Hydrothermal Alteration Minerals Research Articles

Machine learning model for deep exploration: Utilizing short wavelength infrared (SWIR) of hydrothermal alteration minerals in the Qianchen gold deposit, Jiaodong Peninsula, Eastern China

The Jiaodong Peninsula in the eastern North China Craton is renowned globally as a major gold province. Notably, the Jiaojia orefield is an important gold-producing district in this region, and its depths are inferred to offer substantial prospecting potential, underscoring the need for innovative exploration tools to uncover concealed orebodies. The Qianchen gold deposit in the southern part of the Jiaojia orefield is characterized by the disseminated-stockwork-style orebodies at depths of ca. –1000 to –1800 m, with three mineralization stages, namely (I) pre-ore K-feldspar-quartz stage, (II) quartz-sericite-gold-polymetallic sulfide stage (main Au mineralization stage), and (III) post-ore quartz-calcite stage. Systematic short-wavelength infrared (SWIR) spectral analysis reveals that sericite group minerals developing in Stage II are the predominant and wide-distributed alteration minerals at Qianchen. Their spectral characteristics demonstrate a shift in the Al-OH absorption feature wavelength positions (Pos2200) to longer wavelengths (>2205 nm) within the orebodies. This shift is likely due to strong water–rock interactions leading to Fe and Mg substituting for Al in octahedral sites. Orthogonal partial least squares discriminant analysis (OPLS-DA) indicates that the H2O, OH, and FeOH spectral bands (Variable Importance in the Projection (VIP) ≥ 1) of sericite are crucial for distinguishing between gold ores and barren wall rocks. Additionally, Long Short-Term Memory (LSTM) models demonstrate that spectral data of sericite can be used to predict ore samples with an accuracy of 82 %, validated by receiver operating characteristic analysis (84 %), and blind test results demonstrate that the predicted grade closely aligns with the actual grade. Therefore, it is concluded that SWIR spectral characteristics of sericite group minerals can serve as an effective indicator for prospecting the Qianchen concealed gold mineralization. This study highlights the potential of coupling between machine learning and SWIR spectral data of alteration minerals to uncover the concealed lode gold mineralization.

ASTER Data Processing and Fusion for Alteration Minerals and Silicification Detection: Implications for Cupriferous Mineralization exploration in the Western Anti-Atlas, Morocco

Alteration minerals and silicification are typically associated with a variety of ore mineralizations and could be detected using multispectral remote sensing sensors as indicators for mineral exploration. In this investigation, the Visible Near-Infra-Red (VNIR), Short-Wave Infra-Red (SWIR), and Thermal Infra-Red (TIR) bands of the ASTER satellite sensor derived layers were fused to detect alteration minerals and silicification in east the Kerdous inlier for cupriferous mineralization exploration. Several image processing techniques were executed in the present investigation, namely, Band Ratio (BR), Selective Principal Component Analysis (SPCA) and Constrained Energy Minimization (CEM) techniques. Initially, the BR and SPCA processing results revealed several alteration zones, including argillic, phyllic, dolomitization and silicification as well as iron oxides and hydroxides. Then, these zones were mapped at sub-pixel level using the CEM technique. Pyrophyllite, kaolinite, dolomite, illite, muscovite, montmorillonite, topaz and hematite were revealed displaying a significant distribution in relation with the eastern Amlen region lithological units and previously detected mineral potential zones using HyMap imaging spectroscopy. Mainly, a close spatial association between iron oxides and hydroxide minerals, argillic, and phyllic alteration was detected, as well as a strong silicification was detected around doleritic dykes unit in Jbel Lkest area. A weighted overlay approach was used in the integration of hydrothermal alteration minerals and silicification, which allowed the elaboration of a new mineral alteration map of study area with five alteration intensities. ASTER and the various employed processing techniques allowed a practical and cost effective mapping of alteration features, which corroborates well with field survey and X-ray diffraction analysis. Therefore, ASTER data and the employed processing techniques offers a practical approach for mineral prospection in comparable settings.

