Extraction and Purification of Quartz for in situ Cosmogenic Nuclide Exposure Dating

¹⁰Be and ²⁶Al in situ cosmogenic nuclide exposure dating is a relatively new dating technique, which is widely used in geoscience research. Normally, the BeO and Al₂O₃ measured by AMS are prepared from purified quartz samples. Therefore, it is key to develop a method to extract pure quartz from rock sampled in fieldwork. Based on the experimental procedure of Kohl and Nishiizumi, a comparison was made for the different etching effects on samples by using heated water bath oscillator and hot-dog machine (roller) with different grain size of 0.25-0.50 mm and 0.50-1.0 mm. The 1% or 2% HF-HNO₃ were applied to dissolve the silicates in the hot-dog roller machine with a solid/liquid ratio of 15. Detailed heavy liquid (sodium polytungstate) separation steps for quartz purification are also described in this paper. The pretreatment method was verified by using quartz from the river area around North Qilian Mountain. The results indicate that SiO₂ content in the purified quartz is greater than 98% and the Al content is less than 200 μg/g, by using X-ray Difrraction (XRD) and Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). The high purity quartz was obtained by the established pretreatment method which met the requirements for ¹⁰Be and ²⁶Al exposure dating.