1. 1 Department of Earth Resources Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
2. 2 Geological Survey of Tanzania (GST), P.O. Box 903, Kikuyu Avenue, Dodoma, Tanzania
3. 3 Department of Earth and Environmental Sciences, Botswana International University of Science and Technology (BIUST), Palapye, Botswana
4. 4 Geological Survey of Japan, Advanced Industrial Science and Technology (AIST), Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan