Rare Earth Elements Plus Yttrium Research Articles

New advances on the carbon isotope and rare earth elements chemostratigraphy of the late Ediacaran Tamengo Formation (Corumbá Group, Brazil)

The Tamengo Formation (Corumbá Group, midwest Brazil) is a carbonate-dominated succession of major importance to unravel the environmental and biological changes during the Ediacaran–Cambrian transition in Gondwana. Although it has been extensively studied in terms of sedimentology, isotope geochemistry, biostratigraphy, and geochronology, these studies are constrained to the Corumbá region. This work presents new sedimentological, C and O isotope chemostratigraphy, and rare earth elements (REE) plus yttrium (REY) data of four sections of the Tamengo Formation in the Serra da Bodoquena region, approximately 200 km south of Corumbá, discussing how these new data are related to the type sections. The sections present ooid grainstones, with hummocky, swaley, and wavy structures, interbedded with mudstones and shales, indicating deposition of fine particles by suspension fallout in-between periods of high-energy, with reworking by storm waves. The δ13Ccarb curves show positive plateaus with minor, short-lived negative excursions linked to facies variations, which are related to a large δ13Ccarb depth gradient in a redox-stratified water column. The REY profiles present middle REE (MREE)-bulge patterns and absent to slightly positive Ce anomalies, consistent with MREE adsorption onto Fe–Mn oxyhydroxides in the water column followed by release in pore waters. Subsequently, REY remobilization during anoxic diagenetic stages resulted in the MREE-bulge pattern and overprinted some of the original seawater REY features, including the Ce anomalies. The Tamengo Formation in the Serra da Bodoquena region represents a storm-dominated carbonate ramp, as previously interpreted for this unit in the Corumbá region. Nevertheless, there is a significant shift of 2 ‰ in the peaks of δ13Ccarb data between both localities, which may be related to differences in the overall sector of the carbonate ramp. There are also substantial variations in the δ13Ccarb record of the Tamengo Formation and other coeval Gondwana basins, such as the Nama and Itapucumi groups, with different peak values, which may be related to latitudinal differences on the inorganic carbon isotope composition or to the degree of basin restriction.

REE + Y signatures of the Navay phosphate deposit, SW Venezuela: Seawater paleoredox conditions and diagenetic implications

Phosphate rock occurrences in western Venezuela are well-known in Cretaceous sedimentary sequences, which are associated to the Caribbean-Tethyan passive margin, along an SW-trend belt of the Venezuelan Andes chain. In this study, the geochemical characteristics of the Navay phosphate deposit were investigated to discuss the ocean paleo-oceanographic conditions and diagenetic controls that prevailed during the deposit formation. The rare earth elements plus yttrium (REY) concentrations were determined and normalized with the Post-Archean Australian Shale (PAAS) values to generate the REY patterns. Our results reveal a typical seawater signature, except for the absence of a marked negative Ce* anomaly (Ce/Ce* = 0.76–1.00). The determined seawater REY patterns, along to the calculated ratios for (La/Sm)N = 0.78–1.00, and (La/Yb)N = 0.34–0.66, are similar to the modern oceanic water ratios. These data point to a lack of diagenetic alteration on the primary REY signatures, which corresponds with a terrigenous-free marine sediment source for the REY content present in the deposit. In brief: i) the slightly negative anomalies displayed by the Ce* and Eu*, accompanied by the Mn depletion, ii) a relative enrichment of some transition metal elements (V, Cr, and Cu), and iii) the low Mo/U ratios, are all of them considered as geochemical indicators of suboxic to anoxic conditions, which were predominated during the phosphogenetic processes of the deposit. Furthermore, our data reveals an economic potential of the phosphorites as a raw material to produce phosphoric acid (H3PO4) as well as a source of supply for rare earth elements, by means of: i) relative high grades of P2O5 (15.46–30.09 wt %), ii) low CaO/P2O5 ratios (1.22–1.28), iii) a lack of organic matter, chert or chalcedony, iv) a low content of Mg (0.07–0.22%), v) REE concentrations varying from 141.82 to 256.53 μg/g, with an average value of 208.14 μg/g; and vi) concentrations for toxic elements (i.e., V, Cr, Co, Ni, Cu, Zn, As, Sr, Pb, and U) below or at the acceptable levels, in comparison to commercial phosphorites worldwide.