Short-Wavelength Infrared Characteristics and Indications of Exploration of the Jiawula Silver–Lead–Zinc Deposit in Inner Mongolia

For the Jiawula lead–zinc deposit, as easily accessible resources become depleted, mines are becoming deeper to replenish ore reserves. Identifying large, continuous, and high-grade ore bodies in deep areas has become a daunting problem. Moreover, separating lead–zinc-bearing complex ore bodies from waste material and extracting them from associated minerals are also difficult. Thus, pioneering exploratory strategies and technological methodologies are required to make breakthroughs in mineral discovery. Based on extensive-scale structural lithofacies mapping, this paper uses short-wave infrared (SWIR) spectroscopy technology to investigate hydrothermal alteration minerals in the mining area. It has identified a total of 16 hydroxyl-bearing alteration minerals, including chlorite, muscovite, illite, calcite, ankerite, kaolinite, and smectite. These minerals establish zoning characteristics around the ore bodies and on their flanks. They comprise a segmented assemblage that follows the pattern of comb-textured quartz–illite–chlorite–carbonate → muscovite–illite–chlorite–ankerite → illite–smectite–chlorite → chlorite–kaolinite–calcite. Deep-zone illitization with a lower Al–OH absorbance peak wavelength (<2206 nm) and higher crystallinity indices (>1.1) and chloritization with higher Fe–OH absorbance peak wavelengths (>2254) and higher crystallinity indices (>3.0) are indicators of potential hydrothermal centers in the deeper regions. By finding hydrothermal centers and connecting their spatial distribution with existing ore bodies, a pertinent relationship between diabase + andesite, Fe-chlorite + illite, and high-grade mineralization has been established. They correspond well with the lithology-alteration mineralization. This research provides a basis for predicting the positioning of concealed ore bodies deep inside a mine or at the periphery.

The application of PRISMA hyperspectral satellite imagery in the delineation of distinct hydrothermal alteration zones in the Chilean Andes: The Marimaca IOCG and the Río Blanco-Los Bronces Cu-Mo porphyry districts

This study provides an overview of the application of hyperspectral imagery acquired by the Italian satellite mission “PRecursore IperSpettrale della Missione Applicativa” (PRISMA), for mapping hydrothermal and supergene mineral alteration zones associated with different Cu deposits in the Chilean Andes. Study areas include the Marimaca Copper Project in the Naguayán district (Antofagasta Province), hosting Late Jurassic – Early Cretaceous iron oxide-copper–gold mineralizations and the Río Blanco-Los Bronces district (Santiago Region) known for its Late Miocene – Early Pliocene copper-molybdenum porphyry deposits. These mineral systems exhibit hydrothermal alteration haloes extending over several kilometers, with upward and outward mineral zonation.To characterize the surface-exposed alteration, the satellite imagery was processed using a multiple feature extraction workflow targeting the relative abundances and compositions of specific supergene and hydrothermal alteration minerals, including Fe-oxides and hydroxides (hematite-goethite), phyllosilicates (micas-kaolinite-chlorite), hydroxyl-bearing sulfates (alunite-natroalunite-jarosite) and epidote. The results reveal a zonation from proximal sulfates (natroalunite to alunite) and Al-rich white mica (ranging from 0.3 km-wide for the area identified to the east of the Marimaca deposit to 1 km-wide in correspondence of the Los Sulfatos deposit, respectively) to distal Al-poor white mica (0.2 to 0.5 km-wide, respectively) and an outer chlorite-epidote zone. In the Marimaca Project area, the structurally-controlled alteration evolves west to east from chlorite-rich to phengitic white mica (Al-poor). A NNE-SSW trending supergene leached cap covers a 6 km-long and up to 2 km-wide area from north to south. Our study documents how spaceborne hyperspectral imaging spectroscopy can support mineral exploration by enabling non-invasive reconnaissance mapping of the outcropping rocks, providing specific targeting information for follow-up field surveys and drilling campaigns.

