Search Results (512)

Natural mineral waters hosted in volcanic terrains are globally significant, but the co-enrichment mechanisms of metasilicate and strontium remain poorly understood. Here we investigate a Jurassic volcanic-hosted mineral water source in eastern China using hydrochemical analysis, ¹⁴C dating, stable isotopes, and structural analysis. The groundwater is of Ca–Mg–HCO₃ type with slightly alkaline pH (7.44–7.63). Metasilicate (26.4–32.9 mg/L) and strontium (0.40–0.83 mg/L) co-enrichment is governed by plagioclase weathering in a bicarbonate-dominated, weakly alkaline environment where ${\mathrm{S}\mathrm{r}\mathrm{H}\mathrm{C}\mathrm{O}}_3^{+}$ ion pairs enhance strontium mobility. Pearson-corrected ¹⁴C ages of 3900–4900 years reveal that millennial-scale residence time is critical for sufficient water-rock interaction and attainment of regulatory thresholds. A conduit-barrier system formed by NW-trending extensional-shear and NNE-trending compressional-shear faults controls groundwater flow paths and residence times, leading to systematic inter-well hydrochemical differentiation. These findings provide a theoretical basis for the genetic identification, potential evaluation, and sustainable management of high-quality mineral water resources in volcanic terrains. Full article

Groundwater-dependent communities such as De Aar require a better understanding of groundwater systems to ensure sustainable allocation. This study aims to trace recharge sources in unconfined and confined aquifers and identify processes controlling groundwater quality using hydrogeochemistry and environmental tracers. It argues that aquifer delineation and hydraulic parameters alone cannot fully identify recharge sources or geochemical processes; integrating them with hydrogeochemistry and environmental tracers provides stronger evidence to support groundwater allocation. To validate the argument, the study integrated hydrogeochemical analysis, stable isotopes, tritium, radon-222, and statistical methods supported by depth-specific groundwater sampling. The results, interpreted using Piper and Gibbs diagrams, PHREEQC modelling, and scatter plots, show that groundwater evolution is mainly controlled by rock–water interaction, ion exchange, evaporation, and mixing processes. Ca–HCO₃ water indicates recent recharge, while Na–Cl water reflects evaporation effects in both unconfined and confined aquifers, with halite dissolution contributing to Na and Cl enrichment. Isotope results indicate that unconfined aquifer water is isotopically enriched and linked to recent recharge, whereas confined aquifer and spring waters are depleted, suggesting recharge from higher elevations through fractured zones. Tritium dating reveals young (<30 years), intermediate (30–50 years), and old groundwater (60–109 years), while radon results indicate active groundwater flow path, particularly along fractures. These findings demonstrate that groundwater recharge is derived from both local meteoric sources and regional contributions, resulting in predominantly fresh groundwater; however, localized quality concerns should be considered for improved water allocation. Full article

Groundwater contamination by dissolved metals and metalloids in the Chiang Mai Basin is an important drinking-water concern, yet the coupled depth patterns, hydrogeochemical controls, composite contamination status, and screening-level health implications have not previously been assessed in an integrated basin-scale framework. This study evaluated 120 groundwater samples from alluvial wells classified by depth as shallow (≤30 m, n = 40), intermediate (31–60 m, n = 35), and deep (>60 m, n = 45). Samples were analyzed for nine dissolved metals and metalloids (Fe, Mn, As, Cd, Pb, Cr, Zn, Hg, and Se) together with pH, Eh, and total dissolved solids (TDS). The highest exceedance frequencies were observed for Fe (72.5% of samples, >0.3 mg/L acceptability threshold), Mn (65.0%, >0.08 mg/L), and As (45.8%, >10 μg/L). Fe and Mn increased significantly with depth, whereas As was enriched in deep wells but showed no statistically significant depth dependence. Pearson correlation and principal component analysis consistently identified a dominant redox-associated component in which Fe, Mn, and As covaried negatively with Eh, supporting redox-sensitive co-enrichment in deeper groundwater. Contamination factors calculated relative to selected global groundwater background values were >6 for all seven evaluated metals (Fe, Mn, As, Cd, Pb, Cr, and Zn), and the overall pollution load index (PLI) was 9.11, with the highest depth-specific PLI in deep wells (10.42). These indices are interpreted here as background-relative screening tools rather than stand-alone regulatory measures. A screening-level ingestion risk assessment identified arsenic as the dominant toxicological driver, with hazard quotients (HQ) of 1.97 for adults and 4.60 for children, and an estimated lifetime cancer risk (LCR) of 8.87 × 10^–4. The results support targeted monitoring of deeper wells, routine screening for As and Mn, and treatment strategies that can address the co-occurring Fe–Mn–As assemblage in alluvial groundwater. Full article

