Hydrothermal Alteration Mapping Research Articles

Optimization of machine learning algorithms for remote alteration mapping

World-class large to sub-economic small porphyry copper deposits (PCDs) are primarily found in the Kerman Cenozoic Magmatic Arc (KCMA) which is a fascinating area for geological remote sensing investigationsbecause of its well-exposed rocks and roughly vegetated surfaces. Remote hydrothermal alteration mapping is a critical component of mineral exploration and resource assessment, vital for identifying PCDs. This study explored the application of ML techniques, such as quadratic discriminant analysis (QDA), cosine K-nearest neighbor (CKNN), and bagging decision tree (BDT), in remote hydrothermal alteration mapping. Moreover, the study highlights the transformative impact of optimization methods such as grid search (GS), random search (RS), Bayesian optimization (BO), and principal component analysis (PCA) methods in fine-tuning these algorithms to achieve superior results. These algorithms were found accurate and helpful in identifying PCD-related argillic, phyllic, propylitic, and iron oxide/hydroxide alteration-type zones based on field observations, petrographic studies, and XRD analysis. This research revealed evidence for widespread phyllic and silicic alteration zones, as well as confined argillic and iron oxide/hydroxide zones surrounded by wider regions of propylitic alteration. As the field of ML continues to advance, the future holds promise for even more refined and innovative approaches to hydrothermal alteration mapping. This study underscores the pivotal role that optimized ML algorithms play in revolutionizing mineral exploration practices and paving the way for a more sustainable and responsible resource assessment industry.

Contrasting constraints on the temporal and spatial extents of normal faults from the Hilltop and Lewis mining districts, northern Shoshone Range, Nevada, USA

Mapping of rock types, structural geology, and hydrothermal alteration, supported by geochronology and thermochronology, sheds light on the original spatial relationships of hydrothermal systems to intrusions in the northern Shoshone Range in north-central Nevada. Rocks in the Hilltop district are tilted ~35–40°E, as indicated by orientations of flattened pumice fiamme and bedding in sedimentary rocks along a single set of presently low-angle normal faults that initiated at 60–70°W dips. New U-Pb zircon geochronology from two sets of dikes in the Lewis district could suggest late Eocene–early Oligocene extension, but definitive crosscutting relations are lacking to demonstrably support this potential earlier period of normal faulting. Reinterpretation of previously reported apatite fission-track cooling ages with a new palinspastic restoration in the Lewis mining district concurs with middle Miocene extension as documented to the south at the Caetano caldera; however, the depth of burial of the Lewis district—and thus the significance of the apatite fission-track cooling ages—is uncertain. The comparable orientations and tilting history, supported by fault scaling relations, suggest that the temporally coincident extension in the Caetano caldera to the south represents the along-strike continuation of the same system of normal faults as in the Hilltop and Lewis districts, with changes in observed offset, percent extension, and fault spacing attributed to the gradual tipping out of the fault system northward.

Deciphering differential exhumation in the Gangdese orogen in southern Tibet using exposed porphyry alteration systems and geomorphic analysis

Topography and exhumation vary strongly in the Tibetan Plateau, reflecting different geodynamics and surface processes. The Gangdese orogen in southern Tibet is characterized by west-to-east variations in topography and occurrences of the Miocene porphyry copper deposits. We integrated remote sensing based hydrothermal alteration mapping and geomorphological analysis to detect patterns of differential exhumation since the Miocene. High abundances of propylitic and potassic alteration of the eastern Miocene granitoids are identified, indicating >2 km of exhumation since the Miocene. The western Gangdese has intensive phyllic and argillic alteration representing ∼1 km of exhumation. Geomorphic analyses also show E-W changes that most likely resulted from differential rock uplift histories. Channel steepness index values indicate the eastern Gangdese has channel gradients between 211 m1.02 and 457 m1.02, compared to values between 30 m1.02 and 160 m1.02 in the west. Linear inversion of tributaries of the Yarlung river shows a pulse of rock uplift between 25 Ma and 7 Ma with a maximum rate of 110 m/ m.y. in the east. In contrast, the western Gangdese exhibits slower and persistent rock uplift rates between 20 m/m.y. and 40 m/m.y. since 20 Ma. The integrated results record differential exhumation and rock uplift since the Miocene. We invoke the geometric variations of the subducted Indian lithosphere to interpret the E-W differential exhumation since the Miocene. Steeper subduction of the Indian lithosphere beneath the eastern Gangdese induced mantle upwelling, triggering rapid rock uplift and deep exhumation. Conversely, the shallower subduction of the Indian slab in the west generated slow and prolonged rock uplift with less exhumation. Our study refines the exhumation process of the Gangdese since the Miocene.

