Search Results (1,239)

Rare-metal pegmatites of the Kalba–Narym belt (Eastern Kazakhstan) represent an important source of Li, Cs, Ta, Nb, Be, and associated critical metals. Despite extensive geological investigations, the relationships between granites, pegmatites, and late-stage alteration products within the Central Kalba ore district remain insufficiently constrained. This study integrates whole-rock geochemistry and muscovite trace-element data to evaluate regional fractionation trends and rare-metal enrichment within the granite–pegmatite system. The dataset comprises 29 whole-rock samples, including Phase I and Phase II granites, pegmatites, greisens, and hornfels, together with 11 muscovite separates from the Akhmetkino, Yubileynoye, Bakennoye, and Asubulak ore fields. Geochemical evolution was assessed using granite-normalized multi-element patterns and the Cs–Rb, K/Rb–Cs, Li–Rb, Li–Cs, Rb/Sr–Cs, and Ta–Cs relationships. Muscovite compositions were additionally compared with published datasets from the Totoral (Argentina) and Gatumba (Rwanda) pegmatite districts. The results reveal systematic enrichment in Li, Rb, Cs, Nb, and Ta accompanied by depletion in Sr and Ba from granites to the most evolved pegmatites. The strongest geochemical relationship is recorded by the Rb/Sr–Cs system (R² = 0.805), whereas Ta and Cs show only weak correlation (R² = 0.062). Muscovite compositions display decreasing K/Rb and K/Cs ratios and increasing Rb and Cs concentrations from Akhmetkino through Yubileynoye and Bakennoye to Asubulak, defining a regional fractionation sequence consistent with whole-rock geochemistry. The most evolved muscovites overlap compositional fields characteristic of highly fractionated LCT pegmatites. The geochemical patterns identified in both whole-rock and muscovite datasets indicate progressive melt evolution across the Central Kalba district. Late-stage alteration and volatile-rich mineral assemblages record additional fluid-related processes, although their quantitative contribution to rare-metal redistribution remains uncertain. The results identify Cs, Rb/Sr, K/Rb, and K/Cs as useful indicators of relative pegmatite evolution and provide new constraints on the development of rare-metal granite–pegmatite systems in Eastern Kazakhstan. Full article

Natural mineral water standards use compositional criteria to define product identity and distinguish natural mineral water from other drinking water categories. China’s National Food Safety Standard—Drinking Natural Mineral Water (GB 8537) specifies seven alternative minimum threshold parameters for this purpose. This study assessed how these parameters function in four dimensions: regulatory identity, hydrogeological resource recognition, health-related interpretation, and label-based market communication. We compared major international regulatory frameworks, qualitatively synthesized health-related evidence, reviewed representative source-scale hydrogeological evidence from China, and analyzed label information from 150 commercial products. China’s system differs from the Codex and European Union frameworks, which emphasize source authenticity, compositional stability, permitted treatment, and disclosure, and from the United States system, which primarily defines mineral water by total dissolved solids. Regional studies showed that mineral water composition reflects site-specific combinations of lithology, geological structure, recharge, groundwater circulation, and water–rock interaction. The same parameter may occur in more than one hydrogeological setting, whereas different parameters within one groundwater system may arise through distinct geochemical processes. Health-related evidence varies substantially and should not be interpreted as establishing consumer health claims. In the label survey, metasilicic acid, TDS, and strontium were the most frequently declared parameters, while zinc and free carbon dioxide were less frequently declared. We propose a functional framework that distinguishes statutory identity, hydrogeological resource, health/safety, sensory/technical, and consumer-communication roles. This framework clarifies why the seven parameters should not be treated as functionally equivalent and provides a basis for refining natural mineral water standards and label communication. Full article

