High Rare Earth Research Articles

Subduction-collision and rapid uplift of the NW Yangtze block during the Ediacaran-Cambrian transition: new evidence from the shoshonite series

ABSTRACT The NW Yangtze Block has long been regarded as a passive continental margin during Ediacaran and Cambrian. However, with the deepening of the regional geological survey and deep oil and gas exploration, the depositional sequence and palaeogeographic patterns of Ediacaran and Cambrian in the Sichuan basin are not consistent with the general sedimentary evolution process of passive margin more and more. To fully understand the tectonic property and palaeogeography of the NW Yangtze block, a comprehensive study of the whole rock geochemistry, zircon U-Pb chronology and Hf isotopic composition analysis were carried out on the Weimen volcanic rocks, which mainly consist of trachyte, trachy-andesite, andesite, dacite, and rhyodacite in Maoxian area. They have high light rare earth element (LREE) and large ion lithophile element (LILE) concentrations, but are depleted in high field strength elements (HFSE). They are characterized by having high K2O+Na2O (5.60–9.48%), MgO (1.47–4.58%), Ce/Yb (11.67–25.79), and normalized hypersthene (Hy = 2.14–14.17), indicate an unambiguous feature of the shoshonite series. LA-ICP-MS zircon U-Pb dating results show that the volcanic rocks have crystallization ages ranging from 528 Ma to 523 Ma, with positive zircon εHf (t) ranging from + 1.31 to + 5.26. In combination with previous studies, the early Cambrian shoshonite series in Maoxian area are interpreted to be formed in a continental collision setting. Therefore, the discovery of the shoshonite series suggests that the NW Yangtze block has experienced an important process of continental subduction and collisional orogeny in response to the Gondwana assembly, and consequently provided a large amount of terrigenous sources to rapidly fill into the early Cambrian foreland basin.

Corrosion resistance of high entropy rare earth zirconate ceramic to CMAS

Corrosion resistance of high entropy rare earth zirconate ceramic to CMAS

Phase stability and grain growth in (La0.25Gd0.25Yb0.25Y0.25)2Zr2O7 high entropy rare earth zirconate

Phase stability and grain growth in (La0.25Gd0.25Yb0.25Y0.25)2Zr2O7 high entropy rare earth zirconate

High-abundant rare earth La/Ce substituted Nd2Fe14C based permanent magnet materials prepared by mechanochemical method

To balance the utilization of rare-earth resources and reduce the preparation cost, the La and Ce substituted Nd2Fe14C hard magnetic alloys were prepared by a facile mechanochemical method for the first time. A two-step process is typically employed: 1) Decomposition of hydrocarbon and disproportionation of (Nd1-xREx)2.5Fe14B0.08 (RE=La or Ce, x=0–0.3) alloys during high-energy ball milling, Nd+Nd2Fe17+n-hexane→NdH2+δ+α-Fe+Fe7C3; 2) (Nd, RE)2Fe14C hard magnetic powders were obtained via the vacuum annealing at 800 °C for 2 min. The phase relation, magnetic properties and microstructural evolution of (Nd, RE)2Fe14B0.08C0.92 (named Nd-RE-Fe-C-based) alloys were systematically investigated. Substitution of La for x=0.1 Nd in the Nd-RE-Fe-C-based alloy increase the coercivity from 15.6 kOe to 18.6 kOe without reducing the remanence. First-principles calculation was performed to study the mechanism of magnetic properties La and Ce substituted samples. The results showed that La tends to be expelled from 2:14:1 phase to form more minor phases which act as the domain wall pinning center, increasing the coercivity. However, Ce prefers to enter the 2:14:1 phase, diminishing the permanent magnetic properties due to the poor intrinsic magnetic properties. This paper provides a novel viewpoint for the effective utilization of high abundant rare earth and the investigation of low cost Nd2Fe14C permanent magnet materials.