Re-distribution and upgrade of metals induced by the superimposition of later magmatic fluids in the Archean Hongtoushan VMS deposit, NE China

The Hongtoushan copper-zinc deposit is a highly metamorphosed Archean volcanogenic massive sulfide deposit (VMS) in China. After metamorphism, the deposit underwent later fluid superimposition, which is of significance for the re-distribution of metals and upgrading ores. However, the hydrothermal modification mechanism and fluid source remain unclear due to the difficulties in accurately recognizing the mineral textures and assemblages formed by hydrothermal modification. In this study, the mineral texture was investigated to identify the modification mechanism of later fluid and in situ sulfur isotope and trace elements of chalcopyrite were tested to track the source of later fluid and metals. The dominant assemblage formed by superimposed fluid consisted of pyrite, chalcopyrite, sphalerite, minor galena, magnetite, calcite, anhydrite, and hydrothermal alteration minerals, i.e. sericite and chlorite. These minerals infilled the fractures in early pyrite porphyroblasts or precipitated along the grain boundary. Additionally, the pre-existing sulfides were corroded by these minerals. They exhibited replacement and porous textures, indicating that the superimposed fluids resulted in a dissolution-reprecipitation process and formed new sulfides. The hydrothermal metasomatism produced the sericitization of plagioclase and chlorization of biotite, which concurrently liberated silica to form silicification. These interactions suggested that the hydrothermal fluid is acid fluid. The chlorite geothermometer defined the formation temperature of 226–279°C, implying that the superimposed fluid has a moderate temperature. The chalcopyrite precipitated from superimposed fluid either coexisted with pyrite (Ccp 2a) or magnetite (Ccp 2b). The sulfur isotope of Ccp 2a defined a closing zero range (0.75–2.41‰), demonstrating the superimposed fluids were derived from magmatic fluids. In contrast, the Ccp 2b enriched heavy sulfur with a δ34S range of 4.10–8.63‰, which was attributed to the oxidation of fluids. Partial ferrous ions were oxidized to ferric iron, and ferrous and ferric iron precipitated as magnetite. The mineral assemblage changed from chalcopyrite + pyrite, followed by magnetite + chalcopyrite + pyrite, to magnetite + pyrrhotite, representing the local increase of the oxidation state of hydrothermal systems. During the oxidation process, the oxygen fugacity of the superimposed fluid decreased, whereas the pH increased. These results provide crucial evidence on the re-distribution pattern of metals and the post-hydrothermal modification process in the Hongtoushan Cu-Zn deposit.

Assessment of potential cobalt zones by modeling radiometric and ASTER data using the AHP method: A case of the Bou Azzer El Grara inlier, Central Anti-Atlas, Morocco

The Bou Azzer El Grara inlier belongs to the Central Anti-Atlas range, renowned for its mineral deposits. The study carried out on the inlier aims to identify potential areas of cobalt mineralization based on a multi-source methodology of radiometric and remote sensing data processing. The data used includes hydrothermal alteration minerals (argillic, phyllic, propylitic, iron oxides) mapped with Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery using band ratio and principal component analysis (PCA) techniques, potassium enrichment zones through K/eTh and K/eU ratios calculated from radiometric data, as well as geological data (serpentinite outcrops and geological faults). The analytic hierarchy process (AHP) was used to combine the various thematic layers. Validation was carried out through the field studies in several anomalous zones. The mineral prospectivity map generated highlights nine major zones that appear the most favorable for mineralization, some of which coincide with zones in production and others requiring further exploration.

Mapping of surface hydrothermal mineral alterations and geological structures related to geothermal systems in the Songwe region, SW Tanzania

ABSTRACT Geothermal energy is one of the most valuable and preferable renewable energy sources, given that it produces sustainable, dependable, and clean energy. Understanding the geothermal systems, parameters such as heat, fluids, and structures help to identify potential geothermal systems. These parameters are manifested as hot springs, fumaroles, and alteration minerals. Hydrothermal alteration minerals are often used in geothermal system exploration to evaluate factors such as temperature, fluid, and structures. This study employed GIS and remote sensing in the investigation of hydrothermal mineral alterations and delineating geological structures which provided invaluable information for identifying prospective geothermal resource zones. ASTER was utilised to map phyllic, argillic, and propylitic minerals using SPCA, whereas ISO cluster classification was used to detect kaolinite, smectite, calcite, chlorite, and muscovite/illite-rich areas. DEM was used to extract and map geological lineaments. Results have revealed that the regions that were mapped with indicator hydrothermal alteration minerals were also associated with geological structures. The field work, XRD, and ASD laboratory analysis results indicated a good match with the findings from the remote sensing data. The approach applied in this study may be used along with other techniques during the early phases of geothermal exploration to define geothermal potential targets.

