Search Results (42)

The rocks of the Burpala alkaline intrusion contain a wide range of rare minerals that concentrate rare earth elements (REEs), Nb, Th, Li, and other incompatible elements. One of the examples of the occurrence of such mineralization is albite–aegirine rocks located at the contact zone between the intrusion and the host terrigenous–sedimentary rock. In albite–aegirine rocks, cubic crystals of “metaloparite”, partially or completely substituted by bastnäsite-(Ce) and polymorphic TiO₂ phases (anatase and rutile) mainly represent the rare metal minerals. In albite–aegirine rocks, trace element minerals are predominantly represented by cubic crystals of “metaloparite”, which are partially or completely replaced by bastnäsite-(Ce) and polymorphic TiO₂ phases such as anatase and rutile. Additionally, Th-bearing zircon (up to 17.7 wt% ThO₂) and a variety of unidentified minerals containing REEs, Th, and Nb were detected. The obtained data indicate that bastnäsite-(Ce) is the result of the recrystallization of “metaloparite” accompanied by the formation of Th-bearing zircon and Nb-bearing rutile (up to 9.9 wt% Nb₂O₅) and the separation of various undiagnosed, unidentified LREE phases. Our studies show that remobilization of LREEs, HFSEs, and local enrichment of rocks in these elements occurred due to the effects of residual fluid enriched in fluorine and carbon dioxide. Full article

The sulfide mineralization at Xylagani is hosted in metamorphosed mafic massive and pillow lava. It has an Early–Middle Jurassic age and belongs to the Makri unit, which represents the upper crustal section of the Evros ophiolite in the Circum Rhodope Belt, Northern Greece. The protolith of the host rock is basalt that has a boninitic-to-low-Ti tholeiitic composition and was formed in an intra-oceanic supra-subduction zone within a juvenile forearc-to-volcanic arc setting. The volcanic rocks were subjected to ocean-floor metamorphism at very low-grade prehnite–pumpellyite facies and low-grade greenschist facies at temperatures of up to 360 °C and pressures between 1 and 4 kbar. The mineralization shows typical features of a stratabound–stratiform deposit and occurs as silicified lenses and layers with disseminated and massive sulfides and gold. Based on host rock composition, geotectonic setting, and base metal content, the mineralization at Xylagani is classified as a Cu-rich mafic volcanic-associated deposit, i.e., Cyprus-type VMS (volcanogenic massive sulfide). The mineralization consists of pyrite, chalcopyrite, gold, pyrrhotite, sphalerite, galena, and tennantite-(Zn). It was formed at a subseafloor setting where hydrothermal fluids circulated through the host volcanic rocks, resulting in a pervasive alteration (silicification and chloritization) and the development of a replacement VMS deposit. The very low-to-low-grade orogenic metamorphism and related deformation during the Alpine collision in the Middle Jurassic to Early Cretaceous periods remobilized the mineralization and formed milky quartz veins with rare sulfides, crosscutting the metavolcanic rocks. Full article

Heavy metal pollution in sediments and soil is an unavoidable anthropogenic issue with implications for quality of life and is a major long-term remediation challenge. This paper aimed to evaluate an in-situ remediation technique (resuspension) for sediment that may be employed in a variety of contaminated site cleanup programs. Surface sediment samples were obtained from a shallow harbor on the St. Lawrence River, in Canada in 2019. Harbor sediment from the St. Lawrence River in Quebec is anthropogenically polluted by metals. Various experiments were performed using a designed reactor to evaluate sediment resuspension remediation technology. The method is based on sediments with a higher specific surface area that adsorb more metal contaminants. Therefore, the objective was to remove this fraction by the resuspension technique. Results showed that the levels of seven metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) were reduced by removing only 2.63% of the sediment. Removal efficiency values varied from 3.48% for Cd to 32.4% for Cu). The results of the sequential extraction tests imply that the resuspension technique is capable of decreasing the risk of remobilization of heavy metals in the aquatic ecosystem. Therefore, this method could potentially be used to remediate metal–contaminated sediment with minimal sediment removal. Full article

