Distinct Rare Earth Element Research Articles

Apatite trace element geochemistry and cathodoluminescent textures—A comparison between regional magmatism and the Pea Ridge IOAREE and Boss IOCG deposits, southeastern Missouri iron metallogenic province, USA

The southeast Missouri iron metallogenic province contains a remarkable wealth of historically important Fe, Cu, Au, and rare earth element (REE) deposits including the Pea Ridge iron oxide-apatite-rare earth element (IOA-REE) deposit and the Boss iron oxide-copper–gold (IOCG) deposit. These deposits are coeval with silicic and intermediate composition magmatism in the St. Francois Mountains terrane. Magmatism, iron-oxide (±Cu, Au, Co) and apatite formation, and REE mineralization overlapped in space and time, but the specific role of regional magmatism in the metallogenesis of these deposits remains unclear and basic petrogenetic models are still debated.We report results from high-spatial resolution textural and geochemical analyses of apatite from regional igneous and ore rocks to elucidate their petrogenetic histories and evaluate deposit models. Backscattered electron and spectral cathodoluminescence imaging of apatite reveal no primary igneous zoning, but show different domains with intricate rims and dissolution/reprecipitation textures, each with distinctive REE patterns in many samples. Apatite from all samples are nearly endmember fluorapatite containing up to ∼1.3 wt% Cl and F/Cl ratios span nearly three orders of magnitude. Fresh igneous fluorapatite contain low Na2O (≤0.15 wt%) while most Pea Ridge ore samples contain higher Na2O (up to ∼0.45 wt%), and concentrations of sulfur in fluorapatite of all types are generally moderate to low (≤0.3 wt% SO3). Significant amounts of Fe (≤60,000 ppm), Mg (≤30,000 ppm), Mn (≤7000 ppm), and Sr (≤12,000 ppm) are contained in fluorapatite of all sample types, and they also have moderate amounts of As (≤4000 ppm), Ba (≤2000 ppm), Th (≤400 ppm), and U (≤80 ppm). Fluorapatite show an extraordinarily large range of ΣREE (∼0.1–2.0 wt%) and Y (∼100–7000 ppm) concentrations. While fresh igneous fluorapatite share many geochemical features with metasomatized igneous fluorapatite and ore-stage fluorapatite from the Pea Ridge IOA and Boss IOCG ore zones, they also have distinct geochemical signatures that are indicative of unique trace element partitioning and substitution mechanisms. These distinguishing textural and geochemical signatures preclude ore-zone fluorapatite genesis directly from a magma (i.e., crystallization directly from a silicate melt) but are permissive of ore-zone fluorapatite formation by magmatic-hydrothermal fluids derived from the regional magmas. Basinal brines may play an important role in the formation of fluorapatite, especially from the Pea Ridge hematite and Boss magnetite-rich zones. Fluorapatite from different ore zones likely formed by crystallization during pulses of hydrothermal fluids with varying Cl-, Na-, and F-contents, which fundamentally controlled the carrying capacity and solubility of ΣREE + Y and generated geochemically distinctive generations of fluorapatite.Exploration geologists using fluorapatite trace element geochemistry to identify IOA and IOCG deposits should proceed with caution, as more high-quality data from these deposits are needed to improve multivariate discrimination analysis. Fluorapatite from IOA/IOCG deposits can be reasonably discriminated from that of other mineral deposit types (e.g., porphyry/epithermal, skarn, orogenic), but no criteria successfully discriminate yet between IOA and IOCG deposits.

Magma Replenishment as Revealed by Textural and Geochemical Features of Plagioclase Phenocrysts in Subduction‐Related Lavas

Various petrographic features and geochemical characteristics indicative of disequilibrium are preserved in plagioclase phenocrysts from basaltic to andesitic lavas in East Junggar, northwest China. These characteristics indicate that they crystallized in a magma chamber, which was replenished by less differentiated and high‐temperature magmas. The petrographic and geochemical features of the plagioclase phenocrysts are interpreted to record responses to changes in temperature, composition and mechanical effect during magma replenishment. Distinct rare earth element (REE) patterns between cores and rims of the same plagioclase crystal suggest derivation from two end‐member magmas. From core to rim, plagioclase phenocrysts commonly display sharp fluctuations of anorthite (An) content up to 20, which either correspond to reverse zoning associated with ovoidal cores and resorption surface (P1), or normal zoning with euhedral form and no resorption surface (P2). Plagioclase crystals with diverse textures and remarkably different An content coexist on the scale of a thin‐section. Cores of these plagioclases in each sample display a bimodal distribution of An content. From core to rim in P1, concentrations of FeOT and Sr increase remarkably as An content increases. During magma replenishment, pre‐existing plagioclase phenocrysts in the andesitic magma, which were immersed into hotter and less differentiated magmas, were heated and resorbed to form ovoidal cores, and then were overgrown by a thin rim with much higher contents of An, FeOT and Sr. However, pre‐existing plagioclase phenocrysts in the basaltic magma were injected into cooler and more evolved magmas, and were remained as euhedral cores, which were later enclosed by oscillatory zoned rims with much lower contents of An, Sr and Ba.

