1. Northern Territory Geological Survey, PO Box 8760, Alice Springs, NT0871, Australia
2. Department of Geological Sciences, University of Manitoba, 125 Dysart Rd, Winnipeg, MB R3T 2N2, Canada
3. Isotope Geosciences Group, School of Earth Sciences, University of Melbourne, Carlton, VIC 3010, Australia
4. Faculty of Science and Engineering, University of Waikato, Private Bag 3015, Hamilton, New Zealand