Feldspar flotation as a quartz-purification method in cosmogenic nuclide dating: A case study of fluvial sediments from the Pamir

Cosmogenic nuclide (CN) dating relies on specific target minerals such as quartz as markers to identify various geological events including the timing of landscape evolution. The presence of feldspar in the analysed sediment samples poses a challenge to the separation of quartz and affects the chemical procedures for extracting the radioactive CNs ¹⁰Be and ²⁶Al. Additionally, feldspar contaminations also reduce the ²⁶Al/²⁷Al ratio, thus, hindering the accurate determination of ²⁶Al by accelerator mass spectrometry (AMS). Using our samples from Central Asia, the standard physical separation and chemical cleaning-up procedure for quartz-enrichment was not sufficient to quantitatively remove the feldspar. A modified froth flotation mineral-separation technique is presented that overcomes previous global challenges and enables sufficient quartz-enrichment before CN chemistry. We exemplify the need for feldspar flotation as part of the sample preparation procedure using fluvial sediment samples, which contain 16-50 weight percent (wt.%) of feldspar and which still show 9-47 wt.% of feldspar after chemical cleaning without flotation.