PAAS-normalized Rare Earth Elements Research Articles

Geochemistry of dissolved rare earth elements in the Lancang River with cascade dams and implications for anthropogenic impacts

Anthropogenic effects like the construction of cascade dams are increasingly affecting the biogeochemical cycles of rare earth elements (REE) in rivers. However, our understanding on the REE compositions of dissolved loads in rivers under the effect of cascade dams remains limited. In this study, forty-four water samples in the Lancang River were analyzed for REE concentrations to assess the impact of cascade dams. The results showed that total dissolved REE concentrations ranged from 4.0 to 65.7 ng/L, with an average value of 21.8 ng/L. The concentrations in the middle (519.6 ng/L) and lower (331.5 ng/L) reaches were higher than those in the upper reaches (108.1 ng/L). All river samples showed (La/Yb)N values < 1, and the PAAS-normalized REE patterns indicated a substantial enrichment of heavy REE, characterized by negative Ce (0.1–0.9) and positive Eu (1.5–32.1) anomalies. The enrichment of heavy REE can be attributed to their preferential release from minerals during the weathering process and their interaction with inorganic complex anions. The negative Ce anomaly observed is likely the result of redox conditions, while the positive Eu anomaly was inherited from the REE characteristics of the source rocks. Moreover, the Ce anomaly decreased to 0.29 in the Huangdeng reservoir and 0.12 in the Dachaoshan reservoir. The value of Ce anomaly displayed a sharp decline in the middle and lower reaches affected by the cascade reservoirs. The effect of the dams played an important role in Ce anomaly by decreasing the DOC concentrations, and rivers with low DOC concentrations are commonly associated with negative Ce anomaly. This study revealed that cascade dams paly an essential role in the variation of REE in dissolved loads and REE anomaly may have the potential to track anthropogenic activities.

Dissolved rare earth elements in the Pearl River Delta: Using Gd as a tracer of anthropogenic activity from river towards the sea

Growing demands for high-tech uses of rare earth elements (REE) result in their releases into the aquatic environment, but local anthropogenic sources and water chemistry reactions may vary in aquatic systems. In this study, we quantified the yttrium and REEs (REY) in the surface waters of the Pearl River Delta (PRD), Southern China, and investigated their sources and processes controlling the dissolved REY distributions from rivers towards the sea. Spatial variations of dissolved REY concentrations (<0.4 μm) were observed in the surface water due to both natural and anthropogenic sources. Salt-induced flocculation removed colloidal REY from water during estuarine mixing, particularly at low salinity. In contrast, a significant increase of dissolved REY concentration with salinity suggested the occurrence of REY desorption from particles during estuarine mixing. The PAAS-normalized REE patterns (i.e., filtrates <0.4 μm and <3 kDa) showed a significant light REE (LREE) depletion relative to heavy REE (HREE) in dissolved fractions, indicating reactive LREE adsorption onto particles. Positive Gd anomalies in most waters revealed significant impacts from human activities, such as effluents from wastewater treatment plants in the PRD. In particular, the anthropogenic Gd contributed 90 % of the total dissolved Gd along the Pearl River and was conservatively mixed with saltwater in the estuary via the Humen outlet. Positive Sm anomalies were also observed in the PRD, indicating other point sources related to industrial activity. With the increase of urbanization and high demand for green technology, the REY anomalies could be a good indicator of human activities on assessing their fluxes and impacts on the aquatic systems.

Anthropogenic rare earth elements in urban lakes: Their spatial distributions and tracing application

Anthropogenic activities associated with various new technologies are increasingly disrupting the geochemical cycles of rare earth elements (REEs). For example, samarium (Sm) and gadolinium (Gd) have emerged as microcontaminants in the natural waters of developed areas. Surface water samples of 13 urban lakes were collected in Wuhan, the largest city in central China, with a population of over 11 million. The aim of this study was to examine to what extent REE anomalies occur and the relationship between the concentration of anthropogenic REEs in lakes and the surrounding environment. In this study, based on land-use type and point of interest (POIs) data, buffer extraction, density estimation and Spearman correlation analysis were first proposed to identify different sources of anthropogenic REEs, which mainly included hospitals, factories, population, urban land and cropland. The PAAS-normalized REE patterns indicate that all lake samples display pronounced positive Sm and Gd anomalies, ranging from 5.92 to 19.88 and 1.73 to 14.97, respectively. Spearman correlation analysis showed that hospital density was positively correlated with anthropogenic Gd concentration, and a positive relationship between proportion of cropland and the concentration of anthropogenic Sm. By utilizing Gdanth, Smanth, and the conventional ion ratio (NO3−/Cl−), a three-dimensional tracer system was established, and the system accurately obtained a characterization of the impact of WWTPs, hospitals, factories and agriculture on the lakes. Moreover, the results from this hydrochemical method were consistent with the analysis of geographic information systems, which indicated that this anthropogenic contaminant as a tracer was reliable for analysing the source of urban water pollution.

