s.s. ghannadpour

The Zafarghand area is located as a porphyry Cu deposit in the northeast of Isfahan and the southeast of Ardestan, which is a part of the Iran-Central structural zone; More precisely, it is located in the Urmia-Dokhtar volcanic belt. In the porphyry Cu deposits exploration, identifying and determining the alteration zones is of special importance. The aim of the present study is to identify and highlight the alteration zones of Zafarghand area, with the help of fractal geometry in the processing of ASTER sensor satellite images. Accordingly, considering the raster nature and digital form of satellite images, the digital number values of each pixel from the image matrices were considered as samples in a systematic network. Finally, the algorithm of the Concentration-Area (C-A) fractal model was implemented as an efficient method for determining anomaly samples in the set of digital number (DN) values of ASTER satellite image pixels. The alteration zones identified with the help of the aforementioned technique based on their expansion in the region represent the very effective performance of this method. So that, especially in the case of phyllic and propylitic alterations, there is a very high correspondence between the results of satellite image processing and the spread of alterations in field studies. The non-identification of potassic and argillic alterations in the obtained results is also directly related to their limited expansion in the study area. Finally, it could be acknowledged that the application of the fractal C-A method (considering its structural nature) in decision-making has been successful and has proven to be very effective in determining the alteration zones in the Zafarghand area.

Separation and mapping of alteration zones is of special importance in the exploration of porphyry copper types. In order to highlight these alteration zones, remote sensing techniques have been applied. Zafarghand region is located in the southeast of Ardestan and northeast of Isfahan. Based on the division of geological structural zones, it is located in the Central Iran zone and also in the middle part of Urmia-Dokhtar magmatic volcanic arc. In this area, there are different alteration halos, including phyllic, potassic, propylitic, argillic, and slightly siliceous. In this study, argillic, phyllic, propylitic, and clay alterations have been identified using ASTER sensor images. Moreover, LANDSAT 8 images have been employed to identify clay and iron oxide alterations. In this regard, after performing the necessary pre-processing, methods of False Color Combination (FCC), Band Ratio (BR), Least Squares-Fit (LS-Fit), Matched Filtering (MF), and Principal Combination Analysis (PCA) were applied to reveal the zones containing these alterations. Among the applied methods, the LS-Fit and MF in Aster images, as well as the BR method in both images, and the PCA method in Landsat 8 have brought good results.