Lithological, structural and hydrothermal alteration mapping utilizing remote sensing datasets: a case study of Ras Abdah- Abu Hadedah area, Northeastern Desert, Egypt

Lithological, structural and hydrothermal alteration mapping utilizing remote sensing datasets: a case study of Ras Abdah- Abu Hadedah area, Northeastern Desert, Egypt

Mapping hydrothermal alteration zones with short wavelength infrared (SWIR) spectra and magnetic susceptibility at the Pulang porphyry Cu-Au deposit, Yunnan, SW China

Mapping hydrothermal alteration zones with short wavelength infrared (SWIR) spectra and magnetic susceptibility at the Pulang porphyry Cu-Au deposit, Yunnan, SW China

Exploring for structurally concealed Carlin-type mineralization: A case study from the northern Shoshone Range, Nevada, USA

This study integrates results from previous studies with new reconnaissance-scale mapping of rock types, structures, and hydrothermal alteration at Goat Ridge and Tenabo to provide a district-scale cross section and palinspastic restoration of an area in Nevada with high potential for Carlin-type mineralization in the footwall of a dismembered thrust fault. Reinterpretation of legacy drill data in light of recent advances in the understanding of Cenozoic normal faulting in the area with the expected stratigraphy of the Roberts Mountains autochthon allows for deciphering whether previous drill holes piercements of faults are the Roberts Mountains thrust or are tilted normal faults that down-dropped the deep-water siliciclastic rocks of Roberts Mountains allochthon onto the coeval carbonate rocks of the Roberts Mountains autochthon. A cross-sectional reconstruction shows that ∼11.1 km (120 %) of extension was accomplished along one set of faults that initiated at 60-70°and tilted 40°E. Previously underappreciated Mesozoic folds are present, which likely formed with horizontal fold hinges. Because of Cenozoic normal faulting and associated tilting, the hinge lines currently plunge at moderate angles and are offset as they step across each crosscutting fault. The anticlinal fold hinges produced the modern exposures of lower plate rocks in the range. The Eocene paleogeologic map that results from a plan-view structural restoration shows that the hinge lines of the original folds trended northwest-southeast in the southern half of the range but turned northward toward the northern end of the range.Mineralization in the range includes silver-dominated polymetallic veins/lodes, weak porphyry-type, Carlin-type, and siliciclastic-hosted gold deposits of uncertain origin. Porphyry-style and silver-dominated polymetallic vein mineralization is associated with ∼39–40 Ma granodiorites, with the silver-dominated polymetallic veins interpreted as the distal veins around weakly mineralized and/or deeply buried porphyry system(s), probably of the quartz monzonitic-granitic porphyry Mo-Cu subclass of porphyry molybdenum deposits. Crosscutting relationships demonstrate that at least one of “upper plate” gold deposits is Eocene, but a Miocene age cannot be ruled out for the other gold deposits.

INTEGRATING REMOTE SENSING DATA WITH HYDROTHERMAL ALTERATION MAPPING AND GEOCHEMICAL CHARACTERISTICS OF PRECAMBRIAN ROCKS ACROSS MAMBILLA PLATEAU, NORTHEASTERN, NIGERIA

