Impact of using a 3.5 μm film to analyze the chemical composition of crystal samples with a handheld X-Ray Fluorescence equipment

Some potassium-feldspar crystals from lithium-rich aplite-pegmatites from Northern Portugal have been analyzed with a handheld X-Ray-Fluorescence (XRF) equipment. This study compares the impact of analyzing the samples with an XRF film versus analyzing them without it. The film used was a Hitachi Poly-S High Performance XRF Sample Film of 3.5 μm, commonly used for analyzing samples in cups and powders. Although Hitachi alerts for the unsuitability of the film for analyzing light elements, this study helps understand the extent of error that this film can cause when analyzing this type of sample. 15 cleaned potassium feldspar crystals with a size between 1-3 cm have been analyzed with a Bruker S1 TITAN 600 containing an X-ray tube with a 2 W and 5-100 μA Rh anode. The Geomining factory calibration was used for the sample analysis.

The results show that the potassium-feldspars analyzed with the film had their major elements drop by 20-40% for silica (SiO2), 30-50% for aluminum (Al2O3) and 10-20% for potassium (K2O). As for the trace elements, calcium (Ca) dropped by 20-30%, phosphorous (P) by 20-40% and rubidium (Rb) and iron (Fe) have small errors that can vary from plus 0-10% to minus 0-10%. Knowing the film impact will hopefully be of assistance for the correct interpretation of portable XRF results during field campaigns for mineral exploration.

This study was financially supported by FCT, I.P., in the framework of the ICT (UIDB/04683/2020 and UIDP/04683/2020), by the PhD project (2020.05534.BD) and by national funds from MCTES, through FCT, co-financed by ESF through POCH and NORTE 2020. This work is also supported by the Greenpeg project, reference 869274, funded by the Horizon 2020 framework program of the European Union.