Interpreting speleothem carbon isotope (δ13C) records as paleohydrological proxies necessitates a mechanistic understanding of signal transfer within the karst critical zone. This study presents a high-resolution monitoring program (2023–2025) encompassing soil CO2, drip water, and modern carbonate precipitates in Liangfeng Cave, southwest China, specifically assessing the impact of seasonal hydrological extremes. Seasonal variations in soil CO2 concentration and δ13CCO2 broadly corresponded with changes in drip water δ13CDIC, while HCO3- and δ13CDIC exhibited a negative relationship across the monitored sites, consistent with an important contribution from seasonally varying biogenic carbon inputs. However, the transmission of this primary environmental signal exhibits pronounced spatial heterogeneity, modulated by local hydrogeological routing and microclimatic gradients. At proximal, well-ventilated sites, reduced drip rates during hydrological deficits prolong fluid residence times, potentially promoting kinetic 13C enrichment and prior calcite precipitation (PCP), which may contribute to the apparent decoupling of the DIC–carbonate isotopic offset from the seasonal temperature gradient. Conversely, distal, deep-cave sites with stable microclimates appear to show reduced sensitivity to short-term hydrological forcing at the temporal resolution of this study, maintaining a relatively stable isotopic regime. Furthermore, extreme hydrological deficits are associated with pronounced departures from the typical seasonal isotopic pattern, generating substantial positive δ13C anomalies that may reflect kinetic overprinting and complicate their direct interpretation as indicators of aridity. These findings highlight the need to evaluate site-specific kinetic effects in similar shallow or well-ventilated cave settings before paleoclimatic interpretation.
Uncontrolled coal fires in the Jharia coalfield, India, are examples of one of the worst forms of anthropogenic pollution, as they introduce a broad range of geotoxic compounds into the environment. This study examined the occurrence and distribution of fluoride and heavy metals in fire-affected villages of the Jharia region in various environmental media - coal, soil, plants, condensates/ sublimates, standing water, and foliar dust. The levels of fluoride were extraordinary, 411-622 mg kg-1 in coal, 166-147,333 mg kg-1 in condensates, 328-415mg kg-1 in soils, and 134-150 mg L-1 in water samples- way above the normal levels found in the environment. Fe (up to 37,070 mg kg-1), and Zn (268-449 mg kg-1) were highly enriched, and Mn, Mg, Cr, Cu, and Pb were moderately enriched. Geo-statistical indices showed that there is extreme Fe pollution (Igeo = 6.44-7.43) and moderate Zn contamination (Igeo = 1.09-1.30), PLI value (1.59-2.23). The highest bioaccumulation factor (BAF) for fluoride was observed in Ageratum conyzoides (9.34) and Croton bonplandianum (5.47), indicating that they are potential accumulator. The results indicate that during combustion of coal, volatilized minerals, such as fluorapatite, contribute to extensive contamination of the atmosphere and soil in the immediate vicinity, posing a high ecological and human health risk, particularly in areas with high concentrations in the condensates. Further, the hazard quotients and hazard indices (HI) were <1, indicating no significant non-carcinogenic health risk under the assessed exposure conditions. In addition, the elevated carcinogenic risk was observed in some selected condensate samples. There should be continuous monitoring and remediation measures that will reduce fluoride and heavy metal exposure in this susceptible coal-mining area.
The Guska Cu occurrence in the Kurdistan Region is hosted by Miocene sandstones of the Redbed Series within the Zagros Foreland Basin. Copper mineralization is stratabound and confined mainly to plant–bearing grey sandstone horizons, whereas adjacent hematite–pigmented red sandstones are barren. Field observations, petrography, SEM–EDS, whole–rock geochemistry, framboidal–pyrite size distributions, microstructure morphometry, and paragenetic relationships were integrated to constrain the redox evolution and mineralization history. During early diagenesis, broadly contemporaneous oxidizing and reducing conditions developed in adjacent beds, producing hematite pigmentation in the red sandstone and framboidal and crystalline pyrite, marcasite, and pyrrhotite in the grey sandstone. Framboidal–pyrite dimensions (mean = 9.35 μm; SD = 4.69 μm) indicate dysoxic pore–water conditions. Rod–like, filamentous, and rounded C–rich microstructures are morphologically compatible with possible biological material, but their origin and relation to sulfate reduction remain unconfirmed because systematic C–Fe–S–Cu overlap, sulfur–isotope data, and biomarkers are lacking. During later diagenesis, oxidized Cu–bearing pore fluids migrated into the reduced, Fe–sulfide–bearing grey sandstone, where Cu sulfides precipitated at localized redox boundaries. Subsequent meteoric alteration produced cuprite, tenorite, malachite, azurite, and locally native copper. Similar provenance signatures in the red and grey sandstones indicate that Cu enrichment resulted mainly from secondary fluid–rock interaction and redox–controlled redistribution rather than source–rock variation. Guska therefore represents a redox–controlled sediment–hosted Cu occurrence, although its subsurface continuity and economic significance remain undetermined.
