La méthode d'analyse en composantes principales est utilisée couramment pour la cartographie des altérations dans les provinces métallogéniques. Trois techniques d'analyse en composantes principales sont utilisées pour la cartographie des altérations autour d'intrusions porphyriques dans la zone de Meiduk: la méthode sélective, la méthode sélective développée ou Crosta et la méthode standard. Dans cette étude, on compare les résultats de l'application de ces trois techniques différentes sur les bandes Landsat TM. La comparaison est basée principalement sur l'analyse visuelle et les observations des résultats sur le terrain. L'analyse en composantes principales sélective utilisant les bandes 5 et 7 de TM est la plus adéquate pour la cartographie des altérations. Toutefois, les zones végétales sont aussi mises en évidence dans l'image PC2. L'application de la méthode sélective développée sur les bandes 1, 4, 5 et 7 de TM pour la cartographie des hydroxyles met en évidence des halos d'altération autour des intrusions, mais son application à la cartographie des oxydes de fer permet de distinguer une zone étendue avec lithologie sédimentaire. La méthode d'analyse en composantes principales standard par contre permet de rehausser les altérations dans l'image PC5, mais elle est laborieuse en termes de temps machine. La cartographie des hydroxyles utilisant la technique sélective développée ou Crosta est plus appropriée pour la cartographie des altérations autour des masses intrusives porphyriques.

The visible–near infrared (VNIR) and short wave infrared (SWIR) spectral bands of both the level 1B, radiance at sensor, and level 2, AST_07 surface reflectance data products of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument were evaluated and compared for mapping the alteration zones around porphyry copper deposits and occurrences at the northern Shahr‐e‐Babak, SE Iran. The level 1B data were converted to reflectance using internal average relative reflectance (IARR) method whereas the AST_07 dataset was processed as delivered. The porphyry copper mineralization occurs in Eocene, andesitic and basaltic rocks with zonal alteration patterns that are concentric and almost symmetrically arranged. The spectral signatures of alteration index minerals collected from field samples and the United States Geological Survey (USGS) spectral reference library, were considered in directed principal component analysis (DPCA) and spectral angle mapping (SAM) algorithms. Carrying out the DPCA method on three spectral bands enhanced the alteration haloes in the last principal component (PC) images. Generating RGB colour composite images using these PC images differentiated three alteration zones from the host rocks. The SAM results of the IARR calibrated dataset discriminated the propylitic, argillic and phyllic alteration zones. It is concluded that the higher spectral resolution of ASTER instrument is effective for mineral mapping. However, the method of conversion from radiance to reflectance is critical to the validity of the outputs and that the pseudo‐reflectance method using the IARR process may be more reliable than the standard reflectance product.

This paper is an attempt to introduce the role of earth observation technology and a type of digital earth processing in mineral resources exploration and assessment. The sub-pixel distribution and quantity of alteration minerals were mapped using linear spectral unmixing (LSU) and mixture tuned matched filtering (MTMF) algorithms in the Sarduiyeh area, SE Kerman, Iran, using the visible-near infrared (VNIR) and short wave infrared (SWIR) bands of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument and the results were compared to evaluate the efficiency of methods. Three groups of alteration minerals were identified: (1) pyrophylite-alunite (2) sericite-kaolinite, and (3) chlorite-calcite-epidote. Results showed that high abundances within pixels were successfully corresponded to the alteration zones. In addition, a number of unreported altered areas were identified. Field observations and X-ray diffraction (XRD) analysis of field samples confirmed the dominant mineral phases identified remotely. Results of LSU and MTMF were generally similar with overall accuracy of 82.9 and 90.24%, respectively. It is concluded that LSU and MTMF are suitable for sub-pixel mapping of alteration minerals and when the purpose is identification of particular targets, rather than all the elements in the scene, the MTMF algorithm could be proposed.