Abstract
Polymetallic vein-type ores are important sources of precious metal and a principal type of orebody for various base-metals. In this research, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) remote sensing data were used for mapping hydrothermal alteration zones associated with epithermal polymetallic vein-type mineralization in the Toroud–Chahshirin Magmatic Belt (TCMB), North of Iran. The TCMB is the largest known goldfield and base metals province in the central-north of Iran. Propylitic, phyllic, argillic, and advanced argillic alteration and silicification zones are typically associated with Au-Cu, Ag, and/or Pb-Zn mineralization in the TCMB. Specialized image processing techniques, namely Selective Principal Component Analysis (SPCA), Band Ratio Matrix Transformation (BRMT), Spectral Angle Mapper (SAM) and Mixture Tuned Matched Filtering (MTMF) were implemented and compared to map hydrothermal alteration minerals at the pixel and sub-pixel levels. Subtle differences between altered and non-altered rocks and hydrothermal alteration mineral assemblages were detected and mapped in the study area. The SPCA and BRMT spectral transformation algorithms discriminated the propylitic, phyllic, argillic and advanced argillic alteration and silicification zones as well as lithological units. The SAM and MTMF spectral mapping algorithms detected spectrally dominated mineral groups such as muscovite/montmorillonite/illite, hematite/jarosite, and chlorite/epidote/calcite mineral assemblages, systematically. Comprehensive fieldwork and laboratory analysis, including X-ray diffraction (XRD), petrographic study, and spectroscopy were conducted in the study area for verifying the remote sensing outputs. Results indicate several high potential zones of epithermal polymetallic vein-type mineralization in the northeastern and southwestern parts of the study area, which can be considered for future systematic exploration programs. The approach used in this research has great implications for the exploration of epithermal polymetallic vein-type mineralization in other base metals provinces in Iran and semi-arid regions around the world.
Highlights
Since the Bronze Age, polymetallic vein-type ores have been important sources of precious metal and established a main type of deposit for various base-metals [1,2,3,4,5]
The main objectives of this study are (i) to detect hydrothermal alteration mineral zones and assemblages using VNIR and SWIR spectral bands of ASTER data by application of specialized image processing techniques, including Selective Principal Component Analysis (SPCA) [36,37], Band Ratio Matrix Transformation (BRMT) [16], Spectral Angle Mapper (SAM) [38], and Mixture Tuned Matched Filtering (MTMF) [39,40,41]; (ii) to compare the results derived from SPCA and BRMT transformation algorithms and SAM and MTMF spectral mapping algorithms to map alteration minerals at the pixel and sub-pixel levels and (iii) to prospect high potential zones of epithermal Cu-Au mineralization for future systematic exploration programs in the study area
The image processing algorithms implemented in this analysis, including the SPCA, BRMT, SAM, and MTMF provided a consistent way to identify and map hydrothermal alteration zones in the study area
Summary
Since the Bronze Age, polymetallic vein-type ores have been important sources of precious metal and established a main type of deposit for various base-metals [1,2,3,4,5]. The presence of intrusive rocks and hydrothermal alteration zones associated with polymetallic vein-type deposits provide an important guide for exploring this type of ore mineralization especially by the application of advanced satellite remote sensing data [8,9]. ASTER datasets can be used to identify and remotely map hydrothermal alteration zones associated with polymetallic vein-type ore deposits in vegetated regions and well-exposed terrain, especially in a semi-arid environment [8,9,17]. Mahanta and Maiti [8] used ASTER VNIR+SWIR spectral data for mapping alteration zones such as kaolinization, ferruginization, silicification, phosphatization, and sulphidation associated with the polymetallic vein-type mineralization in the South Purulia Shear Zone (SPSZ), East India. Ahmadirouhani et al [9] identified and mapped hydrothermal alteration zones, including propylitic, phyllic, argillic, and gossan with Cu-Fe-Au vein-type mineralization using ASTER VNIR+SWIR spectral bands in the Bajestan region, northern sector of the Lut Block, East Iran
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