1. Instituto de Geociências, Universidade de São Paulo, São Paulo, São Paulo 05508-080, Brazil
2. Center for Mineral Resources Science, Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, Colorado 80401, USA
3. U.S. Geological Survey, MS 963, P.O. Box 25046, Denver, Colorado 80225, USA