Mineral exploration must include the mapping of hydrothermally altered regions, which are typically connected to mineralization. This study presents a strategy for integrating remote sensing data with the geochemical characteristics of Precambrian rocks from the Mambilla Plateau in northern Nigeria. Tectonically, the lineaments were fractures with the following orientations: NE-SW, NW-SE, ENE-WSW, and N-S. The distinct spectral reflectance and absorption properties of remotely sensed Landsat 8 data in the visible, near-infrared, shortwave-infrared, and thermal infrared portions of the electromagnetic spectrum were exploited in various digital image processing approaches. Mapping hydrothermal alteration minerals was done effectively and efficiently using band ratios (red/blue, SWIR 2/NIR, SWIR 1/NIR), spectral band combinations (Kaufmann and Sabins ratios), and principal component analysis. Ferric, phyllic, propylitic, and argillic iron all underwent changes as a result of hydrothermal alteration. Regional metamorphism also resulted in important alteration processes such as epidotization, sericitization, muscovititization, kaolinitization, and chloritization. Geochemically, on average, the Al2O3, SiO2, Fe2O3, CaO, MgO, K2O, Na2O, Li2O content are 12.04 %; 54.83%; 4.76%, 7.16%, 3.02%, 10.22%, 4.53%, 1.35% while MnO, P2O5 and TiO2 are less than 1%. The average base metal composition revealed that 60% of them had positive anomalies, which indicate mineralization, and 40% had negative anomalies. About 50% of the samples had positive anomalies, which indicated strong potential for harbouring mineralization based on the makeup of trace elements. Geochemical studies revealed the presence of lithium, titanium, and silica oxides in substantial concentrations. The local mineralization is governed by structural factors.

The geochemistry, origin, and hydrothermal alteration mapping associated with the gold-bearing quartz veins at Hamash district, South Eastern Desert, Egypt

Integrating diverse techniques and datasets, significantly enhances the accurate identification of various mineral deposits. This work aims to determine different types of mineral deposits in the Hamash district (Southern Eastern Desert, Egypt) by combining structural features (derived from ALOS PALSAR DEM), alteration zones (detected using ASTER and Sentinel-2), and ore mineralogy. Multispectral imaging, such as ASTER and Sentinel-2 satellite data, provides a cost-effective and efficient tool for lithological and hydrothermal alteration mapping utilizing selective band ratios (SBR), directed principal component analysis (DPCA), feature-oriented false-color composites (FFCC), and constrained energy minimization (CEM). The deductions drawn from the analysis of ASTER and Sentinel 2 satellite data are solidly corroborated through meticulous investigations of pre-existing lithological maps in the study area, on-site validation via fieldwork, and robust laboratory analysis, attesting to reliable results. Validation of remote sensing results was performed through field observations, petrographic investigations, X-ray diffraction technique (XRD), and SEM–EDX analyses. Based on ore mineralogy derived from XRD and SEM results the quartz-vein-associated ore minerals in the Hamash district include chalcopyrite, pyrite, hematite, goethite, bornite, covellite, and gold. According to the present paragenesis, the mineralization in the study area is classified into three types: sulfide mineralized zone, transitional zone, and supergene zone. Using an ore microscope, our studies identified that the alteration zones include gold-bearing sulfide minerals as well as the minerals goethite and malachite. In gold-bearing quartz samples, the concentrations of Cu, As, Ag, and Sb are positively correlated with Au at the degree of shear deformation. According to data gathered from the fire assay results, Au content varied from 0.027 to 57.20 ppm, along with Cu (10–6484 ppm), Ag (0.5–20.5 ppm), As (5–2046 ppm), Zn (3–1095 ppm), Pb (2–1383 ppm), and Sb (5–23). Our results confirmed that the Hamash region is one of the most important gold-bearing sites, with gold concentrations ranging from 0.027 up to 57.20 ppm. Furthermore, the current contribution highlighted four stages in the paragenetic sequence of the recorded ores, including magmatic, metamorphic, hydrothermal, and supergene by origin, indicating a considered similarity with the known Egyptian gold sites regarding host rocks, mineralization style, alteration assemblage, and several ore mineral conditions.

