Mineral Mapping Related to Porphyry Copper Deposits Using Aster and Sentinel- 2 Images with Field Studies (A Case Study of Sahib Divan Copper Deposit)

Introduction: The study area is located in the Alborz-Azerbaijan structural zone and on the 1:100,000 Lahrud sheet. In some areas, intrusive masses with a mixture of granodiorite and quartzdiorite of Oligocene age have penetrated into volcanic rocks and in the central parts around the village of Qarahgol and in the southwest of the region, in the Sahib Divan and Dust Biglo area, they are the cause of extensive hydrothermal (kaolinite), silicic and alunite alteration in Upper Eocene latite rocks. 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. In this study, given that the aim of exploring porphyry copper deposits is acidic to intermediate igneous rocks in which extensive argillic, phyllic and propylitic alteration has occurred, special attention has been paid to alunite, siliceous and iron oxide alteration.
Materials and Methods: In order to introduce training samples after geological investigations, 13 samples from Sahib Divan were analyzed by XRD method. Areas that represented the main alterations and their corresponding pixels in satellite images were selected as training samples for the basic spectrum methods. In the present study, MSI data sets of Aster and Sentinel-2A satellites from the 1:100,000 scale of Lahrud have been reviewed with a special focus on the Sahib Divan mine. The main objective of this study is to develop a new method, 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 from the deposit site and using it as training pixels). In the study area, MNF results were extracted from Aster and Sentinel 2A data and in the classification of the base spectrum and using the software spectral library and training samples from the altered areas, three minerals, kaolinite, muscovite and chlorite, were used as indicators for argillic, phyllic and propylitic alteration, respectively.
Results and Discussion: An interesting result obtained from this study was the highlighting of alteration in Aster images of the Sahib Divan mine, which indicated the simultaneous presence of argillic and phyllic alteration in the center and its enclosure by 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 features in the VNIR region and this sensor was more successful in identifying them. After obtaining geological information and conducting XRD studies, basic spectrum mineralogical mapping methods such as BE, LSU, CEM were used, among which, BE method provided the best result for isolating target pixels, especially for detecting different types of changes related to porphyry copper deposits. This was demonstrated using training pixels on Aster 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 isolating iron-bearing minerals such as hematite, jarosite and goethite, and using color combination, it was concluded that it showed the presence of hematite and jarosite simultaneously.
Conclusion: The results of the study of the intrusive masses of the 100,000 Lahrud sheet, silicic veins, and the spread of faults and deformations indicate that, in general, extensive alteration is significant in the central part (Salvat and Niaz Gholi-Moshiran) and southwestern part of the study area (Sahib Divan and Dust Biglo). The products obtained from the processing were compared with the published geological map of the study area, and it was shown that the resulting maps are consistent with the conceptual geological model of the porphyry copper deposit and the alterations are related to the host rock of this type of deposit.