Search Results (398)

Superior-type iron formations (IFs) represent a globally significant source of iron ore; yet, their origin remains a subject of ongoing debate. Early models proposed a continental weathering source for the iron, whereas later interpretations—mainly supported by positive europium (Eu) anomalies—favored a hydrothermal source. However, the hydrothermal model largely relies on REE systematics, and whether iron and REEs in Superior-type IFs share the same source remains uncertain. As iron isotopes directly trace the sources and fractionation history of iron, a spatial co-variation between Fe isotopes and Eu anomalies would shed new light on the iron source issue of IFs. In this study, we present new Fe isotope and REE data from the drill core WILDD004 at Wilgena Hill and integrate them with reported data for two additional drill cores: HKDD4 (Hawks Nest) and GWDD1 (Giffen Well). All three cores are stratigraphically equivalent to the Wilgena Hill Jaspilite Formation but span a lateral distance of ~100 km across the Gawler Craton, South Australia. While the Hawks Nest and Giffen Well samples exhibit both positive Eu anomalies and elevated δ⁵⁶Fe values, the Wilgena Hill samples show positive yet smaller Eu/Eu* (1.17–2.41) and negative δ⁵⁶Fe values (−0.60‰ to −1.63‰). The consistent presence of Eu anomalies and the systematic spatial correlation between δ⁵⁶Fe and Eu/Eu* across all three locations provide direct, Fe-based geochemical evidence for a hydrothermal source of iron in this Superior-type IF. Full article

The presence of lead (Pb) and cadmium (Cd) can have considerable effects on the environment and on humans. The present study examines their levels in two lakes with different trophic levels located in northwestern Poland; their concentrations were determined in water and the bottom sediments, in common reed and in the organs of pike, bream and roach. The work also evaluates Pb and Cd bioavailability in bottom sediments, their potential for biomagnification, their bioaccumulation in the food chain and risk to human consumers. Metal concentrations were determined by graphite furnace atomic absorption spectrometry (GFAAS). The geochemical fractions of the metals were isolated by sequential extraction. Both Pb and Cd demonstrated low bioavailability, with the carbonate fraction playing a key role in their bioconversion. The concentrations of Pb and Cd in some organs and tissue types of fish and reeds correlated with their levels in water and sediments. No biomagnification was observed between the studied fish species. Calculations based on BMDL, TWI and THQ concentrations found Pb and Cd levels in the edible parts of fish to be within permissible limits and not to pose any threat to consumer health. Full article

Quartz from four typical but contrasting peralkaline quartz-saturated granite systems (Khan Bogd and Khalzan Buregte plutons (Mongolia), Ivigtut stock (Greenland), Europa and Madeira plutons (Pitinga magmatic province, Brazil)) was analyzed using LA-ICP-MS to define the range of selected trace element content and trends in their evolution and to compare this content with published data from granitoids of other geochemical types. The evaluation of about 1100 analyses found the studied trace elements mostly in ranges <0.01–18 ppm Li (median 2.41 ppm), 1.2–77 ppm Ti (median 8.2 ppm), 8.3–163 ppm Al (median 42 ppm) and 0.05–5.7 ppm Ge (median 0.98 ppm) (in all cases 5% of the lowest and 5% of the highest values were omitted). Quartz from geochemically less evolved riebeckite-bearing granite plutons shows no Ti/Ge fractionation and displays either a positive Ti–Al correlation or no Ti–Al correlation. More fractionated and potentially mineralized peralkaline magmatic systems were formed within two distinct magmatic episodes: quartz from the older phases is relatively Ti-rich and evolved via Ti decrease with no possible Ge enrichment, while quartz from younger phases is Ti-poor from the beginning and has the ability of enrichment in Al and Ge. Relative enrichment in Al and increase in Ge/Ti value of quartz can serve as a supporting method for the identification of potentially ore-bearing magmatic systems. Full article

