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Fluids in subduction zones significantly influence element mobility, isotope fractionation, and mass transfer. However, unraveling the source, composition, and redox state of fluids in continental subduction zones poses a significant challenge. This study focuses on a granitic melt‐eclogite contact interface, along with adjacent granite and eclogite from the Sulu ultrahigh‐pressure metamorphic belt in East China. The interface exhibits complex mineral assemblages, enriched rare earth elements (REEs), and high field strength elements (HFSEs). Zircon grains from the interface show an age of ∼217 ± 9 Ma, slightly later than peak metamorphism, along with the presence of coesite inclusions. These findings suggest that the interfacial fluid likely formed from the mixing of granitic anatectic melt and aqueous fluid from the eclogite during the initial exhumation of the Sulu terrane. The interaction resulted in the eclogite acquiring substantial REEs and HFSEs, suggesting the interfacial fluid's effective element‐transporting capability and potential supercritical fluid properties. Zircon Ce anomaly and Fe3+/Fe2+ oxybarometer data indicate a highly oxidizing interfacial fluid, analogous to arc magmas in oxygen fugacity. This led to the preferential loss of isotopically heavier Cr from the eclogite during fluid‐eclogite interaction, evidenced by heavier Cr isotopic compositions in the interface (δ53Cr = −0.04 to −0.05‰) compared to adjacent eclogite (δ53Cr as low as −0.11‰). In summary, our results highlight the presence of strong oxidizing and element‐mobilizing fluids in continental subduction zones, offering insights into supercritical fluid recognition and the genesis of oxidizing arc magmas in subduction zones. Plain Language Summary: Fluids are important agents for material migrations in subduction zones, yet the characteristics of fluids in continental subduction zones remain poorly understood, including their redox state, element‐carrying capacity, and isotopic features. In our study, we uncovered a unique interfacial fluid process occurring during the interaction of granitic melt and eclogite in continental subduction zones. This interfacial fluid transported significant amounts of insoluble trace elements into the eclogite, resulting in superchondritic Nb/Ta ratios. These characteristics indicate the interfacial fluid's exceptional element‐transporting capability distinct from silicate melts or aqueous fluids. Additionally, the interfacial fluid demonstrates a strong oxidizing property, comparable to or even exceeding that of arc magmas. This distinctive feature leads to the preferential loss of isotopically heavier Cr in the eclogite during fluid‐rock interaction. In summary, our study provides a compelling demonstration of the presence of strong oxidizing and element‐mobilizing fluids, carrying significant understanding for fluid properties in subduction zones. Key Points: Significant migrations of rare earth elements and high field strength elements are observed in granitic anatectic melt‐eclogite interfaceThe interfacial fluid is highly oxidizing, with oxygen fugacity equivalent to or even surpassing that of arc magmasThe strong oxidizing nature of the interfacial fluid resulted in the preferential loss of isotopically heavier Cr of the eclogite [ABSTRACT FROM AUTHOR]

Germanium (Ge) is a critical raw material for emerging high-tech and green industries, resulting in considerable recent interest in understanding its distribution and geochemical behavior in ore deposits. In this contribution, the distribution of Ge and related trace elements in the Fule Pb-Zn(-Ge) deposit, South China, is investigated to reveal the distribution of Ge in the hydrothermal ores and during sulfide weathering, using multiple microanalytical techniques, including scanning electron microscopy, electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). In the Fule MVT deposit, sphalerite (ZnS) is the most significant Ge-carrier relative to other sulfides, though the five recognized textural types of sphalerite display progressive depletion in Ge from the first sphalerite generation to the late one. In the early stage, sphalerite with fine-grained chalcopyrite inclusions has the highest Ge concentrations, probably accounting for a significant proportion of the total Ge. We interpret that high Ge concentrations in the early sphalerite may be attributable to high Cu activity in the mineralizing fluids. During oxidative weathering, Ge was redistributed from its original host, sphalerite, to the weathering product willemite (Zn2SiO4) rather than smithsonite (ZnCO3), with high levels of Ge (up to 448 μg/g) present in the willemite. The formation of abundant willemite largely prevents the dispersion of Ge during weathering. In principle, willemite-hosted Ge should be fully recoverable, and the Zn-silicate ores may, therefore, be a potential target to meet future demand. This study provides new information on how Ge behaves from sulfide- to weathering-stage in MVT systems, which directly impacts Ge mobility and deportment changes and the development of metallurgical strategies for Ge recovery. [ABSTRACT FROM AUTHOR]