Unusual microstructure and texture transition during hot compression in an extruded Mg-Gd-Zr alloy with fiber texture

In magnesium (Mg) alloys with high rare earth content, slip modes and twinning behaviors are quite different from that in traditional Mg alloys. Deformation mechanisms, i.e., {11−21} twinning and non-basal slips, can activate during deformation process even at room temperature (RT) and contribute effectively to microstructure and texture transition. In order to figure out the influence of temperature on these deformation mechanisms and resultant microstructure and texture transition, compression tests were conducted on an extruded Mg-17.5Gd-Zr (wt%) alloy with <0001> fiber texture at temperature range of RT-450 °C. During compression, both {10−12} and {11−21} twinning behaviors can be governed by Schmid law at RT-350 °C and act as main contributors to texture transition. When the compression tests were carried out above 400 °C, twinning behaviors almost vanished and dynamic recrystallization (DRX) preferred activating within grains with the orientation of <10–10>//compression direction. DRX changed from continuous DRX to discontinuous DRX with the temperature increasing, which can be attributed to the temperature increasing and resultant elimination of sessile structure induced by cross-slip on basal plane. DRXed grains show weak texture and the texture mainly result from the properties of several near coincident site lattice boundaries.

Deformation behavior and microstructure evolution of one novel superalloy with high rare earth gadolinium content: Multi-scale modeling and experimental study

It has been proved that rare earth elements have a positive effect on the performance of superalloys and steels at only trace levels, but rare earth phases are always tricky in the manufacturing process. In this work, one Ni–Mo–Cr-Gd alloy with ultrahigh rare earth Gd content (1.75 wt %) was designed to reveal the influence of hard and brittle Ni5Gd particles on hot deformation behavior and microstructure evolution. The Ni–Mo–Cr-Gd alloy exhibits higher deformation activation energy and smaller processable regions in the processing maps as compared with the Ni–Mo–Cr alloy. Combining electron back scatter diffraction and crystal plastic finite element method, it was found that strain concentrates around Ni5Gd particles, especially at grain boundaries, and rapidly reaches the critical value for recrystallization, which verifies particle stimulated nucleation. The recrystallization fraction decreases with strain rates from 0.01 to 1 s−1 but increases from 1 to 10 s−1, which is because meta-dynamic recrystallization occurs faster when the strain rate is greater than 1 s−1 and Ni5Gd particles promote the process indirectly by introducing more severely deformed matrix. Furthermore, the finite element modeling shows that plastic strain and temperature rise at the central region of samples increase with strain rate increasing, which can explain the unusual fragmentation of Ni5Gd at 1200 °C with the highest strain rate. Our results firstly reveal the evolution mechanism of Gd-containing superalloy during hot deformation, which can help to solve the manufacturing problems of similar alloys.

Achieving high strength-ductility synergy in Mg-Gd-Zn-Zr alloy by controlling extrusion processes parameters

The high rare earth content in current magnesium alloys poses environmental and economic challenges. To address this issue, this study designs a Mg-7.5Gd-6Zn-0.5Zr alloy (GZ76, wt.%) with low rare earth content, high strength, and excellent ductility. The morphology of the as-cast GZ76 alloy is characterized by a dendritic structure consisting of an α-Mg matrix and interdendritic zones comprising W + I phases, interspersed with fragmentary Zn-Zr phases. Furthermore, the extrusion process is employed to meticulously control the microstructure and enhance the mechanical properties of the alloy. This research focuses on investigating the effects of extrusion parameters on magnesium alloys to optimize their extrusion processing conditions. Through systematic manipulation of the extrusion ratio and extrusion speed, a comprehensive analysis is conducted to examine their impacts on grain refinement, texture evolution, distribution of second phase, and mechanical properties of extruded magnesium alloys. The results indicate that due to the insufficient recrystallization process, the microstructure of the as-extruded GZ76 alloys exhibits a bimodal structure, encompassing both fine recrystallized grains and coarse unrecrystallized grains. At larger extrusion ratio, a faster extrusion speed leads to superior mechanical properties of the alloy. Conversely, at smaller extrusion ratio, a slower extrusion speed is more favorable for achieving higher strength. These findings provide valuable insights into optimizing the extrusion parameters for enhancing the performance of magnesium alloys in engineering applications.