The El Bola mafic–ultramafic intrusion (EBMU) in Egypt’s Northern Eastern Desert represents an example of Neoproterozoic post-collisional layered mafic–ultramafic magmatism in the Arabian–Nubian Shield (ANS). The intrusion is composed of pyroxenite, olivine gabbro, pyroxene gabbro, pyroxene–hornblende gabbro, and hornblende-gabbro, exhibiting adcumulate to heter-adcumulate textures. Mineralogical and geochemical analyses reveal a coherent trend of fractional crystallization. Compositions of whole rock and minerals indicate a parental magma of ferropicritic affinity, derived from partial melting of a hydrous, metasomatized spinel-bearing mantle source, likely modified by subduction-related fluids. Geothermobarometric calculations yield crystallization temperatures from ~1120 °C to ~800 °C and pressures from ~5.2 to ~3.1 kbar, while oxygen fugacity estimates suggest progressive oxidation (log fO₂ from −17.3 to −15.7) during differentiation. The EBMU displays Light Rare Earth element (LREE) enrichment, trace element patterns marked by Large Ion Lithophile Element (LILE) enrichment, Nb-Ta depletion and high LILE/HFSE (High Field Strength Elements) ratios, suggesting a mantle-derived source that remained largely unaffected by crustal contribution and was metasomatized by slab-derived fluids. Tectonic discrimination modeling suggests that EBMU magmatism was triggered by asthenospheric upwelling and slab break-off. Considering these findings alongside regional geologic features, we propose that the mafic–ultramafic intrusion from the ANS originated in a tectonic transition between subduction and collision (slab break-off) following the assembly of Gondwana. Full article

Carbonaceous–siliceous–argillaceous rock-type uranium deposits, a major uranium resource in China, pose significant environmental risks due to heavy metal contamination. Geochemical investigations in the former Zoige uranium mine revealed elevated As, Cd, Cr, Cu, Ni, U, and Zn concentrations in soils and sediments, particularly at river confluences and downstream regions, attributed to leachate migration from ore bodies and tailings ponds. Surface samples exhibited high Cd bioavailability. The integrated BCR and mineral analysis reveals that Acid-soluble and reducible fractions of Ni, Cu, Zn, As, and Pb are governed by carbonate dissolution and Fe-Mn oxide dynamics via silicate weathering, while residual and oxidizable fractions show weak mineral-phase dependencies. Positive Matrix Factorization identified natural lithogenic, anthropogenic–natural composite, mining-related sources. Pollution assessments using geo-accumulation index and contamination factor demonstrated severe contamination disparities: soils showed extreme Cd pollution, moderate U, As, Zn contamination, and no Cr, Pb pollution (overall moderate risk); sediments exhibited extreme Cd pollution, moderate Ni, Zn, U levels, and negligible Cr, Pb impacts (overall extreme risk). USEPA health risk models indicated notable non-carcinogenic (higher in adults) and carcinogenic risks (higher in children) for both age groups. Ecological risk assessments categorized As, Cr, Cu, Ni, Pb, and Zn as low risk, contrasting with Cd (extremely high risk) and sediment-bound U (high risk). These findings underscore mining legacy as a critical environmental stressor and highlight the necessity for multi-source pollution mitigation strategies. Full article