Fluid evolution of Triassic and Jurassic W mineralization in the Xitian ore field, South China: Constraints from scheelite geochemistry and microthermometry

Rare earth element (REE)-enriched scheelite is widely distributed in many ore deposits, and has been utilized in a broad range of geochronological and geochemical studies. In an effort to decipher skarn and quartz vein-hosted W mineralization process, scheelite from Triassic and Jurassic granites, skarn ores and quartz vein-hosted ores in the Xitian ore field (South China) were analyzed for major and minor element content and fluid inclusion microthermometry. All scheelite grains show homogeneous backscatter electron and cathodoluminescence response and uniform W and Ca distribution. The chondrite-normalized REE patterns of scheelite from Triassic granites to skarn ores show similar Pr–Sm-enrichments and negative Eu anomalies but different HREE contents. In contrast, the chondrite-normalized REE patterns of scheelite from Jurassic granites to quartz vein-hosted ores changes from flat with slight LREE enrichment, to concave with remarkable LREE depletion. The homogenization temperatures and salinities of fluid inclusions from the scheelite in Triassic granites and skarn ores are similar, both reduce significantly from the Jurassic granites to quartz vein-hosted ores. Combined with pressure, pH and mineral assemblage analysis, we propose that the REE signatures in the ore-forming fluids of skarn-type W deposits are mainly controlled by crystallization of REE-enriched skarn minerals (e.g., garnet, diopside, epidote). The similarity in LREE patterns and Y/Ho ratios between the Triassic granite and skarn ore scheelite indicates that the skarn ore-forming fluid was derived from the Triassic granite, while the distinct REE patterns and variable Y/Ho ratios in scheelite from Jurassic granites and quartz vein-hosted ores imply possible fluid-mixing for Jurassic W mineralization. In light of these results, REE-rich scheelite could serve to discriminate fluid source and document mineralization processes in a complex ore-forming system.

Allanite Petrochronology in Fresh and Retrogressed Garnet–Biotite Metapelites from the Longmen Shan (Eastern Tibet)

Linking the timing of allanite growth to metamorphic conditions in metapelites is particularly chal-lenging because of the large variety of allanite textures and chemical compositions. This studyfocuses on five garnet–biotite metapelites retrogressed to different extents, from the internal do-main of the Longmen Shan (eastern Tibet) from which few petrochronological data documentingthe metamorphic ages are available. Microstructural observations were combined with whole-rockcompositions, detailed mineral characterization, phase equilibria modelling, andin situU–Th/Pb al-lanite dating to gain insights into the allanite reactivity relative to other rock-forming minerals. Allsamples experienced similar peak temperatures of 560–600C. Allanite is the main rare earth elem-ent (REE)-bearing accessory mineral but it exhibits different textures, such as epidote rims with dis-tinct REE contents as well as late inclusion-like dissolution features. Garnet is, along with allanite,critical to reconstruct the REE budget of these rocks. In the two samples where allanite is observedas inclusions in garnet, garnet shows no textural zoning and a low Y content ( 520C). Thisrelative chronology is confirmed byin situU–Th/Pb allanite dating: pre-garnet allanite shows agesofc.200 Ma, whereas syn- to post-garnet allanite has ages ofc.180 Ma. The timing of allanite ap-pearance strongly correlates with the biotite-in reaction predicted by the models and observed inmicrostructures. In the two samples collected close to the major Wenchuan Shear Zone—deformedup to mylonitization and retrogressed under greenschist-facies conditions (3–461 kbar, 350–400C)—allanite still preserves the peak metamorphic ages (c.200 andc.180 Ma). Allanite and itsepidote rims, however, are fragmented and partly replaced by a retrograde assemblage of QzþPb-depleted (<100 ppm) monazite, providing an age<90–100 Ma. Our results allow different meta-morphic stages for the studied transect in the central Longmen Shan to be refined: a prograde pathatc.200 Ma, a thermal relaxation and exhumation fromc.180 Ma, and a late greenschist overprint.This study also shows that when allanite is the principal phase in a mineral assemblage datable byU–Th/Pb, detailed observations of allanite textures may be highly informative in constraining thetiming of its growth relative to other major mineral phases.

Rare Earth Element Labeling as a Tool for Assuring the Origin of Eggs and Poultry Products

Laying hens were fed terbium and thulium supplemented feed in order to introduce a distinctive rare earth element pattern that allows discrimination of labeled from unlabeled poultry products. Samples of egg yolk, egg shells, meat, bones, liver, blood, and feces were analyzed using either conventional or laser ablation inductively coupled plasma mass spectrometry. Already after a short time of administering supplemented feed, terbium and thulium enrichment could be unambiguously detected in the products, while absolute terbium and thulium contents remained low enough to ensure safety for the customer. This method could potentially be applied to specifically label foodstuffs produced in certain regions or under certain conditions, in order to ensure food authenticity.