Controlling factors and impacts of river-borne neodymium isotope signatures and rare earth element concentrations supplied to the Canadian Arctic Archipelago

Determining the factors controlling the neodymium (Nd) isotopic compositions (expressed as εNd) and rare earth element (REE) concentrations of rivers is imperative to improve our understanding of the distribution of these water mass tracers in the ocean. Here we present the first measurements of <0.45 μm-filtrate REE concentrations (i.e., the concentration of truly dissolved, nano-particulate and colloidal REEs passing through a 0.45 μm filter, hereafter referred to as dissolved) and εNd in rivers draining into the Canadian Arctic Archipelago (CAA). Results show a large variation in both REE concentrations (Nd=[8;37,260] pmol/kg) and εNd ([−32.1;−15.1]) in the thirteen rivers sampled. Dissolved REE concentrations increase with increasing fractions of metamorphic rocks and ice cover in the rivers' watersheds, while εNd and PAAS-normalized REE patterns are inherited from the watershed's bedrock lithology. The four rivers draining watersheds composed of Precambrian metamorphic rocks exhibit the highest REE concentrations, the least radiogenic εNd, and shale-normalized patterns enriched in light REEs. The remaining nine rivers drain mainly or exclusively sedimentary bedrock and have lower REE concentrations, more radiogenic εNd and generally show heavy REE enrichment, with variable negative cerium (Ce) anomalies. The presence of ice sheets in the drainage area, and the ionic strength, pH, and dissolved organic carbon concentration of river water are the main factors determining riverine dissolved REE concentrations by controlling the formation and stabilization of colloids. We estimate a flow of dissolved Nd transported by Arctic rivers discharging into the CAA equivalent to the Nd flux of seawater entering the CAA. Depending on the percentage of Nd removal during mixing with seawater, the impact of river water on the εNd of seawater exiting the CAA could be modest (if 90% removal) or more significant (if ≪90% removal). This riverine contribution could potentially impart a climate-sensitive εNd signature to the seawater reaching Baffin Bay, with possible implications for the use of εNd in paleoceanographic reconstructions of water mass distribution.

Influence of diagenetic processes and terrestrial/anthropogenic sources in the REE contents of the Cascais submarine canyon (Iberian western coast)

Temporal variations of rare earth elements (REE) and their fractionation patterns, major elements, Pb and Hg were determined in two multicores collected at 445 and 2100 m water depth (mwd) in the Cascais submarine canyon (CSC). The PAAS-normalized REE patterns suggest mixing of Tagus estuarine and marine sediments, marked by MREE (Nd‐Dy series) enrichment and by positive Eu-anomaly, with marine sediments. The positive Eu/Eu* implies incorporation of detrital feldspar minerals derived from the estuary. Ce/Ce*, (La/Yb)PAAS and (Nd/Yb)PAAS show differences between the two cores. Core 252-35 from the shallower site is enriched in HREE (Ho‐Lu series) over LREE (La‐Pr series), a pattern also found in the Tagus estuary in the vicinity of an abandoned chemical complex, where the environment is affected by the legacy of massive-sulfide ores processing. There seems to be only limited down-canyon sediment transport to the deeper reaches where core 252-32 was collected. This deeper site shows Ce/Ce* peaks coinciding with low (La/Yb)PAAS values suggesting preferential diagenetic remobilization of LREE relative to HREE. Upcore Pb/Al and Hg/Corg trends observed in both cores indicate dispersion of the anthropogenic component from the estuary through the CSC, which is less obvious from the ∑REE/Al trends particularly in the deeper site. This may suggest the influence of diagenetic processes in the REE signal, associated with relatively low sediment accumulation rates.

Contrasting Depositional Environment of Iron Formation at Endengue Area, NW Congo Craton, Southern Cameroon: New Insights from Trace and Rare Earth Elements Geochemistry

The Endengue Banded Iron Formation (BIF) is located in the northwestern edge of the Congo craton in Cameroon. Here, we report geochemical data of trace and rare earth elements (REE) of the Endengue BIF samples from the Archean Ntem complex and investigate their environmental setting. Two types of BIF occur at Endengue area, both containing minimal contamination from terrestrial material. Total REE (ΣREE) contents in the Type 1 BIF are extremely low, ranging from 0.34 to 1.83 ppm, similarly to pure chemical sediments while Type 2 BIF displays ΣREE contents ranging from 2.98 to 24.26 ppm. The PAAS-normalized REE + Y patterns of the two BIF types display LREE enrichment relative to HREE and weak positive Eu anomaly, most likely suggesting that the source of iron and siliceous of the Endengue BIFs is mainly from the contribution of low-temperature hydrothermal alteration of the crust. Type 1 BIF shows very low Nd content (* and positive Ce anomalies which suggests suboxic or anoxic seawater similar to the depositional environment of Elom BIF in Archean Ntem complex. In contrast, Type 2 BIF displays low to moderate Nd contents (1 and 100 ppm with the exception of sample LBR65) with negative correlation between Nd and Ce/Ce* and negative Ce anomalies. These features indicate precipatation of Type 2 BIF from oxic iron-rich solution that changed to oxidized surface by rapid precipitation of the hydrothermal Fe. The Endengue BIFs were deposited in the continental margin ocean in presence of low-temperature hydrothermal fluids mixed with seawater, similar to Paleoproterozoic Kpwa-Atog Boga BIFs within the Nyong group and other Paleoproterozoic Superior-type BIFs worldwide.

