Shale-normalized Rare Earth Element Research Articles

Anthropogenic gadolinium in the Tone River (Japan): an update showing a 7.7-fold increase from 1996 to 2020

BackgroundAnthropogenic gadolinium (Gd), originating from Gd-based contrast agents (GBCAs) used in magnetic resonance imaging (MRI), is widely identified in the aquatic environment with concerns about toxicity and accumulation. We aimed to present new data on anthropogenic Gd in the Tone River, which has the largest drainage area in Japan, and then to compare the current data with those obtained in 1996.MethodsThe water samples were collected on August 9−10, 2020, at 15 different locations of the Tone River in Japan. The concentrations of the rare earth elements (REEs) were measured by inductively coupled plasma-mass spectrometry and normalized to Post-Archean Australian Shale to construct shale-normalized REE patterns. The degree of Gd-anomaly was defined as the percentage of anthropogenic Gd to the geogenic background and used to compare the water samples from different locations. Pearson’s correlation coefficients were calculated.ResultsAll the samples displayed positive Gd anomalies. The Gd-anomaly ranged from 121 to 6,545% and displayed a repeating decrease-and-increase trend. The Gd-anomaly showed strong positive correlations to the number of hospitals (r = 0.88; p < 0.001) and their MRI units (r = 0.89; p < 0.001).ConclusionsOur study revealed notable anomalies of Gd concentrations in river water in Japan, with strong positive correlations to the number of major hospitals and their MRI units. Compared with the previous report in 2000, the Gd-anomaly in Tone River increased from 851% (sampled in 1996) to 6,545%, i.e., 7.7 times, reflecting the increased use of GBCAs in hospitals.Relevance statementNotable Gd concentration anomalies in river water in Japan were observed. This result underlines the importance of more extensive research on anthropogenic gadolinium, and investigations of risks to human health as well as the development of effective removal technologies may be necessary.Key points• All water samples from Tone River displayed positive Gd anomalies.• The Gd anomalies increased to 7.7 times higher over the past 24 years.• Correlations between Gd values and the number of hospitals and MRI units were observed.Graphical

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 mid-REE-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.

Surface water oxygenation and low bioproductivity during deposition of iron formation of the Jacadigo Group (Brazil): Insights from combined cadmium – Chromium isotopes

The Banda Alta Formation (Urucum district, Mato Grosso do Sul, Brazil) comprises ∼600 Ma Fe and Mn deposits, which are among the world's youngest and largest Neoproterozoic sedimentary Fe and Mn formations (IF; MnF). These have been deposited in a redox-stratified, marine sub-basin (Jacadigo Basin), which was strongly influenced by glacial advance/retraction cycles with temporary influx of continental freshwater and upwelling of metal-enriched deep anoxic seawater. Cr and Cd isotopes measured on meticulously separated hematite mesobands from drill core samples are relatively homogenous throughout the ca. 325 m thick sequence sampled in the Banda Alta Fm., with average authigenic δ53Cr values of +0.93 ± 0.24 ‰ (2σ; n = 23) and δ114Cd values of −0.14 ± 0.14 ‰ (2σ; n = 15). The significant enrichment of Cr, in parallel with the strong enrichments of other redox sensitive elements (U, Mo), attests for effective and efficient reduction removal processes in the surface waters during cycles where upwelling Fe2+-rich waters reached the oxygenated surface layer exposed to the atmosphere during episodic glacier retreat stages. Assuming a similar quantitative and efficient removal pathway of dissolved Cd by iron oxyhydroxides, the so-inferred average δ114Cd signature of −0.14 ± 0.14 ‰ in the Jacadigo Basin surface water is significantly lower than signatures of modern ocean surface waters with a range of δ114Cd of ca. ∼0.4 to ∼1 ‰ and even lower than the signature of modern ocean deep waters with δ114Cd of ∼0.3 ‰. It possibly attests to reduced primary production levels and lower nutrient utilization rates during deposition of the Late Neoproterozoic Jacadigo Group, compared to today. This despite the inferred oxidized surface water layer that must have prevailed during this time, as implied by the strongly positively fractionated Cr isotope signatures and pronouncedly negative Ce-anomalies recorded in the seawater-like, shale-normalized Rare Earth Element and Yttrium (REY) patterns exhibited by the hematite mesobands. Data presented herein speak for: (1) a stable, isotopically heavy Cr input to the Jacadigo Basin at the time of deposition, implying high atmospheric O2 levels in the Late Neoproterozoic (2) likely quantitative, reductive incorporation / adsorption processes of dissolved Cr and Cd, respectively, into/onto precipitating iron oxyhydroxides, and (3) the prevalence of low nutrient concentrations and utilization rates in the Jacadigo Basin during glacier retreat cycles. Banded iron formations are considered suitable archives for reconstructing redox and bioproductivity levels in past marine depositional basin, including those prevalent in Neoproterozoic glacial conditions, via employing the CrCd isotope double tracer to iron-rich mesobands.

