Search Results (787)

The karst landscape of Trenggalek Regency, located in several sub-districts including Dongko, Kampak, and Watulimo, is shaped by the Wonosari Formation and is characterized by springs and underground rivers. Due to water scarcity in the region, local communities heavily depend on these natural water sources. This study assesses the groundwater quality of 16 springs and 20 underground rivers to evaluate their suitability for consumption and associated health risks. Using the groundwater quality index (GWQI), human health risk assessment (HHRA), and statistical methods, various physicochemical parameters were analyzed, including pH, total dissolved solids (TDS), electrical conductivity (EC), and concentrations of iron (Fe²⁺), manganese (Mn²⁺), calcium carbonate (CaCO₃), and sulfate (SO₄). Water generally meets the World Health Organization standards for safe drinking. However, correlation analysis reveals notable mineral dissolution and possible anthropogenic influence. TDS strongly correlates with EC (r = 0.97), while Fe²⁺ shows significant relationships with Mn and TDS. Conversely, CaCO₃ shows a negative correlation with EC and TDS, suggesting alternative sources beyond rock weathering. The HHRA indicates higher non-carcinogenic health risks from Fe²⁺ contamination in underground rivers compared to springs. The study’s novelty comes in its integrated assessment of groundwater quality and health hazards in Trenggalek’s karst region, which uses GWQI, HHRA, and statistical analysis to show geochemical interactions and highlight iron-related health issues in underground rivers. Full article

The Weimei Formation, the most complete Upper Jurassic sedimentary sequence in the Tethyan Himalaya, is crucial for understanding the tectono-sedimentary evolution of the northern Indian margin. However, its depositional environment remains debated, with conflicting shallow- and deep-water interpretations. This study integrates sedimentary facies, petrography, zircon geochronology, and geochemical analyses to constrain the provenance, depositional environment, and tectonic setting of the Weimei Formation. The results reveal that the sedimentary system primarily consists of shoreface, delta, and shelf facies, with locally developed slope-incised valleys. Detrital zircon ages are concentrated at ~468 Ma and ~964 Ma, indicating a provenance mainly derived from the Indian continent. Geochemical characteristics, such as high SiO₂, low Na₂O–CaO–TiO₂ contents, right-leaning REE patterns, and significant negative Eu anomalies, suggest the derivation of sediments from felsic upper crustal recycling within a passive continental margin. Stratigraphic comparison between southern and northern Tethyan Himalayan sub-zones reveals a paleogeographic “uplift–depression” pattern, characterized by the coexistence of shoreface–shelf deposits and slope-incised valleys. This study provides key evidence for reconstructing the Late Jurassic paleogeography of the northern Indian margin and the tectonic evolution of the Neo-Tethys Ocean. Full article

The Permian Kupferschiefer shale, a key stratigraphic unit within the Zechstein sequence of the Fore-Sudetic Monocline, represents both a metal-rich lithofacies and a potential source rock for hydrocarbon generation. This study presents a comprehensive geochemical characterization of selected Kupferschiefer samples obtained from the Legnica–Głogów Copper District (LGOM) and exploratory boreholes. Analytical methods included Rock-Eval pyrolysis, Py-GC/FID, elemental analysis, TG-FTIR, biomarker profiling, and stable carbon isotope measurements. Results indicate that the shales contain significant amounts of Type II and mixed Type II/III kerogen, derived primarily from marine organic matter with minor terrestrial input. The organic matter maturity, expressed by T_max, places most samples within the oil window. Rock-Eval S2 values exceed 60 mg HC/g rock in some samples, confirming excellent generative potential. Py-GC/FID data further support high hydrocarbon yields, particularly in samples from the CG-4 borehole and LGOM mines. The thermal decomposition of kerogen reveals multiple degradation phases, with evolved gas analysis identifying sulfur-containing compounds and hydrocarbons indicative of sapropelic origin. Isotopic compositions of bitumen and kerogen suggest syngenetic relationships and marine depositional settings, with samples from a North Poland borehole showing isotopic enrichment consistent with post-depositional oxidation. Kinetic parameters calculated using the Kissinger–Akahira–Sunose method demonstrate variable activation energies (107–341 kJ/mol), correlating with differences in organic matter composition and mineral matrix. The observed variability in geochemical properties highlights both regional and facies-dependent influences on the shale’s generative capacity. The study concludes that the Kupferschiefer in southwestern and northern Poland exhibits substantial hydrocarbon generation potential. This potential has been previously underestimated due to the unit’s thinness, but localized zones with high TOC, favorable kerogen type, and low activation energy could be viable exploration targets for natural gas. Full article

