A quantitative thermogravimetric method has been developed for the routine analysis of goethite and kaolinite in a Western Australian iron ore sample. Standards were used to construct calibration graphs based on the mass loss due to the dehydroxylation of goethite and kaolinite. The haematite content is calculated from the total soluble iron content in the sample. The method is precise (maximum relative standard deviation of 3.3%) and accurate (within +/- 10%), provided the crystallinity and particle size of the minerals in the standards are matched to the minerals in the unknown samples. The method was applied to the characterisation of an iron ore tailing and used to assess the performance of a selective flocculation process for upgrading the tailing.