1. Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences , Langfang, Hebei 065000 , China
2. Laboratory of Geophysical EM Probing Technologies , Ministry of Natural Resources, Langfang, Hebei 065000 , China
3. Qinghai No. 3 Geological and Mineral Exploration Institute , Qinghai Provincial Bureau of Geology and Mineral Resources, Xining, Qinghai 810008 , China