Hydrothermal alteration mapping and mineralization potential assessment in the Taznakht region (Morocco) through integrated ASTER imagery, airborne radiometric and magnetic data

Remote sensing (RS) technologies have emerged as efficient and cost-effective tools for the rapid identification of hydrothermal alteration zones, thereby supporting mineral exploration. The Zafarghand area in northeastern Isfahan Province, situated within the Central Iran structural zone of the Urmia–Dokhtar magmatic arc, hosts a porphyry system with multiple alteration types, including phyllic, propylitic, argillic, potassic, and silicic zones. This study aimed to develop an unsupervised and data-driven framework for mapping hydrothermal alteration using high-resolution satellite imagery. To achieve this, Sentinel-2 data were processed through a β-Variational Autoencoder (β-VAE) Deep Learning (DL) model, enriched by Discrete Wavelet Transform (DWT), and subsequently clustered with a Gaussian Mixture Model (GMM). The proposed approach successfully identified alteration zones and iron-bearing minerals (Fe²⁺, Fe³⁺, and iron oxides) at a 20-m spatial resolution. Validation using geochemical data showed classification accuracies of 94.74% and 95.74% for the phyllic and propylitic zones, respectively. In addition, buffered pixel-based validation using confusion matrices yielded overall accuracies of 94.5% and 86.9% for the phyllic and propylitic maps, confirming the statistical robustness of the proposed framework. Due to the limited distribution of argillic and silicic alteration, the depth of the potassic zone, and the lack of sufficient geochemical data for their validation, this study mainly focused on identifying phyllic and propylitic alteration along with iron oxides.These findings demonstrate that integrating DL, wavelet analysis, and probabilistic clustering with Sentinel-2 imagery provides a robust framework for detecting hydrothermal alteration zones. While the current study primarily focused on phyllic, propylitic, and iron-oxide zones due to limitations in data availability, the framework is transferable to other porphyry systems, provided that suitable reference data exist for validation.

Mapping hydrothermal alteration zones of Gebel MU'TIQ area using ASTER and aeromagnetic data in central eastern desert, Egypt

Most high-temperature geothermal areas have a similar resistivity signature, reflecting the alteration state of the system, as is the case for the Reykjanes high temperature system. A geothermal system has an intermediate resistivity core (30–100 Ωm), overlain by a low resistivity cap (1–10 Ωm); at Reykjanes this cap reaches the surface. Hence, the study of the shallow subsurface can provide insights into the state of the system and deeper processes. Traditionally, geothermal systems are studied using electromagnetic methods, which have a large penetration depth but a low resolution. This is sufficient to characterize the system, but capturing dynamics requires sufficiently large changes and careful survey design. In this study, we explore the potential of the combined use of three geo-electric methods: electrical resistivity tomography (ERT), induced polarization (IP), and self-potential (SP), to characterize the shallow (<50 m) subsurface at Reykjanes and interpret it in a dynamic context, without the need for repeated measurements. The observed resistivity signature reflects the typical resistivity distribution known at the site. The addition of SP allows for the identification of active geothermal processes, which are highly variable and localized. The IP signal revealed a shallow (<20 m) sealing structure, prohibiting fluid and gas migration, causing the absence of hydrothermal surface expressions. Such a seal can be potentially hazardous due to over-pressurization and could not be identified from resistivity imaging alone. Here we demonstrate that shallow structures can act as a proxy for deep processes. Furthermore, we show that the combination of the tree methods is invaluable in studying these complex systems and recommend this for future studies.

Mapping Hydrothermal Alteration Zones and Structural Features in Allawi and Hangaliya Areas, South-Central Eastern Desert of Egypt: Prospecting Gold Mineralization Using ASTER and PALSAR Satellite Imagery

Mineral chemistry, ASTER hydrothermal alteration mapping, and geotechnical characterization of granitic rocks of the Arabian-Nubian Shield; A case study from Wadi El-Hima, South Eastern Desert, Egypt

The use of remote sensing and geographic information system techniques in mineral exploration is still underutilised. There is a need to explore the potential of new robust remote sensing and geographic information system techniques in the field of mineral exploration. In this study, we mapped the argillic alteration associated with epithermal gold-silver mineralisation. A band ratio of band5/band6 and Crósta technique on Advanced Spaceborne Thermal Emission and Reflection Radiometer within the Google Earth Engine Environment was applied. The bands 5 and 6 were selected for the band ratio after critically analysing and comparing the illite spectral extracted from the Advanced Spaceborne Thermal Emission and Reflection Radiometer image and the illite spectral obtained from the United States Geological Survey spectral library. The band ratio and Crósta technique identified and mapped the Ovacik goldmine and other argillic alteration zones. Even though both methods mapped out the argillic alteration zones associated with gold-silver mineralisation, the Crósta technique produced the optimal argillic alteration. The study demonstrates the analytical capabilities of Google Earth Engine in image processing and analysis for mineral exploration, such as discovering hydrothermal alteration associated with mineralisation.

