Gas migration from abandoned legacy wells has been implicated in serious gas-related incidents in southwestern Ontario, with regional investigations identifying Silurian gas-bearing intervals as potential contributors. Direct interval-specific pressure and geochemical data for the Silurian succession remain limited. Re-entry of an undocumented legacy wellbore (T012794) uncovered during excavation in Wheatley, Ontario, enabled characterization of Silurian intervals using mud gas profiles, drill stem tests (DST), and compositional and isotopic analyses.The A2 Carbonate interval had the strongest pressure response and was the only interval to return gas through the DST, identifying it as the strongest candidate contributing reservoir among the tested intervals. Several geochemical indicators overlapped among the Silurian intervals, reflecting natural local geochemical similarity or cross-formational mixing facilitated by legacy wellbores, historical activity, fractures, or faults.The Lower Bass Islands interval exsolved gas differed from the other T012794 gases with more 13C-depleted C1, elevated C2/C3 ratios, and H2S presence. These characteristics were consistent with mixing, secondary alteration, or local geochemical variability but did not resolve the contributing factors. Detection of H2S in the exsolved gas suggested association with formation fluids and that thermogenic gases could interact with H2S-bearing fluids during upward migration.Overlapping regional geochemical datasets may provide insufficient resolution for local well-integrity assessments. Site-specific pressure and geochemical data from discrete stratigraphic intervals provide better constraints on contributing reservoir intervals. At T012794, this approach identified the A2 Carbonate interval as the leading candidate for thermogenic gas contribution and the Lower Bass Islands as a potential H2S-bearing interval.
Although large amounts of organic-rich marine shale were deposited in the foreland basin, the mechanisms governing organic matter enrichment remain debated. The Early Silurian Longmaxi shale in the Upper Yangtze Block provides critical insights into the mechanisms of organic-matter enrichment within a foreland basin. This study integrates seismic stratigraphy, sedimentology, and geochemistry to unravel the influence of tectonic and depositional dynamics on organic matter enrichment. The Longmaxi shale, deposited within a transgressive system tract, is bounded at the top by a maximum flooding surface (MFS) marked by a silty-laminated mudstone unit with a high gamma-ray peak in the lower part of low gamma-ray response, and at the base by an angular unconformity at the Ordovician-Silurian boundary, formed during forebulge migration. The Longmaxi shale consists of four parasequences, with pinch-out lines migrating northwestward toward the Chuanzhong Forebulge Uplift, reflecting westward progradation driven by high sediment flux from the Cathaysia Block. Redox-sensitive proxies (Corg/P and MoEF/UEF ratios) reveal a vertical shift from anoxic (Parasequences 1–2) to suboxic (Parasequences 3–4) conditions during the Rhuddanian sea-level rise; meanwhile, nutrient flux indicators (P and Baex concentrations) show an upward increase of primary productivity. Generally, total organic carbon (TOC) content correlates strongly with the redox-sensitive (the Corg/P ratio) and sedimentation rate (Ti, Al) proxies, but weakly with the primary productivity proxy, Baex concentration. These patterns suggest that organic matter enrichment in the Early Silurian Longmaxi shale of the Upper Yangtze Block was primarily controlled by deepwater oxygen level and inorganic particle dilution. Deglaciation-driven freshwater input enhanced watermass circulation and deepwater oxygenation, thus reduced the preservation efficiency of organic matter, particularly in the foredeep adjacent to the Cathaysia Block. Additionally, although elevated sedimentation rates enhanced primary productivity via increased nutrient supply, the associated dilution by inorganic detrital particles resulted in a marked reduction in organic matter abundance in the foredeep. These findings highlight that high-quality shale gas reservoirs were most likely developed in intervals characterized by persistent anoxia and minimal detrital dilution, providing a predictive framework for sweet spot identification in foreland basin settings.
The expansion of lithium mining in Europe is essential for securing strategic raw materials, but it raises increasing challenges for long-term tailings management. Arsenic (As), present at trace levels in lithium ores, can partition into mine wastes during beneficiation, yet its mineral hosts and solid-phase speciation remain poorly constrained due to low concentrations and diffuse distribution. This limits predictions of arsenic behaviour during processing, leaching, and storage, while current assessments often rely on bulk data that overlook key mineralogical controls. Here, we combine quantitative mineral deportment with As K-edge XANES to characterise arsenic distribution and speciation in ores and residues from three major European lithium projects. Arsenic occurs across sulfide, sulfarsenide, silicate, oxide, and phosphate phases, typically at trace levels but within abundant minerals. Sulfarsenides are dominated by As(–I), whereas other phases show mixed speciation (As(–I), As(III), As(V)). Linear combination fitting indicates overall dominance of As(–I) and As(V), with As(III) minor and sample-specific. XANES of leaching residues reveal the oxidation of arsenic released during arsenopyrite dissolution to As(V), followed by its immobilisation under specific pH conditions, demonstrating that arsenic leaching behaviour at disposal sites is strongly controlled by weathering conditions. Coupled with traditional leaching approaches, this mineral-centric framework quantifies the contribution of As-bearing phases and their control on release across environments, supporting more targeted tailings management and improved environmental strategies for lithium production.