Shanxi Province in China is one of the world’s major bauxite producers. The co-existence of coal and bauxite mining makes this province particularly prone to acid mine drainage (AMD) and, thus, a significant area for investigating heavy metal mobility in an aluminum-rich geological environment. In this study, heavy metal leaching from bauxite under simulated AMD conditions and the geochemical mechanisms controlling their mobility were examined in this study. XRF analysis demonstrated that the bauxite is predominantly composed of Al₂O₃, Fe₂O₃ and SiO₂, while XRD, FTIR, and SEM-EDS revealed that diaspore and kaolinite dominate bauxite, together with accessory Fe- and Ti-bearing phases, providing reactive surfaces for adsorption and precipitation. After batch leaching with synthetic acidic sulphate solutions (pH = 3), Ca(OH)₂ neutralization was regulated. The data reveal that pH is the key factor controlling heavy metal mobility. Acidic conditions enhanced metal release while alkaline conditions favored hydroxide precipitation, surface complexation and co-precipitation. The removal efficiency was 91%–99% for Cd and Zn, 100% for Cd and Zn, 69%–90% for Cr, 35%–100% for Cu, 92%–100% for Ni and up to 100% for Pb. The chemical and mineralogical composition played an indirect role by providing adsorption sites but did not prevent the release of metals under acidic conditions. These results reveal that pH adjustment is the major mechanism controlling heavy metal immobilization in AMD-impacted bauxite systems and contributes to the knowledge of geochemical processes controlling metal mobility in acidic mine drainage. Full article

This study integrates conventional sediment geochemistry with explainable machine learning to investigate the provenance of surface sediments from Wular Lake, Kashmir Valley, NW Himalaya. Twenty-two samples were analysed for 49 geochemical variables (10 major oxides, 25 trace elements and 14 rare earth elements), complemented by XRD mineralogy, which reveals an assemblage dominated by quartz, muscovite/illite, chlorite and feldspar. The Chemical Index of Alteration (CIA = 68.5–75.1, mean 72.1), corroborated by CIW, PIA and the A–CN–K trend, indicates moderate weathering under a cold temperate climate, and the Index of Compositional Variability (ICV > 1), together with uniformly low Zr/Sc ratios (3.4–6.0), which preclude significant zircon addition through recycling, records compositionally immature, first-cycle detrital input. Conventional discrimination ratios and the Herron system classify the sediments as geochemically equivalent to shale, and elevated Fe₂O₃/K₂O (2.6–4.0), Al₂O₃/TiO₂ (12.6–16.0), Cr/Th and Co/Th ratios record a substantial mafic imprint. Chondrite-normalised REE patterns show pronounced LREE enrichment ((La/Yb)_N = 8.0–19.4), moderate negative Eu anomalies (Eu/Eu* = 0.56–0.73) and negligible Ce anomalies (Ce/Ce* = 0.98–1.03), with Eu/Eu* discriminating felsic crystalline from mafic volcanic contributions. A three-stage pipeline (principal component analysis (PCA) → random forest → SHapley Additive exPlanations (SHAP)) achieved a median leave-one-out cross-validation (LOO-CV) accuracy of 95.5% (n = 22; Wilson 95% CI 78%–99%), and unsupervised k-means clustering reproduced the same three geochemically distinct provenance end-members: siliceous-mature, detrital-mafic and carbonate-bearing, without reference to the assigned labels (Adjusted Rand Index = 1.0). Because the training labels derive from the same geochemical dataset, the classification quantifies the internal consistency of the provenance model, but does not provide independent validation. SHAP analysis reveals that trace elements (Cr, Co, Sc, Ni, Zn) carry greater discriminating power than do conventional major-oxide ratios, demonstrating that explainable machine learning robustly supplements and extends traditional provenance approaches. Full article

Pyrite occurs in a wide range of ore-forming environments, and its trace element and rare earth element (REE) compositions are important geochemical indicators for determining its genetic origin, thereby providing valuable constraints for ore deposit research and mineral exploration. Machine learning, as a data-driven technique, offers new insights into the genesis types of pyrite by comprehensively analyzing data and uncovering underlying patterns. In this study, representative pyrite samples with diverse morphologies, including both sedimentary and hydrothermal types, were collected. Based on electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), a comprehensive analysis of pyrite genesis was conducted. Furthermore, an artificial neural network (ANN) machine learning algorithm was employed to establish a classification model, and the predictive performance of this trained model was compared against that of traditional discrimination methods. The results show that when only trace elements were used as input features, the training set yielded a classification accuracy of 64.3% for sedimentary pyrite and 93.9% for hydrothermal pyrite. In the testing set, sedimentary pyrite was classified with an accuracy of 100%; however, this result may reflect the limited sample size rather than the model’s true generalization ability and therefore should be interpreted with caution. Feature importance analysis identified Cu, Zn, Te, Bi, and Pb as the key variables of this model. When both trace and rare earth elements (REEs) were used, the detection accuracy for sedimentary pyrite and hydrothermal pyrite in the training set was 87.5% and 100%. However, the combined trace + rare earth elements model exhibited a clear overfitting tendency: its overall training accuracy reached 95.2%, but its validation accuracy (88.9%) was lower than that of the trace-only model (93.8%). Feature importance analysis indicated that Pb, Ho, Zn, Ag, and Ce contribute substantially to the model. The machine learning model proposed in this study is convenient and efficient, providing a novel basis for determining the genetic types of complex pyrite. Full article

