Application of Rapid X-Ray Diffraction (Xrd) and Cluster Analysis to Grade Control of Iron Ores

Abstract

Traditionally, grade control of iron ores has relied on elemental analysis of sampled materials such as blast cone drill cuttings. This analysis provides a standard elemental suite (Fe, SiO₂, Al₂O₃, P, Mn, S, MgO, CaO and TiO₂ along with loss on ignition) that is used in grade control to assign mined material as grade blocks to high grade, low grade or waste destinations. However, the mineralogy of the sample is often not considered or at best inferred from visual geological logging of the sampled material. As such, mineral contaminants such as gibbsite, kaolinite and substituted goethite that cannot be identified visually and/or by chemical analysis alone are often not quantified. To address this issue Rio Tinto Iron Ore (RTIO) has trialled the application of rapid X-ray diffraction (XRD) to grade control in iron ore mining. RTIO provided PANalytical with 110 samples from two of its mine sites, referred to here as deposits A and B. The samples included high grade, low grade and waste materials. All samples were analyzed qualitatively and quantitatively for major phases such as hematite Fe₂O₃ and goethite FeOOH and minor phases including kaolinite Al₂Si₂O₅(OH)₄, gibbsite Al(OH)₃, quartz SiO₂ and calcite CaCO₃. Automated Rietveld quantification was undertaken for all samples to determine the phase composition. Substituted goethite was identified as a discrete phase. The analysis of the resultant mineralogical data was undertaken in three steps: data clustering, phase identification and phase quantification. Once the mineralogy of the samples was established the spatial distribution of the detected minerals was plotted for both deposits. Based on these plots the stratigraphy could be demarcated and mineralogically characterised. The additional information also provided the opportunity to blend and/or isolate these minerals throughout the defined theoretical grade blocks which included high grade, high grade with minor gibbsite, high grade beneficiation, low grade beneficiation, low grade other and waste. As such material with a propensity for higher degrees of beneficiation was identified and domained. Conversely, material with limited upgrade potential could be identified and not submitted to traditional forms of beneficiation. Based on this trial, rapid XRD analysis and associated cluster analysis was shown to offer additional criteria for the definition of theoretical grade blocks in iron ore mining which is potentially advantages compared with definitions based only on chemistry.