Investigation of alteration zones associated with porphyry and epithermal mineralizations using remote sensing and fractal modelling in the Bostan Abad-Mianeh region, NW Iran

The aim of the present study is to utilize satellite image interpretation to identify hydrothermal alteration zones in the Bostan Abad-Mianeh region, north-western Iran. This region lies within the Alborz–Azerbaijan zone, one of the main host zones of Iranian porphyry and related deposits. The least square fitting (LS-Fit) method was used to interpret the images, leading to the detection of argillic, iron oxide, phyllic, propylitic and silicification alterations. To determine the intensity of the alterations, the concentration-perimeter (C-P) fractal model was applied. The results show that the maximum intensity of argillic and phyllic alterations in the study area is concentrated in the southern, and central and northern regions, respectively; for propylitic alteration in the northwestern, northern and southern parts; for iron oxide alteration in the northwestern, northeastern and southern sectors; and for silicification alteration in the southern, northern, and southwestern parts. Field observations and XRD results validated the alteration zones initially detected through remote sensing data interpretation. The results were evaluated and verified using the logratio matrix, confirming the robustness and reliability of the methodology. It was demonstrated that the C–P fractal and LS–Fit methods are capable of determining hydrothermal alteration zones with high potential in the study area.