Rare Earth Element Signatures Research Articles

A distinctive rare earth element signature for pyrite oxidation and glacial weathering

The application of rare earth elements (REE) and neodymium (Nd) isotopes to authigenic Fe-(oxyhydr)oxide phases leached from marine sediments can be used for reconstructing past ocean circulation and chemical weathering patterns on nearby continental landmasses. To explore the behaviour of REE during chemical weathering in glacial environments, we analyzed the authigenic fraction of glacimarine sediments from the continental shelf off northern Svalbard (Arctic Ocean), where the evolution of ice sheet dynamics since the last deglaciation is well constrained. Our results show that leached authigenic fractions in Svalbard sediments exhibit shale-normalized REE patterns characterized by anomalously high mid-REE enrichment relative to both light- and heavy-REE, as expressed by concavity index values (CI > 2.5) that significantly depart from typical REE signatures for leached fractions in marine and river sediments worldwide. Using a compilation of literature data, we provide compelling evidence that the occurrence of pronounced mid-REE enrichment in authigenic fractions of Svalbard marine sediments links to terrestrial oxidation of pyrite following glacial weathering. While future investigation will be required to further understand the detailed mechanism accounting for the observed REE decoupling and its link to pyrite oxidation, we propose that preferential dissolution of MREE-enriched rock-bearing minerals such as apatite following glacial erosion, sulfide weathering and subsequent release of sulfuric acid could release a distinctive REE signature in glacial surface environments. Our findings suggest that the use of authigenic REE in the sedimentary record could provide a means for tracing glacial weathering and associated biogeochemical sulfur and iron cycling across geological times.

Sedimentary environment of basal Ediacaran barite growth on Baltica in E. Finnmark, N. Norway, and subsequent dissolution/reprecipitation

Basal Ediacaran barite, which has mass-anomalous depleted 17O, supporting Snowball Earth models, likely grew in shallow-marine settings, but sedimentological constraints lack details. Environmental conditions in the Varanger Palaeovalley during the basal Ediacaran are well preserved in the Nyborg Formation, where barite forms < 15 mm high synsyn-sedimentary crystal fans on Archean basement or thin intervening sediments. Sedimentary evidence suggests crystal fans formed in low-energy, very shallow-marine to subaerial facies. Rare earth element and yttrium signatures in associated carbonates suggest non-saline growth environments. Post-depositional fluid-flow replaced crystal fan barite with silica (now quartz) and redeposited barite as: <1 × 0.2 mm “dispersed” grains in sediments below fans; <5 mm grains replacing calcite filling desiccation cracks; <1 mm grains in basement fissures; <3 µm grains replacing matrix calcite; irregular grains in detrital sheet-silicate + calcite grains. Caledonian dissolution-reprecipitation reworked barite into brittle fractures and stylolites. Barite Δ17O values are amongst the most negative (-0.9 – -1.25 ‰) and δ18O values the lowest recorded (9.9 – 16.9 ‰) anywhere, consistent with a high latitude Baltica at ∼ 635 Ma. δ34S values (17.7 – 24.5 ‰) lie within the known range for basal Ediacaran barite.

Quantifying provincial in-use stocks of rare earth to identify urban mining potentials in the Chinese mainland

Recycling of rare earth elements (REE) can help to offset the increasing demand for REE minerals and enhance the diversification of the REE supply chain. The development of low-carbon technologies, such as new energy vehicles and wind turbines has expedited the accumulation of REE as “urban mines”. This trend offers prospects for the progress of REE recycling initiatives targeting end-of-life products. This study conducts a dynamic material flow analysis (combined top-down and bottom-up method) of nine products containing NdFeB permanent magnets (their scrap is regarded as the most important secondary resource of rare earth) in the Chinese mainland at a provincial level to identify end-of-life products and provinces with high urban mining potentials. Results indicate that e-bikes, wind turbines, and air conditioners have the most significant REE recycling potentials in the Chinese mainland. Provinces with large populations and robust economies, such as Guangdong and Jiangsu, exhibit greater potential for REE recycling. This study illustrates significant provincial disparities in the end-of-life recycling potentials of REEs in the Chinese mainland and highlights the significance of provincial-level assessments of urban mining potential in the planning of the REE recycling industry.