In situ geochemistry of middle Ordovician dolomites of the upper Mississippi valley

AbstractThe dolomitization and diagenetic history of Ordovician carbonates of southern Wisconsin is complex. Previous studies attributed dolomitization to various diagenetic factors and environments. In this study, high‐resolution, in situ laser ablation inductively coupled mass spectrometry analysis of rare earth element patterns of dolomite was used to assess the diagenetic fluids responsible for dolomitization of the Ordovician Decorah Formation. Integrated geochemical data and petrographic evidence suggest that the dolostones are formed in two different diagenetic realms: shallow burial and hydrothermal. Shallow burial dolomites exhibit three distinct rare earth element patterns. Dolomite from the middle portion of the Guttenberg Member exhibits light rare earth element enrichment consistent with early burial dolomitization. Dolomites of the Carimona, Specht's Ferry and Lower Guttenberg members are often burrow associated and exhibit medium rare earth element enrichment associated with Fe‐oxide desorption in anoxic porewaters. Leaching of Mg from co‐occurring volcanic ash during alteration is a probable source that contributed to the dolomitization. Extensively dolomitized samples in the upper Guttenberg and Ion Member exhibit evidence of hydrothermal dolomitization. The relationship of these heavily dolomitized samples to interbedded limestones provides evidence for a recently proposed hydrothermal dolomitization model invoking pressure solution of calcite and precipitation of dolomite. These early burial and hydrothermal depositional models are consistent with models proposed for overlying and underlying Ordovician dolostones.

Fractionation process of high-silica magmas through the lens of zircon crystallization: A case study from the Tengchong Block, SW China

The generation of high-silica magma is generally considered to occur as a result of liquid-crystal segregation from a crystal mush. Yet whether high-silica melts could undergo significant fractionation process after the segregation remains unclear. This study contributes to this topic through the lens of zircon geochemistry of the ~130 Ma high-silica granite in the Tengchong block, SW China. The high-silica granite, with SiO2 ~76%, displays low Zr/Hf and EuN/Eu*N, and high Rb/Sr ratios. The zircons crystallized from the granite can be divided into two groups. The group 1 zircons are characterized by lower Hf (<12,200 ppm), and show relatively lower U (710–1103 ppm, averaging 891 ppm) and Yb (688–1106 ppm, averaging 903 ppm), and higher EuN/Eu*N (0.11–0.18). By contrast, the group 2 zircons have higher Hf (>12,200 ppm), and display elevated U values (936–2429 ppm, averaging 1557 ppm) and Yb values (755–1556 ppm, averaging 1134 ppm), as well as lower EuN/Eu*N (0.01–0.1). The increasing Hf content from group 1 to group 2 zircons, presence of fluorite inclusions in high-Hf zircon, and similarity in Hf isotope between the two groups of zircon consistently support the high-silica granite has witnessed a highly fractionated crystallization process. The presence of these two groups of zircons is considered to reflect two-stage in-situ fractionation processes, which display distinct REE (rare earth elements) compositions in the magma system in response to differing precipitated mineral assemblages. In light of the change of zircon REE within each group, the percentage of minerals co-precipitating with zircons in each stage was estimated. The results showed that 35.24% quartz, 18.60% feldspar, 0.25% apatite, 0.14% zircon, 0.12% allanite, and 0.05% titanite fractionated in the early stage, and 67.50% quartz, 23.41% feldspar, 0.15% zircon, 0.10% allanite, 0.07% apatite, and 0.06% titanite fractionated in the second stage. The discovery of different zircons and corresponding estimation in this study provide a new line of evidence for the fractionation of high-silica melt.

Soil geochemistry as a tool for the origin investigation and environmental evaluation of urban parks in Mashhad city, NE of Iran

The total concentration of major oxides and trace elements, sequential extraction of heavy metals, and Pb isotope signatures of park soils were investigated in Mashhad, the largest city in northeastern Iran. The geochemical characteristics of park soils show two different trends: high silica soils (HSS) and low silica soils (LSS). The elements such as Mg, Fe, As, Co, Cr, Cu, Mn, Ni, Pb, Sn, and Zn were concentrated in LSS, while HSS samples were enriched of Si, Ga, Li, Nb, Ta, Th, U, Y, Z, and rare-earth elements (REE). The REE composition and chondrite—normalized patterns of LSS [low ∑REE (20–68 mg kg−1) and low LaN/YbN (1.9–7.4)]—are compatible with ultramafic-derived soils. The HSS samples display distinct REE composition with high ∑REE (102–336 mg kg−1) and LaN/YbN (13–51) which would be originated from granitoid, metamorphic, and sedimentary derived soils. The available percentage of heavy metals in the park soils is much higher than natural samples. The Pb characteristics of park soils are distinct from natural soils. These samples are less radiogenic than natural soils with lower 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 206Pb/207Pb, and higher 208Pb/206Pb ratios. The calculated contributions of possible sources in Mashhad park soils release 6.6 and 93.4% for natural and anthropogenic (industrial and leaded petrol) sources, respectively. The central parks exhibit the highest pollution of heavy metals in Mashhad indicating high traffic intensity in this area. The concentration of potentially toxic elements in the surface soils of Mashhad parks is lower than the national maximum permissible concentration, but many of them such as Cd, Cu, Mo, Pb, Sn, Se, and Zn are highly enriched relative to non-urban soils.