The Great Xing’ an Range is located in the eastern part of the Xing’ an-Mongolian Orogenic Belt, which is an important component of the Central Asian Orogenic Belt. To determine the emplacement age and petrogenesis of the granitoids in the Gegenmiao and Taonan areas of the central Great Xing’an Range, and to investigate its tectonic setting, petrographic studies, zircon U-Pb geochronology, whole-rock Sr-Nd isotopic analysis, zircon Hf isotopic analysis, and detailed geochemical investigations of this intrusion were carried out. The results indicate the following, in relation to the granitoids in the study areas: (1) The zircon U-Pb dating of the granitic rocks in the study areas yields ages ranging from 141.4 ± 2.0 Ma to 158.7 ± 1.9 Ma, indicating their formation during the Late Jurassic to Early Cretaceous; (2) the geochemical characteristics indicate that these rocks belong to the calc-alkaline series and peraluminous, classified as highly fractionated I-type granites with adakite features; (3) the Sr-Nd isotopic data show that the εNd(t) values of Gegenmiao granitic rocks are 2.8 and 2.1, while those of Taonan granitic rocks range from −1.5 to 0.7; (4) the Zircon εHf(t) values of the granitic rocks from Gegenmiao and Taonan vary from 2.11 to 6.48 and 0.90 to 8.25, respectively. They are interpreted to have formed through partial melting of thickened lower crustal material during the Meso-Neoproterozoic. The Gegenmiao and Taonan granitic rocks were formed in a transitional environment from post-orogenic compression to extension, which is closely associated with the Mongolia–Okhotsk tectonic system. Full article

Late Paleozoic to Early Mesozoic granitoids in the East Kunlun Orogenic Belt (EKOB) provide critical insights into the complex and debated relationship between Paleo–Tethyan magmatism and tectonics. This study presents integrated bulk-rock geochemical and zircon isotopic data for the Xingshugou monzogranite (MG) to address these controversies. LA-ICP-MS zircon U-Pb dating constrains the emplacement age of the MG to 247.1 ± 1.5 Ma. The MG exhibits a peraluminous and low Na₂O A₂-type granite affinity, characterized by high K₂O (4.69–6.80 wt.%) and Zr + Nb + Ce + Y (>350 ppm) concentrations, coupled with high Y/Nb (>1.2) and A/CNK ratios (1.54–2.46). It also displays low FeO^T, MnO, TiO₂, P₂O₅, and Mg^# values (26–49), alongside pronounced negative Eu anomalies (Eu/Eu* = 0.37–0.49) and moderately fractionated rare earth element (REE) patterns ((La/Yb)_N = 3.30–5.11). The MG exhibits enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs; such as Sr and Ba), and depletion in high field strength elements (HFSEs; such as Nb, Ta, and Ti), collectively indicating an arc magmatic affinity. Zircon saturation temperatures (T_Zr = 868–934 °C) and geochemical discriminators suggest that the MG was generated under high-temperature, low-pressure, relatively dry conditions. Combined with positive zircon ε_Hf(t) (1.8 to 4.7) values, it is suggested that the MG was derived from partial melting of juvenile crust. Synthesizing regional data, this study suggests that the Xingshugou MG was formed in an extensional tectonic setting triggered by slab rollback of the Paleo-Tethys Oceanic slab. Full article

This study contributes new mineralogical, whole-rock geochemical, and magnetic susceptibility data to the well-established petrogenesis of the Miocene of Limnos volcanic rocks in the Aegean region. The combined examination of volcanic samples from the Katalakon, Romanou, and Myrina units demonstrates that they belong to a genetically related high-K calc-alkaline to shoshonitic suite that was formed by fractional crystallization in a continental arc setting and derived from a subduction-modified mantle source, contaminated by continental sediments. Different magmatic processes and crystallization conditions are reflected in modest compositional differences in magnetite (Ti, Al substitution) and ilmenite (Mg, Al, Fe–Ti ratios), as well as variations in trace elements between the units (e.g., elevated Nb–Zr in Romanou, high LREE in Myrina, and Ba in Katalakon). According to the magnetic data, bulk magnetic susceptibility is largely determined by magnetite abundance, whereas magnetic domain states are influenced by the grain size and shape, as euhedral grains are associated with stronger responses. The coupled geochemical and magnetic results indicate the diversified and transitional character of the Agios Ioannis Subunit in the Katalakon Unit. Full article