Microbially induced fabrics in the Upper Ediacaran coated grain dolostone, Northeast Sichuan Basin, SW China: Implications for reconstruction of the paleoceanic environment

In the Upper Ediacaran Dengying Formation of the Sichuan Basin, the presence of abundant, well-preserved microbial carbonates provides a unique opportunity to study Precambrian paleoceanography and microbial carbonate origins. Particularly, the underexplored coated grain dolostones of this formation, characterized by distinct microbially induced fabrics and intragranular dissolution, offer crucial insights for understanding late Ediacaran microbial mineralization and diagenetic sequences. Utilizing selected typical samples, we conducted detailed petrographic and geochemical analyses, revealing a dynamic interplay between microbial processes and sedimentary dynamics. We observe the coexistence of constructive micrite envelopes with microbially induced fabrics such as clots and laminations, highlighting microbial biomineralization's key role in fabric formation. The sedimentary dynamics critically determines the formation processes of the coated grains: low-energy settings foster grain agglomeration and consolidation through clot precipitation between grains, while high-energy settings favor smaller grains binding to microbial mats. Geochemically, micrite envelopes play an essential role in preserving distinct rare earth element (REE) signatures. The weak negative Ce anomalies and positive Eu anomalies within these envelopes point to a suboxic to anoxic depositional environment, directly indicative of the microenvironmental conditions conducive to microbial mineralization processes. Furthermore, our study sheds light on the structural evolution of coated grains with hollow nuclei, proposing that their internal pore formations are influenced by both mineral instability and selective dissolution by meteoric freshwater. These findings not only provide fresh insights into complex diagenetic processes in the Dengying Formation but also substantially advance our understanding of early microbial life and environmental adaptations during the Precambrian.

Retentiveness of rare earth elements in garnet with implications for garnet Lu‐Hf chronology

AbstractIncorporation of rare earth elements (REE) in garnet enables garnet chronology (Sm‐Nd, Lu‐Hf), and imparts a garnet‐stable signature on cogenetic phases, which allows petrochronology and general petrogenetic tracing of garnet stability in minerals and melts. Constraints on the uptake and redistribution mechanisms, as well as on the diffusive behaviour of REE in garnet are required for allowing accurate interpretation of REE signatures and ages. Garnet REE profiles are often measured to gain insight into the nature and cause of REE zoning. Interpretation of such profiles is nevertheless complicated by poor constraints on the extent of diffusive relaxation. This is especially relevant for Lu, which, according to experiments, has a relatively high diffusivity and thus may re‐equilibrate with possible consequences for Lu‐Hf chronology. To provide new insight into the REE systematics of garnet, we applied quantitative trace‐element mapping of garnet grains from metamorphic rocks that record peak temperatures above 750°C and cooling rates as low as 1.5°C Ma−1. Garnet in all samples preserves Rayleigh‐type or oscillatory growth zoning with sharply defined interfacial angles that match the garnet habit. Re‐equilibration of REE compositions appears restricted to domains with nebulous and patchy zoning, which likely form by interface‐coupled dissolution and re‐precipitation reactions mediated by fluids or melts, rather than REE volume diffusion. The possible effect of Lu diffusion in the analysed grains was investigated by comparing the observations to the results from 2D numerical modelling using Lu diffusivities from recent diffusion experiments. This test indicates that Lu diffuses significantly slower in natural garnet than experiments predict. The retentiveness of REE in garnet demonstrates the reliability of REE signatures in magmatic tracing and petrochronology and establishes Lu‐Hf chronology as a robust means of dating garnet growth and recrystallization in metamorphic rocks, including those that underwent high‐ or ultrahigh‐temperature conditions.

Hyper-enrichment of heavy rare earth element in highly evolved granites through multiple hydrothermal mobilization

Abstract Highly evolved granites can be important hosts of rare earth element (REE) resources, and more importantly, they commonly serve as the protolith for regolith-hosted REE deposits to form during weathering. Highly evolved granites in the Zudong pluton, South China are extremely rich in the HREE (up to 8,000 ppm total HREE) and display significant REE fractionation. Moreover, the HREE enrichment is positively correlated with the degree of REE fractionation, indicating a unique process in preferentially enriching the HREE during the evolution of the granites. Multiple stages of hydrothermal re-mobilization of the REE can account for the HREE mineralization and these are recorded in the texture and composition of the zircon. In these processes, fluctuations in the F activity of the fluid caused alternating dissolution-reprecipitation and continuous growth of the zircon. REE were repeatedly mobilized and enriched in the fluid to precipitate the major HREE mineral synchysite-(Y), and partially incorporated into the growth zone of zircon while other elements were largely lost to the fluid during extensive dissolution of the rock-forming minerals. LREE were also likely substantially mobilized in the late hydrothermal stage and lost through complexation with Cl, causing the significant LREE depletion and thus REE fractionation. This process continuously enriched host granites in the HREE to a potentially economic grade, making them favorable protoliths for subsequent supergene regolith-hosted HREE deposits.

