Concentrations Of Light Rare Earth Elements Research Articles

Comprehensive refertilization of the Archean–Paleoproterozoic lithospheric mantle beneath the northwestern North China Craton: Evidence from in situ Sr isotopes of the Siziwangqi peridotites

Petrological observations and in situ major and trace element and Sr isotopic data for spinel-facies harzburgite and lherzolite xenoliths from the Siziwangqi region provide constraints on the nature and evolution of the lithospheric mantle beneath the northwestern North China Craton (NCC). These peridotites can be divided into high-Mg# peridotites (Fo > 91) and low-Mg# peridotites (Fo < 91), according to olivine forsterite (Fo) contents. The high-Mg# peridotites are harzburgites, which are characterized by high Mg# (91.0–91.8), as well as low CaO (0.41–1.17 wt%) and Al2O3 (0.62–2.03 wt%) contents. The clinopyroxenes have light rare earth element (LREE) depleted to slightly enriched patterns, and variable but dominantly radiogenic Sr isotopic compositions (0.7031–0.7053). These features indicate that the high-Mg# peridotites are remnants of Archean–Paleoproterozoic refractory lithospheric mantle, which then experienced variable refertilization. In contrast, the low-Mg# peridotites are mainly lherzolites and minor harzburgites, which have low Mg# (89.2–90.9), and high CaO (0.98–3.53 wt%) and Al2O3 (1.38–3.85 wt%) contents, relative to the high-Mg# peridotites. The clinopyroxenes in low-Mg# peridotites have similar REE patterns as those in the high-Mg# peridotites, and some grains show increasing LREE contents from core to rim. These clinopyroxenes have relatively depleted Sr isotopic compositions (0.7021–0.7045). The low-Mg# peridotites are interpreted to be the reaction products of high-Mg# peridotites and asthenospheric melts. The lithospheric mantle beneath the Siziwangqi region experienced an earlier metasomatic event related to subduction of Paleo-Asian oceanic materials, as evidenced by the relatively high 87Sr/86Sr ratios (up to 0.7053) and depletion of Rb, Ba, Pb, Nb and Ta in clinopyroxenes. The clinopyroxenes in both high- and low-Mg# peridotites have low (La/Yb)N and high Ti/Eu ratios, positive correlations between 87Sr/86Sr and Mg# and Ca/Al, negative correlations between 87Sr/86Sr and Na2O, TiO2, Ti/Eu, and Σ(middle REEs + heavy REEs), and decreasing 87Sr/86Sr ratios from core to rim. These observations imply that the lithospheric mantle beneath the Siziwangqi region experienced later multi-stage refertilization by asthenospheric melts. Therefore, we conclude that the lithospheric mantle beneath the northwestern NCC has been comprehensively refertilized by multiple stages of peridotite–melt reactions, similar to the northern margin of the NCC, which had a significant role in the transformation of the lithospheric mantle.

Sill Intrusion into Pyroxenitic Mush and the Development of the Lower–Upper Critical Zone Boundary of the Bushveld Complex: Implications for the Origin of Stratiform Anorthosites and Chromitites in Layered Intrusions

