Library and field-referenced spectra applied in enhancing extraction effects of remotely-sensed hydrothermal alteration minerals: a case study at the Muteh gold mining district in Iran

The orogenic gold mineralisation at the Muteh mining district in Iran is hosted by silica-iron oxide veins associated with phyllic (sericite), argillic (kaolinite), and propylitic (chlorite) hydrothermal alterations. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data of the district were initially processed by using library spectra and standard image processing techniques to map minerals associated with gold mineralisation. Image processing techniques were also applied to the Sentinel-2A and Landsat-8 satellite data to map lineaments and alterations. Then, the spectral behaviour of 24-field alteration samples, mostly associated with gold mineralisation, was obtained from a handheld spectrometer and applied to the ASTER data using the spectral angle mapper (SAM) and matched filtering methods for mapping favourable alteration and iron oxide minerals. The identified minerals were compared with the known gold deposits and validated by further field sampling and chemical analyses. The results showed that favourable alteration minerals, identified by the ASTER data using field-referenced spectra, are better correlated with the zones of gold mineralisation, compared to those identified by using library spectra. Processing ASTER data by using field-reference spectra and the SAM method is recommended for mapping favourable alteration minerals in similar geologic settings for organic gold exploration elsewhere.