Geochemistry and U-Pb zircon geochronology of the Nkout banded iron formations and associated metasiliciclastic rocks, NW Congo craton, southern Cameroon

ABSTRACT The Nkout banded iron formations (BIFs)-hosted iron deposit is located in the Ntem Complex at the northwestern part of the Congo craton, southern Cameroon. We report geochronological and geochemical data of magnetite BIFs and interlayered mica schists from the Nkout iron ore deposit. The BIFs show typical features of chemical precipitates characterized by seawater-like shale-normalized rare earth elements plus yttrium spectra. Weak positive Eu anomalies indicate the contribution of high-temperature hydrothermal fluids to the BIFs, with low detrital input. The absence of true Ce anomalies indicates that the BIFs were likely to be deposited in anoxic seawater. LA-ICP-MS U-Pb detrital zircon data for the BIFs and associated metasiliciclasltic rocks constrained the maximum depositional age at ca. 2.8 Ga, suggesting that the Nkout BIFs are likely the oldest iron formations in the Ntem Complex. Our zircon U-Pb isotope data indicate that the Nkout succession experienced lower-amphibolite facies metamorphism at ca. 2.0 Ga, which correlates with the regional tectono-thermal event linked to the convergence and assembly of terranes between the Congo and São Francisco cratons during the Eburnean-Transamazonian orogeny.

The role of depositional environment and chemical composition on the triple oxygen isotope ratios of ferromanganese precipitates and their endmember components

Ferromanganese precipitates - crusts, nodules, and hydrothermal deposits – typically exhibit negative Δ'17O values. These deviations are thought to reflect partial incorporation of dissolved atmospheric O2, a component with strongly negative Δ'17O values, seawater oxygen, and deep sea O2 into Mn-oxide minerals, in combination with the other major mineralogical endmember components (Fe-oxyhydroxide and silicate minerals), and kinetic processes such as oxidation at mineral surfaces and biological respiration. Our understanding of the triple oxygen isotope systematics of these materials are limited, however; in the current body of literature, triple oxygen isotope data has only been generated for marine hydrogenetic (i.e., metals accrete directly from seawater) Fe-Mn crusts and Mn nodules. This study evaluates the underlying chemical and environmental factors contributing to the bulk triple oxygen isotopic composition of Fe-Mn precipitates of different genetic types (i.e., hydrothermal, hydrogenetic, mixed-type) from a variety of formation environments (e.g., volcanic arc, pull-apart basin, hotspot, freshwater lake). To improve our understanding of the triple oxygen isotope systematics of natural Fe-Mn precipitates and better constrain the endmember components, we isolate and measure close approximations of the Mn-oxide, Fe-oxyhydroxide, and silicate fractions. Hydrothermal Fe-Mn deposits show greater variation in δ'18O and Δ'17O values (6.0 to 29.6 ‰ and −0.286 to 0.007 ‰, respectively) than hydrogenetic Fe-Mn crusts (5.1 to 11.9 ‰ and −0.200 to −0.086 ‰, respectively). Lacustrine Mn nodule δ'18O and Δ'17O values (5.1 to 8.8 ‰ and −0.230 to −0.090 ‰, respectively) are similar to marine hydrogenetic Fe-Mn crusts, primarily reflecting tropospheric O2. The triple oxygen isotope ratios of nearly pure Mn-oxide samples cluster into distinct groups based on oxygen source, and mass-balance mixing models suggest a significant proportion of incorporated oxygen was photosynthetic in origin. The layered Fe-Mn precipitates in this study show irregular to rhythmic patterns of δ'18O and Δ'17O values depending on formation environment that mostly do not correlate with Mn, Fe, and Si contents. Shale-normalized rare earth element and yttrium (REYSN) patterns and anomalies (CeSN/CeSN*, EuSN/EuSN*, and YSN/HoSN), which can provide insight on formation conditions (e.g., redox, oxygen fugacity, and REY speciation of fluids), are compared with the triple oxygen isotope data. The REYSN anomalies increase from the bottom to the top of the profile of the layered marine sample, suggesting conditions became more oxic over time. Although the triple oxygen isotope ratios correlate with the Eu anomaly in most Fe-Mn precipitates, hydrothermal input can limit their utility as indicators of oxygen fugacity. The triple oxygen isotope ratios of Fe-Mn precipitates reflect complex processes and mixing of multiple sources. Constraining these oxygen sources will assist future studies in interpreting paleoenvironmental conditions (e.g., the saturation state and triple oxygen isotope ratios of dissolved O2 in bottom water) at the time of Fe-Mn precipitate formation.