Preparation of large specific surface rare earth oxides from calcium-containing rare earth solution by carbon dioxide carbonization method☆

The calcium-containing rare earth solution is generated during the recovery processes of NdFeB waste, which is treated as wastewater by enterprises. In this paper, the carbon dioxide carbonization method was applied to the separation of rare earths and calcium in the solution, as well as the preparation of rare earth oxides with a large specific surface. It is shown that the process of CO2 carbonization of solution includes reactions such as the dissolution, diffusion and ionization of CO2, the carbonate precipitation of rare earth ions, and the neutralization of hydrogen ions. At a pH of 4.5, the carbonization precipitation rate is effectively controlled, enabling homogeneous precipitation and ensuring both high precipitation yield and rare earth oxides purity. In this way, the crystallization of carbonization products is a process dominated by the oriented attachment theory and coexisting with the Ostwald ripening theory, resulting in abundant pores formed by multiple layers of stacking in the products. With the optimal carbonization conditions, the rare earth precipitation yield solution reaches 99.32%. The obtained carbonization products are crystalline (LaCe)(CO3)3·8H2O, and the purity of the rare earth oxides is as high as 99.22 wt%. The specific surface area of the rare earth oxides reaches 94.7 m2/g, and its adsorption efficiency for tetracycline hydrochloride in solution can reach 92.6% in a short time. The rare earth oxides are expected to be used as an adsorption material for wastewater treatment and other adsorption environments.

Geochemistry of Volcanic Rocks in Ponelo Island, North Gorontalo, Indonesia

Ponelo Island is located in the northern part of Sulawesi, which is still an enigma regarding the genesis of the volcanic rocks found on this island. Therefore, the objective of this study is to understand the petrogenesis and tectonic implication of these volcanic rocks. Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) to obtain trace and rare earth elements is the method of this study. The volcanic rocks found on Ponelo Island consist of basalt and basaltic andesite rocks with a calc-alkaline affinity. The transition data suggested a highly fractionated cause of low transition element (Ni=17-38 ppm; Cr=13-47) compared to primary magma concentration, anomalies negative of Ba, Sr, and Ti of spider diagrams, and negative anomaly of Eu (Eu/Eu*=0.88-0.99). Relationship between low concentration between Ce/Y (0.74-0.76) and La/Yb vs Sm/Yb ratio indicated ~5% spinel-lherzolite mantle source partial melting. On the other hand, incompatible element ratios, such as Ba/Nb (39.03-45.28), Ba/Th (75.52-82.67), Rb/Nb (3.93-6.22), K/Nb (1772.22-2703.45), Ba/La=13.67-14.57, Th/La (0.17-0.18), La/Nb (2.91-3.16), depleted Nb/U (6-6.74), and also lack of xenolith or enclaves indicate cryptic crustal contamination. The slab-derived fluid indicated by ratios of Rb/Y (0/019-0/05), Nb/Y (0.10-0.11), Th/Yb (0.52-0.61), and Ba/La ratio (13.29-14.57). Ponelo volcanic rocks shows typical calc-alkaline island arc tectonic setting particularly with enrichment in ion lithophile element (LILE) and light rare earth elements (LREE) along with depletion in high field strenght elements (HFSE) and heavy rare earth elemets (HREE), as shown by spider diagrams.

Late Paleozoic–Early Mesozoic subduction history of Mudanjiang Ocean: New insights from greenschist in the Heilongjiang Complex, NE China

This paper presents zircon U-Pb ages, whole-rock major and trace element data, and Sr-Nd-Hf isotopic compositions for the greenschists from the Heilongjiang Complex in NE China. Based on the geochronological and geochemical characteristics, the greenschists from the Heilongjiang Complex can be categorized into three series: Early Permian tholeiitic series (275 ± 1 Ma and 273 ± 1 Ma), Middle Permian alkaline series (261 ± 1 Ma), and Early Jurassic alkaline series (179 ± 1 Ma). The Early Permian tholeiitic greenschist samples are characterized by remarkable negative Nb and Ta anomalies, and they exhibit relatively low whole-rock (87Sr/86Sr)i values (0.703896–0.704252), along with positive εNd(t) values (+7.66 to +8.65) and positive εHf(t) values (+0.92 to +11.51), implying that their protoliths originated from the partial melting of a depleted mantle wedge that has been metasomatized by subducted slab fluids. The Middle Permian alkaline greenschist samples have high Nb (17.3–19.0 ppm), TiO2 (1.40–1.64 wt%), and P2O5 (0.60–0.68 wt%) concentrations, and they are enriched in large ion lithophile elements and light rare earth elements, and depleted in high field strength elements and heavy rare earth elements, with high whole-rock (87Sr/86Sr)i values (0.709434–0.709949), negative εNd(t) values (−4.73 to −4.72) and varied εHf(t) values (−10.11 to +4.86), which compositionally align with those of Nb-enriched basalts. Based on the geochronological and geochemical characteristics, we propose that the protolith generation of Middle Permian alkaline greenschists was associated with the partial melting of a mantle wedge that had been metasomatized by subduction slab-derived melts. The Early Jurassic alkaline greenschist samples display OIB affinities, characterized by whole-rock (87Sr/86Sr)i values ranging from 0.705161 to 0.705926, εNd(t) values between +6.16 and +6.19, and εHf(t) values from +3.44 to +9.32, indicating the formation of the protolith for the Early Jurassic alkaline greenschist was related to the upwelling of the asthenosphere resulting from slab break-off. By integrating regional geological data, we can trace the subduction evolution of the Mudanjiang Ocean back to the Early Permian, and the slab break-off during the Early Jurassic likely corresponded to the early stage of the closure of the Mudanjiang Ocean.

