Fractionated Rare Earth Element Patterns Research Articles

Numerical Modeling of REE Fractionation Patterns in Fluorapatite from the Olympic Dam Deposit (South Australia)

Trace element signatures in apatite are used to study hydrothermal processes due to the ability of this mineral to chemically record and preserve the impact of individual hydrothermal events. Interpretation of rare earth element (REE)-signatures in hydrothermal apatite can be complex due to not only evolving fO2, fS2 and fluid composition, but also to variety of different REE-complexes (Cl-, F-, P-, SO4, CO3, oxide, OH− etc.) in hydrothermal fluid, and the significant differences in solubility and stability that these complexes exhibit. This contribution applies numerical modeling to evolving REE-signatures in apatite within the Olympic Dam iron-oxide-copper-gold deposit, South Australia with the aim of constraining fluid evolution. The REE-signatures of three unique types of apatite from hydrothermal assemblages that crystallized under partially constrained conditions have been numerically modeled, and the partitioning coefficients between apatite and fluid calculated in each case. Results of these calculations replicate the measured data well and show a transition from early light rare earth element (LREE)- to later middle rare earth element (MREE)-enriched apatite, which can be achieved by an evolution in the proportions of different REE-complexes. Modeling also efficiently explains the switch from REE-signatures with negative to positive Eu-anomalies. REE transport in hydrothermal fluids at Olympic Dam is attributed to REE–chloride complexes, thus explaining both the LREE-enriched character of the deposit and the relatively LREE-depleted nature of later generations of apatite. REE deposition may, however, have been induced by a weakening of REE–Cl activity and subsequent REE complexation with fluoride species. The conspicuous positive Eu-anomalies displayed by later apatite with are attributed to crystallization from high pH fluids characterized by the presence of Eu3+ species.

Elemental and Sr-Nd isotopic geochemistry of Mesoproterozoic sedimentary successions from NE Lesser Himalaya, northern India: Implications for Proterozoic climate and tectonics

The sedimentation history of northeastern Himalayan Proterozoic basins is poorly known. In the current study, we examine major, trace, rare earth elements (REEs) and Sr-Nd isotope geochemistry of pelites and quartzites from Mesoproterozoic metasedimenatary sequences of Bomdila and Rupa Groups, NE Himalaya in order to understand provenance, tectonic setting and paleoweathering conditions of deposition. The salient geochemical parameters, such as, high SiO2 and Al2O3 concentrations, relatively low MgO values, typical enrichment of immobile incompatible elements (Al2O3/TiO2 = 32.2, Th/Sc = 2.1), fractionated REE patterns (La/Ybn = 28) and a strong negative europium anomaly (Eu/Eu∗ = 0.3–0.7) indicate dominant felsic source for Bomdila sediments. Bomdila sediments show significantly radiogenic εNd0.95Ga values (−10.25 to −17.90, avg. −15.24) compared to Bundelkhand craton (avg. −26) and Singhbhum craton (avg. −30) and yield much younger TDM ages (2.3–2.7 Ga) compared to Archean Bundelkhand (3.2–3.5 Ga) and Singhbhum cratons (3.4–3.9 Ga). These results clearly rule out any significant detritus contribution from old cratonic sources. εNd and TDM data of Mesoprterozoic Bomdila sediments envelop the signature of Lower Proterozoic Inner Lesser Himalayan (ILH) terrane. Prominent U-Pb age peaks at 1702, 1651, ∼1400, 1248 and 1118 Ma in detrital zircons indicate major contribution from Late Paleoroterozoic to Late Mesoproterozic sources. However, initial Nd isotope ratios and TDM do not favour any juvenile inputs. We argue that ILH source terrain may have been extensively reworked during Late Paleoroterozoic to Late Mesoproterozic time and could have been part of a long lived orogenic belt.. Severe depletion of Ca, Na and Sr in Bomdila sediments indicate intense chemical weathering of the source region, and can be attributed to warm and humid climatic conditions, a conclusion which is consistent with the CO2-rich atmosphere during Mesoproterozoic period.