Natural geogenic effects lead to alterations in soil heavy metal concentrations. This study assesses the presence of elevated trace-element concentrations in the Oued Irriri watershed in southeastern Morocco. ASTER satellite imagery, geochemical, and aeromagnetic data are combined to determine the origin of these anomalies. Processing of ASTER images delineated alteration zones coinciding with areas of high heavy metal anomalies by detecting hydrothermal alteration minerals, including muscovite, montmorillonite, illite, hematite, jarosite, chlorite, and epidote. Principal Component Analysis (PCA) of geochemical data distribution in soils enabled the characterization of variations in trace-element concentrations, the extraction of geochemical anomalies, and the identification of potential sources of contamination. Comparing satellite image processing results with geochemical analyses facilitated the production of a geogenic enrichment map. The study results indicate high enrichment levels of zinc, Molybdenum, and bismuth in the western basin, of purely lithological origin. Hydrothermal alteration surfaces intersect geochemical anomaly zones in the north and northeast, primarily showing the impact of fault rooting on the surface deposition of Cu, Ba, Hg, and Pb-rich deposits. This study developed a geogenic enrichment map indicating naturally affected areas, identifying potential risks to eco-environmental systems, and better preventing the effects of geogenic enrichment. Full article

To elucidate the hydrochemical characteristics and evolution mechanisms of shallow groundwater in the alluvial–coastal transitional zone of the Tangshan Plain, 76 groundwater samples were collected in July 2022. An integrated approach combining Piper and Gibbs diagrams, ionic ratio analysis, multivariate statistical methods (including Pearson correlation, hierarchical cluster analysis, and principal component analysis), and PHREEQC inverse modeling was employed to identify hydrochemical facies, dominant controlling factors, and geochemical reaction pathways. Results show that groundwater in the upstream alluvial plain is predominantly of the HCO₃–Ca type with low mineralization, primarily controlled by carbonate weathering, water–rock interaction, and natural recharge. In contrast, groundwater in the downstream coastal plain is characterized by high-mineralized Cl–Na type water, mainly influenced by seawater intrusion, evaporation concentration, and dissolution of evaporite minerals. The spatial distribution of groundwater follows a pattern of “freshwater in the north and inland, saline water in the south and coastal,” reflecting the transitional nature from freshwater to saline water. Ionic ratio analysis reveals a concurrent increase in Na⁺, Cl⁻, and SO₄²⁻ in the coastal zone, indicating coupled processes of saline water mixing and cation exchange. Statistical analysis identifies mineralization processes, carbonate weathering, redox conditions, and anthropogenic inputs as the main controlling factors. PHREEQC simulations demonstrate that groundwater in the alluvial zone evolves along the flow path through CO₂ degassing, dolomite precipitation, and sulfate mineral dissolution, whereas in the coastal zone, continuous dissolution of halite and gypsum leads to the formation of high-mineralized Na–Cl water. This study establishes a geochemical evolution framework from recharge to discharge zones in a typical alluvial–coastal transitional setting, providing theoretical guidance for salinization boundary identification and groundwater management. Full article

Sodalite is a common feldspathoid in alkaline systems, with some varieties exhibiting notable fluorescence due to impurity activators. This study reports the first documented occurrence and characterization of fluorescent sodalite from the classic Ditrău Alkaline Massif, Romania, where its optical properties were previously undescribed. Sodalite-bearing syenite samples from different perimeters of the massif were investigated using macroscopic UV fluorescence, petrographic microscopy, and vibrational spectroscopy (Raman and FT-IR). The sodalite occurs as a late-stage, interstitial and poikilitic mineral, often associated with alteration to cancrinite. Under long-wave UV (365 nm) light, it exhibits spatially variable fluorescence, from absent in parts of the western Prişca perimeter to strong, uniform orange in the eastern Aurora perimeter. Raman and FT-IR spectroscopy confirmed the mineral’s identity and revealed subtle spectral variations, particularly the presence of a minor cancrinite component in some analyses. The vibrant orange fluorescence is consistent with activation by disulfide radical anion ($S_2^{·-}$) activators, formed in the sulfur- and chlorine-rich late-stage fluids characteristic of the massif’s evolution. The geographic variation in fluorescence intensity serves as a potential indicator of the geochemical heterogeneity of these fluids across the massif, linking the strongest fluorescence to the most evolved portions of the igneous complex. This finding opens a new avenue for using fluorescence as a tool for petrogenetic investigation in this classic locality. Full article