IDENTIFYING POTENTIAL PORPHYRY CU MINERALIZATION AT THE KIRAZLI DISTRICT IN BIGA PENINSULA (NW TURKEY): INSIGHTS FROM THE MAPPING HYDROTHERMAL ALTERATION BY USING SHORTWAVE INFRARED (SWIR) SPECTROMETRY

The Kirazlı mineral district is located at the center of the Biga peninsula metallogenic province, in a geological setting characterized by an extensional tectonic environment. The district hosts a high-sulfidation (HS) ore body with a total reserve of 33.86 Mt @ 0.69 g/t Au and 9.42 g/t Ag within a large-scale hydrothermal alteration. Although the ideal magmatic-hydrothermal models present the spatial and temporal association of HS-epithermal and porphyry Cu deposits, the porphyry Cu potential at the Kirazlı has not been evaluated, yet. Therefore, the mineral-based alteration mapping with the help of SWIR reflectance spectroscopy was carried out. Our study demonstrates that nine different mineral zone have been distinguished and mapped: (1) Silicification, (2) Alunite, (3) Kaolinite, (4) Dickite, (5) Illite, (6) Pyrophyllite, (7) Chlorite, (8) Sericite, and (9) Montmorillonite zones. Collectively, these alterations exhibit a zoned pattern, from central massive silicification to residual silica, NW-SE oriented alunite, and marginal montmorillonite-illite zones within widespread kaolinite – dickite dominated alteration in Kirazlı main zone. The occurrence of pyrophyllite and sericite dominates at the SE of the Kirazlı district, which refers to relative temperature increase. Subsequent drilling confirms the potential for deep prospecting of porphyry Cu mineralization in the region.

Towards better delineation of hydrothermal alterations via multi-sensor remote sensing and airborne geophysical data

Integrating various tools in targeting mineral deposits increases the chance of adequate detection and characterization of mineralization zones. Selecting a convenient dataset is a key for a precise geological and hydrothermal alteration mapping. Remote sensing and airborne geophysical data have proven their efficiency as tools for reliable mineral exploration. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Advanced land imager (ALI), Landsat 8 (L8), and Sentinel 2 data are widely-used data among various types of remote sensing images in resolving lithological and hydrothermal alteration mapping over the last two decades. ASTER is a well-established satellite in geological remote sensing with detailed Short-wave infrared (SWIR) range compared to visible and near-infrared region (VNIR) that controls iron-associated alteration detection. On contrary, ALI has excellent coverage of the VNIR area (6 bands), but does not possess the potentiality of ASTER for the SWIR and thermal regions. Landsat 8 is widely used and highly recommended for lithological and hydrothermal alteration mapping. The higher spatial (up to 10 m) resolution of Sentinel 2 MSI has preserved its role in producing accurate geological mapping. Notwithstanding the foregoing, implementing the four datasets in a single study is time-consuming. Thus, an important question when commencing an exploration project for hydrothermal alterations-related mineralization (orogenic mineral deposits in the current research) is: which dataset should be adopted to fulfill proper and adequate outputs? Here the four widely recommended datasets (ASTER, ALI, L8, and sentinel 2) have been tested by applying the widely-accepted techniques (false color combinations, band ratios, directed principal component analysis, and constrained energy minimization) for geological and hydrothermal alteration mapping of Gabal El Rukham-Gabal Mueilha district, Egypt. The study area is covered mainly by Neoproterozoic heterogeneous collection of ophiolitic components, island arc assemblage, intruded by enormous granitic rocks. Additionally, airborne magnetic and radiometric data were applied and compared with the remote sensing investigations for deciphering the structural and hydrothermal alteration patterns within the study area. The results demonstrated a different extent from one sensor to another, highlighting their varied efficacy in detecting hydrothermal alterations (mainly hydroxyl-bearing alterations and iron oxides). Moreover, the analysis of airborne magnetic and radiometric data showed hydrothermal alteration zones that are consistent with the detected alteration pattern. The coincidence between high magnetic anomalies, high values of the K/eTh ratio, and the resultant alterations confirm the real alteration anomalies. Over and above that, the remote sensing results and airborne geophysical indications were verified with fieldwork and petrographic investigations, and strongly recommend combining ASTER and Sentinel 2 results in further investigations. Based on the outputs of the current research, we expect better hydrothermal alteration delineation by adopting the current findings as they sharply narrow the zones to be further investigated via costly geophysical and geochemical methods in mineral exploration projects.