High-temperature geothermal systems in southern Tibet are commonly associated with crustal magmatism and active faulting, but how magmatic heat, fault-controlled circulation, and shallow fluid processes jointly shape their surface hydrochemical signatures remains poorly constrained. Here, we investigate the Daggyai geothermal field on the northern margin of the Yarlung Zangbo Suture Zone using a field-derived dataset of 27 geothermal water samples. In situ physicochemical measurements, major and trace element concentrations, and δD and δ18O compositions were integrated with field structural observations, mineral–fluid equilibrium assessment, geothermometry, Cl-based binary mixing calculations, and isotope reconstruction. The waters comprise 22 alkaline samples (Group 1), three acidic samples (Group 2), and two weakly acidic mixed-type samples (Group 3). Group 1 waters are enriched in Cl, B, Li, and As and preserve the clearest signatures of deep reservoir fluids. Group 2 waters are interpreted as steam-heated waters formed through the condensation and oxidation of H2S-bearing vapor in shallow groundwater, whereas Group 3 records mixing between deep and shallow fluid components. Mineral–fluid equilibrium relationships and Na–K geothermometry indicate a deep reservoir temperature of 252.6–262.5 °C. Reconstructed deep-fluid isotope compositions exhibit pronounced 18O enrichment relative to local meteoric water, consistent with high-temperature water–rock interaction and a magmatic-fluid contribution. These results support a process-based model in which intracrustal magmatic heat sustains the high-temperature reservoir, while deep faults govern meteoric recharge and geothermal-fluid ascent; boiling and near-surface mixing subsequently generate the observed hydrochemical diversity. This study distinguishes deep magmatic and structural controls from shallow geochemical overprinting and provides a transferable framework for the genetic interpretation and resource evaluation of high-temperature geothermal systems in southern Tibet.
Salts produced in traditional saltpans represent a potentially valuable natural resource for wellness and therapeutic applications. However, their properties must be properly assessed to support their safe and effective use in thalassotherapy and dermatological treatments. This study characterized salt samples from traditional and semi-industrial saltpans located in the Ria Formosa (southern Portugal) and Ria de Aveiro (northwest Portugal) coastal lagoons, aiming to evaluate their potential for thalassotherapy and dermatological applications, with particular attention to the influence of oxygen exposure after collection. Twelve representative salt samples were collected and analyzed for mineralogical identification and chemical composition (major, minor, and trace elements, soluble organic matter), complemented by Raman spectroscopy, SEM-EDS, and GC-MS analyses. All samples revealed halite as the dominant mineral phase, with the presence of accessory evaporite minerals, including gypsum, calcite, kieserite, and anhydrite. Raman and SEM-EDS analyses revealed the occurrence of hydrated Mg-sulfates at crystal surfaces, suggesting secondary crystallization processes during evaporation. Comparative analyses between wet and dried samples showed that atmospheric exposure promotes mineralogical diversification, including dehydration reactions and carbonate precipitation. In contrast, submerged salts preserved simpler assemblages dominated by halite, gypsum, and Mg-sulfates, with an absence of PTEs, reflecting a high purity level. Geochemical analyses confirm Na-Cl-type salts with minor Mg, Ca, K, and S contributions, while trace elements such as Cr, Ni, and Zr occur mainly as detrital impurities. These findings highlighted the mineralogical characteristics of Portuguese saltpan-derived salts and support their potential valorization for thalassotherapy and wellness-related applications, while emphasizing the importance of safety assessment.