The use of rare earth element profiles as a proxy for a fractionation source and mine-waste provenance

Rare earth elements (REEs) have been determined in acid mine drainage samples from the Wiśniówka area, south-central Poland. Two benchmark acid pit ponds, i.e., Podwiśniówka (PwIIb) and Wiśniówka Duża (WD), have shown diverse contents of sulfates, phosphates, REEs and metal(loid)s. Moreover, these ponds exhibit different NASC-normalized REE concentration patterns: (i) a positive middle REE anomaly in PwIIb and (ii) a positive heavy REE anomaly in WD, regardless of sampling time. This MREE anomaly has also been highlighted in a small tailings pile pool showing high contents of metal(loid)s, including As (3.86 g/L) and REEs (90.1 mg/L). In contrast, the light REE (LaEu)-rich profiles are recorded in all Upper Cambrian rock series of the study area. However, the Pw geologic section is distinctly enriched in pyrite, goethite/hematite and carbonaceous clayey-silty shales compared to its WD counterpart that contains a lesser amount of these components, but many more quartzite/sandstone beds. The Pw mineral-lithologic pattern favors selective partitioning of heavy REEs to abundant Fe- and Al-oxyhydroxides and organic matter. Both very short solute transport from sheer rock faces to pit ponds and a low pH of acid waters (mean of 2.3 to 3.0) indicate that scavenging/adsorption and mineral co-precipitation of REEs in a water column may be negligible. This inference is also backed up by overlapping REE profiles at different depths of acid pit ponds. Taken together, this implies that preferential fractionation of REEs takes place primarily during on-site weathering of pyrite and REE-bearing minerals in different rock media thus leading to changes in the Pw- and WD shale-normalized REE concentration patterns at source. The characteristic Pw roof-shaped (convex-up) profile in water samples has been used as a proxy for tracing the most detrimental Podwiśniówka As-bearing mine-waste that were scattered within the mining area a couple of years ago.

Genesis of the Longwanggou iron deposit in the Yudongzi Complex, South China: Implications for the redox state of seawater at the onset of the Great oxidation Event

Banded iron formations (BIFs) deposited during the onset of the Great Oxidation Event (GOE) are crucial to understanding fundamental changes in the redox conditions of Earth’s surface environments, however, they are poorly understood in South China. Here, we investigate the petrographic, geochronological, and geochemical characteristics of a set of continuous magnetite quartzite samples from a drill core through the Longwanggou iron deposit in the Yudongzi Complex, South China. These magnetite quartzite samples exhibit diagnostic features of BIFs — 1) they comprise alternating magnetite and quartz layers at the centimeter–millimeter scales, 2) they are dominantly composed of SiO2 + Fe2O3T (87.8–95.8 wt%, average = 91.4 wt%), and 3) they are characterized by shale-normalized rare earth elements plus yttrium patterns similar to seawater. The maximum depositional age of the Longwanggou BIF (i.e., magnetite quartzite) is constrained to ca. 2.49 Ga based on U–Pb dating of detrital zircon grains from chlorite schist that is intercalated with the BIF. The metamorphic complex of the Yudongzi Complex that hosts the BIF was intruded by ca. 2.5–2.45 Ga granitoid gneisses, indicating that the BIF must be older than 2.45 Gyr. Accordingly, the depositional age of the Longwanggou BIF is constrained to ca. 2.49–2.45 Ga, coincident with the onset of the GOE. The positive Eu anomalies (1.3–4.2; average = 2.2) that occur throughout BIF samples suggest a continuous flux of submarine, high-temperature hydrothermal fluids to the ocean at the Archean–Proterozoic boundary. Based on elemental mass balance, the proportion of submarine, high-temperature hydrothermal fluids that contributed to the deposition of the BIF was less than 0.1%. Unlike BIFs deposited during the GOE, the Longwanggou BIF samples lack negative Ce anomalies, suggesting that the water column in which the BIF was deposited was at least locally anoxic during the onset of the GOE. Identification of the Longwanggou BIF provides new constraints for the Precambrian evolution of South China and lays the foundation for further study of the environmental changes at the Archean–Proterozoic boundary.

