1. Nevada Bureau of Mines and Geology, University of Nevada, Reno, Nevada, U.S.A.
2. U.S. Geological Survey, Moffett Field, California, U.S.A.
3. U.S. Geological Survey, Golden, Colorado, U.S.A.
4. Department of Earth Sciences, University of Oxford, Oxford, United Kingdom
5. California Geological Survey, San Mateo, California, U.S.A.