Search Results (78)

Underground hydrogen storage (UHS) in carbonate and siliceous formations presents a promising solution for managing intermittent renewable energy. However, experimental data on hydrogen–rock interactions under representative subsurface conditions remain limited. This study systematically investigates mineralogical and petrophysical alterations in dolomite, calcite-rich limestone, and quartz-dominant siliceous cores subjected to high-pressure hydrogen (100 bar, 70 °C, 100 days). Distinct from prior research focused on diffraction peak shifts, our analysis prioritizes quantitative changes in mineral concentration (%) as a direct metric of reactivity and structural integrity, offering more robust insights into long-term storage viability. Hydrogen exposure induced significant dolomite dissolution, evidenced by reduced crystalline content (from 12.20% to 10.53%) and accessory phase loss, indicative of partial decarbonation and ankerite-like formation via cation exchange. Conversely, limestone exhibited more pronounced carbonate reduction (vaterite from 6.05% to 4.82% and calcite from 2.35% to 0%), signaling high reactivity, mineral instability, and potential pore clogging from secondary precipitation. In contrast, quartz-rich cores demonstrated exceptional chemical inertness, maintaining consistent mineral concentrations. Furthermore, Brunauer–Emmett–Teller (BET) surface area and Barrett–Joyner–Halenda (BJH) pore distribution analyses revealed enhanced porosity and permeability in dolomite (pore volume increased >10×), while calcite showed declining properties and quartz showed negligible changes. SEM-EDS supported these trends, detailing Fe migration and textural evolution in dolomite, microfissuring in calcite, and structural preservation in quartz. This research establishes a unique experimental framework for understanding hydrogen–rock interactions under reservoir-relevant conditions. It provides crucial insights into mineralogical compatibility and structural resilience for UHS, identifying dolomite as a highly promising host and highlighting calcitic rocks’ limitations for long-term hydrogen containment. Full article

Understanding the mechanical properties of the constituent minerals of shales is of significance for gaining insight into the macroscopic mechanical behavior of shales. In this paper, a method combining nanoindentation with a TESCAN Integrated Mineral Analyzer (TIMA) was used to determine the mechanical properties of shale constituent minerals. The hardness and elastic modulus of five independent mineral phases and a mixed phase were detected. The order of the hardness of these five independent mineral phases is dolomite (4.90 ± 2.33 GPa) > wollastonite (4.84 ± 0.54 GPa) > ankerite (4.17 ± 1.37 GPa) > quartz (3.98 ± 0.67 GPa) > calcite (2.03 ± 0.29 GPa), and the order of the elastic modulus is dolomite (104.89 ± 11.25 GPa) > ankerite (103.70 ± 19.62 GPa) > wollastonite (100.78 ± 6.66 GPa) > quartz (88.04 ± 14.58 GPa) > calcite (78.20 ± 3.85 GPa). The mechanical properties of the shale mineral grain junctions are weaker than those inside the grains. When shale is subjected to an external load, it is more prone to intergranular failure. The proposed method in this study can rapidly and accurately probe the in situ mechanical properties of shale minerals. The results of this study enrich the database of in situ mechanical properties of shale minerals and provide a new insight into the macroscopy failure mode of shale. Full article