Abstract Layered mafic–ultramafic intrusions are the fossilized remnants of magmatic plumbing systems and provide excellent natural laboratories to investigate the processes of magma differentiation and solidification. The Rustenburg Layered Suite is the plutonic mafic–ultramafic part of the Bushveld Complex of South Africa and it has traditionally been assumed to have formed from an upwardly aggrading (and in-sequence) crystal pile in a melt-dominated chamber. In this study, we present field and petrological observations, complemented with detailed plagioclase mineral chemistry [molar An, light rare earth elements (LREE) and strontium isotopes] for the first stratiform anorthosite layer (MG3F anorthosite) at the Lower–Upper Critical Zone boundary (LCZ–UCZ) in the eastern limb of the Bushveld Complex. We use these data to test the overarching paradigm of a melt-dominated chamber for the magmatic evolution of the Rustenburg Layered Suite. The MG3F anorthosite is immediately overlain by the MG3 chromitite and both are surrounded by pyroxenite. A distinctive ‘egg-box’ structure, consisting of round pyroxenite blocks mantled by chromitite, marks the LCZ–UCZ boundary, and represents an erosional disconformity at the base of the MG3F anorthosite. The MG3F anorthosite is laterally continuous for hundreds of kilometers in the eastern limb. In the northern–central sector of the eastern limb, the 1·5 m thick MG3F anorthosite is characterized by non-cotectic proportions of foliated plagioclase and chromite chains that lie parallel to the foliation. The MG3F anorthosite is divisible into two sub-layers on the basis of (1) a compositional break in plagioclase molar An, LREE and strontium isotope composition and (2) a peak in chromite mode (up to 12 vol%). In the lower half of the layer plagioclase LREE concentrations increase upward, molar An shows a marginal decrease upward and strontium isotopes are relatively homogeneous (87Sr/86Sr2·06Ga 0·7056–0·7057). In the upper half of the layer, plagioclase LREE concentrations decrease upward, molar An shows a marginal increase upward and strontium isotopes show strong inter- and intra-grain variability (87Sr/86Sr2·06Ga 0·7053–0·7064). Strontium isotopes in interstitial plagioclase in the immediate footwall and hanging-wall pyroxenites show similar 87Sr/86Sr2·06Ga values to the MG3F anorthosite and decrease with distance from the MG3F anorthosite. In the southern sector of the eastern limb, the 4 m thick MG3F anorthosite exhibits identical stratigraphic compositional trends in terms of molar An in plagioclase. We infer that the MG3F anorthosite formed by two successive sill-like injections of magma into a resident viscoplastic pyroxenitic crystal mush. An initial pulse of plagioclase-saturated melt underwent in situ fractional crystallization, manifested as upwardly decreasing molar An and upwardly increasing LREE in plagioclase in the lower half of the MG3F anorthosite. Sill intrusion caused deformation of the viscoplastic pyroxenite mush and vortices of superheated liquid generated by frictional viscous heating caused disaggregation of the footwall pyroxenitic mush. Disaggregated blocks of pyroxenitic mush reacted with the superheated liquid (a hybrid chromite-saturated melt) to produce chromite-rich rims at the base of the MG3F anorthosite (egg-box structure). A second sill-like injection of magma then entered the chamber that halted in situ crystallization. This sill was a plagioclase slurry that contained isotopically distinct plagioclase laths compared with those present in the previous sill. The upward increase in molar An of plagioclase, and decreasing LREE, may be explained by the slurry becoming more primitive in melt composition with time. The second sill also caused mush disaggregation and renewed the production of a hybrid chromite-saturated melt. Chromite crystals were then mobilized and injected as slurries at the interface between the sill and resident mush towards the back of the flow, culminating in the development of the MG3 chromitite. Our model for the development of the Lower–Upper Critical Zone boundary questions the existence of a melt-dominated chamber and it has implications for the origin of stratiform anorthosites (and chromitites) in crustal magma chambers.

The Southeastern Saurashtra dyke swarm, Deccan Traps: Magmatic evolution of a tholeiitic basalt–basaltic andesite–andesite–rhyolite suite

The Deccan Traps continental flood basalt (CFB) province of India contains several dyke swarms, which are dominated by tholeiitic basalts and basaltic andesites. The Southeastern Saurashtra dyke swarm, containing mainly these rock types, also contains an andesite and several rhyolites. Based on petrographic, mineral chemical, and whole-rock major and trace element and Sr-Nd isotopic data, we discuss the magmatic evolution and pressure-temperature conditions of crystallisation of these dyke magmas. The tholeiitic basalts and basaltic andesites have low to moderate TiO2 contents. The andesite and the rhyolites have low CaO, MgO, Fe2O3t, TiO2 and P2O5, and high K2O, Rb, Ba and light rare earth element contents. Thermobarometric calculations for equilibrium mineral–whole-rock pairs indicate plagioclase crystallisation at 1200–1170 °C, overlapping with clinopyroxene crystallisation at 1181–1143 °C, and a pressure range of 0.1–3.6 kbar indicating crystallisation during magma ascent or storage at shallow crustal levels. Major and trace element modelling is consistent with the rhyolites being produced by advanced fractional crystallisation of basaltic parental magmas. However, a broad trend of increasingly radiogenic Sr and nonradiogenic Nd isotopic ratios, from the mafic rocks through the andesite to the rhyolites, suggests a combined assimilation and fractional crystallisation (AFC) process between basaltic magma and ancient granitic crust. The rhyolites contain the largest crustal contributions and display the most “enriched” Sr-Nd isotopic characteristics yet recorded from the Deccan Traps (εNdt = −20.6, (87Sr/86Sr)t = 0.74855). The widespread occurrence of mafic enclaves in the rhyolite dykes suggests that processes such as magma mixing may also be responsible for some of the andesitic rocks known in Saurashtra.

Stagnant slab front within the mantle transition zone controls the formation of Cenozoic intracontinental high-Mg andesites in northeast Asia

AbstractThe geochemistry of Cenozoic intracontinental high-Mg andesites (HMAs) in northeast Asia, together with regional geophysical data, offers an opportunity to explore the genetic relationship between the formation of intracontinental HMAs and subduction of the Pacific plate. Compared with primary HMAs in arcs, Cenozoic intracontinental HMAs in northeast Asia have lower Mg# [100 × Mg/(Mg + Fe2+)] values (53–56) and CaO contents (5.8–6.6 wt%), higher alkali (Na2O + K2O) contents (5.15–6.45 wt%), and enriched Sr-Nd-Hf isotopic compositions (87Sr/86Sr = 0.7056–0.7059; εNd = −4.9 to −3.4; εHf = −4.7 to −2.6) as well as lower Pb isotope ratios (206Pb/204Pb = 16.76–19.19; 207Pb/204Pb = 15.42–15.45; 208Pb/204Pb = 36.71–37.11). These Cenozoic intracontinental HMAs are similar to Cenozoic potassic basalts in northeast China with respect to their Sr-Nd-Pb-Hf isotopic compositions but have higher SiO2 and Al2O3 contents and lower K2O, MgO, and light rare earth element contents. These features indicate that these Cenozoic intracontinental HMAs originated from the mantle, where recycled ancient sediments and water contributed to partial melting of peridotite. Combined with the presence of a large low-resistivity anomaly derived from the mantle transition zone (MTZ) near these intracontinental HMAs, and their occurrence above the stagnant slab front within the MTZ (at 600 km depth) in northeast Asia, we conclude that the stagnant slab front, with high contents of recycled ancient sediments and water, has controlled the formation of Cenozoic intracontinental HMAs in northeast Asia.