In the pursuit of raw materials independence. A comparative analysis of Donald Trump and Joe Biden policies towards rare earth elements

The main aim of the presented article is to find similarities and differences in the approach to the strategic role of rare earth elements during the presidencies of Donald Trump and Joe Biden in the United States of America. Rare earth elements are the core instruments of modern technological development in many areas and fields – both civil and military. Due to their growing importance, they have been the object of political rivalry between the People’s Republic of China and the United States of America for at least twenty years. The increasing global demand for rare earth elements and their strategic importance in various industries has highlighted the issue of the approach of political leaders to these critical minerals, espiecialy when it comes to ensuring secure and sustainable supply chain. The research problem of the considerations undertaken in this article is to assess implications and effectiveness of Donald Trump and Joe Biden Policies towards rare earth elements. The research shows that while both administrations recognized the significance of rare earth elements, their approaches differed in terms of priorities, strategies, and emphasis on environmental sustainability.

Depositional condition of Paleoproterozoic Francevillian carbonate rocks revisited from rare earth element contents

The Paleoproterozoic Francevillian Group in the eastern Gabonese Republic has been recently attracting increasing attention because it includes distinctive macroscopic structures interpreted as eukaryotic fossils. Therefore, its depositional setting and associated redox conditions need to be clearly understood. To clarify these, petrological studies and rare earth element (REE) abundances of carbonate rocks of the Francevillian Group in the Lastoursville basin were determined with ICP-MS coupled with a laser ablation sampling technique. Detailed microscopic observations indicate that dolostones in this basin underwent the complicated diagenetic history, including sparitization, decomposition of organic matter, reduction of ferromanganese oxides, silicification, and later calcification. The dolostones of lower Francevillian B (FB) Formation show heterogeneous textures formed by alterations during diagenesis. By the alterations, changes of REE abundances and degrees of positive Y anomalies appear to have occurred. This indicates that REE signatures in carbonate rocks can vary during diagenesis. Characteristically high Mn contents in the dolostones of upper FB Formation were derived from the reduction of ferromanganese oxides in sediments. The signatures of REE abundance in dolostones can be explained by the mixing of seawater and ferromanganese oxide components. In that sense, the dolostones inherited the trace element characteristics of precursor ferromanganese oxides even after the diagenesis. Y/Ho values of the most primary parts of each sample exceed 33, the newly determined threshold value for marine carbonate rocks based on our compilation. The magnitude of the La anomaly values also falls within the range of that of Holocene reefal microbialites. These indicate that a precursor of the dolostone of the Francevillian Group was deposited in a marine environment. In addition, presence of Ce anomalies in the upper FB Formation suggests that the Paleoproterozoic ocean was oxidized to such an extent as for Ce to be preferentially absorbed by ferromanganese oxides.

Towards deciphering the source of rare earth elements in kerogen: Seawater or diagenetic porewater origin?

The composition of rare earth elements (REEs) in kerogen has long been hypothesized to preserve signatures of shallow seawater, assuming that kerogen primarily originates from biomass inhabiting the shallow photic zone. In this study, we examine the composition of REEs in kerogen samples obtained from the Ediacaran Dongkanshang and Fengtan sections in South China. Through a meticulous screening process, we provide evidence that kerogen samples exhibiting patterns of heavy rare earth element (HREE) enrichment are free from acid-insoluble mineral contamination and preserve unaltered REE signatures. This study reveals that kerogens display low total rare earth element (ΣREE) concentrations. As kerogen samples exhibit higher levels of HREE enrichment, the Ce/Ce*, Eu/Eu*, and Y/Ho ratios show an upward trend. Moreover, all the kerogen samples exhibit chondritic Y/Ho ratios (with an average of 32). These findings imply that REEs in kerogens are of diagenetic origin and influenced by the ambient redox conditions. Our results suggest that the distribution patterns of REEs in kerogens derive from porewater within methanogenic zones, as opposed to the oxic seawater photic zone. Consequently, the formation of kerogen could potentially occur within a similar domain as the methanogenic zones, where kerogens can assimilate REEs from pore fluids and incorporate them into their macromolecular structures.

