1. The University of Texas at Austin, John A. and Katherine G. Jackson School of Geosciences, Bureau of Economic Geology, University Station, Box X, Austin, Texas 78713-8924, USA.(corresponding author); .
2. Zhejiang University, School of Earth Sciences, Hangzhou 310027, China..
3. Chengdu University of Technology, College of Geophysics, Dongsanlu, Erxianqiao, Chengdu 610059, China..