Source of dolomitizing fluids and dolomitization model of the upper Permian Changxing and Lower Triassic Feixianguan formations, NE Sichuan Basin, China

Dolostone reservoirs have been found in the Changxing (P2c) and Feixianguan (T1f) formations in both the east and west platform edges of the Kaijiang-Liangping trough; they are the main natural gas exploration targets in the NE Sichuan Basin. In this study, the sources of the dolomitizing fluids were determined, and a dolomitization model was established based on petrography, rare earth elements (REEs), major and trace element data, and 87Sr/86Sr ratios. The dolostone and limestone samples with ΣREE values of >5 ppm exhibit relatively flat PAAS-normalized REE patterns; their Zr, Sc, and Th concentrations increase with increasing ΣREE; and their Rb/Sr ratios are generally greater than 0.01, suggesting that these samples were likely contaminated by terrigenous components. Therefore, only the REEs and 87Sr/86Sr ratios of samples with ΣREE values of <5 ppm were selected to constrain the dolomitizing fluids. The PAAS-normalized REE patterns of the P2c–T1f dolostones, which are characterized by LREE depletion, negative Ce anomalies (Ce/Ce* of 0.70–0.85), and relatively high Y/Ho ratios (49.0–152.4), are similar to those of the unaltered coeval limestones, suggesting that the dolomitizing fluid was sourced from fluids similar to coeval seawater. The Ce/Ce* values of the dolostones are lower than those of the unaltered limestone, suggesting that the source of the dolomitizing fluids had more oxidizing conditions and most probably contained evaporated seawater from an evaporite platform. The Eu/Eu* values of the P2c dolostone in the west platform (means of 4.95 and 2.76 for the YB and XLC gas fields, respectively) are notably higher than the Eu/Eu* values of the P2c and T1f dolostones in the east platform (mean 1.29 and 1.39 in the PG gas field, respectively), suggesting that the P2c dolostone in the west platform was formed under more reducing conditions and at a deeper burial depth. The 87Sr/86Sr ratios of the T1f and P2c dolostones in the east platform (such as in the Puguang gas field) are similar to those of the co-existing early T1f limestone, while the 87Sr/86Sr ratios of the P2c dolostone in the west platform (such as in the Yuanba gas field) are higher than those of the coexisting P2c limestone but are close to those of the late T1f dolostone in the east platform. This indicates that the dolomitizing fluids were mainly from the early T1f and late T1f evaporated seawater on the east and west platforms, respectively. Driven by the density difference between the evaporated seawater and normal seawater, the evaporated seawater flowed downward and laterally into the limestone in the high-energy reefs and shoals through the original pores and the early selective dissolution pore system and/or through synsedimentary fractures. The continual seepage of evaporated seawater and the relatively high temperatures (50–60 °C) resulted in the large-scale shallow burial dolomitization in the NE Sichuan Basin.

Major, trace and rare earth element (REE) geochemistry of the Oligocene stratiform manganese oxide-hydroxide deposits in the Nikopol, Ukraine

The Nikopol manganese deposit is situated in the west and north of Nikopol, Ukraine and one of the world's largest deposits among the sedimentary manganese deposits. The Nikopol Oligocene basin consists of two structural stages, Precambrian crystalline basement rocks and sedimentary cover rocks (Cretaceous to Quaternary). Nikopol Ore horizon is traced in a thickness varying from several cm to 4.5 m and a single stratum from the west to the eastwards to about 250 km. Nikopol manganese ore horizon was separated to three different units; carbonate ore, mixed carbonate-oxide ore, and oxide ore. The main minerals of supergene oxidation zone in Nikopol manganese deposits are: manganite, pyrolusite, todorokite, cryptomelane, birnessite, rancieite. The manganese oxide-hydroxide ores were analyzed for major oxides using ICP-AES and, trace and rare earth elements (REE) using ICP-MS. The mean major oxide contents of the manganese ores are 40.7 wt% MnO, 4.1 wt% Fe2O3, 15.6 wt% SiO2, 4.17 wt% for Al2O3, and 7.1 wt% for CaO. The average Mn/Fe, Co/Ni, Co/Zn, and Zr/Hf ratios in the Nikopol manganese deposit are 25, 0.54, 1.15, and57, respectively. The total REE contents are between 60 and 197 ppm, with a mean of 108 ppm. The PAAS-normalized REE patterns of the Nikopol manganese oxide ores have similar trends and show MREE (middle rare earth element) and HREEs (heavy rare earth element) enrichments. The Ce/Ce* values of manganese oxide-hydroxide ores collected from the study area vary from 0.88 to 1.43, with the mean of 1.16. Most of manganese samples have positive Ce anomalies except for a few samples, indicating that ore-forming rocks were primarily marine chemical or biogenic deposit. The Eu/ Eu* anomalies of the manganese oxide-hydroxide ores are close to 1 with a range of 0.68 to 1.12 (mean: 0.96). The Y concentrations vary from 9.1 to 47.1 ppm, with an average of 18.2 ppm and show negative Y anomalies, except for three samples. The Pb isotope ratios are 19.0 for 206Pb/204Pb, 15.7 for 207Pb/204Pb and 39.4 for 208Pb/204Pb isotopes. All these data indicate that the Nikopol manganese oxide-hydroxide ores formed rapidly within oxic/suboxic seawater as reflected by Ce anomalies close to 1 in compared to similar environments, low-oxygen fugacity in source of the hydrothermal fluids, volcanogenic input or hydrothermal contributions to seawater, and high Co, Ni, Cu, Sr, Ba and As and low V, Rb, Nb, Hf, U, Th, Pb and Zn values. Also, our results point out that the metals were transported from both a hydrothermal source in deeper water (chemical discrimination diagrams) and terrestrial sources (Pb isotopic data). The metals formed to the Mn-oxide ores syngenetically likely came from water depths deeper than the area where the carbonate-ore deposits formed.