Interstitial carbonates in pillowed metabasaltic rocks from the Pilbara Craton, Western Australia: A vestige of Archean seawater chemistry and seawater-rock interactions

Calcites hosted in the interpillow void spaces of extremely well preserved, 3.47–3.12 Ga pillow lavas of the Archean Pilbara Craton, Australia, provide new geochemical insights into the composition of Archean seawater and its interaction with basaltic crust. We present a comprehensive dataset of major and trace elements, radiogenic 147Sm-143Nd, 87Rb-87Sr, and stable C-O isotopes for these calcites.Based on their elemental composition and Post-Archean Australian Shale-normalized rare earth element and yttrium (REYPAAS) patterns, two types of calcites can be distinguished. Type I (n = 9) are coarse-grained calcites with elevated Mn concentrations (478–14,790 ppm) and high REY concentrations that match the basaltic host rock compositions. Petrographic textures in combination with geochemical data indicate precipitation from boiling seawater trapped between pillows during basalt eruption. Small light-REYPAAS depletions, only slightly super-chondritic Y/Ho (34.5–39.1), and low δ18O(VSMOW2) (9.25–16.66 ‰) suggest relatively high fluid-rock interactions of boiling seawater with the basaltic host rock. These characteristics are similar to those of interstitial carbonates found in modern mid-ocean ridge basalts. Type II carbonates (n = 6) are fine-grained, low-Mn (13.7–420 ppm) calcites that exhibit comparably high Sr concentrations (825–2,516 ppm) and anoxic modern seawater-like REYPAAS patterns, strong super-chondritic Y/Ho (39.1–55.8) and δ18O(VSMOW2) values of 9.10–13.18 ‰. These features hint to direct calcite precipitation from seawater within the degassing space with little fluid-rock interaction.Almost all (Type I and Type II) of the calcites investigated here, combined with their respective host rocks, yield well-defined Sm-Nd isochron ages for the Apex (3,466 ± 23 Ma), Euro (3,365 ± 43 Ma), Honeyeater (3,187 ± 33 Ma), and Bradley (3,131 ± 24 Ma) formations. Only calcites from the Mt. Ada Basalt and their associated host rocks show a ∼ 100 Ma younger Sm-Nd isochron age (3,361 ± 22 Ma) compared to the U-Pb zircon age of formation.Highly radiogenic initial Sr isotope compositions of the high-Mn calcites (Type I) and low Sr concentrations, suggest Sr remobilization for these calcites. In contrast, the low-Mn calcite (Type II) exhibit higher Sr concentrations and lower 87Sr/86Sr(i) of 0.7010–0.7011 at 3.34 Ga and 0.70137 at 3.12 Ga, suggesting increasing influence of crustal weathering on the composition of Paleoarchean seawater through time, and progressive decoupling from the Archean mantle (87Sr/86Sr(i) = 0.7003–0.7007).

Seasonal variations of dissolved rare earth elements and anthropogenic gadolinium in the highly urbanized river basin, Busan, Korea

Anthropogenic gadolinium (Gdanth) has been reported in rivers as a result of magnetic resonance imaging. We collected seasonal water samples from the Suyeong River Basin, to investigate seasonal variations in dissolved rare earth elements (REEs) and Gdanth in highly urbanized areas. The post-Archean Australian shale-normalized REE patterns indicate a significant influence of terrestrial source inputs during the summer. Although higher concentrations of dissolved REEs were measured in summer than in winter, the Gdanth concentrations exhibited similar levels. During winter, the concentrations of Gdanth showed conservative mixing trends downstream of the wastewater treatment plant (WWTP), whereas no clear trend was observed in summer. Moreover, the estimated daily discharge of Gdanth accounts for approximately 11–22% of the number of MRI tests performed, when the WWTP treats only 6% of Busan area size. Our results suggests that the elevated Gdanth level in the highly urbanized river basin is a major concern.

Well-preserved clotted micrite in a diagenetically altered Jurassic seep deposit

Geochemical analyses of ancient seep carbonates provide information on past environmental conditions and the chemical composition of seep fluids, allowing for the reconstruction of the evolution of chemosynthesis-based faunal communities in the Phanerozoic. However, diagenetic processes commonly mask the primary composition of ancient seep carbonates, impeding a reliable reconstruction of formation environments. The potential for the preservation of primary element patterns in microcrystalline carbonate, which is typically the volumetrically dominant phase in seep limestones, is poorly constrained to date. This study investigates Jurassic seep limestones from the Blue Mountains of eastern Oregon, USA. The seep limestones are mostly composed of three carbonate phases, (1) clotted microcrystalline calcite (clotted micrite), (2) banded and botryoidal, fibrous calcite cement, and (3) equant calcite cement. Mineralogically, these three carbonate phases are now calcite characterized by low magnesium/calcium (Mg/Ca) ratios. The fibrous crystal habit and flat crystal terminations indicate that the precursor mineral of the banded and botryoidal cement was originally aragonite. Cathodoluminescence imaging of banded and botryoidal cement shows partially dull to non-luminescence, suggesting that only parts of this phase experienced diagenetic alteration. However, low strontium (Sr) content and positive europium (Eu) anomalies of botryoidal cement indicate that this phase was affected by diagenetic alteration. Equant calcite exhibits the largest crystal size and the highest manganese/strontium (Mn/Sr) ratios, suggesting that this phase was the product of later-stage diagenesis, probably having precipitated during progressive burial. High Sr contents and low Mn/Sr ratios of clotted micrite indicate that this phase was less affected by diagenetic alteration and has the highest preservation potential with respect to the original seep fluid composition. Shale-normalized rare earth element and yttrium (REY) patterns of clotted micrite are close to those of modern seawater, agreeing with a primary composition of clotted micrite. In spite of its small crystal size, which is generally believed to favor recrystallization, our study suggests that clotted micrite has the potential to reliably record information on fluid composition. Given the dominance of microcrystalline carbonate in many seep limestones, this phase may prove to be a valuable archive – ideally alongside other authigenic minerals – in cases where its pristine composition can be confirmed by independent petrographical and geochemical proxies.

