The application of pXRF for the chemical and mineralogical characterisation of heavy mineral sands

Heavy mineral sands (HMS) are a resource of Ti-minerals, zircon, monazite and the critical elements Hf and REEs. Portable field techniques capable of measuring the geochemical composition, such as portable XRF (pXRF), may assist in identifying and quantifying the multiple minerals present in HMS. In this study, we assess the application of pXRF for the characterization of garnet-magnetite mineral sands from the Namibian coastline. Forty-six HMS samples from the northern Namibian coast were analysed by pXRF for SiO₂, Ti, Mn, Fe, Zr, Th, Y, V and Hf. The HMS were analysed as powdered and unground samples to test whether minimal sample preparation yields reliable results. Our tests show that pXRF results of unground sands scatter widely due to sample heterogeneity. Powdered samples, however, can be measured precisely and can be corrected with conventional lab analyses. Some spectral interferences specific for this material occur, e.g., Th on Pb and Bi and Hf on Cu. Selectively corrected pXRF data of powdered HMS were compared to XRD Rietveld data to determine proportions of heavy minerals (Ti minerals, Fe oxides, zircon, garnet). Geochemical and mineralogical data correlated well for garnet and moderately for Fe-oxides and Ti-minerals. Additionally, the presence of zircon and monazite is indicated by Zr, Hf and Th concentrations, which demonstrates that pXRF is a useful tool for HMS characterization.