REE Distribution Research Articles

Geochemistry of Neoproterozoic Nagod Limestones from the Girgita Mine, Bhander Group, Madhya Pradesh, India

Vindhyan limestone of the Bander Group (Late Neoproterozoic) in the Maihar area, Satna district, is a part of an anticlinal fold and it forms an outlier in the study area. Geochemical analysis reveals that the proportion of Rare Earth Elements (REEs; La-Lu) in limestones varies between 14.8 ppm and 49.5 ppm. The Eu and Ce anomalies (normalized against Post Archean Australian Shale; PAAS) range from ~ 0.53 to 0.69 and ~ 0.57 to 1.07, respectively. The results of this study revealed that the limestones were principally controlled by the admixture of detrital materials, i.e., (i) The low values of REEs (ii) high values of Y/Ho (iii) positive correlation between REEs and Si, Al, Ti, V, Co, Ni, and Nb, and (iv) slightly negative correlation between CaO and REEs. Further, the variations in Ce anomaly may be due to the influx of detrital materials and positive Ce anomaly was attributable to the shallow marine depositional condition. The distribution of REEs (Chondrite normalized values) illustrates different patterns in the Nagod limestone due to the degree of differentiation in terms of LREEs and HREEs and Eu anomaly. The variations in elemental concentrations and the REE patterns revealed the mixing of detrital materials in the Nagod limestones.

Geochemical records and environmental analysis of the Ediacaran-Cambrian boundary in Eastern Yunnan, South China

The Ediacaran–Cambrian transition is characterized by an unprecedented change in biosphere, lithosphere, and atmosphere. However, the identification of this transition and its global correlation remains debated. East Yunnan is a region of utmost importance in the study of the Ediacaran-Cambrian transition. Although strata from this region have been well studied, recognition of the base of the Cambrian continues to be controversial. This paper presents, a carbon chemostratigraphic isotope and trace element profile through the Dengying and Zhujiaqing formations in the Sujiawa section in East Yunnan. Through carbon isotope and trace element analyses of the Dengying and Zhujiaqing formations we attempt to regionally correlate the section and discuss the paleo-marine redox environment changes during this period. The Fe content of samples is low and the Mn/Sr ratios of the majority of the Sujiawa section samples is lower than 10 and shows no correlations with δ13Ccarb and δ18Ocarb values, indicating that the samples retain near-primary δ13Ccarb characteristics. The carbon isotope profile from the Sujiawa section, shows a prominent negative δ13Ccarb in the basal Zhongyicun Member (N1’, −7.3‰) that most likely represents the prominent negative excursion recorded in Ediacaran-Cambrian strata across the world. REE patterns and Y/Ho ratios were used to screen samples, to ensure that the primary seawater REE features and Ce anomalies were preserved. The samples satisfying this screening process show seawater-like REE distribution patterns in leached carbonates and may have recorded Ce anomalies of the seawater from which the carbonates precipitated. These data show that the Baiyanshao Member has Ce/Ce* values between 0.57 and 0.88, the Daibu Member between 0.56 and 0.83, and the Zhongyicun Member between 0.60 and 0.96. The Ce anomalies through the section indicates that the region experienced suboxic-oxic-anoxic conditions throughout the Ediacaran-Cambrian period. Carbon isotope and trace element analyses indicate that the strata record a negative carbon isotope excursion event and anoxic conditions during the period of deposition. This study complements the carbon chemostratigraphic information and trace element data in the region and provides valuable clues for understanding the lithofacies changes through the Ediacaran and Cambrian in different regions of South China.

ALKALINE RHYOLITES OF THE PECHALNINSKY ORE FIELD (NORTH-EAST OF RUSSIA) – A POTENTIAL LARGE-VOLUME SOURCE OF HEAVY RARE EARTH ELEMENTS

Trachyriolites and komendites of the Pechalninsky ore field contain high potentially industrial concentrations of a number of rare metals and REE. The enrichment coefficients vary from several times (Zn, Ga, LREE) to tens (Be, Y, Zr, Nb, Rb and heavy HREE). The REE distribution indicates a uniform enrichment of the HREE relative to the LREE, with a ratio (La/Yb)N in the range from 0.16–1.01). All samples show strongly negative Eu anomalies, with values of Eu/Eu* – 0.13. A comparative analysis with similar objects known in the world in alkaline volcanites has shown that the Pechalninsky ore field can become an unconventional large-volume source of HREE.