Enrichment and Fractionation of Rare Earth Elements in an Estuarine Marsh Soil Receiving Acid Discharges from Legacy Sulfide Mine Wastes

This paper provides new insights into the geochemical cycling of rare earth elements (REEs) in acid sulfate soils developed on salt marsh sediments of the Huelva estuary (Spain) as a result of sulfide mineral oxidation in abandoned ore stockpiles. The study was aimed at determining the REE abundance, fractionation pattern and mineralogical control of the dispersal and retention of REEs in the soil system. Forty-one samples were collected at 13 core sampling sites along two transects extending across the degraded marshland, and they were subjected to XRD, ESEM-EDS and ICP-MS analyses. Measurements revealed that the soil receiving acid discharges has relatively high concentrations of ΣREEs (174.77 ± 19.77 mg kg−1) compared to local baseline concentrations. Shale-normalized REE patterns are generally flat, but a slight middle REE (MREE) enrichment is consistently apparent in all soil samples, involving relatively low LaN/GdN ratios (0.83 ± 0.08) and GdN/LuN ratios up to 1.42. The convex-upward REE pattern supports the possibility that iron oxy-hydroxide minerals play an important role in MREE retention through adsorption and co-precipitation mechanisms. Efflorescent sulfate salts left on the topsoil by the evaporation of acid waters show a strong depletion of light REEs (LaN/GdN = 0.16 ± 0.10) and act as a temporary reservoir of labile MREEs and heavy REEs during dry periods.

Anthropogenic Gadolinium Accumulation and Rare Earth Element Anomalies of River Water from the Middle Reach of Yangtze River Basin, China

Anthropogenic rare earth elements (REEs), such as gadolinium (Gd), lanthanum (La), and samarium (Sm), have emerged as microcontaminants in surface waters. In this study, surface water samples were collected from the middle Yangtze River basin from the metropolitan region of central China (Wuhan). We further evaluated the REE characteristics and anthropogenic Gd contribution. The total dissolved REE concentration in the river ranged as 6.76–99.31 ng L–1, the lowest value globally. Furthermore, the Post-Archean Australian Shale-normalized REE patterns, the negative anomaly of Ce, and the positive anomaly of Sm, Eu, and Gd indicated that heavy REE enrichment occurred in the water body. The anthropogenic Gd (Gdanth) concentration in Fuhe River and Hanjiang River was higher than that in the other rivers, with the difference ascribed to wastewater treatment plant (WWTP) discharges. The total daily discharges of Hanxi WWTP (HX-W) and Sanjintan WWTP (SJT-W) effluent were 53.5 and 13.5 g Gdanth, respectively. These values equate to 31.1 and 12.7 g Gdanth d–1 for HX-W and SJT-W per million people. Therefore, the quantitative evaluation of Gdanth in natural water near large cities warrants more attention.

Uptake of trace elements into authigenic carbonate at a brine seep in the northern Gulf of Mexico