A comparison of global rare earth element (REE) resources and their mineralogy with REE prospects in Sri Lanka

Rare earth elements (REEs), a group of 17 elements comprises 15 lanthanides, scandium and yttrium, are largely attracting the world’s attention due to their importance in a wide variety of advanced technological applications. Global REEs production is mainly sourced from resources, such as carbonatites, alkaline igneous rocks, placers, laterites, and ion-adsorption clays. Recently, REE demand has been escalating, especially due to the REE applications in renewable energy and defense sectors, expecting a worldwide shortage of REE supply in the future. Therefore, REEs have been widely accepted as strategic elements in the world, which compels to prospect for new and alternative REE resources. In this context, Sri Lanka has a favorable geological setting which implies the presence of REE mineralization. Previous geochemical studies in Sri Lanka have reported significant concentrations of REEs in different geological formations and mineral resources. Accordingly, Pulmoddai and other beach placer deposits, Eppawala carbonatite, alluvial placer deposits, and pegmatites have been identified as potential REE resources in Sri Lanka. Monazite, apatite, allanite, and zircon are the primary rare earth (RE) minerals found in the preceding resources. The Pulmoddai mineral sand deposit is considered as the most potential REE resource in the island, which is enriched in monazite containing more than 61% of light rare earth elements (LREEs). Similarly, Eppawala carbonatite contains high concentrations of LREEs. However, despite their significant REE enrichments, to date, no attempt has been made to recover these REE prospects, which essentially conceals their potential of catering for both local and global REE supply chains.

Conditions for the crystallization of fluorite in the Mushgai-Khudag complex (Southern Mongolia): Evidence from trace element geochemistry and fluid inclusions

The Mushgai-Khudag complex is part of the Late Mesozoic Central Asian carbonatite province. Fluorite mineralization is manifested throughout the province, including the Mushgai-Khudag complex. We have investigated the geochemical features and fluid inclusions of fluorites from different types of fluorite-bearing rocks. Fluorite from quartz-fluorite rocks has rare earth element (REE) concentrations in the range of 10500−144300 ppm and the highest light REE contents, with (La/Yb)N = 56−960. Fluorite from the fluorite-apatite-celestine rocks has slightly lower REE enrichment, especially light REE content, with concentrations of 200−5900 ppm and (La/Yb)N = 18−204. Fluorite from the fluorite-calcite rocks is characterized by REE contents of 22−1100 ppm and a variable (La/Yb)N of 0.6−59. These variations in the fluorite REE composition from different types of rocks were probably caused by the fact that at elevated temperatures, fluorine-containing light REE complexes are more stable than fluorine-containing heavy REE complexes. The progressive enrichment of medium and heavy REEs in the latter fluorite is related to fluid evolution. The homogenization temperature and salinity values of fluid inclusions in the Mushgai-Khudag fluorites vary between 550 and 185 °C and from rather high to 2 wt.%, respectively. The parental fluids of the fluorite-bearing rocks evolved from quartz-fluorite rocks to fluorite-apatite-celestine rocks to fluorite-calcite rocks. The key component was changed from sulfate to carbonate-chloride along with the high to medium temperature decrease (∼500−245 °C).

Distribution of rare earth elements in PM10 emitted from burning coals and soil-mixed coal briquettes

Emission from burning coals is one of the major sources of the airborne particles in China. We carried out a study on the rare earth elements (REEs) in the inhalable particulate matter (PM10) emitted from burning coals and soil-coal honeycomb briquettes with different volatile contents and ash yields in a combustion-dilution system. Gravimetric analysis indicates that the equivalent mass concentration of the PM10 emitted from burning the coals is higher than that emitted from burning the briquettes. The ICP-MS analysis indicates that the contents of total REEs in the coal-burning PM10 are lower than those in the briquette-burning PM10. In addition, the contents of the light rare earth elements (LREEs) are higher than those of the heavy rare earth elements (HREEs) in the PM10 emitted from burning the coals and briquettes, demonstrating that the REEs in both the coal-burning and briquette-burning PM10 are dominated by LREEs. The higher contents of total REEs and LREEs in the coal-burning PM10 are associated with the higher ash yields and lower volatile contents in the raw coals. A comparative analysis indicates that the La/Sm ratios in the PM10 emitted from burning the coals and briquettes, being lower than 2, are lower than those in the particles from gasoline-powered vehicle emission.