Geological Significance of Rare Earth Elements in Marine Shale of the Upper Permian Dalong Formation in the Lower Yangtze Region, South China

The rare earth elements (REEs) provide significant geological information and serve as a reliable indicator for predicting the paleoclimate, paleoenvironment, and paleotectonic evolution of sedimentary rocks. The REEs, major elements, and trace elements of 75 marine shale samples collected from the Late Permian Dalong Formation at the Fantiansi (FTS) and Putaoling (PTL) sections in the Lower Yangtze region were analyzed. The results revealed that the major elements Al2O3, K2O, and TiO2 were primarily influenced by clay minerals associated with terrigenous detrital, whereas SiO2 and Na2O were not affected by clay minerals. The ΣREE values obtained from the Late Permian Dalong Formation at the Fantiansi (FTS) and Putaoling (PTL) sections in the Lower Yangtze region were found to be lower than those of the Post-Archean Average Shale (PAAS) (184.8 μg/g). The study of REE indicators related to the source, redox conditions, and tectonic settings led to the following conclusions: (a) ΣREE showed strong positive correlations with TiO2, Al2O3, K2O, and Na2O, but exhibited relatively weak correlations with Fe2O3 and P2O5, suggesting that REEs were mainly associated with clay minerals, but were also influenced by pyrite, phosphates, and other minerals; (b) The high values of Ce/Ce*, MoEF, UEF, and Corg/P were mainly concentrated in Stages I, II, III and V of the Dalong Formation at the FTS and PTL sections, and the corresponding strong anoxic environment was more conducive to the preservation of organic matter; (c) The diagram between La/Yb and ΣREE, Al2O3-TiO2, TiO2-Zr, and La/Th-Hf bivariate diagrams indicated that the provenance of the rocks from the Dalong formations was primarily felsic igneous rocks; (d) Discriminant-function diagrams and La-Th-Sc, Th-Sc-Zr/10 and Th-Co-Zr/10 triangular diagrams show that the clastic sediments of the Dalong formations were derived most likely from continental island arcs. This study corresponds to the background of the transition from continental margin to continental collision structure in South China during the Late Permian.

ASSESSMENT OF TRACE AND RARE EARTH ELEMENT DISTRIBUTION AND SPECIATION IN BAUXITE DEPOSITS ACROSS EKITI AND ONDO STATES, NIGERIA

The growing significance of rare earth elements (REEs) in advanced electronic technologies and the nuclear industry, coupled with concerns about geopolitical dynamics and supply market vulnerabilities, has reignited global interest in securing domestic and economically viable sources of REEs through dedicated research and developmental pursuits. Bauxite, a naturally occurring mineral primarily composed of aluminum, has been identified to harbor an abundance of sought-after rare earth minerals, thereby rendering it a promising unconventional reservoir of REEs contingent upon geological and mineralogical characteristics. Nigeria, endowed with substantial bauxite deposits prominently situated in Ondo and Ekiti states, stands to offer an intriguing avenue for exploration. In this study, the utilization of inductively coupled plasma mass spectrometry (ICP-MS) facilitated the quantification of trace elements within samples obtained from six distinct production sites spanning Ondo and Ekiti states in Nigeria. The aim was to elucidate correlations between multi-elemental REE compositions and geographical origins. Employing both single quadrupole (SQ) and multi-collection sector field (MS) modes, concentrations of Pb, Cd, As, Zn, Mn, Al, Ca, Ni, K, Na, Mg, Cu, Fe, Ti, P, Cr, and Si were rigorously determined. Remarkably, ICP-MS analysis consistently revealed a palladium (Pd) concentration of 228.05 ppb across all sampled materials, factoring in a dilution factor of 175x. Consequently, the actual concentration of the digested solution was established at 39.91 ppm mg/L. The outcomes of this investigation hold potential significance in categorizing Nigerian bauxite deposits as viable REE sources, as well as in engineering tailored techniques to efficiently recover these elements. Such findings harbor promising economic prospects for the nation, positioning the solid mineral sector as a pivotal driver of Nigeria's burgeoning economy.

