Normalized Rare Earth Elements Patterns Research Articles

Cryptic metasomatism in clino- and orthopyroxene in the upper mantle beneath the Pannonian region

AbstractClino- and orthopyroxenes in anhydrous spinel peridotite xenoliths from Pliocene alkali basalts of the western Pannonian Basin have been analysed for trace elements by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Clinopyroxenes show highly variable mantle normalized REE (rare earth elements) patterns but basically can be classified into three major groups: LREE-depleted, LREE-enriched and U-shaped patterns. As the REE patterns of clinopyroxenes usually reflect the REE patterns of the host peridotite, the three major REE patterns define three geochemically different groups of xenoliths. LREE-depleted xenoliths generally have undeformed protogranular textures, while the more deformed xenoliths with porphyroclastic and equigranular textures have LREE-enriched trace element patterns. The U-shaped pattern is very distinctive and is generally associated with poikilitic textures. The HREE content of the clinopyroxenes suggest that most of the xenoliths experienced less than15% partial melting, with the lowest degree occurring in the LREE-depleted xenoliths, and the highest degree in LREE-enriched xenoliths. Cryptic metasomatism frequently accompanies deformation. Metasomatic enrichment of incompatible trace elements can be observed not only in clinopyroxenes but also in coexisting orthopyroxenes. The metasomatic agents were probably alkaline mafic melts of asthenospheric origin and some may relate to upper Cretaceous alkali lamprophyre magmatism. Geochemical signatures of subduction-related melts or fluids have not been found in the anhydrous LREE-enriched xenoliths, although poikilitic xenoliths with U-shaped normalized REE patterns may indicate the influence of subduction-related melts.

Rare earth elements in tropical surface water, soil and sediments of the Terengganu River Basin, Malaysia

The 14 stable rare earth element (REE) concentrations and distribution patterns were investigated for surface waters ( n=51), soils ( n=52) and sediments ( n=42) from the tropical Terengganu River basin, Malaysia. The chondrite normalized REE patterns of soils developed on four geological units showed enrichment of LREE, a pronounced negative Eu, and depletion of HREE with an enrichment order granite>>metasedimentary>alluvium>volcanic. The REE patterns in sediments reflected the soil REE patterns with an overall order of abundance LREE>>MREE>HREE, however, positive Ce anomaly was either weak or absent in sediments. The chondrite normalized REE patterns for sediments also produced near-neighbor concentration anomalies (Eu-Gd-Tb). The dissolved ∑REE concentrations increased systematically in surface waters with distance from the upstream (<1 μg/L) to the downstream (∼54 μg/L) along the flow path revealing TDS as one of the major controls. River waters registered 85 times higher average ∑REE concentration than the lake waters. While soils and sediments registered a positive Ce anomaly, lake surface waters showed a slight negative anomaly. This was possibly due to the fixation of Ce onto the secondary oxides of Fe and Al and seemed to be immobile under the prevailing pH-redox conditions. The chondrite normalized REE patterns of river water carried strong signature of local geology which significantly differed from lake water REE patterns especially the MREE (Nd to Ho). Dissolved REE concentrations were measured to be higher than other large tropical rivers such as Amazon, Congo and Sepik. Principal component analysis of two main components (accounting for 99.6%) revealed three groups: HREE, LREE and anomalous.

Rare earth and trace element geochemistry of termite mounds in central and northeastern Namibia: Mechanisms for micro-nutrient accumulation

Rare earth element (REE) and trace element concentrations of ten termite mounds and adjacent topsoil from central and northeastern Namibia were used to investigate the processes underlying the alteration of soil chemical and physical properties by termites ( Macrotermes spp.). Accumulation of micro-nutrients in the mounds was of particular interest because of the ecological implications of the enhanced availability of these scarce elements. The absolute concentrations of REE and trace elements, including nine micro-nutrients (B, Fe, Mn, Ni, Cu, Zn, Se, Mo and Cd), were greater in termite mounds compared to topsoil, suggesting a possible external supply of enriched materials or accumulation of in situ weathering products of the underlying bedrock. Similarities between the chondrite normalized REE patterns of the samples and those of the average upper continental crust (UCC) and Post-Archaean Average Australian Shale compositions indicated that the mounds and topsoil at each site originated from the same host bedrock. Coherent behavior between two incompatible elements (Th and La) in both topsoil and mound samples suggested that the two sets of samples were exposed to two different weathering processes. The relatively low Zr/Sc ratios, fine particle sizes and the persistence of positive Eu anomalies of the mounds relative to UCC were interpreted as reflecting (1) a lack of grain sorting effects and (2) active transport of materials rich in primary clay minerals and trace elements from the deeper regolith to the surface by termites. Lower permeability of mound materials may also prevent leaching of primary minerals and trace elements. Titanium and Zr enrichment in most mound samples (8 samples) was attributed to the decomposition of biotite by Macrotermes with the concomitant release of Ti and Zr into the mounds, suggesting the termites' ability to transform soil minerals and enhance chemical weathering. This was further corroborated by a substantial increase in Th/U ratios in most mounds relative to topsoil. Because of the oxidizing conditions of the mounds, Ti and Zr are likely to be adsorbed onto Fe-oxides. Positive Ce anomalies relative to UCC and the high pH values in the mounds indicate calcrete aggradation or mound aeration as a result of burrowing activities of the termites and evaporation from mounds. The impacts of the changes in environmental conditions and the termite activities on the mound geochemistry are highlighted by heavy REE (HREE) as well as Fe and Mn retentions in the mounds. Heavy REE and light REE (LREE) are likely to coprecipitate with carbonate complexes and Fe- and Mn-oxyhydroxides, and in the process, scavenge a series of micro-nutrients such as Zn, Cu, Cd and Co. A substantial enrichment of Se in mounds, despite the oxidizing conditions of the mounds, could be attributed to active transport of Se-enriched materials from deep soil horizons. The study demonstrated the suitability of REE and trace element geochemistry for assessing the influence of Macrotermes on the physico-chemical properties of semi-arid soils.