Microstratigraphic geochemical characteristics of ferromanganese crust from central pacific: Implication for the role of Fe and Mn in REY enrichment

Rare earth elements plus yttrium (REY), well-known critical metals for many new and emerging technologies and as proxies in geological events, are one type of the most important high-tech metals in ferromanganese (Fe-Mn) crusts. The REY(III) are accumulated in Fe-Mn crusts through adsorption by Fe-Mn (oxyhydr)oxides. However, negative correlations between Mn and REY in some Fe-Mn crusts reveal a controversial role of Mn oxides in REY enrichment, which remains equivocal. In this study, texture, structure, mineralogy, and microstratigraphic geochemistry with the growth of a Fe-Mn crust (MP2D32A) from the Line Islands archipelago were analyzed using multiple microanalysis methods. The Fe-Mn crust is characterized by laminar structures, stromatolite-like structures, and micronodules that are primarily composed of low-crystalline Fe-vernadite and ferrihydrite. Throughout the profiles of MP2D32A, the contents of elements are more or less interdependent. Analysis of elemental correlations from the MP2D32A samples and 847 collected data sets from non-phosphatized hydrogenetic Fe-Mn crusts shows Fe plays a positive role and Mn plays multiple roles in REY accumulation during Fe-Mn crust formation. The REY content increases initially and then decreases with increasing Mn content and Mn/Fe ratio and the turning points (i.e., highest REY contents) mainly occur at an Mn content of ∼18–26% and an Mn/Fe content ratio of ∼0.8. These fundamental results provide novel insights into understanding the influence of Fe and Mn in REY accumulation in the Fe-Mn crusts and are very significant in enhancing our understanding of the REY geochemical processes in the ocean.

Influence of Phosphatization in REY Geochemistry in Ferromanganese Crusts in Line Islands, Central Pacific

Ferromanganese (Fe-Mn) crusts are potential marine deposits for many high-tech metals and are exciting proxies for recording the oceanic paleoenvironment. During their growth, phosphatization generally occurs, causing the remobilization and reorganization of the elements and minerals in Fe-Mn crusts. Rare earth elements plus yttrium (REY), well-known critical metals for many new and emerging technologies, as well as valuable geological proxies, are the important critical metals in Fe-Mn crusts. The REY occurrence is closely influenced by the phosphatization processes, which still remain discursive. In this study, the textures, structures, and REY geochemistry of the growth of an Fe-Mn crust sample (MP2D32A) from the Line Islands archipelago were analyzed using multiple microanalysis methods. The analyzed Fe-Mn crust is mainly characterized by the presence of laminated and concentric colloforms. Massive fine particles and some veins of carbonate-rich fluorapatite (CFA) were observed in the old part of MP2D32A, demonstrating that this sample underwent phosphatization. The phosphatized and non-phosphatized layers, as well as the CFA veins, display distinctly different PAAS-normalized REY patterns. Higher REY contents in the phosphatized layer than those in the non-phosphatized layer suggest the positive role of phosphatization in REY enrichment. Moreover, the phosphatized layer contains higher REY contents than the CFA, implying that the REY enrichment in the phosphatized layer is not only influenced by CFA and Fe-Mn (oxyhydr)oxides but also other factors, such as the probable PO43− complexation induced by Fe oxyhydroxides. The synergistical sorption of REY(III) and HPO42− ions on Fe oxyhydroxides should facilitate REY enrichment during the phosphatization processes. These fundamental results provide novel insights into the influence of phosphatization in REY geochemical behaviors in the Fe-Mn crust.

Chronology and critical metals enrichment mechanism of ferromanganese nodules from the Parece Vela Basin, Philippine Sea

Ferromanganese nodules are potential economic metal resources enriched with Mn, Co, Ni, Cu, Ti, and rare earth elements plus yttrium (REY). The mineralogy, magnetic scanning, and geochemistry of ferromanganese nodules from the Parece Vela Basin in the Philippine Sea were documented to verify critical metals variations during nodule growth. Based on in situ magnetic scanning, the nodules from the basin were found to initially form during the late Pliocene. At ∼1.6 Myr, the growth structure of the nodules changed remarkably from lamellar to columnar. The inner part has a dense lamellar structure with unstable buserite I, whereas the outer layers are columnar with stable todorokite (or buserite II). The growth rate of the nodule decreased from 4.39 to 2.82 mm/Myr, which may have been related to the persistently weakening of deep-sea sedimentary dynamics in the Philippine Sea since ∼1.6 Myr. The slower growth rate facilitates the enrichment of Ce, resulting in a higher REY content and strong positive Ce anomalies in the columnar structure. The mineralogical compositions and Mn/Fe ratios indicate that the nodules were primarily hydrogenetic with low diagenetic influences. The contents of Ni and Cu increase rapidly, but the trends of Co and REY display an inflection point from the hydrogenetic to diagenetic. REY was primarily enriched in Mn mineral phases, and hydrogenesis dominated the enrichment of REY. Hydrogenesis is beneficial for the enrichment of Ti, Ge, Se, Nb, and Sn. However, diagenesis facilitated the enrichment of Ga, Cd, Li, Tl, Zn, Mo, and W in the nodules of the Parece Vela Basin.