Geochemical evidence on the depositional environment of Nummulites accumulations around Elazig, Sivas, and Eskişehir (Turkey) in the middle Eocene sub-epoch

The main objective of this study was to investigate the major, trace, and rare earth element (REEs) contents, in order to reconstruct the physico-chemical parameters of the marine paleoenvironment which hosted the investigated Nummulites accumulations. The studied samples were collected from Kirkgecit Formation-Elazig, Mamuca Formation, and Bogazkoy Formation in Ipresian-Lutetian ages. All Nummulites samples for major oxides, trace, and rare earth elements were analyzed by using inductively coupled plasma atomic emission spectroscopy (ICP-MS). The CaO contents in Nummulites range from 52.52 to 54.41 wt%. The (Tb/Yb)n–(La/Yb)n ratios of Nummulites show that all rare earth element (REE) contents were depleted during the sedimentation. The PAAS-normalized REE patterns of the Nummulites show similar trends that indicate a weak decrease to heavy REEs from light REEs. All Nummulites have negative Ce and positive Eu anomalies. The Y/Ho values vary between 28 and 41, and these values are close to that of sea water and carbonate rocks. Our findings show that Nummulites had several physicochemical features such as increases in ƒO2 and pH or decrease in temperature in the shallow marine environment.

Elemental Composition and Organic Petrology of a Lower Carboniferous-Age Freshwater Oil Shale in Nova Scotia, Canada.

A 59 m-thick section of a freshwater oil shale interbedded with marlstone of Lower Carboniferous (Tournaisian) age from the Big Marsh area in Antigonish Basin, Nova Scotia, Canada, was examined using reflected light microscopy, Rock-Eval pyrolysis, X-ray diffractometry analysis, inductively coupled plasma-mass spectrometry for elemental analysis, and prompt γ for boron concentration. The oil shale was deposited in a lacustrine environment based on geology, sedimentology, variation in organic matter, and boron content (28–54 ppm). Organic petrology classified the oil shale into three broadly distinct types. Type A oil shale is a coastal facies shale containing terrestrially derived macerals, such as vitrinite and inertinite, sporinite, with some lamalginite, and amorphous bituminous matrix. Type B oil shale was deposited in a shallow-water facies and contains mostly lamalginite and some vitrinite and sporinite. Type C oil shale is a relatively deep-water facies, associated with open-water Torbanite-type oil shale and contains mostly Botryococcus colonial telalginite. The oil shale is thermally mature (Tmax is 441–443 °C). Total organic carbon (TOC) varies from 5.8 to 7.3 wt %, and the hydrogen index is between 507 and 557 mg HC/g TOC. The rate of sedimentation as determined by the Th/U ratio indicates possibility of three sedimentation periods: an irregular but mostly slow rate of sedimentation from the base of the section up to 68 m, followed by a regular and slow rate between 68 and 53 m, and a regular and fast rate between 53 m and the top of the section. The higher Th/U ratio during deposition of the shallow-water facies was due to the input of allochthonous U. The redox conditions, as reflected in the variation of Cr to Mo, U, and Ni + V, indicate that the oil shale was deposited under suboxic–dysoxic conditions. The high organic productivity by phytoplankton and bacteria is characterized by a low Cr and high V/Cr ratio and suboxic conditions. In contrast, the well-oxygenated and uniform, warm-temperature upper water level supports a dysoxic environment. Variation of Sr/Ca vs Mn/Ca ratios indicates that most samples have low values, a characteristic of colder water and high terrigenous influx. The post-Archean Australian shale (PAAS)-normalized rare earth elements (REEs) follow three trends. Type A oil shale has the highest concentration of total REEs (648 ppm) and light REEs (LREEs, 605 ppm) as compared with type C (269 and 233 ppm), which are less than half of type A. Type B oil shale has the lowest total REEs (184 ppm) and LREEs (152 ppm). The concentration of heavy REEs decreased from 43 ppm in type A oil shale to 36 ppm in type C oil shale. Comparison of PAAS-normalized REEs for the three oil shale types indicates a reduction of the negative Eu anomaly with depth, which is possibly related to sedimentary sorting as a result of accumulation of fine sediments in the deeper water zone of the lake. The concentration of most elements of environmental concern is similar to and/or lower than the world shale. However, there are instances of higher concentrations of hazardous elements (e.g., As, Cd, Mo, and Se).