Rare Earth Element Enrichment in Late Archean Manganese Deposits from the Iron Ore Group, East India

AbstractThe major, trace and rare earth element (REE) composition of Late Archean manganese, ferromanganese and iron ores from the Iron Ore Group (IOG) in Orissa, east India, was examined. Manganese deposits, occurring above the iron formations of the IOG, display massive, rhythmically laminated or botryoidal textures. The ores are composed primarily of iron and manganese, and are low in other major and trace elements such as SiO2, Al2O3, P2O5 and Zr. The total REE concentration is as high as 975 ppm in manganese ores, whereas concentrations as high as 345 ppm and 211 ppm are found in ferromanganese and iron ores, respectively. Heavy REE (HREE) enrichments, negative Ce anomalies and positive Eu anomalies were observed in post‐Archean average shale (PAAS)‐normalized REE patterns of the IOG manganese and ferromanganese ores. The stratiform or stratabound shapes of ore bodies within the shale horizon, and REE geochemistry, suggest that the manganese and ferromanganese ores of the IOG were formed by iron and/or manganese precipitation from a submarine, hydrothermal solution under oxic conditions that occurred as a result of mixing with oxic seawater. While HREE concentrations in the Late Archean manganese and ferromanganese ores in the IOG are slightly less than those of the Phanerozoic ferromanganese ores in Japan, HREE resources in the IOG manganese deposits appear to be two orders of magnitude higher because of the large size of the deposits. Although a reliable, economic concentration technique for HREE from manganese and ferromanganese ores has not yet been developed, those ores could be an important future source of HREE.

Distinguishing subalpine soil types using extractible Al and Fe fractions and REE geochemistry

Only a few paleoecological studies have attempted to use the geochemistry of lacustrine sediments to reconstruct the history of soil genesis. The geochemical signatures of modern soils must firstly be determined before using them to investigate lake sediments. Our study explores the geochemical variability between eight subalpine soil profiles from the internal zone of the Alps to find relevant sediment tracers for present-day soils. Based on the concentrations of secondary Al- and Fe-bearing phases, as well as major element and Rare Earth Element (REE) geochemistry, different subalpine soil types can be clearly differentiated in the study area. Although formed in similar geomorphological settings, the soil typologies are diverse: Podzol group soils are developed under old-growing coniferous forest, whereas Cambisols occur under present-day old-meadows. By applying PCA including pedological and geochemical parameters, we can clearly discriminate between Podzol and Cambisol samples, revealing differences that reflect the intensity of chemical weathering. In contrast, deep and surface samples can be distinguished using the degree of physical weathering. The proportions of organic-bound Al and Fe are significantly higher in Podzols, thus providing a sediment tracer to reconstruct the intensity and degree of podzolisation. The increase of Light REE fractionation from the C-horizons to the topsoil horizons is explained in terms of soil processes. The high-field-strength element Nb is used to estimate enrichment or depletion relative to the unweathered parent material. The resulting normalized REE patterns indicate that Podzol profiles are more depleted than Cambisols. Moreover, normalized REE patterns of A- and B w-horizons are similar in the Cambisol profiles, whereas the E- and B s-horizons of Podzols exhibit large variations. Normalized REE patterns may thus provide a precise tracer of the degree of weathering of materials. Hence, we suggest that REE behaviour and soil weathering are clearly related. This study also highlights the effects of millennial-scale agricultural practices on soils, e.g. the eventual depodzolization related to deforestation.

