Abstract
Research on wall rock alteration is of great importance to the understanding and exploration of ore deposits. The microscopic changes of the same mineral in different alteration zones can provide information about the migration and enrichment of ore-forming elements. In this paper, a typical profile of a high-grade iron ore body in Gongchangling iron deposit was investigated and sampled. The samples were checked by polarized microscopy, and alterations zonation were delineated according to the hydrothermal mineral assemblages and paragenesis. Moreover, hyperspectral images of wall rocks from each alteration zone were obtained by Norsk Elektro Optikk (NEO) HySpex-320 m imaging system. A customer Interactive Data Language (IDL) software package was used to process the images, and spectral features were extracted from the selected samples. The results indicate that spectral characteristics manifest obviously regular variations; i.e., from proximal to distal for the high-grade iron ore body, the wavelengths at ca. 1200 nm of chlorite and garnet, which accounts for most of the hydrothermal alteration minerals, become longer, and the absorption depths gradually smaller. The spectral features at 1200 nm of chlorite and garnet are always caused by the crystal field effect of Fe2+; therefore, the wavelength variations indicate the increase of Fe2+ and a reduced environment, which can provide more detailed information about the metallogeny and water–rock interaction. Since the hyperspectral features of the altered rocks can disclose unique mineralogical and structural information, the conventional classification of alteration zonation should be combined with the spectral feature, i.e., spectral alteration zonation, which is of great help to the understanding of the forming conditions of wall rock alteration and also the high-grade iron ore bodies.
Highlights
Hydrothermal alteration is a common phenomenon in mineral deposits, which is of great significance to the metallogenic stage analysis and mineral exploration [1]
Spectral alteration zoning proved to be a fast and effective method to indicate systematic changes in data extracted from mineralogical maps
The HySpex imaging hyperspectral data of Gongchangling high-grade ore in Anshan-Benxi 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
Summary
Hydrothermal alteration is a common phenomenon in mineral deposits, which is of great significance to the metallogenic stage analysis and mineral exploration [1]. The wall rock alterations have zoning characteristics, where the mineral assemblage can be used to recognize the mineralization characteristics and element migration rules [2]. The scope of the alteration far exceeds the size of the deposit, which reduces the scale of the exploration effectively [3]. Based on the observations in the field, the different alteration mineral assemblages and the ACF-AKF Sci. 2020, 10, 8369 occurring in nature can be seen [4], which can be used to infer the physicochemical conditions of the alteration reactions
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