Fe2O3, 9% quartz SiO2, 1% kaolinite/halloysite Al2Si2O5(OH)4, and 0.5% anatase/rutile TiO2. Other minerals within the bauxite that may influence the alumina refinery performance include: • Boehmite: generally occurring below 1%, this can cause premature precipitation of dissolved gibbsite ........

The Huntly and Willowdale mines employ conventional open pit mining practices and equipment. The fleet is mixed between contract and owneroperator, depending on the nature of the task at hand. Owner operator equipment is used for mining the bulk of the Mineral Reserve, operating in areas away from those subject to environmental restrictions. Contract mining operates smaller equipment, day shift only, in environmentally (noise) sensitive areas and at the perimeter of the mining area.

The Huntly mine currently operates at a nominal mining capacity up to 27 Mtpa. In recent years, licenses were gained for the export of a proportion of the bauxite produced. The Willowdale mine operates at a nominal production rate of 11 Mtpa.

Dilution and ore loss are not reported separately to the Mineral Reserve. Internal and edge dilution is modelled at the mine planning stage through the application of 15 m by 15 m mining blocks to the Mineral Resource model. These regularized blocks contain proportional estimates of ore and contaminants and are optimized through the application of a Lerchs-Grossman algorithm developed specifically for the operation. This variation of the conventional Lerchs-Grossman algorithm is applied vertically, given that the shallow nature of the mineralization precludes geotechnical considerations. Blocks that do not satisfy grade and contaminant parameters against revenue are thus excluded from the mine plan.

Mining recovery from Huntly ........

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