Geogenic fluoride (F–) and iodine (I–) contamination in groundwater poses a persistent threat to public health and the sustainability of drinking-water supply systems, particularly in data-scarce regions where preventive management remains challenging. However, effective groundwater management is often constrained by fragmented monitoring networks and limited decision-support tools capable of translating complex environmental information into actionable risk guidance. In this study, we develop an explainable decision-support framework to support sustainable groundwater management by integrating enhanced stacking ensemble learning, SHAP-based interpretation, and self-organizing maps (SOM). Using 292 groundwater samples and 40 environmental predictors, exceedance probabilities of F– (≥1.0 mg/L) and I– (≥0.08 mg/L) were mapped across the lower Yellow River floodplain, Northern China. The optimized stacking models achieved high predictive performance, with AUC values of 0.94 for F– and 0.92 for I–. Spatial predictions reveal distinct yet overlapping high-risk belts, with 43% of the region exposed to elevated fluoride risk and 57% to iodine risk, indicating that nearly half of the floodplain faces long-term groundwater quality constraints. Feature attribution analysis demonstrates that hydrochemical conditions dominate contamination risk, while hydrogeology, sedimentary environment, climate, human activities and soil physicochemical properties further regulate spatial heterogeneity. SOM clustering further clarified the coupled effects of hydrogeological settings and geochemical processes on F– and I– enrichment. This study demonstrates how transparent and reproducible AI tools can enhance groundwater-quality prediction and guide sustainable water management in large alluvial plains and other data-scarce, hydrogeochemically complex regions.
Lithium (Li), boron (B), rubidium (Rb), and cesium (Cs) are critical elements for emerging technologies, yet their occurrence modes and governing mechanisms in hypersaline lacustrine environments remain poorly understood. This study integrates sequential extraction, mineralogical analysis, and hydrogeochemical characterization of sediments from representative salt lakes on the northern Qinghai-Xizang Plateau to elucidate the speciation and controls of these four elements. Sequential extraction was combined with mineralogical, geochemical, and hydrochemical analyses to determine six operationally defined fractions, which were further grouped into five pools for statistical comparison and cross-study evaluation. The results reveal distinct geochemical fractionation: Li and B exist predominantly in water-soluble and acid-soluble phases, demonstrating high mobility. Specifically, Li is retained in composite pore brines, whereas B exhibits transitional behavior from fluid transport to mineral precipitation. Conversely, Rb and Cs are largely sequestered in the residual fraction through divergent fixation pathways: Rb is incorporated into the illite lattice via isomorphic substitution, whereas Cs is preferentially trapped at edge sites and structural defects, yielding higher exchangeability and environmental sensitivity. Mantel tests demonstrate that Li distribution is associated with total dissolved solids (TDS) and competitive cation interactions, B with pH and carbonate-borate co-precipitation, and Rb/Cs with K-bearing clay minerals. Overall, element partitioning in hypersaline sediments is governed by the coupled effects of hydrogeochemical evolution and clay mineral interfacial reactions. These findings provide a geochemical framework for understanding critical element behavior in high-salinity basins and support resource evaluation in salt lake systems.
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.
