6
thermal infrared wavelength ranges (Geng Zhang et al.,
2024).
The Spectral Angle Mapper (SAM) is a tool that per-
mits rapid mapping of the spectral similarity of image spec-
tra to reference spectra. The reference spectra can be either
laboratory or field spectra or extracted from the image. The
algorithm determines the spectral similarity between two
spectra by calculating the “angle” between the two spec-
tra, treating them as vectors in a space with dimensionality
equal to the number of bands (nb) (Kruse et al., 1993).
Based on selected spectral signatures of precise rocks and
minerals from the spectral library of the United States
Geological Survey (USGS) (Figure 5), which allowed to
corroborate the areas of interest defined with the previ-
ous spectral techniques, in addition to better zonating the
hydrothermal alteration halos, based on the mineralogi-
cal assemblages proposed by El-Desoky et al. (2021) and
the metallogenic environment of the study area. With this
base, a map of zones with mineralogical assemblages typi-
cal of hydrothermal alterations is obtained according to the
metallogenic environment.
RESULTS AND DISCUSSIONS
RGB Band Combination Analysis
Color composites provide images with different color
tones that both highlight the structural characteristics
and match the unique spectral characteristics of the rock
compositions being studied. For the present research, the
combination of RGB 943 bands (Figure 6a) was used to
determine with greater precision the areas with concentra-
tion of oxides, which are presented in yellow coloration
or yellowish associations, extending a main area from the
Chilca population center to the NE to the Siete Vueltas
population center, another in the surroundings of the
Rambra and Limbe population centers and the last one,
between the population centers Suso and Sapuc. The
combination of RGB 461 bands (Figure 6b) was used to
identify clay minerals and oxides, areas with clays are dif-
ferentiated by purple-colored, which extending over most
Figure 5. USGS laboratory reflectance spectra (Clark, 1999)
of SWIR bands of ASTER
Figure 6. ASTER Band combination (a) RGB 943 -oxides concentration (b) RGB 461 – clays and oxides concentration
thermal infrared wavelength ranges (Geng Zhang et al.,
2024).
The Spectral Angle Mapper (SAM) is a tool that per-
mits rapid mapping of the spectral similarity of image spec-
tra to reference spectra. The reference spectra can be either
laboratory or field spectra or extracted from the image. The
algorithm determines the spectral similarity between two
spectra by calculating the “angle” between the two spec-
tra, treating them as vectors in a space with dimensionality
equal to the number of bands (nb) (Kruse et al., 1993).
Based on selected spectral signatures of precise rocks and
minerals from the spectral library of the United States
Geological Survey (USGS) (Figure 5), which allowed to
corroborate the areas of interest defined with the previ-
ous spectral techniques, in addition to better zonating the
hydrothermal alteration halos, based on the mineralogi-
cal assemblages proposed by El-Desoky et al. (2021) and
the metallogenic environment of the study area. With this
base, a map of zones with mineralogical assemblages typi-
cal of hydrothermal alterations is obtained according to the
metallogenic environment.
RESULTS AND DISCUSSIONS
RGB Band Combination Analysis
Color composites provide images with different color
tones that both highlight the structural characteristics
and match the unique spectral characteristics of the rock
compositions being studied. For the present research, the
combination of RGB 943 bands (Figure 6a) was used to
determine with greater precision the areas with concentra-
tion of oxides, which are presented in yellow coloration
or yellowish associations, extending a main area from the
Chilca population center to the NE to the Siete Vueltas
population center, another in the surroundings of the
Rambra and Limbe population centers and the last one,
between the population centers Suso and Sapuc. The
combination of RGB 461 bands (Figure 6b) was used to
identify clay minerals and oxides, areas with clays are dif-
ferentiated by purple-colored, which extending over most
Figure 5. USGS laboratory reflectance spectra (Clark, 1999)
of SWIR bands of ASTER
Figure 6. ASTER Band combination (a) RGB 943 -oxides concentration (b) RGB 461 – clays and oxides concentration