Radiometric Mapping for The Identification of Hydrothermally Altered Zones Related to Gold Mineralization in Ife–Ilesa Schist Belt, Southwestern Nigeria

This study presents the interpretation of airborne gamma ray spectrometric data to delineate hydrothermally altered zones related to gold mineralization in the Ife–Ilesa Schist belt. K/eTh, Kd and F–Maps highlighting Potassic alterations related to gold mineralization were processed on the Oasis Montaj software and subsequently integrated using fuzzy logic modeling to produce the hydrothermal alteration map of the study area. The C–A fractal analysis was applied to the final hydrothermal map and was able to classify the study area into background, very low, low, moderate, high and very high alteration. These classes reflect the pervasive hydrothermal alteration style of the study area. The hydrothermally altered areas are evident on granitoids and areas proximal to it indicating that granitoids are proxies of heat source. Occurrence of active mining sites in the area agrees with the generated hydrothermal alteration map of the study area with 81% agreement. It therefore shows that radiometric method is a veritable method in mapping hydrothermal alteration areas. The use of radiometric method only cannot reliably map areas of gold mineralization as mineralization can be associated with several other processes. Hence, other methods involving geochemical and magnetic methods including GIS tools can be employed for further prospecting.

Litho-structural and hydrothermal alteration mapping for mineral prospection in the Maider basin of Morocco based on remote sensing and field investigations

Landsat 8 OLI images were processed using band ratio (RB), principal component analysis (PCA), composite ratios (CR) 4/2–6/7-6/5 were used to map lithology, geological structures, and hydrothermal alteration zones. The studied area, Jbel Boulachrhal, is characterized by copper, barite, and amethyst mineralization and is in the Maider basin at the level of Morocco's eastern Anti-Atlas, which is formed by Paleozoic landfills. This vein-type mineralization, which oriented NE-SW, NNE-SSW, to E-W corresponds to the main orientations of mapped faults using remote sensing and confirmed by the field study, and is revealed by the lineaments extracted from the processing of Landsat 8 Oli. The mineralization is polymetallic, with copper oxide and sulfide dominating, as well as quartz, amethyst, lead, and barite. Remote sensing techniques combined with field research have showed that high lineament density areas that frequently correlate with areas of hydrothermal alteration are highly related to the occurrences of these mineralizations. These findings indicate that satellite image processing techniques (lineament density and hydrothermal alteration zones) will most likely be used in mining exploration.

Two‐dimensional inversion of airborne radiometric data for source concentrations: Application to Cu–Au targeting at Mara Rosa Magmatic Arc, Brazil

AbstractAirborne radiometrics (radiometric surveying) has been used in many applications, such as geological mapping, environmental studies, mineral exploration and lithology mapping. The standard processing of gamma‐ray spectrometry data provides good results when the acquisition conditions such as the flight and sensor orientation are constant. In practice, abrupt changes in flight height when flying in mountainous terrain are common, and standard processing neglecting this factor can lead to erroneous interpretation. The primary cause is the fact that the successive corrections applied to radiometric data in standard processing do not consider the effective sampled area of a survey (i.e. the field of view), which can have significant and variable overlaps between adjacent samples due to changing observation height. For this reason, standard height and sensitivity corrections may lead to incorrect estimates of the concentrations of the radioelements on the ground. To ameliorate this problem, we have developed a two‐dimensional inversion‐based processing method that incorporates the aircraft height, replaces the sensitivity correction and accounts for a positivity condition using a logarithmic barrier. Some minerals associated with potassium, uranium and thorium allow the mapping of hydrothermal alteration, especially potassium which is an important constituent of hydrothermal fluids. We demonstrate the new methods by comparing the standard processing results with the inversion‐based processing of airborne gamma‐ray spectrometry data in the gold deposit‐rich area of Mara Rosa Magmatic Arc, Brazil. The inversion‐based processing results enhance the anomalies and suppress the interpolation artefacts as well as increase the signal‐to‐noise ratio. The application of airborne radiometric transformed maps also improved the footprint knowledge around Cu–Au mineralization and highlighted potential areas for further studies.