Geochemical characteristics and tectonic setting of the bimodal volcanic rocks in Sepikou region of eastern Tianshan

The Sepikou region is located in the eastern Bogda Mountains of the east Tianshan. The Bogda belt is mainly composed of Carboniferous strata, including the Lower Carboniferous Qijiaojing Formation (C1q), Upper Carboniferous Liushugou Formation (C2l), and Qijiagou Formation (C2qj). Here, we report the petrology, geochemistry, and geochronology of bimodal volcanic rocks from the Upper Carboniferous Liushugou Formation, which is widely distributed in the Sepikou region. The basalts, basaltic andesite, and keratophyre have similar petrochemical characteristics and exhibit the high‐Na, low‐K characteristics belonging to calc‐alkalic rocks. These are characterized by the high abundance of K, Rb, Th, Ba, the depletion of HFSE (Nb, Ta, Zr, and Hf), and the slight depletion of Ti. Chondrite‐normalized rare‐earth elements (REE) patterns for basalts‐keratophyre show right‐leaning parallel curve clusters, together with a slight enrichment in light rare‐earth elements (LREE) contents and low heavy rare‐earth elements (HREE)/LREE ratios. The keratophyre exhibits slightly negative Eu anomalies. Compared with the basalts, the rhyolites have high alkali contents, slightly high ∑REE contents, low heavy rare‐earth elements/LREE ratios, negative εSr(t) (−9.1 to −12.0), low 87Sr/86Sr initial ratio, highly positive εNd (t) (+5.3 to +6.4), and low Pb isotope ratios. The fractionated REE patterns with prominent negative Eu anomalies suggest they were chiefly derived from the mantle magma underplated basaltic body remelting from the depleted mantle source. The LA‐ICP‐MS analysis on zircons from quartz keratophyre and rhyolite yield similar ages of 314.9 ± 1.2 and 314.0 ± 1.1 Ma, respectively, suggest that the major bimodal volcanism took place in the Late Carboniferous epoch. The quartz keratophyre zircons, with the 176Hf/177Hf ratios of 0.282897–0.283097, have highly positive εHf (10.99–19.97) and depleted mantle model ages between 180 and 628 Ma. The mafic rocks were chiefly derived from the depleted mantle with the partial incorporation of crustal components. The bimodal volcanic rocks were formed under a continental rift setting. The rift experienced extension in the early period of the Early Carboniferous and its final closure arose after a late period of the Late Carboniferous.

Rare Earth Elements Behaviour at West Coast of Peninsular Malaysia Rocky Shore Ecosystem Using Saccostrea cucullata as Bioindicator

This study focuses on the assessment of rare earth elements (REEs) in rocky shore ecosystem along west coast region of Peninsular Malaysia coastal waters, describing their partitioning in selected body part of Saccostrea cucullata and deliberating on interspatial variability. Samples were digested using Teflon Bomb technique and concentrations of 14 naturally occurring REEs were measured using ICP-MS technique, along with selected trace metals for additional data. The REEs fractionation patterns normalized to chondrite were remarkably similar, indicating a common source of the REEs. Consistent REEs abundance patterns were found in all samples, with enrichment of LREE over HREE, which implies that REEs are transported as a coherent group through west coast of Peninsular Malaysia aquatic ecosystems. Quantification of anomalies calculated using values normalized to chondrite data presented ratios higher than unity for Ce and ratios lower than unity for Eu in all sites. Filter feeder S. cucullata is considered to be highly potential as a bioindicator for REEs, undoubtedly due to its feeding behaviour that is much related to suspended particles as REEs sources. Comparative results showed that the values are considerably below the safety limit, with the exception of Ce and Nd in the soft tissue of S. cucullata.

Petrography, geochemistry, and provenance of the Chalki rocks in Kurdistan region, North Iraq

Outcrops of the Paleozoic Chalki volcanic rocks are restricted to part of the northern Thrust Zone of Iraq close to Iraqi-Turkish border. Petrographically, the volcanic rocks from the Chalki area are mainly layered, appearing fresh in the field and exhibiting some basaltic lava flows. Porphyritic, amygdaloidal, and microlite-porphyric are the main observed textures. Phenocrysts of primary phases (i.e., olivine, iron oxides) are in a groundmass of feldspars and clinopyroxene. Chalki Formation is intercalated with Pirispiki Formation which consists of thin to medium bedded, greenish gray marl, red mudstone, and veins of calcite. The Chalki rocks are mafic of theolitic basalt type. Geochemically, they have high chromium and nickel concentrations in most samples. Rare earth element (REE) patterns illustrate parallel to sub-parallel, moderately fractionated REE patterns. The low heavy REE (HREE) contents in the studied samples appear to be due to partial melting of metamorphosed oceanic crust leaving HREE-rich accessory minerals (i.e., garnet) as a residual phase in the source. No Eu anomalies were observed in the Chalki samples which may indicate a back-arc basin pattern. The non-subduction signature of the Chalki rocks is confirmed by the Nb/Yb versus Th/Yb diagram, which shows that most of the studied rocks fall in the compositional field of non-arc-related rocks—well within the field of the mid-ocean ridge basalt (MORB)-ocean island basalt (OIB) mantle array.