Rare earth element tetrad effect and negative Ce anomalies of the granite porphyries in southern Qiangtang Terrane, central Tibet: New insights into the genesis of highly evolved granites

Highly evolved granites are geochemically similar to the mature continental crust, and are sometimes associated with W-Sn-Nb-Ta and rare-metal mineralizations. These rocks have important implications for tracing the compositional evolution of continental crust and magma metallogenesis. They were commonly considered to have been produced by partial melting of crustal materials or by high-degree fractional crystallization.In this study, we report on high SiO2 granite porphyries in the Xiabie Co area of southern Qiangtang Terrane, central Tibet, which provide new insights into the petrogenesis of the highly evolved granites. Zircon dating results indicate that they were generated in the late Early Cretaceous (107 ± 1 Ma). They consist mainly of orthoclase, albite, and quartz, with accessory minerals including zircon, fluorite, and Fe-Ti oxides. Geochemically, they have high SiO2 but low MgO, Fe2O3T, CaO, and P2O5, and are enriched in Rb but depleted in Ba, Sr, Eu, and Ti, similar to highly evolved granitic rocks. They are characterized by distinct rare earth element (REE) tetrad effects and negative Ce anomalies. They also have slightly higher εNd (t) values (−0.99 to −0.36) than those of the adjacent early granites (−2.05 to −3.01), and relatively high and variable zircon εHf(t) values ranging from −0.3 to +5.4. Compared to typical highly evolved granites and petrological experiment data, we suggest that the Xiabie Co granite porphyries represent highly evolved melts produced by fractional crystallization. The interaction between fractionated melts and F-rich aqueous fluids played an important role in the genesis of their REE tetrads effect. Involvement of meta-sedimentary rocks that went through surficial chemical weathering into their source region is the predominant reason for the generation of negative Ce anomalies. This indicates that, in addition to fractional crystallization, the melt-fluid interactions and partial melting of source materials also play important roles in the generation of highly evolved granites.

On the way to ‘zero waste’ management: Recovery potential of elements, including rare earth elements, from fine fraction of waste

Abstract Existing schemes of solid waste handling have been improved implementing advanced systems for recovery and reuse of various materials. Nowadays, the ‘zero waste’ concept is becoming more topical through the reduction of disposed waste. Recovery of metals, nutrients and other materials that can be returned to the material cycles still remain as a challenge for future. Landfill mining (LFM) is one of the approaches that can deal with former dumpsites, and derived materials may become important for circular economy within the concept ‘beyond the zero waste’. Perspectives of material recovery can include recycling of critical industrial metals, including rare earth elements (REEs). The LFM projects performed in the Baltic Region along with a conventional source separation of iron-scrap, plastics etc. have shown that the potential of fine-grained fractions (including clay and colloidal matter) of excavated waste have considerably large amounts of potentially valuable metals and distinct REEs. In this paper analytical screening studies are discussed extending the understanding of element content in fine fraction of waste derived from excavated, separated and screened waste in a perspective of circular economy. Technological feasibility was evaluated by using modified sequential extraction technique where easy extractable amount of metals can be estimated. Results revealed that considerable concentrations of Mn (418–823 mg/kg), Ni (41–84 mg/kg), Co (10.7–19.3 mg/kg) and Cd (1.0–3.0 mg/kg) were detected in fine fraction (

The Influence of Basaltic Islands on the Oceanic REE Distribution: A Case Study From the Tropical South Pacific

