Mapping the porphyry copper alteration zones at the Meiduk area, SE Iran, using the advanced spaceborne thermal emission and reflection radiometer (ASTER) data

The SWIR spectral bands of the AST_07 and IAR calibrated datasets of ASTER instrument were evaluated and compared for mapping the alteration zones around porphyry copper deposits and occurrences at Meiduk area, SE Iran. The porphyry copper deposits are hosted by the Eocene andesitic and basaltic rocks and the zonal alteration patterns are concentric and almost symmetrically arranged. The field sample spectra as well as spectra from USGS library were applied for determining the absorption bands of each mineral at the spectral range of ASTER. The Spectral signatures of index minerals in phyllic, propylitic and argillic alteration zones were considered in directed principal component analysis (DPCA) and Spectral Angle Mapping (SAM) algorithms. Carrying out selective or directed PCA method on four and three spectral bands enhanced the alteration haloes in the last PC images. Generating R-G-B color composite image using the end member PC images differentiated three alteration zones from the host rocks. Spectral Angel Mapping algorithm was implemented on SWIR AST_07 and IAR calibrated datasets using both the field and USGS spectra for index minerals of alteration zones. The SAM results of IAR calibrated dataset revealed that it is possible to delineate the propylitic, argillic and phyllic alteration zones validated by the field evidences, while the AST_07 dataset does not map the similar alteration zones. It is concluded that although the higher spectral resolution of ASTER instrument is effective for mineral mapping, the degree of data calibration is critical for validity of the outputs.