Processing and interpretation of ASTER TIR data for mapping of rare-metal-enriched albite granitoids in the Central Eastern Desert of Egypt

Regional Lithological Mapping Using ASTER-TIR Data: Preliminary Case Study for the Tibetan Plateau and the Surrounding Area

“…Not as strong but similar as the sulfates, K-feldspars and Na-feldspars exhibit opposite spectral features of quartz. If the rocks are rich in both quartz and feldspar, which often occurs in igneous rock, typically for the granitic rocks, QI is expected to be relatively low [15,17,19,30]. The spectral emissivity property of the rock type shown in Figure 3 (c) supports this expectation.…”

“…The mixture of quartz and feldspar does not generally occur in sedimentary rocks, which suggests high QI functions well as an indicator of quartz-rich sedimentary rocks. The previous studies have confirmed that high QI is a distinct indicator for quartz-rich sedimentary rocks [14][15][16][17][18][19][21][22][23]26,29,30], and low QI is a distinct indicator primarily of sulfate minerals [15][16][17]30] and secondary of feldspar-rich silicate rocks [15,17,19,30]. The spectral emissivity of carbonate rock which is composed of the two major carbonate forming minerals on Earth, calcite and dolomite, is shown in Figure 3 (a).…”

“…Prior studies have confirmed that a high CI signal is a good indicator for the presence of marine sedimentary rocks that are composed of calcite and / or dolomite [14][15][16][17][18][19]21,24,25]. It should be considered that the atmospheric anomalies like the clouds and the mists can also cause relatively high CI as discussed in section 4.1.…”

“…We can find the bodies denoting deep greenish color widely in the northern (> 33°N) part of the study area often interbedded within the high QI quartzose layers, which can be the sulfate layers accumulated in the neo-Tethys geological setting. Not as strong as sulfates, but feldspar-rich rocks typically a part of granitic rocks also show low QI [15,17,19]. The bodies around the lines "J" and the point "K" in the Gandise Mountains (annotated in Figure 2), as well as the bodies around the points "L", "M" and "N", are the examples of the rock type with dark bluish green color (Figures 4).…”

“…Especially, Quartz Index (QI), Carbonate Index (CI) and Mafic Index (MI) defined for the ASTER-TIR data are finely analyzed theoretically and practically, and the performance of the indices in extracting geological information is confirmed [14]. Many studies have applied the indices (e.g., [13][14][15][16][17][18][19]) and other workers have proved the usefulness and stability of the indices in the local geological case studies (e.g., [20][21][22][23][24][25][26][27][28][29]). Despite ASTER radiance registered at the sensor data without atmospheric corrections applied are adopted for the calculation of the indices, the recognized scene dependency is quite weak if the atmospherically well conditioning data are selected [17].…”