Synergetic use of the Sentinel-2, ASTER, and Landsat-8 data for hydrothermal alteration and iron oxide minerals mapping in a mine scale

Abstract

Many of the known Tertiary porphyry Cu deposits (PCDs) are situated in the Central Iranian Volcanic Belt (CIVB). The study area is located in the southern part of the CIVB and southern part of the Kerman Cenozoic magmatic arc. This research highlights the significance of the synergetic use of operational land imager aboard the Landsat-8 (OLI), Sentinel-2, and advanced space-borne thermal emission and reflection radiometer (ASTER) data for exploration of copper mineralization in a mine scale. Multispectral images in the visible and near infrared bands of (0.451.0 μm) the OLI and Sentinel-2 were used to identify the gossan zones. ASTER short wave infrared (SWIR) data with the wavelength between 1.65 and 2.43 μm were used for mapping hydrothermal alteration zones. Laboratory spectra obtained from minerals such as muscovite and illite (phyllic alteration), kaolinite and montmorillonite (argillic alteration), epidote and chlorite (propylitic alteration) were applied in mixture tuned matched filtering (MTMF) algorithm on the ASTER data to enhance the existence of these minerals. The spectra of the index minerals from each alteration type were used in this algorithm and the abundances of minerals in the MTMF image were rescaled to be within the ranges of 34-54 %, 54-74 % and 74-100 %. The studied mineralized zone is associated with the iron rich phyllic and argillic hydrothermal alteration types which can be best detected by using integrated ASTER, OLI, and Sentinel-2 images. The diamond drill cores data also indicate that copper is more enriched below the gossan zones. The gossan index minerals (GIM) including goethite, jarosite, and hematite were identified by X-ray diffraction (XRD) method, spectral analyses, and petrographic examinations. The Sentinel -2 data proved to provide remarkably better mapping result for iron oxide minerals than the OLI and ASTER data. The directed principal component analysis (DPCA) method, In the data of the Landsat-8 and Sentinel2 were used for mapping of the gossan index minerals such as goethite, jarosite and hematite and the argillic, phyllic and propylitic hydrothermal alteration types were enhanced using the MTMF methods. The hydrothermal alteration pattern and the distribution of the gossans in the study area show a porphyry-type mineralization. This study showed that the synergetic use of different satellite images with different spatial and spectral resolutions can be used for mineral exploration in a large scale. The use of laboratory spectra obtained from hydrothermal alteration minerals in MTMF method depicts that the alteration minerals were mapped more accurately relative to those MTMF images that are derived from standard spectral libraries. The samples collected from the surficial hydrothermal alteration zones as well as diamond drill cores showed that the copper mineralization occurres mainly along the border of the phyllic and argillic alteration zones, and the magnetite mineralization in the propylitic zone. ARTICLE INFO