IMPROVING EFFICIENCY OF QUARTZ ISOLATION FOR COSMOGENIC 10BE EXPOSURE DATING

Quartz isolation from whole rock samples collected for cosmogenic ¹⁰Be exposure dating is both time and acid intensive. In order to use quartz for ¹⁰Be dating, the cation content needs to be sufficiently low for successful ion chromatography. The amount of acid and time spent on each rock sample can often be attributed to difficulty in the removal of aluminum associated with feldspars. Feldspar can be difficult to isolate from quartz using heavy liquid (LST) separation because of overlap in mineral densities. In order to reduce the time and cost of processing ¹⁰Be samples we designed four experiments to evaluate multiple aspects of common quartz isolation procedures, outlined by Kohl and Nishiizumi (1992). Variables include the number of acid/sonication bath treatments, the duration of individual acid/sonication bath runs, whether manual shaking of samples during acid/sonication bath treatments improves efficiency and acid concentration (HF/HNO₃). Each experiment uses splits of one sample. Aluminum content, our main metric for quartz purity, is measured using inductively coupled plasma mass spectroscopy (ICP-AES) at different stages of each experiment. The first experiment compares the aluminum content of samples that were put into either three 48-hour-long acid baths or one six-day-long acid bath. The second experiment tests whether or not periodic shaking during pre- and post-LST acid baths removed more aluminum per bath than with sonication alone. The third experiment compares bath duration and acid concentration according to commonly used procedures among academic labs. The fourth experiment compares the aluminum content and quartz yield of samples that were treated with varying concentrations of HF/HNO₃ (0.5%, 2%). Using aluminum content as a quantitative measure of quartz purity, and by comparing quartz yield by weight, we will present our results of the efficiency of the different quartz isolation techniques tested.