Geochronology and geochemistry of granodiorite at Jinwozi Au deposit: Tectonomagmatic evolution for Palaeozoic Beishan Orogen (Central Asian Orogenic Belt) in NW China

The Beishan Orogen (southern Central Asian Orogenic Belt) contains many Palaeozoic gold ore‐hosting intrusions, whose age, petrogenesis and tectonic setting are yet to be well understood. In the Mazongshan arc of the Beishan Orogen, the Jinwozi granodiorite contains high K2O (2.71–5.69 wt%), A/CNK (1.10–1.49) and 10000Ga/Al (mostly &gt;2.6), and has high Nb (15–21 ppm), Zr (337–451 ppm) and light rare earth element contents (∑LREE = 207–257 ppm), but low Sr (92–208 ppm) and negative Eu anomalies (δEu = 0.55–0.70), with calculated Zr saturation temperature of 910–860°C. They exhibit typical features of peraluminous A‐type granites formed in subduction‐related settings. The rocks have high large‐ion lithophile element and Hf contents, but low contents in certain high‐field‐strength elements. In addition, the zircon εHf(t) values (−3.6 to −0.1) indicate partial melting of the crust, while the two‐stage model ages (TDM2 = 1385 to 1611 Ma) and several Palaeozoic magmatic rocks with Mesoproterozoic‐inherited zircon suggest the occurrence of Mesoproterozoic crustal accretion. The ore‐hosting granodiorite pluton at the Jinwozi Au deposit was LA‐ICP‐MS zircon U–Pb dated to be Silurian (ca. 428–422 Ma), older than the previously suggested Late Palaeozoic ages and before the interpreted amalgamation timing of the Beishan Orogen. We propose that the Jinwozi granodiorite is derived from pre‐existing crustal material recycling.

Geochemistry and geochronology of Carboniferous magmatic rocks in the Sawur Mountains, northern West Junggar, NW China: implications for accretionary orogeny

The accretionary orogeny of the Central Asian Orogenic Belt (CAOB) has been a popular topic over the past decades due to its complex tectonic process. The Carboniferous magmatism in the Sawur Mountains of the northern West Junggar plays an important role in understanding the accretionary process of West Junggar. Detailed geological mapping has revealed that the Carboniferous Heishantou Formation in the Sawur Mountains consists mainly of pillow lavas, basaltic andesites, dacites, tuffs and sedimentary rocks, which were intruded by the Lasite intrusion. The pillow lavas display low SiO2 and TiO2 as well as high MgO and FeOt contents and enrichment in light rare earth elements (LREEs) and Nb–Ta, suggesting derivation from an enriched lithospheric mantle in an oceanic island setting. With the oceanic crust subduction, they were scraped off and accreted in a fore-arc setting. Basaltic andesites exhibit high SiO2 and Al2O3 contents, low Mg#, Zr, and Nb contents as well as Nb/La ratios, and a clear depletion of Nb–Ta, indicating derivation from a mantle wedge affected by the inputs of slab-derived fluids in an island arc setting. Dacites possess calc-alkaline and adakitic geochemical features with high Sr and Ba contents, high Th/Yb ratios, enrichment in LREEs, low Nb/La ratios, a depletion of Nb–Ta and positive eHf(t) values (10.3–15.0). Accordingly, they are interpreted as being derived from the melting of subducted oceanic crust mixed with minor sediments in an island arc setting. Magmatic zircons from dacite yield a weighted 206Pb/238U mean age of 326.8 ± 1.6 Ma, constraining the crystallization age of the dacite as well as the timing of the oceanic crust subduction. The Lasite intrusion that intruded the Heishantou Formation is K-feldspar granite, exhibiting pronounced I-type affinity and a high potassic calc-alkaline series. This granite shows low Na2O and Mg# (36.9–40.3) values; low Zr and Y contents as well as 10,000 × Ga/Al ratios; high LREE, K and Pb contents; and a depletion of Nb and Ta. Altogether, the low (87Sr/86Sr)i (0.7037–0.7043) and positive eNd(t) (6.22–6.36) and eHf(t) (10.1–15.5) values suggest that the granites were derived from the partial melting of a juvenile lower crust affected by mantle materials in a subduction setting. The zircon weighted 206Pb/238U mean age of 316.6 ± 2.8 Ma represents the intrusive age of the granite and related subduction during the late Carboniferous. All of the above geochemistry and geochronology of the magmatic rocks constrain the subduction–accretion tectonics in the Sawur Mountains of the northern West Junggar during ~ 327–317 Ma and confirm the subduction of the Paleo-Asian Ocean (PAO) lasted until the late Carboniferous in this region.