The Virunga Volcanic Province (VVP), located in the western branch of the East African Rift System, hosts a variety of alkaline lavas erupted from closely spaced volcanic centers. However, the magmatic system of this region, particularly in its eastern sector, remains insufficiently constrained. In this study, we present a petrological and geochemical investigation of basaltic to trachytic lavas from the eastern VVP. Thermobarometric analysis of mineral phases indicates that basalts originated from magma storage zones between 4 and 30 km deep, with crystallization temperatures of ~1200 °C and melt H₂O contents lower than 1 wt%. In contrast, more evolved magmas crystallized at similar depths, but at lower temperatures (~1050 °C) and higher H₂O contents, ranging from 2 to 4 wt%. Thermodynamic modelling suggests that extensive (up to 70%) fractional crystallization of an assemblage dominated by olivine, clinopyroxene, and plagioclase can produce the more evolved trachytic derivatives from basaltic parental melts. When integrated with previous studies from other VVP volcanoes, our findings deepen the understanding of the architecture of the magmatic system beneath the region, suggesting it resembles a well-developed multi-level plumbing system. Full article

Rare earth elements (REEs) are critical mineral resources that play a pivotal role in modern technology and industry. Currently, the global supply of light rare earth elements (LREEs) remains adequate. However, the supply of heavy rare earth elements (HREEs) is associated with substantial risks due to their limited availability. Ion-adsorption type rare earth deposits (IAREDs), which represent the predominant source of HREEs, have become a focal point for exploration activities, with a notable increase in global interest in recent years. This study systematically collected stream sediments and stream water samples from the Jiaping IARED in Guangxi, as well as from adjacent granitic and carbonate background areas, to investigate the exploration significance of geochemical surveys for IAREDs. Additionally, mineralized soil layers, non-mineralized soil layers, and bedrock samples from the weathering crust of the Jiaping deposit were analyzed. The results indicate that stream sediments originating from the Jiaping IARED and granite-hosted background regions display substantially elevated REE concentrations relative to those from carbonate-hosted background areas. Moreover, δEu values in stream sediments can serve as an effective indicator for differentiating weathering products derived from granitic and carbonate lithologies. Within the mining area, three coarse-grained fractions of stream sediments (i.e., +20 mesh, 20–60 mesh, and 60–150 mesh) exhibit REE concentrations comparable to those observed in both granite-hosted and carbonate-hosted background regions. However, the HREEs content in the finer -150-mesh stream sediments from Jiaping IARED is markedly higher than that in the two background regions. The (La/Sm)_N versus (La/Yb)_N ratios of -150-mesh stream sediments in the Jiaping IARED may reflect the mixing processes involving HREE-enriched ore layer, non-mineralized layer, and LREE-enriched ore layer. This observation implies that fine-grained (-150-mesh) stream sediments can partially inherit the REE characteristics of mineralized layers within IAREDs. Scanning electron microscopy (SEM) observations indicate that the enrichment of REEs in fine-grained stream sediments primarily originates from REE-rich accessory minerals derived from parent rocks and mineralized weathering crusts. A comparative analysis reveals that the concentrations of REEs in stream water collected during the rainy season are significantly higher than those collected during the dry season. Moreover, the levels of REEs, especially HREE, in stream water from the Jiaping IARED substantially exceed those in background areas. Collectively, these findings suggest that the geochemical signatures of REEs in rainy season stream water possess diagnostic potential for identifying IAREDs. In conclusion, the integrated application of geochemical surveys of stream water and -150-mesh stream sediments can effectively delineate exploration targets for IAREDs. Full article