One of the largest global known lithium brine resources is the Salar de Uyuni (SDU) in the Bolivian Altiplano, yet presently, lithium exploitation is limited. Large-scale lithium extraction could impact regional water resources, which are used by local indigenous communities. Here, we investigate the water quality and geochemistry of shallow groundwater in the vicinity of the SDU, evaluating geochemical factors that control the occurrence of geogenic contaminants. We present a suite of geochemical analyses of shallow groundwater (n=63) used as a primarily drinking water source by communities surrounding the SDU. Integrated water quality data shows that concentrations levels in most groundwater exceeded the World Health Organization drinking water recommended threshold values for at least one contaminant. We show that salinity, arsenic, boron and lithium are the major geogenic constituents that pose risks to human health. These results are consistent with established patterns of geogenic water quality issues reported for other water resources in the high Andes. Our analysis shows that low salinity groundwater west of the SDU is characterized by low δ2H and δ18O with a slope that mimics the Local Meteoric Water Line and distinctively high boron, B/Li, Mg/Li, and low 87Sr/86Sr, indicating water-rock interactions with associated andesitic rocks. Groundwater from the Rio Grande watershed and eastern of the SDU have higher δ2H and δ18O and 87Sr/86Sr, reflecting local recharge and different lithological sources with a radiogenic Sr isotope composition. Through the region we identified hot spots of saline groundwater with low B/Li and Mg/Li ratios with relatively low δ2H, δ18O, as well as 87Sr/86Sr ratios that are different from those of the SDU brines, indicating rather mixing with underlying saline geothermal waters. Future large-scale lithium extraction could intensify groundwater pumping that would be likely to cause regional groundwater level drawdown and further increase the impact of underlying saline geothermal waters, exacerbating the already impaired quality of water resources for indigenous communities in the SDU vicinity.
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.
The use of hydraulic fracturing techniques to liberate hydrocarbons from unconventional, tight formations, has increased in the past two decades. Of environmental concerns raised about the process, the potential impact of the wastewater recovered from these operations, called flowback water (FBW), is among the most discussed. FBW is a complex fluid, containing numerous inorganic and organic constituents, many of which may be highly mobile in the subsurface and can pose potential risks to near-surface ecosystems. Components of the fluid may interact with each other, either synergistically or antagonistically, resulting in varied sorption behavior, and furthermore, transient effects induced by groundwater flow may also impact these reactions. In this study, batch and column experiments were conducted using FBW (TDS 145,000 – 168,000 mg/L) and sediments collected from a region of hydraulic fracturing operations in west-central Alberta. In our batch experiments, we found that for many of the dissolved inorganic compounds (e.g. Sr, Cu, and Ni), sorption was depressed, likely a result of competition with other constituents within the fluid and the high ionic strength of the FBW. Column experiments were also conducted to address how groundwater flow may influence sorption, and it was found that some dissolved inorganic constituents (e.g. Sr, Li, and B) exhibited depressed sorption compared to the batch experiments. We argue that sorption is characterized by two stages: a fast adsorption phase onto external sorption sites, followed by a slow absorption phase into internal sorption sites, with the latter process negated by groundwater flow. However, metals exhibited enhanced retention in the presence of flow, possibly due to the anaerobic conditions in the column and precipitation of heavy metal-bearing solids sequestered these elements. Our results demonstrate the importance and need to consider both the full complexity found in real, field-collected FBW samples as well as groundwater flow, as co-contaminant interactions can have profound impact on the sorption behavior of individual solution components. Our results also suggest that many of the dissolved metals in FBW are likely highly mobile in the subsurface. This indicates that retention of these metals, even in high organic matter and high clay-content soils (which should act as a sink), is likely to be minimal, suggesting that if released into the environment, FBW may pose a risk to down-gradient ecosystems.
The influence of rock–water interaction processes on heat transfer efficiency during the long-term operation of Enhanced Geothermal Systems (EGS) remains poorly understood, which highlights the necessity of systematic research on geochemical evolution and its impact on reservoir performance. Based on single-fracture water-rock reaction experiments and core-scale reactive transport models, relevant reaction kinetic parameters were calibrated and optimized, and a site-specific reactive solute transport model was established by integrating geological characteristics of the study area. A 35-year long-term simulation was carried out to systematically analyze the spatiotemporal evolution of dissolved solute concentrations in geothermal fluids, focusing on the dynamic changes of key solutes (including SiO2, Na+, K+) and their response to water-rock reactions. The results confirm that feldspar dissolution is the core driver of solute concentration changes and reservoir geochemical evolution, while biotite and anorthite, due to their low content and weak reactivity, have no significant impact on the overall geochemical process and solute transport. SiO2 precipitation, as a secondary factor, only causes local changes without affecting the overall geochemical evolution trend dominated by feldspar dissolution. This study clarifies the intrinsic relationship between water-rock reactions, solute concentration changes and geothermal fluid evolution, provides a reliable theoretical basis and technical support for the long-term stable operation of EGS.
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.
