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Infrared Microspectroscopy of Bauxitic Pisoliths

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Bauxite ore in the deposit at Weipa, Queensland, Australia occurs as pisoliths which are small, approximately spherical, pebbles with diameters in the range 0.5 to 2 cm. The distribution of various mineral species within the pisoliths has been determined by the use of reflectance infrared microspectroscopy of a large suite of pisoliths obtained from different parts of the Weipa orebody. The method allows the significant minerals of the bauxite to be analyzed including gibbsite (aluminium trihydroxide), boehmite (aluminium oxyhydroxide), quartz, and the clay, kaolinite. These minerals are readily distinguished by their IR spectrum. The iron minerals, present in small amounts, could not be detected. Specular reflectance spectra of sectioned pisoliths were measured, and the spectrum was utilized directly without the application of the Kramers-Kronig transformation. Polished pisolith sections were also mapped at a spatial resolution of 100 μm with the use of a computer-controlled microscope stage, and the mineral composition at any point was estimated by measuring relevant areas of the spectrum. Semi-quantitative results were obtained by relating the reflectance spectra for a particular pisolith thin section to the transmittance spectra for the same points. The transmittance spectra of the pisoliths were correlated with spectra of pure standards by application of a multicomponent Q-matrix approach. Principal component analysis of the mineral distribution data allowed the suite of pisoliths to be subdivided into groups with similar mineralization.

Keywords: Bauxite; Infrared microspectroscopy; Minerals; Principal component analysis; Reflectance

Document Type: Research Article


Affiliations: Centre for Instrumental and Developmental Chemistry, Queensland University of Technology, P.O. Box 2434, Brisbane, Queensland 4001, Australia

Publication date: November 1, 1995

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