Estuaries are dynamic ecosystems exposed to a wide range of stressors, including metal (loid) contamination. The assessment of the behavioral characteristics of the species inhabiting these ecosystems may provide a new point of view on chemical contamination since these behaviors generally regulate population dynamics and ecosystem stability. Therefore, this study aimed to investigate the changes in behavioral patterns of three estuarine benthonic species (the native polychaete Hediste diversicolor, the non-native polychaete Arenicola marina, and the native clam Scrobicularia plana) when exposed to different concentrations of the metalloid arsenic (0, 0.5, 1.5, 4.5, 13.5, 40.5 mg/kg sediment). Behavioral assessment included bioturbation activity (measured by fluorescent particle remobilization) and determination of the maximum penetration depth by each species, both after 1 and 21 days of exposure. After 21 days of exposure, the ability of each species to burrow was evaluated. Results showed that the bioturbation activity of S. plana was immediately reduced by exposure to As (day 1) but disappeared with exposure time (day 21), whereas A. marina bioturbation activity was significantly increased from day 1 to day 21, expressing their highest values in sediments of 4.5, 13.5, and 40.5 mg of As/kg on day 21. For H. diversicolor, no changes were observed within each time or between the times. Results of the burrowing assay showed that A. marina nearly doubled its burrowing time, as well as increased in double its maximum penetration depth at As concentrations ≥1.5 mg/kg sediment. These results suggest that native species can be quite resilient to chemical contamination over time. However, the greater particle remobilization by the non-native species A. marina when exposed to As may cause displacement of the native fauna, disrupting the natural mutualism created in these environments, and possibly decreasing estuary functionality and biodiversity. Behavioral assessments under chemical exposure may improve the establishment of more feasible protection goals for more sustainable estuaries. Full article

Despite decreasing anthropogenic mercury (Hg) emissions in Europe and the banning and restriction of many persistent organic pollutants (POPs) under the Stockholm Convention, Mediterranean marine mammals still have one of the highest body burdens of persistent pollutants in the world. Moreover, the Mediterranean basin is one of the most sensitive to climate change, with likely changes in the biogeochemical cycle and bioavailability of Hg, primary productivity, and the length and composition of pelagic food webs. The availability of food resources for marine mammals is also affected by widespread overfishing and the increasing number of alien species colonizing the basin. After reporting the most recent findings on the biogeochemical cycle of Hg in the Mediterranean Sea and the physico-chemical and bio-ecological factors determining its exceptional bioaccumulation in odontocetes, this review discusses possible future changes in the bioavailability of the metal. Recent ocean–atmosphere–land models predict that in mid-latitude seas, water warming (which in the Mediterranean is 20% faster than the global average) is likely to decrease the solubility of Hg and favor the escape of the metal to the atmosphere. However, the basin has been affected for thousands of years by natural and anthropogenic inputs of metals and climate change with sea level rise (3.6 ± 0.3 mm year⁻¹ in the last two decades), and the frequency of extreme weather events will likely remobilize a large amount of legacy Hg from soils, riverine, and coastal sediments. Moreover, possible changes in pelagic food webs and food availability could determine dietary shifts and lower growth rates in Mediterranean cetaceans, increasing their Hg body burden. Although, in adulthood, many marine mammals have evolved the ability to detoxify monomethylmercury (MMHg) and store the metal in the liver and other organs as insoluble HgSe crystals, in Mediterranean populations more exposed to the metal, this process can deplete the biological pool of Se, increasing their susceptibility to infectious diseases and autoimmune disorders. Mediterranean mammals are also among the most exposed in the world to legacy POPs, micro- and nanoplastics, and contaminants of emerging interest. Concomitant exposure to these synthetic chemicals may pose a much more serious threat than the Se depletion. Unfortunately, as shown by the literature data summarized in this review, the most exposed populations are those living in the NW basin, the main feeding and reproductive area for most Mediterranean cetaceans, declared a sanctuary for their protection since 2002. Thus, while emphasizing the adoption of all available approaches to mitigate anthropogenic pressure with fishing and maritime traffic, it is recommended to direct future research efforts towards the assessment of possible biological effects, at the individual and population levels, of chronic and simultaneous exposure to Hg, legacy POPs, contaminants of emerging interest, and microplastics. Full article