Mineralogy and geochemistry of sands along the Manzanillo and El Carrizal beach areas, southern Mexico: implications for palaeoweathering, provenance and tectonic setting

AbstractThe provenance of sands from the Manzanillo (MN) and El Carrizal (CAR) beach areas along the Mexican Pacific coast (southern Mexico) was investigated based on their modal composition, mineralogy and geochemical data. The average quartz, feldspar and lithic fragment (QFL) ratios revealed that the proportion of quartz is higher in CAR sands than in MN sands. In comparison with MN, the CAR sands are enriched in SiO2 content with higher SiO2/Al2O3 ratio indicating that sediment recycling is greatest for the CAR sands. The variation in K2O/Al2O3 and Na2O/K2O ratios between the MN and CAR sands specified a difference in the relative proportion of plagioclase. The chemical index of alteration (CIA) and Plagioclase Index of Alteration (PIA) values revealed a moderate weathering intensity in the source areas. The MN sands are characterized by a low degree of rare earth element (REE) fractionation (LaCN/YbCN = ~6–7), whereas the CAR sands define fractionated REE patterns (LaCN/YbCN = ~8.8–16.8). The fractionated REE pattern with elevated total low REE (∑LREE) content of the CAR sands suggested that sediment sorting is higher for the CAR than MN sands. Small negative and positive Eu anomalies (Eu/Eu* = ~0.91–1.23) of MN sands indicated the derivation of sediments from felsic‐intermediate source rocks. The CAR sands showed higher concentration of ∑LREE than total heavy REE (∑HREE) and characterized by a significant negative Eu anomaly (Eu/Eu* = ~0.46–0.78), suggested that the source rock is felsic type. The result obtained by the comparison of REE patterns of the beach sands to the probable source rocks is also consistent with this observation. The compositional differences identified between the MN and CAR beach areas suggested that longshore current in the mixing and homogenization of sands is not significant. The new tectonic discriminant‐function‐based multidimensional diagrams showed an arc setting (active) for the MN sands and a rift setting (passive) for the CAR sands, which is consistent with the regional geology of southern Mexico. Copyright © 2016 John Wiley & Sons, Ltd.

Geochemical behaviors of rare earth elements in groundwater along a flow path in the North China Plain

Rare earth element (REE) geochemistry is a useful tool in delineating hydrogeochemical processes and tracing solute transport, which can be used to reveal groundwater chemical evolution in the complexed groundwater systems of the North China Plain (NCP). Groundwaters and sediments were collected approximately along a flow path in shallow and deep aquifers of the NCP to investigate REE geochemistry as a function of distance from the recharge zone. Groundwater REE concentrations are relatively low, with ranges from 81.2 to 163.6ng/L in shallow groundwaters, and from 65.2 to 133.7ng/L in deep groundwaters. Speciation calculation suggests that dissolved REEs mainly occur as dicarbonato (Ln(CO3)2−) and carbonato (LnCO3+) complexes. Although along the flow path groundwater REE concentrations do not vary substantially, relatively lower HREEs are observed in central plain (Zone II) compared to recharge area (Zone I) and discharge plain (Zone III). Shale-normalized REE patterns are characterized by different degrees of enrichment in the HREEs, as indicated by the variation in average (Er/Nd)NASC value. The similar REE compositions and shale-normalized REE patterns of shallow and deep groundwaters demonstrate that interactions of groundwaters between shallow and deep aquifers possibly occur, which is likely due to the long-term groundwater over-exploration. Cerium anomalies (Ce/Ce∗=CeNASC/(LaNASC×PrNASC)0.5) generally increase from Zone I, through Zone II, to Zone III, with trends from 0.79 to 3.58, and from 1.22 to 2.43 in shallow groundwaters and deep groundwaters, respectively. This is consistent with the variations in oxidation–reduction potential and redox sensitive components (i.e., dissolved Fe, Mn, NO3− and As concentrations) along the flow path. Positive Ce anomaly and redox indicators suggest that redox conditions progressively evolve from oxic to moderate anaerobic in the direction of groundwater flow. In the recharge zone (Zone I), groundwater low positive Ce anomalies are likely due to partially oxidative scavenging of Ce(III) to Ce(IV), and HREE enrichment would result from preferential scavenging of the LREEs relative to the HREEs during Fe/Mn oxides/oxyhydroxides precipitations, which is well supported by the low concentrations of dissolved Fe and Mn. In the down-gradient (Zone II and Zone III), reductive dissolution of Fe/Mn oxides/oxyhydroxides increases positive Ce anomalies along the flow path. The positive correlations between (Er/Nd)NASC values and dissolved Fe/Mn concentrations suggest that reductive dissolution of Fe/Mn oxides/oxyhydroxides, as well as readsorption, are the geochemical controls on groundwater REE fractionation patterns. Groundwaters mostly have positive Eu anomalies (Eu/Eu∗=EuNASC/(SmNASC×GdNASC)0.5), which would be the result of chemical weathering of feldspars (e.g., plagioclase) detected in aquifer sediments by XRD technique.