The Rare Earth Elements (REEs) have been widely used to investigate marine biogeochemical processes as well as the sources and mixing of water masses. However, there are still important uncertainties about the global aqueous REE cycle with respect to the contributions of highly reactive basaltic minerals originating from volcanic islands and the role of Submarine Groundwater Discharge (SGD). Here we present dissolved REE concentrations obtained from waters at the island-ocean interface (including SGD, river, lagoon and coastal waters) from the island of Tahiti and from three detailed open ocean profiles on the Manihiki Plateau (including neodymium (Nd) isotope compositions), which are located in ocean currents downstream of Tahiti. Tahitian fresh waters have highly variable REE concentrations that likely result from variable water–rock interaction and removal by secondary minerals. In contrast to studies on other islands, the SGD samples do not exhibit elevated REE concentrations but have distinctive REE distributions and Y/Ho ratios. The basaltic Tahitian rocks impart a REE pattern to the waters characterized by a middle REE enrichment, with a peak at europium similar to groundwaters and coastal waters of other volcanic islands in the Pacific. However, the basaltic island REE characteristics (with the exception of elevated Y/Ho ratios) are lost during transport to the Manihiki Plateau within surface waters that also exhibit highly radiogenic Nd isotope signatures. Our new data demonstrate that REE concentrations are enriched in Tahitian coastal water, but without multidimensional sampling, basaltic island Nd flux estimates range over orders of magnitude from relatively small to globally significant. Antarctic Intermediate Water (AAIW) loses its characteristic Nd isotopic signature (-6 to-9) around the Manihiki Plateau as a consequence of mixing with South Equatorial Pacific Intermediate Water (SEqPIW), which shows more positive values (-1 to -2). However, an additional Nd input/exchange along the pathway of AAIW, eventually originating from the volcanic Society, Tuamotu and Tubuai Islands (including Tahiti), is indicated by an offset from the mixing array of AAIW and SEqPIW to more radiogenic Nd isotope compositions.

Mineralogical and Geochemical Discrimination of the Occurrence and Genesis of Palygorskite in Eocene Sediments on the Northeastern Tibetan Plateau

AbstractPalygorskite is a widely used indicator of semiarid to arid environments in paleoclimate studies. In this study, we present detailed mineralogical and geochemical investigations exploring the genesis of palygorskite found in Eocene fluvial sediment in the northern Qaidam Basin on the northeastern Tibetan Plateau. The presence of two types of palygorskite is revealed, based on their crystallinity characteristics and distinctive rare earth element (REE) patterns in the coexisting clay fraction. Well‐crystallized palygorskite samples are characterized by remarkably negative Ce anomalies and obvious middle rare earth element enrichment. Poorly crystallized palygorskite samples generally exhibit positive Ce anomalies and less pronounced middle rare earth element enrichment, which resemble those of nonpalygorskite‐bearing clay samples. Given the presence of an overall oxidized fluvial sedimentary environment, we attribute the well‐crystallized palygorskite (which has textures comprising long, interwoven fibers) to direct precipitation (i.e., neoformation) occurring within a reducing environment during early/postdepositional processes while the poorly crystallized palygorskite (which is characterized by short, club‐shaped single crystals) originates as catchment‐delivered detritus. These poorly crystallized palygorskites occur mostly in 49.5–47.0 Ma and are accompanied by decreasing kaolinite content, increasing chlorite content, and abundant xerophytic spore‐pollen from the Qaidam Basin, and its neighboring Xining Basin. Collectively, these evidences suggest that a less humid climate followed after the Early Eocene Climate Optimum.

Indication of rare earth element characteristics to dolomite petrogenesis—A case study of the fifth member of Ordovician Majiagou Formation in the Ordos Basin, central China

Abstract Rare earth elements (REEs), as important geochemical tracers, can well reflect the information carried by diagenetic fluids. In this paper, petrological and REE characteristics are studied to investigate diagenetic fluid information and dolomite petrogenesis using samples from the fifth member of Ordovician Majiagou Formation (Ma5) in the Ordos Basin based on the comprehensive analysis of C, O, and Sr isotopes. Three types of dolomites are identified in the study area, namely the dolomicrite, micrite-silty dolomite, and silty dolomite. Different types of dolomites have distinct total REE contents, among which the dolomicrite has the highest average total REE content and that could be possibly attributed to the abundant algal and argillaceous materials. All the three types of dolomites are featured by lower total contents of REEs than marine micrite, enriched light rare earth elements (LREEs) and deficit heavy rare earth elements (HREEs), which could result from the constant diffusion of REEs in the late diagenetic environment as well as the stronger complexing capacity of HREEs than LREEs. REE partition patterns in three types of dolomites are similar to those in marine micrite, which indicate the dolomitization fluids to be seawater or marine-origin fluids. In the dolomicrite, an obvious negative Eu anomaly (average value 0.63) and a faint negative Ce anomaly (average value 0.94) suggest that the sedimentary environment should be featured by low temperature and weak oxidation. Meanwhile, negative δ13C excursion (average value - 1.23‰), positive δ18O excursion (average value −7.59‰), and high mean 87Sr/86Sr ratios (average value 0.70992) along with petrological characteristics demonstrate the dolomicrite to originate from penecontemporaneous dolomitization. In the micrite-silty dolomite, the obvious negative Eu anomaly (average value 0.69) and the medium negative Ce anomaly (average value 0.72) indicate such kind of dolomites should be formed in the sedimentary environment characterized by low temperature and weak oxidation-weak reduction. The negative δ13C excursion (average value −0.43‰), positive δ18O excursion (average value −7.29‰), and relatively low mean 87Sr/86Sr ratios (average value 0.70955) identify the micrite-silty dolomite to be product of seepage reflux dolomitization in the supratidal zone. In the silty dolomite, the weakened negative Eu anomaly (average value 0.75) indicates relatively high temperature, and the obvious negative Ce anomaly (average value 0.66) implies reducing environment. Based on analysis of values of δ13C (average value −0.65‰) and δ18O (average value −6.46‰) as well as ratios of 87Sr/86Sr (average value 0.70958), silty dolomite is regarded to form due to burial dolomitization.

