Document Type : علمی - پژوهشی
Authors
1 Department of Geology, Faculty of Science, University of Mohaghegh Ardabili, Ardabil, Iran
2 Graduated student of M.Sc. Department of Geology, Faculty of Science, University of Mohaghegh Ardabili, Ardabil, Iran
3 Department of Geology, Faculty of Science, University of Mohaghegh Ardabili
Abstract
The studied area is located in the structural zone of Alborz-Azerbaijan and on the sheet 1:100000 of Lahrud. In some areas, intrusive bodies with a combination of granodiorite and quartzdiorite with Oligocene age have penetrated into the volcanic rocks, and in the central parts around the village of Qaragol and in the southwest of the region, in the area of Sahib Divan and Doust Biglo, they are the agent of extensive hydrothermal alteration (kaolinite), siliceous and alunite in upper Eocene latitic rocks. In order to introduce training samples after geological surveys, 13 samples from the Sahib Divan analyzed by XRD method. The areas that were representative of the major alterations and the pixels corresponding to them in satellite images were selected as training samples for the base spectrum methods. In the study area, the MNF results were extracted from Aster and sentinel 2A data and used in the classification of the base spectrum and using the software spectral library and training samples from the altered areas of the three minerals kaolinite, muscovite and chlorite respectively was used as indicators for argillic, phyllic and propylitic alteration. The interesting result obtained from this research was highlighting the alteration in the images of the Aster of Sahib Divan mine, which indicated the simultaneous presence of argillic and phyllic alteration in the center and its enclosure with propylitic alteration, which is consistent with the conventional pattern of porphyry deposits. Also, the analysis of Sentinel images showed that hematite, jarosite, goethite and limonite show strong absorption characteristics in the VNIR region and this sensor has been more successful in identifying them. The resulting products were also compared with the published geological map of the studied area and the findings have shown that the resulting maps support the conceptual geological model in the porphyry copper deposit.In the present study, the Aster and Sentinel-2A MSI datasets from the 1:100,000 sheet of Lahrud have been examined with a special attitude to Sahib Divan mine. The main goal of this study is to create a new method by considering remote sensing data, especially Aster and Sentinel 2, in identifying alterations associated with porphyry copper deposits. This identification was based on two approaches: identification of hydrothermal alteration zones associated with porphyry copper deposits (through spectral library) and direct identification of alteration zones and copper-bearing minerals (through direct sampling of the deposit site and using it as a training pixel). In this research, taking into account that the purpose of exploring porphyry copper deposits, acidic to intermediate igneous rocks in which extensive argillic, phyllic, and propylitic alteration had occurred, special attention was paid to alunitic, silicic, and iron oxide alteration. Recent technological advances in the field of spectral/spatial resolution of satellite data in classification algorithms have created interesting opportunities and solutions for geological mapping. Therefore, after taking the geology and conducting XRD studies, base spectrum mineralogical mapping methods such as BE, LSU, CEM were used, among which the BE method gave the best result for separating the target pixels, especially for detecting different types of changes related to porphyry copper deposits. It was shown using training pixels on Aster's images. Although Sentinel images did not achieve satisfactory results for clay minerals due to low spectral resolution in the short infrared range, they were favorable for separating iron-containing minerals such as hematite, jarosite, and goethite, and by using a color combination, it was concluded that it shows the presence of hematite and jarosite at the same time. The results of the investigation of the intrusive masses of the 100000 sheet of Lahrud, siliceous veins and the spread of faults and deformations show that, in general, the extensive altreation in the central part (Salavat and Niaz Qoli-Mashiran) and the southwest of the study area (Saheb Divan and Dust Biglo) is significant. The products obtained from the processing were compared with the published geological map of the studied area and it was shown that the resulting maps correspond to the conceptual geological model of the porphyry copper deposit and the alterations are related to the host rock of this type of deposit.
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