Two Distinct Fractional Crystallization Mechanisms of A-Type Granites in the Nanling Range, South China: A Case Study of the Jiuyishan Complex Massif and Xianghualing Intrusive Stocks

The petrogenesis of A-type granites with different occurrences in the Nanling Range remains unclear. In this study, a case study of the Jiuyishan complex massif and Xianghualing intrusive stocks was conducted to determine this problem. The Jiuyishan complex massif is composed of four units (Jinjiling, Pangxiemu, Shaziling and Xishan). These four units have similar zircon U-Pb ages of approximately 153 Ma, with high Zr + Nb + Ce + Y contents (>350 ppm), high 10,000 Ga/Al ratios (>2.6), and a high crystallization temperature, indicating A-type affinities. They show a gradual change in lithology and geochemistry, implying a fractional crystallization process. These units also have similar εNd(t) values (−8.2 to −5.8) and zircon εHf(t) values (−7.5 to −2.2) except for the Shaziling MMEs (mafic microgranular enclaves) (−14.2 to 4.8), demonstrating their lower crustal source. However, the Shaziling unit may have contributed mantle-derived magma based on the geochemical data of its hosted MMEs. In comparison, the two Xianghualing intrusive stocks have similar geochemical features but exhibit highly evolved features (high Rb, U, Y, Ta and Nb contents and low Eu, Ba, Sr, P, Ti, Ca, Mg and Fe contents, with V-shaped REE distribution patterns). They have different zircon U-Pb ages of approximately 160 Ma and 155 Ma. The two stocks also have similar whole-rock εNd(t) values (−6.5 to −5.7) and zircon εHf(t) values (−7.6 to −2.7) and equally illustrate a lower crustal source region. Combining with their vertical zonation, they may have experienced remarkable fractional crystallization with possible assimilation processes. We propose that the Jiuyishan complex and Xianghualing stocks have two distinct fractional crystallization mechanisms during their formation. The Jiuyishan complex was formed by in situ crystal mush fractionation, while the Xianghualing stocks were formed by flowage differentiation during magma ascent or gravitational settling during magma solidification after emplacement. However, more than one mechanism affected the fractional crystallization processes of these granitic rocks.

Carbonatite-related delicate REE mineralization processes revealed by fluorocarbonates and monazite: Insights from the giant Bayan Obo REE-Nb-Fe deposit, China

Fluorocarbonates and monazite are common economic REE minerals in carbonatite-related REE deposits, such as the largest known REE deposit at Bayan Obo, China. The geochemical evolution of REE minerals is a sensitive and effective indicator of delicate REE mineralization processes. In this study, the fluorocarbonates and monazites were classified into three generations, corresponding to three REE mineralizing stages. The first generation (Gen-1) of bastnäsite and monazite are generally characterized by elevated La/Ce, La/Nd and La/Lu ratios, with right-declining chondrite normalized REE distribution patterns. They have low Th and radiogenic Sr content, with forming age of about 1.3 Ga and εNd(t) around 0, indicating a primary origin and orthomagmatic crystallization from carbonatite melts. The second generation (Gen-2) of REE minerals, formed at 1.25–1.2 Ga, normally constitute banded aggregates with associated hydrothermal gangue minerals (fluorite, aegirine, sodium amphibole etc.). The Gen-2 REE minerals are featured by moderate-low La/Ce, La/Nd, La/Lu ratios but slightly elevated 87Sr/86Sr0 ratios, indicating a Mesoproterozoic hydrothermal origin related to carbonatitic fluids. Gen-2 bastnäsite and monazite precipitated earlier in low-fluid/rock-ratio environment with right-declining LREE distribution patterns, while the subsequent Gen-2 parisite and huanghoite display convex LREE patterns and higher OH/F ratios, indicative of relative La-depletion and increased ambient fluid/rock ratios during progressive hydrothermal REE mineralization. The third generation (Gen-3) of REE minerals are generally megacrysts in the vein-type ores formed in the early Paleozoic REE mineralization stage (470–420 Ma). The Gen-3 REE minerals are typified by significantly variable REE, Sr and Nd isotopic components, indicating extensive hydrothermal metasomatism and intense contamination of crustal material. Induced by activities of early Paleozoic subduction-related fluids, Gen-3 REE minerals were formed through local REE re-enrichment within the ore-hosting dolomite, rather than by introduction of REE from external sources. In this case study, a comprehensive model of the delicate REE mineralization processes of the giant Bayan Obo REE-Nb-Fe deposit has been established. This study highlights the great potential of fluorocarbonates and monazites widely distributed in carbonatite-related REE deposits as universal geochemical indicators of late-stage evolution of carbonatite and delicate magmatic-hydrothermal REE mineralization processes.