Strategic lithium resources are critical to national security and have attained heightened importance in contemporary geopolitical, economic, and military contexts. Persistent geochemical anomalies of lithium were first identified in coal-bearing claystones of the Middle Jurassic Xishanyao Formation at the Liuhuanggou Coal Mine in the southern Junggar Basin, Xinjiang. In this study, a suite of analytical techniques, including X-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry, X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy, time-of-flight secondary ion mass spectrometry, and sequential chemical extraction, was employed to investigate the provenance, depositional environment, and modes of lithium occurrence in the claystone. Results indicated that the claystone at the Liuhuanggou Coal Mine was dominated by moderately felsic rocks. The notable enrichment of lithium in the Liuhuanggou coal mine claystone indicates favorable metallogenic potential. Lithium was primarily hosted in the aluminosilicate-bound fraction with inorganic affinity and was structurally incorporated within clay minerals, such as kaolinite, illite, and Fe-rich chlorite (chamosite). Lithium-rich claystone was deposited under intense chemical weathering conditions in a transitional, slightly brackish environment characterized by elevated temperatures and low oxygen levels. These findings advance our understanding of sedimentary lithium mineralization mechanisms and offer direct practical guidance for lithium resource exploration and metallogenic prediction in the Xinjiang region, thereby supporting the development of efficient extraction technologies. Full article

The Lower Submember of the Second Member of the Lianggaoshan Formation (LGS2-LS) in the Fuling area, southeastern Sichuan Basin, represents the deepest lacustrine depositional stage of the formation and constitutes an important target for shale oil and gas exploration. Based on core observations, thin-section petrography, X-ray diffraction, geochemical analyses, and sedimentary facies interpretation from representative wells, this study characterizes the lithofacies types, sedimentary environments, and depositional evolution of the LGS2-LS. Results show that the LGS2-LS is dominated by clay–quartz assemblages, with average clay mineral and quartz contents of 44.6% and 38.8%, respectively, and can be subdivided into shallow and semi-deep lacustrine subfacies comprising eight microfacies. Geochemical proxies indicate alternating warm-humid and hot-arid paleoclimatic phases, predominantly freshwater conditions, variable redox states, and fluctuations in paleoproductivity. Sedimentary evolution reveals multiple transgressive–regressive cycles, with Sub-layer 6 recording the maximum water depth and deposition of thick organic-rich shales under strongly reducing conditions. The proposed sedimentary model outlines a terrigenous clastic lacustrine system controlled by lake-level fluctuations, transitioning from littoral to shallow-lake to semi-deep-lake environments. The distribution of high-quality organic-rich shales interbedded with sandstones highlights the LGS2-LS as a favorable interval for shale oil and gas accumulation, providing a geological basis for further hydrocarbon exploration in the southeastern Sichuan Basin. Full article

The Baorao Trough of the Jiergalangtu Sag, located in the central Erlian Basin, is rich in petroleum resources. However, due to a lack of systematic geochemical characterization and comparative studies with other source rocks, the hydrocarbon generation potential of its Jurassic strata remains unclear. In this study, 125 samples from the Baorao Trough were analyzed to evaluate their hydrocarbon generation potential, identify organic matter sources and depositional environments, and characterize hydrocarbon generation and expulsion. Results show that source rocks from the first member of the Tengge’er (K₁bt₁) Formation and the Aershan (K₁ba) Formation have high organic matter content, favorable kerogen types, and have reached low to medium maturity. In contrast, Jurassic source rocks are predominantly Type III kerogen and highly mature. K₁bt₁ was deposited in a weakly oxidizing to reducing, brackish environment, while K₁ba formed under weakly reducing, saline conditions. Jurassic source rocks also developed in weakly reducing, brackish to saline settings. Notably, saline and reducing environments promote the development of high-quality source rocks. The lower total organic carbon (TOC) threshold for effective source rocks in the study area is 0.8%, and the hydrocarbon expulsion threshold for vitrinite reflectance ratio (R_o) is approximately 0.8%. Accordingly, K₁bt₁ and K₁ba have undergone partial hydrocarbon expulsion but remain within the oil-generating window, indicating strong oil-generating potential. Jurassic source rocks likely experienced early thermal cracking of Type III kerogen, with generated oil migrating or escaping during early geological activity. However, some gas-generating potential remains. These findings provide significant evidence for assessing resource potential, predicting the distribution of high-quality source rocks and favorable exploration areas. Full article