Clays such as hectorite are major geological sinks for lithium, yet the mechanisms controlling its release during acid dissolution remain poorly constrained. Hectorite from the McDermitt Caldera (Nevada–Oregon, USA) represents one of the most significant clay-hosted Li deposits. Here we combine size separation, mineralogical characterization, and pH- and acid-dependent dissolution experiments with kinetic modeling to elucidate Li release from colloidal hectorite. The colloidal fractions (<1 μm) host nearly 99% of the total lithium, whereas coarser fractions are dominated by quartz, feldspar, and carbonates. The separated (fluo)hectorite exhibits a formula of (Na0·043K0·018Ca0.090) (Li0·329Mg2·538Fe0·107Mn0.005) (Si3·908Al0.092)O10(OH)1·0F1.0 with an apparent solubility constant of log K = −5.7. Dissolution experiments using five acids (H2SO4, HCl, HNO3, H3PO4, and citric acid; 0.02-2 M) reveal a multistep, incongruent release sequence of Ca → Mn → Fe → Al → (Si, Li, Mg, F), reflecting preferential dissolution of isomorphic substitutions. A two-step kinetic model captures this behavior, showing that Li and Mg release from octahedral sites is rate-limiting and that dissolution rates increase with increasing proton activity. A minimum of ∼16.3 protons added per Li released can be achieved by optimizing acid concentration according to reaction stoichiometry. These findings define the structural controls and rate laws governing Li release and provide a mechanistic foundation for efficient and sustainable extraction from clay-hosted lithium resources.
Serpentinization of peridotites is a major source of natural hydrogen (H2), a prospective energy resource and presently a focus of geological exploration worldwide. The Ronda Peridotite Massif (Southern Spain) is one of the world's most extensive peridotite outcrops and hosts numerous gas-bearing hyperalkaline springs and seeps related to serpentinization. However, H2 has been observed only in a few springs at variable, generally low concentrations. Here, we report a new observation of a seep (Vega Escondida) with a large H2 concentration (∼46 vol%), associated with nitrogen, methane, and heavier hydrocarbons; this represents the highest H2 concentration ever documented on the land surface in Western Europe. In addition to episodic free-gas (bubbling) manifestations, the spring water associated with the seep contains ∼540 μM of dissolved H2 and transports to the surface ∼500 L H2 day-1. Lower H2 amounts have been observed in two other springs. The high H2 seep is located at the intersection of two faults separating peridotite and sedimentary flysch rocks, and acting as a preferential pathway for H2 migration from serpentinization fronts that, based on available gravimetric data, should be shallower than 8 km, where temperatures are estimated to not exceed 200 °C. In these conditions, H2 generation rates by serpentinization are not high enough to directly and continuously sustain the relevant H2 flow at the surface. Higher H2 production may have occurred, thanks to higher temperatures, during and after the Miocene peridotite emplacement (around 20 My ago). A comparison with previous investigations reveals that the H2 concentration changes considerably over time at all investigated sites, whereas the bulk and clumped isotope composition of methane associated with H2 is substantially invariable. All data converge on the hypothesis that the Vega Escondida gas stems from a reservoir within the peridotite massif or the adjacent flysch, where H2 (and methane) accumulated over geological time, and that variable interactions with hyperalkaline aquifers, microbial consumption, and seepage intensity modulate the H2 flow to the surface.
Iron nanoparticles (FeNPs) are an important but analytically challenging component of iron in glacier meltwater due to their low concentrations, high particulate loads, and strong dissolved iron backgrounds. Here, we optimized and validated a single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS) method for the size-resolved characterization and quantification of FeNPs in glacier meltwater. By integrating SP-ICP-MS measurements with conventional operational definitions of iron fractions, the <0.45 μm dissolved iron pool is partitioned into nanoparticle iron and baseline dissolved iron. Additionally, when the dissolved Fe background is <0.37 ng mL-1, it provides a coherent framework compatible with established glacial geochemical datasets. Method evaluation demonstrates that both the filtration strategy and dissolved iron background exert first order controls on the detection of FeNPs. Results show that the 0.45 μm filtration offers the most robust balance between removing coarse-particle interference and retaining representative FeNPs populations. In contrast, finer filtration leads to their systematic underestimation, whereas not filtering samples elevates and distorts particle pulse intensities and inflates SP-ICP-MS-derived particle sizes. The application of the proposed optimized method to meltwaters from the Tibetan Plateau’s Kuoqionggangri and Rongbuk glacier systems reveals a consistent iron partitioning scheme, with particulate iron dominating total iron and FeNPs constituting a persistent but quantitatively subordinate fraction of the <0.45 μm pool. Despite variability in iron concentrations and hydrological settings, FeNPs exhibit stable modal particle diameters within the 19.6 to 46.8 nm range, indicating a reproducible nanometer-scale signature of glacially derived iron. Overall, this study establishes SP-ICP-MS as a robust and operationally constrained method for resolving iron nanoparticles in glacier meltwater and provides a practical basis for consistent size-resolved investigations of iron in cryospheric environments.