Infrared spectroscopy as a tool for hydrothermal alteration mineral analysis to support geothermal reservoir characterization at The Geysers, California, USA

Infrared reflectance spectroscopy (IRS), an analytical method for characterizing geologic materials, is becoming more commonly applied to geothermal energy applications. However, few case studies are available in the literature and are restricted to relatively few volcanic/geologic environments. We present an interpretation of reservoir mineralogy using IRS on drill cuttings from an active magmatic-heat-sourced geothermal system hosted in metamorphic rocks known as “The Geysers”, located in northern California and operated by Calpine Corp. Wavelength ranges investigated include the Short Wave Infrared (SWIR; 1000–2500 nm) and the Long Wave Infrared (LWIR; 2.5–20 μm). We apply this technique to a 2848 m-deep geothermal production well in the northwest Geysers, inferred to overlie a Holocene intrusion and zone of partial melt as indicated by geophysics. We utilized this non-destructive technique to analyze every drill-cuttings sample (3000+ measurements collected at ∼3.3 m intervals). We identify a zonation in mineralogy that changes from illite + chlorite ± kaolinite ± smectite ± calcite at shallow depths (0–1000 m), to illite + chlorite ± calcite at intermediate depths (1000–2200 m), to actinolite + biotite + chlorite ± tourmaline at greatest depths (2200–2848 m). We find the change at 2200 m is proximal to the inferred transition from the “normal” temperature reservoir (∼240 °C vapor-dominated convective zone) to the high temperature reservoir (up to 400 °C, conduction-dominated). We identify a possible association between 1900 nm H2O absorptions and current steam entry locations. The results of the SWIR and LWIR analysis are consistent with some caveats with newly collected bulk rock X-Ray Diffraction (XRD) data, and support and compliment previous work at the Geysers utilizing XRD and petrographic analysis.

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 Artulândia prospect area: A newly discovered Paleoproterozoic Zn–Pb–Cu-(±Ag–Bi) VHMS mineralization in Campinorte Magmatic Arc, Central Brazil

The Artulândia prospect area is a recently-mapped, non-auriferous VHMS mineralization within Paleoproterozoic rocks in Central Brazil. The mineralization is hosted in a felsic-dominated bimodal volcano-sedimentary sequence that formed during the onset of Campinorte Magmatic Arc. The Zn–Pb–Cu-(±Ag–Bi) VHMS mineralization occurs as massive sulfide lenses and sulfide disseminations. Surrounding the sulfide lenses, two proximal hydrothermal assemblages are identified: (i) Tremolite-spessartine (±clinochlore-epidote) assemblage, associated with the sphalerite-pyrite aggregates and (ii) Clinochlore-carbonate (±tremolite-talc-serpentine) assemblage encompassing chalcopyrite, galena, and sphalerite. Besides these two assemblages, three others are considered distal to the mineralization, and interpreted to represent the stringer zone: (i) Biotite-spessartine (±chamosite-tourmaline) assemblage, with disseminated sphalerite + pyrite + galena, (ii) Biotite-sericite-carbonate (±chamosite) assemblage, with disseminated pyrite + sphalerite and (iii) Biotite-carbonate assemblage, with pyrite and traces of sphalerite intergrown with biotite lamellae. The mineralogy of the assemblages results from the Paleoproterozoic, syn-volcanic metamorphism (Neoproterozoic, Brasiliano Orogeny) of hydrothermal alteration minerals. The mineralogy and mineral chemistry data of the assemblages show that proximal assemblages formed under great influence of Fe–Mg–Ca-rich fluids. The highest grades of base metals are restricted to the sulfide lenses: Zn (1.4% wt.), Pb (1.0% wt.%), and Cu (1.8% wt.). Anomalous contents of Mo (>180 ppm), Bi (>700 ppm) and Ag (>60 g/t) occur in the proximal hydrothermal assemblages. Gold grades as high as 270 ppb are directly related to chalcopyrite-enriched zones. The δ34S measurements in pyrite vary from +8.77‰ to +10.99‰. These values are compatible with Paleoproterozoic deposits in which the isotope composition reflects a mix of seawater and leached sulfur from host rocks.