Geochemistry and tectonic setting of the Paleoproterozoic metavolcanic rocks from the Chirano Gold District, Sefwi belt, Ghana

Major and trace elements, including rare earth elements (REEs) data are presented for metavolcanic rocks of the Paleoproterozoic Birimian Sefwi belt to determine the geochemical characteristics as well as the possible tectonic setting of emplacement of these rocks. In order to accomplish the aim of the study, the petrographical characteristics of the rocks were examined coupled with analysis of the rocks for their whole-rock major and trace elements contents by ICP-AES and ICP-MS methods respectively. The rocks have been classified as basalt/basaltic andesites and dolerites based on their textural and mineralogical compositions. It is observed that the rocks have suffered various degrees of alteration evident in the overprinting of primary minerals such as pyroxenes and plagioclase by chlorite, epidote, sericite and others. Generally, the rocks are moderately deformed and may have experienced at least greenschist metamorphism. The basalt/basaltic andesites are derivative magmas [Mg# (20–51), Cr (10–220 ppm) and Ni (5–137 ppm)], and show flat REE to fractionated REE patterns with (La/Sm)N = 1.36–3.90, (La/Yb)N = 1.17–5.32 and strong negative to non-existent Eu anomalies (Eu/Eu* = 0.51–1.03). N-MORB-normalised multi-element diagrams show that the rocks have geochemical patterns characterised by enrichment in LILE relative to HFSE and in LREE relative to HREE. The basalt/basaltic andesites exhibit characteristics of subduction zone-related magmas, such as pronounced negative Nb–Ta anomalies, slightly negative Hf and variable negative Ti anomalies. The dolerites do not vary much from the basalts and basaltic andesites. The MgO and Fe2O3 values of the dolerite range from 2.97 to 6.93 and 5.98 to 14.35 wt.% respectively, corresponding to Mg#s of 38–62. LREEs enrichment over HREEs with (La/Sm)N ranging from 0.61 to 4.61 and (Gd/Yb)N ranging from 0.99 to 2.91 is also typical of these rocks. The dolerites also exhibit quite invariable Eu anomalies (Eu/Eu* = 0.81–1.00) and display a pronounced Nb–Ta trough and a minor negative Ti anomaly, suggesting arc characteristics. The metavolcanic rocks from the study area generally exhibit subduction-related setting characteristics with evidence of a sub-lithospheric contamination.

Detection and Monitoring of REEs and Related Trace Elements with an Itrax™ Core Scanner in the Ría de Huelva (SW Spain)

The Ria de Huelva is one of the most polluted areas in Western Europe because of the high acid mining activity together with the chemical industries located in its margins. This strong anthropogenic pressure results in the liberation of high concentrations of metals and rare earth elements (REEs) to the Ria. In this work, an Itrax™ Core Scanner (Itrax) has been used for the first time to detect and to study REEs distribution in a sediment core. Its high sensitivity (until 5 μg·g −1 for Er) was confirmed by comparing its semi-quantitative results with concentration values obtained from inductively coupled plasma mass spectrometry (ICP-MS). In this way, establishing equivalences between Itrax continuous data and concentration data have been possible to detect pollution levels caused by REEs and related trace elements along the whole sediment core reducing the discrete analyses and therefore saving time and money. Moreover, Itrax was confirmed as a fast screening and monitoring tool to study REEs fractionation patterns and to identify the environmental changes responsible of these patterns.