Hypersaline seafloor environments formed by brine seepage represent role model examples of extreme marine ecosystems; they may for example help to identify potential habitats for life on other planets. Trace and rare earth elements (REEs) are crucial components enabling microbial life at brine and hydrocarbon seeps. However, the behavior of trace elements at brine seeps is currently poorly understood. Because authigenic carbonates forming at brine seeps archive information on the composition of seepage fluids, we have analyzed carbonates collected from a brine seep site (Mississippi Canyon 709, MC709 for short) of the northern Gulf of Mexico (GoM). The dominance of low-magnesium (Mg) calcite among the carbonate minerals, moderately low δ13Ccarb values (average: −26.1‰, VPDB), as well as the presence of oil in carbonates suggest concomitant seepage of brine fluids and crude oil at this site. High δ18Ocarb values (up to +4.5‰, VPDB) suggest the involvement of 18O-rich fluids during carbonate precipitation, likely resulting from mineral-water reactions in deeper sediments. Significant enrichments of barium (Ba), strontium (Sr), and lithium (Li) in the samples suggest that deep ascending brine fluids contributed to carbonate formation. Enrichments in molybdenum (Mo), arsenic (As), and antimony (Sb) and a correlation between Mo, As, and Sb enrichment factors (EF) and the authigenic iron fraction (Fe/Al ratios) suggest that iron particulate shuttle processes were involved in scavenging of dissolved Mo, As, and Sb from seawater. This notion is strengthened by the co-variation of MoEF and UEF and the shale-normalized REE patterns of the brine-seep carbonates. This study allows to constrain the enrichment mechanisms of trace and REE elements at brine seeps, providing the foundation for an improved understanding of the distribution and behavior of trace metals, as well as their role in microbial metabolisms in the local hypersaline environment.

Rare Earth Elements of Sediments in Rivers and Estuaries of the East Coast of India

The rare earth elements (REE) in the clay fraction of sediments in 15 rivers and their estuaries along the east coast of India were analysed in this study. The total REE content (ΣREE) varied from 130.98 to 289.85 μg/g and from 70.89 to 352.61 μg/g in rivers and estuaries respectively. The ΣREEs of estuarine clays (except the Brahmani and Baitarani) was lower than in rivers. The Post-Archean average Australian Shale-normalized REE patterns in rivers and estuaries were similar and categorized into three types. The REE patterns reflect the composition of dominant geological formations in river basins and extent of sediment mixing from different sources during transport. Hydrodynamic conditions controlled the abundance and fractionation of REE in the estuaries. The Sm/Nd ratios of clays were largely controlled by mineral composition and Y/Ho ratios were affected by sedimentary processes in the estuaries.

Banded iron formation from Antarctica: The 2.5 Ga old Mt. Ruker BIF and the antiquity of lanthanide tetrad effect and super-chondritic Y/Ho ratio in seawater

Here we report the first detailed geochemical data for Banded Iron-Formation (BIF) from Antarctica. Micro drill cores were taken from adjacent magnetite/haematite and metachert bands from the 2.5 Ga old Mt. Ruker BIF, Prince Charles Mountains, East Antarctica. Low concentrations of Al, Zr, Hf, and Sc reveal the purity of the samples. The chemical composition matches closely that of other early Precambrian BIF, except for an enrichment of Ni, and high Ba/Sr ratios in the metachert. Shale-normalized Rare Earths and Yttrium (REYSN) patterns show all the features of modern seawater such as depletion of light vs heavy REYSN, positive anomalies of LaSN, GdSN, and YSN (i.e. super-chondritic Y/Ho ratios) and the W-type lanthanide tetrad effect (LTE), but positive EuSN and no CeSN anomalies (and no positive Eu anomalies in chondrite-normalized REY patterns). This distribution is fully compatible with that of other pure Early Precambrian BIFs, suggesting high-temperature hydrothermal input of REY into seawater and a redox level of the atmosphere-hydrosphere system too reducing for Ce oxidation. The uniform, super-chondritic Y/Ho ratios in adjacent iron-oxide and metachert BIF bands most strongly suggest that the conspicuous banding does not result from post-depositional separation of an initially homogenous Fe-silicate precipitate, but argues for a primary origin of the banding. The super-chondritic Y/Ho ratios fit well within the range reported for other BIF worldwide, corroborating that positive Y anomalies, although possibly of smaller size than today, have always been a characteristic feature of seawater. The Mt. Ruker BIF further complements the set of Early Precambrian marine chemical sediments in which the W-type LTE has been observed, and demonstrates the antiquity of the LTE in seawater. These subtle features reveal that the distribution of the redox-insensitive REY in seawater did not change significantly over the almost 4 billion years geological record of seawater. The super-chondritic Y/Ho ratios and W-type LTE in this and other oxide-facies BIF are in marked contrast to the REY distribution in Modern and Cenozoic oxidic hydrogenetic ferromanganese crusts, pointing towards fundamentally different removal mechanisms of REY from Modern vs Early Precambrian seawater.