In the saline–alkaline lake (SAL) systems of the Nhecolândia region, Brazilian Pantanal, soils exhibit complex mineralogical assemblages controlled by sediment inheritance, pedogenesis, and hydrogeochemical gradients. This study investigates the distribution and transformation of 2:1 phyllosilicates along representative SAL toposequences. Soil samples were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), supported by granulometry and adjustment of the FTIR spectra. Mineralogical data were integrated with geochemical (Al, K, Mg, Ca, Na) and pH data and examined using principal component analysis (PCA). Greenish loamy horizons act as key morphological controls on hydrogeochemistry, regulating solute retention along mid- to downslope transitions. Illite is more strongly associated with upslope positions, whereas downslope alkaline environments are associated with smectitic phases (e.g., montmorillonite and Mg-rich varieties such as saponite) and mixed-layer minerals structures (e.g., illite–smectite and montmorillonite–vermiculite structures). These assemblages are consistent with non-linear transformation pathways, with illite as a possible transitional phase between micas and expandable structures. The PCA results suggest a primary mineral distribution structured by fine-material content and depth, while pH and alkalinity emerge as key geochemical controls that differentiate mineral stability fields and reinforce the hydrogeochemical compartmentalization of the profiles. Geochemical data show strong associations of Al, Mg, and K with fine-fraction accumulation. The integration of these approaches highlights that a 2:1 phyllosilicate assemblage results from multiple superimposed pedogenetic pathways, offering a conceptual framework for studying complex soil–lake systems. Full article

Hydrogeochemistry is a practical and low-impact tool for mineral exploration that relies primarily on groundwater as sampling media. It is particularly valuable for blind or deeply buried deposits where surface geochemical methods are ineffective, as groundwater acts as a natural integrator of geochemical signals from depth. This study presents a PRISMA 2020-compliant systematic review of hydrogeochemical exploration practices published between 1946 and 2025, synthesizing 118 empirically screened case studies from diverse geological and climatic settings. The review evaluates the geochemical processes governing aqueous dispersion halos, including sulphide oxidation, water–rock interaction, redox controls, and physicochemical speciation, and assesses how these processes influence pathfinder behaviour and anomaly expression. Quantitative synthesis highlights consistent patterns in hydrogeochemical footprints across major mineral systems and demonstrates the effectiveness of thermodynamically informed and multivariate interpretation strategies over simple concentration-based approaches. Emerging trends identified include the growing application of non-traditional stable isotope fractionation, nanoparticle geochemistry using single-particle ICP-MS, and integration of hydrogeochemical datasets with GIS, geophysics, and machine learning-based prospectivity modelling. Unlike recent narrative reviews, this study provides a fully reproducible, structured evaluation of the global evidence base and formalizes a standardized end-to-end workflow. Full article