Submarine groundwater discharge of rare earth elements to a tidally-mixed estuary in Southern Rhode Island

Rare earth element (REE) concentrations were analyzed in surface water and submarine groundwater within the Pettaquamscutt Estuary, located on the western edge of Narragansett Bay in Rhode Island. These water samples were collected along the salinity gradient of the estuary. Rare earth element concentrations in the majority of the groundwater samples are substantially higher than their concentrations in the surface waters. In particular, Nd concentrations in groundwater range from 0.43nmolkg−1 up to 198nmolkg−1 (mean±SD=42.1±87.2nmolkg−1), whereas Nd concentrations range between 259pmolkg−1 and 649pmolkg−1 (mean±SD=421±149pmolkg−1) in surface waters from the estuary, which is, on average, 100 fold lower than Nd in the groundwaters. Groundwater samples all exhibit broadly similar middle REE (MREE) enriched shale-normalized REE patterns, despite the wide variation in pH of these natural waters (4.87≤pH≤8.13). The similarity of the shale-normalized REE patterns across the observed pH range suggests that weathering of accessory minerals, such as apatite, and/or precipitation of LREE enriched secondary phosphate minerals controls groundwater REE concentrations and fractionation patterns. More specifically, geochemical mixing models suggest that the REE fractionation patterns of the surface waters may be controlled by REE phosphate mineral precipitation during the mixing of groundwater and stream water with incoming water from the Rhode Island Sound. The estimated SGD (Submarine Groundwater Discharge) of Nd to the Pettaquamscutt Estuary is 26±11mmolNdday−1, which is in reasonable agreement with the Nd flux of the primary surface water source to the estuary, the Gilbert Stuart Stream (i.e., 36mmolday−1), and of the same order of magnitude for a site in Florida.

REE partitioning in riverine sediments around the Yellow Sea and its importance in shelf sediment provenance

We sought to identify the characteristics and their controlling factors of rare earth element (REE) fractionation patterns in two chemically partitioned (labile and residual) fractions of Korean (KR) and Chinese riverine (CR) sediments. We also investigated their sediment origins in the Yellow Sea based on REE signatures. The results showed that the upper continental crust (UCC)-normalized REE fractionation patterns were remarkably different for labile and residual fractions, even between KR and CR sediments. Notably, KR sediments in both residual and labile fractions exhibited a striking enrichment of light REEs (LREEs), unlike CR sediments, with no obvious fractionation. Such LREE enrichment is relatively much stronger in the coarse-grained sandy sediments. The peculiar LREE enrichment in both fractions of KR sediments was preferentially linked to grater felsic granitic compositions, compared with CR sediments that were close to those of the UCC (granodiorite with relatively more mafic minerals), consisting of a mixture of various rock types. Application of these REE signatures to the provenance of Yellow Sea sediments provides an important clue to the cause underlying the lack of correlation between the mud budget and the river discharge in Korean coastal regions as well as the ultimate fate of CR sediments. The REE fractionation signals, especially in residual fractions may shed light on the major existing phases affecting REE fractionation as well as the origin of sediments in the Yellow Sea.

Uraninite chemistry as forensic tool for provenance analysis

Electron microprobe and laser ablation-inductively coupled plasma mass spectrometric (LA-ICPMS) analyses were carried out on individual uraninite grains from several localities worldwide, representing a variety of different U-deposit types ranging in age from Mesoarchaean to the Mesozoic. For the first time, concentration data on a comprehensive set of minor/trace elements in uraninite are presented, i.e. LA-ICPMS concentration data for Th, Si, Al, Fe, Mn, Ca, Mg, P, Ti, V, Cr, Co, Ni, Pb, Zn, As, rare earth elements (REE), Y, Zr, Nb, Mo, Ag, Ta, W, Bi, and Au. Most of these elements could be detected in significant quantities in many of the studied examples. The results obtained in this study, supplemented by previously published data on major element and REE concentrations, reveal systematic differences in uraninite composition between genetically different deposit types and also, for a given genetic type, between different locations.Low-temperature hydrothermal uraninite is marked by U/Th>1000, whereas high-temperature metamorphic and magmatic (granitic, pegmatitic) uraninite has U/Th<100. Our new data also confirm previous observations that low-temperature, hydrothermal uraninite has low total REE contents (<1wt%) whereas higher temperature uraninite can contain as much as several percent total REE. Genetically different uraninite types can be further identified by means of different REE fractionation patterns. Systematic differences between primary uraninite from different localities could be also noted with respect to the abundances of especially Y, V, W, Zr, Nb, Ta, and to a lesser extent Mo, P, Bi, and As. Our findings open up the possibility of using uraninite chemistry as provenance tool, both for geological applications, as exemplified in this study by the application to uraninite in the Mesoarchean Witwatersrand Basin (South Africa), as well as for forensic purposes to track down the likely source of illegally mined uraninite. Uraninite chemistry provides strong support for a palaeoplacer model for the U-mineralisation in the auriferous and uraniferous conglomerates of the Witwatersrand, in which individual uraninite particles display chemical characteristics typical of high-temperature (magmatic) uraninite and a great variation in trace element concentrations that point to a variety of (magmatic) source rocks.