This study focuses on the Hailijing sandstone-hosted uranium deposit in the Songliao Basin. Through a combination of petrographic analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and geochemical analysis, the epigenetic alteration of the deposit was systematically investigated, and the alteration zonation was delineated. On this basis, the metallogenic mechanisms were further explored. The results indicate that six major types of alteration can be identified in the ore-bearing strata of the Hailijing uranium deposit: hematitization, limonitization, carbonatization, pyritization, clay mineralization (including kaolinite, illite, and illite-smectite mixed-layer), and baritization. The mineral assemblages at different stages of alteration vary: during the sedimentary diagenetic stage, the assemblage consists of “hematite + clay minerals + II-type pyrite (framboidal pyrite) + III-type pyrite (euhedral granular pyrite)”; during the uranium mineralization stage, it transitions to “ankerite + barite + I-type pyrite (colloidal pyrite) + minor kaolinite”; and in the post-ore stage, alteration is characterized by calcite cementation in red sandstones. Based on petrological, mineralogical, and geochemical characteristics, as well as the spatial distribution of the host gray sandstones, it is inferred that during uranium mineralization stage, the ore-bearing strata underwent reduction by uranium-rich reducing fluids sourced from the Lower Cretaceous Jiufotang Formation. The primary red sandstones of the Lower Yaojia Formation, formed under arid to semi-arid conditions, experienced varying degrees of reduction, resulting in a color transition from light red, brownish red, and yellowish brown to grayish-yellow and gray. Accordingly, four alteration zones are distinguished in the Hailijing uranium deposit: the primary red zone, weakly reduced pink zone, moderately reduced grayish-yellow zone, and strongly reduced gray zone. Furthermore, as the uranium-rich reducing fluids migrated from a high-temperature, high-pressure deep system to the low-temperature, low-pressure ore-bearing sandstone strata near the surface, uranium was unloaded, precipitated, and enriched, ultimately forming multi-layered and tabular-shaped uranium orebodies within the gray sandstone. This study elucidates the epigenetic alteration processes and metallogenic mechanisms of the Hailijing uranium deposit, providing a critical theoretical basis for further uranium exploration in the southern Songliao Basin. Full article

The Drake Goldfield, also known as Mount Carrington, is located in north-eastern New South Wales, Australia. It contains a number of low–intermediate-sulfidation epithermal precious metal deposits with a current total resource of 724.51 metric tons of Ag and 10.95 metric tons of Au. These deposits occur exclusively within the Drake Volcanics, a 60 × 20 km NW-SE trending sequence of Late Permian volcanics and related epiclastics. Drilling of the Copper Deeps geochemical anomaly suggests that the volcanics are over 600 m thick. The Drake Volcanics are centered upon a geophysical anomaly called “the Drake Quiet Zone” (DQZ), interpreted to be a collapsed volcanic caldera structure. A total of 105 fresh carbonate samples were micro-drilled from diamond drillcores from across the field and at various depths. A pXRD analysis of these carbonates identified five types as follows: ankerite, calcite, dolomite, magnesite, and siderite. Except for three outlier values (i.e., −21.32, −19.48, and 1.42‰), the δ¹³C_VPDB generally ranges from−15.06 to −5.00‰, which is less variable compared to the δ¹⁸O_VSMOW, which varies from −0.92 to 17.94‰. μ-XRF was used to analyze the elemental distribution, which indicated both syngenetic/epigenetic relationships between calcite and magnesite. In addition, a total of 53 sulfide samples (primarily sphalerite and pyrite) from diamond drillcores from across the Drake Goldfield were micro-drilled for S isotope analysis. Overall, these have a wide range in δ³⁴S_CDT values from −16.54 to 2.10‰. The carbon and oxygen isotope results indicate that the fluids responsible for the precipitation of carbonates from across the Drake Goldfield had complex origins, involving extensive mixing of hydrothermal fluids from several sources including those of magmatic origin, meteoric fluids and fluids associated with low-temperature alteration processes. Sulfur isotope ratios of sulfide minerals indicate that although the sulfur was most likely derived from at least two different sources; magmatic sulfur was the dominant source while sedimentary-derived sulfur was more significant for the deposits distal from the DQZ, with the relative importance of each varying from one deposit to another. Our findings contribute to a greater understanding of Au-Ag formation in epithermal environments, particularly in collapsed calderas, enhancing exploration strategies and models for ore deposition. Full article