Granitoids Geological and Geochemical Features Study at Akchatau Massif

. The aim of the work is to identify the geological and geochemical features of the granitoids of the Akchatau massif. This article discusses the petrochemical data of the first and second phase introduction of the Akchatau massif, as well as the petrogenesis of rocks and the distribution conditions of tungsten and molybdenum. To diagnose the distribution of elements, the data were normalized by UCC. According to the results of the analysis, it was found that the chemical analysis of REE for granites is less than for leukogranites. It was also found that the REE distribution graph in the rocks of the Akchatau massif repeats the line of the upper crust.

Phosphate mineralization in leucogranites of the Peshcherninsky stock (Reftinsky massif, Middle Urals)

Relevance. Phosphate mineralization of Devonian intrusions in the Eastern zone of the Middle Urals is currently poorly understood, the data obtained may be important for interpreting the origin of rocks, especially in the case when standard methods of geochemical analysis of rocks do not give a clear picture. Xenotime and monazite are minerals concentrating rare earth elements, and REE distribution graphs are a very important characteristic of rocks. Objective – study of the chemical composition of phosphates in leucogranites of the Peshcherninsky stock. Research methodology. Determination of the chemical composition of the samples was carried out on a Cameca SX100 electron probe microanalyzer at the Common Use Center Geoanalyst, analyst V. A. Bulatov. The analysis was carried out at an accelerating voltage of 15 kV using crystal analyzers TAP, LPC0, LPET, PET, LLIF, LIF. The electron probe current was 10 nA (apatite) and 60 nA (REE, Th phosphates). The pulse accumulation time at the peak maximum was 10 s (for most elements) and 20 s (for REE, Th, U, Pb). During the analysis, on a Cameca SX100 electron probe microanalyzer, the following were used as standards: apatite (for analysis of the content of P, Ca), chlorapatite (Cl), fluorine-phlogopite (F), diopside (Mg, Si), albite (Na, Al), orthoclase (K), rhodonite (Mn), SrSO4 (Sr), TiO2 (Ti), Fe2 O3 (Fe), SrSO4 (Sr), BaSO4 (S), Cr2 O3 (Cr), pyromorphite (Pb) and aluminosilicate glasses doped with REE (La, Ce, Y, Sm, Pr, Nd, Th, U, Tm, Eu, Tb, Dy, Gd, Er, Yb, Lu, Ho). Due to the use of a low probe current in the analysis of apatites, the detection limits for elements were: 300–600 ppm for S, Cl, Al, Mg, Si, Ca, Na and 2000–2500 ppm for P, F, Fe, Mn, Cr. For REE phosphates, the following detection limits were achieved using an increased probe current: 100–200 ppm for Si, Ca, Cr, K, Al, Mg, Ti, Pb, 300–500 ppm for Na, S, P, Mn, Y, Th, U, 1200–1500 ppm for Sr, Nd, Ce, 1700–2000 ppm for La, Tm, Tb, 2500–2800 ppm for Yb, Dy, Lu, Pr, 3500–4700 ppm for Eu, Sm, Gd, Ho. Results. For the first time in Russia, cheralite was found and described in a plutonic rock. The article presents the first data on the chemical composition of phosphates (apatite, monazite, xenotime, cheralite) from the leucogranites of the Pescherninsky stock, which formed at the final stage of the formation of the polychronous and polyformational Reftinsky gabbro-granitoid massif. Conclusion. Apatite belongs to the fluorine variety with an admixture of manganese, monazite is represented by the cerium variety, and xenotime is represented by yttrium. Cheralite has a transitional trace element composition, and depending on the zone, it can be attributed to both cerium and yttrium varieties. The admixture of manganese in apatite may indicate partial mixing of the melt with sedimentary or metasedimentary rocks.

Mineralogical features of gabbroic rocks from Mindyak mafic-ultramafic massif

The mineralogical features of several samples of gabbroids from the eastern part of the Mindyak mafic-ultramafic massif have been studied. The compositions of rock-forming and accessory minerals are given. The rocks underwent autometamorphic transformations with the replacement of the primary pyroxene-plagioclase association to amphibole and essentially sodium feldspar secondary assemblage. Typical accessory minerals are titanite, ilmenite, titanomagnetite, and apatite. The gabbroids of the massif cover a wide range of compositions from melanogabbro to diorites, also demonstrating significant variations in the contents of petrogenic oxides and trace elements. In terms of REE distribution, most of the studied samples of gabbroids are comparable to basalts of mid-ocean ridges, but often differ from them in high concentrations of strontium and some other rare elements. The gabbroids of the eastern part of the massif have U-Th mineralization in association with aggregates of xenomorphic zircon grains. The origin of these finds has not been established in the present study. Estimates of the PT conditions by the amphibole barometer show the presence of two maxima of values – 2.8–5.1 kbar and less than 2 kbar, which most likely fix two different stages in the formation of rocks – autometamorphism in the magma chamber during cooling and interaction with magmatic fluids (magnesian hornblende), and low-temperature (greenstone) transformations (actinolite).