Geochemical and geochronologic constraints for Paleozoic magmatism related to the orogenic collapse in the Qimantagh–South Altyn region, northwestern China

Abstract Voluminous and discrete early Paleozoic bimodal magmatic suites are thought to be the result of post-collisional extension following the amalgamation of East Kunlun and Altyn Tagh. In this paper, four representative magmatic units were studied for their geochemical fingerprint in conjunction with geochronological studies. The 467–445 Ma Mangya mafic suite shows E-MORB type rare earth element (REE) patterns that are the result of asthenospheric interaction with a metasomatized subcontinental lithosphere. High-K calc-alkaline granodiorites, intruded at ca. 450 Ma, are characterized by high Mg#, the least fractionated REE pattern without an Eu anomaly, as well as high Sr and low Rb/Sr ratio. We interpret these geochemical signals to result from lower crustal melting of garnet amphibolite at pressures between 16 and 22 kbar. A 430–420 Ma A-type granite is interpreted to result from the melting of metaigneous rocks at middle to lower crustal depths. Lastly, a late magmatic pulse occurs between 400 and 380 Ma and is represented by the Alk granite. The Alk granite is interpreted to be a product of metapelite melts and is associated with a smaller volume of mafic melts. U–Pb zircon geochronology of Paleozoic igneous rocks of the Qimantagh–South Altyn reveals that most of the magmatic episodes are either coeval with, or post, extensional deformation. This phase of extension is supported by the exhumation of HP/UHP metamorphic rocks and crustal anatexis. Collectively, the evolutionary stages documented in this study correspond to a succession of post-collisional, postorogenic and, ultimately, within plate magmatic episodes. The overall features support orogenic collapse via removal of a thickened lithospheric root beneath the East Kunlun–Altyn Tagh collisional orogen during early Paleozoic.

Geochemistry of rare-earth elements in shallow groundwater, northeastern Guangdong Province, China

Shallow groundwater and hot springs were collected from northeastern Guangdong Province, Southeast China, to determine the concentrations and fractionation patterns of rare-earth elements (REE). The results show that the La, Ce and Nd of REEs are abundant in groundwater and rock samples, and the ΣREE contents in groundwater and rock samples range from 126.5 to 2875.3 ng/L, and 79.44 to 385.85 mg/L, respectively. The shallow groundwater has slightly HREE-enriched PAAS-normalized patterns. However, the granitic rocks PAAS-normalized patterns, with remarkable negative Eu anomalies, are different from that of shallow groundwater. The enrichment of HREE is considered to be controlled by REE complexation and readsorption for most groundwater has Ce and Eu positive anomalies. The Ce and Eu anomalies in groundwater are controlled by redox conditions. Moreover, the Fe-contain sediments dissolution and/or the reduction of Fe oxyhydroxides are another factor contributing to Ce anomalies. The Eu anomalies in groundwater are controlled by the preferential mobilization of Eu2+ during water-rock interaction compared to Eu3+.

Rare Earth Elements Fractionation in Native Vegetation from the Moncorvo Iron Mines, NE Portugal

Fractionation of Rare Earth Elements (REE) and the accumulation and translocation indexes were measured and determined in the native vegetation [Halimium lasianthum (Lam.) Spach subsp. alyssoides (Lam.) Greuter; Cytisus multiflorus (L’Hér.) Sweet; and Cistus monspeliensis L.; Cistus ladanifer subsp. ladanifer; Lavandula stoechas L.] from the iron mining area of Moncorvo (NE Portugal). There is no correlation between the amounts of REE in rhizosphere and in plants. The REE concentration as the fractionation follows roots>leaves>stems in plants. A slightly enrichment in HREE were found in rhizosphere and plants (roots and stems), whereas the leaves are enriched in LREE. The accumulation and translocation depend of internal complexes ligands. The redox and pH conditions of the rhizosphere conditioned the REE uptake. Greatest bioaccumulation ability of heavy REE (HREE) was found in C. monspeliensis, followed by H. lasianthum that also, has a high capacity of the REE translocation to the aerial parts, contrary to C. monspeliensis. An M-type tetrad effect was determined mainly for HREE (Gd-Ho series) indicating a complexation of REE. The greatest differences in the REE fractionation patterns (mainly for HREE) are observed in stems, as a consequence of the transport function of this organ. Cerium anomaly indicates that the pH and redox conditions affected the uptake of Ce by plants, where the free ionic species are dominated in roots and leaves (positive anomaly), and stems (negative anomaly). Also the Eu-anomaly is greater in roots and leaves than in steams probably by participation in metabolic functions due to similarity with calcium.