NEW GEOCHEMICAL AND AGE DATA ON THE OPHIOLITES FROM THE OTHRYS AREA (GREECE): IMPLICATION FOR THE TRIASSIC EVOLUTION OF THE VARDAR OCEAN

This paper presents new radiolarian biostratigraphic and volcanic geochemical data for the Agoriani Melange Unit and Fourka Unit, which represent the basal part of the Othrys ophiolitic nappe (central Greece). The Agoriani Melange Unit is the base of the Othrys ophiolitic nappe, consists of a tectono-sedimentary melange that is, in turn, tectonically overthrust by the Fourka Unit, which consists of basalt-radiolarian chert sequences. Geochemical data show that, in the study area, the Agoriani Melange includes alkaline within-plate basaltic (WPB) and normal-type mid-ocean ridge (N-MORB) sequences in the pillowfacies, while the Fourka Unit mainly consists of normal-type mid-ocean ridge basaltic (N-MORB) sequences, as well as low-K tholeiitic (L-KT) sequences, both in occurring in the pillow-facies. Alkaline WPB have a clear enriched nature, with high concentration of high field strength elements (HFSE), relative enrichment in light (L-) rare earth elements (REE) with respect to heavy (H-) REE, and high Nb/Y (> 0.7), Ce/Y (> 1.5) Ta/Hf (> 0.35), Th/Yb (> 0.7) and Ta/Yb (> 0.3) ratios. N-MORB rocks have a more depleted nature with flat N-MORB normalized HFSE patterns, flat or slightly LREE depleted chondrite normalized REE patterns, and low Nb/Y (< 0.3), Ce/Y (< 0.5) Ta/Hf (< 0.1), Th/Yb (< 0.08) and Ta/Yb (< 0.05) ratios. L-KT basalts show an evident subduction- related geochemical signature exemplified by depletion of Ta, Nb, Zr, and Ti relative to other HFSE, slight LREE/HREE enrichment, and relative enrichment of Th with respect to Ta. Biostratigraphic data for the Fourka Unit show that radiolarites associated with N-MORBs were deposited, on the whole, in Middle and Late Triassic time. In particular the late Anisian - early Ladinian age found in one stratigraphic section represents the oldest age ever reported for a MORB sequence in the Hellenides. Radiolarites deposited over the L-KT basaltic sequence are early Carnian - middle Norian/Late Norian in age. The radiolarites associated with alkaline WPB in the Agoriani Melange did not yield determinable radiolarians, while a radiolarite sequence in this melange not associated with basalts is middle Bathonian to late Bathonian/early Callovian in age. The data presented in this paper provide new constraints on the early (Middle- Late Triassic) phase of evolution of the Vardar Ocean in the Hellenides. The MORBs are interpreted to have erupted during Middle-Late Triassic time, related to the initial opening of the Vardar oceanic basin. The L-KT basalts are interpreted to have erupted during Middle-Late Triassic time (i.e., in part contemporaneously with MORBs), in the ocean-continent transition zone adjacent to the rifted continental margin. Moreover, we speculate that the alkaline WPB have formed in oceanic seamounts or in the ocean-continent transition zone adjacent to the rifted continental margin.

Geochemistry, K–Ar geochronology and Sr–Nd–Pb isotope compositions of pitchstone in Gohado, southwestern Okcheon Belt, South Korea

Abstract Geochemical and Sr–Nd–Pb isotope characteristics, as well as K–Ar geochronology of a massive pitchstone (volcanic glass) stock erupted into Late Cretaceous lapilli tuff and rhyolite in the Gohado area, southwestern Okcheon Belt, South Korea, are reported. The pitchstones are highly evolved with SiO2 contents ranging from ∼72 to 73 wt%, K2O/Na2O ratios of 1.04–1.23 and low MgO/FeOt values (0.17–0.20). The pitchstones are weakly peraluminous and the ASI (molar Al2O3/Na2O + K2O + CaO) values are significantly lower than 1.1. The pitchstones also display a general calc‐alkaline nature with significant alkali contents. The rare earth elements (REE) compositions show moderately fractionated nature with (La/Yb)N ranging from 11 to 16. Chondrite normalized REE patterns show relative enrichment of light REE over heavy REE and moderate Eu anomaly (Eu/Eu* ratio varies from 0.53 to 0.57). A distinct negative Nb anomaly is observed for all pitchstones on a primitive mantle normalized trace element diagram, typical of subduction‐related magmatism and crustal‐derived granites. All these features are characteristic of I‐type granites derived from a continental arc. The pitchstones have Zr contents of 98.5–103.5 ppm with zircon thermometry yielding temperatures of 749–755°C (mean 752°C). The K–Ar analyses of representative pitchstone samples yielded ages of 58.7 ± 2.3 and 62.4 ± 2.1 Ma with a mean age of 61 Ma. The rocks show nearly uniform initial 87Sr/86Sr isotopic ratios of 0.7104–0.7106 and identical 143Nd/144Nd initial ratio of 0.5120. The rocks display negative εNd (61 Ma) values of −12. The depleted mantle model ages (TDM) range from 1.54 Ga to 1.57 Ga. The Pb isotope ratios are 206Pb/204Pb = 18.522–18.552, 207Pb/204Pb = 15.642–15.680 and 208Pb/204Pb = 38.794–38.923. These ratios suggest that the Gohado pitchstones were formed in a continental arc environment by partial melting of a 1.54 Ga to 1.57 Ga parental sources of lower crustal rocks probably of mafic or intermediate compositions.