Shale reservoirs offer significant potential for CO₂ geological sequestration due to their extensive nanopore networks and heterogeneous pore systems. This study comparatively assessed the CO₂ storage potential of the Lower Silurian Longmaxi and Lower Cambrian Qiongzhusi shales through an integrated approach involving organic geochemical analysis, mineralogical characterization through X-ray diffraction (XRD), mercury intrusion capillary pressure (MICP), low-pressure nitrogen and carbon dioxide physisorption, field-emission scanning electron microscopy (FE-SEM), stochastic 3D microstructure reconstruction, multifractal analysis, and three-dimensional succolarity computation. The results demonstrate that mineral assemblages and diagenetic history govern pore preservation: Longmaxi shales, with moderate maturity and shallower burial, retain abundant organic-hosted mesopores, whereas overmature and deeply buried Qiongzhusi shales are strongly compacted and mineralized, reducing pore availability. Multifractal spectra and 3D reconstructions reveal that Longmaxi develops broader singularity spectra and higher succolarity values, reflecting more isotropic meso-/macropore connectivity at the SEM scale, while Qiongzhusi exhibits narrower spectra and lower succolarity, indicating micropore-dominated and anisotropic networks. Longmaxi has nanometer-scale throats (D₅₀ ≈ 10–25 nm) with high CO₂ breakthrough pressures (P₁₀ ≈ 0.57 MPa) and ultra-low RGPZ permeability (mean ≈ 1.5 × 10⁻² nD); Qiongzhusi has micrometer-scale throats (D₅₀ ≈ 1–3 μm), very low breakthrough pressures (P₁₀ ≈ 0.018 MPa), and much higher permeability (mean ≈ 4.63 × 10³ nD). Storage partitioning further differs: Longmaxi’s median total capacity is ≈15.6 kg m⁻³ with adsorption ≈ 93%, whereas Qiongzhusi’s median is ≈12.8 kg m⁻³ with adsorption ≈ 70%. We infer Longmaxi favors secure adsorption-dominated retention but suffers from injectivity limits; Qiongzhusi favors injectivity but requires reliable seals. Full article

The Hugushan banded iron formation (BIF) is one of the most representative iron ore deposits in the central part of the North China Craton, and its ore formation mechanism remains highly controversial. This study presents whole-rock and Fe–Si–O isotope geochemical evidence, offering a new perspective on the ore formation mechanism of the Hugushan BIFs. The samples from the upper and lower parts of the Hugushan BIFs are characterized by slight enrichment of heavy and light Fe isotopes, respectively. Additionally, the samples from the upper part of the Hugushan BIFs show characteristics of slightly positive Ce anomalies and negative La anomalies, suggesting that the shallow ancient seawater was in a partially oxidized state, whereas the deep seawater remained in a reductive environment during the depositional period. The low Al₂O₃ and TiO₂ concentrations, as well as the depletion of Zr and Hf in the Hugushan BIFs, suggest that the contribution of terrestrial detrital materials to deposition is extremely limited. The BIFs all exhibit positive Eu anomalies, and the quartz in the BIFs is depleted in ³⁰Si, a characteristic similar to that observed in siliceous rocks formed in hydrothermal vent environments and during hydrothermal plume activity. Additionally, the δ¹⁸O values of quartz in Hugushan BIFs are similar to the O isotope compositions of hydrothermal sedimentary siliceous rocks, further suggesting that the silicon in BIFs originates primarily from seafloor hydrothermal activity. The combination of Eu/Sm, Sm/Yb, and Y/Ho ratios indicates that the major components (iron and silica) of the Hugushan Iron Ore Deposit originated from the mixing of high-temperature hydrothermal fluids with seawater, with the hydrothermal fluid contributing slightly less than 0.1%. The magnetite and quartz bands in the BIFs exhibit inhomogeneous and covariant δ⁵⁶Fe and δ³⁰Si isotope characteristics, suggesting that the alternating siliceous and ferruginous layers are products of original chemical deposition in the ocean. Periodic hydrothermal activity and ocean transgression caused the recurring deposition of siliceous and ferruginous layers, resulting in the characteristic banded structure of the Hugushan Iron Ore Deposit. Full article

