Search Results (11)

In this work, authigenic microbial mineral formation in groundwater near the uranium sludge storage at SC Chepetsky Mechanical Plant (ChMP) (Glazov, Russia) was analysed in field and laboratory experiments using thermodynamic modelling when the microbial community was activated by a mixture of acetate, glucose and whey. It was found that the mineral basis of the barrier consisted of aggregated soil particles with freshly deposited phases of carbonate and sulphide minerals of different degrees of crystallinity. An important factor in the formation of calcium phases is microbial denitrification, which is accompanied by an increase in pH values of the medium. The main factors of uranium immobilisation in the biogeochemical barrier were revealed, including its reduction to insoluble forms of uranium dioxide, adsorption on ferrous and sulphide-ferrous minerals, as well as the formation of phosphate phases through the addition of phosphorus-containing whey and co-precipitation or co-crystallisation in calcite phases. Full article

Clay mineral authigenesis at continental margins plays an important role in global marine element cycles. However, despite being increasingly used as tracers for both modern and past oceanographic conditions, the behavior of the rare earth elements (REEs) and their isotopes during marine clay authigenesis still remains poorly known. In this study, we report on a detailed geochemical investigation of glauconite from the West African continental shelf, near the mouth of the Congo River. Elemental, neodymium, and hafnium isotope analyses were conducted on both acid leachate and separated clay-size fractions of glauconite pellets, in order to investigate the behavior of REE during the formation of authigenic clays. Our data indicate that kaolinite dissolution and subsequent Fe-bearing clay authigenesis act as a net source of REEs to seawater. We show that enhanced glauconitization, as inferred from increasing Fe and K contents, is accompanied by significant decoupling of the REE toward markedly LREE-enriched shale-normalized patterns in neoformed clay separates. Using both Nd and Hf isotopes and SEM observations, we rule out any seawater influence and argue that this shift primarily reflects the progressively overwhelming presence of insoluble nanocrystals of detrital LREE-rich phosphates, which are known to occur in close association with kaolinite in tropical soils. Due to their marked insolubility in surface environments, such nanocrystals can be preserved during kaolinite dissolution and subsequently incorporated into the aggregates of authigenic green clays forming the peloids. Most strikingly, we show that the combined influence of net REE loss (due to kaolinite dissolution) and decoupling (due to subsequent entrapment of inherited LREE-bearing accessory phases into neoformed clay minerals) is accompanied by preferential release of a dissolved REE fraction characterized by seawater-like distribution patterns. These findings reinforce the emerging view that clay mineral dissolution and authigenesis at continental margins possibly play a major role in marine REE cycling. Full article

The sedimentary basin of Podillya (Volyno-Podillya-Moldavia) is situated in the southwest of the Ukrainian crystalline shield and belongs to the middle part of the Upper Neoproterozoic section of the Moguiliv-Podilska Group. By analyzing the primary oxide, trace, and rare-earth element compositions of the phosphate nodules in the area, this study sought to shed light on the potential precipitation characteristics of the Ediacaran Sea, where phosphate nodules were created. The mean major oxide contents of the nodules were 50.8 wt.% CaO, 34.2 wt.% P₂O_5, 5.29 wt.% SiO₂, 4.77 wt.% LOI, 1.69 wt% Fe₂O₃, 1.63 wt% Al₂O₃, and 0.35 wt.% MnO. The average trace element concentrations were 183 ppm Ba, 395 ppm Sr, 13.4 ppm Ni, 32.7 ppm Cr, 62.2 ppm Zn, 764 ppm Y, 16 ppm V, 10.8 ppm As, 75.8 ppm Cu, 84 ppm Pb, 2.1 ppm U, 1.7 ppm Th, and 4.2 ppm Co. The trace element contents were generally low and indicated an assemblage of Cu, Y, As, Cd, and Pb enrichments in comparison to PAAS. The total REE concentrations varied from 1638 ppm to 3602 ppm. The nodules had medium REE (MREE) enrichments and showed similar REE patterns normalized to PAAS. All the nodules had strongly negative Ce, Pr, and Y anomalies and substantially negative Eu anomalies, with four samples being exceptions. These abnormalities suggest that oxic and suboxic sea conditions existed at the time the nodules formed. The extremely high REE concentrations are thought to be the result of REEs being redistributed between the authigenic and detrital phases that were created during the diagenetic equilibration of phosphate with pore water. The genetic hypothesis for phosphate nodule formation states that the nodules were generally formed in oxic and suboxic seawater and were precipitated on slopes in response to a significant upwelling from a deeper basin with abundant organic matter under anoxic/suboxic conditions. The majority of the organic material at the water–sediment interface of the seafloor underwent oxidation before phosphate was released into the pore water of the sediment. Full article

