Arizona Geological Survey OPEN-FILE REPORT OFR 08-06

Arizona Geological Survey
weighing of the remaining particles, on average 3% of the sample was removed at this step. We then
used a 5% mixture of HF (hydrofluoric acid) and HNO 3 (nitric acid) to begin the process of etching quartz
grains and dissolution of other minerals using a typical sample‐to‐liquid ratio of 30 grams/liter (g/L) and
a temperature of 50‐60º C for 8 hrs. Beginning with this step, all samples were held in HDE plastic
containers to avoid boron (B) contamination, which is critical because the spectral emission signals of B
and Be are overlapping; Pyrex glass (a borosilicate) is a common source of B contamination. Agitation
was applied using a sonicator, which uses ultrasonic waves to induce particle motion and produce 55‐
60°C heat. The resulting loss of sample averaged 19% during this step. The remaining sample was put
through a magnetic separator (Frantz) to remove any particles with magnetic properties, which typically
included magnetite, apatite, and most of the micas; this step removed an additional 9% of the sample.
Then the samples were further etched with a 1% HF/HNO 3 solution at a ratio of 15 g/L for 5‐6 times in a
sonicator or a hot‐dog roller, which rotated and heated round plastic bottles bearing the samples and
solutions. A sample was considered to be completed when a small aliquot yielded an Al concentration of