Radioactive remote signatures derived from Sentinel-2 images and field verification in West Sulawesi, Indonesia.

Mamuju, West Sulawesi, is an area in Indonesia with high radiation levels. A high radiation dose rate was detected in Adang volcanic rock. Activities related to radioactive minerals contained in rocks and soil may release hazardous radiation into the environment. The study area generally exhibits a highly irregular morphology that provides limited access because of the high slope gradient of the volcanic terrain. Therefore, it is challenging to identify and map minerals carrying radioactive elements via Sentinel-2 remote sensing. Since optical satellite images are superior in land cover detection, we proposed a mapping technique for radioactive carrier minerals based on vegetation indices verified by chlorophyll field measurements. We applied band rationing to identify the distribution of hydrothermal alteration minerals and vegetation stress, while field chlorophyll measurements of Dryopteris marginalis and Nephrolepis exaltata were conducted. The Sentinel-2 color composite of images with 4/2, 8A/11, and 11/12 RGB band ratios revealed the distribution of iron oxide, ferromagnesian silicates, and clay minerals. High levels of uranium (U) were scattered in leucite basalt rocks, with a broad distribution of iron oxide minerals and small amounts of ferromagnesian minerals. In contrast, the presence of thorium was not affected by the presence of these minerals. In addition, band rationing of chlorophyll spectra captured by the red edge vegetation index (REVI) was used as the basis for vegetation stress mapping related to radiation exposure based on the chlorophyll content in ferns in the study area. The REVI image showed an anomalous vegetation stress concordant with the high radioactivity. To obtain more accurate results, ground measurements were also performed to identify the vegetation stress due to the presence of minerals carrying radioactive elements. The areas with radioactive mineralization and vegetation stress were located upstream of the Mamuju River and the Botteng and Ahu areas in Tapalang.

Application of Spectral Analysis and Image Processing Methods to Discriminate Hydrothermal Alteration Minerals Around the Tutakdağı (Şebinkarahisar-Giresun) Lead–Zinc Deposits, Northeastern Turkey

Application of Spectral Analysis and Image Processing Methods to Discriminate Hydrothermal Alteration Minerals Around the Tutakdağı (Şebinkarahisar-Giresun) Lead–Zinc Deposits, Northeastern Turkey

The synergistic use of WorldView-3 and EO1-Hyperion data for the identification of lineaments and hydrothermal alteration minerals in the Chadormalu iron oxide-apatite deposit area, Central Iran

The synergistic use of WorldView-3 and EO1-Hyperion data for the identification of lineaments and hydrothermal alteration minerals in the Chadormalu iron oxide-apatite deposit area, Central Iran

Detecting Oxides Mineralization Utilizing Remote Sensing and Comprehensive Mineralogical Analysis: A Case Study Around Mikbi-Zayatit District, South Eastern Desert, Egypt

Undoubtedly, involving more tools, datasets, and techniques for detecting the mineralized areas sharply narrow the zones to be investigated and delivered, in most cases highly potential zones. Consequently, this study is an attempt to apply remote sensing data including Sentinel 2 and ASTER, field observations, petrography of the hydrothermal alteration processes, ore microscopic investigations, X-ray examinations, and EDX analysis to detect and emphasize mineralization types at Wadi Mikbi and Wadi Zayatit district, South Eastern Desert, Egypt. Towards accurate lithological mapping, remote sensing data, previous geological maps, and the field investigations recorded serpentinites, ophiolitic metagabbros, amphibolites, epidosite, arc-related metasediments (schists and quartzites), metagabbro-tonalite complex, dunite, olivine gabbros, and granitic rocks encountered in the study district. Additionally, various hydrothermal alteration zones have been primarily outlined using ASTER and Sentinel 2 data by implementing informative band ratios and constrained energy minimization techniques. The mineralogical studies have confirmed most of the remotely-detected hydrothermal alteration minerals. Ore microscopy, XRD technique, and EDX microchemical analysis of representative mineralized samples of the study district identified magnetite, ilmenite, titanomagnetite, chromite, magnesioferrite, quartz, apatite, clinochlore, plagioclase, pyroxene and epidote. Cross-linking remote sensing results, field observations and laboratory studies revealed that the dominant hydrothermal alteration processes include oxidization, serpentinization, carbonatization, epidotization, silicification, zoisitization, muscovitization, sericitization, and chloritization. Spatial overlay analysis of the resultant altered features, structural dissection, field observations, and analytical studies were integrated to build a mineral potentiality map of the study district.