Karst bauxite is a major source of aluminum and contains high concentrations of trace elements such as Li, Ga, Sc, and rare earth elements (REEs). It is regarded as a potential non-conventional REE source due to the increasing demand for REEs. This study provides new mineralogical and geochemical evidence of a Lindai bauxite deposit in central Guizhou Province, aiming to analyze the genesis of REE minerals and reveal the forms of REEs occurring in these deposits. The results indicate that a large number of detrital and authigenic rare-earth phosphate minerals, including monazite and xenotime, were identified. In terms of their genesis, the authigenic monazite was mainly precipitated under alkaline and reducing conditions, whereas the authigenic xenotime was formed in acidic and reducing conditions. The mineralogical evidence detected by scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) and a TESCAN Integrated Mineral Analyzer (TIMA) suggests that the REEs in the Lindai bauxite exhibit multiple forms, including rare-earth phosphate minerals (monazite and xenotime) and REE scavenging by hematite and anatase phases. Among them, the anatase controls some LREE (such as La, Ce, and Pr) distributions in addition to monazite, whereas the hematite also controls relatively large amounts of Sm, Eu, and HREE (such as Gd, Tb, Dy, Ho, Er, Tm, and Lu) distributions. According to the calculation of the percentage of REE-bearing mineral phases obtained by a TIMA analysis, REE scavenging by hematite accounted for 93.28% of all forms of REEs, REE scavenging by anatase accounted for 5.88%, monazite accounted for 0.67%, and xenotime accounted for 0.17%. This study provides new evidence of the forms of REEs occurring in Carboniferous karst bauxite in central Guizhou Province. Full article

Uralian parietal and rock art (cave paintings and pictographs, or “pisanitsy”) represents a unique archaeological and cultural phenomenon, comprising 90 sites stretching for more than 800 km from north to south, which date from the Paleolithic era extending into the present Holocene epoch. The identification of the nature of prehistoric colorants provides an insight into their provenance, manufacture and utilization, as well as contributing to the conservation and restoration of drawings. The studies of mineral, elemental and organic phase composition of the colorant micro-samples from the drawings of Ignatievskaya cave and Idrisovskaya II and Zmiev Kamen’ pictographs (Southern and Middle Urals, Russia) discussed in the present work were carried out using a special set of microspectroscopic methods (SEM-EDS and Raman spectroscopy) offering high spatial resolution. The fatty acid composition of the organic phase was analyzed by GC–MS. The technology of colorant manufacture could have included thorough grinding and mixing of unheated hematite with an organic binder made from animal fat and a clayey extender in order to achieve the desired hue and intensity of the color. It is possible that the colorant was applied in layers (Idrisovskaya II and Zmiev Kamen’ pictographs). The development of authigenic phosphate and sulfate (gypsum) mineralization, which is observed in all studied sites, as well as oxalate encrustation on the Idrisovskaya II pictograph, indicates the conditions and processes of secondary mineral formation. Full article

The distribution of authigenic phosphates in the sedimentary sequence of prehistoric Denisova Cave (Altai, South Siberia) has important archeological implications. The sampled Late Pleistocene–Early Holocene sedimentary sequence in the East Chamber of the cave consists of argilo-sandy-phosphatic sediments intercalated with guano layers of insectivorous bats. The sediments bear partially degraded N-rich organic matter (OM); chitin fragments enriched in S, P, Zn, and Cu; and a set of phosphates. The guano layers record at least three prolonged episodes of cave occupation by colonies of insectivorous bats between 10 kyr and 5 kyr BP, after people had left the cave or visited it rarely in small groups. The formation of phosphates follows the OM biodegradation pathways, with acidic leaching and gradual neutralization of P-rich solutions. The depth profile of authigenic phosphates shows a suite of mineral assemblages that mark a trend from acidic to slightly alkaline pH conditions of guano degradation (from top to bottom): ardealite, taranakite, and leucophosphite corresponding to acidic environments; whitlockite, brushite, and hydroxylapatite, which are stable under slightly acidic and neutral conditions; and hydroxylapatite in coexistence with calcite and stable at the bottom of the leaching profile under alkaline conditions. Authigenic phosphates can be used as reliable indicators of human non-occupation (abandonment) periods of Denisova Cave. Acidic leaching is responsible for disturbance and/or elimination of archaeological and paleontological materials in Late Pleistocene–Early Holocene sediments that were exposed to at least three “acidic waves”. Full article

