Distribution and modes of occurrence of U and Th in oil shale

The concentrations and modes of occurrence of U and Th in 23 oil shale samples from China were studied. The concentrations of U and Th were determined by inductively coupled plasma-mass spectrometry. The occurrence of U and Th in Huadian and Luozigou oil shale was investigated using six-step sequential chemical extract method. The concentrations of U in oil shale are within 10×10^-6 and average of 3.92×10^-6. The concentrations of Th in oil shale are within 20×10^-6 and average of 10.51×10^-6. The abundances of U and Th in oil shale are slightly higher than in crust and close to sedimentary rocks. The experimental results of floating and sinking roughly equal that of the sequential chemical extraction in U and Th. The U and Th in oil shale are mainly existed in minerals.