The Hongtoushan Cu-Zn volcanogenic massive sulfide (VMS) deposit, located in the Hunbei granite–greenstone terrane of the North China Craton, has undergone a complex, multi-stage metallogenic evolution. The deposit comprises three main types of massive ores: Type-1 ores, characterized by a sulfide matrix enclosing granular quartz and dark mineral aggregates; Type-2 ores, distinguished by large pyrite and pyrrhotite porphyroblasts and a small amount of gangue minerals; and Type-3 ores, mainly distributed in the contact zone between the ore body and gneiss, featuring remobilized chalcopyrite and sphalerite filling the cracks of pyrite. The metallogenic process of the Hongtoushan deposit is divided into three main stages: (1) an early mineralization stage forming Type-1 massive ores; (2) a metamorphic recrystallization stage resulting in Type-2 massive ores with distinct textural features; and (3) a late-stage mineralization event producing Type-3 massive ores enriched in Cu, Zn, and other metals. This study integrates sulfur isotope, trace elements, and fluid inclusion data to constrain the sources of ore-forming materials, fluid evolution and metallogenic processes of the deposit. Sulfur isotope analyses of sulfide samples yield ${\delta }^{34}$S values ranging from −0.7 to 4.2 (mean: 1.8 ± 1.5, 1$\sigma$), suggesting a predominant magmatic sulfur source with possible contributions from Archean seawater. Trace element analyses of pyrite grains from different ore types reveal a depletion of rare earth elements, Cu, and Zn in Type-2 massive ores due to metamorphic recrystallization, and a subsequent re-enrichment of these elements in Type-3 massive ores. Fluid inclusion studies allowed for identifying three types of ore-forming fluids: Type-1 (avg. $T_h$: 222.9; salinity: 6.74 wt.% NaCl eqv.), Type-2 (avg. $T_h$: 185.72; salinity: 16.56 wt.% NaCl eqv.), and Type-3 (avg. $T_h$: 184.81; salinity: 16.22 wt.% NaCl eqv.), representing a complex evolution involving cooling, water–rock interaction and fluid mixing. This multi-disciplinary study reveals the interplay of magmatic, hydrothermal and metamorphic processes in the formation of the Hongtoushan VMS deposit, providing new insights into the fluid evolution and metallogenic mechanisms of similar deposits in ancient granite–greenstone terranes. Full article

Mercury (Hg) is a toxic metal that is easily released into the atmosphere as a gas or a particulate. Since Hg has serious health impacts based on human exposure, it is a major concern where it accumulates. Southern Florida is a region of high Hg deposition in the United States. It has entered the southern Florida environment for over 56 MY. For the past 3000 to 8000 years, Hg has accumulated in the Everglades peatlands, where approximately 42.3 metric tons of Hg was deposited. The pre-industrial source of mercury that was deposited into the Everglades was from the atmosphere, consisting of combined Saharan dust and marine evasion. Drainage and the development of the Everglades for agriculture, and other mixed land uses have caused a 65.7% reduction in the quantity of peat, therefore releasing approximately 28 metric tons of Hg into the southern Florida environment over a period of approximately 133 years. Both natural and man-made fires have facilitated the Hg release. The current range in mercury release into the southern Florida environment lies between 994.9 and 1249 kg/yr. The largest source of Hg currently entering the Florida environment is from combined atmospheric sources, including Saharan dust, aerosols, sea spray, and ocean flux/evasion at 257.1–514.2 kg/yr. The remobilization of Hg from the Everglades peatlands and fires is approximately 215 kg/yr. Other large contributors include waste to energy incinerators (204.1 kg/yr), medical waste and crematory incinerators (159.7+ kg/yr), and cement plant stack discharge (150.6 kg/yr). Minor emissions include fuel emissions from motorized vehicles, gas emissions from landfills, asphalt plants, and possible others. No data are available on controlled fires in the Everglades in sugar farming, which is lumped with the overall peatland loss of Hg to the environment. Hg has impacted wildlife in southern Florida with recorded excess concentrations in fish, birds, and apex predators. This bioaccumulation of Hg in animals led to the adoption of regulations (total maximum loads) to reduce the impacts on wildlife and warnings were given to consumers to avoid the consumption of fish that are considered to be contaminated. The deposition of atmospheric Hg in southern Florida has not been studied sufficiently to ascertain where it has had the greatest impacts. Hg has been found to accumulate on willow tree leaves in a natural environment in one recent study. No significant studies of the potential impacts on human health have been conducted in southern Florida, which should be started based on the high rates of Hg fallout in rainfall and known recycling for organic sediments containing high concentrations of Hg. Full article