Implications for the contribution of Pacific plate subduction to fluorite mineralization in southeast China: Evidence from Nanzhou large fluorite deposit, Fujian province

In SE China, there are numerous Mesozoic igneous rocks and a tectonically active area known as the Wuyi Fluorite Mineralization Belt. The Nanzhou fluorite deposit can effectively represent most hydrothermally filled fluorite deposits strictly controlled by the fault zones. These were mainly trending NE, NNE, followed by NW, and nearly EW. It is the epitome of fluorite mineralization in the Wuyi fluorite metallogenic belt, which can provide clues for the subduction of the Mesozoic Pacific plate to the Eurasian plate. As the surrounding rocks of the Nanzhou fluorite ore bodies, the zircon U-Pb isotopic age of the Anjiang syenogranite is 147±1 Ma, while the biotite plagioclase granulite of the Xiafeng Formation in the Wanquan group is 817±3 Ma and 811±3 Ma. However, fluorite is of hydrothermal origin. It yields an Sm-Nd isochron age of 103.8±5.0 Ma and an Rb-Sr isochron age of 106±15.0 Ma, more than c.a. 40 Ma younger than the Anjiang Syenogranite, indicating fluorite is a product of late hydrothermal mineralization. The right-leaning REE distribution curves of most fluorite samples are similar to those of Yanshanian Anjiang syenogranite and biotite plagioclase granulite of the Xiafeng Formation, which indicates that fluorite is closely related to the surrounding rocks. Most fluid inclusions in fluorite have salinities of 0.5–2.24 wt% NaCl eqv and low homogenization temperatures of 140–200 °C. The inclusions include a NaCl-H2O system with δDV-SMOW between −79.7 to −77.6‰ and δ18OV-SMOW values range from 0.4 to 2.1‰. The (87Sr/86Sr)i ratios of the fluorite, which are between 0.717427 and 0.719482, are characteristic of a crustal contribution. Based on the above description, the mineralized fluid of Nanzhou fluorite deposit belongs to the NaCl-H2O system with medium-low temperature and low salinity, which is obviously different from the magmatic hydrothermal fluid. In addition, the age of fluorite mineralization is younger than that of igneous rocks by ca. 40 Ma, so they are not correlated. It is proposed that the ore-forming fluid may be involved in atmospheric precipitation and circulate within the northeastward fault with increasing geothermal gradient to form Nanzhou-fluorite deposit. The Nanzhou-fluorite deposit was formed in 103.8±5.0 Ma and 106±15.0 Ma, which corresponds to the plate subduction and rollback period of the Late Cretaceous (in ca. 110–70 Ma). The formation of the Nanzhou deposit has important implications for the subduction of the Pacific plate to the Eurasian plate.

Survival of whole-rock Sm–Nd isotope system from REE redistribution and mineral-scale isotopic resetting amid hydrothermal alteration in REE-rich Fe-Cu deposit

The 147Sm–143Nd isotope system has long been used as a powerful tracer and geochronometer for a wide range of geological process, yet the robustness of Sm–Nd system has been questioned in the presence of multistage hydrothermal alteration. Here we provide robust evidence for the survival of whole-rock Sm–Nd isotopes from REE redistribution and mineral-scale isotopic resetting during multistage fluid infiltrations in the Lala Fe-Cu-REE deposit in Kangdian region, southwestern China.The Lala deposit is hosted in the ∼1.72–1.68 Ga rift-related Hekou Group and contains variable proportions of REE-rich apatite and fluorite in the ores. Both of the apatite and fluorite grains show textures of extensive metasomatic alteration, during which large amounts of REE, especially LREE, were leached out and mostly re-incorporated into newly-formed monazite, bastnäsite, and xenotime. Quantifying REE distribution budget at thin-section scale confirms that the amounts of REE (1583–5403 ppm) leached from primary apatite and fluorite are compatible with those (1636–5526 ppm) incorporated in the newly crystallized REE minerals, indicating that REE are internally redistributed within investigated samples. The whole ores yield an 18-point 147Sm–143Nd errorchon date of ∼1.71 Ga, which is in accordance with the other analogous Fe-Cu deposits in Kangdian region, and supports a ∼1.71 Ga primary mineralization at Lala. By contrast, SHRIMP 232Th–208Pb dating of texturally constrained monazite yield a crystallization age of ∼0.92 Ga, which corresponds well with the combined monazite-bastnäsite-apatite Sm–Nd isochron ages of representative samples, demonstrating a major REE redistribution and Sm–Nd isotopic resetting event at this time. The results suggest that Sm–Nd mobility was limited to within the whole-rock scale or even within the thin-section scale in the vast majority of cases, such that the whole-ore Sm–Nd isotopic system largely remained closed, despite complete resetting of the major REE minerals during younger fluid infiltration events. Our study exemplifies the apparent “decoupling” of Sm–Nd isotopic systems between macro- and microscales, which can advance our understanding of the complex history of hydrothermal systems. Our findings of a major transition (80–96%) in REE repositories also highlight the economic significance of hydrothermal alteration for modifying ore mineral assemblages, which resembles a natural REE refinement process and helps create beneficial REE resources to meet the society increasing demands.