Geological structure and hydrothermal alteration mapping for mineral deposit prospectivity using airborne geomagnetic and multispectral data in Zuru Province, northwestern Nigeria

Spatial associations involving alterations and structures are common with orogenic systems, however porphyry deposits are not spatially well defined especially due to overprinting of alteration types. In this study, multi-disciplinary geoscience information from digitally-enhanced airborne data over Zuru province, northwest Nigeria were analyzed and synthesized to unravel uncertainties about the spatial alignment of both structural and hydrothermal features in porphyry prospects. Processed aeromagnetic data showed the tectonic regime and the associated lineaments of the Anka province which presumably controlled the mineral localization and distribution in the province. The multispectral interpretations of the hydrothermal expressions illustrated the major alteration zones such as potassic, phyllic, argillic and propylitic domains. The delineated surface structures in the province are regarded as the main reason for alteration zone formation in the country rocks where the traversed lineaments in the existing rocks symbolizes a plumbing system responsible for hydrothermal fluid flow, and hence mineral bearing alteration zones were developed. Spatial analysis involving contrast estimation was performed to quantify the spatial relationship between known mineral deposits and geologic features that can influence mineralization. Propylitic alterations are noticeable as prominent alteration zones with mineral deposits, whereas the phyllic alterations presented the lowest possibility of mineral occurrence. Further spatial analysis involving statistical contrast estimation between mineral deposits and a deep-seated regional structure showed maximum spatial relationship around the 35-km buffer zone. The mineral deposits exhibit spatial association with the trans-current lineament assertive of a strong influence of the geologic structure on mineral deposition and regional pluton emplacement.

Mapping Hydrothermal Alteration Zones Associated with Copper Mineralization using ASTER Data: A Case Study from the Mirjaveh Area, Southeast Iran

In this research, ASTER satellite images and the combined algorithm of band ratios with the method of logical operators with the determination of the threshold limit based on ground, laboratory and experimental studies have been used in order to highlight hydrothermal alterations. Image transformation techniques such as specialized band ratio and principal component analysis are used to map lithologic units and alteration minerals. Supervised classification technique, i.e. Spectral Angle Mapper (SAM) is applied to detect subtle differences between index alteration minerals associated with actual copper localities in the region. The results show that the integration of image transformation techniques and supervised classification of ASTER data with field studies and geochemical exploration is highly effective in targeting new copper mineralization prospects. Copper mineralization is found in siliceous veins that strike from north-south to northeast-southwest across the region. Remote sensing evidence supports the presence of propylitic and argillic alteration, which can be useful for searching for copper-gold type deposits. Kaolinite and pyrophyllite play a role in identifying arzilic alteration zones, and muscoite, epidote and chlorite minerals are very important in identifying pyropilitic and phyllic areas and in mineral exploration. Based on remote sensing processing, according to the detection of various alterations (phyllic, pyrophyllite and argillic) in this area, possible copper mineralization was detected in the central part of the studied area. The approach used in this research provides a quick and cost-effective means of initiating comprehensive geological and geochemical exploration programs in the study area and elsewhere in similar areas.

Litho-structural and hydrothermal alteration mapping for delineation of gold potential zones within Kaiama, northwestern Nigeria, using airborne magnetic and radiometric data

Litho-structural and hydrothermal alteration mapping for delineation of gold potential zones within Kaiama, northwestern Nigeria, using airborne magnetic and radiometric data

Use of Modern Multi- and Hyperspectral Space Images for Mapping Hydrothermal Alteration and Lithological Units in the Arctic

Use of Modern Multi- and Hyperspectral Space Images for Mapping Hydrothermal Alteration and Lithological Units in the Arctic

Hydrothermal Alteration Mapping Using Landsat 8 and ASTER Data and Geochemical Characteristics of Precambrian Rocks in the Egyptian Shield: A Case Study from Abu Ghalaga, Southeastern Desert, Egypt