Bioconcentration and translocation of rare earth elements in plants collected from three legacy mine sites in Portugal

Rare earth elements (REE), a group of emerging contaminants with commercial and technological applications, share many physical and chemical characteristics and have thus been used as accurate tracers of various environmental samples. They have been shown to increase in receiving waters following the dissolution of host-rock material during mining activities. In this study, spontaneous vegetation and related media were collected from three Portuguese legacy mine sites in November 2020 to evaluate the phytoavailability and fate of REE. Water, soil and plant data were analyzed in the context of the 1) prevailing geochemical context, 2) the mining context, and 3) plant effects. This study presents the REE signatures for different plant species and links the signatures to a potential source of bioavailable REE. The REE accumulated in plant tissue seems to reflect the REE signature of surface waters in the mining areas, showing enrichment in middle REE. Although the soils, sediments, and waters in this study had similar features, certain plants seemed better adapted to translocating Light REE and Eu over others. Given that REE are readily available within the field conditions of a mining site, this study shows how plant physiology and biologic preference towards particular REE contribute to the fractionation of REE and create a unique signature dependent on plant type.

Rare earth element signatures of Paleoproterozoic Sallopat phosphorites of Aravalli Basin, India: implications for diagenetic effects and depositional environment

Rare earth element signatures of Paleoproterozoic Sallopat phosphorites of Aravalli Basin, India: implications for diagenetic effects and depositional environment

Rare earth element bioaccumulation and cerium anomalies in biota from the Eastern Canadian subarctic (Nunavik)

Recent increases in the demand for rare earth elements (REE) have contributed to various countries' interest in exploration of their REE deposits, including within Canada. Current limited knowledge of REE distribution in undisturbed subarctic environments and their bioaccumulation within northern species is addressed through a collaborative community-based environmental monitoring program in Nunavik (Quebec, Canada). This study provides background REE values (lanthanides + yttrium) and investigates REE anomalies (i.e., deviations from standard pattern) across terrestrial, freshwater, and marine ecosystems in an area where a REE mining project is in development. Results are characteristic of a biodilution of REE, with the highest mean total REE concentrations (ΣREE) reported in sediments (102 nmol/g) and low trophic level organisms (i.e., biofilm, macroalgae, macroinvertebrates, common mussels, and reindeer lichens; 101–102 nmol/g), and the lowest mean concentrations in higher-level consumers (i.e., goose, ptarmigan, char, whitefish, cod, sculpin and seal; 10−2 - 101 nmol/g). The animal tissues are of importance to northern villages and analyses demonstrate a species-specific bioaccumulation of REE, with mean concentrations up to 40 times greater in liver compared to muscle, with bones and kidneys presenting intermediate concentrations and the lowest in blubber. Further, a tissue-specific fractionation was presented, with significant light REE (LREE) enrichment compared to heavy REE (HREE) in consumer livers (LREE/HREE ≅ 101) and the most pronounced negative cerium (Ce) anomalies (<0.80) in liver and bones of fish species. These fractionation patterns, along with novel negative relationships presented between fish size (length, mass) and Ce anomalies suggest metabolic, ecological, and/or environmental influences on REE bioaccumulation and distribution within biota. Background concentration data will be useful in the establishment of REE guidelines; and the trends discussed support the use of Ce anomalies as biomarkers for REE processing in animal species, which requires further investigation to better understand their controlling factors.

Distribution, mode of occurrence, and significance of rare-earth elements in coal from Samaleswari open cast coal blocks, Odisha, India with their provenance and paleodepositional environment

Distribution, mode of occurrence, and significance of rare-earth elements in coal from Samaleswari open cast coal blocks, Odisha, India with their provenance and paleodepositional environment

Seafloor hydrothermal circulation at a rifted margin of the South China Sea: Insights from basement epidote veins in IODP Hole U1502B

