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

Cosmogenic nuclide (CN) dating relies on specific target minerals such as quartz as markers to identify geologic events, including the timing of landscape evolution. The presence of feldspar in 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 contamination reduces the ²⁶Al/²⁷Al ratio, thus hinders the accurate determination of ²⁶Al by accelerator mass spectrometry (AMS). Using fluvial sediment samples from Central Asia, which contain 16-50 weight percent (wt.%) of feldspar, we show that the standard physical separation and chemical cleaning-up procedures for quartz-enrichment reduces the feldspar content to only 9-47 wt.%. We present a new froth flotation mineral-separation device and procedure that allows for very effective quartz enrichment before CN chemistry. Our flotation cell, which has a volume of 600 cm³, is built of borosilicate glass, holds up to 90 g of sample, and achieves quartz and feldspar separation in ≤2 h for very feldspar-rich samples. We trace the stepwise enrichment of quartz to 95-100% purity with our procedure by X-ray diffraction analysis.