Major to ultra trace elements in rainfall collected in suburban Tokyo

Major to ultra trace elements such as rare earth elements (REEs), platinum group elements (PGEs) in 20 rainfall events from suburban Tokyo were determined by inductively coupled plasma mass spectrometry (ICP-MS). Anion species were also determined by an ion chromatography (IC). The concentrations of PGEs were so low that only Pt was detected in some rainfall events. Enrichment factors (EFs), refer to soil and sea salt components, were calculated for the measured elements (with Al and Na as references). Be, (Na), Mg, (Al), Si, Cl, K, Fe, Rb, Sr, REEs (except La, Gd), Ta, and U were mostly originated from natural materials (soil and sea salt). For Li, B, Ca, Mn, Sr, Ba, and Cs, the contribution of natural materials was significant. EFs for Cu, Zn, As, Se, Sb, Cd, Pb, Bi, Ag, Te, Au, Pt, SO 4-S and NO 3-N exceeded 100 indicating non-crustal, non-sea salt origin, presumably anthropogenic; however, contribution of volcanic gases could not be excluded for As, Se, Te and Bi. Pt seemed to be uniformly distributed worldwide and a catalyst for automobile emission control may be the main source. Au also showed uniform distribution. On the other hand, EFs for Zr, Nb, Hf and Th were less than unity. Probably these elements resided in acid resistant refractory fine minerals that did not decompose with acid treatment, and did not evaporate and ionize in the ICP. An alternative explanation is that the concentration of these elements was lower in the soil of the sampling area than the average crust. In the crust normalized REE pattern plot, La, Eu and Gd showed clear positive anomalies. La and Gd could have anthropogenic components. A possible source of La and Gd is cracking catalyst for petrol refining, but this source does not fully explain the anomaly. The source of Gd may also be Gd-DTPA (Gadolinium (III) diethyltriaminepentaacetic acid) used for Magnetic Resonance Imaging (MRI) contrast agents. The Eu origin may be soil with higher concentration than the crust average.

Analysis of Uranium Bearing Samples for Rare Earth and Other Elements by k0-Based Internal Monostandard INAA Method

A k0-based internal monostandard instrumental neutron activation analysis (IM-INAA) method was applied for the multielement analysis in uranium bearing samples. Spectral interference correction factors in INAA due to neutron induced fission of uranium for La, Ce, Nd, Zr, Ru, and Mo as well as activation of uranium for Sm and Lu were evaluated using elemental standards. The correction factors were validated by standard addition method in a synthetic sample containing known amount of natuural uranium. For evaluating the accuracy of the IM-INAA method, the low uranium containing SRM 1633a (coal fly ash) obtained from NIST was used. For method validation of analysis of uranium bearing sample, SRM 1633a spiked with uranium (about 0.05%) was analyzed by IM-INAA method. The standardized IM-INAA method was applied to analyze uranium ore samples obtained from Jaduguda and Bhatin mines, Jharkhand, India for multielement content including U, Th, and rare earth elements (REEs). Chondrite normalized REE patterns were plotted for obtaining Ce and Eu anomalies.

Seasonal dissolved rare earth element dynamics of the Amazon River main stem, its tributaries, and the Curuaí floodplain

We present a comprehensive dissolved rare earth element (REE) data set for the Amazon River and its main tributaries, Rio Negro, Solimões, and Madeira, as well as the Curuaí floodplain. The two‐year time series show that REE vary seasonally with discharge in each of the tributaries, and indicate a hydrologically dominated control. Upper crust normalized REE patterns are relatively constant throughout the year, with Ce/Ce* anomalies being positively related to discharge. We propose revised annual dissolved REE fluxes to the surface Atlantic Ocean based on an integration of the seasonal data. For Nd (&lt;0.22 μm) this results in an average flux of 607 ± 43 T/yr, which is at least 1.6 times larger than the previous estimate of 374 T/yr (&lt;0.45 μm) based on low water stage data. Moreover, during the high water season the maximum Nd flux measures 1277 t.yr−1, constituting 30% of the required flux to the Atlantic Ocean (Tachikawa et al., 2003). Consequently, a smaller contribution of Nd from atmospheric and river particle desorption is required than was previously suggested. A mass balance of Amazon tributaries and observed fluxes at Óbidos indicates that dissolved LREE behave quasi‐conservatively. Conversely, the HREE mass balance presents a deficit during the high water stages, which could be related to the passage of water through the floodplain system accompanied by solid/dissolved phase transfer.