Uranium exploration in southeastern Mongolia remains constrained by fragmented Soviet-era datasets and limited modern synthesis. This study addresses the problem of integrating historical geological records with contemporary exploration methods to evaluate uranium mineralization potential. A comprehensive GIS-based database was compiled from Soviet reports legally acquired from the Mineral Resources Authority of Mongolia and expanded with geological, geophysical, and drilling data collected between 2006 and 2011. Methodological advances included remote sensing detection of anomalous radioactivity in arid environments, stratigraphic modeling, and hydrogeochemical surveys. The dataset encompasses more than 1100 radioactive anomalies and approximately 300 mineralized zones, with emphasis on the Han Bogd granite massif, Ail Bayan coal deposit, Suujin Tal structural system, Zuunbayan depression, and Naarst structural complex. Results indicate that most anomalous zones are sub-economic, commonly associated with organic-rich facies such as coal seams, while the continuity of mineralized bodies remains uncertain. Nevertheless, the dual consideration of granitic source terrains and coal-bearing sedimentary traps provides new insights into uranium mobility and deposition. The significance of this work lies in its systematic integration of historical and modern data, offering a refined geological framework and highlighting key areas for future investigation, thereby contributing to ongoing discussions on sedimentary uranium resources in Mongolia. Results indicate that most anomalous zones are sub-economic, commonly associated with organic-rich facies such as coal seams, while the continuity of mineralized bodies remains uncertain. Importantly, the study highlights granitic intrusions and volcanic complexes as the primary uranium sources, with coal-bearing and sedimentary basins acting as secondary depositional environments. The dual consideration of source terrains and depositional traps provides new insights into uranium mobility and deposition. Full article

Physicochemical and microbiological parameters are important indicators of drinking water quality. This study assessed the quality of groundwater used for drinking in four regions of Kosovo at 16 locations using an integrated assessment framework that combined physicochemical, microbiological, and Water Quality Index (WQI) approaches. The results reveal substantial spatial variability in water quality. While most physicochemical parameters remained within recommended limits, elevated values of total dissolved solids (up to 2792.5 mg/L), electrical conductivity (up to 2768.5 µS/cm), nitrate (up to 60.75 mg/L), and phosphate (up to 0.875 mg/L) were observed at several locations, indicating localized hydrogeochemical and anthropogenic influences. Dissolved oxygen levels were generally low (0.68–5.49 mg/L), reflecting limited aeration conditions in groundwater systems. Microbiological analysis revealed critical contamination, with Escherichia coli concentrations up to 299.9 CFU/100 mL, and all sampling sites exceeded permissible limits, indicating widespread fecal pollution and rendering the groundwater unsafe for direct consumption. WQI assessment further confirmed this condition, where 93.75% of locations were classified as medium quality using the NSF-WQI method, whereas the WA-WQI method categorized 68.75% of samples as poor and 6.25% as very poor. The novelty of this study lies in the integrated evaluation of hydrogeochemical processes and microbiological contamination using dual WQI methods and multivariate statistical analysis, providing a comprehensive understanding of groundwater degradation pathways. The findings are significant for policymakers, environmental managers, and public health authorities, highlighting the urgent need for groundwater treatment, improved sanitation infrastructure, and sustainable water resource management strategies in vulnerable regions. Full article

Investigating the cycling characteristics of dissolved inorganic carbon (DIC) in karst groundwater within arid and semi-arid regions is crucial for understanding its role in the global carbon cycle and its contribution to atmospheric carbon sinks. This study is centered on the Liulin Spring area of North China, based on sampling data from April 2019. We employed hydrogeochemical analysis and environmental isotopic tracing methods to (1) characterize the spatial distribution of DIC along the groundwater flow path; (2) elucidate the sources of HCO₃⁻; (3) calibrate groundwater ¹⁴C ages. Results indicate that the HCO₃⁻ concentration initially increases and then decreases along the flow path, peaking in the spring discharge zone. Conversely, δ¹³C values initially decrease and then increase, reaching a minimum in the discharge zone, exhibiting a negative correlation with the HCO₃⁻ concentration. The contribution of soil/biogenic CO₂ dissolution to HCO₃⁻ ranges from 26% to 62%, with the highest values (56–62%) observed in recharge, runoff, and discharge zones and lower values (26–49%) observed in stagnant zones; this contribution generally decreases towards the western boundary. Calibrated ¹⁴C ages are significantly reduced and align better with expected groundwater dynamics. Full article

