1. a 750 West Greenwich Place, Palo Alto, California, 94303
2. b U.S. Geological Survey, Stanford USGS Micro-Isotopic Analytical Center , Stanford University , Stanford, California, 94305
3. c Department of Geology , University of Maryland , College Park, Maryland, 20742
4. d Central Research Institute of Geological Prospecting for Base and Precious Metals , Varshavskoye Shosse 129B, Moscow, 113545, Russia
5. e Taymyrian Committee for Natural Resources , Post Box 1374, Noril'sk, 663300, Russia
6. f Denver Federal Center , U.S. Geological Survey , Denver, Colorado, 80225