原地宇宙成因核素暴露测年方法中石英的提取

摘要

原地宇宙成因核素10Be和26Al的暴露年龄测定是近年来发展较快的测年技术,已在地学研究中得到广泛应用.该方法需要选用经一系列前处理过程获得的纯净石英作为待测样品,制备成BeO和Al2O3以供加速器质谱仪测量.因此获得高纯度的石英样品,是该测年方法的关键环节之一.本研究在已有报道的石英提纯化学流程的基础上,尝试对流程进行部分优化,通过实验对比不同粒径组分、不同固液比水浴振荡器和滚筒HF - HNO3蚀刻效果,确定使用HF - HNO3(1％或2％,固液比15.0 g/L)滚筒加热法刻蚀样品以去除铝硅酸盐,多钨酸钠重液分离样品中的石英和其他组分.优化的分离纯化流程应用于处理采自祁连山北缘河流阶地含石英的岩石样品,经纯化的石英纯度可达98％以上,Al的含量小于200 μg/g,表明采用优化的提取流程获得了高纯度的石英样品,可以满足10Be和26Al暴露测年所需样品要求.%Be and Al in situ cosmogenic nuclide exposure dating is a relatively new dating technique, which is widely used in geoscience research. Normally, the BeO and A12O3 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-HNO, 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 |JLg/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 26A1 exposure dating.