Silicic volcanic rocks, a main regional source of geogenic arsenic in waters: Insights from the Altiplano-Puna plateau, Central Andes

Volcanic rocks are a common, worldwide source of geogenic arsenic (As) that can affect water quality detrimentally. Nonetheless, variations of As concentration within different types of volcanic rocks and questions related to the original source of As in magma are not yet fully understood. We compiled published As data from the abundant Cenozoic volcanic rocks of the Altiplano-Puna plateau, considered the main source of As for waters in the region. These data indicates that volcanic rocks in the Altiplano-Puna have a mean As concentration of 9.1 mg/kg, which is almost 2 times higher than the upper continental crust. Arsenic increases within the more silicic compositions such as dacites and rhyolites as well as from mafic monogenetic volcanic edifices to stratovolcanoes of intermediate composition, silicic calderas and ignimbrite fields. The rate and composition of crustal assimilation by the magmas (enhanced by the crustal thickness up to >70 km) strongly influence the As concentration in volcanic rocks. The assimilation of argillaceous shale-type sediments represents the most important source of As in the magmas. The eruption dynamics has an enormous effect on As concentration. The higher the explosivity of an eruption, the higher the amount of ash that will be formed. Arsenic can be sorb onto ash particles so that fall deposits produced during explosive volcanic eruptions are prone to high As concentrations. Large volume ignimbrites formed after caldera collapses in the Altiplano-Puna are often the result of sustained explosive eruptions related to low, dense pyroclastic fountaining eruptions where highly concentrated pyroclastic density currents (PDC, flowing pyroclastic mixtures of particles and gas) are able to maintain high temperatures for long periods. Then As released from volatiles may remain for longer time in the emplacing PDC and can be sorbed onto ash particles, resulting in deposits with a higher As concentration. Post eruption hydrothermal alteration and sulfide mineralization produce As enrichment up to 100 times in the volcanic rocks (957 mg/kg) of the region, but can be very heterogeneous. Volcanism and its related products are the main source of As in the region. Once As is released from the volcanic sources, the semiarid climate, the occurrence of Na-HCO3 water types, and alkaline pH further enhance As concentrations in surface water and groundwater.

Remote sensing and geochemical investigations of sulfide-bearing metavolcanic and gabbroic rocks (Egypt): Constraints on host-rock petrogenesis and sulfide genesis

Field geology, geochemical analyses and multi-sensor remotely sensed data of Landsat-8, ASTER and Sentinel-2 were used to detect various types of hydrothermal alteration and sulfide-gold mineralization in Neoproterozoic metavolcanic and gabbroic rocks from Darhib and El-Beida areas in the South Eastern Desert (SED) of Egypt. We also used RADAR data of Sentinel-1 using PCI Geomatica software to decipher the structural lineaments that control this mineralization. Different styles of disseminated to massive sulfide deposits include: 1) undeformed magmatic disseminated ores in Darhib gabbros, metavolcanic rocks and metabasic dykes; 2) deformed (remobilized) massive ores mostly of a magmatic-hydrothermal origin in Darhib tremolite talc rocks along E-W shear zones; 3) hydrothermal sulfide ores along El-Beida NW–SE shear zones. Cu-Zn massive ores represent the main sulfides in the Darhib silicified tremolite-talc rocks and meta-andesites, and occur as bands, veins and patches along Darhib E-W shear zones. Discontinuous occurrences of sulfide ores-bearing tremolite-talc rocks indicate that major shear zones act as structural controls on mineralization. Sulfide ores consist chiefly of chalcopyrite, sphalerite, pyrite and galena as well as minor covellite and bornite. These ores are highly concentrated along E-W striking Darhib shear zones and resulted from granite-derived hydrothermal fluids that form/and or accumulate sulfide minerals from the sulfide-bearing metavolcanic rocks around shear zones. Two stages of hydrothermal alterations are recorded in the Darhib talc mine including pre- (talcification, amphibolitization and carbonatization) and syn- (silicification and chloritization) sulfide ore alterations. Disseminated sulfide mineralization hosted in Darhib gabbros, metavolcanic rocks and metabasic dykes is of a magmatic origin, similar to Cu-Ni sulfide deposits hosted in gabbroic varieties in worldwide mafic–ultramafic intrusions. On the other hand, El-Beida gold-sulfide-bearing quartz and quartz carbonate veins are hosted in ferruginated and silicified metavolcanics/ metavolcaniclastic rocks along NW–SE shear zones (Najd Fault System trend). These are spatially associated with regional convergent structures (high-angle convergent wrench structures), suggesting orogenic gold type mineralization. The E-W with minor WNW-ESE shear zones in Darhib and NW-SE trending shear zones in El- Beida structurally controlled sulfides and gold mineralization in the SED of Egypt. El-Beida sulfide mineralization occurs as disseminated ores that consist mainly of pyrite, chalcopyrite, covelite and chalcocite with occasional occurrence of gold. The spatial occurrence of native gold in ferrigenous alteration zones indicates the role of iron in gold precipitation through buffering of gold-bearing complexes. Mineralogical and geochemical data of Darhib and El-Beida sulfide-bearing rocks indicate that they crystallized from depleted mantle sources in a back-arc basin setting, starting with the generation of arc-like volcanic rocks in a nascent BAB stage followed by the emplacement of plutonic equivalent of MORB/OIB-like rocks such as gabbroic intrusions in a mature BAB.