Chloridizing roasting studies of spent NdFeB magnets for recovery of rare earth values

The increased demand for rare earth elements in advanced technological applications and supply shortages call for metal recovery from secondary sources. Permanent magnet (Nd2Fe14B or NdFeB) may serve as a potential secondary source due to its high rare earth (Nd+Pr+Dy: ∼30 %) content and its vast application. The present study utilizes a chloridizing roasting (CaCl2.2 H2O) pre-treatment process followed by water leaching, acid leaching (0.5 M HCl, S/L =1/10 g/ml, 90 °C, 3 h), oxalic acid precipitation and calcination (850 °C, 2 h) to obtain mixed rare earth oxides. The process was optimized based on temperature (400–700 °C), dosage (CaCl2.2H2O: NdFeB=0.5:1–2.5:1), and time (30–120 min) on the rare earth dissolution. The theoretical activation energy for the chloridizing roasting process is estimated as 22.3 (OFW) and 16.7 kJ/mol (KAS), while the experimental activation energy for Nd and Dy dissolution was determined to ∼29.3 and ∼17.7 kJ/mol, respectively depicting product layer diffusion-controlled kinetics. Higher dosages of CaCl2.2H2O (1.5:1 and 2:1) favored NdOCl formation, thereby, higher dissolution; however, further higher dosage (2.5:1) leads to reduced Nd dissolution due to higher CaO formation and acid consumption by Ca during leaching. Incomplete oxidation at lower temperatures (400 °C) and iron dissolution impair the Nd dissolution and selectivity. Excessive oxidation at >700 °C favors the formation of NdFeO3, decreasing Nd dissolution. The maximum dissolution of Nd was ∼89 %, while for Dy, it was ∼88 % at optimum conditions of 600 °C, 90 min, 2:1. Water leaching post-roasting leads to ∼87 % Ca removal and the precipitation efficiency of rare earth oxalates was 99 %. The overall extraction for rare earth elements was ∼89 %, and 1 kg of NdFeB powder can yield ∼285 g of rare earth oxides (∼239 g Nd2O3, ∼14 g Dy2O3) with 96 % purity. Further, this study demonstrates that using CaCl2.2 H2O as a solid chlorinating agent in chlorination roasting enhances recovery rates of mixed rare earth oxides while providing a safer and more environment-friendly alternative for industrial applications.

Garnet as a carrier of HREEs in highly fractionated peraluminous granite: Implications for the formation of ion-absorption HREE deposits

Ion-absorption rare earth element (REE) deposits in South China are the world’s most important source of heavy REEs (HREEs). These deposits were formed by the weathering of granitic rocks whose formation involved primary HREE enrichment. Previous studies have identified the key role of late-stage magmatic evolution, especially the magmatic–hydrothermal transition stage played in HREE enrichment, but the detailed processes need further investigation. Garnet is a common HREE carrier in parent rocks and also a main contributor of these elements in formation of ion-absorption HREE deposits. Here, we investigate textural and compositional variations in garnets from parent rock (muscovite granite) of the Dabu ion-absorption HREE deposit to constrain the primary HREE enrichment of the parent rock during late-stage magmatic evolution. Mass-balance calculations reveal that garnet accounts for ∼67 % of the Y and 64 % of the REEs in the Dabu muscovite granite. The garnets can be classified into three types: i) magmatic garnets (Grt-1A) are intergrown with plagioclase, K-feldspar, and quartz, host both melt and mineral inclusions, and have high REE + Y contents (6488–19,215 ppm); ii) magmatic–hydrothermal garnets (Grt-1B) occur as overgrowths on Grt-1A, host both melt and fluid inclusions, and have intermediate REE + Y contents (2681–8683 ppm); and iii) hydrothermal garnets (Grt-2) are intergranular with quartz and altered biotite, host primary fluid inclusions, and have the lowest REE + Y contents (476–1247 ppm). The texture and composition of the three types of garnet indicate that the magma have undergone a transition from a volatile-undersaturated to a volatile-oversaturated aqueous system. The fluid, from which some REE minerals precipitated, present in the magma system was derived from the magma itself rather than from an external source, as evidenced by the similarity in Nd isotopic composition between the REE minerals and the whole-rock samples. During this transition, the presence of high-HREE garnet prevents the HREE partitioning into refractory minerals (e.g., zircon, REE-bearing phosphate) or extracting from the magma system by the fluid. Our findings show that granites containing high-HREE garnet have high potential for forming ion-absorption HREE deposits and that garnet can reliably record their magmatic evolution.