Rare earths release from dissolving atmospheric dust and their accumulation into crystallising halite: The Dead Sea example

The industrial extraction of Y and lanthanides (hereafter defined as Rare Earth Elements, REE) often requires the achievement of leaching procedures removing these metals from primary rocks and their transfer in aqueous leachates or incorporated in newly forming soluble solids. These procedures are the most dangerous to the environment in relation to the composition of leachates. Hence, the recognition of natural settings where these processes currently occur, represents a worthy challenge for learning how to carry out similar industrial procedures under natural and more eco-friendly conditions. Accordingly, the REE distribution was studied in the brine of Dead Sea, a terminal evaporating basin where brines dissolve atmospheric fallout particles and crystallise halite.Our results indicate that the shale-like fractionation of shale-normalised REE patterns in brines, inherited during the dissolution of atmospheric fallout, changes because of the halite crystallisation. This process leads to crystallising halite mainly enriched in elements from Sm to Ho (medium REE, MREE) and coexisting mother brines enriched in La and some other light REE (LREE). We suggest that the dissolution of atmospheric dust in brines corresponds to the REE extraction from primary silicate rocks, whereas halite crystallisation represents the REE transfer into a secondary more soluble deposit with reduced environmental health outcomes.

Distribution of trace elements between phases in the Carbonate–Phosphate System with Fluorine at 500 MPa

The distributions of Ti, Zr, Nb, La, Sm, Yb, and Y were experimentally studied between phosphate and carbonate melts with various Ca and Na concentrations and equilibrium solid phases: apatite (in 12 experiments) and buchwaldite, CaNaPO4 (in two experiments). The experiments were carried out in an internally heated pressure vessel at a pressure of 500 MPa in the CaCO3 + NaPO3 + NaF system with variable proportions of phosphate and carbonate, and with the addition of H2O, H2C2O4 and mixture of trace-element oxides. The temperatures in runs V-1-8 were conducted as 1000 °C for melting for 24 h, then for crystallization at 650 °C for 7 days, and quenching; the temperatures in runs VI-1-5 - 1000 °C for 1 day and immediate quenching. The proportion of phosphate and carbonate in the starting mixtures was expressed as χ(P2O5) (mol. %), where χP2O5=nP2O5nP2O5+nCaO×100%. The experimental products were analyzed by electron probe microanalysis. The following two types of quenched melts were obtained depending on χ(P2O5): (i) calcite-rich melt with 20 mol% Na2O at χ(P2O5) < 30% and (ii) sodic carbonate–phosphate melt with a low CaO concentration at χ(P2O5) > 30%. The solubilities of ZrO2, TiO2, and Nb2O5 in the calcite-rich quenched melts at 650 °C were low and limited by the crystallization of Zr, Ti, and Nb oxides. At the temperatures 1000 °C these oxides are dissolved in the melts, and their concentrations in the melts increased with increasing χ(P2O5). The TiO2 and ZrO2 distribution coefficients between apatite and melt are 0.06–0.2 and 0.4–1.0, respectively. The REE distribution coefficients between apatite and coexisting melt rich in Ca carbonate increase with increasing χ(P2O5) from 1.3 to 3.3 for La2O3, from 0.4 to 3.4 for Sm2O3, from 1.4 to 1.9 for Yb2O3, and from 0.8 to 2.9 for Y2O3. The REE distribution coefficients between apatite and the sodic carbonate–phosphate melt increase by a few orders of magnitude with increasing χ(P2O5), particularly significantly for La2O3 and Sm2O3, to 110 and 75, respectively, and to >32 and 20 for Yb2O3 and Y2O3. The TiO2 and ZrO2 distribution coefficients between buchwaldite and melt do not depend on χ(P2O5) and are 0.1 and 1.05, respectively. The REE distribution coefficients between buchwaldite and melt coexisting with it in the experiments are 1.5 times lower than the distribution coefficients between apatite and melt and increase from ∼1.1 for all REE at χ(P2O5) = 25.8%, to 3.6, 2.9, 3.2, and 2.0, respectively, for La2O3, Sm2O3, Yb2O3 и Y2O3 at χ(P2O5) = 41.7%.