Origin of convex tetrads in rare earth element patterns of hydrothermally altered siliceous igneous rocks from the Zinnwald Sn–W deposit, Germany

The chondrite-normalized rare earth element (REE) patterns of whole rock samples from evolved granitic systems hosting rare metal deposits sometimes show a split into four consecutive curved segments, referred to as tetrads. In the present contribution, a rigorous statistical method is proposed that can be used to test whether geological significance should be attributed to tetrads that are only of limited size. The method involves a detailed evaluation of element and sample specific random and systematic errors that are constrained on the basis of independent repeated preparations and analyses of sample and reference materials. Application of the proposed method to samples from the granite-hosted Zinnwald Sn–W deposit, Germany, revealed that at least two tetrads in normalized whole rock REE patterns have to be analytically significant to rule out that fractional crystallization led to the unusual behavior of the REEs. Based on the analysis of altered albite granite and greisen samples from the endocontact of the Zinnwald granite massif, it is demonstrated that the lanthanide tetrad effect is responsible for the formation of the convex tetrads. Geological and petrological evidence suggests that the tetrads in the samples developed prior to greisenization and related cassiterite precipitation. In contrast to the endocontact samples, the rhyolitic wall rocks are typified by normalized REE patterns having tetrads that are variable in size and frequently close to the limit of analytical significance. The sizes of the tetrads apparently correlate with the intensity of albitization, but show no relation to subsequent alteration processes including greisenization and low-temperature argillization. This observation proves that curved segments in normalized whole rock REE patterns can be introduced during hydrothermal fluid–rock interaction.

Seasonal and spatial variations of rare earth elements in rainwaters, river waters and total suspended particles in air in South Korea

In order to investigate the seasonal and spatial variations of rare earth element (REE) concentrations in natural waters in the central part of South Korea, rain and river waters were collected during 2003–2004. Total suspended particles (TSP) in air were also sampled to investigate the effect of the Asian dust (the Yellow sand) on the chemistry of rainwaters. All samples showed that the absolute concentrations of the light REEs (LREEs) were higher than those of the heavy REEs (HREEs). The post-Archean Australian shale (PAAS)-normalized REE patterns indicate that the REEs in TSP and rainwaters were affected by Asian dust and anthropogenic contaminant, whereas those of river waters were mainly controlled by the geology of their drainage basin and seasonal changes in water regime. The calculated fluxes and yields of total REEs (REEs plus Y) in the South Han River were much greater than those in the North Han River due to the more widespread distribution of sedimentary rocks in the drainage area and more efficient chemical weathering.

Rare earth element abundances in some seawaters and related river waters from the Osaka Bay area, Japan: Significance of anthropogenic Gd

Some major and trace elements in seawaters and related river waters from the Osaka Bay area, Japan were analyzed in order to examine rare earth element (REE) behaviors, especially the relationship between anthropogenic gadolinium (Gd) and nutrient concentrations. The local silicic rock normalized REE patterns for the seawaters show features of light REE depletion, negative Ce anomaly, and very small Eu anomaly. Moreover, some samples have obvious positive Gd anomalies due to contamination of Magnetic Resonance Imaging (MRI) contrast agents in medical use. We calculated the anthropogenic Gd concentrations by subtracting the assumed natural Gd concentration from the measured one. The anthropogenic or excess Gd concentrations of the seawater samples are well correlated with nutrient concentrations (NH4-N, NO2-N, NO3-N, PO4-P). Because both anthropogenic Gd and nutrients are abundant in sewage treatment plant (STP) effluents and much less abundant in non-contaminated river and seawaters, the observed trends can be explained by dilution of STP effluents with non-contaminated river and seawaters. It was found that the nutrient concentrations for a hypothetical STP effluent calculated by using these correlation lines are consistent with the average nutrient contents for the STP effluents in the study area. Moreover, we made a rough estimation of Gd budget in Osaka Bay. The estimated amount of the Gd MRI contrast agents consumed in the area seems to be consistent with the excess Gd concentrations of river and STP waters. The Gd observations in this study suggest that the Gd anomaly data can be used as a geochemical tracer of wastewater component in urban areas.

