1. Natural Resources Canada, Geological Survey of Canada, 601 Booth Street, Ottawa ON KJA OE8, Canada;
2. Natural Resources Canada, Geological Survey of Canada, 601 Booth Street, Ottawa ON KJA OE8, Canada; Minnesota Geological Survey, 2642 University Avenue West, St Paul, MN, 55114-1057, USA
3. Natural Resources Canada, Geological Survey of Canada (Atlantic), Box 1006, Dartmouth, B2 Y 4A2, Canada