ASTER-based alteration mapping and structural analysis of the Saheb Divan hydrothermal system, NW Iran: Implications for exploration programs

Abstract

The Saheb Divan area, situated within the Arasbaran metallogenic belt in northwest Iran, exhibits extensive hydrothermal alterations indicative of potential porphyry Cu-Mo-Au mineralization. This study integrates remote sensing on Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite data and field-based investigations to map alteration zones and structural lineaments. A comprehensive set of image processing techniques, including False Color Composite (FCC), Band Ratio (BR), Minimum Noise Fraction (MNF), Least Squares Fit (LS-Fit), and Spectral Feature Fitting (SFF), was applied to ASTER Visible and Near Infrared (VNIR) and Short Wavelength Infrared (SWIR) bands to detect key alteration minerals and delineate alteration zones.

Among these techniques, SFF emerged as the most effective method, providing high accuracy in mapping phyllic, argillic, advanced argillic, and silicification zones. SFF achieved detection accuracies of 90 % for argillic and 88 % for advanced argillic alterations, outperforming LS-Fit (85 % and 80 %). For phyllic zones, both methods showed comparable accuracy (SFF: 86 %, LS-Fit: 84 %), while LS-Fit performed better in iron oxide-bearing zones (78 % vs. 70 % for SFF). For propylitic zones, SFF had a slight advantage (82 % vs. 78 %), demonstrating its strength in capturing detailed spectral features. The combination of these techniques facilitated the identification of alteration zones, with validation achieved through fieldwork and X-ray diffraction (XRD) analysis. These analyses confirmed distinct mineral assemblages: sericite, illite, kaolinite, alunite, chlorite, and quartz associated with phyllic, argillic, and advanced argillic alterations, respectively. The final integrated map revealed three major alteration zones: a large western zone, a medium-sized central zone, and a smaller southeastern zone. These zones displayed overlapping phyllic and advanced argillic alterations with peripheral propylitic halos, indicative of potential porphyry systems. The western zone, characterized by intense alteration, was identified as the highest-priority target for exploration drilling. Field observations further highlighted the role of structural controls, with faults acting as conduits for hydrothermal fluid circulation.

This study highlights the efficiency of ASTER-based techniques, especially SFF and LS-Fit, in detecting hydrothermal alteration zones by a quantitative comparison approach. By integrating remote sensing with laboratory analyses, the research provides a comprehensive framework for reducing exploration costs and enhancing targeting precision in challenging terrains. The findings underscore the potential for porphyry mineralization in the Saheb Divan area and offer valuable insights for future exploration programs.