Chemical evolution of seawater in the Transvaal Ocean between 2426 Ma (Ongeluk Large Igneous Province) and 2413 Ma ago (Kalahari Manganese Field)

Drill core and outcrop samples of pure marine chemical sediments (banded iron formation (BIF), manganese formation (MnF), jaspilites, lutites, and cherts) from the transition of the ~2426 Ma old Ongeluk Formation into the 2413 Ma old Hotazel Formation, Transvaal Supergroup, South Africa, reveal remarkable changes of seawater chemistry in the Transvaal Ocean. Similar to pre-Ongeluk chemical sediments, the shale-normalized rare earths and yttrium (REYSN) patterns of jaspilites intercalated with the volcanic rocks of the Ongeluk large igneous province and directly overlying cherts do not show positive EuSN anomalies, indicating that high-temperature (>250 °C) hydrothermal fluids did not contribute significantly to the REY budget of ambient waters. However, a 10 cm drill core section in the lower Hotazel Formation is characterized by conspicuous positive EuSN anomalies, revealing temporary inflow of water masses strongly affected by high-temperature hydrothermal fluids. After this short episode, the REYSN pattern of Transvaal seawater returned to that of pre-Ongeluk times, showing heavy REYSN enrichment, positive LaSN, GdSN and YSN anomalies, but no CeSN or EuSN anomalies. Higher up in the stratigraphy, the Hotazel Formation shows negative CeSN anomalies in some of the lutites, BIFs and MnFs, reflecting Ce depletion in ambient seawater. All Hotazel lutite, BIF, and MnF samples studied show unradiogenic εNd(t) values (−0.5 ± 0.2 to −2.4 ± 0.2), indicating a mostly continental REY source. The REY distribution and Nd isotope data combined suggest that oxidative terrestrial weathering of this continental crustal source supplied most of the dissolved REY to local “Transvaal seawater”. Precipitation of the Hotazel lutites, BIFs and MnFs with negative CeSN anomalies, therefore, suggests that oxic conditions prevailed on the Kaapvaal Craton and in Hotazel seawater already at ~2.413 Ga, i.e. 80 m.y. before the disappearance of mass-independent sulfur isotope fractionation (MIF-S) that defines the Great Oxidation Event at ~2.33 Ga.

Carbonates and cherts as archives of seawater chemistry and habitability on a carbonate platform 3.35 Ga ago: Insights from Sm/Nd dating and trace element analysis from the Strelley Pool Formation, Western Australia

Carbonates and cherts in the 3.35 billion-year-old Strelley Pool Formation (Fm.; Australia) host stromatolites that are among the oldest remnants of life on Earth. However, it is still not entirely clear whether these mineral phases are authigenic precipitates, and whether they represent reliable geochemical archives of early Earth environments. Here we present major/trace-element and Nd-isotope data of stromatolitic carbonates, associated crystal-fan carbonates, and cherts in the Strelley Pool Fm. (i) to assess the reliability of these chemical sediments as geochemical archives of the fluids from which they precipitated, (ii) to date the time of formation of carbonate and silica phases, and (iii) to trace the sources of elements prevailing in microbial habitats 3.35 Ga ago.Stromatolitic carbonates plot together with the stratigraphically underlying Marble Bar cherts on a Sm-Nd regression line yielding 3253 ± 320 Ma. In contrast, associated crystal-fan carbonates together with altered Marble Bar cherts yield 2718 ± 220 Ma, suggesting that their Sm-Nd isotope system was reset after deposition. Both types of carbonates, as well as white cherts, show shale-normalized rare earth element and yttrium patterns (REYSN; with the exception of redox-sensitive Ce and Eu and heavy REYSN to middle REYSN depletion) that are parallel to those of modern seawater, indicating a predominantly seawater-derived origin. Positive EuSN anomalies (2.1–2.4), combined with heterogeneous ɛNd3.35Ga values between −3.2 and +5.8 within individual alternating stromatolite laminae, further support that the dissolved fraction of seawater on the ancient carbonate platform was variably affected by both continental weathering and high-temperature hydrothermal fluids contributing elements of both young mafic or older felsic rocks. In conclusion, trace element and Nd isotope data presented here match well with the depositional environment, as characterized based on lithological, geochemical, and stratigraphic relationships, on an early continent, showing at least episodic emergence above the sea level, supporting microbial life on a shallow marine platform.

Geochemical Behavior of REE in Stream Water and Sediments in the Gold-Bearing Lom Basin, Cameroon: Implications for Provenance and Depositional Environment