The study of noble metal minerals of the Ural–Alaskan-type (UA-type) complexes has been traditionally focused on their platinum-bearing dunites and chromitites, while clinopyroxenites have been poorly considered. In this study, we report the first detailed data on the noble metal mineral assemblage in clinopyroxenites of the Kachkanar intrusion, which is a part of a UA-type complex and is renowned for its huge Ti-magnetite deposits. High concentrations of Pd, Au and Ag are closely linked to Cu-sulfide mineralization in amphibole clinopyroxenites, in which they form Pd-Ag-Au minerals: keithconnite Pd_3−xTe, sopcheite Ag₄Pd₃Te₄, stutzite Ag_5−xTe₃, hessite Ag₂Te, merenskyite PdTe, kotulskite Pd(Te,Bi), temagamite Pd₃HgTe, atheneite (Pd,Hg)₃As, potarite PdHg, electrum AuAg and Hg-bearing native silver. Among those, six mineral phases are first reported for clinopyroxenites of the Ural platinum belt. Our evidence supports a petrological model, suggesting that during fractionation of high-Ca primitive magmas at high oxygen fugacity, Pt, Os, Ir, Ru and Rh accumulate in early olivine–chromite cumulates, while Pd, Au and Ag reside in the melt until sulfide saturation occurs and then concentrate in sulfide mineralization. Subsequently, this sulfide mineralization is likely affected by cumulate degassing, which results in a partial resorption of the sulfides and Pd, Au and Ag remobilization by fluid. Second-stage concentration of the sulfides and the chalcophile noble metals in the amphibole-rich rocks may occur when H₂O from the fluid reacts with pyroxenes to form amphiboles, and the fluid becomes oversaturated with sulfides and chalcophile elements. Full article

Quantifying and identifying the introduction of metal in ore deposits that have experienced multiple overprinting hydrothermal events remains an elusive yet essential goal in metallogenic studies. Here, we constrain the origin of Co in the Idaho Cobalt Belt (ICB) that experienced two distinct metal-rich events that introduced Co and Cu. We performed a detailed petrographic study of sulfide ore at Iron Creek in the ICB, in concert with the quantification of trace metal element concentrations and copper isotope values to identify the introduction of Co in the system. The pyrite displays various degrees of alteration, with the highest Co concentrations (up to 6 wt.%) in less-altered pyrite grains (e.g., sharp edges, absence of altered boundaries and fissures) and highest δ⁶⁵Cu isotope value. The most-altered pyrite grains (e.g., corroded grains, round and altered boundaries) have lower Co contents and lower δ⁶⁵Cu isotope values that match the copper isotope values of the chalcopyrite. The least-altered pyrite shows a narrow δ⁶⁵Cu range between −0.39‰ to −0.58‰. In contrast, the most-altered pyrite grains are isotopically depleted, showing a δ⁶⁵Cu range from −1.35‰ to −0.90‰. Chalcopyrite shows a δ⁶⁵Cu range between −1.07‰ and −0.77‰. We interpret, from the Cu isotope compositions and Co concentrations in pyrite, that the Co was originally introduced into the siliciclastic host rock package in a Mesoproterozoic SEDEX environment. The heavier Cu was then preferentially leached in a second event, resulting in isotopically lighter Cu in the altered pyrite. Remobilization of the SEDEX cobalt was likely associated with CO₂-rich metamorphic fluids present in the region during the Mesoproterozoic East Kootenay orogeny, the late Mesoproterozoic Grenville orogeny, and the Late Jurassic to Late Cretaceous Cordilleran orogeny. Full article

This paper investigates the monazite grains from the Dibrova rare-earth-thorium-uranium (U-Th-REE) mineral deposit within the Azov Megablock of Ukrainian Shield. U-Th-REE mineralization is associated with K-feldspar-quartz metasandstones and metagritstones (hereafter quartzites) and pegmatoids. The latter possibly represent products of ultrametamorphism/granitization of initially sedimentary clastic rocks during tectono-magmatic activation during the Paleoproterozoic. Ores are composed of quartz as a principal mineral, feldspar, sillimanite, muscovite, monazite, brannerite, uraninite, zircon, rutile, and sulfides. The purpose of this work was to obtain insights into the genesis of the mineral deposit by studying the monazite grains, their chemistry, and ages. Petrographic research work was carried out that included studying/analyzing the monazites from various monazite-bearing rocks (quartzites, pegmatoid, and biotite schist samples). A variety of methods and tools were used, including optical microscopy study, X-ray fluorescence (XRF) mapping of selected samples, as well as scanning electron microscope (SEM) and electron microprobe (EPMA) characterization of monazites, including U-Th-Pb monazite chemical dating. U-Pb-Th chemical electron microprobe dating of the monazites yielded two major distinct monazite age groups at 3.0–2.8 Ga and 2.2–2.0 Ga. The first age group corresponds to the time of formation of the Archean granitoids, which served as a source of monazite for its clastic sedimentation during the Paleoproterozoic in the Dibrova suite sediments. The second age group corresponds to the reprecipitation (i.e., remobilization) of monazite during the Paleoproterozoic tectono-magmatic activation. The location of the mineral deposit within the deep mantle-crustal Devladivska shear zone is another favorable factor for the remobilization and transport of metals. New data on the age of mineralization yield a more complete understanding of the geological history and formation of the complex polyphase rare-earth-uranium-thorium Dibrova mineral deposit. Full article