Geochemical taphonomy of the Standing Rock Hadrosaur Site: Exploring links between rare earth elements and cellular and soft tissue preservation

The Standing Rock Hadrosaur Site (SRHS) in South Dakota preserves a mass-death assemblage of the hadrosaurine dinosaur Edmontosaurus annectens in the Upper Cretaceous Hell Creek Formation. A previous study of SRHS bones found many of them to yield microstructures morphologically consistent with vertebrate osteocytes, blood vessels, and proteinaceous matrix upon demineralization with weak acid. To examine the geochemical history of these specimens in detail, we herein document the intra-bone distribution of rare earth elements (REE) within nine of these previously-examined Edmontosaurus limb bones from SRHS. Laser ablation-inductively coupled plasma mass spectrometry was used to determine the trace element composition of the specimens, which revealed the bones to possess unusually low REE concentrations for bones of Mesozoic age, consistent and steep declines in light REE concentrations with increasing cortical depth, and uniformly low concentrations of middle REE and elements with moderate and low diffusivities through the middle cortex. These attributes imply: (1) at least partial preservation of early-diagenetic trace element signatures; (2) that trace element uptake occurred primarily during a single, early-diagenetic phase, and; (3) that the duration of trace element diffusion was brief in these bones. As we previously reported, low permeability of the fine-grain host matrix and early-diagenetic cementation of portions of the host matrix by precipitation of siderite concretions impeded pore fluid replenishment; this partial hindrance of fluid flow was also likely responsible for the minimal trace element uptake observed in the nine SRHS specimens further studied herein. From a paleontological perspective, minimal trace element uptake reflects minimal chemical alteration, meaning bones from this site are predicted to be ideal candidates for preservation of original organics according to hypotheses previously advanced by geochemical studies. Because low REE concentrations reflect limited interaction with groundwaters during diagenesis, we propose that late-diagenetic overprinting of early-diagenetic REE profiles was minimal and that hydrolytic degradation of soft tissues was limited in the burial environment at SRHS. Mitigation of biomolecular decay by hydrolysis would favor ultrastructure stabilization and is therefore advanced as a partial explanation for the preservation of cells and soft tissue microstructures in these fossil bones.

Cretaceous ultrapotassic magmatism from the Sava-Vardar Zone of the Balkans

Late Cretaceous global plate reorganization associated with the inception of counterclockwise rotation of Africa relative to Europe initiated in the Balkan region small-volume magmatism of diverse geochemical signature along the enigmatic Sava-Vardar Zone. We study a Late Cretaceous lamprophyric sill in Ripanj village near Belgrade to constrain this magmatic episode. The lamprophyre is characterized by high contents of Na, P, Fe and Al, and low contents of K, Ca and Mg. Its original nature (Na, K, Ca and Mg) is concealed by intense alteration (albitization of feldspar and partial chloritization of phlogopite) that erased the ultrapotassic affinity of the rocks and resulted in extremely low K/Na ratios. The recalculated chemical composition demonstrates that the rocks are ultrapotassic, with K2O and MgO >3 wt % and K2O/Na2O > 2, and belong to the durbachite-vaugnerite series, i. e., the plutonic equivalents of minettes and kersantites.Two phlogopite concentrates gave Ar–Ar ages of 86.80 ± 0.5 Ma and 86.90 ± 0.5 Ma. Our combined elemental and Sr–Nd–Pb isotope data (87Sr/86Sr 0.70667–0.70677, 143Nd/144Nd 0.512426–0.512429, 206Pb/204Pb 18.82–19.13, 207Pb/204Pb 15.67–15.68, 208Pb/204Pb 38.92–39.19) for representative lamprophyric samples suggests magma derivation from a light rare earth elements (LREE) and K enriched, metasomatized mantle source. The content of LREE of the rocks is enriched, whereas heavy rare earth elements (HREE) is depleted. Rare earth elements (REE) of the whole rock and REE of diopside all indicate that garnet was present in their source.There are two viable and mutually-excluding geodynamic scenarios for the Late Cretaceous magmatism in the Balkans: (i) If the Sava-Vardar ocean still existed in the Late Cretaceous and was subducted under the European plate with arc volcanism along the Apuseni-Banat-Timok-Panagyurishte-Srednjogorje belt, coeval magmatism in the Sava-Vardar Zone occurred in a fore-arc setting, and may be related to ridge subduction; (ii) If the Mesozoic ocean closed already during the Upper Jurassic or Lower Cretaceous, the Late Cretaceous volcanism within the Sava-Vardar Zone represents intracontinental volcanism associated with transtensional tectonics.

