## 5 Results
### Mapping Absorption Features of Chlorite from the HySperx Data  
According to the HySperx data processing model, the wavelength position of OH, Fe-OH, and Mg-OH absorptions of chlorite were mapped. Figure 17 illustrates that there are obviously two kinds of chlorite, which have different absorption wavelengths of OH, Fe-OH, and Mg-OH. The absorption wavelengths of OH, Fe-OH, and Mg-OH related to high-grade ore (Q-2 and Q-11) are mostly between 1400 and 1410, 2260 and 2265, and 2360 and 2370, nm, respectively, whereas those related to BIFs (Q-4 and Q-13) are between 1390 and 1400, 2245 and 2255, and 2330 and 2350 nm. This result is consistent with the result of ASD spectrometer.  
Figure 16: Photomicrographs of the samples (plane-polarized light): (**a**) the photomicrograph of Q-2; (**b**) the photomicrograph of Q-4; (**c**) the photomicrograph of Q-9; (**d**) the photomicrograph of Q-11; (**e**) the photomicrograph of Q-12; (**f**) the photomicrograph of Q-13.  
In order to verify the results of the spectral analysis, the chlorite in the Q-2, Q-11, Q-4, and Q-13 was analyzed by EPMA (Table 1). Note that when Na\({}_{2}\)O \(>\) 1.0%, CaO \(>\) 0.5%, or K\({}_{2}\)O \(>\) 0.5%, data were discarded as they suggested severe contamination by adjacent minerals. The structural formula of chlorite was calculated based on 28 oxygen atoms (Table 2). The distribution of the corresponding wavelengths and the cations in the octahedral sheet of chlorite are summarized in Figure 18.  
Figure 18 illustrates that there are obviously two types of chlorites (Figure 18a): the wavelengths of OH, Fe-OH, and Mg-OH of chlorite related to high-grade iron ore (Q-2 and Q-11) are located at 1405-1410, 2260-2265, and 2360-2370 nm, respectively, whereas the corresponding wavelengths related to BIFs (Q-4 and Q-13) are all shorter. On the other hand, similar conclusions can be drawn from the molecular formula of the chlorite: the Fe content in Q-2 and Q-11 is higher than that in Q-4 and Q-13, whereas the Mg is just the opposite (Figure 18b). The AlVI in these two samples are approximately equal.  
The absorption depth is also one of the spectral features. The absorption depths of OH, Fe-OH, and Mg-OH bands of chlorite in Q-11 and Q-13 are illustrated in Figure 19. In comparison with the wavelength, there is no obvious difference between the absorption depths of these samples.  
Figure 17: Results of the absorption wavelength position mapping of chlorite: (**a**) mineral map; (**b**) wavelength of OH; (**c**) wavelength of Fe-OH; (**d**) wavelength of Mg-OH.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Comment** & **K\({}_{2}\)O** & **Na\({}_{2}\)O** & **SiO\({}_{2}\)** & **TiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **FeO** & **MgO** & **MnO** & **CaO** & **Cl** & **P\({}_{2}\)O\({}_{5}\)** & **Total** \\ \hline Q-2-01 & 0.01 & 0.01 & 22.39 & 0.05 & 19.16 & 35.87 & 6.60  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \hline
**Comment** & **Si** & **AI\({}^{\text{IV}}\)** & **AI\({}^{\text{VI}}\)** & **Ti** & **Fe\({}^{\text{3+}}\)** & **Fe\({}^{\text{2+}}\)** & **Mn** & **Mg** & **Ca** &  
Figure 19: Results of the absorption depth of chlorite: (**a**) mineral map; (**b**) absorption depth of OH; (**c**) absorption depth of Fe-OH; (**d**) absorption depth of Mg-OH.  
Figure 18: Scatter diagrams of the wavelength and molecular formula of chlorite: (**a**) scatter diagram of OH, Fe-OH, and Mg-OH bands and (**b**) scatter diagram of Mg, Fe, and AlVI cations; the data have been normalized.