Geochemical Characteristics of Rare Earth Elements in Soils from Puding Karst Critical Zone Observatory, Southwest China

Soil samples from eight soil profiles under different land-use types were collected at the Puding Karst Critical Zone Observatory, Southwest China, to investigate the distribution, fractionation, and controlling factors of rare earth elements (REEs). The total REEs contents in topsoil ranged from 149.97 to 247.74 mg kg−1, the contents in most topsoil were higher than local soil background value (202.60 mg kg−1), and the highest content was observed in topsoil under cropland. The REEs contents in surface soils from lower slopes sites were higher than that of middle and upper slope sites, and the highest contents were observed in cropland. The PAAS-normalized REEs pattern in soils showed MREEs significantly enriched relative to LREEs and HREEs, and HREEs were enriched relative to LREEs. The results showed that clay content, pH, soil organic carbon, total phosphorus, and Fe content were the main factors influencing the distribution of REEs in karst soils, and soil organic carbon (SOC), Fe content showed better linear relationship with REEs.

Diagenetic evolution of the upper Devonian phosphorites, Alborz Mountain Range, northern Iran

The upper Devonian, mixed siliciclastic‑carbonate stratigraphic succession of the Geirud Formation in the Alborz Mountain Range, north of Iran, hosts numerous phosphorites and phosphatic rocks. These phosphorites, which represent one of the most globally important deposits in the Devonian, have gained little attention regarding their genesis and diagenetic evolution. This study focuses mainly on the post-depositional changes that occurred during shallow to deep burial diagenetic evolution and subaerial weathering of the Geirud phosphorites. The phosphorites consist of phosphatic massive mudclasts, detritus-rich lithoclasts, bioclasts and bones formed by several stages of phosphogenesis and erosion, reworking, winnowing and condensation associated with Famennian sea level changes. The phosphatic clasts consist of early diagenetic, poorly crystalline, carbonate fluorapatite (CFA) and pyrite cementing detrital quartz, illite, muscovite, rutile and zircon. Phosphatic clasts are intensely compacted with sutured grain contacts, along which dissolution and reprecipitation of chemically-refined, well crystalline CFA with a bright blue cathodoluminescence and illite occurred during deep burial diagenesis. Similarly, quartz shows deformation planar features; overgrowth cement was developed as a result of pressure dissolution in phosphatic sandstones, followed by precipitation of ferroan dolomite, ankerite and chlorite in secondary porosity. Subaerial weathering led to oxidation of pyrite and generation of acidic pH condition, under which Ca and P from phosphates, Fe and S from pyrite, Fe, Ca, Mg and Mn from ferroan carbonates and Al and Si from aluminosilicates were released to form goethite, psilomelane, calcite, gypsum and crandallite.The PAAS-normalized rare earth elements (REEs) show bell-shaped patterns with middle (REEs) enrichment, positive Eu anomaly and a weak negative Ce anomaly. This implies recrystallization of CFA in phosphorites and phosphatic rocks during deep burial diagenesis, deviating from the modern seawater-like REE patterns. In this regard, deep burial diagenesis affecting the upper Devonian Geirud phosphorites is possibly a common process in the Proterozoic-Paleozoic phosphorites in northern Iran and elsewhere in the world.

Geochemistry and origin of the Neoproterozoic Dahongliutan banded iron formation (BIF) in the Western Kunlun orogenic belt, Xinjiang (NW China)