Partitioning and Migration of Trace Elements during Coal Combustion in Two Coal-Fired Power Plants in Hefei City, Anhui Province, Eastern China

Coal-fired thermal power plants that meet the huge energy demand of China largely contribute to carbon emissions, environmental pollution, and human health issues. To investigate the impact of coal-fired power plants on the environment in the most developed region of eastern China, samples of feed coal, limestone, slag, fly ash, and flue gas desulfurization (FGD) gypsum were collected from two coal-fired power plants in Hefei City, Anhui Province, China. The concentrations of trace elements in these samples were determined using inductively coupled plasma mass spectrometry (ICP-MS). The results show that the feed coal was slightly rich in V, Cr, Se, In, Sb, Pb, and Ga compared to common Chinese coal. Most trace elements were concentrated in fly ash, especially in the fine particles. Only Sc, Cr, Rb, and Ba were enriched in slag. The smaller the particle size of the fly ash, the higher the fraction of volatile trace elements. The elemental concentrations of old fly ash, which was precipitated in the well of the flue gas pipeline, did not show noticeable differences from fresh fly ash. In addition, the short-time storage of fly ash did not influence the trace elements. To understand the possibility of recovering rare earth elements from coal combustion by-products, the outlook coefficients (Coutl) of coal combustion by-products for the Wanneng (WN) and Tianyuan (TY) power plants were calculated, and they were found to be promising for rare earth elements plus yttrium (REY) recovery. However, as per the evaluation diagram of cut-off grade and Coutl values, all feed coal and its by-products from these two coal-fired power plants are projected to be ‘unpromising’. Therefore, the coal combustion by-products from the WN and TY coal-fired power plants were not candidates for REY recovery.

The Effect of Physical Separation and Calcination on Enrichment and Recovery of Critical Elements from Coal Gangue

Critical metallic elements in coal gangue have great utilization potential, especially due to the current shortage of these metals. This paper focused on examining the feasibility of physical separation (screening and float-sink tests) and calcination treatment for the enrichment of critical elements (Li, Ga, and rare earth elements plus yttrium (REY)) from coal gangue. The impacts of these enrichment methods on the acid leaching recovery of these elements were then studied. Screening tests indicated that Li and Ga were enriched in >0.125 mm size fraction and the content of REY was highest in <75 μm size fraction. Float-sink tests showed that high-density fractions were enriched in Li and Ga, and low-density fractions were enriched in REY. Physical separation cannot significantly improve the leaching rate of Li, Ga, and REY. Notably, Li, Ga, and REY were enriched significantly, and their acid leaching recoveries were increased by 54~68% after calcination under 400 °C. Sequential chemical extraction tests showed that the majority of insoluble Li, Ga, and REY was converted into soluble forms at the above temperature, which is attributed to the formation of amorphous metakaolinite and the decomposition of organic matter. Based on the results, a conceptually combined flowsheet was proposed for the extraction of Li and Ga from coal gangue.

Rare earth elements plus yttrium (REY) in phosphorites from the Tébessa region (Eastern Algeria): Abundance, geochemical distribution through grain size fractions, and economic significance

Rare earth elements and yttrium (REY) have gained greater attention for being largely used in various high-tech applications and green energies. Recently, supply shortage and high demand on REY led to target secondary resources such as phosphorites. Algerian sedimentary phosphorites, which are located mainly in the Tébessa region, Eastern Saharan Atlas, are relatively enriched in REY according to recent whole-rock analyses. The aim of this study is to explore variation of REY contents and other geochemical features with respect to particle size fractions. In addition, the economic significance of the P-deposits was assessed using new indicators, such as the outlook coefficient of REY composition (Coutl) and the percentage of critical element in total ΣREY (REYdef). Three friable whole-rock samples from two P-deposits (Djebel El Kouif and Kef Essenoun) were sieved and retained fractions (f) of <45 μm, 45–125 μm, 125–250 μm, 250–500 μm and >500 μm were analyzed for their major and REY contents using ICP-MS techniques. Principal Component Analysis (PCA) was applied on centred log-transformation (clr) data, which are adapted to such compositional dataset, as well as Variance Analysis (one-way ANOVA) technique. The results show that the samples yield P2O5 grades ranging from 20 to 36 wt% and total REY contents in selected 15 samples vary in the considered grain size fractions as follows: f<45μm = 325 ppm–719 ppm; f45–125μm = 309 ppm–893 ppm; f125–250μm = 314 ppm–1029 ppm, f250–500μm = 354 ppm–809 ppm, f>500μm = 308 ppm–652 ppm. The one-way ANOVA reveals that there is no significant difference of REY concentrations between the grain size fractions. However, the REY grades strongly based on both the studied deposits and the stratigraphic position of the hosting samples (p-value ≤ 0.01); this is also confirmed by PCA. REY geochemical signatures (normalized REY distribution patterns and Ce, Eu, and Y anomalies) are similar in the grain size fractions from the same hosting samples indicating synchronized evolution of all rock components, where REY distribution is mostly controlled by the depositional environment, irrespective of grain size in the rock. The Coutl coefficient shows values between 1.89 and 6.85 and REYdef varies from 47.44 % to 64.90 %. However, the upper sub-layer of Kef Essenoun phosphorites that yielded the lowest ∑REY contents, shows markedly the highest Coutl (6.61–6.85) and REYdef (64.31–64.90), pointing to more promising source for extracting individual critical REY elements, even in low P-grade phosphorite ores.

