The application of portable XRF spectrometry (pXRF) for determining concentrations of uranium (U), thorium (Th) and potassium (K) was evaluated using a combination of 12 Certified Reference Materials, 17 Standard Reference Materials, and 25 rock samples collected from areas of known U occurrences or mineralization. Samples were analysed by pXRF in Soil, Mining Cu/Zn and Mining Ta/Hf modes. Resulting pXRF data were compared to published recommended values, obtained by total or near total digestion methods with ICP-MS and ICP-OES analysis. Results for pXRF show a linear relationship, for thorium, potassium, and uranium (<5000 ppm U) as compared to the recommended concentrations. However, above 5000 ppm U, pXRF results show an exponential relationship with under reporting of pXRF concentrations compared to recommended values. Accuracy of the data can be improved by post-analysis correction using linear regression equations for potassium and thorium, and samples with <5000 ppm uranium; an exponential correction curve is required at >5000 ppm U. In addition, pXRF analyses of samples with high concentrations of uranium (e.g. >1 wt.% U) significantly over-estimated potassium contents as compared to the published values, indicating interference between the two elements not calibrated by the manufacturer software.