Neoarchaean crustal growth by combined arc–plume action: evidence from the Kadiri Greenstone Belt, eastern Dharwar craton, India

AbstractField and geochemical studies combined with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating set important constraints on the timing and petrogenesis of volcanic rocks of the Neoarchaean Kadiri greenstone belt and the mechanism of crust formation in the eastern Dharwar craton (EDC). The volcanic rocks are divided into three suites: tholeiitic basalts, calc-alkaline high-Mg# andesites and dominant dacites–rhyolites. The basalts (pillowed in places) show flat rare earth element (REE) and primordial mantle-normalized trace element patterns, but have minor negative Nb and Ta anomalies. They are interpreted as mantle plume-related oceanic plateau basalts whose source contained minor continental crustal input. The andesites are characterized by high Mg# (0.66–0.52), Cr and Ni, with depletion of high-field strength elements (HFSE) and enrichment of light REE (LREE) and large-ion lithophile elements (LILE). They were probably derived from a metasomatized mantle wedge overlying a subducted slab in a continental margin subduction zone. The dacites–rhyolites are silicic rocks (SiO2=61–72 wt%) with low Cr and Ni, K2O/Na2O mostly 0.5–1.1, highly fractionated REE patterns, enrichments of LILE and distinctly negative HFSE anomalies. One rhyolite sample yielded a zircon U–Pb age of 2353±32 Ma. This suite is similar to potassic adakites and is explained as the product of deep melting of thickened crust in the arc with a significant older crustal component. Collision between a continental margin arc with an oceanic plateau followed by slab break-off, upwelling of hot asthenosphere and extensive crustal reworking in a sustained compressional regime is proposed for the geodynamic evolution of the area. This is in corroboration with the scenario of EDC as a Neoarchaean hot orogen as suggested recently by some workers.Supplementary material:Details of whole-rock major and trace element determination, Nd isotope analysis and zircon U–Pb dating and trace element analysis, the geographical coordinates of the samples and the values of the international rock standards analysed are available at http://www.geolsoc.org.uk/SUP18660

Geochemical signatures of uranium oxides in the Lufilian belt: From unconformity-related to syn-metamorphic uranium deposits during the Pan-African orogenic cycle

The Pan-African Lufilian belt (Zambia and Democratic Republic of Congo) is known for its world-class copper and cobalt deposits. In addition, the Lufilian Copperbelt hosts several uranium occurrences concentrated within deformed siliciclastic rocks of the basal Neoproterozoic Katanga Supergroup. We report LA-ICPMS and EMP analyses of the rare earth element (REE) and yttrium (Y) abundances (designated as the REY signatures) of uranium oxides from two uranium mineralizing events of the Lufilian belt previously dated at 652±8Ma and 530±6Ma by the U–Pb method on uraninite. Uranium oxides dated at ca. 650Ma from the External fold-and-thrust belt are characterized by (i) bell shape REE patterns centered on middle REE (MREE), (ii) positive europium (Eu) anomalies and (iii) relatively low Y contents. In contrast, uranium oxides dated at ca. 530Ma from the Domes region are characterized by (i) REE patterns but with a less pronounced light REE (LREE) fractionation, (ii) negative Eu anomalies and (iii) higher Y contents. Moreover, the External fold-and-thrust belt also contains uranium mineralization dated at ca. 530Ma having the same characteristics as the ca. 530Ma uranium oxides from the Domes region (a moderately fractionated REE pattern and a negative Eu anomaly).As REY signatures are known to reflect mineralizing processes, the distinct geochemical signatures of the two uranium oxide generations (ca. 650Ma and ca. 530Ma) provide meaningful information about the uranium cycle during the Pan-African orogeny. Compared to the REY signatures of the known worldwide uranium deposit types, the REY signature of uranium oxides dated at ca. 650Ma of the External fold-and-thrust belt is similar to the REE patterns from unconformity-related U deposits (Athabasca in Canada and Kombolgie in Australia). Uranium oxides of the Domes region and some of the External fold-and-thrust belt display similar characteristics to syn-metamorphic U deposit (Mistamisk in Canada). Accordingly, we propose that the two stages of uranium oxide crystallizations within the Lufilian belt, at ca. 650 and ca. 530Ma, occurred under distinct physico-chemical conditions. The first stage, at ca. 650Ma, may be related to late diagenesis hydrothermal processes, at the basement/cover interface, with the circulation of highly saline basinal brines linked to evaporites of the Roan Group. This Pan-African unconformity-related uranium deposit is the youngest of this type described to date. The second stage may be connected to metamorphic fluid circulations, at about 530Ma, during the Lufilian orogeny in the Domes region and also in the External fold-and-thrust belt.