Stream water and associated bottom sediments were sampled within the Lom Basin, and their rare earth element (REE) concentrations have been used to decipher their provenance and environment of deposition. Stream waters in the lower Lom Basin have variable Post Archean Australian Shale-normalized REE concentrations (0.24–4978 ng/l), positive Ce anomalies (Ce/Ce* ranges from 1.08 to 8.03), a general positive Eu anomaly (Eu/Eu* varies from 0.9 to 15.2, average = 4.9) and are slightly enriched in the light rare earth elements (LREE/HREE varies from 1.7 to 10.3). Similarly, the sediments are slightly depleted in heavy rare earth elements (HREE), have a predominant negative Ce anomaly, but show a ubiquitous positive Eu anomaly. The dissolved REE content is controlled by the near-neutral pH of the stream water and adsorption onto Fe and Mn oxyhydroxides. The variable LREE/HREE ratios and Eu anomalies observed in the sediments indicate that these sediments are sourced mainly from felsic rocks with little mafic input. Moreover, Ce anomalies and redox-sensitive trace elemental ratios of Ni/Co, V/(V + Ni), V/Cr, Cu/Zn and V/Ni revealed the sediments were deposited under oxic to reducing conditions. Variations in the concentration of REE in the stream water and sediment indicate that Fe and Mn oxyhydroxides are important sinks for the HREE. The newly generated data will guide future studies and environmental policy makers.

Hydrothermal signatures in sediments from eastern Southwest Indian Ridge 63°E to 68°E

Hydrothermal vent incidence is proportional to the spreading rate of the mid-oceanic ridges (MORs) (Baker et al., 1996). However, the ultra-slow spreading Southwest Indian Ridge (SWIR) is unique and has a relatively higher incidence of hydrothermal vent fields compared with other ultra-slow spreading ridges (German et al., 1998; Baker and German, 2004). In the present study, sediment samples from the less studied easternmost section of the ultra-slow spreading SWIR are investigated to decipher the signatures of hydrothermal activity. The sediments are mainly composed of calcium carbonate (55–85%), Fe-Mn-(oxyhydr)oxide (13–27%), and residual aluminosilicate phases (2–17%). The metalliferous nature, low Mn concentration (393–1772 ppm), negative Ce, and positive Y anomalies in the shale-normalized rare earth element (REE) pattern of the bulk sediments provide evidence for the presence of hydrothermal inputs in most of the sediments. The fractionation among lighter REEs over heavier REEs in bulk sediments indicates the high-temperature hydrothermal plume fall-out to the sediments. The leached fraction also shows similar negative Ce and positive Y anomalies, and indicates that the Fe-Mn-(oxyhydr)oxide precipitates in these sediments may be dominantly of hydrothermal origin. In addition to hydrothermal Fe-Mn-(oxyhydr)oxide phases, the residual fraction of the sediments also consists of minor quantities of hydrothermally sourced sulfate phases. Otherwise, the residual fraction is significantly dominated by mid-oceanic ridge basalt (MORB) derived components in addition to serpentinized peridotite and terrigenous material.Among the studied sediments, sample E-3-16 from Fuji Dome (influenced by hydrothermal activity) has high zinc concentrations, which indicates the possibility of a new vent field in the vicinity. The present study also introduces a new geochemical tool (Zn/Fe vs Co/Zn proxy) for assessing the contribution of hydrothermal components in the sediments. The Zn/Fe vs Co/Zn proxy will be more useful in MOR settings hosting sulfides dominated by sphalerite.The influence of hydrothermal activity in most of the studied sediments from the eastern SWIR indicates that the ultra-slow spreading eastern SWIR has the potential to possess a larger number of hydrothermal vent fields.

Anthropogenic Rare Earth Elements: Gadolinium in a Small Catchment in Guizhou Province, Southwest China.

Rare earth elements (REEs), known as “industrial vitamins”, are widely used in medical treatment, industry, agriculture, etc. However, with the increasing demand for REEs, excess REEs, such as gadolinium (Gd), are considered micropollutants in the environment. In this paper, the distributions of dissolved REEs were analyzed in three small streams, in order to determine the extent and occurrence of Gd anomalies. The shale-normalized REE patterns in the three streams were less smooth with heavy REEs higher than light REEs, for a weak reaction of the heavy REE complexes. A negative Ce (cerium) anomaly and positive samarium (Sm) and europium (Eu) anomalies were observed in the three streams and the negative Ce anomaly was affected by the pH of the alkaline rivers. However, a positive Gd anomaly was found in only a typical urban small stream, Jinzhong. With a population of approximately 60,000, Jinzhong runs by a hospital and through wastewater treatment plants (WWTPs). The concentrations of Gd in Jinzhong ranged from 1.54 to 86.65 ng/L with high anthropogenic Gd proportions (63.64%–98.07%). Anthropogenic Gd showed significant seasonal variations and distinct spatial disparities from upstream to downstream, and it was associated with certain ions such as Cl−. Anthropogenic Gd could be attributed to gadopentetic acid (Gd-DTPA), which is used in magnetic resonance imaging (MRI) in hospitals. This type of Gd was shown to be correlated with municipal wastewater. Due to the high stability and low particulate reactivity in water, anthropogenic Gd has great potential to serve as a tracer to prove the presence of medical wastewater.