The study area that is part of Tarom volcano-plutonic zone which host many hydrothermal base metal deposits located in Zanjan, NW Iran. Understanding the tectonic events that can cause mineralization and hydrothermal alteration are significant factor in assessing the exploration potential of different structures. In this research, hydrothermal alteration such as Iron oxide, argillic, phyllic, and propylitic zones were determined by Spectral Angle Method (SAM) and also lineaments identified by high pass filters and hill-shade DEM techniques on Advanced Space borne Thermal Emission and Reflection Radiometer (ASTER) data. Field studies revealed most alteration and mineralization occurred in NE-SW fractures and control mineralization.
The use of satellite images for mineral exploration has been very successful in pointing out the presence of minerals such as alunite, pyrophyllite, kaolinite, sericite, illite, muscovite, smectite, and carbonate which are important in the identification of hydrothermal alterations [
Tarom area (
This area belongs to West-Central Alborz and lesser Caucasus hinterland [
This area has an active tectonics regim [
propylitic, silica, chlorite, alunitic, zeolite alteration zones have been identified. Zanjan province has a particular mineral resource position among the structural domains of Iran. All kinds of metamorphic basement rocks, ophiolites (ancient oceanic lithosphere), and magmatic arcs can be observed in this province.
As a result, various types of mineral resources exist in this territory, which have made this province a high- potential mineral resource domain in Iran [
The ASTER is an advanced optical sensor comprised of 14 spectral channels ranging from the visible to thermal infrared region. It will provide scientific and also practical data regarding various field related to the study of the earth [
To this end, at the beginning of the path, data set AST_L1B_010_8200745110108311331 in hierarchical data format (HDF) was used for this research and radiance correlation such as wavelength, dark subtract and log residual by ENVI4.4 software which is essential for multispectral images, were implemented.
By using of spectral angle mapper method alteration zones were determined. SAM method is a classification technique that permits rapid mapping by calculating the spectral similarity between the image spectrums to reference reflectance spectra. SAM measures the spectral similarity by calculating the angle between the two spectra, treating them as vectors in n-dimensional space [
Three mineral spectral representative of iron oxide include jarosite, hematite, goethite, three mineral spectral representative of argillic zone include kaolinite, dickite and halloysite, three minerals spectral representative of phyllic alteration consist of illite and muscovite and epidote representative of propylitic zone were selected (
Lineament extraction in this study is performed in Manual method. In manual extraction method, the lineaments are extracted from satellite image by using visual interpretation. The lineaments usually appear as straight lines or “edges” on the satellite images which in all cases contributed by the tonal differences within the surface material. The knowledge and the experience of the user is the key point in the identification of the lineaments particularly to connect broken segments into a longer lineament [
False color images are produced for manual lineament extraction because they increase the interpretability of the data. Different combinations of three bands are examined and the best visual quality is obtained with a false color image utilizing three 7, 4, and 2 (in blue, green and red respectively).
This false color combination made it easier to identify linear patterns of vegetation, geologic formation boundaries, river channels, geological weakness zones. Moreover, filtering operations are used to emphasize or deemphasize spatial frequency in the image. The filtering operation will sharpen the boundary that exists between adjacent units. Furthermore, standard GIS techniques have been carried out to help in the evaluation of the lineaments detected. Digital Elevation Model (DEM) has the advantage of representing the vertical extension of the earth's surface by assigning height values for every pixel [
Also, hill-shade DEM technique is effective in creating images that enhance geomorphologic features. Therefore, Hill-shades DEM with different azimuth direction and sun angle were used in this study (
To evaluate the ASTER satellite data, discriminate alteration zones and lineaments, field-checks have been verified. In almost all cases, our fieldwork confirmed in showing real alteration and detection of area of lineament by the interpreted remote sensing imagery. The field photographs of the hydrothermally altered rocks are shown in
The use of remote sensing data in the early stages of mineral exploration was very successful for recognition of
the hydrothermal alterations. Moreover, ASTER multi spectral images could be used for the identification of lineaments possibly related to faults. The performance of conventional image processing techniques has been evaluated on ASTER bands. Results show that the integration of the image processing techniques has great ability to detect iron oxide, argillic, phyllic and propylitic. Field checks also confirmed in showing real alteration and detection of area of lineament by the interpreted remote sensing imagery.
This work has funded by the Department of geology, Islamic Azad University, Science and Research branch, Tehran, Iran. Also, Special thanks to vice-president for research in Science and Research branch, Tehran. The authors are grateful to Shahram Rahmani, Exploration Department of Geological Survey of Iran for his sincere help and valuable discussions especially in field checks and interpretation of microscopic sections.