The Neoproterozoic (593–532Ma) Dahongliutan banded iron formation (BIF), located in the Tianshuihai terrane (Western Kunlun orogenic belt), is hosted in the Tianshuihai Group, a dominantly submarine siliciclastic and carbonate sedimentary succession that generally has been metamorphosed to greenschist facies. Iron oxide (hematite), carbonate (siderite, ankerite, dolomite and calcite) and silicate (muscovite) facies are all present within the iron-rich layers. There are three distinctive sedimentary facies BIFs, the oxide, silicate–carbonate–oxide and carbonate (being subdivided into ankerite and siderite facies BIFs) in the Dahongliutan BIF. They demonstrate lateral and vertical zonation from south to north and from bottom to top: the carbonate facies BIF through a majority of the oxide facies BIF into the silicate–carbonate–oxide facies BIF and a small proportion of the oxide facies BIF.The positive correlations between Al2O3 and TiO2, Sc, V, Cr, Rb, Cs, Th and ∑REE (total rare earth element) for various facies of BIFs indicate these chemical sediments incorporate terrigenous detrital components. Low contents of Al2O3 (<3wt%), TiO2 (<0.15wt%), ∑REE (5.06–39.6ppm) and incompatible HFSEs (high field strength elements, e.g., Zr, Hf, Th and Sc) (<10ppm), and high Fe/Ti ratios (254–4115) for a majority of the oxide and carbonate facies BIFs suggest a small clastic input (<20% clastic materials) admixtured with their original chemical precipitates. The higher abundances of Al2O3 (>3wt%), TiO2, Zr, Th, Cs, Sc, Cr and ∑REE (31.2–62.9ppm), and low Fe/Ti ratios (95.2–236) of the silicate–carbonate–oxide facies BIF are consistent with incorporation of higher amounts of clastic components (20%–40% clastic materials). The HREE (heavy rare earth element) enrichment pattern in PAAS-normalized REE diagrams exhibited by a majority of the oxide and carbonate facies BIFs shows a modern seawater REE signature overprinted by high-T (temperature) hydrothermal fluids marked by strong positive Eu anomalies (Eu/Eu∗PAAS=2.37–5.23). The low Eu/Sm ratios, small positive Eu anomaly (Eu/Eu∗PAAS=1.10–1.58) and slightly MREE (middle rare earth element) enrichment relative to HREE in the silicate–carbonate–oxide facies BIF and some oxide and carbonate facies BIFs indicate higher contributions from low-T hydrothermal sources. The absence of negative Ce anomalies and the high Fe3+/(Fe3+/Fe2+) ratios (0.98–1.00) for the oxide and silicate–carbonate–oxide BIFs do not support ocean anoxia. The δ13CV-PDB (−4.0‰ to −6.6‰) and δ18OV-PDB (−14.0‰ to −11.5‰) values for siderite and ankerite in the carbonate facies BIF are, on average, ∼6‰ and ∼5‰ lower than those (δ13CV-PDB=−0.8‰ to +3.1‰ and δ18OV-PDB=−8.2‰ to −6.3‰) of Ca–Mg carbonates from the silicate–carbonate–oxide facies BIF. This feature, coupled with the negative correlations between FeO, Eu/Eu∗PAAS and δ13CV-PDB, imply that a water column stratified with regard to the isotopic omposition of total dissolved CO2, with the deeper water, from which the carbonate facies BIF formed, depleted in δ13C that may have been derive from hydrothermal activity.Integration of petrographic, geochemical, and isotopic data indicates that the silicate–carbonate–oxide facies BIF and part of the oxide facies BIF precipitated in a near-shore, oxic and shallow water environment, whereas a majority of the oxide and carbonate facies BIFs deposited in anoxic but Fe2+-rich deeper waters, closer to submarine hydrothermal vents. High-T hydrothermal solutions, with infusions of some low-T hydrothermal fluids, brought Fe and Si onto a shallow marine, variably mixed with detrital components from seawaters and fresh waters carrying continental landmass and finally led to the alternating deposition of the Dahongliutan BIF during regression–transgression cycles.The Dahongliutan BIF is more akin to Superior-type rather than Algoma-type and Rapitan-type BIF, and constitutes an additional line of evidence for the widespread return of BIFs in the Cryogenian and Ediacaran reflecting the recurrence of anoxic ferruginous deep sea and anoxia/reoxygenation cycles in the Neoproterozoic. In combination with previous studies on other Fe deposits in the Tianshuihai terrane, we propose that a Fe2+-rich anoxic basin or deep sea probably existed from the Neoproterozoic to the Early Cambrian in this area.

Changes in depositional environment for the past 35 years in the Thane Creek, central west coast of India: inferences from REEs, metals and magnetic properties

The role of diagenetic processes in influencing the behaviour of metals (Fe, Mn, Cu, Ni, Zn), rare earth elements (REEs) and environmental magnetic parameters in two sediment cores from a polluted creek environment (the Thane Creek, Mumbai) was investigated. The sediment age was determined using 210Pb analysis. Silty clays were dominant sediments in both the cores. Mineralogy showed the presence of quartz, calcite and plagioclase feldspar in bulk sediments, while smectite was the abundant clay mineral in the finer fraction. The mean ΣREE in both the cores was lower than in post-Archaean average Australian shale (PAAS). The PAAS-normalized REE patterns showed MREE and HREE enrichment with strong positive Eu and Y anomalies. The source rocks in the hinterland played an important role on the REE composition. Magnetic mineralogy showed dominance of magnetite. Both the cores showed low magnetic concentration of Al, Ti, Fe and Mn coinciding with high magnetic grain size at the middle portions. The early diagenetic changes at the middle portion of the cores were masked by significant abundance of clay content at the creek head and with OC and fine magnetite at the lower creek region. Metals (Cu, Ni, Zn; enrichment factor >1.5) and magnetic concentration in sediments were enriched in both the cores suggesting of an anthropogenic source.