Geochemical signature of aquitard pore water and its paleo-environment implications in Caofeidian Harbor, China

Oxygen-18 (18O), deuterium (D), and chemical patterns were determined in pore water samples extracted from 100-m depth in Caofeidian Harbor, China. The stable isotopic composition indicates that aquitard pore water was of meteoric origin and was basically not influenced by evaporation. Seawater diffusion was identified as the main influence on the isotope signature of pore water, according to the δ18O profile and positive correlation between δ18O and Cl–. The chemistry of aquitard pore water is characterized by high total dissolved solids (TDS) decreasing with depth, ranging from 26.89 to 7.26 g/L. The same trend was observed for Cl–, Na+, and Mg2+, as influenced by seawater. However, the typical ion ratios (i.e., Cl/Br, Sr/Ba) of pore water change significantly in different sedimentary facies along the study profile due to the long-term reaction between pore water and sediment, further supporting the finding that pore water was not replaced by modern water or seawater. Therefore, during long-term aquitard residence, the chemical composition of pore water would be influenced by other processes such as reduction of sulfates and cation exchange. The rare earth elements (REEs) of pore water are mainly affected by water–rock interaction. The shale-normalized REE fractionation patterns display enrichment of heavy REEs (HREE) relative to light REEs (LREE) and even greater fractionation degree in marine sediment pore waters (as larger La/YbNASC). The relative reduction environment in the aquitard and preferential mobilization of Eu2+ in the water–rock interaction lead to the development of positive Eu anomalies (1.13 < (Eu/Eu*)NASC < 1.98) and slightly positive Ce anomalies (–0.13 < (Ce/Ce*)NASC < 0.35).

Rare earth element analysis in natural waters by multiple isotope dilution – sector field ICP-MS

The rare earth elements (REEs) are valuable tracers in the earth, ocean and environmental sciences. Ten out of fourteen stable REEs have two or more isotopes, making them suitable for quantification by isotope dilution. We present a plasma mass spectrometry based multiple isotope dilution method for high precision REE concentration analysis in aqueous media. Key aspects of the method are: (i) flexible spiking of ten REEs via two LREE and HREE mixed spike solutions. (ii) Offline pre-concentration and matrix removal, by ion chromatography for freshwater samples and by iron co-precipitation or ion chromatography with the Nobias™ resin for seawater samples. (iii) High sensitivity detection by sector field-inductively coupled plasma mass spectrometry (SF-ICP-MS). (vi) The use of a desolvation micro-nebulization introduction system to lower polyatomic Ba and LREE-oxide interferences on HREEs. The method is suitable for a range of freshwater to seawater type samples, and was validated against SLRS-4, SLRS-5, and CASS-5 reference materials and two GEOTRACES marine inter-comparison samples. Long-term external precision on all REEs was <2% RSD, except La and Ce. Minimum sample volumes are 1 ml for freshwater and 50 ml for seawater. The multispike SF-ICP-MS method should be of particular interest in exploring subtle variations in aqueous REE fractionation patterns and anomalies in large numbers of samples.

Chondrule trace element geochemistry at the mineral scale

Abstract– We report trace element analyses from mineral phases in chondrules from carbonaceous chondrites (Vigarano, Renazzo, and Acfer 187), carried out by laser ablation inductively coupled plasma‐mass spectrometry. Results are similar in all three meteorites. Mesostasis has rare earth element (REE) concentrations of 10–20 × CI. Low‐Ca pyroxene has light REE (LREE) concentrations near 0.1 × CI and heavy REE (HREE) near 1 × CI, respectively. Olivine has HREE concentrations at 0.1–1 × CI and LREE around 10−2 × CI. The coarsest olivine crystals tend to have the most fractionated REE patterns, indicative of equilibrium partitioning. Low‐Ca pyroxene in the most pyroxene‐rich chondrules tends to have the lowest REE concentrations. Type I chondrules seem to have undergone a significant degree of batch crystallization (as opposed to fractional crystallization), which requires cooling rates slower than 1–100 K h−1. This would fill the gap between igneous calcium‐aluminum‐rich inclusions (CAIs) and type II chondrules. The anticorrelation between REE abundances and pyroxene mode may be understood as due to dilution by addition of silica to the chondrule melt, as in the gas‐melt interaction scenario of Libourel et al. (2006). The rapid cooling rate (of the order of 1000 K h−1) which seems recorded by low‐Ca pyroxene, contrasted with the more diverse record of olivine, may point to a nonlinear cooling history or suggest that formation of pyroxene‐rich chondrule margins was an event distinct from the crystallization of the interior.