The pore structure and connectivity of coal are the primary factors influencing the permeability of coal reservoirs. However, clay and carbonate minerals are commonly found filling the pores and fractures within coal. To address the impact of these minerals on fracturing effectiveness, acidic fracturing technology has been introduced. This technique has proven to be an effective measure for enhancing the extraction rate of low-permeability coal seams with high mineral content. In this study, coal samples were treated with a 3% HCl solution, and the changes in the pore structure of the coal before and after acidification were analyzed through low-temperature nitrogen adsorption and X-ray diffraction (XRD) testing. The results were as follows: After acidification, the specific surface area, total pore volume, pore volume in different stages, and average pore size of the coal samples all significantly increased. Specifically, the BET specific surface area grew by an average of 4.8 times and the total pore volume expanded by an average of 7.7 times, with the pore volumes in the pore size ranges of <10 nm and 10–60 nm increasing by an average of 10.1 times and 7.7 times. The smoothness of the pore surface and connectivity of the pore structure in the coal samples improved, as indicated by decreased fractal dimensions D₁ (reflecting pore surface roughness) and D₂ (representing pore size distribution uniformity). The acidification mechanism was mainly attributed to the dissolution of carbonate minerals in the coal, which led to the removal of obstructive minerals such as ankerite and calcite that had accumulated in the coal pores. This resulted in the formation of new micropores and microfractures, achieving pore volume enhancement and pore expansion. Full article

The northeastern Hunan district in the Jiangnan Orogen (South China) holds significant gold resources, whose genesis remains perplexing, especially in terms of the gold source and mineralization process. Yanzhupo (2.50 t @ 2.52 g/t) is a newly discovered gold deposit in the northeastern Hunan district and is characterized by multiple generations of pyrite. Its alteration/mineralization can be divided into three stages: (I) quartz-ankerite-pyrite; (II) quartz-ankerite-chlorite-pyrite-gold; (III) quartz-ankerite-calcite-pyrite. Petrographic observations and back-scattered electron (BSE) imaging revealed six generations of pyrite: Cu-Au rich bright rims (Py1a) and porous cores (Py1b) in Stage I, Py2a with homogenous textures, Py2b with oscillatory zoning and Py2c with homogenous textures in Stage II and Py3 with homogenous textures in Stage III. Galena Pb isotopes, similar to the Wangu deposit, and pyrite chemical compositions show that the ore-forming materials of Yanzhupo came from deep magma, and some metal elements may be extracted from deep basement by fluid-mineral interactions during the upward migration of hydrothermal-magmatic fluid. The positive correlation between Cu and Au in pyrite reflects the oxidized ore-forming fluids. The enrichment of Cu and Au in Py1a reflects the precipitation of pyrite under high temperature fluid, forming the primary enrichment of Au. Porous Py1b is characterized by lower trace elements than Py1a, sharp reaction front and rich chalcopyrite and galena inclusions, indicating Py1b formed via coupled dissolution-reprecipitation (CDR) reactions of Py1a. The CDR reactions promoted by the oxidizing fluid itself re-release Au into the fluid. From Py2a to Py2c, the contents of As, Sb and Pb first increased and then decreased, which may reflect the increase of fluid pH caused by sulfidation of the wall rocks and the impoverishment of ore-forming fluids caused by the precipitation of a large number of elements. The sulfidation of the wall rocks in Stage II destroyed the stability of the Au(HS)₂⁻ and Au (HS)S₃⁻ complexes and led to the deposition of native gold. The barren ore-forming fluids precipitated homogenous Py3 in a stable environment. Therefore, we think that the Yanzhupo gold deposit may have been associated with magmatic-hydrothermal activity, and the mineralization mechanism may be CDR reactions and sulfidation of the wall rocks. Full article

