1. Wuguantun Coal Industry Co., Ltd, Datong 037034, China
2. School of Resources & Geosciences, China University of Mining & Technology, Xuzhou 221116, China
3. China Coal Huajin Group Co., Ltd. Wangjialing Coal Mine, Taiyuan 030001, China
4. School of Mines, China University of Mining & Technology, Xuzhou 221116, China