The phytoaccumulation of Fe, Mn, Cu, Zn, and Pb in Tilia cordata flowers and soils from six locations with varying degrees of anthropopressure in Bydgoszcz city and its surroundings (Poland) was assessed. Additionally, metal concentrations and soil enzymatic activity were analyzed. Enrichment Factor analysis revealed significant Zn enrichment at only one locality, supported by a geoaccumulation index value indicating moderate soil pollution. Total metal content in soils correlated with total organic carbon (TOC), while total iron content correlated with the clay fraction (<0.002 mm). Metal concentrations were comparable to the geochemical background levels for soils in Poland. Assessment of total metal contents in the topsoil surface layer from the six locations indicated that concentrations did not exceed permissible limits established by applicable legislation. The study showed that sampling locations influenced the activities of dehydrogenase (DHA), fluorescein diacetate hydrolysis (FDA), β-glucosidase (GL), and arylsulfatase (AR), and these activities correlated more strongly with pedogenic factors than with metal content. No elevated metal levels were detected in the dry mass of T. cordata flowers. Lead content did not exceed 10 mg·kg⁻¹ dry matter, in accordance with World Health Organization (WHO) recommendations. Continued monitoring of trace element levels in soils and T. cordata flowers, particularly in urban environments, is advisable. Full article

The North China Craton (NCC) experienced extensive destruction and modification of its subcontinental lithospheric mantle during the Mesozoic, a period marked by intensive tectonism, magmatism, and mineralization. Among the key manifestations of this event are the Shizhuzi magmatic complex (SMC) and related Mo-Cu-Au deposits in the Liaodong Peninsula. This study presents new zircon U-Pb ages and Hf isotope data, along with whole-rock major and trace element geochemical data. Meanwhile, by incorporating published datasets, the magmatism and mineralization of the SMC are discussed. Two-stage magmatic activity is identified in the SMC as follows: (1) Stage I (130–126 Ma) associated with mineralization, and (2) Stage II (121–117 Ma), both corresponding to the peak destruction of the NCC. The mineralized granitoids exhibit I-type affinities and formed in an extension setting. Quartz diorites within this suite were derived from the partial melting of an enriched mantle source, and the high-temperature thermal underplating associated with this process subsequently triggered partial melting of the basaltic lower crust, leading to the generation of granodiorites and monzonitic granites. These rocks experienced limited fractional crystallization (dominated by plagioclase + biotite) and are linked to Mo-Cu-Au mineralization. In contrast, the non-mineralized granitoids are high-K calc-alkaline, peraluminous A-type granites, which developed in an extremely extensional tectonic setting. They were derived from partial melting of ancient lower crust and display characteristics of highly fractionated granites, having undergone extensive crystallization differentiation involving plagioclase + K-feldspar during magmatic evolution. The mineralized and non-mineralized granitoids exhibit distinct differences in lithology, major/trace element characteristics, Hf isotopes, and degree of fractional crystallization. Our proposed two-stage magmatic model—coupled with a mineralization phase—provides significant insights into both magmatic processes and metallogenesis in the Liaodong Peninsula. It further offers key perspectives into the Early Cretaceous decratonization of the NCC in terms of its tectonic–magmatic–mineralization evolution. Full article

Spodumene-bearing pegmatites are geochemically anomalous among crystalline rocks and important critical mineral resources in the green energy transition. However, prospecting is challenging due to their small size and the fact that they are often covered by soil and vegetation. This study demonstrates that, rather than being a hindrance, soil cover can enhance geochemical exploration, at least at the prospect scale. This study examines the dispersion pathways of lithium (Li) and its pathfinder elements (Rb, B, Ga, and Sn) from pegmatites (<10 m thick) into metamorphic host rocks and further into overlying undisturbed soils in heavily forested, postglaciated terrain of northeastern Wisconsin, USA. Soil-sample traverses over the world-renowned, lepidolite-type Animikie Red Ace pegmatite and two nearby dikes reveal pronounced <20 m anomalies with up to 1400 ppm of Li, 450 ppm of Rb, 3100 ppm of B, 40 ppm of Ga, and 60 ppm of Sn, greatly exceeding the control soil concentrations from nonmineralized granite and pegmatites. Soils mirror both the magmatic fractionation and alteration of pegmatite bedrock and metasomatic halos in parent host rocks. Metasomatized amphibolite revealed the presence of a holmquistite-ferro-holmquistite mineral. This greenfield pilot exploration led to lithium-rich pegmatite discoveries within the district and demonstrates the applicability of proximal sensors for soil exploration in Wisconsin and beyond. Full article

