Quantifying the bucket: Quartz purification of 125-63 µm material for in-situ cosmogenic nuclide analysis.
Dr Ross Whitmore1, Dr Kevin Norton2, Dr. Luisa Ashworth2, Dr. Andrew Mackintosh1
1Monash University, Clayton, Australia, 2Victoria University of Wellington, Kelburn, New Zealand
Quartz purification is a necessary and critical step to producing robust and reproducible results in terrestrial cosmogenic nuclide studies. Previous quartz purification work has centred on coarse sample material (1 mm-500 µm) and is anecdotally effective down to ~250 µm. The success of these purification procedures is evident by the large amount of peer reviewed research published each year using the quartz/10Be system. However, even though quartz is ubiquitous in the environment not all rocks contain quartz grains/crystals sufficiently large to be purified with these relatively aggressive procedures. When very-fine quartz is purified this way, it tends to be totally digested.
We tested HCl/HF purification on very-fine sand (125-63 µm), using two 10% HCl leaches to remove oxide forming minerals and phyllosilicates, followed by one 2.5% HF leach and six subsequent 1% HF leaches to remove quartz overgrowths. In addition to this quartz purification test we also quantify major element, 9Be and 10Be removal through the leaching process. For the analysis we retained each post-leach acid supernate and collected a 1 g subsample of the rinsed and dried quartz.
Our results show that more than 99.9% of the meteoric 10Be is removed by the first 10% HCl leach with 10Be removal plateauing after the first 1% HF leach. We also document that Al is pervasive in these very-fine-grained samples and that removing it is more challenging than removing meteoric 10Be. Additionally, our data suggest a correlation between reduced Al and increased 9Be ion-beam strength when the sample is being measured in an accelerator mass spectrometer. Ultimately, this quartz purification method is robust and reliable for removing major elements, meteoric 10Be, and 9Be from material between 125 µm and 63 µm in size.
Ross has a broad background in the Geosciences. He has worked on the mid to late-Paleozoic Tectonostratigraphic evolution of the North American West, the landscape evolution of the Transantarctic Mountains in Victoria Land, on the evolution of large outlet glaciers in the Western Ross Sea region of Antarctica, and developed new geochemical techniques to expand the type of rocks and sediments suitable for terrestrial cosmogenic nuclide analysis. Ross is currently consulting on the design of a new Geochemistry lab and planning future Antarctic fieldwork at Monash University.