To better understand the seafloor hydrothermal circulation at the passive rifted margins, we present a detailed geochemical investigation of epidote veins in eight altered basalts from IODP Hole U1502B, which is located in the continental-oceanic transition zone at the northern margin of South China Sea (SCS). The studied epidotes have XFe values [XFe = Fe3+/ (Fe3+ + Al3+)] of 0.21 to 0.37, suggesting Fe-rich epidote in composition and equilibration in lower greenschist facies. The occurrence of cataclastic and zoning structures in the epidotes suggests variations in mineral growth environment. Combined rare earth element and Sr-isotope signatures of these epidotes revealed the involvement of three types of circulating fluids, i.e., modified seawater (negative Ce anomaly, and 87Sr/86Sr = ∼0.708), hydrothermal fluid (positive Eu anomaly, and 87Sr/86Sr = ∼0.706), and magmatic fluid (negative Eu anomaly, and 87Sr/86Sr = ∼0.704). These observations suggest that basement epidote veins in Hole U1502B were likely formed under a tectonically active and open environment, with the growth process and compositions of epidotes varying during the evolution of circulating fluids. A new seafloor hydrothermal circulation model is envisaged at Hole U1502B, in which an intrusive dike instead of a magma chamber supplied the heat source, and the extensional faults formed during continental breakup to seafloor spreading provided the channel of upwelling circulating fluids. The low heat flux of intrusive dikes caused the shallow occurrence depth of basement epidote veins, which were formed in the discharge zone of the hydrothermal system. Our study provides new mineral chemistry constraints on the hydrothermal process and environment at the passive rifted margin of SCS, which is different from those suggested for a typical fast-spreading mid-ocean ridge.

Petrogenesis and Geochronology of A1-Type Rhyolites in the Late Late Triassic of the East Kunlun Orogenic Belt: Constraints on the End of the Paleo-Tethys Orogenic Event

The rhyolites which are widely exposed to the northern margin of the East Kunlun orogenic belt were chosen as a research object to discern the post-orogenic tectonic evolution of the East Kunlun orogenic belt and reconstruct the post-collision orogenic processes of the Buqingshan- A’nyemaqen Ocean. We researched zircon U-Pb ages and geochemistry characteristics of the Late Triassic rhyolites in the eastern segment of the East Kunlun Orogenic Belt in the northern Tibetan Plateau. Zircon U-Pb dating yields coeval ages of 200.4 ± 1.4 Ma and 202.8 ± 1.2 Ma for the Keri rhyolites of the East Kunlun Orogenic Belt, indicating that the volcanic rocks were formed in the Late Triassic Rhaetian–Early Jurassic Hettangian. The Keri rhyolite is a product of the late magmatism of the Elashan Formation volcanic rocks. The rhyolites include rhyolitic brecciated tuff lavas and rhyolitic tuff lavas. The rhyolites are peraluminous and are high-K calc-alkaline, with high contents of SiO2, K2O, TFe2O3, and low P2O5 contents. The A/CNK ratios range from 0.97 to 1.09, indicating that the rhyolites are metaluminous to weakly peraluminous. The chondrite-normalized rare earth element (REE) distribution shows a significant negative Eu anomaly and low total REE concentrations. All samples are depleted in high field strength elements (HFSEs, e.g., Eu, Sr, Ti, and P), heavy rare earth elements (HREEs), and enriched in large ion lithophile elements (LILEs, e.g., Rb, Zr, Nd, Th, and U) and light rare earth elements (LREEs). The Keri rhyolite has the characteristics of A1-type magmatic rock, formed in an anorogenic environment after the closure of the Paleo-Tethys Ocean, and was the product of late magmatism in the Elashan Formation volcanic rocks.

Geochemical processes and indicative significance of rare earth elements in high arsenic geothermal fluids in Batang, western Sichuan, China

Geothermal resource development and utilization is one of the major energy issue worldwide. Many researches have been carried out about the geochemical characteristics and geological characteristics of high arsenic(As) geothermal fluids, but the content of rare earth elements(REEs) in high As geothermal fluids, there are still some questions that deserve to be discussed. For example, the content, fractionation characteristics, geochemical processes and indication of REEs in high As geothermal fluids are not well understood, which limits further research on chemical characteristics such as enrichment of REEs in geothermal fluids. In this study, based on field tests and laboratory analysis in the Batang area of western Sichuan, it was found that the overall content of REEs in high As geothermal fluids in the study area was low. After normalized the REEs in geothermal fluids with chondrite, it was found that the geothermal fluids were enriched in light REEs and depleted in heavy REEs. Meanwhile, the cold water mixing, pH, TDS, temperature and HCO3− concentration of the geothermal fluid extremely affect of ree partitioning on the rare earth element partitioning characteristics of the geothermal fluid, and both Ce and Eu show positive anomalies in the normalized model of REEs of the geothermal fluid. It is worth noting that the As concentration in the geothermal fluid gradually decreases as the Eu/Eu* value increases, and the As concentration in the geothermal fluid is more enriched when the Ce/Ce* value is in the range of 2–3. And it was found that the changes in pH, TDS, temperature, HCO3−, and redox environment in the geothermal fluid due to 67%∼79% cold water mixingunder the condition of the large cold water mixing ratio had a large impact on the fractionation characteristics of REEs. Therefore, the characteristic changes of Ce and Eu in a reduced geothermal fluid system may be indicative of As enrichment in geothermal fluids.