This study developed a copper mineral prospectivity map for the Koldar massif, Kazakhstan, using an integrated approach combining geophysical and satellite methods. A strong spatialgenetic link was identified between faults and hydrothermal mineralization, with faults acting as key conduits for ore-bearing fluids. Lineament analysis and density mapping confirmed the high permeability of the Koldar massif, indicating its structural prospectivity. Hyperspectral and multispectral data (ASTER, PRISMA, WorldView-3) were applied for detailed mapping of hydrothermal alteration (phyllic, propylitic, argillic zones), which are critical for discovering porphyry copper deposits. In particular, WorldView-3 imagery facilitated the identification of new prospective zones. The transformation of magnetic and gravity data successfully delineated geological features and structural boundaries, confirming the fractured nature of the massif, a key structural factor for mineralization. The resulting map of prospective zones, created by normalizing and integrating four evidential layers (lineament density, PRISMA-derived hydrothermal alteration, magnetic, and gravity anomalies), is thoroughly validated, successfully outlining the known Aktogay, Aidarly, and Kyzylkiya deposits. Furthermore, new, previously underestimated prospective areas were identified. This work fills a significant knowledge gap concerning the Koldar massif, which had not been extensively studied using satellite methods previously. The key advantage of this research lies in its comprehensive approach and the successful application of high-quality hyperspectral imagery for mapping new prospective zones, offering a cost-effective and efficient alternative to traditional ground-based investigations.

• EnMap data used for lithological and hydrothermal mapping. • UMAP, SMACC, PCA and spectral resampling methods applied. • Validated with geophysical, field, petrographic, and SEM-EDX analyses. • Structural, textural, and alteration analyses identified gold mineralized zones. This study conducted a rigorous evaluation of Environmental Mapping and Analysis Program (EnMap) data in geological applications, specifically focusing on lithological and hydrothermal alteration mapping. This research represents one of the earliest attempts to apply EnMap data for such purposes, and the first to integrate EnMap and airborne geophysical data for geological mapping over the entire Arabian Nubian Shield. To ensure a comprehensive appraisal, we selected a study area characterized by complex Precambrian rocks, including igneous, metamorphic, and sedimentary formations, alongside structural intricacies and hydrothermal activities. Our study utilized various image-processing techniques, including principal component analysis (PCA), Uniform Manifold Approximation and Projection (UMAP), Sequential Maximum Angle Convex Cone (SMACC) endmember analysis, and spectral resampling. These techniques successfully discriminated ophiolitic serpentinite, volcaniclastic metasediments (as part of the ophiolitic mélange matrix), metavolcanics, metagabbro-diorite, syn -orogenic granite, post-orogenic granite, Nubian sandstone, and Wadi deposits. Additionally, they revealed the prevalence of OH-bearing minerals and iron oxides as the primary hydrothermal alteration products within the study area. By correlating the findings with USGS spectral libraries and airborne geophysical data, we determined the efficacy of EnMap data in these applications. Our findings were further validated through multiscale observations, field investigations, petrographic analyses, and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX). In addition to endorsing the use of the UMAP algorithm and EnMap data for future applications, this study highlights key alteration zones that could serve as potential targets for future gold exploration, alongside insights into bauxite ore occurrences.