Composition and Formation Conditions of Neoproterozoic Phosphorites of the Middle Urals

Phosphorite breccias compose a 6-m member in the Vendian terrigenous Kernos Formation in the basin of the Mezhevaya Utka and Sylvitsa rivers in the Middle Urals. Phosphorite pebbles and gravel are accumulations of fragments of redeposited crusts, originally formed in the early diagenesis near the surface of sandy-argillaceous deposits below the water-sediment boundary. Phosphorite is represented by fluorocarbonate apatite with unit cell parameter a from 0.9359 to 0.9363 nm, spectral mode parameters in Raman spectra (FWHM = 1–2 cm–1 and position from 963 to 966 cm–1), and a band at 1095 cm–1 in IR spectra. The absorption bands at ~1430 and 1453 cm–1 in the IR spectra correspond to the substitution of the orthophosphorus group by the carbonate ion (B-type). According to thermal analysis data, the CO2 content in apatite varies in the range of 0.04–0.8%, and the admixture of dispersed organic matter in the form of aliphatic compounds is 0.3–0.8%. Apatite is represented by two generations: primary in the form of basal structureless fine-crystalline cement and secondary in the composition of euhedral crystals up to 10 µm in size. Both generations corrode detrital quartz grains. Secondary apatite is enriched in P2O5, CaO, and F and contains less SiO2, FeO, Al2O3, MgO, and K2O than primary apatite. The PAAS-normalized REE distribution has a smoothed profile with a La/Yb ratio of about 2 and positive Ce- and Eu anomalies in enrichment phosphorites. The average value of F/P2O5 is 0.09 and corresponds to that in typical fluorocarbonate apatites that have undergone catagenesis. The high values of 87Sr/86Sr (from 0.7130 to 0.7253) in detrital phosphorites of the Kernos Formation suggest their deposition in a desalinated wave-dominated shallow-marine paleobasin near a significant inflow of continental waters or catagenetic recrystallization.

Rare earth elements distribution in topsoil from Ditrău Alkaline Massif area, eastern Carpathians, Romania

This paper gives an overview of the REEs distribution in topsoil from Ditrău Alkaline Massif area under influence of basic natural factors (parent material and soil acidity). Seventy-six soil samples were collected in accord with the most representative bedrock types and concentrations of the elements were determined using inductively coupled plasma mass spectrometry. The ΣREEs contents in soil developed on alkaline rocks ranges from 52.59 to 579.20 μg/g, with an average value of 235.76 μg/g, significantly higher than the average value of Earth's crust (179.7 μg/g). Y content varies between 5.50 and 58.80 μg/g with an average of 21.67 μg/g. The soils are enriched in LREEs (La to Eu) and depleted in HREEs (Gd to Lu) and Y. This trend is expressed by the wide variations of the LREEs/HREEs, (La/Yb)ch, (La/Sm)ch and (Gd/Yb)ch ratios. The REE chondrite - normalized plots show for most soils strongly negative anomalies for cerium and europium and positive anomalies for gadolinium and dysprosium. The pH of soils is generally acidic to weakly acidic and has an insignificant role in REEs fractionations in soil. The spatial distribution of REEs is strongly related to the lithology of the study area, displaying minor to negligible effects of enrichment factors and a low geoaccumulation index, corresponding to the lack of anthropic contamination. The distribution of the elements in topsoil tends to mimic elemental accumulation in the parental bedrock, with a potential to highlight mineralized zones.

Geochemical characteristics of the Rajmahal coals in Dhulia North Block, Eastern India: implication to their utilization and environment.