Reconstruction of hydrothermal fluid composition of the Kamthai carbonatite complex, India using lattice strain model: Implications for LREE/HREE fractionation

The composition of the fluid phase is often a poorly constrained variable in many ore deposits. In this study, we used calcite-fluid partition coefficients extrapolated to the P-T conditions of mineralization using the lattice strain model to reconstruct the composition of the hydrothermal fluids associated with different stages of the hydrothermal alteration and secondary rare earth element (REE) mineralization in the Kamthai carbonatite complex of western India. We identified three generations of calcite including magmatic, two generations of secondary/hydrothermal, as well as partially reequilibrated magmatic grains. The magmatic and partially reequilibrated calcite are unusually enriched in the REE, particularly the LREE, and Sr, which were incorporated via coupled cationic substitutions from highly differentiated brine- and incompatible element-enriched carbonatitic melts. Calcite and carbocernaite were the important primary phases that sequestered the REE from the carbonatite magma. Textural and geochemical evidence suggest that magmatic calcite and carbocernaite underwent extensive partial to complete reequilibration through dissolution and reprecipitation during hydrothermal alteration. The prominent chemical changes during the alteration of calcite involved loss of substantial REE, Sr, Fe, and Mn, and transition from LREE-dominated to LREE-poor compositions. The REE released during hydrothermal alteration were incorporated in secondary REE minerals such as REE-(fluor)carbonates, REE-(hydroxyl)carbonates, ancylite, and cerianite. The reconstructed chemistry of the carbonatite melt and the hydrothermal fluid, together with the trace element chemistry of secondary calcite, point towards progressive decrease in the REE contents. However, the HREE were conserved and ƒO2 increased from the most primitive to the most evolved fluid. The REE were redistributed as alkali‑carbonate-hydroxyl complexes, which can explain the LREE/HREE fractionation observed between the early and the late-stage hydrothermal fluid. Precipitation of the LREE-bearing secondary minerals is attributed to a decrease in temperature of the hydrothermal fluid as a consequence of mixing of the carbonatite-derived fluid with a relatively cooler and oxidized fluid. Such mixing explains the observed negative Ce-anomaly in hydrothermal calcite.