Improved comprehensive performance of high entropy rare earth aluminate as T/EBC materials by phase structure regulation

To optimize the comprehensive performance of rare earth (RE) aluminates as thermal/environmental barrier coatings (T/EBCs), we engineered six kinds of novel high-entropy RE aluminate multiphase ceramics with the coexisting garnet and perovskite phases by regulating equivalent ionic radius of RE3+, and the relationship between the microstructure and thermal properties, as well as resistance to CMAS corrosion was investigated in-detail. The findings revealed that the garnet (5RE0.2)3Al5O12 content gradually decreased in multiphase ceramics with the increasing equivalent ionic radius of RE3+. The interaction between garnet and perovskite grains can decrease grain size, which in turn enhanced phonon scattering, thereby leading to the decrease in thermal conductivity. Moreover, the synergistic effect in the different dissolution rates of garnet and perovskite phases can form a dense garnet/apatite barrier layer at corrosion front, thereby contributing to CMAS corrosion resistance. These results provide a robust theoretical foundation for the advancement of next-generation T/EBCs.

Influence of doping soda-lime-silica glasses with Gd2O3, In2O3, and La2O3 on the enhancing of their physical, opto-mechanical and radiation shielding properties

A series of soda-lime-silicate glasses doped Gd2O3, In2O3, and La2O3 rare earth ions was prepared using the melt-quenching technique. The prepared glass samples are designed depending on a chemical composition of (15-X)Na2O – 30CaO – 55SiO2 –XM2O3, where X = 1.0 mol% and M = Ga (NCSG), In (NCSI), and La (NCSL). The amorphous state of the synthesized samples confirmed by XRD analysis, and structural changes were studied via density (ρg), molar volume (Vm), Oxygen molar volume (Vo), and Oxygen packing density (OPD). The mechanical and shielding attenuation parameters of the produced glasses were also projected. The ρg of prepared glasses increased from 2.742 to 2.829 g/cm3 as a result of M2O3-dopant with high molecular weight rare earth oxides. Whereas, the physical parameters Vm, Vo, and OPD were behave in the same trend. Elastic moduli were improved when Na2O replaced with M2O3. The M2O3/Na2O replacement led to increase stiffer and rigidity of the prepared glasses. The NCSL sample was possessed the lowest optical energy band (Eopt.) values (3.45 eV and 2.63 eV for direct and indirect transitions). The NCSL glass sample possessed the highest mass (MAC) and linear (LAC) absorption capacity. In addition, the same glass sample verified the lowest values of half-value layer (HVL) and mean free path (MFP). Thus, the sample coded as NCSL sample including La2O3 is a superior for optical and radiation shielding capacities among all studied glasses. Therefore, the studied glasses can be applied for several optical and radiation shielding applications.

Removal of Rare Earth Elements from complex mixtures by using manganese ferrite nanoparticles: Optimization through surface response methodology

The crucial role of Rare Earth Elements (REEs) in the development of hi-tech in addition to their limited availability have urged countries to develop sustainable alternatives to their conventional primary sources (ore mining). Sorption technologies using magnetic materials such as spinel ferrite nanoparticles provide efficient removal of REEs from contaminated solutions and ease of separation through application of an external magnetic field. However, there is still limited knowledge available regarding the optimal operational conditions in which to use these materials, especially in complex aqueous mixtures with different REEs. In this study, we have used Surface Response Methodology (SRM) applied to MnFe2O4 nanosorbents to identify their ideal sorption conditions of pH (4–8), REEs concentration (1–5 μM) and sorbent mass (20–180 mg L−1) in a mixture of nine REEs in water samples of distinct salinity (NaCl: 0–30 g L−1). Our results indicated that high pH favored REEs sorption because of the material's surface charge, which promoted interactions with REEs ions at pH 6–8. Yttrium was the least removed element, but total removal was achieved for lowest REEs concentration using 151 mg L−1 of sorbent. High removals were also obtained for the concentration of 5 μM (100 % removal, except for Y and La). Salinity did not impair sorption significantly (<10 %), which was owed to the high sorbent mass used in those assays. An increase in sorbent mass and initial REEs concentration also promoted faster kinetics. The spinel type MnFe2O4 nanoparticles showed great promise in a realistic application, which is the next proposed step in this line of research.