Seep dynamics as revealed by authigenic carbonates from the eastern Qiongdongnan Basin, South China Sea

Methane-related authigenic carbonates play a significant role in the marine carbon cycle and atmospheric CH4 budget. To elucidate the relationship between seeping methane and authigenic carbonate precipitation, we analyze a 72-cm long methane-related carbonate column from the W08 site in the Qiongdongnan Basin, South China Sea. Mineralogical composition, stable carbon and oxygen isotopes, major and trace element contents, and three-dimensional internal structure have been analyzed.Based on the results obtained, four types of carbonate are identified. The first type recorded decreasing content of rare earth elements plus yttrium (REEY) and increasing carbonate porosity. This is attributed to the gradual increase in methane flux intensity, raising the rate of carbonate deposition and thus reducing the time for elemental uptake. The second type of carbonate displays the same δ18O values as the theoretical equilibrium results, the maximum REEY contents, and the densely cemented carbonate structure, indicating a reduction in gas hydrate decomposition. The third type of carbonate formation occurring at the sediment-water interface shows a synchronous and significant enrichment of Mo, V, and Cd contents, suggesting the high hydrogen sulfide flux, which is subject to intensive methane flux and sulfate reduction. The fourth type is the late infill aragonite, which exhibits lower elemental contents compared to early cement due to less exposure to host sediments, while the difference in δ18O and δ13C values is not significant. The compilation of (Tb/Yb)N and Y/Ho ratios of cold-seep carbonates worldwide suggests that the methane flux could alter the space of redox zones (e.g. Fe reduction zone) and thus affect the sink of MREE.X-ray computed tomography (CT) reveals the internal structure of the methane-related carbonate. The continuous pore system probably suggests an intense fluid/gas pressure, and the in situ brecciations imply the carbonate precipitation did not entirely block the methane release to the water column. A better understanding of authigenic carbonates is fundamental to evaluating how carbonates modulate the carbon balance in the methane seeps.

Rare Earth Element Geochemistry of Late Cenozoic Island Carbonates in the South China Sea

Marine carbonates, precipitating from seawater through inorganic geochemical and biogeochemical processes, are considered to have recorded the seawater geochemical signatures reflecting the marine environmental conditions during their formation. However, they are susceptible to post-depositional diagenetic alteration. The redox conditions and chemical composition of the diagenetic fluid may be different from those of the overlying seawater. Therefore, assessing whether carbonate rocks that have experienced variable diagenesis could still preserve primary seawater geochemistry is a prerequisite before inferring ancient marine environments using geochemical tracers such as the cerium anomaly (Ce/Ce*). Here, we investigate rare earth elements plus yttrium (REY) geochemical features of reefal carbonates from the XK-1 core in the Xisha Islands of the South China Sea. We aim to evaluate whether island carbonates have the potential to preserve reliable primary seawater REY geochemical characteristics after experiencing meteoric diagenesis, marine burial diagenesis, or dolomitization. The results show that even after variable diagenetic alteration, all carbonate samples exhibit seawater-like REY patterns, which are characterized by negative Ce anomalies (Ce/Ce* &lt; 1), distinctively high Y/Ho ratios (&gt;44), and uniform depletion of light rare earth elements (LREE) relative to heavy rare earth elements (HREE) ((Pr/Yb)N &lt; 1). This suggests that the original seawater REY signatures are retained, regardless of varying degrees of changes in the mineralogical composition, diagenetic fluid composition, and redox state. The unmodifiable REY characteristics in carbonates during diagenesis can be attributed to three aspects: (1) during meteoric diagenesis, the low REY content of meteoric fluids and the short-term reactions between fluids and carbonates make it difficult to significantly alter the REY composition of carbonates; (2) during marine burial diagenesis, the ubiquitous cementation creates a relatively closed environment that facilitates the inheritance of REY signatures from primary carbonates; (3) during dolomitization, the dolomitizing fluids derived from penecontemporaneous seawater would not destroy but rather promote the preservation of the original seawater REY signatures in dolostones. The Ce/Ce* variations indicate that the Xisha carbonates have been deposited under constantly oxic conditions since the Neogene, consistent with paleontological and redox-sensitive element geochemical evidence.

