X-ray fluorescence analysis for the determination of potassium in small quantities of silicate minerals for K-Ar dating

X-ray fluorescence analyses were used to determine the potassium contents of silicate minerals with K2O concentrations between 1 and 13wt.%. This method is based on lithium tetraborate fused glass discs with 50mg of sample at ~1:120 dilution. The results show that this high-dilution minimises matrix effects and that both precision and accuracy are below 1.5% for all the silicate minerals analysed, whatever their composition. This analytical procedure is useful for K determination in small samples of mineral separates needed to establish K-Ar geochronology, without using acid digestion.