Pogo is identified as a deep-seated, intrusion-related gold deposit. Carbonate minerals have a close spatial relationship to hydrothermal gold mineralization in all of its principal ore zones. The carbon and oxygen isotopic ratios of carbonate minerals (siderite, ankerite, and calcite) present within the deposit illustrate the isotopic evolution of the ore-forming fluid. The initial hydrothermal fluid phase is interpreted to be magmatic in origin. The fluid evolution was characterized by a gradual decrease in δ¹⁸O and a slight increase in δ¹³C with decreasing temperature. The dominant carbon-bearing species was CO₂, with methane introduced sporadically. Siderite is associated with early-stage mineralization and occurs with ankerite in main-stage ore assemblages. Calcite is recognized in the later stages of mineralization. Gold in the Pogo deposit occurs as native gold, Au-Bi-Te minerals, inclusions in sulfide minerals, or as “invisible gold”. The latter is found in pyrite, chalcopyrite, arsenopyrite, and quartz, based on ion microprobe analysis. The presence of invisible gold in these minerals has significant metallurgical implications for gold processing at the Pogo mine. Full article

This study employs logging, petrology, and geochemistry to investigate the characteristics, origin, and hydrocarbon significance of fractures and (ferro) dolomite veins in a buried hill in the Qiongdongnan (QDN) Basin, South China Sea. We show that the study area is mainly characterized by three stages of fracturing with medium-high dipping angles. The orientation of the fractures is mainly NNW–SSE, consistent with the fault system strike formed by the Mesozoic–Cenozoic tectonic activity in the basin. (Ferro) dolomite veins in the fractures can be classified into three stages, all of which can be even observed in individual fractures. The first stage is the powdery crystal dolomite veins grown mainly on the fracture surface, which have the highest strontium isotope values, as well as high contents of the Mg element and extremely low contents of the Fe and Mn elements. The first-stage veins were formed in a relatively open oxidized environment, and the vein-forming fluids exhibit characteristics of mixing formation water and atmospheric freshwater within the fractures. The second stage, involving fine-crystal dolomite veins, was formed in a buried diagenetic environment where groundwater mixed with deep hydrothermal fluids, and contained the highest carbon isotope values, more Fe and Mn elements, and less Mg element than the first stage. The third stage of medium-crystal ankerite veins was formed in the latest stage, with the lowest strontium and oxygen isotope values. This was mainly a result of deep hydrothermal formation in which the rock-forming material formed from the interaction between the hydrothermal fluid and the iron-rich and aluminosilicate minerals in the surrounding granite of the fractures. We conclude that the multi-phase tectonic movements form a massive scale reticulated fracture inside the granite buried hill, which effectively improves the physical condition of the gas reservoirs. The gas reservoirs remain of high quality, despite the filling of the three stages of (ferro) dolomite veins. Full article

The Qinshui Basin is located in the southeast of Shanxi Province, China. It is one of the most abundant coal resources from Permo-Carboniferous North China. It is rich in coal and coalbed methane resources. However, the accumulation of coalbed methane is complex and the enrichment law has not been fully understood because of the high heterogeneity of coal reservoirs in the Qinshui Basin. The examination of dissimilarities between tectonically deformed coals (TDCs) and primary coals at multiple scales holds paramount importance in advancing our understanding of the occurrence and flow patterns of coalbed methane, and in providing guidance for exploration efforts. In the present study, the samples from the Jincheng Mine, Qinshui Basin, were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), CO₂ gas adsorption and 3D X-ray micro-computed tomography. The results showed that the dominant minerals in coal were illite, kaolinite, and calcite, with minor amounts of quartz and ankerite. In comparison to primary coal, tectonism could increase the microfractures density of type A (the fracture of width ≥ 5 μm and length > 10 mm) in TDCs. In CO₂ gas adsorption in mylonite coal, it was observed that the volume of micropores (<2 nm) was significantly reduced leading to a decrease in gas adsorption capacity. The result of Micro-CT scanning revealed that the minerals occurred as veins in primary coal, but as irregular aggregates in TDCs. Moreover, tectonism had a staged impact on fracture structure, which was initially closed in cataclastic coal and then formed into granulated coal during the tectonic evolution. The effects of tectonism on coal structure had an impact on the connectivity of micropores at the micrometer scale by the destruction of the pore throat structure, increasing the heterogeneity of the reservoir. These findings help to better understand the changes in TDC structure at different scales for developing effective strategies for coalbed methane exploration and production. Full article