Contribution to the characterization of the Nevado del Ruiz geothermal conceptual model based on rock properties dataset

The assessment of the geothermal resources available in a specific area requires a detailed knowledge of the thermal and hydraulic properties of host rock formations. These properties were quantified with rock samples mainly collected at the intersection between Nereidas, Cueva-Pirineos, and La Tosca-El Descanso faults, to the West of the Nevado del Ruiz volcano (Colombia), to improve the characterization of this volcanic geothermal system. The geological formations analyzed in this study are the Cajamarca Complex, PRE-Ruiz lava flows, Andesites unit, and volcanic member of the Quebradagrande Complex. A 3D geological conceptual model for the study area and a geological cross-section are presented. 113 laboratory measurements allowed to quantify thermal conductivity (TC) and diffusivity (TD), heat capacity (HC), porosity, and permeability of the rock samples collected. The Cajamarca Complex is the lithology with the highest TC (2.9 W m−1 K−1), but with the lowest primary permeability (0.038mD) and porosity (3.4%). Regarding extrusive igneous rocks, the Andesites unit present significative porosity (10.7%), and the PRE-Ruiz lava flows show a low TC (1.5 W m−1 K−1). The results of 6 petrographic analyses of thin sections of the PRE-Ruiz lava flows and Cajamarca Complex helped to justify the values of their thermal properties. Quartz-filled veinlets and garnet are identified in the volcanic member of the Quebradagrande Complex. Both minerals indicate that fluids might have circulated at high temperature. It is the first time that garnet is identified in rock samples of this region; since it can be the result of high temperature hydrothermal alteration mineral, its origin must be confirmed, and its identification provides new insights about the geothermal resources in the area. The conceptual model, the thin section results, and the quantification of rock properties are relevant public data for future geothermal development. All data reported in this manuscript are disclosed as supplementary material, providing a significant scientific contribution in the form of an open dataset that can be used as a basis for future hydrothermal modelling of the Nevado del Ruiz geothermal system, where is the most advanced geothermal development project in Colombia, and other similar geothermal systems.

How a basement fault has controlled Pb- Zn ore deposition within the Zagros Fold-Thrust Belt? a focus on remote sensing approaches

ABSTRACT The Zagros fold and thrust belt as one of the structurally complex areas have been considered chiefly only for hydrocarbon reserves, despite having other mineral deposits like the Surmeh lead and Zinc mine. This study was conducted in the Fars region, one of the structural zones in the Zagros, to detect hydrothermal alteration minerals associated with Pb–Zn mineralization and fracture distribution using ASTER, Landsat 8, and Sentinel 2 satellite imagery. Using different algorithms and approaches, we demonstrate the interesting distribution of Pb-Zn-related mineral deposits controlled by structures on different scales. These methods included the spectral band ratios and spectral angle mapping for alteration detection and manual extraction of structural lineaments (i.e. fault and fractures) from ETM+. Also, an augmented circular scanline method, along with areal sampling, was used to prepare a fracture intensity map of the area. According to the results, the intersection of NW-SE and N-S trending fracture sets are promising areas for Pb-Zn-related mineral exploration. These fracture sets are likely associated with the main Karebas tear fault and its horsetail splay terminal. The findings of this study were validated by field observation of the Pb-Zn deposit and its related mineral associations in the area.

Mineral Prospectivity Mapping of Porphyry Copper Deposits Based on Remote Sensing Imagery and Geochemical Data in the Duolong Ore District, Tibet

Several large-scale porphyry copper deposits (PCDs) with high economic value have been excavated in the Duolong ore district, Tibet, China. However, the high altitudes and harsh conditions in this area make traditional exploration difficult. Hydrothermal alteration minerals related to PCDs with diagnostic spectral absorption features in the visible–near-infrared–shortwave-infrared ranges can be effectively identified by remote sensing imagery. Mainly based on hyperspectral imagery supplemented by multispectral imagery and geochemical element data, the Duolong ore district was selected to conduct data-driven PCD prospectivity modelling. A total of 11 known deposits and 17 evidential layers of multisource geoscience information related to Cu mineralization constitute the input datasets of the predictive models. A deep learning convolutional neural network (CNN) model was applied to mineral prospectivity mapping, and its applicability was tested by comparison to conventional machine learning models, such as support vector machine and random forest. CNN achieves the greatest classification performance with an accuracy of 0.956. This is the first trial in Duolong to conduct mineral prospectivity mapping combined with remote imagery and geochemistry based on deep learning methods. Four metallogenic prospective sites were delineated and verified through field reconnaissance, indicating that the application of deep learning-based methods in PCD prospecting proposed in this paper is feasible by utilizing geoscience big data such as remote sensing datasets and geochemical elements.