Copper is typically acknowledged as a critical mineral and one of the vital components of various of today’s fast-growing green technologies. Porphyry copper systems, which are an important source of copper and molybdenum, typically consist of large volumes of hydrothermally altered rocks, mainly around porphyry copper intrusions. Mapping hydrothermal alteration zones associated with porphyry copper systems is one of the most important indicators for copper exploration, especially using advanced satellite remote sensing technology. This paper presents a sophisticated remote sensing-based method that uses ASTER satellite imagery (SWIR bands 4 to 9) to identify hydrothermal alteration zones by combining the discrete wavelet transform (DWT) and the median absolute deviation (MAD) algorithms. All six SWIR bands (bands 4–9) were analyzed independently, and band 9, which showed the most consistent spatial patterns and highest validation accuracy, was selected for final visualization and interpretation. The MAD algorithm is effective in identifying spectral anomalies, and the DWT enables the extraction of features at different scales. The Urmia–Dokhtar magmatic arc in central Iran, which hosts the Zafarghand porphyry copper deposit, was selected as a case study. It is a hydrothermal porphyry copper system with complex alteration patterns that make it a challenging target for copper exploration. After applying atmospheric corrections and normalizing the data, a hybrid algorithm was implemented to classify the alteration zones. The developed classification framework achieved an accuracy of 94.96% for phyllic alteration and 89.65% for propylitic alteration. The combination of MAD and DWT reduced the number of false positives while maintaining high sensitivity. This study demonstrates the high potential of the proposed method as an accurate and generalizable tool for copper exploration, especially in complex and inaccessible geological areas. The proposed framework is also transferable to other porphyry systems worldwide.

Located north of the town of Gouramma, the Mougueur inlier in the eastern High Atlas of Morocco a part of the Hercynian chain of the Paleozoic Era. It is known for its richness in carbonate vein mineralization (e.g., siderite, ankerite) and Zn–Pb (± Fe, Cu, and Mg) association. The current research integrated remote sensing datasets (e.g., ASTER and Landsat OLI), field observations and petrographic investigations to explore structural and hydrothermal alteration zones linked to the mineralization. Our results revealed that the key tectonic structures trend NE to E–W, control the distribution of mineralization in the Mougueur Inleir and meso-cenozoic cover. Hydrothermal alteration mapping identified abundant iron-bearing minerals and quartz, closely associated with fault zones sush as Tit N’Ali, Tijane, Talharit, and Tamelahl. A spatial overlay analysis of alteration indices, lineaments, geological field surveys shows that anomaly zones correlate strongly with known mineralized structures, suggesting that mineralization is primarily structurally controlled. This integrated methodology demonstrates the power of remote sensing techniques for identifying potential exploration targets and offers a promising tool for future mineral prospecting in similar terrains.

ABSTRACT The copper belt of Anti-Atlas is recognized with several mineral occurrences of Cu, Zn, Mn, Ag, Au, and iron. We used ASTER and OLI in lithological and mineral detection and mapping. The lithological mapping was performed using principal components analysis (PCA), minimum noise fraction (MNF), and two classifiers: maximum likelihood (ML) and support vector machine (SVM). The hydrothermally altered zones were detected based on ASTER VNIR/SWIR bands by the integration of Ninomiya indices and constrained energy minimization (CEM) algorithm. In our study area, the enhanced band combinations of ASTER MNF1, PC4, and PC2 and OLI MNF1, PC5, and PC3 were applied for lithological discrimination. The OLI and ML classification shows the best lithological mapping accuracy with an overall accuracy of 91.74% and a 0.90 Kappa coefficient, followed by SVM with an overall accuracy of 88.82% and a 0.86 Kappa coefficient using the same sensor. The hydrothermal alteration mapping reveals alunite, chlorite, calcite, epidote, illite, kaolinite, montmorillonite, muscovite, and pyrophyllite minerals, principally in phyllic and argillic altered areas. The adopted methodology for lithological and mineralogical mapping can be used in other regions with similar criteria to the study area.

Lineaments and hydrothermal alteration mapping in the Arkawit area, NE Sudan: insights from remote sensing

Fusing satellite imagery and ground geochemical data to map alteration zones for gold exploration in western Nigeria

Integration of multi-method ASTER data analysis and geometric average modeling for hydrothermal alteration mapping and mineral prospectivity assessment of copper deposits, Anti-Atlas, Morocco