Dengfeng Coalfield represents a significant coalfield in Henan Province, North China. It is therefore essential to gain an understanding of the mineralogy and geochemistry of the Dengfeng coal, both from a geochemical perspective and in terms of the wider environmental context. In this study, a total of 27 coal bench samples were collected from the No. II1 coal of the Dengfeng Coalfield. The mineral species and major elements were quantitatively analysed using the X-ray diffraction and X-ray fluorescence methods, respectively. The minerals in the Dengfeng coal are dominated by ammonian illite and kaolinite with average contents of 3.73% and 7.47%, respectively. These are followed by calcite (2.74% on average) and ankerite (0.49%). The mean value of the kaolinite Hinkley index, which is a quantitative measure of kaolinite crystallinity, is 1.26. This suggests that kaolinite formation is primarily driven by diagenetic recrystallisation. The ammonian illite exhibits an average d₀₀₁ of 10.2995 Å, indicative of a prevalence of NH₄⁺ interlayer cations, with K⁺ also present in notable quantities. The ratio of NH₄⁺ to (NH₄⁺ + K⁺) has an average value of 0.90, which is indicative of the predominance of NH₄⁺. The mean value of the illite Kübler index, which is a quantitative measure of illite crystallinity, is 0.264. This suggests that the diagenetic conditions correspond to the rank of the Dengfeng coal. The kaolinite present in the Dengfeng coal is suggested to have been derived from terrigenous detritus and subsequently subjected to diagenetic recrystallisation, resulting in a relatively high Hinkley index. The ammonian illite in the Dengfeng coal was predominantly formed through the conversion of the precursor kaolinite, with the influence of seawater during peat accumulation favouring the conversion of kaolinite to ammonian illite. Full article

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. Full article

The Hayabusa2 space mission recently retrieved 5.4 g of material from asteroid Ryugu, providing the first direct access to pristine material from a carbonaceous asteroid. This study employs a novel combination of non-invasive synchrotron X-ray techniques to examine microscale chemistry (elemental distributions and element-specific chemical speciation and local structure) inside Ryugu grains without physically cutting the samples. Manganese primarily occurs in carbonate: Mn-bearing dolomite with minor earlier ankerite. Iron sulfides present as large single grains and as smaller particles in the finer-grained matrix are both predominantly pyrrhotite. At the 5 μm scale, Fe sulfides do not show the mineralogical heterogeneity seen in many carbonaceous meteorites but exhibit some heterogeneous localized oxidation. Iron is present often as intergrowths of oxide and sulfide, indicating incomplete replacement. Trace selenium substitutes for S in pyrrhotite. Copper is present as Fe-poor Cu sulfide. These results demonstrate multiple episodes of fluid alteration on the parent body, including partial oxidation, and help constrain the sequence or evolution of fluids and processes that resulted in the current grain-scale mineralogical composition of Ryugu materials. Full article

