GEOCHEMICAL AND MINERALOGICAL CHARACTERISTICS OF BAUXITES, DARLING RANGE, WESTERN-AUSTRALIA

The lateritic bauxites of the Darling Range, Western Australia vary greatly in chemical and mineralogical properties and it is shown that this is due partly to the parent materials ranging from granitic to doleritic rocks. Gibbsite is the dominant form of Al in the friable and duricrust zones. Goethite is the major Fe oxide mineral and is highly Al substituted (16-33 mole %) whereas hematite shows lower Al substitution (3-11 mole %). Halloysite and kaolinite are mostly responsible for the reactive silica content of these bauxites. Maghemite (0-10%) and secondary microcrystalline corundum (0-3.5%) occur only in duricrust and their abundances are very highly correlated indicating a common origin and they may have been formed during forest fires. The abundances of several elements are highly correlated due to the association of these elements within specific minerals, such as Ti, Mn and V in residual ilmenite grains. The mineralogical and chemical properties of the Darling Range bauxite deposits are compared with those of other large bauxite deposits in Australia and overseas. These properties are also related to problems in processing bauxite using the Bayer process. Darling Range deposits differ from other Australian and many other of the world deposits in that they are low grade (34.5% Al2O3) and high in silica (21% SiO2) and Fe (21% Fe2O3). The provision of detailed information on the mineral and chemical constituents of these bauxites has enabled refinery operators to improve the efficiency of the Bayer process.