AUSTRALIS: a new tool for the study of isotopic systems and geochronology in mineral systems

AUSTRALlS (AMS for Ultra Sensitive TRAce eLement and Isotopic Studies) is a microbeam accelerator mass spectrometry (AMS) system designed for in situ microanalysis of geological samples for trace elements and radiogenic and stable isotope data. The AMS method eliminates molecular and isobaric interferences in in situ mass spectrometric measurements, opening up new opportunities in geochronology and tracer applications. Tests have been carried out for measurements of Pb, S and Os isotopes, conducted mainly at 1 5 MV accelerating voltage. In Pb and S tests, precision as high as 0.3%o has been obtained, made possible by a fast isotope switching system to counter the effect of instabilities in the ion source and beam transport system. Elimination of molecular interference is demonstrated in these measurements from galena. Initially, fractionation effects varied within 2% over longer periods for Pb, and were larger for S isotopes, but this has now been significantly improved to better than 0.5% after all the critical beam-transport elements were put under computer control. High sensitivity was demonstrated in the Os isotope measurements in iron meteorite and sulfides. The trace-element capability was demonstrated in Au measurement, where sub-ppb detection sensitivity was achieved in NiS. Copyright (2002) Geological Society of Australia