Phase equilibria modelling using major and trace element compositions of zoned garnet and clinopyroxene from southwestern Tianshan eclogites, China

We present major and trace element zoning in clinopyroxene and garnet in the low-temperature eclogites from southwestern Tianshan ultrahigh-pressure metamorphic belt. The clinopyroxene crystals in the matrix exhibit three distinct growth zones, including the aegirine-rich core, a transition mantle and the omphacite rim. The aegirine core has weak Ce anomaly, flat light rare earth element pattern, and slightly enriched heavy rare earth element contents. The omphacite rim has lower trace element contents, and is depleted in large-ion lithospheric elements, light and heavy rare earth elements. The garnet zonation is featured by the core-to-rim increase in pyrope and grossular contents, and distinct rare earth element patterns: the core has left-leaning rare earth element patterns and the rim is depleted in both light and heavy rare earth elements. Phase equilibria modelling based on the phase assemblage and mineral zoning patterns reveal that the aegirine eclogite was heated and buried along the ca. 8°C/km geotherm in the cold subduction zone, and reached the peak metamorphic condition of 23–25kbar, 540–560°C. The jadeite content in the clinopyroxene increases along the prograde-to-exhumation P-T path (Jd: from 0.25 to 0.45), with the transitional mantle corresponds to the peak conditions. The omphacite rim with the highest jadeite content (Jd∼45) formed during decompression. For a Fe3+-rich clinopyroxene, the maximum in Jd component does not necessarily represent the peak pressure, so the conventional thermobarometers should be used with caution for mineral assemblages with such complicated zonation patterns. The variation of oxygen fugacity correlates with the changes in mineral assemblage, P-T condition, and the bulk-rock Fe3+/FeT ratio. The oxygen fugacity is not always positively correlated with the Fe3+/(Fe3++Al) or Fe3+/FeT ratio in clinopyroxene. Rare earth element zoning garnet and clinopyroxene are modelled based on mass balance. The modelled growth zonation closely resembles the observed compositional profiles, suggesting that rare earth elements are passively distributed among phases near chemical equilibrium during the mineral growth.

Using geochemistry of rare earth elements to indicate sediment provenance of sand ridges in southwestern Yellow Sea

The Jianggang Harbour-centered radial sand ridge (RSR) is the largest sand body in the Yellow Sea. Its formation and evolution are of interest for scientists of various fields; however, the sediment provenance is uncertain. In this study, rare earth element (REE) geochemical compositions of the RSR sediments together with their potential sources are investigated to identify the provenance of the RSR sediments. The typical parameters ((La/Yb)N, (La/Sm)N and (Gd/Yb)N) as well as the upper continental crust-normalized patterns of REEs can only be associated with source rocks, and thus can be used as effective tracers for the origin and sources of sediments. However, the REE contents of sediments are affected by many factors, such as particle sorting and chemical weathering. Onshore RSR sediments are different in REE geochemical composition from offshore RSR sediments to some extent, suggesting that not all of the offshore RSR sediments have the same sources as the onshore RSR sediments. Meanwhile, the sediments adjacent to the northeast of Cheju Island and at Lian Island near the Lianyun Harbour were not the source of the RSR sediments due to their distinctive REE patterns, δEu, (La/Yb)N, (Gd/Yb)N and (La/Sm)N. The Korean river sediments could be dispersed to the Jiangsu Coast slightly impacting the fine fractions of the RSR sediments, particularly the offshore RSR sediments. Additionally, geochemical comparisons show that the modern Yellow River was responsible for the onshore RSR sediments, whereas the sediment loads from the Yangtze River could serve as a major contributor to the RSR, particularly the offshore RSR. In addition, the offshore RSR could also be partly fed by an unknown source due to some high values of (La/Yb)N, (La/Sm)N and La contents differing from those of the Chinese and Korean river sediments.

The impact of transport processes on rare earth element patterns in marine authigenic and biogenic phosphates

