A Comparative Study of Landsat‐7 and Landsat‐8 Data Using Image Processing Methods for Hydrothermal Alteration Mapping

Abstract

Comparing spaceborne satellite images of Landsat‐8 Operational Land Imager (OLI) and Landsat‐7 Enhanced Thematic Mapper plus (ETM+) was undertaken to investigate the relative accuracy of mapping hydrothermal alteration minerals. The study investigated the northern part of Rabor, which contains copper mineralization occurrences, and is located in the Kerman Cenozoic magmatic assemblage (KCMA), Iran. Image processing methods of band ratio, principal component analysis (PCA), and spectral angle mapper (SAM) were used to map the distribution of hydrothermally altered rocks associated with the porphyry copper mineralization. The band ratio combination of both sensors for mapping altered areas showed similar outcomes. PCA exposed variations in the spatial distribution of hydroxyl‐bearing minerals. The representation of hydrothermal areas using OLI data was more satisfactory than when using ETM+ data. SAM analysis found similar results for mapping hydroxyl‐bearing zones. Verification of the results came through ground investigation and laboratory studies. Rock samples (n = 56) were collected to validate results using thin sections, X‐ray diffraction (XRD) and spectral analyses. Field observations and laboratory analysis revealed that phyllic and propylitic alterations dominate the alteration zones in the study area. Argillic and iron oxides/hydroxides alterations were observed to a lesser degree. The results indicate that alteration maps prepared by OLI data using PCA for visual interpretation are more suitable than those of ETM+ due to a higher radiometric resolution and lower interference between vegetation and altered areas. As the spectral bandwidth of ETM+ band 7 covers absorption feature of propylitic alteration, better mapping of propylitic alterations is achieved using ETM+ data.

Automated mineralogy based on micro-energy-dispersive X-ray fluorescence microscopy (µ-EDXRF) applied to plutonic rock thin sections in comparison to a mineral liberation analyzer

“…It calculates the spectral similarity of two spectra, which is described by the angle between the vectors of both spectra. The angle of the spectral similarity can have values from 0 to π/2 in radians (Masoumi et al, 2017). The vectors are in an n-dimensional space, where n is the number of bands (here, element lines) (Masoumi et al, 2017).…”

Location Mapping of Hydrothermal Alteration Using Landsat 8 Data: A Case of Study in Prestea Huni Valley District, Ghana

“…RS is a powerful technique in identifying hydrothermally altered rocks, structures, lineaments, oxidation products, morphology, lithological units, vegetation anomalies and other valuable information to geologists (Goetz et al, 1982;Goetz, 2009).It is broadly acknowledged that hydrothermal alteration plays an important role in mineral prospecting. The necessary dispersal of alteration zones around the limited borders of an ore body helps narrow down the exploration events into smaller targets (Masoumi et al, 2017). Hydrothermal mineralization alteration is a process which alters the mineralogy and chemistry of the host rocks resulting in creating mineral assemblages which differ according to the setting, degree and time of the alteration processes (Mia and Fujimitsu, 2012;Sadiya et al, 2014).…”

“…Spectral ratioing (arithmetic operations) and three band combinations of remotely sensed data can detect the above-mentioned minerals and discover buried deposits (Masoumi et al, 2017). Band ratioing have been used by different authors to examine and interpreted remotely sensed data to map hydrothermally alteration relating to minerals deposit patterns.…”

Lithological Classification Using Sentinel-2A Data in the Shibanjing Ophiolite Complex in Inner Mongolia, China

“…Due to its lower cost and higher accessibility than hyperspectral data, multispectral imagery, such as Landsat-5 TM, Landsat-7 ETM+ (enhanced thematic mapper plus), Landsat-8 OLI (operational land imager), and ASTER, is broadly utilized to extract lithologic, mineral, and structural information in metallogenic provinces [6][7][8]. As one of the world's earliest and longest continuously acquired collection of spaceborne moderate-resolution land remote sensing data, the Landsat series has been applied in geology for decades [6,[9][10][11], for applications such as hydrothermal alteration (ferric iron and hydroxides) extraction, lithological discrimination, and geotectonic interpretation.…”

“…Results from lithological classification using different remote sensing datasets and classifiers from the last few years. Multispectral; 3 Knowledge-based systems; 4 Hyperspectral; 5 Airborne Thematic Mapper;6 Object-based image analysis; 7 Jeffries-Matusita;8 Hyperspectral and Infrared Imager;9 Genetic algorithm coupled with the Spectral Angle Mapper.…”