In the semi-arid Batna Belezma region of northeastern Algeria, groundwater is a vital resource for agriculture and drinking water. However, the climate leads to intense evaporation, which affects its quality. This study aims to identify the key hydrogeochemical processes that control groundwater composition in the Merouana Basin and to evaluate the predictive performance of machine learning (ML) models. A total of 30 groundwater samples were analyzed using multivariate statistical techniques, including Principal Component Analysis (PCA), and were modeled using PHREEQC to assess mineral saturation states. Additionally, ML-based regression models, including K-Nearest Neighbors (KNN), Support Vector Machine (SVM), Random Forest (RF), and Extreme Gradient Boosting (XGB),were employed to predict groundwater chemistry. The results indicate that the dominant ion distribution follows the following trend: Ca²⁺ > Mg²⁺ > Na⁺ and HCO₃⁻ > SO₄²⁻ > Cl⁻. Alkaline earth metals (Ca²⁺ and Mg²⁺) constitute the major fraction of total dissolved cations, reflecting carbonate equilibrium and dolomite dissolution processes. In contrast, Na⁺ represents a smaller proportion of the cationic load; however, its hydro-agronomic significance is substantial due to its influence on sodium adsorption ratio (SAR) and soil permeability. The PHREEQC modeling showed that calcite and dolomite precipitation promote evaporite dissolution, while most samples remain undersaturated with respect to gypsum. The PCA results reveal high positive loadings of Mg²⁺, Cl⁻, SO₄²⁻, HCO₃⁻, and EC, suggesting that ion exchange and seawater mixing are the primary controlling processes, with carbonate weathering playing a secondary role. To enhance predictive assessment, several supervised machine learning models were tested. Among them, the Random Forest model achieved the highest predictive performance (R² = 0.96) with low RMSE and MAE values, confirming its robustness and reliability. The results indicate that silicate weathering and mineral dissolution are the primary mechanisms governing groundwater chemistry. The integration of multivariate statistics and machine learning provides a comprehensive understanding of groundwater evolution and offers a reliable predictive framework for sustainable water resource management in semi-arid environments. Geochemical model performance showed a high global accuracy (GPI = 0.91), confirming a strong agreement between observed and simulated chemical data. However, the HH value (0.81) indicates some discrepancies, particularly for specific ions or extreme conditions. Full article

For the purpose of investigating the hydrochemical signatures and formation processes of mine water at the Feicheng Coal Mine, a total of 61 samples, including fifth limestone water (FLW), old goaf water (OGW), and ordovician limestone water (OLW), were collected and examined via statistical and hydrochemical approaches. The assessment of mine water suitability for irrigation employed sodium percentage (Na%), sodium adsorption ratio (SAR), permeability index (PI), and magnesium hazard ratio (MHR). The mine water proves slightly alkaline, featuring Na⁺ as the leading cation and SO₄²⁻/HCO₃⁻ as the leading anions. By average concentration, cations decrease in the order Na⁺ > Ca²⁺ > Mg²⁺, and anions decrease as SO₄²⁻ > HCO₃⁻ > Cl⁻. The hydrochemical types of OLW and FLW samples were primarily Ca-HCO₃ and Ca-Mg-Cl, whereas the OGW samples were predominantly of the Na-Cl-SO₄ and Na-HCO₃ types. Rock weathering serves as the main control on water chemistry, with hydrochemical components sourced largely from evaporite and carbonate dissolution. The sodium present in the water is likely attributable to silicate mineral dissolution or cation exchange processes. Cation exchange, with forward exchange dominant, is also a key hydrogeochemical process in the study area. SI results reveal that calcite and dolomite have reached saturation, while gypsum and halite remain undersaturated and tend to dissolve further. Irrigation suitability assessments indicate that most of the water quality in the Feicheng Coal Mine is excellent or good. A limited number of samples exhibited relatively high salinity, and most of them can be directly irrigated. To this end, this study proposes targeted treatment solutions, thus facilitating mine water development and utilization. Full article