Nicotianamine (NA) is a low-molecular-weight N-containing metal-binding ligand, whose accumulation in plant organs changes under metal deficiency or excess. Although NA biosynthesis can be induced in vivo by various metals, this non-proteinogenic amino acid is mainly involved in the detoxification and transport of iron, zinc, nickel, copper and manganese. This review summarizes the current knowledge on NA biosynthesis and its regulation, considers the mechanisms of NA secretion by plant roots, as well as the mechanisms of intracellular transport of NA and its complexes with metals, and its role in radial and long-distance metal transport. Its role in metal tolerance is also discussed. The NA contents in excluders, storing metals primarily in roots, and in hyperaccumulators, accumulating metals mainly in shoots, are compared. The available data suggest that NA plays an important role in maintaining metal homeostasis and hyperaccumulation mechanisms. The study of metal-binding compounds is of interdisciplinary significance, not only regarding their effects on metal toxicity in plants, but also in connection with the development of biofortification approaches to increase the metal contents, primarily of iron and zinc, in agricultural plants, since the deficiency of these elements in food crops seriously affects human health. Full article

We evaluated the mobility of a wide suite of economic metals (Ni, Co, REE, Sc, PGE) in Ni-laterites with different maturities, developed in the unconventional humid/hyper-humid Mediterranean climate. An embryonic Ni-laterite was identified at Los Reales in southern Spain, where a saprolite profile of ~1.5 m thick was formed at the expense of peridotites of the subcontinental lithospheric mantle. In contrast, a more mature laterite was reported from Camán in south-central Chile, where the thicker (~7 m) weathering profile contains well-developed lower and upper oxide horizons. This comparative study reveals that both embryonic and mature laterites can form outside the typical (sub)-tropical climate conditions expected for lateritic soils, while demonstrating a similar chemical evolution in terms of major (MgO, Fe₂O₃, and Al₂O₃), minor (Ni, Mn, Co, Ti, Cr), and trace (REE, Y, Sc, PGE, Au) element concentrations. We show that, even in the earliest stages of laterization, the metal remobilization from primary minerals can already result in uneconomic concentration values. Full article

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. Full article

Geopolymers are inorganic, chemically resistant aluminosilicate-based binding agents, which remove hazardous metal ions from exposed aqueous media. However, the removal efficiency of a given metal ion and the potential ion remobilization have to be assessed for individual geopolymers. Therefore, copper ions (Cu²⁺) were removed by a granulated, metakaolin-based geopolymer (GP) in water matrices. Subsequent ion exchange and leaching tests were used to determine the mineralogical and chemical properties as well as the resistance of the Cu²⁺-bearing GPs to corrosive aquatic environments. Experimental results indicate the pH of the reacted solutions to have a significant impact on the Cu²⁺ uptake systematics: the removal efficiency ranged from 34–91% at pH 4.1–5.7 up to ~100% at pH 11.1–12.4. This is equivalent to Cu²⁺ uptake capacities of up to 193 mg/g and 560 mg/g in acidic versus alkaline media. The uptake mechanism was governed by Cu²⁺-substitution for alkalis in exchangeable GP sites and by co-precipitation of gerhardtite (Cu₂(NO₃)(OH)₃) or tenorite (CuO) and spertiniite (Cu(OH)₂). All Cu-GPs showed excellent resistance to ion exchange (Cu²⁺ release: 0–2.4%) and acid leaching (Cu²⁺ release: 0.2–0.7%), suggesting that tailored GPs have a high potential to immobilize Cu²⁺ ions from aquatic media. Full article

This study aimed to describe the interannual variability of dense shelf water cascading and open ocean convection in the Gulf of Lions (NW Mediterranean) based on long-term temperature and current records and its impact on particle fluxes and associated metals. These observations highlight the predominant role of the rare intense events of dense shelf water cascading (1999/2000, 2005/2006, 2012/2013) in the basinward export of particles, which are mainly brought by rivers. Measurements of particulate trace metals in 2012 indicate that the monitored intense cascading event may be responsible for a significant fraction (~15%) of the annual input to the shelf. To this first process is added the effect of somehow more recurrent deep convection events (2005, 2009–2013) that remobilize the deep sediments, receptacle of coastal inputs, and disperse them rapidly at the scale of the northern Mediterranean basin, and gradually over the entire western basin. Coastal and oceanic dense water formations are key physical processes in the Mediterranean margins, whose reduction in intensity and recurrence has already been observed and also anticipate in climate scenarios that will likely change the dispersion pathways of chemical particles in this region. Full article