This paper reports the mineralogy and geochemistry of the Late Permian C1 Coal from Bole and Laibin mines in eastern Yunnan, Southwestern China (C1 Coal in Laibin mine is composed of three layers termed B1, B2, and B3). The coals are characterized by medium-high ash yields and very low sulfur contents. Compared with average values of trace element concentrations in hard coals worldwide, the Bole and Laibin coals are enriched in V, Co, Cu, Zn, and Se, which were mainly derived from the sediment-source region of the Kangdian Upland. Major minerals in the coal samples and roof and floor strata include quartz, interstratified berthierine/chamosite (B/C), as well as kaolinite, mixed layer illite/smectite, calcite, pyrite, and anatase. Unlike a pure chamosite, the 7 Å peak of interstratified B/C is sharp and narrow, while the 14 Å peak is broad and weak, or absent in some coal samples. Interstratified B/C was largely precipitated from low-temperature Fe-rich and Mg-rich hydrothermal fluids or, in some cases, is an alteration product of kaolinite. Secondary phases of quartz, calcite, pyrite, kaolinite, chalcopyrite, gypsum, and REE-phosphates in the coal samples are the dominant authigenic minerals formed at syngenetic and early diagenetic stages. Four intra-seam partings in C1 Coal, B1, and B3 layers are identified as tonsteins derived from felsic volcanic ashes. These tonsteins consist mainly of cryptocrystalline kaolinite with graupen and vermicular textures, and minor amounts of high-temperature quartz, zircon, apatite, monazite, and anatase. The floor of the C1 Coal in the Bole mine is a tuffaceous claystone and consists of altered high-Ti basalt volcaniclastics, characterized by high concentrations of Zr, Nb, V, Co, Cu, and Zn, low Al₂O₃/TiO₂ ratio (~4.62), high Ti/Y ratio (~900), enrichment of middle rare earth elements, and positive Eu anomalies. Full article

The aim of this research was to study the rare earth (REE) minerals in ooidal ironstone deposits of the West Siberian basin and the Turgai depression. Authigenic minerals (monazite and cerite) were described, and their main mineral form was identified as light rare earth element phosphate (LREE-phosphate) in this study. LREE-phosphate is included in ferruginous ooids, peloids, and oncoids and forms a consistent mineral association with Fe-hydroxides (goethite and its hydrated amorphous derivatives) and Fe-rich layered silicates (Fe-illite-smectite, chamosite, berthierine). The constancy of the mineral association in two deposits of different ages indicates a general mechanism behind the formation of these minerals. LREE-phosphates (authigenic monazite) are characterized by microscopic sizes (up to 24 μm), diverse morphology (mainly spherical or xenomorphic), and occupy spaces between the micro-cortex in ferruginous spheroids. This mineral can be found in other deposits of ooidal ironstone. According to its mineralogical and chemical characteristics, LREE-phosphate mainly belongs to the authigenic (nodular or “gray”) monazite. However, the incomplete (not 100%) correspondence of Kikuchi bands with the reference monazite does not allow its reliable identification. Based on its small size, chemical leaching or bacterial interaction is recommended to extract REE from ooidal ironstone while predicting the associated removal of phosphorus from iron ore due to its dominant phosphate mineral form. Ooidal ironstone should be considered a complex deposit and an unconventional natural type of REE ores as an example of the largest Bakchar and Lisakovsk deposits. Full article

Karst bauxite deposits are currently investigated as a new resource for rare earth elements (REE) in order to avoid present and future supply shortfalls of these critical metals. The present work focuses on the geochemistry and mineralogy of the REE in karst bauxite deposits of the Catalan Coastal Range (CCR), NE-Spain. It is revealed that the studied bauxitic ores have a dominant breccia and local ooido-pisoidic and pelitomorphic texture. The bauxitic ores are mostly composed of kaolinite and hematite, as well as of lesser amounts of boehmite, diaspore, rutile and calcite. The mineralogy and major element composition indicate incomplete bauxitization of an argillaceous precursor material possibly derived from the erosion of the Mesozoic Ebro massif paleo-high. The studied bauxites are characterized by ∑REE (including Sc, Y) between 286 and 820 ppm (av. 483 ppm) and light REE to heavy REE (LREE/HREE) ratios up to 10.6. REE are mainly concentrated in phosphate minerals, identified as monazite-(Ce) and xenotime-(Y) of detrital origin and unidentified REE-phosphates of a possible authigenic origin. REE remobilization presumably took place under acidic conditions, whereas REE entrapment in the form of precipitation of authigenic rare earth minerals from percolating solutions was related to neutral to slightly alkaline conditions. During the bauxitization process no significant REE fractionation took place and the REE distribution pattern of the bauxitic ores was governed by the REE budget of the precursor material. Finally, adsorption as a main REE scavenging mechanism in the studied CCR bauxite deposits should not be considered, since the presented data did not reveal significant REE contents in Fe-and Mn-oxyhydroxides and clay minerals. Full article