This study evaluates the geological attributes of rocks within the Abu Ghalaga area using spatial, geochemical, and petrographic approaches. ASTER and Landsat imagery processed using band ratio and principal component analysis were used to map hydrothermal alterations, while a regional tectonic evaluation was based on automated extraction of lineaments from a digital elevation model. Geochemical and petrographic analyses were then employed for discrete scale evaluation of alteration patterns of rocks across the study location. Based on satellite image processing, alteration patterns across the study area are widespread, while evidence from lineament analysis suggests a dominant NW–SE tectonic trend accompanied by a less dominant ENE–WSW direction. The different rock units exposed in the studied district are arranged chronologically from oldest to youngest as arc metavolcanic group (basalt and rhyolite), arc metagabbro–diorite, gneissose granite (granodiorite and tonalite), and dykes (aplite and felsite). Various types of igneous and metamorphic rocks have propylitic, phyllic, and argillic zones. Geochemical data indicate that the studied rocks are classified into granite, granodiorite, gabbroic diorite, and gabbro. Geochemically, the rocks have a sub-alkaline magma type. The granodiorite–tonalite is derived from the calc–alkaline magma nature, while gabbro and diorite samples exhibit tholeiitic to calc–alkaline affinity. The tectonic setting of the studied rocks trends toward volcanic arc granite (VAG). Based on petrographic, geochemical, and remote analyses, sericitization, chloritization, epidotization, kaolinitization, carbonatization, and silicification are the main alteration types present in the study area. As a result of lineaments analysis, the existing fractures and structural planes form valid flow paths for mineral-bearing hydrothermal solutions.

Improving the accuracy of hydrothermal alteration mapping based on image fusion of ASTER and Sentinel-2A data: a case study of Pulang Cu deposit, Southwest China

Mapping hydrothermal alteration is an important means of mineral exploration, therefore, effective improvement of the accuracy of identification of hydrothermal alteration minerals is a hot topic. In this study, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Sentinel-2A data were selected for the Pulang copper deposit, to improve the accuracy of hydrothermal alteration mineral mapping. Three data fusion methods of Principal Component Analysis (PCA), Gram–Schmidt (GS) and High-Pass Filtering (HPF) were employed, and method of spectral matching was introduced to obtain high spatial resolution and high spectral fidelity fused data. The comparison showed that the HPF fusion method had the best effect. The fused data by the HPF fusion method were then implemented to map hydrothermal alteration minerals by using a multifractal-based method of PCA + Spectrum–Area. Through the verification of a field investigation, the results exhibited a similar hydrothermal alteration distribution, compared with the results obtained from the original ASTER data, but with higher identification accuracy. Therefore, the case study strongly suggests that the image fusion method with spectral matching is an effective tool to increase spatial resolution, while maintaining high spectral fidelity. Thus, it is a valuable and economic method for improving the identification accuracy of hydrothermal alteration minerals. HIGHLIGHTS The spectral matching method was introduced to unify the surface reflectance of ASTER and Sentinel-2A data. Principal Component Analysis (PCA), Gram-Schmidt (GS) and High-Pass Filtering (HPF) methods were employed to fuse AST ER and Sentinel-2A data. The results show that the extraction accuracy of hydrothermal alteration minerals based on AST ER - Sentinel-2A fused data has 6.98% higher than that of original ASTER data.

Aeromagnetic and Landsat-8 data interpretation for structural and hydrothermal alteration mapping along the Central and Southern Eastern Desert boundary, Egypt

Pan-African basement rocks cover the study area along the boundary between Central and Southern Eastern Desert with small exposed sedimentary sequences. Several vein-type gold mineralization with hydrothermal alteration zones have long been known in the study area. Aeromagnetic and remote sensing imagery data were integrated for mapping the structural elements and hydrothermal alteration zones related to gold mineralization. By aeromagnetic imagery inspection, the structural complexity and porphyry intrusions density maps have been effectively constructed by applying Enhanced Center for Exploration Targeting (CET) techniques. Major NW shear zones along with NNW-SSE, WNW-ESE, NS, and NE-SW are the main trends controlling gold mineralization. On the other hand, applying band ratios and constrained energy minimization (CEM) technique on Landsat-8 data pointed out alteration minerals associated with the hydrothermal fluids. Calcite, sericite, and chlorite are the common alteration minerals detected, while goethite and epidote are less common in alteration zones of the area under study. A combination of CET structural complexity, circular features, and alteration zones produced a potential mineralization map pointing out numerous prospective zones for mineralizing gold. The predictive map was validated by projecting the known gold prospects at the study area, reflecting an agreement between the known gold occurrences and the higher classes of the predictive zone. The discussed techniques in the current research can be adopted as a direct indicator for structural mapping and detecting the alteration zones related to gold mineralization elsewhere.