Can Portable XRF Handle Concentrated Ore Samples?

Ore deposits are inconsistent in nature, having high concentrations of metals in one area but much lower concentrations in other areas. The grade may be high at the surface, but diminish with depth to the point where it isn’t worthwhile to further explore the deposit, or vice versa. Mining geologists perform ore grade control to figure out where the most profitable ore deposits are in terms of location and mineral concentration variability. The data collected during grade control processes helps mining geologists create models or maps of where the best targets are so that they can make the most efficient and economical drilling and excavation decisions. This information not only ensures a mining plan that will yield a sufficient return on investment, ore grading and mineral concentration are necessary processes in making the final product (i.e. metal) from the original raw material. After ore minerals are identified and extracted, samples are prepared for analysis using a variety of techniques depending on the physical and chemical properties. These include mechanical separation, such as screening, to chemical separation including floatation and acid leaching. The product of such processing is a uniform and homogeneous mineral concentrate with relatively simple composition and mineralogy. Field-portable x-ray fluorescence (FPXRF) instruments provide fast acquisition of geochemical data for mine mapping and ore deposit modeling. FPXRF is an established technique for easily determining elemental constituents for most natural low concentration samples, but it’s now  emerging as an effective analytical tool for high grade ore concentrates and grade control as well. While the application of FPXRF for concentrated ore samples can be more challenging, a recent study has determined that for concentrated mineral samples, FPXRF employing Empirical Mode can often provide reliable and accurate data. The Fundamental Parameter (FP) factory modes are general purpose modes that work well for a wide variety of sample types. The FP mode is also “standardless” and does not require known samples to obtain quantitative results. However, FP modes are not best for high concentration processed samples because the concentration of metal of interest is usually reported less than the true value if regular FP method is used. Empirical Mode is a more useful portable XRF method for analyzing concentrate samples considering their homogeneous composition. For applications where the samples require specialized processing to supply the most accurate results, the empirical testing mode provides users with the ability to have their own application-specific empirical calibrations. In empirical calibration, the user must first analyze known samples to obtain the count intensity, which is then plotted using off-line software to generate the calibration curve. This curve data is then put back onto the analyzer which can then be run to give immediate results.  These calibration equations may then be overlaid onto existing FP or Compton Normalization calibration models, or used to create completely new modes to optimize analytical results for specific applications. Once an empirical calibration is uploaded, the analysis can be used for maintaining the correct grade control. Results from a study to evaluate FPXRF for the analysis of concentrated mineral samples using Empirical Mode indicate it is a very effective tool to provide reliable and accurate data. In a future article, we’ll discuss specific examples in an application note that demonstrates the correlation of molybdenum (Mo), copper (Cu) and iron (Fe) data between portable XRF and lab in molybdenite (MoS₂) concentrate samples.