As the residual products of severe chemical weathering, bauxite deposits serve both as essential economic Al-Fe resources and geochemical archives that reveal information about the parent rocks’ composition, paleoenvironments and paleoclimates, and the tectonic settings responsible for their genesis. The well-developed Early Paleocene bauxite deposits of the Salt Range, Pakistan, provide an opportunity for deciphering their ore genesis and parental affinities. The deposits occur as lenticular bodies and are typically composed of three consecutive stratigraphic facies from base to top: (1) massive dark-red facies (L-1), (2) composite conglomeratic–pisolitic facies (L-2), and (3) Kaolinite-rich clayey facies (L-3). Results from optical microscopy, X-ray powder diffraction (XRPD), and scanning electron microscopy with Energy-Dispersive X-Ray Spectroscopy (SEM-EDS) reveal that facies L-1 contains kaolinite, hematite, and goethite as major minerals, with minor amounts of muscovite, quartz, anatase, and rutile. In contrast, facies L-2 primarily consists of kaolinite, boehmite, hematite, gibbsite, goethite, alunite/natroalunite, and zaherite, with anatase, rutile, and quartz as minor constituents. L-3 is dominated by kaolinite, quartz, and anatase, while hematite and goethite exist in minor concentrations. Geochemical analysis reveals elevated concentrations of ${\mathrm{Al}}_2$${\mathrm{O}}_3$, ${\mathrm{Fe}}_2$${\mathrm{O}}_3$, ${\mathrm{SiO}}_2$, and ${\mathrm{TiO}}_2$. Trace elements, including Th, U, Ga, Y, Zr, Nb, Hf, V, and Cr, exhibit a positive trend across all sections when normalized to Upper Continental Crust (UCC) values. Field observations and analytical data suggest a polygenetic origin of these deposits. L-1 suggests in situ lateritization of some sort of precursor materials, with enrichment in stable and ultra-stable heavy minerals such as zircon, tourmaline, rutile, and monazite. This facies is mineralogically mature with bauxitic components, but lacks the typical bauxitic textures. In contrast, L-2 is texturally and mineralogically mature, characterized by various-sized pisoids and ooids within a microgranular-to-microclastic matrix. The L-3 mineralogy and texture suggest that the conditions were still favorable for bauxite formation. However, the ongoing tectonic activities and wet–dry climate cycles post-depositionally disrupted the bauxitization process. The accumulation of highly stable detrital minerals, such as zircon, rutile, tourmaline, and monazite, indicates prolonged weathering and multiple cycles of sedimentary reworking. These deposits have parental affinity with acidic-to-intermediate/-argillaceous rocks, resulting from the weathering of sediments derived from UCC sources, including cratonic sandstone and shale. Full article

The transformation of smectite to illite documents multi-scale water–rock–hydrocarbon interaction dynamics. Current studies predominantly emphasize the influence of inorganic systems on this process, while overlooking the dynamic regulation by organic matter and the synergistic effects of multiple controlling factors under actual geological conditions. In this study, we conducted integrated semi-open pyrolysis experiments on natural samples from the Chang-7 Member and hydrothermal experiments using synthetic analogs. The illitization process of smectite was characterized through XRD analysis and SEM observations, while organic geochemical testing was employed to track the corresponding thermal evolution of organic matter. The semi-open pyrolysis results reveal that significant changes in illite–smectite (I/S) mixed layer minerals and illite content/morphology occur above 320 °C, which coincides with the critical threshold for extensive organic matter evolution. Thermal degradation of organic matter generates pore space, thereby enhancing water–rock interactions involving clay minerals. This demonstrates the co-evolution of organic matter and smectite, and indicates that temperature indirectly influences illitization by regulating organic matter thermal evolution. The hydrothermal simulation experiments demonstrate the early-stage characteristics of illitization. Unlike long-term geological evolution, K⁺ under experimental conditions primarily originates from the aqueous medium due to kinetic constraints on feldspar dissolution. Notably, organic matter regulates K⁺ partitioning dynamics—increased organic matter content hinders K⁺ incorporation into smectite interlayers, thereby suppressing the illitization process. Cross-system experimental analysis reveals that organic matter exhibits temporally dependent dual functionality, serving both mediating and modulating roles within inorganic diagenetic systems. This study delineates diagnostic-stage-dependent mechanisms governing smectite illitization through multifactorial synergistic interplay, establishing a predictive framework applicable to organic-rich systems exemplified by the Chang-7 Shale. Full article