Rare earth elements and yttrium as tracers of waste/rock-groundwater interactions

Increasing concentrations of Rare Earth Elements (REE) plus yttrium (REY) are entering the environment due to human activities. The similar chemical behaviour across the whole REY, i.e. the lanthanide series (lanthanum to lutetium) and yttrium, allows their use as tracers, fingerprinting rock-forming processes and fluid-rock interactions in earth science systems. However, their use in fingerprinting waste and particularly low-level radioactive waste has not received much attention, despite the direct use of REE in the nuclear industry and the traditional use of REE as proxies to understand the environmental mobility of the actinide series (actinium to lawrencium). The highly instrumented low-level radioactive waste site at Little Forest (Australia) allows a detailed REY study, investigating interactions with local strata, neighbouring waste forms and shallow groundwater flows. Groundwater samples and solids from cored materials were recovered from 2007 to 2012 from the study site and regional baseline sites in the same geological materials. The REY in water samples were analysed by automated chelation pre-concentration (SeaFast, ESI) followed by ICP-MS determination, while solid samples were analysed using Neutron Activation Analysis (NAA) and X-ray fluorescence scanning (ITRAX). Solid rocks showed no REY departed from typical Upper Crust compositions in either Little Forest or regional background sites. Shallow groundwater from ~4–5 m, at or slightly below waste trench levels, showed water-waste interaction as a marked enrichment, relative to shale-normalised patterns, in samarium, europium and gadolinium, with depleted yttrium. Leachate samples from the neighbouring urban landfill show different REY normalised patterns. REY distribution changes with depth through increased interaction with shales and sandstones. Variations in pH and redox conditions lead to widespread precipitation of Fe-hydroxides, which scavenge REY with differential uptake by precipitating solids, resulting in increases in Y and higher Y/Ho ratio in the groundwater along the flow path. Our study revealed that the Little Forest low-level radioactive waste has a REY fingerprint different to that of groundwater in surrounding land uses. REY can be used to fingerprint diverse waste sources, assess the mobility of lanthanides inferring the mobility of selected actinides, and to trace the fate of REY during groundwater recharge. The approach presented can refine source allocation and trace pollutant mobility in current and legacy urban, mixed and radioactive waste sites around the world.

Geochemistry of Neogene Mengtuo lignite in the Lincang from western Yunnan, southwestern China: Implications for its sediment material provenance and model of element enrichment

The Mengtuo Basin is proximal to the Bangmai Basin, which holds the world-class coal-hosted Ge deposit and shares the same sediment material provenance as the Lincang batholith. Herein, the mineralogy and geochemistry of Neogene Mengtuo lignite were reanalyzed using supplementary data on major element oxides and minerals. The results indicated that Mengtuo lignite is a medium-ash lignite A. The minerals in lignite are composed of quartz, kaolinite, illite, chamosite, bassanite, and rutile. Compared to common Chinese coals, Mengtuo lignite is significantly enriched in Sb, Cs, and W, enriched in Rb and U, and slightly enriched in Be, As, Cd, Bi, and Th. The rare earth elements plus yttrium (REY) are characterized by significantly positive Ce and Gd anomalies and negative Eu anomalies. A positive Ce anomaly is inherited from the sediment source material. The local Lincang granite around the Mengtuo Basin dominates the mineralogy and geochemistry of lignite and carbonaceous mudstone. Because of the lack of hydrothermal fluids, an indispensable condition for Ge mineralization in the Mengtuo Basin, a large-scale coal-hosted Ge deposit cannot be discovered.

Phosphorite generative processes around the Precambrian-Cambrian boundary in South China: An integrated study of Mo and phosphate O isotopic compositions

Large phosphorite deposits in Central Guizhou, China, were formed around the Precambrian/Cambrian boundary (PC/C), including the Ediacaran (Doushantuo stage) and early Cambrian (Gezhongwu stage). Among them, Gezhongwu phosphorite from Zhijin are enriched in rare earth elements (REE) plus yttrium (REY), reaching 3.503 million tons. Although phosphorites have attracted great attention, the specific sources P and REY remained unclear. To determine the P and REY sources and establish a phosphogenic model of PC/C phosphorite, we present an integrated dataset of Mo and phosphate O isotopes for the first time, along with carbonate C and O isotopes, geology, petrology, and geochemistry. In all samples, δ18Op, Y/Ho, and Zr/Hf decreased from the Ediacaran to the early Cambrian, indicating increased terrigenous weathering fluxes while decreased upwelling water input. Furthermore, terrigenous weathering delivery significantly elevated marine REY concentrations in the Cambrian in Zhijin. The Ceanom and δ98/95Mo suggest that seawater was oxidized in the later Ediacaran and became entirely oxic in the early Cambrian. The positive feedback between oxygen levels in atmosphere and primary productivity caused progressive oxygenation in ocean–atmosphere system and enable phosphorites to be formed by different mechanisms. Results show that the Lower Doushantuo consist of abiotic intraclasts and exhibited “seawater-like” REY types, indicating abiological and mechanical reworking phosphogenesis. The Upper Doushantuo and Gezhongwu Formation contained mainly microbial debris and abiogenic intraclasts, and exhibit “hat-shaped” REY plots, suggesting microbially mediated phosphogenesis. Based on this data set, we developed a phosphogenic model illustrating formation of these two phosphorite deposits, wherein the Lower Doushantuo phosphorite formed through the reworking of pre-existing phosphatic sediments in anoxic and abiotic ocean, whereas the Upper Doushantuo and Gezhongwu phosphorite formed via microbial metabolisms in oxic and biotic conditions. Our study has implications on the PC/C phosphorite generative processes, as well as paleoenvironmental conditions.