Rare earth element signature modifications induced by differential acid alteration of rocks in the Iberian Pyrite Belt

The efficient use of REE as tracers of weathering processes requires further data acquisition to establish robust connections between mechanisms, mineral assemblages and REE concentration patterns. Here, results are provided corresponding to rocks from four locations in the Iberian Pyrite Belt that were altered with different intensity by sulfuric fluids. The acidic alteration was mild (pH 5–7) in Calañas and El Villar, while strong (pH below 3 to 5) in Quebrantahuesos and Tharsis. The main REE reservoir before alteration were phyllosilicates (and plagioclase/feldspar in El Villar only). Mild alteration generated mainly kaolinite while illite and some plagioclase/feldspar were preserved. Mildly altered rocks approximately preserved the relative REE concentrations of their precursors, interpreted as indicating a low fluid/rock ratio environment where binding sites in minerals outnumbered those in fluids. Strong acid alteration produced alunite, jarosite, beudantite and goethite, with partial illite preservation. Where illite and/or goethite were major minerals, this alteration generated REE patterns enriched in light REE over heavy REE or did not modify the relative REE concentrations of the original rock. However, samples where REE concentrations were controlled by alunite or jarosite had LREE > > HREE. In alunite the maximum concentration corresponded to Nd and Sm. In jarosite concentrations decreased from La to Lu, except that a positive Eu anomaly was preserved from the precursor. These REE concentration patterns are interpreted as due to crystallographic factors, controlled by the best fit of REE with charge 3+ in the 12-fold coordination site of K in jarosite and alunite. This site is larger in jarosite and fits La best, whereas the smaller site in alunite best fits Nd and Sm. Goethite REE signature is variable, perhaps due to two formation routes, (1) silicates ➔ goethite and (2) silicates ➔ jarosite ➔ goethite. Our interpretations of REE concentration in alunite, jarosite and goethite are novel and provide new routes to further develop REE as tracers of acid alteration processes.

Mesoarchean banded iron-formation from the northern Yangtze Craton, South China and its geological and paleoenvironmental implications

Banded iron formations (BIFs) are important sedimentary rocks used for reconstructing the geochemical and environmental evolution of Precambrian Earth surface conditions. Here, we describe the oldest BIFs of Mesoarchean age in the Yemadong Formation, and their implications for paleo-environmental evolution of the Mesoarchean Ocean in the northern Yangtze Craton, South China. U-Pb dating of metamorphic zircons obtained from metavolcanic rocks interbedded within the Yemadong Complex, record two major tecto-thermal events at 2901 ± 8 Ma, in agreement with a Mesoarchean origin of the Dujiagou BIFs, and as recently as 775 Ma. A high SiO2 + total Fe2O3 content of 90.95–94.62 wt%, moderate 0.54–1.42 wt% Al2O3 + TiO2, and broadly elevated levels of incompatible elements, point to a predominantly chemical origin of the BIF deposit, with a minor but influential terrigenous input. Rare Earth Element (REE) plus Yttrium patterns normalized against Post Archean Average Shale composition are characterized by the depletion of light REE relative to heavy REE. However, extremely weak Eu and Ce anomalies, together with low average chondrite Y/Ho ratios compared to average Mesoarchean BIF values, indicate that the primary REE composition of the rocks may have been diluted to some extent by terrigenous input, pointing to proximity or connection of the depositional setting to a continental margin environment. Despite potential terrigenous dilution of the syngenetic seawater-hydrothermal chemical composition, the preservation of an inherited hydrothermal REE signal in some samples, point to submarine hydrothermal provenance of the Dujiagou BIFs, as is the case for most Precambrian BIFs. Positive δ56Fe values, ranging from 0.25 to 0.45 ‰, characteristic of primary Archean BIFs, suggest partial oxidation of reduced Fe(II) to divalent (Fe(II)/Fe(III)) magnetite-rich BIFs in a broadly reducing Archean Ocean lacking a persistent and pervasive redoxcline before the rise of atmospheric oxygen.