Understanding how liquid hydrocarbons flow through nanoporous shale matrices is essential for predicting shale oil productivity and evaluating unconventional resources. Despite substantial advances in geological and geochemical characterization, the physical and chemical mechanisms governing oil mobility in tight shale media remain incompletely constrained. This knowledge gap has become particularly evident through an anomalous phenomenon: the prolific production of low-volatile black oil from low- to medium-maturity, extremely tight shale reservoirs, where such viscous oils were previously expected to exhibit limited mobility. This unexpected behavior challenges existing physical models of oil flow. In this Perspective, we revisit the key controls on oil mobility by integrating available geological, geochemical, and reservoir evidence, including the influence of lithofacies on pore systems, the effects of thermal maturity and organic matter on fluid properties, the mechanisms of overpressure generation, and the interactions between hydrocarbons and shale matrices. We particularly emphasize the physical–chemical interaction processes between hydrocarbons and shale matrices, which have been largely overlooked in previous models. Based on these analyses, we propose a conceptual cross-scale migration–accumulation framework for shale oil and discuss its implications using representative shale systems from North America and China. The available evidence indicates that oil mobility is jointly controlled by mineral composition, pore structure, pressure coefficients, hydrocarbon physical–chemical properties, and hydrocarbon–matrix coupling. Thermal maturity emerges as a key parameter because it modulates several of these controls and therefore affects effective oil flow. Despite regional differences, broadly comparable controls may operate across different shale systems. Laminated carbonate-rich shales deposited under saline conditions exhibit high oil mobility even at low maturity, whereas clay-rich freshwater lacustrine shales require higher maturity to achieve comparable flow. The proposed framework links pore-scale processes with reservoir- and basin-scale accumulation and may provide a conceptual basis for evaluating movable oil resource potential in different shale systems. Full article

Regional multi-isotope mapping provides an effective means of investigating deep crustal composition and crustal reworking processes. The western margin of the Yangtze Craton has experienced multiple episodes of magmatism, crustal reworking, and mineralization since its formation, making it an ideal region for exploring the relationship between deep crustal evolution and metallogenic systems. In this study, Sr-Nd-Hf isotopic and whole-rock geochemical mapping was conducted based on compiled geochronological, geochemical, and isotopic datasets, integrated with deep geophysical data, to reconstruct the Precambrian crustal composition and reworking processes of the region. The results reveal significant crustal heterogeneity in the western margin of the Yangtze Craton. West of the Anninghe Fault Zone, rocks exhibit depleted Nd-Hf isotopic signatures (ε_Hf(t) = 0 to +17; ε_Nd(t) = 0 to +6), low I_Sr values (0.702–0.710), and high Nb/Ta (14–26) and Zr/Hf (36–46) ratios, indicating derivation from the remelting of juvenile mafic lower crust and providing direct evidence for Proterozoic underplating of mantle-derived magmas. In contrast, rocks east of the Anninghe Fault Zone show enriched Nd-Hf isotopic signatures (ε_Nd(t) = −9 to 0; ε_Hf(t) = −7.5 to 0), higher I_Sr values (0.711–0.726), and lower Nb/Ta and Zr/Hf ratios (8–13 and 21–35), suggesting remelting of ancient continental crust. Mineralization is closely associated with crustal architecture. IOCG deposits mainly occur in juvenile crustal domains, whereas Sn polymetallic and phosphate deposits are associated with ancient reworked crust. Under the Precambrian subduction setting, continuous arc magmatism promoted juvenile crust growth, whereas asthenospheric upwelling facilitated ancient crustal reworking, jointly controlling the spatiotemporal distribution of metallogenic systems along the western margin of the Yangtze Craton. Full article