Rare earth and yttrium elements (REY) patterns of mesostructures of Miaolingian (Cambrian) thrombolites at Jiulongshan, Shandong Province, China

The relationship between the thrombolitic mesostructures and their depositional environments is still poorly understood due to inconsistent results by sedimentary investigation. Rare earth elements plus yttrium (REY) in ancient microbialites have been extensively applied to paleoenvironmental studies owing to their fractionation in different depositional environments. In order to investigate the environmental controls on thrombolitic mesostructures, we present the REY concentrations and patterns of four types of mesostructures of the Miaolingian (Cambrian) thrombolites in the Changhia Formation at the Jiulongshan section, Shandong Province, China. The REY compositions of those thrombolites show two distinctive groups: (1) light REY depleted patterns with negative Ce anomalies in spotted (SM) and layered mesostructures (LM) of thrombolites; and (2) flat patterns with weak Ce anomalies in dendritic (DM) and meshed mesostructures (MM) of thrombolites. Controlling factors analysis reveals that terrigenous detritus inputs have stronger influence on REY in SM and LM. In contrast, early diagenetic porewaters from underlying sediments have more serious impacts on REY concentrations and patterns in DM and MM. Our results clearly indicate that SM and LM were formed under oxic marine settings with minor terrigenous inputs, whereas DM and MM formed under suboxic marine settings suffered from early diagenetic porewater from underlying sediments. This new geochemical evidence suggests that thrombolitic mesostructures were strongly influenced by paleoenvironment, and REY of thrombolites with controlling factors analysis can be utilized as effective proxies for paleoenvironments.

Rare earth elements in the terminal Ediacaran Bambuí Group carbonate rocks (Brazil): evidence for high seawater alkalinity during rise of early animals

Rare earth elements plus yttrium (REY) mass fractions of ancient carbonate rocks are used to track changes in chemistry of past seawater. Here we investigate REY patterns in two carbonate sections from the Ediacaran Bambuí Group, São Francisco Basin (Brazil), which comprise its two lowermost transgressive-regressive second-order sedimentary sequences. Shale normalised distributions vary with the sequence stratigraphy framework. In the basal 2nd-order sequence, carbonate samples from the basal sequence transgressive systems tract display light REY (LREY) distributions slightly depleted to enriched that reflect input of freshwater, possibly in a post glacial episode. Upwards, carbonate rocks from the early highstand systems tract (EHST) yielded LREY enriched distributions, which progressively turns into LREY shale normalized depleted distributions on samples from the late highstand systems tract (LHST). This portion of the sequence also displays Y positive anomaly in some cases. Carbonate samples from the upper second-order sequence do not display coherent patterns. Ce/Ce* values > 1 in most samples throughout the two sections suggest permanent anoxia of seawater. The REY change from the EHST to LHST in the basal sequence marks an important paleoenvironmental overturn in the basin, with increasing alkalinity in seawater driving REY fractionation and LREY depletion. Confinement of the basin in the inner areas of West Gondwana due the uplift of marginal neoproterozoic orogens probably changed the weathering style of source areas to more congruent, thus delivering a higher ionic influx to a restricted setting, increasing alkalinity during LHST. Cloudina sp. fragments were reported in this stage of the Bambuí Group and in carbonate rocks with high Sr mass fractions in other West Gondwana basins, supporting the hypothesis that the high alkalinity of seawater during late Ediacaran may have driven the appearance of the first biomineralizing organisms.

