Fig. 1. Samples of different grades

Fig. 2. The reflectance spectrums of hematite samples with different grades

Fig. 3. The linear correlation analysis of reflectivity and the grades of hematite

Fig. 4. The reflectivity variation of per unit grade of hematite with different grades in 350~2 500 nm band

Fig. 5. The linear fitting map of the slope in 1 000~1 250 nm and hematite grade

Fig. 6. The reflectance spectrums of magnetite amples with different grades

Fig. 7. The fitting map of the mean value of 350~2 500 nm reflectivity and magnetite grade