The Galale Cu–Au deposit lies on the northern margin of the western Gangdese metallogenic belt, near the western edge of the Gangdese arc within the Bangong–Nujiang suture zone. Unlike the well-studied Miocene Cu belt in southern Gangdese, this region remains insufficiently investigated, particularly in terms of geochemical characterization, leading to an ambiguous metallogenic model and a debated tectonic setting—specifically, the unresolved issue of subduction polarity across the Bangong–Nujiang suture. This tectonic ambiguity has important implications for understanding magma sources, metal transport pathways, and, consequently, for guiding mineral exploration strategies in the area. To address this, we conducted zircon U–Pb dating on the ore-related quartz diorite and granodiorite, yielding crystallization ages of 84.05 ± 0.34 Ma and 77.20 ± 0.69 Ma, respectively. Integrated with previous data, these results constrain mineralization to 83–89 Ma, which includes both skarn-type Cu–polymetallic and porphyry-type Cu mineralization. Regional comparisons support a tectonic model involving slab rollback and southward subduction of the Bangong–Nujiang oceanic lithosphere. Geochemical analyses of quartz diorite, granodiorite, and monzonitic granite show high-K calc-alkaline, peraluminous I-type affinities, with enrichment in LREEs and LILEs, and depletion in HREEs and HFSEs. Notably, the monzonitic granite is marked by high SiO₂, Sr/Y, and Rb/Sr ratios, low Zr/Hf, strong LREE enrichment, weak Eu anomalies, and pronounced Nb–Ta depletion, indicating high oxygen fugacity and favorable conditions for Mo mineralization. The deposit formed through tectono-magmatic processes related to the closure of the Bangong–Nujiang Neo-Tethys Ocean. Subduction and subsequent lithospheric delamination induced partial melting of mantle and crustal sources, generating quartz diorite and granodiorite intrusions. Magmatic fluids interacted with carbonate wall rocks to form skarn assemblages, concentrating ore metals along structures. The mineralization formed within the contact zones between intrusions and surrounding country rocks. Late-stage granite porphyry intrusions (~77 Ma), inferred from major, trace, and rare earth element compositions to have the highest Mo potential, may represent an extension of earlier skarn mineralization in the area (83–89 Ma). This study presents the first comprehensive geochemical dataset for the Galale deposit, refines its metallogenic model, and identifies key geochemical indicators (e.g., Sr, Y, Nb, Rb, Zr, Hf) for Mo exploration. Full article

The chemical composition of bottom sediments in the northern part of Lake Umbozero, located in close proximity to a closed rare metal mine in the Murmansk Region, was studied. This study is a continuation of our research into the impact of closed rare metal mines and tailings on the environment. Samples were collected using an open gravity sampler in two sections of the lake in three replicates. The content of rare earth elements was determined using inductively coupled plasma mass spectrometry. The total content of elements was determined both in the surface layers of bottom sediments and in the deep layers that were formed in the preindustrial period and, thus, characterize the geochemical background of the study area. The average ∑REE in the surface layers of bottom sediments of Lake Umbozero in the wastewater reception area (Site 1) reaches 774 mg/kg, while for the area located north of the discharge site (Site 2), ∑REE was 208 mg/kg. The enrichment factor (EF), the geoaccumulation index (I_geo), the coefficient of the index of potential ecological risk (E_ir) and the index of potential ecological hazard (RI) were calculated. Assessing the total pollution of bottom sediments of Lake Umbozero with rare earth elements, the value of potential ecological risk reaches values corresponding to the level of low and moderate ecological risk of pollution (RI_{Site 1} = 164; RI_{Site 2} = 104). The conducted correlation analysis allowed us to establish the main phases containing rare earth elements in the bottom sediments of Lake Umbozero—oxyhydroxide complex compounds with iron and manganese. Full article