## 5 Results
### Minerals Identification from the HySpex Data  
According to the HySpex data processing model, the endmember spectral library is shown in Figure 14. The chlorite, sericite, calcite, biotite, tourmaline, quartz, magnetite, and pyrite were extracted from the HySpex images.  
Figure 12: The point spectra of the samples: (**a**) samples near high-grade iron ore and (**b**) samples near banded iron formations (BIFs).  
Figure 13: Scatter diagram of the wavelength positions near 2250 and 2350 nm extracted from the point spectra.  
Chlorite is a widespread alteration mineral in the Qidashan mining district, which manifests diagnostic absorptions around 2250 and 2350 nm [6,17]. Spectral absorption features ranging from 2245 to 2265 nm commonly result from Fe-OH vibration. Absorptions caused by Mg-OH vibration commonly occur in the 2330-2370 nm range [16]. The specific wavelength position of Fe-OH absorption feature varies with Fe and/or Mg content in octahedral sheet, i.e., Mg-rich chlorite is generally between 2245 and 2255 nm, whereas Fe-rich chlorite tends to be around 2265 nm. The Mg-OH wavelength for the pure chlorite rich in Mg is around 2330 nm and for Fe-rich chlorite is 2365 nm [24]. Some scholars believe that the OH absorption near 1400 nm is also positively correlated with the total Fe content in chlorite [17].  
White mica is characterized by a major Al-OH band near 2200 nm and a subordinate absorption band near 2340 nm. The observed wavelength of the Al-OH band covers a wide range from 2185 to 2225 nm. This wavelength range indicates a compositional variation from paragonitic (Al-rich and Na-bearing, with Al-OH band near 2190 nm) through muscovite (K-rich and Al-rich, Al-OH band at around 2200 nm) to phengitic (Al-poor and Mg-rich or Fe\({}^{2+}\)-rich, with Al-OH band \(>\) 2210 nm) [24,38]. The wavelength of the Al-OH absorption in the Qidashan HySpex data range from 2196 to 2205 nm, suggestive of muscovite affinity.  
Carbonate minerals mainly include calcite, magnesite, and dolomite. They can be distinguished by the absorption feature around 2300 nm. The vibration absorption band of CO\({}_{3}\)\({}^{2}\) in carbonate is located around 2340 nm for calcite, 2300 nm for magnesite, and 2320 nm for dolomite [39, 40, 41]. The main absorption band of biotite is the vibration of Mg-OH located around 2340 nm [16]. Tourmaline produces diagnostic absorptions at 2200 and 2360 nm, which are mainly caused by the Fe-OH and Mg-OH [6]. The spectrum of quartz is flat and no diagnostic absorption feature in SWIR except for OH and H\({}_{2}\)O; Magnetic and pyrite are opaque minerals that are known for low reflectivity and a few spectral features in the SWIR. Therefore, the VNIR data were used for mapping of these opaque minerals.  
Figure 15 shows the results of mineral mapping from the HySpex data. Samples near BIFs were Q-4, Q-12, and Q-13 and near high-grade iron ore were Q-2, Q-9, and Q-11. Q-9 is sercite quartz schist whose main minerals are quartz and sercite, accompanied by tourmaline veil  
Figure 14: The endmember spectral library for the short-wave infrared spectroscopy (SWIR) mineral mapping.  
are BIFs and high-grade iron ore, respectively. Except for magnetite, Q-2 is accompanied by strong chloritization and pyridization, whereas Q-12 is mainly composed of banded quartz and magnetite with a width of about 1 mm. Q-4, Q-11, and Q-13 contain both chlorite and quartz. Q-11 is mainly composed of chlorite with minor quartz and pyrite. Q-4 and Q-13 contain more quartz than chlorite, which belong to chlorite quartz schist. Moreover, Q-4 and Q-13 also contain small amounts of calcite and biotite. The Leica DM4P microscope was used to check the classification results (Figure 16).  
Figure 15: The result of hyperspectral mineral mapping: (**a**) the photo and mineral map of Q-2; (**b**) the photo and mineral map of Q-4; (**c**) the photo and mineral map of Q-9; (**d**) the photo and mineral map of Q-11; (**e**) the photo and mineral map of Q-12; (**f**) the photo and mineral map of Q-13.