Rare earth elements (REEs) are commonly used proxies to reconstruct water chemistry and oxygen saturation during the formation of authigenic and biogenic phosphates in marine environments. In the modern ocean REEs exhibit a distinct pattern with enrichment of heavy REEs and strong depletion in cerium (Ce). The wide range of REE enrichment patterns found in ancient marine phosphates lead to the proposition that water chemistry has been very different in the Earth’s past. However, both early and late diagenesis are known to affect REE signatures in phosphates altering primary marine signals.Herein we present a dataset of REE signatures in 38 grain specific LA-ICP-MS measurements of isolated phosphate and carbonate grains in three discrete rock samples. The phosphates mainly consist of authigenic phosphates and phosphatized microfossils that formed in a microbially mediated micro-milieu. In addition, isolated biogenic and reworked phosphatic grains are also present. The phosphates are emplaced in bioclastic grain- to packstones deposited on a carbonate ramp setting in the central Mediterranean Sea during the middle Miocene Monterey event. The results reveal markedly different REE patterns (normalized to the Post Archean Australian Shale standard) in terms of total enrichment and pattern shape. Analyses of REE diagenesis proxies show that diagenetic alteration affected the samples only to a minor degree. Grain shape and REE patterns together indicate that authigenic, biogenic and reworked phosphates have distinct REE patterns irrespective of the sample.Our study shows that while REE patterns in phosphates do reflect water chemistry during authigenesis, they are often already heavily altered during reworking, a process, which can occur in geologically negligible timespans. REE patterns are therefore more likely to reflect complex enrichment processes after their formation. Similarities in the REE patterns of reworked and biogenic phosphate further suggest that the frequently observed hat-shaped pattern in biogenic phosphates can result from increased middle REE (Neodymium to Holmium) scavenging during taphonomic processes prior to final deposition. Cluster analysis coupled with sedimentological and previously published geochemical data (bulk carbon isotope and X-ray fluorescence spectrometry) allowed the characterization of REE patterns of phosphates in terms of their formation conditions and depositional history, such as the distinction of phosphates formed in situ from reworked and transported phosphate grains.

Visible and short-wave infrared reflectance spectroscopy of REE phosphate minerals

Reflectance spectroscopy in the visible to short-wave infrared regions (500 to 2500 nm) was carried out using natural samples of the rare earth element (REE) phosphate minerals monazite, xenotime, and britholite. Samples were characterized by scanning electron microscopy and electron microprobe analysis. Absorption band positions were recorded with their probable origins, and spectral variability among the samples is discussed. Spectral features of these minerals are driven primarily by 4 f -4 f intraconfigurational electronic transitions of trivalent lanthanides. The distinct REE distributions of monazite, xenotime, and britholite drive their bulk spectral patterns, which in turn are sufficiently distinct to enable spectral classification. Spectral variability of some specific REE-related absorptions are interpreted to be driven by differences of the coordination polyhedra for the lanthanide cations between the crystal structures. Spectra of these minerals were also compared against carbonatite-hosted REE bearing fluorapatite. The work presented here strengthens the growing foundation for the interpretation of reflectance spectra of these REE phosphate minerals and enables exploitation of the observed features by the remote sensing community for detection, identification, and quantification of REE phosphate minerals. This is especially relevant for hyperspectral imaging spectroscopy with high spatial resolution, where the spectral response of a pixel becomes increasingly dominated by mineralogy.

Acidic drainage drives anomalous rare earth element signatures in intertidal mangrove sediments

Sedimentary rare earth element (REE) signatures can provide powerful insights into nearshore biogeochemical processes and anthropogenic influences. Despite this, there is limited research investigating REE behaviour in sediments influenced by coastal acid sulfate soils (CASS). Here, we explore REE abundance and fractionation in intertidal mangrove sediments that received CASS drainage for ~15–20y within the Hastings Catchment in NSW, Australia. Sediments close to the CASS discharge point (<200m) were compared with those further downstream (1300–1600m), and at a nearby control site. Average ΣREE concentrations were highest near the CASS discharge point (148–186mg/kg), and decreased with distance downstream (111–146mg/kg) and in control sediments (70mg/kg). Reactive Fe concentrations (defined by 1M HCl extractability) were also significantly higher in surface sediments (0–6cm) near the CASS discharge point. Middle-REE (MREE) enrichments dominated fractionation patterns at all sites (>1.5), with a high proportion (63–100%) of REEs residing in the reactive (1M HCl extractable) sediment fraction. Interestingly, the degree of MREE enrichment was significantly correlated with Ce anomalies (r2=0.72, P<0.001) and the heavy-REE (HREE) to light-REE (LREE) ratios (HREE/LREE, r2=0.74, P<0.001) in the reactive sediment fraction, only in those sites situated closest to the CASS drainage. The observed high MREE enrichments, positive Ce anomalies (>1) and HREE/LREE ratios (>1) are consistent with reactive Fe(III) oxides/oxyhydroxides driving REE retention in these sediments. This study indicates that CASS drainage alters REE signatures in receiving sediments by (1) providing a source of REEs, thereby enhancing sedimentary REE concentrations, and (2) causing accumulation of reactive Fe(III) phases with a high affinity for REEs. Together, these two factors drive the development of distinctive REE signatures in CASS-impacted sediments. The recognition of such signatures may provide a promising tool for identifying coastal sediments receiving anthropogenic CASS drainage inputs.