The borehole coal samples of Dhulia North Block from the Rajmahal Basin, Eastern India, were systematically analyzed based on the chemical composition and concentration of major and trace elements (including rare earth elements, REEs) to assess the distribution of REEs and their environmental implications with utilization potential. TheDhulia North Block coals are characterized by the predominant majoroxides of SiO2, Al2O3, and Fe2O3, accounting for 94% of the total ash composition, indicating the presence of quartz, clay-rich minerals, and pyrite. Compared with the average world coal ash, the total REE content in the analyzed samples ranged from 341.0 to 810.4ppm, which is substantially higher. Hot humid climate conditions with intermediate igneous source rocks of the basin were demonstrated by the major oxide ratios (Al2O3/TiO2 < 20) and plots of TiO2 with Al2O3 and Zr. The redox-sensitive elements such as V, Ni, Cr, and Co found in the Dhulia North Block coal indicate that an oxic sedimentary environment existed in the basin when coal was formed. The low sulfur content (1% in most samples) indicates freshwater conditions in the basin at the time of organic matter deposition. The outlook coefficient (Coutl) varies between0.7 and 1.6, indicating that the Dhulia North Block coals are a prospective source of REEs. The Dhulia North Block coals are characterized by low H/C and O/C atomic ratios ranging from 0.56 to 0.90 and 0.10 to 0.22, respectively, and contain type-III kerogens, indicating gas-prone source rock. Further, the basic-to-acid oxide ratio suggested that Dhulia North Block coals were suitable for utilization during combustion processes.

Distribution of Li, Ga, Nb, and REEs in coal as determined by LA-ICP-MS imaging: A case study from Jungar coalfield, Ordos Basin, China

Previous studies on modes of occurrence of Li, Ga, and Nb in coal are primarily based upon statistical analyses due to the low concentrations of these elements and the lack of methods of direct analysis. Laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) can be used for the in-situ determination of trace elements in minerals. The strong heterogeneity and diversity of macerals lead to a lack of suitable internal calibration elements required for LA-ICP-MS-based analysis of trace elements in coal, making the determination of trace elements in organic matter in coal challenging. In this study, the previously investigated high-Al and Li-Ga-Nb enriched No. 6 coal in the Haerwusu Mine of the Jungar Coalfield, Ordos Basin, China, was chosen for revealing the distribution and modes of occurrence of Li, Ga, Nb, and rare earth elements (REEs; REY if Y included) in coal, using the LA-ICP-MS method of mapping (imaging) technology. The results indicate that the majority of Ga and Nb present within the coal was concentrated within a specific collotelinite layer. Gallium and Nb have an organic association and are rare within minerals (i.e., clay minerals and boehmite). Lithium is homogeneously distributed throughout the clay minerals in the collodetrinite. Most of the La and Ce in the coal are concentrated in La- and Ce-enriched minerals, including monazite, bastnaesite, and lanthanite. The other REEs are concentrated in the Ga- and Nb-enriched collotelinite, along with small amounts of La and Ce. A similar characterization processing may be used to determine the modes of occurrences of trace elements in other organic-rich rocks or fine-grained sediments.

Origin of heavy rare earth elements in highly fractionated peraluminous granites

Rare earth elements (REEs + Y) play an important role in modern industry. Heavy REEs (HREEs) are particularly critical because of their relative scarcity in nature. Global HREE resources are predominantly present in granitoid weathering crusts in southern China. Although it is well known that REEs are generally enriched in alkaline rocks, in contrast, the parental granitoids in most Chinese HREE deposits are peraluminous. Here, we examined different REE mineral compositions, distribution patterns, and Nd isotope ratios of the granitoid complex in Zudong, South China, whose weathering crusts form the largest HREE deposits globally. The complex is composed of granodiorite, biotite-muscovite, and muscovite alkali-feldspar granites, whose REE patterns change from HREE depletion to enrichment relative to light REEs (LREEs) with increasing negative Eu anomalies. They are not fractional crystallization products from the same parental melts owing to the different zircon U-Pb ages (∼191, ∼169, and ∼154 Ma for granodiorite, biotite-muscovite, and muscovite granites, respectively). However, magmatic zircons from the three types of granitoids show consistent initial Hf isotope compositions [εHf(t) = 3.4 to 8.6], indicating they evolved from the same sources. The granodiorite contains primary LREE minerals with low εNd(t) values (−13.8 to −10.1), decoupled from high zircon Hf isotopes. This indicates a garnet-containing basement source resulted in Lu (HREE) remaining preferentially in the garnet phase, with Hf entering the melt. This contradicts the high HREE concentration recorded in the biotite-muscovite and muscovite granites, which contain abundant HREE minerals associated with muscovite, fluorite, and recrystallized quartz. The whole-rocks and their secondary REE minerals show variable and higher initial Nd isotope ratios [εNd(t) = −3.7 to 2.9 and −11.4 to −7.1 for biotite-muscovite and muscovite granites, respectively] than the early granodiorites and their primary REE minerals, indicating minimal 143Nd was derived from radioactive decay of 147Sm in the basement and wall rocks. This constrained the contribution of external REE-, volatile-rich liquids, which drove the segregation of highly evolved silicate melts from the magma chamber. This increased volatile saturation and fluid exsolution, which may have mobilized the HREEs and metasomatized the granites during their emplacement. Therefore, we infer that external fluid metasomatism appears to be crucial for the HREE enrichment in highly fractionated peraluminous granites.

