## 6 Conclusions  
Spectral alteration zoning proved to be a fast and effective method to indicate systematic changes in data extracted from mineralogical maps. The same mineral composition changes to some degree, and this method can easily identify the microscopic mineral differences between the alteration rocks with the same or similar mineral assemblages. In this paper, the HySpex imaging hyperspectral data of Gongchangling high-grade ore in Anshan-Benzi area were used for mineral identification and spectral alteration zoning, and the following conclusions are drawn:  
1. The microscopic observation and hyperspectral mineral identification indicate that the main minerals in the altered rocks of Gongchangling high-grade ore are garnet, chlorite, quartz and magnetite. According to the type, content and paragenesis of hydrothermal minerals, the alteration type can be divided into three alteration zones: the chlorite-garnet zone, the garnet-chlorite zone and the chlorite zone.  
2. The wavelength positions of characteristic altered minerals in the altered wall rocks shift significantly. The absorption depth of chlorite and garnet increases from proximal to distal to the high-grade iron ore body. It is indicated that with the gradual decrease in the content of Fe\({}^{2+}\), there is a change in the water-rock interaction and the relatively reductive environment of the formation for whole alteration rock. This rule can be used as an exploration rule of similar rich iron ore bodies in the future.  
3. Since the spectral features of some specific minerals can manifest special mineralogical, compositional or crystal information, the convectional alteration zonation combined with the hyperspectral features of particular minerals can provide more detailed metallogenetic information; thus, the nomenclature of spectral alteration zonation is promoted in this paper. As for Gongchangling high-grade iron ore, three spectral alteration zones were allocated, i.e., the proximal short-wavelength large depth chlorite-garnet zone, the transitional garnet-chlorite zone and the distal long-wavelength small depth of chlorite zone.  
4. Using the regular changes of the spectral characteristics of Fe\({}^{2+}\) at 1200 nm as the basis for zonation, we proposed a new concept of spectral alteration zonation, which could obtain more information concerning mineralization. The method of spectral alteration zoning mainly studies information of altered minerals, such as texture, composition and crystal coordination, to reveal the genesis of ore deposits, which is suitable not only for iron ore deposits but also for hydrothermal deposits developed by other altered rocks.  
Conceptualization and writing--original draft preparation, K.S.; Writing--review and editing and supervision, E.W.; methodology and software, Y.Y. and J.F.; validation, X.Y. and D.H. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key Research and Development Program of China (grant 2016 YFC0801603).  
We thank DiMap for access to the HySpex instruments used in the PSML, and we are also deeply indebted to the Gongchangling iron deposit, Anshan Iron and Steel Group, for their kind help in field investigation and sampling.  
The authors declare no conflict of interest.