Trace-element composition of hydrothermal zircon and the alteration of Hadean zircon from the Jack Hills, Australia

Hydrothermal zircon can be used to date fluid-infiltration events and water/rock interaction. At the Boggy Plain zoned pluton (BPZP), eastern Australia, hydrothermal zircon occurs with hydrothermal scheelite, molybdenite, thorite and rutile in incipiently altered aplite and monzogranite. The hydrothermal zircon is texturally distinct from magmatic zircon in the same rocks, occurring as murky-brown translucent 20–50 μm-thick mantles on magmatic cores and less commonly as individual crystals. The hydrothermal mantles are internally textureless in back-scatter electron and cathodoluminescence images whereas magmatic zircon is oscillatory zoned. The age of the hydrothermal zircon is indistinguishable from magmatic zircon, indicating precipitation from a fluid evolved from the magma during the final stages of crystallization. Despite indistinguishable U-Pb isotopic compositions, the trace-element compositions of the hydrothermal and magmatic zircon are distinct. Hydrothermal zircon is enriched in all measured trace-elements relative to magmatic zircon in the same rock, including V, Ti, Nb, Hf, Sc, Mn, U, Y, Th and the rare-earth elements (REE). Chondrite-normalized REE abundances form two distinct pattern groupings: type-1 (magmatic) patterns increase steeply from La to Lu and have Ce and Eu anomalies—these are patterns typical for unaltered magmatic zircon in continental crust rock types; type-2 (hydrothermal) patterns generally have higher abundances of the REE, flatter light-REE patterns [(Sm/La) N = 1.5–4.4 vs. 22–110 for magmatic zircon] and smaller Ce anomalies (Ce/Ce* = 1.8–3.5 vs. 32–49 for magmatic zircon). Type-2 patterns have also been described for hydrothermally-altered zircon from the Gabel Hamradom granite, Egypt, and a granitic dyke from the Acasta Gneiss Complex, Canada. Hadean (∼4.5–4.0 Ga) zircon from the Jack Hills, Western Australia, have variable normalized REE patterns. In particular, the oldest piece of Earth—zircon crystal W74/2-36 (dated at 4.4 Ga)—contains both type-1 and type-2 patterns on a 50 μm scale, a phenomenon not yet reported for unaltered magmatic zircon. In the context of documented magmatic and hydrothermal zircon compositions from constrained samples from the BPZP and the literature, the type-2 patterns in crystal W74/2-36 and other Jack Hills Hadean (JHH) zircon are interpreted as hydrothermally-altered magmatic compositions. An alteration scenario, constrained by isotope and trace-element data, as well as α-decay event calculations, involving fluid/zircon cation and oxygen isotope exchange within partially metamict zones and minor dissolution/reprecipitation, may have occurred episodically for some JHH zircon and at ∼4.27 Ga for zircon W74/2-36. Type-2 compositions in JHH zircon are interpreted to represent localized exchange with a light-REE-bearing, high δ 18O (∼6–10‰ or higher) fluid. Thus, a complex explanation involving “permanent” liquid water oceans, large-scale water/rock interaction and plate tectonics in the very early Archean is not necessary as the zircon textures and compositions are simply explained by exchange between partially metamict zircon and a low volume ephemeral fluid.

Rare earth element geochemistry of groundwater in the Palouse Basin, northern Idaho–eastern Washington

Concentrations of rare earth elements (REE) were determined in groundwaters from the Palouse Basin, located in northern Idaho and eastern Washington. Samples were taken from wells and springs tapping waters in four different rock units: loess, Wanapum Basalt, Grande Ronde Basalt, and Moscow Mountain Granite. In general, unfiltered aliquots of the waters had higher concentrations of REE than those filtered through a 0.45 μm filter, sometimes by several orders of magnitude, indicating the presence of REE as suspended particles or large colloids. Overall REE concentrations in the waters decrease, and the unfiltered and filtered aliquots become more similar in concentration, with increasing depth within the stratigraphic section (i.e. loess → Wanapum → Grande Ronde). There are some distinctions in NASC (North American Shale Composite)-normalized REE patterns among the four groups of waters, but there is considerable variation among the waters within each group. When normalized to their host rocks, most filtered and many unfiltered aliquots of groundwaters from all four units show depletion of the LREE relative to the HREE. The results are consistent with a model in which meteoric water enters the basalt aquifers via the loess, picking up a heavy particulate and some dissolved REE load, followed by infiltration downward through the units. While moving downwards, the waters are subjected to natural filtration processes in which the particulate REE are largely removed.