Microstructure and Properties of Mg-Gd-Y-Zn-Mn High-Strength Alloy Welded by Friction Stir Welding.

Mg-Gd-Y-Zn-Mn (MVWZ842) is a kind of high rare earth magnesium alloy with high strength, high toughness and multi-scale strengthening mechanisms. After heat treatment, the maximum tensile strength of MVWZ842 alloy is more than 550 MPa, and the elongation is more than 5%. Because of its great mechanical properties, MVWZ842 has broad application potential in aerospace and rail transit. However, the addition of high rare earth elements makes the deformation resistance of MVWZ842 alloy increase to some extent. This leads to the difficulty of direct plastic processing forming and large structural part shaping. Friction stir welding (FSW) is a convenient fast solid-state joining technology. When FSW is used to weld MVWZ842 alloy, small workpieces can be joined into a large one to avoid the problem that large workpieces are difficult to form. In this work, a high-quality joint of MVWZ842 alloy was achieved by FSW. The microstructure and properties of this high-strength magnesium alloy after friction stir welding were studied. There was a prominent onion ring characteristic in the nugget zone. After the base was welded, the stacking fault structure precipitated in the grain. There were a lot of broken long period stacking order (LPSO) phases on the retreating side of the nugget zone, which brought the effect of precipitation strengthening. Nano-α-Mn and the broken second phase dispersed in the matrix in the nugget zone, which made the grains refine. A relatively complete dynamic recrystallization occurred in the nugget zone, and the grains were refined. The welding coefficient of the welded joint exceeded 95%, and the hardness of the weld nugget zone was higher than that of the base. There were a series of strengthening mechanisms in the joint, mainly fine grain strengthening, second phase strengthening and solid solution strengthening.

Are nano-colloids controlling rare earth elements mobility or is it the opposite? Insight from A4F-UV-QQQ-ICP-MS

Rare earth element (REE) mobility in the environment is expected to be controlled by colloids. Recent research has detailed the structure of iron-organic colloids (Fe-OM colloids), which include both large colloids and smaller nano-colloids. To assess how these nano-colloids affect REE mobility, their interactions with REE and calcium (Ca) were investigated at pH 4 and 6. Using Asymmetric Flow Field Flow Fractionation (A4F) combined with UV and Triple Quadrupole Inductively Coupled Plasma Mass Spectrometry (QQQ-ICP-MS), Fe-OM nano-colloids were separated from bulk Fe-OM colloids and their REE and Ca content were analyzed. Without REE and Ca, nano-colloids had an average diameter of approximately 25 nm. Their structure is pH-dependent, with aggregation increasing as pH decreases. At high REE loadings (REE/Fe ≥ 0.05), REE induced a size increase of nano-colloids, regardless of pH. Heavy REE (HREE), with their high affinity for organic matter, formed strong complexes with Fe-OM colloids, resulting in large aggregates. In contrast, light REE (LREE), which bind less strongly to organic molecules, were associated with the smallest nano-colloids. Low REE loading did not cause noticeable fractionation. Calcium further enhanced the aggregation process at both pH levels by neutralizing the charges on nano-colloids. These findings indicate that REE can act as aggregating agent controlling their own mobility, and regulating colloid transfer.