Use of rare earth element geochemistry to constrain the source of dolomitizing fluid for dolomitization of the Lower Triassic Feixianguan Formation, Jiannan area, China

Abstract Rare earth element (REE) concentration and pattern may provide useful information to constrain the source of dolomitizing fluid. However, REE data measured from carbonates might be complicated by diagenetic alterations or clastic components. It is necessary to identify and evaluate such influences before interpreting REE data properly. REE determined in two types of dolostone, including the fine crystalline (D1) and the medium crystalline dolostone (D2), from the Lower Triassic Feixianguan Formation in the Jiannan area display different concentrations and PAAS-normalized patterns. The D1 dolostone that formed by an early near-surface dolomitization has the relatively higher total REE concentrations (ΣREE) and displays near-flat REE patterns similar to that of the PAAS-normalized North American Shale, implying some influences of the clastic components. This is supported by the fact that the D1 has extremely high Fe and Mn contents but dull to no cathodoluminescence. Contrarily, D2 dolostone has lower ΣREE values. Their REE patterns are characteristics of LREE depletion, negative Ce anomalies, and positive La anomalies consistent with the features of the host limestone that yields the seawater-like features. The lack of correlation between dolomite content and their ΣREE, Ce/Ce*, or (Nd/Yb) SN indicates that clastic components are minor and that dolomitization has no or only a minor impact on REE signatures of the precursor limestone. All those suggest that dolomitization associated with D2 was likely associated with seawater-derived fluids. The distinct REE features of the D1 dolostone are mainly attributed to the contamination of the clastic components rather than the indicators of the different dolomitizing fluid, and thereby provided no information on the sources of dolomitizing fluid. Therefore, the degree of contamination should be evaluated before interpreting the REE data properly, especially for dolostones that formed at or near-surface environments.

Anatexis of ultrahigh-pressure eclogite during exhumation in the North Qaidam ultrahigh-pressure terrane: Constraints from petrology, zircon U-Pb dating, and geochemistry

Plagioclase-rich leucosomes and K-feldspar–rich veins are widely distributed within retrogressed eclogite in the Xitieshan area of the North Qaidam ultrahigh-pressure metamorphic terrane, western China. In this contribution, a combined study of petrology, zircon internal structure, zircon U-Pb age, zircon trace-element composition, whole-rock geochemistry, and Sr-Nd isotopes in plagioclase-rich leucosomes and K-feldspar–rich veins provides insight into the nature and timing of partial melting in these rocks. Petrological evidence for partial melting is provided by elongated, highly cuspate feldspars, quartz along grain boundaries (e.g., muscovite, garnet, and clinopyroxene), and felsic veinlets composed of quartz and feldspar along the boundaries of garnet, clinopyroxene, and clinopyroxene-plagioclase symplectite in the metabasite. Whole-rock geochemistry suggests that the plagioclase-rich leucosomes have lower contents of both rare earth elements (REEs) and high field strength elements (HFSEs) but higher large ion lithophile elements (LILEs; e.g., Rb, Ba, K, Sr, and Pb) than the metabasite hosts. The plagioclase-rich leucosomes may be divided into two subgroups according to their distinct REE patterns: (1) higher total REE content with or without weak negative Eu anomalies, and (2) lower total REE content with conspicuous positive Eu anomalies. The Eu-rich group also shows higher Sr content than those in the Eu-poor group. However, the K-feldspar–rich veins show higher REE, HFSE, and LILE concentrations than the plagioclase-rich leucosomes and metabasites. The inherited cores of K-feldspar–rich veins are of typical magmatic origin (oscillatory zoning with high Th/U ratios, enriched heavy [H] REEs, and negative Eu anomalies), yielding 206 Pb/ 238 U ages ranging from 904 ± 8 Ma to 915 ± 28 Ma. The zircon cores of plagioclase-rich leucosomes and mantles of K-feldspar–rich veins exhibit no zoning or weak zoning, with flat HREE patterns and no negative Eu anomalies, and they contain mineral inclusions of garnet and clinopyroxene, implying that these zircon domains were formed during an episode of eclogite-facies metamorphism with 206 Pb/ 238 U ages ranging from 444 ± 10 Ma to 452 ± 9 Ma. Internal textures and mineral inclusions (quartz, plagioclase, and K-feldspar) and trace-element systematics (steep HREE patterns with negative Eu anomalies and low Th/U ratios) of the zircon rims from plagioclase-rich leucosomes and K-feldspar–rich veins are similar to anatectic zircon. These anatectic zircon domains yielded 206 Pb/ 238 U ages ranging from 430 ± 10 Ma to 440 ± 12 Ma, and 406 ± 12 Ma to 430 ± 13 Ma, respectively. An integrated study of petrology, geochronology, and geochemistry demonstrated that the metabasites of the North Qaidam ultrahigh-pressure terrane likely experienced initial partial melting with plagioclase-rich leucosome formation under eclogite-facies conditions and partial melt crystallization during the granulite-facies stage, triggered by dehydration melting involving zoisite and rare muscovite. The K-feldspar–rich veins within the metabasites may be the result of injected melts that were derived from partial melting of nearby gneisses.