To elucidate the geochemical features of produced water in coalbed methane (CBM) wells of the Gujiao Block and their indicative significance for production, systematic testing of ion composition and total dissolved solids (TDS) of produced water from ten CBM wells was conducted through five discrete sampling campaigns over an 18-month period. Combined with production performance data, the spatiotemporal evolution patterns, controlling factors, and the response relationship with productivity were analyzed. The results show that the water chemistry type of produced water in the study area is mainly identified as the Na-HCO₃ type. The TDS averages 1716.62 mg/L. The hydrochemical characteristics are primarily controlled by water/rock interactions, with Na⁺ and K⁺ mainly derived from silicate mineral weathering and dissolution, coupled with cation exchange processes. The Na/Cl ratio suggests that halite dissolution contributes to both Na⁺ and Cl⁻, whereas the excess Na⁺ relative to Cl⁻ likely reflects cation exchange or dissolution of Na-bearing silicate minerals. As drainage proceeded, Na⁺ and K⁺ concentrations increased, Ca²⁺ decreased, Cl⁻ increased, and SO₄²⁻ first increased and then decreased. Spatially, TDS increases from north to south, with the central-southern region representing a stagnant groundwater zone. Productivity response analysis reveals that Na⁺, HCO₃⁻, and TDS all show a trend of initially slow increase followed by rapid increase with increasing gas production. A negative trend is observed between gas production and the concentrations of Cl⁻, Ca²⁺, Mg²⁺, and SO₄²⁻. The productivity response index for the Gujiao Block ranges from 3.75 to 42.43, with an average of 17.78. As the productivity response index increases, gas production initially decreases and then increases. The findings clarify the geochemical evolution mechanisms of produced water in the Gujiao Block, providing a scientific basis for productivity evaluation of CBM wells. Full article

Bauxite residue (red mud) is a highly alkaline byproduct of the alumina refining process generated in large volumes worldwide. Most alumina operations currently rely on long-term storage facilities due to the high costs and technical constraints of residue reuse technologies. Therefore, understanding the mechanical behaviour of bauxite residue is critical to minimising environmental contamination risks, preventing structural failures, and ensuring the long-term stability of storage facilities. However, obtaining reliable geotechnical parameters is challenging due to the residue’s complex composition and chemical characteristics, particularly given the current fragmented state of the literature. This review compiles an extensive database of bauxite residue parameters across alumina operations worldwide, synthesising existing knowledge and research needs. The database encompasses 940 data points extracted from 63 studies across 25 countries. The findings reveal considerable variability in parameter values across countries, potentially exacerbated by inconsistencies in experimental methodologies. Few studies have integrated geochemical conditions, such as pH and salinity, with geomechanical behaviour, thereby limiting understanding of the mechanisms that govern key parameters, including strength and deformability. Enhancing the predictability of bauxite residue behaviour requires the development of standardised experimental protocols that explicitly account for the coupled effects of chemistry and mechanics to support reliable risk assessments of storage facilities. Full article