The Tohamiyam area is located in the Red Sea Hills in East Sudan. Remote Sensing and GIS investigations were carried out in the study area using the ASTER data on VNIR and SWIR in mineral prospecting. It has increased recently because of its relatively low cost, broad coverage, and unique integral bands, susceptible to alteration minerals. The study aimed to delineate the hydrothermal alteration zones related to mineralization. The area is a part of the Haiya terrane (HT) of the late Proterozoic Arabian-Nubian Shield (ANS). The Haiya terrain consists predominantly of arc-back arc low-grade metavolcanic-sedimentary sequences decorated with dismembered ophiolitic rocks and intruded by granitoid intrusions of different ages. The ASTER semi-hyperspectral data have been treated with a Mixture Tuned Matched Filtering (MTMF) classifier. The MTMF classifier matches the spectral signatures of the indicator minerals with similar spectra from the ASTER–USGS spectral library. MTMF classifier images portrayed at least many sites as highly probable alteration mineralization zones in the NE part of the study area, which conforms with the results obtained from Aster data. This study revealed that the results of mineral prospecting investigations obtained from ASTER data show that they can distinguish the spectral signatures of the indicator minerals and delineate the alteration halos related to mineralization zones. The results of remote sensing applications with field geochemical data show that the spectral and spatial analysis of optical semi-hyperspectral data in mineral exploration investigations is strengthened. This study recommends remote sensing and machine learning technology in mineral studies through hydrothermal alteration within the basement complex rocks of the Nubian Shield in Red Sea hills.

ABSTRACT The study evaluates how Landsat-5 Thematic Mapper (TM), Landsat-7 Enhanced Thematic Mapper Plus (ETM+), and Landsat-8 Operational Land Imager (OLI) satellite data can be used to detect and map hydrothermally altered minerals in the Malanjkhand copper mines of Madhya Pradesh, India. By employing band ratio and principal component analysis (PCA) methods, the study generates detailed spatial distributions of hydrothermally altered rocks linked to porphyry copper mineralization in the region. The study also finds that the band ratio combinations and the PCA method effectively distinguished hydrothermally altered minerals, vegetation, and iron oxides in the satellite images. Furthermore, the research reveals that Landsat-8 OLI data outperformed Landsat-5 TM and Landsat-7 ETM+ data in detecting hydrothermally altered minerals using the PCA technique. The correlation of identified minerals with the satellite images from Landsat sensors, supported by spectroscopic and petrographic studies, underscores the comprehensive approach taken in this study to enhance the understanding of hydrothermal alteration zones and improve the efficiency of mineral exploration. In conclusion, the research emphasizes the suitability of Landsat-8 OLI data for visual interpretation of hydrothermal alteration mapping, highlighting its higher radiometric resolution and reduced interference between vegetation and altered minerals.

Mapping hydrothermal alteration in regolith using white micas and chlorite as vectors towards gold mineralization

Fusing multi-source (remote sensing and geophysical) data and diverse approaches validation in targeting hydrothermal alteration and structural anomalies enhances the potential for accurately detecting and characterizing mineralization zones. Sentinel 2 data and ASTER were processed for lithological and hydrothermal alteration mapping in the rare metal-rich Umm Naggat area (Egypt). Different image processing techniques were implemented, including false color composites, minimum noise fraction, band rationing, band math, mineral indices, relative absorption band depth, and constrained energy minimization. The rare metal-bearing Umm Naggat younger granite (NYG) pluton was lithologically discriminated and intra-differentiated to mafic-rich biotite granites, mafic-poor alkali feldspar granites, and albitized granites. Extensive hydrothermal alterations, such as albitization, ferrugination, propylitization, argillization, and phyllitization, overprint the NYG pluton. Normalized standard deviation, automatic lineament extractions, and trend analysis highlighted the key structural directions (NW, NNW, NNE, and NE) and distinguished the NYG pluton as a moderate to high structural density zone. The high structural density and intensive alteration zones are spatially associated and more localized within the NYG pluton than the surrounding rocks. Spatial overlay analysis confirmed that the hydrothermal alterations and fluid circulation systems are structurally-controlled. Furthermore, the hydrothermal alteration mapping and structural analysis outcomes were verified by combining fieldwork, slab polishing, petrographic investigations, and mineral chemistry through semi-quantitative scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and quantitative electron probe microanalysis (EPMA) analysis. As a result, the hydrothermal genesis of rare metal-bearing minerals (Nb-rutile, Nb-ilmenite, and columbite) close to or incorporated within alteration minerals (chlorite, muscovite, and hematite) is confirmed from the alteration zones (propylitic, phyllic, and ferruginated). In addition, biotite muscovitization and chloritization significantly contribute to the secondary rare metal enrichment. The current study emphasizes the extensive distribution of secondary rare metal-bearing minerals within the entire NYG pluton (not only limited to the northern albitized granite as depicted by previous studies), which might shed light on these hydrothermally-altered younger granites as a new potential source for Nb and Ta in Egypt.

Integrated remote sensing and geochemical studies for enhanced prospectivity mapping of porphyry copper deposits: A case study from the Pariz district, Urmia-Dokhtar metallogenic belt, southern Iran