Distribution and fractionation of rare earth elements and Yttrium in suspended and bottom sediments of the Kali estuary, western India

Concentrations of rare earth elements (REE) and yttrium (Y), and major metals (Al, Fe and Mn) were measured in suspended particulate matter (SPM) and bottom sediments of the Kali estuary, western India, for their distribution and fractionation. The contents of SPM and metals in it were more uniform along the longitudinal transect during the monsoon. During the post- and pre-monsoons, low SPM in the upper/middle estuary coincided with high Fe and Mn and total REE (∑REE). But in the lower estuary SPM and its ∑REE content increased seaward, while Fe and Mn decreased. The Y/Ho ratios decreased seaward during the monsoon but increased during the post-monsoon. Sm/Nd ratios were more uniform along the transect during monsoon but decreased marginally seaward in other seasons. The Post-Archean Average Australian Shale (PAAS)-normalized REE patterns exhibited middle REE and heavy REE enrichment with positive Ce ($${\text{Ce}}/{\text{Ce}}^{*}$$ ), Eu ($${\text{Eu}}/{\text{Eu}}^{*}$$ ) and Y anomalies. The $${\text{Ce}}/{\text{Ce}}^{*}$$ increased but $${\text{Eu}}/{\text{Eu}}^{*}$$ decreased marginally seaward. The fine-grained sediments showed higher ∑REE and lower Y/Ho ratios than in coarse-grained sediments. The PAAS-normalized REE patterns of sediment were similar to that of SPM. The results revealed two processes, colloidal flocculation and coagulation of metals in the low-salinity zone and an estuarine turbidity maximum in the high salinity zone. Rare earths and yttrium (REY) in SPM and sediments primarily reflected the source rock composition than that of chemical weathering. Apart from physico-chemical processes, the mineralogy and grain size of sediments controlled the distribution and fractionation of REY in the estuary.

Anthropogenic rare earth elements and their spatial distributions in the Han River, South Korea

Rare earth elements (REE) consist of lanthanides (from La to Lu), together with yttrium and scandium, in which anthropogenic REE, such as gadolinium (Gd), lanthanum (La), and samarium (Sm), has emerged as micro-contaminants in natural waters in highly developed countries. Here, we collected water samples in the Han River (HR) and its tributaries flowing through Seoul Capital Area, the world's second largest metropolitan area in order to examine how and to what extent anthropogenic REE anomalies may occur. Water samples show higher light REE concentrations than heavy REE concentrations, while wastewater treatment plant (WWTP) samples display much higher heavy REE concentrations due to high Gd concentration. The PAAS-normalized REE patterns indicate that WWTP samples display the pronounced positive Gd anomalies, in which anthropogenic Gd from magnetic resonance imaging (MRI) diagnostic system occurs as a form of Gd complexation with either Cl− or SO42−. Due to the WWTP, both the HR and tributaries show also positive Gd anomalies and the anthropogenic Gd concentrations increase as a function of the distance from the Paldang dam. This result indicates a positive correlation between populaton, number of MRI instruments, and positive Gd anomaly. Similarly, positive La and Sm anomalies exist in the HR, indicating that the HR is also affected by their point sources. Based on the discharge rate and anthropogenic REE concentrations, their fluxes are estimated to be 952 ± 319 kg/yr, suggesting that this amount of fluxes could disturb REE distribution in the Yellow Sea, and pose harmful effects on aquatic ecosystems.

Natural and anthropogenic sources of atmospheric dust at a remote forest area in Guizhou karst region, southwest China

The abundance and distribution patterns of Rare Earth Elements (REE) in atmospheric dust in a typical karst forest area of the Maolan National Nature Reserve Park in Southwest China were determined during the period from May 2009 to January 2011. Total REE concentrations (ΣREE) recorded moderate seasonal variation, ranging from 31.0 mg kg −1 to 88.2 mg kg −1 , with an average of 53.5 mg kg −1 , similar to the ΣREE of local topsoil. The values of ΣREE were negatively correlated with the corresponding dust deposition fluxes, which may be due to different rates of deposition as a function of particulate size. PAAS-normalized REE patterns of the dust showed slightly positive Ce anomalies and enrichment in light REE. Most dust samples had similar PAAS-normalized REE patterns to local topsoil, whereas others were similar to the anthropogenic input material from urban areas.

Preliminary Data of REE in Algerian Phosphorites: A Comparative Study and Paleo-redox Insights

This study deals with the preliminary data of rare earth elements (REE) obtained on northeastern Algerian phosphorites from the Tébessa region. These phosphorites are located in two different basins: the northern basin represented by Dj. El Kouif, Dj. Dyr and Tazbant showings and the southern basin with the giant Dj. Onk phosphate deposit. The host sedimentary formation is Late Paleocene to Early Eocene. Twenty-six (26) samples from the four (4) localities were collected and analyzed for their REE contents using the ICP-MS technique. Phosphates from the southern basin (Dj. Onk deposit) show ∑REE contents ranging from 174.41 and 906.39ppm (average ∑REE = 623.01ppm), while the northern phosphorites have lower ∑REE contents (from 125.45 to 472.44ppm; average = 265.57ppm). PAAS-normalized REE patterns and binary Box plot of (Sm/Pr)N vs (Sm/Yb)N show HREE enrichments for samples from the northern localities while most samples from the southern basin are HREE depleted. Normalized (La/Yb)N vs (La/Sm)N plot shows that (La/Sm)N ratios of all samples are similar to those of modern seawater (from 0.83 to 1.55). However, the (La/Yb)N ratios of the two basins are significantly higher (from 0.67 to 1.18), which indicates an early diagenesis. The Ce/Ce* vs Pr/Pr* diagram shows that the observed Ce anomaly was not affected by diagenesis and more likely represents a proxy for redox conditions. The obtained results substantiate that the northern phosphorites were formed in more oxic environment with more pronounced negative Ce anomalies, whereas the southern phosphorites have lower Ce anomalies. Northern phosphorites are different from those from the south probably because the northern basin was more connected to an open sea as did the Sra Ouartan basin in northern Tunisia. These results have also been confirmed by statistical method studies, such as factorial discriminate analysis.

