Hydrothermally altered mineral mapping using synthetic application of Sentinel-2A MSI, ASTER and Hyperion data in the Duolong area, Tibetan Plateau, China

Abstract

The Duolong area is in a strong potential copper mineralization zone associated with felsic intrusions, and several porphyry copper deposits (PCDs) have been identified. The PCDs are characterized by hydrothermal alteration zones. In this study, Sentinel-2A MultiSpectral Instrument (MSI), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and Hyperion data are combined to map hydrothermally altered minerals. Three temporal Sentinel-2A MSI images are processed by integrating the Crosta technique and the anomaly-overlaying selection method to map iron oxides and hydroxyl-bearing minerals. These approaches are implemented to omit interference-induced false anomalies. The six shortwave infrared (SWIR) bands of ASTER are used to extract information on Al-OH and Mg-OH group minerals. The distribution of Al-OH minerals in the ASTER image map corresponds to that of hydroxyl-bearing minerals in the MSI image map. A combination of minimum noise fraction (MNF), pixel purity index (PPI), n-dimensional visualizer (n-D Visualizer) and matched filtering (MF) is adopted to process the Hyperion image to obtain accurate hydrothermal alteration mapping results. The overall accuracy for mineral mapping is 92.75% and the kappa coefficient is 0.89. The results of the Hyperion image are spatially consistent with those of the Sentinel-2A MSI and ASTER images. The image processing results were validated by field investigations and spectral reflectance measurements. Hydrothermally altered rocks correspond well with the five PCDs in the Duolong area. Three mineralization prospects associated with felsic intrusions are discovered in accordance with the results. The methodologies and data are effective in detecting porphyry copper mineralization in other arid areas.