To assess the environmental impact of uranium mining operations in southern Kazakhstan, the elemental and radionuclide composition of soil samples collected from settlements in the Kyzylorda Region was investigated. The analysis was carried out using X-ray fluorescence (XRF) and gamma-ray spectrometry. Mean concentrations and variation ranges were determined for 28 chemical elements, including uranium, lead, antimony, and gamma-emitting radionuclides such as ¹³⁷Cs, ⁴⁰K, ²³²Th, ²³⁸U, ²²⁶Ra, ²¹⁰Pb, and ²⁴¹Am. The analysis of the specific activities of the artificial radionuclides ¹³⁷Cs and ²⁴¹Am was carried out in order to assess the influence of the Semipalatinsk Test Site on the soils of the study area. Based on the obtained data, heavy metal pollution indices, ecological risk indices, and radiological parameters were calculated to evaluate the potential environmental and human health impacts. Most elements were present at levels below average crustal abundances, suggesting limited anthropogenic influence. Slight exceedances for uranium, lead, and antimony are likely associated with regional geochemical features. Radiological assessment indicated that the radiation environment remains within internationally accepted limits. The lifetime cancer risk values for exposure of humans to natural radionuclides ²²⁶Ra, ²³²Th, ⁴⁰K and ¹³⁷Cs from soil at 1 m above ground level ranged from 0.19 × 10⁻³ to 0.30 × 10⁻³, with an average of 0.24 × 10⁻³. Nearly all sampling points remained below the risk threshold of 0.29 × 10⁻³, indicating minimal radiological hazard. The carcinogenic risk remained within the acceptable regulatory range for both adults (2.0 × 10⁻⁵) and children (4.4 × 10⁻⁵), whereas the non-carcinogenic hazard index for children (1.3) slightly exceeded the screening threshold of 1. This finding identifies children as the most sensitive receptor group under the conservative assumptions of the applied screening methodology. The study demonstrates the applicability of combined chemical and radiometric methods for comprehensive environmental assessments in uranium mining regions. The results are of interest both in terms of methodology and in understanding the local geochemical and radiological landscape. Full article

Radioactive and chemical contamination of aquatic systems remains a key environmental concern in areas affected by historical nuclear testing. The objective of this study was a comprehensive geochemical and ecotoxicological screening assessment of bottom sediments in the Shagan River, which partially flows through the Balapan test site within the Semipalatinsk test site. This 2 km stretch is potentially affected by groundwater discharge hydraulically connected to the Atomnoye Lake retaining zone. A total of 21 bottom sediment samples were collected over a 2 km stretch, and their elemental composition was determined using inductively coupled plasma mass spectrometry (ICP-MS). Bottom sediment quality was assessed using the geoaccumulation index (Igeo) and ecotoxicological criteria, including the threshold effect concentration (TEC), probable effect concentration (PEC), least impact level (LEL), and high impact level (SEL). The results revealed significant spatial heterogeneity in the element distribution and local geochemical anomalies. Manganese (Mn) and molybdenum (Mo) corresponded to the Igeo index category of severe contamination, while zinc (Zn) demonstrated an extremely high contamination level (Igeo = 6), exceeding the PEC threshold by 16 times. Mn concentrations also exceeded the SEL by 15 times. These results provide a baseline geochemical profile for a previously understudied and ecologically sensitive section of the Shagan River, identifying zones of local geochemical enrichment in bottom sediments and laying the foundation for further hydrogeochemical, mineralogical, granulometric, and ecotoxicological studies. Full article

Located in the northeastern Tibetan Plateau, the Qaidam Basin hosts abundant strategic lithium (Li) and boron (B) salt lake resources crucial for national resource security. Existing studies focus on individual lakes, lacking systematic Li-B geochemical and source–transport–sink research across the geothermal–river–lake system. Based on 40 water samples from 16 lakes and multi-isotope and hydrochemical data, this study explores Li-B spatial distribution, isotopic evolution and enrichment rules. The results reveal prominent spatial heterogeneity of Li and B distributions. The contents of riverine Li and B are higher than the global average level, and terminal salt lakes show the highest enrichment degree. Specifically, southern lakes are Li-dominant, while northern lakes are B-dominant, with both reaching industrial exploitation grades. Significant Li and B isotopic fractionation occurs throughout the hydrological system, with geothermal fluids presenting depleted isotopic compositions and lake waters showing enriched features. H-O isotopic evidence and Gibbs diagram analysis indicate that surface waters in the basin are primarily recharged by atmospheric precipitation, and their hydrochemical compositions are jointly controlled by rock weathering and strong evaporative concentration, accompanied by distinct north–south hydrogeological zonation differences. Source analysis demonstrates that Li is mainly derived from high-temperature water–rock interactions of Li-rich volcanic and granitic rocks in the southern East Kunlun Mountains, whereas B originates from ultrahigh-pressure B-rich metamorphic rocks along the northern North Qaidam margin. The migration and accumulation sequence of Li and B follows the pathway: geothermal fluid emission → fluvial transportation → terminal lake enrichment. Evaporation and mineral precipitation are the dominant factors controlling elemental enrichment and isotopic fractionation. This basin-wide study supplements salt lake critical mineral metallogenic theories and guides efficient Li-B exploration and sustainable development. Full article

