Determination of Hydrothermal Alteration Zones Using Remote Sensing Methods in Tirka Area, Toroud, NE Iran

Abstract

The aim of current study is the identification of hydrothermal alteration by remote sensing methods in Tirka area, NE Iran. The field of study with area about 13 km2 (scale: 1:20,000) is part of the Toroud–Chahshirin magmatic belt, which is located in central Iran structural zone. Hydrothermal alteration zones are interpreted based on Advanced Spaceborne Thermal Emission and Reflection Radiometer remote sensing data. In the first stage, atmospheric, topographic and geometric corrections were performed on satellite imagery. Then, different image interpretation techniques consisting of band ratio, principal component analysis, minimum noise fraction, least squares fitting (LS-Fit), spectral angle mapper and spectral feature fitting (SFF) methods were used. Therefore, VNIR bands for iron oxide alteration, SWIR bands for argillic, phyllic and propylitic alterations, and TIR bands for silicification were applied. The results showed iron oxide and propylitic alterations occurred at the SW and the argillic and phyllic alteration zones were existed in the northern and SE parts of the area. Silicification happened sporadically in the region. Lineaments were processed by false color composite, high-pass filters and hill-shade digital elevation model methods, and two NW–SE and NE–SW major trends were revealed. Field observation and laboratory analysis were used for accuracy of satellite studies. Finally, alteration and lineament maps were integrated for the recognition of high-potential mineralization. Petrographic studies showed that SFF and LS-Fit methods are more reliable than other techniques for the determination of hydrothermal alterations.