The Sanandaj–Sirjan Zone and Zagros Fold–Thrust Belt in Iran host numerous Mediterranean-type karst bauxite deposits; however, their formation mechanisms and critical raw material potential remain ambiguous. This study combines mineralogical and geochemical analyses to explore (1) the formation of authigenic minerals, (2) the role of microbial organic processes in Fe cycling, and (3) the assessment of their critical raw materials potential. Mineralogical analyses of the Late Cretaceous Daresard and Middle–Late Permian Yakshawa bauxites reveal distinct horizons reflecting their genetic conditions: Yakshawa exhibits a vertical weathering sequence (clay-rich base → ferruginous oolites → nodular massive bauxite → bleached cap), while Daresard shows karst-controlled profiles (breccia → oolitic-pisolitic ore → deferrified boehmite). Authigenic illite forms via isochemical reactions involving kaolinite and K-feldspar dissolution. Scanning electron microscopy evidence demonstrates illite replacing kaolinite with burial depth enhancing crystallinity. Diaspore forms through both gibbsite transformation and direct precipitation from aluminum-rich solutions under surface conditions in reducing microbial karst environments, typically associated with pyrite, anatase, and fluorocarbonates under neutral–weakly alkaline conditions. Redox-controlled Fe-Al fractionation governs bauxite horizon development: (1) microbial sulfate reduction facilitates Fe³⁺ → Fe²⁺ reduction under anoxic conditions, forming Fe-rich horizons, while (2) oxidative weathering (↑Eh, ↓moisture) promotes Al-hydroxide/clay enrichment in upper profiles, evidenced by progressive total organic carbon depletion (0.57 → 0.08%). This biotic–abiotic coupling ultimately generates stratified, high-grade bauxite. Finally, both the Yakshawa and Daresard karst bauxite ores are enriched in critical raw materials. It is worth noting that the overall enrichment appears to be mostly driven by the processes that led to the formation of the ores and not by the chemical features of the parent rocks. Divergent bauxitization pathways and early diagenetic processes—controlled by paleoclimatic fluctuations, redox shifts, and organic matter decay—govern critical raw material distributions, unlike typical Mediterranean-type deposits where parent rock composition dominates critical raw material partitioning. Full article

Regolith-hosted rare-earth element (REE) deposits are some of the most important types of REE deposits. The relationship between Late Paleozoic and Early Mesozoic granite and regolith-hosted REE deposits is still poorly studied. Detailed geochronology, geochemistry, and rare-earth mineralogy analyses of Early Triassic granite in the South China Block were conducted. The geochronological results showed that four representative granite samples yielded formation ages of 245 ± 1 Ma, 244 ± 1 Ma, 244 ± 1 Ma, and 244 ± 2 Ma, respectively. The granites show geochemical affinity to A-type granite. They are characterized by enrichment in Rb, Th, and U, are depleted in Ba, Sr, P, and Ti, and show obvious negative Nb and Ta anomalies. They have high light rare-earth element (LREE) and low heavy rare-earth element (HREE) contents, with obvious negative Eu anomalies. They were derived from the partial melting of a sediment source and underwent intense fractional crystallization during the magma evolution process. They contain a certain number of rare-earth-element-bearing minerals, such as monazite, xenotime, apatite, and zircon. Their REE compositions and mineral associations are similar to those of the parent rocks from typical regolith-hosted REE deposits in South China. The highly weathered horizon at the ridge of the granite weathering crust profile has the highest REE content. A comprehensive analysis indicated that the degree of magma evolution, geomorphology, and weathering are important factors controlling the formation of regolith-hosted REE deposits in the area. Full article