Hydrogenetic, Diagenetic and Hydrothermal Processes Forming Ferromanganese Crusts in the Canary Island Seamounts and Their Influence in the Metal Recovery Rate with Hydrometallurgical Methods

Four pure hydrogenetic, mixed hydrogenetic-diagenetic and hydrogenetic-hydrothermal Fe-Mn Crusts from the Canary Islands Seamount Province have been studied by Micro X-Ray Diffraction, Raman and Fourier-transform infrared spectroscopy together with high resolution Electron Probe Micro Analyzer and Laser Ablation Inductively Coupled Plasma Mass Spectrometry in order to find the correlation of mineralogy and geochemistry with the three genetic processes and their influence in the metal recovery rate using an hydrometallurgical method. The main mineralogy and geochemistry affect the contents of the different critical metals, diagenetic influenced crusts show high Ni and Cu (up to 6 and 2 wt. %, respectively) (and less Co and REY) enriched in very bright laminae. Hydrogenetic crusts on the contrary show High Co and REY (up to 1 and 0.5 wt. %) with also high contents of Ni, Mo and V (average 2500, 600 and 1300 μg/g). Finally, the hydrothermal microlayers from crust 107-11H show their enrichment in Fe (up to 50 wt. %) and depletion in almost all the critical elements. One hydrometallurgical method has been used in Canary Islands Seamount Province crusts in order to quantify the recovery rate of valuable elements in all the studied crusts except the 107-11H, whose hydrothermal critical metals’ poor lamina were too thin to separate from the whole crust. Digestion treatment with hydrochloric acid and ethanol show a high recovery rate for Mn (between 75% and 81%) with respect to Fe (49% to 58%). The total recovery rate on valuable elements (Co, Ni, Cu, V, Mo and rare earth elements plus yttrium (REY)) for the studied crusts range between 67 and 92% with the best results for Co, Ni and V (up to 80%). The genetic process and the associated mineralogy seem to influence the recovery rate. Mixed diagenetic/hydrogenetic crust show the lower recovery rate for Mn (75%) and Ni (52.5%) both enriched in diagenetic minerals (respectively up to 40 wt. % and up to 6 wt. %). On the other hand, the presence of high contents of undigested Fe minerals (i.e., Mn-feroxyhyte) in hydrogenetic crusts give back low recovery rate for Co (63%) and Mo (42%). Finally, REY as by-product elements, are enriched in the hydrometallurgical solution with a recovery rate of 70–90% for all the studied crusts.

Redox-sensitive trace element distribution in the Loma Negra Formation in Argentina: The record of an Ediacaran oxygenation event

The limestones of the Loma Negra Formation provide an excellent opportunity to examine the behaviour of rare earth elements plus yttrium (REY) due to the near-zero diagenetic alteration of the carbonate system. The terrigenous supply to this unit was minimal or scarce in relation to the depth of seawater in which the limestones accumulated. The interpreted palaeoenvironment suggests that limestones could have originated by suspension fall-out in a shallow, open marine ramp. The diagenetic features, composition, and original microtextures are considered good criteria for investigating their REY composition. Burial diagenesis products were limited and limestones largely preserved their original texture and organic matter, as well as their isotope and trace element composition. The study of REY distribution in the Loma Negra Formation in different settings of the Tandilia System revealed systematic chemostratigraphic patterns related to uniform palaeo-redox conditions. The general light rare-earth element depletion, marked positive La, Y, and Gd anomalies, as well as the clear negative Ce anomalies, are further features typically ascribed to oxidizing seawater conditions. From these results, it can be concluded that the Loma Negra Formation documents an oxygenation event that stands out in the overall anoxic Ediacaran ocean. This record may be correlated with the mid-Ediacaran oxygenation event (ca. 580 Ma). This may support the hypothesis that the Clymene Ocean was well oxygenated and connected during the Ediacaran, at least in the southwestern border of Gondwana.

Fine scale study of major and trace elements in the Fe-Mn nodules from the South China Sea and their metallogenic constraints

Many marine Fe-Mn polymetallic nodules may contain high concentrations of Mn, Cu, Ni, Zn, Co and rare earth elements plus yttrium (REY). To determine the occurrence and enrichment processes of these metals in the Fe-Mn nodules, we conducted high resolution mineralogical and geochemical studies on the Fe-Mn nodules collected from the South China Sea. In-situ EPMA and LA-ICP-MS analyses and elemental imaging were performed on individual microlayers of the nodules to reveal the major and trace element distributions.The whole-rock mineralogical and chemical compositions of the Fe-Mn nodules indicate a hydrogenetic origin. The Mn mineral phases are mainly composed of nanocrystalline vernadite with interlayered 10 Å and 7 Å phyllomanganates, such as todorokite, birnessite, and buserite. Fe(-Ti) oxides/hydroxides are intergrown and essentially X-ray amorphous feroxyhyte and goethite. We recognize two main types of microlayers: Type-A layer (suboxic diagenetic precipitates) containing a high Mn/Fe ratio and high concentrations of Cu, Ni, Zn, Ba, Li and Mg, and Type-B layer (oxic hydrogenetic accretions) with low fractionation of Mn and Fe and high contents of Co, REY, Ti, Sr and Pb. Furthermore, elemental mapping indicates that the enrichments of Co and REY are mainly associated with Fe mineral phases rather than Mn ones, which are enriched in Mg, Cu, Ni, Zn, Li and Ba. Two mineralization processes and metal distributions in the individual microlayers are identified in the Fe or Mn mineral phases. The occurrence of 10 Å and 7 Å phyllomanganates in Type-A layers are commonly enriched in trace metals such as Ni, Cu, Zn, Li, Ba, and Mg, whereas the metals for the Type-B layers include Co, Ti, Pb, Sr, REY, which may be carried by the intergrowing Fe(-Ti) oxyhydroxides and vernadite. Thus, hydrogenesis and diagenesis facilitate the enrichment of Fe-Co-Ti-Sr-Pb-REY and Mn-Ni-Zn-Cu-Li-Ba-Mg, respectively, during the mineralization of the South China Sea nodules.