Geochemical and isotopic analysis of bitumen-lined transport container vessels, so called ‘torpedo jars’, from the Sasanian to Early Islamic period fort of Fulayj in Oman confirms the presence of two distinct compositional categories that can be matched to contemporary sources in different areas of southwest Iran. It appears that the bitumen used to line jars was extracted from different geographic areas, hinting at the existence of multiple production locations for this vessel class. In terms of the function of the jars, organic residue analysis provides a positive identification of biomarkers associated with the storage and transportation of red wine. These results provide the first published confirmation of the long-suspected association between torpedo jars and wine transportation from the core urbanised zone of the Sasanian and Early Islamic imperial heartlands towards the Persian Gulf and Indian Ocean maritime sphere. The results have added significance as the samples are derived from relatively accurately dated archaeological contexts spanning the period before and after the Islamic conquest. Full article

Soils developing in ultramafic (serpentinite) provinces are naturally enriched in Mg, Ni and Cr, which makes it difficult to separate the natural geochemical background from technogenic contamination near chrysotile asbestos mining operations. This problem is examined for the agricultural soils in the impact zone of the Zhitikara chrysotile asbestos quarry (Kostanay Region, Kazakhstan), one of the largest such operations in the world. The elemental composition of the soils was characterised by portable X-ray fluorescence, verified against ICP-OES, and complemented by X-ray diffraction. When contamination was assessed against the global crustal background (upper continental crust), nickel and chromium appeared enriched; however, relative to the local geochemical background, these elements fall within the natural lithogenic range, showing that global crustal values generate false-positive contamination signals in ultramafic terrains. Magnesium was the only element enriched above the local background and the only one that decreased systematically with distance from the quarry, identifying it as the most sensitive tracer of aerogenic serpentinite dust among the elements measured. The discordance between total and acid-soluble chromium is consistent with chromium being hosted mainly in a refractory chromite phase, so that total chromium contents overestimate the environmentally relevant fraction. The study demonstrates the pitfall of applying global crustal backgrounds in ultramafic provinces and supports a locally referenced, differentiated approach to soil-contamination assessment in such settings. Full article

Long-term open-air storage of coal gangue (CG) can generate leachates containing oxidizable components contributing to chemical oxygen demand (COD), together with sulfate (SO₄²⁻) and fluoride (F⁻), yet their source-term behavior remains poorly understood. In this study, batch and column leaching tests were conducted on multi-source CG samples and combined with ToF-SIMS (surface compositional mapping), solid-phase TOC gradient leaching, and PHREEQC-XGBoost-SHAP modeling (coupled geochemical–machine learning analysis). Batch-leachate COD levels ranged from 4.6 to 68.0 mg/L, while SO₄²⁻ and F⁻ concentrations reached maxima of approximately 317 and 1.29 mg/L, respectively. During column leaching, COD levels and SO₄²⁻ concentrations were highest at low liquid-to-solid ratios (L/S) and subsequently decreased, with maximum initial values of 186.6 and 3074 mg/L, respectively, whereas F⁻ exhibited delayed and persistent release at approximately 0.3–2.3 mg/L. Solid-phase TOC did not directly predict the COD response, and ToF-SIMS revealed aliphatic organic fragments associated with aluminosilicate surfaces that weakened or were redistributed after leaching. The COD–DOC discrepancy further indicated that dissolved organic matter alone could not fully explain the COD response, although the possible contribution of inorganic reducing species requires direct verification. Within the modeled framework, the sulfate source-term coefficient accounted for 69.4–76.9% of the modeled influence at L/S = 0.5–2.0 L/kg, while the influence of the HFO surface complexation increased during later leaching. In contrast, the F⁻ source-term coefficient remained dominant over L/S = 0.5–10.0 L/kg, accounting for 97.0–97.9% of the modeled influence. These findings support parameter- and stage-specific monitoring and pollution control at CG disposal sites. Full article