Studies of mineral-forming processes in modern peat bogs can shed light on metal concentrations and their cycling in similar environments, especially in geological paleoanalogs. In terms of the mineralogical and geochemical evolution of peat bog environments, the Vasyugan Swamp in Western Siberia is a unique scientific object. Twelve peat samples were collected from the Vasyugan Swamp up to the depth of 275 cm at 25 cm intervals. The studied peat deposit section is represented by oligotrophic (0–100 cm), mesotrophic (100–175 cm), and eutrophic (175–275 cm) peat, and this is underlain by basal sediments (from 275 cm). About 30 minerals were detected using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The observed minerals are divided into detrital, clay, and authigenic phases. The detrital minerals found included quartz, feldspar, ilmenite, rutile, magnetite, zircon, and monazite. When passing from basal to oligotrophic bog sediments, the clay minerals changed from illite-smectite to kaolinite. Authigenic minerals are represented by carbonates (calcite and dolomite), iron (hydro-)oxides, galena, sphalerite, pyrite, chalcopyrite, Zn-Pb-S mineral, barite, baritocelestine, celestine, tetrahedrite, cassiterite, REE phosphate, etc. The regular distribution of mineral inclusions in peat is associated with the (bio)geochemical evolution of the environment. The formation of authigenic Zn, Pb and Sb sulfides is mainly confined to anaerobic conditions that exist in the eutrophic peat and basal sediments. The maximum amount of pyrite is associated with the interval of 225–250 cm, which is the zone of transition from basal sediments to eutrophic peat. The formation of carbonate minerals and the decreasing concentration of clay in the association with local sulfide formation (galena, sphalerite, chalcopyrite, stibnite) begins above this interval. The peak of specific carbonation appears in the 125–150 cm interval of the mesotrophic peat, which is characterized by pH 4.9–4.5 of pore water. Kaolinite is the dominant clay mineral in the oligotrophic peat. Gypsum, galena, chalcopyrite, sphalerite, and relicts of carbonate are noted in association with kaolinite. Changes in oxygen concentrations are reflected in newly formed mineral associations in corresponding intervals of the peat. This can be explained by the activity of microbiological processes such as the anaerobic oxidation of methane (AOM) and bacterial sulfate reduction (BSR), expressed in specific carbonatization (100–225 cm) and sulfidization (175–250 cm), respectively. Full article

Two Fe–Mn crusts among 35 samples, from six seamounts in the Canary Island Seamount Province, were selected as representatives of the endpoint members of two distinct types of genetic processes, i.e., mixed diagenetic/hydrogenetic and purely hydrogenetic. High-resolution analyses pursued the main aim of distinguishing the critical elements and their association with mineral phases and genetic processes forming a long-lived Fe–Mn crust. The Fe–Mn crust collected on the Tropic Seamount is composed of dense laminations of Fe-vernadite (>90%) and goethite group minerals, reflecting the predominance of the hydrogenetic process during their formation. Based on high-resolution age calculation, this purely hydrogenetic crust yielded an age of 99 Ma. The Fe–Mn crust collected on the Paps Seamount shows a typical botryoidal surface yielding an age of 30 Ma. electron probe microanalyzer (EPMA) spot analyses show two main types of manganese oxides, indicating their origin: (i) hydrogenetic Fe-vernadite, the main Mn oxide, and (ii) laminations of interlayered buserite and asbolane. Additionally, the occurrence of calcite, authigenic carbonate fluor-apatite (CFA) and palygorskite suggests early diagenesis and pervasive phosphatization events. Sequential leaching analysis indicated that Co, Ni, Cu, Ba and Ce are linked to Mn minerals. Therefore, Mn-oxides are enriched in Ni and Cu by diagenetic processes or in Co and Ce by hydrogenetic processes. On the other hand, Fe-oxides concentrate V, Zn, As and Pb. Moreover, the evidence of HREE enrichment related to Fe-hydroxides is confirmed in the mixed hydrogenetic/diagenetic crust. Full article