Geochemistry of Rewalsar Lake sediment, Lesser Himalaya, India: implications for source-area weathering, provenance and tectonic setting

Major, trace and rare earth element (REE) chemistry of fresh-water lake sediments, stituated in the middle Siwalik Formation (Pliocene), have been investigated. The log (Fe2O3/K2O) vs log (SiO2/Al2O3) plot of sediments discriminate the rock types of the catchment which are remarkably similar to those observed in thinsections. The Chemical Index of Alteration (CIA) between 75.2 to 78.1 and Chemical Index of Weathering (CIW) between 79.5 to 89.8 are higher than Post-Archean Australian Shale (PAAS), indicating moderate to high weathering at source area. The PAAS normalized REE patterns are similar and differentiate the major rock types on the basis of abundance of REEs in accordance to clay minerals, grain size, with the highest concentration in the finest grain sediments. It also indicates poor mixing of sediments. The consistency of REEs in sediments with those of rock types illustrate almost unaltered, unmodified transport of these from the provenance to the detritus deposited in the basin and also shows that the REEs are enriched in phyllosilicates. The major elements, Fe2O3, TiO2, MgO, K2O show strong positive correlation with Al2O3 and follow the trend of the latter, and REEs also indicate same characteristics, hence phyllosilicates are likely to be the promising host for REEs. The negative correlation of La, Yb and Y with Zr and positive correlation with REEs and Al2O3 do not indicate Zr control on REE distribution in the present case. The petrographic character of minerals in thinsection of rocks as well as of lake sediments and low Na2O/K2O ratio in the latter show short distance transport, textural immaturity and sorting of grains. The higher Zr/Th and Zr/Yb ratios in coarser sediments than in fine grain detritus are supporting evidence of sedimentary sorting. Chondrite normalized REE patterns and negative Eu anomaly of the lake sediments are similar to that of PAAS indicating that they may have been originally derived from differentiated silicic (felsic) and/or recycled sedimentary source and deposited in foreland basin. However, petrographic character, REEs and high field strength elements estimated on sediments, tends to support metamorphic source area for middle Siwalik detritus and is consistent to the observations made on rocks exposed in the catchment area, attesting to the rise of Himalaya in phases, exposing fresh rocks for erosion/weathering, lying northward in Lesser Himalayan domain. Plot of sediment chemistry of lakes on tectonic delineation diagrams show that Rewalsar detritus derived from middle Siwalik rocks are from passive margin setting. The discriminant function plots of sediment samples also indicate that they are derived from craton interior or a quartzose sedimentary orogenic terrain and deposited in a passive margin setting. The chemistry of Rewalsar sediments is thus a proxy for the middle Siwalik rocks deposited in the foreland basin and throw light on provenance, source area weathering, and tectonic setting of the source rock.

Genesis of Mg-Fe Carbonates from the Sierra Menera Magnesite-Siderite Deposits, Northeast Spain: Evidence from Fluid Inclusions, Trace Elements, Rare Earth Elements, and Stable Isotope Data

The Mg-Fe carbonate deposits of Sierra Menera, underneath exploited goethite gossan, are located in the Iberian Range of northeasten Spain within the Late Ordovician dolomitic formation of the Sierra Menera unit. MgO and FeO contents of the carbonates range between 13.74 and 44.02 and 5.52 and 41.73 wt percent, respectively, corresponding to the breunnerite and pistomesite members. The morphology, petrographic, mineralogical, and geochemical characteristics of the Mg-Fe carbonates are consistent with a metasomatic hydrothermal origin by replacement of a dolomitic protolith as the result of the influx of hot Fe-Mg–rich fluids under acid and reducing conditions. These deposits have similarities to Alpine-type magnesite deposits (Austria, Slovakia, western Carpathian Mountains, Pyrenees) and Mississippi Valley-type Fe deposits (Basque-Cantabrian basin, northern Spain). The Mg-Fe carbonates have normalized rare earth element (REE) patterns characterized by low light REE/heavy REE ratios and positive Eu anomalies. Dolomite rocks that host Mg-Fe occurrences have been recrystallized to saddle dolomite crystals and have less fractionated normalized REE patterns but are also characterized by positive Eu anomalies. These patterns are distinct from the pristine host dolomite, which has REE distribution typical of marine carbonates. Based on REE, fluid inclusion, and stable isotope data, the Mg-Fe carbonates are interpreted to have been formed by interaction between hot (100°–150°C), 18O-enriched, and saline (20 wt % NaCl equiv) iron-rich hydrothermal fluids and marine carbonates. Recrystallization of the host dolomite resulted from moderate to low fluid/rock ratios ( >10). The Mg-Fe carbonates were partially replaced by late dolomite (redolomitization) due to the action of more dilute solutions. Although this event resulted in 18O depletion, REE patterns and 13C values of the precursors were preserved.