This study focuses on the geochemistry of Rare Earth Elements (REE) and Li in the hyperalkaline soda brine of the remnant Rincón de Parangueo (RDP) maar lake, Mexico, a system characterized by the ongoing precipitation of trona, thermonatrite, halite and sylvite. Total REE concentrations in water range between 13.5 and 26.9 μg kg-1, while higher concentrations (688-1,302 μg kg-1) were found in the associated bulk mineral precipitates (trona, thermonatrite, halite and sylvite). Lithium concentrations are higher than REE concentrations, in both RDP waters and bulk minerals. Lithium concentrations in RDP waters and bulk minerals precipitated are quite similar, ranging from 53.8 to 126.5 mg kg-1 and from 51.3 to 149.1 mg kg-1, respectively. Post Archean Australian shale (PAAS) normalized REE patterns in the waters increase from La to Lu. In contrast, PAAS normalized REE patterns of the bulk minerals are different from those of waters, also increasing from La to Lu but with a less pronounced trend. The distribution coefficient (KD) of REE and Li were calculated between the bulk precipitated minerals and the coexisting lake water. KD values of REE decrease from La to Lu and are significantly higher (6-1154), compared to KD values of Li (0.5-0.8). The REE patterns in waters, which increase from La to Lu, can be explained by the KD values, indicating preferential removal of LREE relative to HREE during mineral precipitation. Similar lithium concentration ranges in waters and bulk minerals are consistent with the low KD of Li, indicating a limited removal of Li from the solution during mineral precipitation.
Mercury (Hg) contamination in coastal sediments poses significant ecological and health risks, necessitating comprehensive assessments under the Minamata Convention. This study investigates the spatial distribution and potential ecological risks of Hg in surface sediments from 15 diverse Cuban coastal environments. Sediment samples were collected and analyzed for total Hg (ranging from 0.001 to 16.5 mg·kg-1), and a reference value of 0.090 ± 0.059 mg·kg-1, defined as the geochemical background level for Hg in marine sediments, was derived using a cumulative distribution function method. Contamination degree was assessed using the Contamination Factor (CF), and the ecological risk was quantified using the Ecological Risk Index, the Threshold Effect Level (TEL), the Probable Effect Level (PEL), and the novel Composite Environmental Vulnerability Index (CEVI). Results revealed pronounced Hg enrichment in anthropogenically influenced sites, with Sagua la Grande River and Havana Bay exhibiting extremely high CF values and frequent exceedances of the PEL, identifying them as regional hotspots driven by industrial legacies and urban pressures. The CEVI effectively linked Hg levels to industrial and population factors. Compared to global hotspots, these findings provide a critical baseline for Cuba, supporting Minamata Convention monitoring and urging future studies to focus on temporal data, speciation, and bioaccumulation.
Uraniferous black slates of the Biryeri deposit in the Ogcheon Metamorphic Belt (OMB), South Korea, record multistage uranium enrichment within a rift-related black shale system subsequently modified by hydrothermal activity and regional metamorphism. This study integrates mineralogical, whole-rock geochemical, fluid inclusion, Raman spectroscopic, and stable isotope (C–O–H–S) data to constrain the origin and evolution of mineralization in black slate and interbedded coaly slate. The two lithologies exhibit contrasting mineral assemblages. Black slate contains mainly coffinite and brannerite, whereas the coaly slate is dominated by uraninite associated with quartz veins, V-rich muscovite, goldmanite, molybdenite, and Ni-bearing sulfides. The coaly slate is strongly enriched in U (up to 1,651 ppm), V, Mo, and Ni and shows Mn depletion. High V/Cr and V/(V + Ni) ratios, elevated U and Mo enrichment factors, positive Eu anomalies, and high U/Th and Nd/Yb ratios indicate modification by high-temperature (>250 °C) hydrothermal fluids under strongly reducing conditions. Fluid inclusions temperatures of 253–450 °C and isotope data are consistent with the magmatic water range, with limited seawater or meteoric input. Carbon and sulfur isotopes indicate a marine black shale precursor subsequently overprinted by thermochemical sulfate reduction. Uranium mineralization at the Biryeri deposit reflects a multi-stage evolution involving black shale sedimentation in a rift-related marine basin, magmatic–hydrothermal remobilization and upgrading, and low-grade metamorphic recrystallization, highlighting the key role of magmatic fluids in concentrating uranium within black shale system under reducing environments.