The diagenetic evolution of sandstone is very complicated under the conditions of high temperatures and pressures in deep-water, deep-buried regimes, which have great influence on reservoir quality. This study investigates the typical reservoir target of Neogene deep-water, submarine-fan sandstones under high-temperature, high-pressure regimes in the Qiongdongnan Basin, South China Sea. Utilizing a thin section, scanning electron microscope (SEM), mineral geochemistry combined with burial history evolution, complex diagenetic events, and main controlling factors of the sandstone in the Neogene Meishan Formation were determined. The results show that the evolution of sandstone reservoirs is initially controlled by depositional framework compositions and subsequently modified by eogenetic and mesogenetic alterations during progressive burial. Eogenetic alterations mainly include the following: (1) mechanical compaction; (2) dissolution of feldspar; (3) low-Fe calcite cementation. Mesogenetic events were identified as the following: (1) dissolution of feldspar; (2) ferroan calcite and ankerite formation; (3) precipitation of quartz and clay mineral. Mechanical compaction is greatly influenced by the original depositional framework composition, and sandstone samples enriched in high contents of detrital clay matrix always experienced extensive mechanical compaction. Different phases of carbonate cement during different diagenetic regimes lead to continuous destruction on reservoir porosity. The dissolution of unstable feldspar minerals during eogenetic and mesogenetic environments leads to the development of secondary porosities and would enhance the quality of the reservoir. Overpressure formation is pervasively developed owing to early disequilibrium compaction and subsequent natural gas charging. Only well-sorted sandstones with low contents of detrital clay matrix could resist early mechanical compaction, lead to ample residual original porosities, and then undergo extensive mineral dissolution to generate sufficient secondary porosities. Subsequently, these porosities would be effectively protected by overpressure formation. Poor-sorted sandstones with high contents of detrital clay matrix would experience strong mechanical compaction and extensive destruction of original porosities. Thus, these sandstones are difficult to have significant dissolution and are unable to be effectively protected by overpressure formation. Therefore, the interplay between the original framework composition and the corresponding diagenetic pathways coupled with overpressure formation would result in strong reservoir heterogeneity for the deep-buried sandstones during progressive burial. Full article

The migration of 32 elements from natural zeolitized tuffs from the Beli Plast and Golobradovo deposits (Bulgaria) was determined in ultrapure, tap, mineral, and coal mine waters in order to evaluate their desorption and adsorption properties. The tuffs are Ca-K-Na and contain clinoptilolite (90 and 78wt.%, respectively), plagioclase, sanidine, opal-CT, mica, quartz, montmorillonite, goethite, calcite, ankerite, apatite, and monazite. The desorption properties are best revealed during the treatment of ultrapure, tap, and mineral water, whereas the adsorption properties are best manifested in coal mine water treatment. The concentrations of Al, Si, Fe, Na, Mn, F, K, Pb, and U increase in the treated ultrapure, tap, and mineral water, while the content of K, Be, Pb, and F increase in the treated mine water. The tuffs show selective partial or complete adsorption of Na, Mg, Sr, Li, Be, Mn, Fe, Co, Ni, Cu, Zn, Al, Pb, U, and SO₄²⁻. They demonstrate the ability to neutralize acidic and alkaline pH. Sources of F are presumed to be clinoptilolite and montmorillonite. The usage of zeolitized tuffs for at-home drinking water treatment has to be performed with caution due to the migration of potentially toxic and toxic elements. Full article

Carbon steel and bentonite are materials selected as engineered barriers for high-level radioactive waste confinement. Their long-term interaction must be evaluated to confirm the barrier’s stability. Three laboratory experiments of the carbon steel—Mg-bentonite interaction were conducted for 1, 6, and 22 months under a hydrothermal gradient. Changes in bentonite’s water content, specific surface area, and cation exchange capacity were measured. Mineralogy was studied by X-ray diffraction and scanning electron microscopy. The redistribution of aqueous species and the redox state of iron were determined across the bentonite columns. Results indicated water saturation after 22 months. The specific surface area of bentonite was reduced near contact with the steel, while the cation exchange capacity mostly decreased at 3–6 mm from the steel interface. The corrosion rate decreased with time and bentonite enriched in Fe in the first 1.5 mm from the steel contact. The formation of new Fe-bearing minerals, such as di-tri ferri-sudoite, magnetite, hematite, maghemite, lepidocrocite, siderite and ankerite was observed. Aqueous species redistributed in the porewater of bentonite with decreasing concentrations of Fe and Cl as a function of time and increasing concentrations of Na, Ca and SO₄ after 22 months. This occurs under conditions where the bentonite is saturated with Mg, which conditioned the formation and nature of iron clay minerals with time. Full article