Identifying Accessory Mineral Saturation during Differentiation in Granitoid Magmas: an Integrated Approach

Numerical reconstructions of processes that may have operated during igneous petrogenesis often model the behaviour of important trace elements. The geochemistry of these trace elements may be controlled by accessory mineral saturation and fractionation. Determination of the saturation point of accessory minerals in granitoid rocks is ambiguous because assumptions about crystal morphology and melt compositions do not always hold. An integrated approach to identifying accessory mineral saturation involving petrography, whole-rock geochemical trends, saturation calculations and mineral chemistry changes is demonstrated here for a compositionally zoned pluton. Within and between whole-rock samples of the Boggy Plain zoned pluton, eastern Australia, the rare earth element (REE)-enriched accessory minerals zircon, apatite and titanite exhibit compositional variations that are related to saturation in the bulk magma, localized saturation in intercumulus melt pools and fractionation of other mineral phases. Apatite is identified as having been an early crystallizing phase over nearly the whole duration of magma cooling, with zircon (and allanite) only saturating in more felsic zones. Titanite and monazite did not saturate in the bulk magma at any stage of differentiation. Although some trace elements (P, Ca, Sc, Nb, Hf, Ta) in zircon exhibit compositional variation progressing from mafic to more felsic whole-rock samples, normalized REE patterns and abundances (except Ce) do not vary with progressive differentiation. This is interpreted to be a result of limitations to both simple ‘xenotime’ and complex xenotime-type coupled substitutions. Our data indicate that zircon REE characteristics are not as useful as those of other REE-rich accessory minerals as a petrogenetic indicator.

Hydrothermal rare earth elements mineralization in the Barra do Itapirapuã carbonatite, southern Brazil: behaviour of selected trace elements and stable isotopes (C, O)

The Barra do Itapirapuã carbonatite is located in southern Brazil and belongs to the Cretaceous Ponta Grossa alkaline–carbonatitic province related to the opening of the South Atlantic. The carbonatite complex is emplaced in Proterozoic granites and is mainly composed of plutonic magnesio- to ferrocarbonatite, with smaller amounts of subvolcanic magnesiocarbonatite. Hydrothermal alteration of the carbonatite has led to the formation of quartz, apatite, fluorite, rare earth fluorocarbonates, barite and sulfides in variable proportions. Trace element data, δ 13 C and δ 18 O are presented here, with the aim of better understanding the geochemical nature of hydrothermal alteration related to rare earth elements (REE) mineralization. The non-overprinted plutonic carbonatite shows the lowest REE contents, and its primitive carbon and oxygen stable isotopic composition places it in the field of primary igneous carbonatites. Two types of hydrothermally overprinted plutonic carbonatites can be distinguished based on secondary minerals and geochemical composition. Type I contains mainly quartz, rare earth fluorocarbonates and apatite as hydrothermal secondary minerals, and has steep chondrite normalized REE patterns, with Σ REE+Y of up to 3 wt.% (i.e., two orders of magnitude higher than in fresh plutonic samples). In contrast, the Type II overprint contains apatite, fluorite and barite as dominant hydrothermal minerals, and is characterized by heavy REE enrichment relative to the fresh samples, with flat chondrite normalized REE patterns. Carbon and oxygen stable isotope ratios of Types I and II are elevated ( δ 18 O +8 to +12‰; δ 13 C −6 to −2‰) relative to the fresh samples. Hydrothermally overprinted carbonatites exposed to weathering show even higher δ 18 O values ( δ 18 O 13 to 25‰) but no additional REE enrichment. The subvolcanic carbonatite has anomalously high δ 13 C of up to +1‰, which suggests crustal contamination through interaction with carbonate-bearing metasediments.

Rare earth elements in apatite: Uptake from H 2O-bearing phosphate-fluoride melts and the role of volatile components

The partitioning of rare earth elements (REEs) between fluorapatite (FAp) and H 2O-bearing phosphate-fluoride melts has been studied at about 700 and 800°C and 0.10–0.15 GPa. REE uptake patterns, i.e., plots of D(REE:FAp/melt), are convex upwards and peak near Nd for single-REE substituted FAp at minor (0.03–0.25 wt% REE 2O 3) abundances, and binary(LREE + HREE)-substituted FAp, and hexa-REE-substituted FAp at minor to major (0.25–7.8 wt% REE 2O 3) abundances. Partition coefficients for minor abundances of REE and depolymerized phosphate melts are about 5, 8, and 1 for La, Nd, and Lu, respectively and broadly comparable to those for early fluorapatite in the fractionation of melts of basaltic composition. The Ca2 site exerts marked control on the selectivity of apatite for REE because it preferentially incorporates LREE and its effective size varies with substitution of the A-site volatile anion component (F, Cl, OH). Using simple crystal-chemical arguments, melt(or fluid)-normalized REE patterns are predicted to peak near Nd for fluorapatite and be more LREE-enriched for chlorapatite. These predictions are consistent with data from natural rocks and laboratory experiments. The wide variation in D(REE:apatite/melt) in nature (from <1 for whitlockite-bearing lunar rocks to about 100 for evolved alkalic rocks) is attributed largely to the influence of the volatile components.