Microbial and hydrothermal dolomite formation in Early Cretaceous lacustrine sediments in Yin'e Basin: Insights from petrology and geochemistry

Dolomite is widely present in geological history, but its origin has always been a prominent problem that troubles sedimentologists. For lacustrine dolomite, current research has not yet provided a reliable explanation for its complex genesis mechanism. The Early Cretaceous lakes in Northwest China host various morphological dolomites, providing valuable materials for exploring the origin of dolomites. According to their petrological and mineralogical characteristics, it can be divided into thick laminated dolomite, thin laminated dolomite, dolomitic mudstone, and vein dolomite. The ratios of trace elements and rare earth elements show that these dolomites precipitated in a brackish–suboxic environment. The high δ13C values (>8 ‰VPDB) of thick laminated dolomite and some thin laminated dolomite suggest the involvement of methane-producing microorganisms in the precipitation of dolomite, and the appearance of microscale/nanoscale spherical dolomite aggregates and the dispersed organic matter around dolomite particles jointly confirm that microbial-mediated biological activity promotes dolomite precipitation. The dolomite stoichiometry (mole % MgCO3) confirms that thick laminated dolomite was deposited in a restricted shallow water environment, while dolomitic mudstone is mainly deposited in relatively open water areas. The thin laminated dolomite in the shale laminae represents short-term or seasonal climatic and environmental fluctuations. In addition, some carbonate minerals of dolomitic mudstone in shallow water environment recrystallized by post-depositional hydrothermal effect, resulting in δ18O value decreased (<−10 ‰VPDB). The vein dolomite is characterized by high rare earth content and low δ13C and δ18O values, and its Sr isotope (0.712894 ± 0.000374) values reflect that the hydrothermal fluid may have been formed by the mixing of infiltrating lake water and crustal magmatic water. According to the characteristics of fluid inclusions, it is inferred that the hydrothermal fluid has the characteristics of low temperature (108.3 °C–159.8 °C), medium salinity (3.5 wt%–14.3 wt% NaCl) and high density (0.95–1.00 g/cm3). The microbial mediation and tectonic hydrothermal fluids play an important role in the formation of the Early Cretaceous lacustrine dolomite.

Decoding Apatite in Volcanic Carbonatitic breccia from Mongra, Northwest of Amba Dongar Carbonatite Complex, Gujarat, India: Insights to Genesis &amp; Rare Earth Element Budgets

Chemical variations in apatite in context to carbonatites and trace element partitioning between apatites and carbonatite-rich liquids are important in assessing the petrogenesis and evolution of the carbonatites as well as the associated carbonatitic breccia due to apatite's sensitivity to surrounding magma composition. Volcanic carbonatitic breccia is one of the constituent rock types found outside the ring structure of the Amba Dongar Carbonatite Complex (ADC) situated in western India. In the present work, we report the mineral chemistry of apatites from the carbonatitic breccias of the Mongra region (ADC outer core) and compare them to apatites from ADC carbonatites. Apatite chemistry from Mongra displays a larger concentration of rare earth elements, manganese, and chlorine when compared to those of ADC carbonatites. Morphology and distinct zoning of these apatites represent late-stage magmatic processes with high heavy rare earth element concentrations (high Lutetium), followed by interaction of fluids from the surrounding alkaline rocks. Variation in sulphur concentration in the apatites of this study indicates crystallisation under mildly reducing conditions. Integrated field observations, petrography, and apatite mineral chemistry from the Mongra region allow for an understanding of the genesis of apatites in the ADC outer core, with possible implications for late-stage mineral-melt interactions.

Structural insight of fluorophosphate glasses through F/O ratio: case study of Raman and NMR spectra

Fluorophosphate glass has excellent characteristics such as low nonlinear refractive index, anomalous partial dispersion, low phonon energy, high UV transparency and high rare earth doping concentration, etc. The two anion ions of fluorine (F) and oxygen (O) and their F/O ratio in fluorophosphate glasses provide important structural characteristics of the specific glass. To explore this, a series of fluorophosphate glass samples with theoretical F/O ratios ranging from 1 to 7 were prepared, Raman spectroscopy and 31P nuclear magnetic resonance (NMR) spectroscopy were mainly employed to elucidate the structural polyhedrons made of the network chain. The underlying correlation between the Qn units and F/O ratio was explored, i.e., the Q2 unit dominate when the F/O ratio is less than 0.3, and predominantly Q2 or Q1 unit is predominant as F/O ratio ranges from 0.3 to 1, it comes to be Q1 or Q0 unit as F/O ratio further increase to 4, while it becomes Q0 when the F/O ratio is greater than 4. The applicability of this interval estimation was verified by comprehensive analyzing a variety of structural results of fluorophosphate glasses with various glass compositions. The explored interrelation between the F/O ratio and structural property is of great significance for developing low nonlinear and UV transparent fluorophosphate glasses.