Preliminary Resource Potential Assessment of Placer Light Rare Earth Elements (LREEs) from mid-Siwalik Sediments of a late Miocene Himalayan Foreland Basin, Pakistan

The present study has assessed the preliminary placer LREEs resource potential of mid-Siwalik Group Dhok Pathan Formation from Surghar-Shingar Range of NW Himalayan foreland Fold-and-Thrust-Belt and regarded them as indicative resources only. The analytical results of bulk samples of sandstone did not show any anomalous concentration of REEs. However, the ICP-MS results of heavy minerals laminations (black sands) revealed high concentrations (ppm) of LREEs (La: 975, Ce: 2831, Pr: 193, Nd: 746, Sm: 127, Gd: 98.70). We identified monazite-(Ce) [Ce, La, Nd]PO4 as the primary LREEs-bearing mineral through Electron Probe Micro Analysis (EPMA). The representative quantitative micro-mineral analysis of monazite confirmed promising concentration of Rare Earth Oxides (REOs) maximum (in weight %) - La2O3: 16.20, Ce2O3: 37.82, Pr2O3: 4.77, Nd2O3: 21.72, Sm2O3: 5.23, Gd2O3: 4.88. Considering the thickness, lateral extension and depositional setting of host sediments along-with anomalously high concentrations of LREEs, it has been concluded that these Siwalik sediments host good indicative placer resource potential for low-cost recovery of LREEs.

Preliminary Resource Potential Assessment of Placer Light Rare Earth Elements (LREEs) from mid-Siwalik Sediments of a late Miocene Himalayan Foreland Basin, Pakistan

The present study has assessed the preliminary placer LREEs resource potential of mid-Siwalik Group Dhok Pathan Formation from Surghar-Shingar Range of NW Himalayan foreland Fold-and-Thrust-Belt and regarded them as indicative resources only. The analytical results of bulk samples of sandstone did not show any anomalous concentration of REEs. However, the ICP-MS results of heavy minerals laminations (black sands) revealed high concentrations (ppm) of LREEs (La: 975, Ce: 2831, Pr: 193, Nd: 746, Sm: 127, Gd: 98.70). We identified monazite-(Ce) [Ce, La, Nd]PO4 as the primary LREEs-bearing mineral through Electron Probe Micro Analysis (EPMA). The representative quantitative micro-mineral analysis of monazite confirmed promising concentration of Rare Earth Oxides (REOs) maximum (in weight %) - La2O3: 16.20, Ce2O3: 37.82, Pr2O3: 4.77, Nd2O3: 21.72, Sm2O3: 5.23, Gd2O3: 4.88. Considering the thickness, lateral extension and depositional setting of host sediments along-with anomalously high concentrations of LREEs, it has been concluded that these Siwalik sediments host good indicative placer resource potential for low-cost recovery of LREEs.

Mineralogy, rare earth elements geochemistry and genesis of the Keban-West Euphrates (Cu-Mo)-Pb-Zn skarn deposit (Eastern Taurus metallogenic belt, E Turkey)

The Keban-West Euphrates (Cu-Mo)-Pb-Zn skarn deposit occurs mainly around the contact zone of the Permo-Triassic/Permo-Carboniferous metamorphic rocks and Late Cretaceous plutonic rocks in the Eastern Taurus orogenic belt. The skarn formation, in this orogenic belt formed by the Hercynian and Alpine orogenies, is associated with Late Cretaceous alkali syenite intrusion of calcareous rocks. The syenite intrusion is characterised by temporal and spatial zonation, producing several stages of skarnisation. The initial contact metamorphism formed broad halos of hornfels and marble. Subsequent metasomatism by high temperature and hypersaline fluids formed anhydrous calc-silicate assemblages (garnet, pyroxene and wollastonite), partially overprinted by lower temperature and saline fluid hydrous assemblages (epidote, chlorite and calcite) and sulphide minerals (mainly pyrite) as the concentration of sulphur increased. The ore skarn assemblage like pyrite, chalcopyrite, molybdenite, sphalerite, galena, fluorite, magnetite, pyrrhotite, fahlore and native gold occurs as ore minerals, whereas garnet, pyroxene, calcite, epidote, chlorite and quartz constitute the main gangue minerals. The Keban plutonic rocks are syenitic in composition with high contents of Al2O3, Na2O + K2O, Zr, Nb, Ta, Th, Rb and rare earth elements (REEs). The major and trace elements composition of the Keban pluton is consistent with those of Zn-Cu-Mo-W skarn plutons. The skarn litho-units show higher concentrations of light REEs compared with heavy REEs. The skarn zone samples display the most prominent REE-enriched pattern, and the depletion pattern in the ore zone is only subordinate to that of the host rock (limestone). The La/Y ratios of the West Euphrates skarns vary from 0.9 to 26.4 with the highest ratios in the ore zone (average = 13.35). The ratios of the plutonic rocks and skarn zones reflect near-neutral to alkali conditions, whereas the ore zone and host rock ratios are characteristic of alkali conditions. The garnet-dominated endoskarn shows high contents of REE (∑REE) compared with the metaluminous syenite porphyry-hosted exhibiting Eu and Ce enrichment, indicating derivation of the magmatic fluids for skarnisation from the alkali syenitic magma. Conversely, the limestones show lower REE concentrations relative to the metaluminous syenite porphyry-hosted rocks. The calcic exoskarn (garnet and clinopyroxene) and ore zone containing high ∑REE, significant positive Eu and Ce anomalies and high Pr/Yb(n) ratios are dominantly of magmatic origin.