The simultaneous immobilization of arsenic (As) and antimony (Sb) in groundwater is challenged by their competitive interactions, which are strongly influenced by pH fluctuations and complex speciation. Based on permeable reactive barrier (PRB) technology, this study demonstrates the feasibility of manipulating the intrinsic alkalinity of goethite-based fillers using cement to effectively immobilize As(V) and Sb(V) in co-contaminated groundwater. Ordinary Portland cement (OPC), slag-modified Portland cement (SPC), and sulphoaluminate cement (SAC) with distinct hydration reaction were used as binders to fabricate goethite-based fillers with varying solid-phase alkalinity gradients. Batch experiments revealed that the OPC-filler with the highest alkalinity demonstrated preferable immobilization capacity for both As(V) and Sb(V) compared with the SPC- and SAC-fillers under varying initial pH, coexisting ions, and natural organic matter conditions. Duration tests confirmed that the OPC-filler could maintain stable immobilization of both As (>98%) and Sb (>86%) under high-flow-rate accelerated conditions, whereas the other fillers showed rapid Sb breakthrough. Integrated post-test characterizations and geochemical modeling revealed a dual immobilization pathway in the filler: As(V) was primarily immobilized via adsorption onto goethite, whereas Sb(V) immobilization was enhanced by the high-alkalinity microenvironment, which promoted the precipitation of calcium with Sb(V). These findings demonstrate that engineering the intrinsic solid-phase alkalinity of goethite-based PRB filler is an effective strategy for achieving simultaneous immobilization of As(V) and Sb(V) in groundwater.
The dissolution of manganese (Mn) (hydr)oxides induced by low-molecular-weight organic compounds (LMWOCs) critically influences Mn and carbon cycling, yet limited high-resolution characterization hinders mechanistic understanding. Here, we investigated the dissolution kinetics of Mn(III/IV) (hydr)oxides mediated by citric acid, pyruvic acid, oxalic acid, and hydroquinone, as well as the controlling factors (LMWOC type and concentration, pH, and coexisting ions), by real-time and in-situ electrochemical quartz crystal microbalance (EQCM), complemented by grazing-incidence wide-angle X-ray scattering (GIWAXS) and kinetic modeling. Hydroquinone and citric acid promoted significant dissolution at pH 5 and 6, with hydroquinone dominating initially but slowing later; at pH 7, hydroquinone remained highly effective, far surpassing citric acid. In contrast, pyruvic acid and oxalic acid at pH 5, 6, and 7 showed negligible dissolution. Citric acid– and hydroquinone–mediated dissolution exhibited characteristic S-shaped kinetics with induction, acceleration, and deceleration stages, indicating an autocatalytic pathway, whereas pyruvic acid and oxalic acid showed no such pattern. Analysis of controlling factors showed that citric acid–mediated dissolution increased with increasing citric acid concentration and decreasing pH. Coexisting ions, including NO3-, Cl-, SO42- (5–50 mM), and Mg2+, Ca2+, Zn2+ (0.5–4 mM), inhibited the dissolution. Notably, HPO42- and P2O74- (0.1–1 mM) and Mn2+ (0.5–4 mM) exhibited concentration-dependent dual effects on dissolution, arising from competing promotive and inhibitory processes. GIWAXS analysis revealed that citric acid–mediated dissolution of Mn(III/IV) (hydr)oxides was facet-dependent, whereas exogenous Mn2+ promoted non-selective citric acid–mediated dissolution. This study provides insights into complex interfacial geochemical processes on redox-active minerals.
Fe(II)-bearing geologic media are a promising sink for the consumption of dissolved oxygen (DO) remaining in geologic formations after backfilling of radioactive waste repositories, which prevents redox-sensitive radionuclides from becoming soluble and mobile in groundwater. To assess the effect of DO, the DO consumption rate has been measured using commercially available oxygen electrodes and electrochemical techniques; however, when performing DO consumption experiments in closed systems with respect to DO, DO consumption associated with electrochemical measurements, independent of water–rock interactions, remains an issue that requires improvement. To address this, we propose a measurement system for quantifying DO consumption. Accordingly, DO consumption experiments on Fe(II)-bearing rock samples were performed using a luminescence-based oxygen sensor without oxygen consumption. The samples used in this study were selected as sedimentary samples that had been previously investigated, because the applicability of the sensor was evaluated, as well as the addition of the rate data. Consequently, the DO concentration in the experimental solution decreased as previously observed. However, this decrease in DO can be primarily attributed to the consumption of DO by Fe(II)-bearing minerals in the rock samples, rather than interference from the oxygen sensor. The resulting second-order rate constants strongly support the previously reported rate data and improve reproducibility for this measurement system. These findings contribute to preliminary predictions of recovery from oxic to anoxic conditions in geologic formations and provide insight into the temporal evolution of subsurface DO in the vicinity of a repository.