Distribution of Rare Earth Elements plus Yttrium among Major Mineral Phases of Marine Fe–Mn Crusts from the South China Sea and Western Pacific Ocean: A Comparative Study

Marine hydrogenetic Fe–Mn crusts on seamounts are known as potential mineral resources of rare earth elements plus yttrium (REY). In recent years, increasing numbers of deposits of Fe–Mn crusts and nodules were discovered in the South China Sea (SCS), yet the enrichment mechanism of REY is yet to be sufficiently addressed. In this study, hydrogenetic Fe–Mn crusts from the South China Sea (SCS) and the Western Pacific Ocean (WPO) were comparatively studied with mineralogy and geochemistry. In addition, we used an in situ REY distribution mapping method, implementing laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and a sequential leaching procedure to investigate the partitioning behavior of REY in the Fe–Mn crusts. The typical Fe–Mn crusts from SCS were mainly composed of quartz, calcite, vernadite (δ-MnO2), and amorphous Fe oxides/hydroxides (FeOOH). The Fe–Mn crusts from the Central SCS Basin and the WPO contained quartz, δ-MnO2, FeOOH, todorokite, and phillipsite. Furthermore, geochemical analysis indicated that the typical SCS crusts had a higher growth rate and lower REY concentrations. The LA-ICP-MS mapping results showed that the δ-MnO2 and FeOOH dominated the occurrence phases of REY in the SCS crusts. Four mineral phases (i.e., easily exchangeable and carbonate, Mn-oxide, amorphous FeOOH, and residual aluminosilicates) in these Fe–Mn crusts were separated by a sequential leaching procedure. In the SCS and WPO crusts, the majority of total REY (ΣREY) was distributed in the Mn-oxide and amorphous FeOOH phases. The post-Archean Australian shale-normalized REY patterns showed that light REY (LREY) and heavy REY (HREY) were preferentially adsorbed onto δ-MnO2 and FeOOH, respectively. It is noteworthy that ~27% of ΣREY was associated with the residual aluminosilicates phase of the WPO crusts. The La/Al ratios in the aluminosilicates phase of the typical SCS crusts were the values of the upper crust. We conclude that large amounts of terrigenous materials dilute the abundance of REY in the SCS crusts. In addition, the growth rates of Fe–Mn crusts have a negative correlation with the FeOOH-bound and aluminosilicate-bound REY. As a result of the fast growth rates, the SCS crusts contain relatively low concentrations of REY.

Evidence of warm seas in high latitudes of southern South America during the Early Cretaceous

The Berriasian–early Valanginian time interval is well represented in the Rio Mayer Formation in the Río Guanaco area (Austral Basin, Argentina). From this locality, well preserved belemnite shells of the genus Belemnopsis sp. and black shales are used to unravel the main palaeoenvironmental conditions of the seas at these high palaeo-latitudes (60°) of southern South America during the Early Cretaceous. Rare earth elements plus yttrium (REY) analyses performed in belemnites rostra reveal Ce anomalies and Y/Ho values that together suggest high oxidizing superficial seawater conditions. On the other hand, sedimentological, ichnological and geochemical (TOC, Ce anomaly and MnO) data, analyzed from the black shale matrix of belemnites, show that they may have been deposited on the bottom of the basin under oxygen deficiency. Cathodoluminescence, scanning electron microscopy, major and trace element geochemistry allowed determining the best preserved microtextures of the belemnites in order to obtain reliable δ18O and δ13C results. Palaeotemperatures calculated from the δ18O results, characterized the studied marine interval from Austral Basin as warm. The belemnites from this Lower Cretaceous succession may have lived under well oxygenated and warm seawater conditions, which were markedly different from those recorded in seafloor sediments (black shales) deposited under suboxic to anoxic conditions. The integration of global palaeotemperature data for the Berriasian–early Valanginian interval, allows suggesting a different gradient for the austral Patagonia at the Southern Hemisphere in relation to those recorded in the Northern Hemisphere.