Geochronology and geochemistry of the Nanfen iron deposit in the Anshan-Benxi area, North China Craton: Implications for ∼2.55 Ga crustal growth and the genesis of high-grade iron ores

The Nanfen iron deposit, situated in the Anshan-Benxi area of the North China Craton (NCC), hosts scattered banded iron formations (BIFs) and BIF-hosted high-grade iron orebodies (defined by FeOT>80wt.%). The associated roof and bottom rocks, which occur in parallel to orebodies, are mica quartz schist and chlorite hornblende schist (locally interlayers), respectively. The PAAS-normalized rare earth element (REE) patterns indicate that quartz–magnetite banded iron formations (BIFs) are enriched in Heavy REEs with positive La, Eu and Y anomalies, indicating that the Nanfen BIF precipitated from a mixture of ambient seawater and submarine high-T hydrothermal fluids (∼0.1%). In addition, the BIF exhibits low concentrations of Al2O3 and TiO2 with depletion in HFSEs (high field strength elements, e.g., Nb, Ta, Zr, Hf and Ti), suggesting little contamination with continental detritus. Excepting lower Eu/Eu* values, the high-grade iron ores display similar geochemical features to the BIF, likely implying that they have a same iron source but did not form synchronously. Electron microprobe analyses (EMPA) and in situ LA-ICP-MS analyses reveal that in relative to the magnetite grains in high-grade ores, the magnetite grains in the BIF contain higher MnO, MgO and Zn concentrations, and lower Al2O3 and REE abundances, implying different formation conditions. Thus, we argue that high-grade ores are likely to be alteration products of primary BIFs. Chlorite hornblende schist (meta-basalt) samples exhibit low SiO2 contents (43.78–50.30wt.%) with flat chondrite-normalized REE and N-MORB-normalized trace element patterns, which are similar to those of BABB (back-arc basin basalt). The zircon U–Pb dating results indicate that magmatic and metamorphic zircons from chlorite hornblende schist formed at approximately 2552Ma and 2482Ma, respectively. The former volcanic age could constrain the deposition age of the Nanfen BIF, and the latter reflects a subsequent metamorphic event, which is also reflected by the ∼2480Ma hydrothermal zircons selected from the BIF. Moreover, most zircons from chlorite hornblende schist have positive ɛHf(t) values (0.22–7.96) close to the depleted mantle evolutionary curve, implying that the source magma were derived from a depleted mantle with some contamination from ancient crust. Hence, we propose that the Nanfen BIF is a Neoarchean Algoma-type BIF, and its deposition was most likely benefited due to crustal growth.

북동태평양 Clarion-Clipperton 해역 표층 퇴적물의 희토류 조성 및 희토류 광상으로서의 잠재성

The surface sediments from the manganese nodule exploration area of Korea in the Clarion-Clipperton fracture zone were investigated to understand the resource potential of and emplacement mechanism for rare earth elements (REEs). The sediments are categorized into three lithological units (Unit I, II and III from top to bottom), but into two groups (Unit I/II and Unit III) based on the distribution pattern of REEs. The distribution pattern of REEs in Unit I/II is similar to that of Post-Archean Australian Shale (PAAS), but shows a negative Ce anomaly and enrichment in heavy REEs (HREEs). In Unit III, the HREE enrichment and Ce anomaly is much more remarkable than Unit I/II when normalized to PAAS, which are interpreted as resulting from the absorption of REEs from seawater by Fe oxyhydroxides that were transported along the buoyant plume from remotely-located hydrothermal vents. It is supported by the PAAS-normalized REE pattern of Unit III which is similar to those of seawater and East Pacific Rise sediments. Meanwhile, the PAAS-normalized REE pattern of Unit I/II is explained by the 4:1 mixing of terrestrial eolian sediment and Unit III from each, indicating the much smaller contribution of hydrothermal origin material to Unit I/II. The studied sediments have the potentiality of a low-grade and large tonnage REE resource. However, the mining of REE-bearing sediment needs a large size extra collecting, lifting and treatment system to dress and refine low-grade sediments if the sediment is exploited with manganese nodules. It is economically infeasible to develop low-grade REE sediments at this moment in time because the exploitation of REE-bearing sediments with manganese nodules increase the mining cost.