Rare earth element fractionations of the northwestern South China Sea sediments, and their implications for East Asian monsoon reconstruction during the last 36 kyr

Rare earth elements (REEs) fractionations in siliciclastic marine sediments are related to the parent rock properties, weathering degree, grain size, and heavy minerals. The relations between marine sediment REE compositions and regional paleoclimate are not fully understood. Here, the REEs for detrital components of a core retrieved from the northwestern South China Sea (SCS) were measured. Results show the REE (LREE/HREE, (La/Yb)N) and Light REE ((La/Sm)N) fractionation degrees have good responses to the regional paleoclimate over the past 36 kyr. Sea level played a key role in REE fractionations during ~36-24 kyr BP, manifesting as lower REE and LREE fractionation degrees correspond to the decreased sea level. The entire trends for LREE/HREE, (La/Yb)N and (La/Sm)N over the past 20.5 kyr are almost in phase with the regional East Asian summer monsoon (EASM) records. Because REEs are mainly concentrated in heavy minerals, the density difference of heavy minerals is probably the main controlling factor on REE fractionations. Clay minerals and feldspars released during the weathering process have a high content of Light REEs (LREEs). In the warm, wet periods (Holocene Optimum, and Bølling-Allerød), more precipitation promoted weathering and strengthened the estuarine hydrodynamic force, which respectively resulted in high content of clay minerals and feldspars, and high-density heavy minerals (e.g., monazite). The process led to LREE enrichment because the enriched minerals contain higher contents of the LREEs. In contrast, the dry, cold climate conditions during the periods Heinrich 1, Younger Dryas, and Last Glacial Maximum resulted in the reversed REE fractionations, as the weak hydrodynamic force can only carry the low-density heavy minerals (e.g., zircon) that are enriched in HREEs. This model does not seem to apply to 36- 24 kyr BP, probably because of the re-transport of ancient shelf sediments. The study facilitates the understanding of REE application in paleoclimate reconstruction within slope sediments.

Late Paleocene adakitic granitoid from NW Iran and comparison with adakites in the NE Turkey: Adakitic melt generation in normal continental crust

Late Paleocene adakitic granitoids are rare in Iran except in the northwest. We focused on the adakitic Saqqez-Takab pluton, which occupies an area of ~600 km2. New U-Pb zircon dating yield crystallization ages of 58–56 Ma (Thanetian). These granitoids comprises granite, quartz monzonite and monzogranite with granular to mylonitic textures. They have high SiO2 abundances (59.1–78.6 wt%), high ratios of Sr/Y (50–490) and La/Yb ratios (19–237), along with high Ba (779–2466 ppm) and light rare earth element contents (e.g., La = 11–70 ppm). Saqqez-Takab granitoids have compositions that are similar to high-silica adakites, including low Mg- number (Mg# < 0.5), TiO2 (<0.93 wt%), Cr (<38 ppm) and Ni (<55 ppm). K2O/Na2O ratios of these granitoids are high (>0.7), resembling K-rich adakitic granitoids. Initial ratios of 87Sr/86Sr and εNd(t) vary from 0.7044 to 0.7053 and −2.8 to +2.0 respectively. These isotopic signatures differ from those of typical subducting slab-derived adakites (O-type adakite) with high positive εNd(t) and from collision-related adakites (C-type adakite) with negative εNd(t). The geochemical and isotopic characteristics of Saqqez-Takab granitoids are most consistent with magma being produced by amphibole-dominated fractionation of hydrous melts of subcontinental lithospheric mantle accompanied by minor assimilation of lower mafic calc alkaline continental crust. Distribution of similar-ages adakites in the NW Iran and E Pontides of Turkey suggests that these melts formed similarly. Upwelling of hot asthenosphere due to Neotethys slab rollback led to partial melting of lower continental crust calc alkaline mafic rocks and/or amphibole fractionation from mafic magma produced K-rich adakitic rocks in eastern Turkey and NW Iran during the late Paleocene.

Geochemistry and chronology of the biotite granite in the Xiaobaishitou W-(Mo) deposit, eastern Tianshan, China: Petrogenesis and tectonic implications

The Xiaobaishitou W-(Mo) deposit (Central Tianshan Massif, eastern Tianshan, northwestern China) is a skarn-type tungsten-molybdenum deposit associated with a biotite granite intruding the Mesoproterozoic Kawabulag Group. Here we present the results from zircon U-Pb geochronology, whole-rock geochemical, and Sr-Nd-Hf isotopic analyses of the biotite granite. Zircon U-Pb dating shows that the biotite granite crystallized at 246.4 ± 1.7 Ma, suggesting that the Xiaobaishitou deposit formed during the Early Triassic. Bulk rock geochemistry shows that the biotite granite has high Si, Rb, K, and light rare earth element contents, but low Ba, Nb, Sr, P, and Ti. Moreover, the rocks have mostly positive εHf(t) values (−0.06 to 4.60), negative εNd(t) values (−3.87 to −2.40), and corresponding Hf isotope TDM2 ages (1.29–1.71 Ga) and Nd isotope TDM2 ages (1.23–1.36 Ga). These geochemical and isotopic data imply that the Xiaobaishitou biotite granite derived from both mantle- and crustal-derived magmas. By comparison of the Xiaobaishitou biotite granite to nearby granites from the Donggebi and Baishan Mo deposits, we show that Triassic granites of the eastern Tianshan likely formed in an intra-continental tectonic setting, and magmatism and metallogenesis were probably associated with regional extension.