Mesoarchaean banded iron formations of the Fennoscandian Shield: new zirconU-Pb (ID-TIMS and SHRIMP-II) isotope ages of noble metal mineralization and Nd-Sr data on whole rocks

ABSTRACT Banded iron formations (BIFs) are widespread over the world (3.81 Ga to 1.80 Ga) as the Algoma and Superior types. The paper provides new isotope (Nd-Sr, U-Pb) data on associated noble-metal mineralization in Algoma-type BIFs of the Fennoscandian Shield. U-Pb dating of accessory zircon applied to estimate the formation time of noble-metal-bearing skarn and related rocks in the Olenegorsk and Kirovogorsk BIFs, NW Fennoscandian Shield show that they occurred in the interval between the formation of basalt protolith (2.81 Ga amphibolites) and metamorphism in BIFs (2.75 Ga) to the formation of gold-bearing iron-rich skarn with native Au, Ag, Bi and tellurides (2.65 Ga) and low-temperature quartz-zeolite veins with redeposited Au (2.55 Ga). REE distribution in zircons and corresponding rocks indicated an important role of redox reactions in Fe and REE redistribution affected by reducing fluids on haematite-quartz protolith of BIFs.

Clay mineralogy mediated by pH and chemical weathering intensity of Permian–Triassic boundary K-bentonites at Dongpan (Guangxi, South China)

Volcanic ash deposits of the Permian-Triassic (P-T) transition in South China, in addition to being associated with the Permian-Triassic boundary mass extinction, are useful marker beds for regional correlation of sedimentary strata. This study investigates the source(s) of P-T volcanic ash layers in South China by studying their clay mineralogy and geochemical characteristics in deep-marine facies at Dongpan. Mineralogically, the Dongpan deposits consist mainly of clay minerals and quartz, with small amounts of anatase and feldspar. C lay minerals in the volcanic ash layer are mainly composed of R1 mixed-layer illite/smectite (I/S) (56.2–74.8%), smectite (14–22.8%), kaolinite (5.4–27.3%) and illite (1.2–5.3%). The relatively high content of kaolinite and weak illitization of smectite at Dongpan differ from the features of clay-mineral assemblages in other contemporaneous deep-water facies. Our results indicate that strong chemical weathering in an acidic and oxidizing environment characterized by low K+/H+ ratios inhibited uptake of K+ in the interlayers of I/S clay minerals and, thus, illitization of smectite. We infer that weathering intensity rather than redox state was the primary influence on the rate of kaolinization of clay minerals in these deep-marine facies. The Dongpan section exhibits a uniform REE pattern, indicating a single and stable source of volcanic ash during the P-T transition. Trace-element and REE distribution patterns and mixed-layer I/S clay-mineral morphologies are consistent with the source of the volcanic ash at Dongpan being a nearby continent-margin volcanism.

Trace Elements and Pb-O Isotopes of Scheelite: Metallogenic Implications for the Shimensi W-Polymetallic Deposit in South China

The world-class Shimensi tungsten (W)-polymetallic deposit is located in Jiangnan Orogen, with an estimated reserve of 742.5 kt WO3 @ 0.195% W, 403.6 kt Cu and 28 kt Mo. In this paper, the trace elements and Pb-O isotopes of scheelite (the main ore mineral) are presented to study the ore-forming material source and ore-forming fluid evolution. The results show that the REE distribution in scheelite is mainly controlled by the substitution mechanism of 3Ca2+ = 2REE3+ + □Ca (where □Ca is the Ca-site vacancy). Oxygen isotope data indicate that the scheelite mineralization occurred under high-temperature oxygen isotope equilibrium conditions, and that the ore-forming fluid has a magmatic–hydrothermal origin. The variation in scheelite Eu anomalies and the wide range of scheelite Y/Ho ratio indicate that the ore-forming fluid evolves from reducing to oxidizing, and the early-stage and late-stage ore-forming fluid may have been relatively rich in F− and HCO3−, respectively. The significant Mo decrease in scheelite from the early to late stage that are opposite to the influence of fO2 variation may have resulted from the crystallization of molybdenite and Mo-rich scheelite. Lead isotopes of the ore minerals of scheelite, wolframite, molybdenite and chalcopyrite can be divided into three groups, similar to these of feldspars in different granites. Both the Mesozoic porphyritic and fine-grained biotite granites have Pb isotope ratios similar to the ores, which suggests that the former two are the main ore material source.