To identify the sources and driving mechanisms of nitrate contamination in pore water around Nansi Lake, 54 pore water samples were analyzed via hydrogeochemical analysis, Gibbs diagrams, ionic ratios, and principal component analysis (PCA). The pore water is predominantly slightly alkaline, with dominant cations Ca²⁺ and Na⁺, and anions HCO₃⁻ and SO₄²⁻. Nitrate-nitrogen (NO₃⁻-N) concentrations range from 0.82 to 54.31 mg·L⁻¹, with a coefficient of variation of 1.41 and an exceedance rate of 18.52%, indicating significant external inputs. A positive correlation between NO₂⁻ and NO₃⁻ suggests denitrification in some areas. Nitrate concentrations exhibit distinct spatial heterogeneity: high concentrations occur in agricultural/aquaculture lakeside plains and urban areas, low concentrations near coal mining subsidence zones, and transitional zones showing outward diffusion. Nitrate sources are predominantly anthropogenic. High Cl⁻ and low NO₃⁻/Cl⁻ ratios indicate domestic and aquaculture wastewater infiltration, whereas low Cl⁻ and high NO₃⁻/Cl⁻ ratios indicate agricultural fertilizer input. Industrial and natural sources are minor. PCA identified three controlling factors (cumulative variance 69.81%): coal mining and industrial/domestic pollution (39.82%), carbonate rock weathering (19.44%), and agricultural activities (10.55%). Health risk assessment shows no significant risk for adults (hazard quotient (HQ) < 1), but children face localized risks at nine sites (HQs of 1.25–2.26) in intensive farming, urban, and transitional zones. Excessive fertilizer application and sewage leakage are the primary causes, posing methemoglobinemia risks to infants. This study provides a scientific basis for nitrate pollution control and sustainable water management in the Nansi Lake Basin and offers methodological insights for similar lacustrine plain regions. Full article

The hydrogeochemical characterization of shallow volcanic lakes at the Sete Cidades Volcano (São Miguel, Azores) provides new insights into the processes controlling water chemistry in low-depth lacustrine systems within active volcanic environments. Fourteen lakes (0.6–4 m deep) were sampled during two campaigns (winter 2024 and spring/summer 2025), combining in situ physicochemical measurements and major ion analyses along vertical profiles. The lakes are holomictic, cold (11.3–17.6 °C), slightly acidic (pH 5.66–5.95), and weakly mineralized (EC ~65–69 µS/cm), indicating dilute waters of predominantly meteoric origin. Hydrochemical facies are dominated by Na–Cl type, with strong correlations between chloride and conductivity (r = 0.857), supporting a major contribution from marine atmospheric deposition. To move beyond correlation-based interpretation, Gibbs diagrams and saturation indices (PHREEQC) were applied to constrain the dominant geochemical processes. Most samples plot within the precipitation dominance field, while all calculated saturation indices are negative (SI < 0), indicating undersaturation with respect to carbonate, evaporite, and silicate minerals. These results demonstrate that water chemistry is primarily controlled by atmospheric inputs, with only minor contributions from water–rock interaction and negligible influence of evaporation or mineral equilibrium processes. Seasonal increases in HCO₃⁻ and dissolved CO₂ at depth suggest enhanced organic matter decomposition during warmer periods, highlighting the role of biogeochemical processes in modulating carbon dynamics in shallow systems. The absence of a clear hydrothermal signature further distinguishes these lakes from deeper volcanic systems in the Azores. This study provides the first integrated hydrogeochemical framework for shallow volcanic lakes in the region, combining classical hydrochemistry with process-based tools. The results establish a quantitative baseline for assessing environmental change and improve the interpretation of external (atmospheric) versus internal (geochemical and biological) controls in volcanic lake systems. Full article