Seasonal changes in concentrations of trace elements and rare earth elements in shoot samples of Juncus effusus L. collected from natural habitats in the Holy Cross Mountains, south-central Poland

Selected trace elements (Ag, As, Ba, Bi, Cd, Co, Cr, Mn, Cu, Fe, Ni, Pb, Tl, U, Zn) and rare earth elements were determined in 13 samples of Juncus effusus collected from three investigation sites in the Holy Cross Mts., south-central Poland. Sampling was carried out four times during a vegetative season of 2014. Almost all the elements examined showed different seasonal trends in their concentrations, except for Ag, Co and Ni. Maximum concentrations of Ag in samples of three investigation sites were found in May (0.068, 0.062, 0.047 mg/kg) whereas Co (0.124, 0.070, 0.079 mg/kg) and Ni (1.8, 0.998, 2.8 mg/kg) in July, respectively. Mean concentrations of Mn and Cd were higher in shoots (558 and 2.35 mg/kg) than in roots (435 and 1.7 mg/kg). Both these elements revealed much higher concentrations in J. effusus than their typical contents in plant samples. Principal component method allowed us to allocate Ni, Ba, Cd and Cu to one group with the highest positive loadings. The most probable explanation for this correlation is that bioavailability of these metals is increased by J. effusus through a release of oxygen to the rhizosphere. Light rare earth elements concentrations predominate over heavy rare earth elements in the samples examined. A fractionation of lanthanides occurs during their transport from roots to shoots, although this transport is rather limited. All shoot samples have a strong positive Eu anomaly.

Can magmatic zircon be distinguished from hydrothermal zircon by trace element composition? The effect of mineral inclusions on zircon trace element composition

Mineral inclusions, e.g., apatite, titanite, monazite, K-feldspar, are common in magmatic zircons. Although many studies mention that light rare earth element (LREE) contents of zircons could be compromised by an analytical artefact of the accidental sampling of mineral inclusions, how and to what degree these inclusions influence analysis of zircon composition is still not well constrained. Here we report U–Pb ages and trace element abundances for zircon crystals, where apatite and K-feldspar inclusions are observed, from diorite porphyry in the Weibao deposit, East Kunlun Mountains, Northern Tibetan Plateau. Although zircon morphological and chronological evidence consistently advocates a magmatic origin without undergoing significant hydrothermal alteration, 7 of 15 analytical spots show LREE-enriched patterns and low Ce/Ce* ratios which are comparable to those for published “hydrothermal” zircon. Quantitative modelling in this study manifests that these LREE-enriched patterns and low Ce/Ce* ratios can be achieved with only 0.1 to 2 vol% contamination from sub-micrometer apatite inclusions, which in practice are hard to monitor under the LA–ICP–MS (normally with large pit diameter and depth) and conventional microscopes. Titanite, monazite, xenotime, and allanite have similar roles to apatite, and LREE contents of zircon can be significantly elevated with only 0.05 vol% contamination from these inclusions. We therefore suggest that the widely used geochemical discrimination criteria for magmatic and hydrothermal zircon, e.g., (Sm/La)N vs. La and Ce/Ce* vs. (Sm/La)N diagrams and the degree of Ce anomalies, are ambiguous since they are extremely susceptible to contamination by mineral inclusions, and that within single samples only Ce4+/Ce3+ values calculated from zircons of low LREE values probably represent the oxidation state of magmas.

A Baseline Study of the Occurrence of Rare Earth Elements in Animal Feed

The concentrations of rare earth elements (REEs) were determined by ICP-MS in feed for farm animals in three regions of Northwestern Italy. This is the first study aimed at defining the levels and patterns of REEs in feed for different animal species. REEs are in fact emerging as contaminants worldwide, following their applications in industry, technology, medicine, and agriculture. Moreover, in 2016, the first REE-based feed additive—a zootechnical additive for weaned piglets—was authorized in the EU. Therefore, information about the natural content of REEs in animal feed of vegetal origin is required to evaluate the potential use of REEs as a growth promoter. There was a high variability in the REEs content of the animal feed in three different Italian regions, and REEs content varied according to the different animal species for which the feed was intended. Concentrations of light REE (LREE) were higher than those of heavy REE (HREE) in each feed typology. Raw materials were shown to have higher ΣREE concentrations (mean concentration 2.4 mg kg−1) than complete or complementary feed. Considering the animal species, mean ΣREE concentrations were as follows: horse feed (2.7 mg kg−1) > poultry feed > bovine feed > swine feed (0.61 mg kg−1). REE levels in feed were in line with values available in the literature on vegetables; thus, REE concentrations in feed do not constitute a concern for animal health.