## 4 Test Results and Interpretation
### Major SWIR Spectral Characteristics of Altered Minerals  
(1) SWIR spectral characteristics of muscovite (illite) type  
Muscovite minerals have two functional groups: OH + H\({}_{2}\)O and Al-OH. High-crystallinity muscovite can be classified into common muscovite, phengite, and sodium muscovite. After the illitization of muscovite, the composition of the muscovite will change to illite, phengite illite, and sodium muscovite illite. The primary differences are as follows: common muscovite has a sharp absorption peak at a wavelength of 2190 nm; phengite has a sharp absorption peak at the wavelength between 2214 and 2225 nm; and sodium muscovite has a sharp absorption peak at the wavelength between 2184 and 2190 nm. The spectral curves of muscovite and illite are consistent. Their absorption peak wavelength for crystalline water (Pos1400) was near 1400 nm. For the adsorbed water wavelength (Pos1900), it was near 1900 nm, and for the Al-OH wavelength (Pos2200), the peak was near 2200 nm (Figure 5). The depth of their absorption peak represents the maximum depth near the absorption peak in the standardized reflectivity spectrum (Dep1400, Dep1900, Dep2200). Given the prominent absorption peak of Pos1900 in muscovite found in the Jiawula lead-zinc mine, 1900 nm was chosen as the center of adsorbed water, with an extraction radius of 15. The absorption peak of Pos2200 in muscovite was relatively sharp but drifting towards longer wavelengths. Therefore, 2205 nm was chosen as the center for Al-OH, with an extraction radius of 15. The crystallinity of muscovites (ISM) is expressed as the ratio of Al-OH absorption depth (Dep2200) to the absorption feature depth of adsorbed water at 1900 nm (Dep1900). Now that we had extracted the characteristic absorption peaks, absorption depths, and crystallinity from the samples, we used scatter plots to analyze the parameters in a systematic and statistical way and determined that the variation range of muscovite (illite)-type Pos2200 in this mining area was between 2200.26 and 2212.72 nm, with an average value of 2206.49, and the range of ISM values was 0.058-3.193, with an average value of 0.96. (2) SWIR spectral characteristics of chlorite type  
The three primary types of chlorite minerals are Fe-Mg chlorite, Mg-chlorite and Fe-chlorite, and their main features are as follows: Mg-chlorite's absorption peak for adsorbed water is at the 1394 nm wavelength, its peak for crystalline water is between 1880 and 1980 nm (Pos1900), and its absorption peak for Fe-OH is 2245 nm (Pos2250). The Mg-OH  
Figure 4: Frequency distribution of altered minerals in the Jiawula deposit. absorption peak occurs at a 2325 nm wavelength (Pos2350), and a deeper absorption peak indicates more Mg-chlorite. Fe-Mg chlorite has an absorption peak of 1409 nm wavelength for adsorbed water, its wavelength for crystalline water is 2000 nm, its wavelength for Fe-OH is 2254 nm, and its wavelength for Mg-OH is 2347 nm. These wavelengths reflect typical features of Fe-Mg chlorite. Fe-chlorite's absorption peaks for crystalline water are between 1900 and 2000 nm; its absorption peak for Fe-OH is at 2261 nm (slightly shallower than the Mg-OH absorption peak), and the absorption peaks for Mg-OH are between 2355 and 2365 nm. A deeper absorption peak indicates more abundant Fe-chlorite in this area (Figure 5). Because of the steep absorption peak of Pos1900 in chlorite in the Jiawula lead-zinc mining area, 1900 nm was chosen as the center for adsorbed water, with an extraction radius of 15. Given the sharp absorption peak of Pos2250, 2250 nm became the center for Fe-OH, with a radius of 15. Due to the sharp absorption peak of Pos2350, 2350 nm was selected as the center for Mg-OH, with an extraction radius of 15.