The Beishan area of Gansu, China, is the primary candidate site for the geological disposal of China’s high-level radioactive waste (HLW). To assess the long-term safety of this repository, the evolutionary patterns of groundwater and the primary migration vector of radionuclides must be understood. Through experiments and hydrogeochemical simulations of snowmelt samples from the Qilian Mountains and deep rock samples from Beishan, we reveal different hydrochemical compositions and types of the snowmelt and deep groundwater. The results show that the hydrochemical type of Qilian Mountain snowmelt is SO₄–Na·Ca, whereas that of the deep groundwater in the Beishan is Cl·SO₄–Na, indicating substantial differences in the hydrochemical characteristics of the two samples. The water–rock interactions between snowmelt and granite are dominated by the dissolution of silicate minerals and the precipitation of carbonate minerals, accompanied by cation exchange and adsorption. After the interaction, the hydrochemical type of the snowmelt becomes SO₄–Na, with total dissolved solids (TDS) consistently maintained at ~500 mg/L, which is distinct from the TDS range of 1540–2045 mg/L observed for the deep groundwater in the Beishan. Under the experimental and simulation conditions set in this study, the water–rock interactions between Qilian Mountain snowmelt and Beishan granite cannot reproduce the hydrochemical characteristics of the deep groundwater in the Beishan. This study provides theoretical support for the hydrogeological safety assessment of HLW geological repositories. Full article

This study characterizes the hydrochemistry and geochemical signature of the Upper Cretaceous geothermal aquifer in the Zharkunak zone (Eastern Ili Depression, SE Kazakhstan) using certified analytical datasets from five deep wells (5539, 1-RT, 3-T, 1-TP, and 2-TP). The waters are hyperthermal (89–103 °C), alkaline (pH 8.1–9.0), and weakly mineralized (TDS 0.3–1.0 g/L), with sodium-dominated facies ranging from Na–HCO₃–SO₄ to Na–SO₄–Cl. Hydrochemical analysis indicates that water–rock interaction and cation exchange are the primary controls on fluid evolution, with limited influence from evaporation or external salinity sources. Elevated fluoride (up to ~10 mg/L) and dissolved silica (H₂SiO₃, often >50 mg/L) reflect prolonged high-temperature interaction with silicate-rich lithologies under low Ca²⁺ conditions. Trace elements and radon activity (up to 0.32 nCi/L) further support deep, fault-controlled circulation pathways. PHREEQC modeling indicates near-equilibrium to slight supersaturation with respect to silica phases, suggesting a potential risk of silica scaling during cooling, while carbonate scaling remains limited. Although the dataset is based on discharge conditions from a limited number of wells, the results demonstrate that the Zharkunak system has strong geothermal utilization potential, with management considerations related to fluoride, radon, and silica scaling. Future work should focus on integrating isotopic analyses and reactive transport modeling to better constrain subsurface processes and long-term system behavior. Full article

Water accumulation in goafs in Chinese coal mines is a major hidden hazard that can trigger water inrush accidents and may also affect aquifer integrity and regional water security. Reliable delineation of goaf water distribution and identification of water-source types are therefore essential for mine water-hazard control and groundwater protection. This paper reviews the main technical routes for goaf groundwater investigation, including geophysical prospecting, hydrogeochemical and isotopic identification, direct inspection tools, and data-driven intelligent workflows. For geophysical detection, the mechanisms, engineering applicability, and key constraints of the Transient Electromagnetic Method (TEM), Surface Nuclear Magnetic Resonance (NMR), the High-Density Resistivity Method (HDRM), and the Coherent Frequency Component (CFC) electromagnetic wave reflection coherence method are synthesized, with emphasis on interpretation boundaries and uncertainty sources under complex geological conditions. For source identification, conventional hydrochemistry, stable isotopes, and laser-induced fluorescence are summarized, and intelligent recognition models such as neural networks and support vector machines are discussed in terms of workflow positioning and practical performance limits. A unified evaluation rationale is established and a semi-quantitative method–metric matrix is constructed to compare techniques in terms of reliability, deployability, cost level, environmental adaptability, and information value, thereby clarifying their functional roles and complementarities within staged engineering workflows. The synthesis indicates that major bottlenecks include limited deep capability under strong interference, pronounced interpretational non-uniqueness caused by complex geology and irregular goaf geometries, and constrained timeliness and generalization for mixed-source identification. Future directions are summarized as multi-method integration with fusion-driven interpretation, intelligent and quantitative decision support with quality control, and sensor–platform advances enabling more practical three-dimensional investigation, aiming to improve the reliability and engineering usability of goaf groundwater hazard assessment. Full article