1. Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, North Carolina 28214, USA
2. Department of Geology, College of William and Mary, Sadler Center, Williamsburg, Virginia 23185, USA
3. Bureau of Economic Geology, University of Texas at Austin, Austin, Texas 78758, USA
4. Sandia National Laboratories, Albuquerque, New Mexico 87185, USA