Phytoremediation of contaminated soil is an environmentally-friendly approach to minimize the impacts of nutrients and heavy metals on an ecosystem. Hence, selecting appropriate plants with phytoextraction potential is paramount to remediatie contaminated soils. This study aimed to investigate the nutrient and metal contents of four natural aquatic plants, including Cyperus rotundus, Eleocharis dulcis, Typha angustifolia, and Schoenoplectus grossus. They were grown in the meadow of a small reservoir in Sri Lanka to assess their phytoextraction ability using plant and soil samples collected at 32 sampling points in the meadow. Their biological concentration (roots/soil), accumulation (shoots/soil), and translocation (shoots/roots) factors were determined to assess element mobility and phytoextraction ability. Total K, Na, Mg, Ca, Zn, Cu, Fe, Mn, As, Pb, and Cd contents of plants and soil samples were measured using an Inductivity Couple Plasma Optical Emission Spectrophotometer. ANCOVA was used as a statistical test to assess the best plant type in terms of nutrient and metal absorption. Plant shoots exhibited significantly greater values for P, Na, Mg, Zn, Cd, and Fe than their roots. Their biological concentration, accumulation and translocation factors were not different among the four plant species. However, these values were >1 for all the species, indicating their potential to be used as hyperaccumulators. T. angustifolia, with its high potential for nutrient and metal accumulation and the highest aesthetic appeal, was selected as the best overall wetland species for phytoremediation purposes.

Mangroves are halophytic forest plant communities located on saline marshes in estuaries of tropical and subtropical bays. They are one of the most vulnerable ecosystems in the world and are severely threatened by urban development, environmental pollution, aquaculture, and other problems. The Dongchong mangrove forest is a relatively well-preserved mangrove forest in China, with a large area and a typical Excoecaria agallocha landscape, which has significant ornamental and ecological conservation value. The aim of this study is to provide basic support not only for mangrove ecological conservation and restoration, but also to construct and manage nature's reserves. The eco-environmental geological characteristics of mangroves were investigated using geology, geomorphology, pedology, ecology, and other methods, and a typical eco-environmental geological profile of the mangrove in Dongchong was drawn. The results show that the strata in the study area are mainly Quaternary sediments and rhyolites of the Nanshancun Formation of the Early Cretaceous. Faults are developed in the west of Dongchong Mangrove Wetland Park. The main environmental geological problems are uneven ground settlement, ground subsidence, and ground cracks. The concentration of F- in the surface water are high, and the water quality is slightly lower than that of the Class III water standard; however, the groundwater is freshwater with low salinity and hardness. Cd and Tl are locally significant in the surface soil of the study area. N, P, CaCO3, Org, and B are deficient in the soil, whereas the K content is mainly medium. A part of the soil is polluted by heavy metals, particularly As, followed by Cd. However, the mangrove leaves are rich in nutrients, indicating that the lack of soil nutrient elements and heavy-metal pollution are not the major factors limiting the growth of mangroves in this region. Improving the growth environment of mangroves should include expanding the landscape area and reinforcing reserve management. In the rock-soil-plant ecosystem, As, Pb, Cd, and B are significantly rich in the soil, indicating that their contents have a slight correlation with their parent rocks. Ni, Cu, Zn, and K are limited by the parent rock contents, and some elements including P, Mo, and Cr show enrichment capacity in the soil. The BCF >2 of mangroves of the mangrove forests in Dongchong are P and B, indicating that the mangrove trees have a higher absorption capacity for P and B. In contrast, the BCF values of As, Pb, and Cd are relatively low, which, in addition to the weak absorption capacity of the mangrove trees for these elements and combined with the geochemical characteristics of the soils in the study area, are also affected by the high Cd and As contents of the soil. All the data presented in this paper are from the project, "Ecological and Environmental Geological Survey of Shenzhen Nature Reserves," for which we express our sincere gratitude.

Mangroves are halophytic forest plant communities located on saline marshes in estuaries of tropical and subtropical bays. They are one of the most vulnerable ecosystems in the world and are severely threatened by urban development, environmental pollution, aquaculture, and other problems. The Dongchong mangrove forest is a relatively well-preserved mangrove forest in China, with a large area and a typical Excoecaria agallocha landscape, which has significant ornamental and ecological conservation value. The aim of this study is to provide basic support not only for mangrove ecological conservation and restoration, but also to construct and manage nature's reserves. The eco-environmental geological characteristics of mangroves were investigated using geology, geomorphology, pedology, ecology, and other methods, and a typical eco-environmental geological profile of the mangrove in Dongchong was drawn. The results show that the strata in the study area are mainly Quaternary sediments and rhyolites of the Nanshancun Formation of the Early Cretaceous. Faults are developed in the west of Dongchong Mangrove Wetland Park. The main environmental geological problems are uneven ground settlement, ground subsidence, and ground cracks. The concentration of F-in the surface water are high, and the water quality is slightly lower than that of the Class III water standard; however, the groundwater is freshwater with low salinity and hardness. Cd and Tl are locally significant in the surface soil of the study area. N, P, CaCO3, Org, and B are deficient in the soil, whereas the K content is mainly medium. A part of the soil is polluted by heavy metals, particularly As, followed by Cd. However, the mangrove leaves are rich in nutrients, indicating that the lack of soil nutrient elements and heavy-metal pollution are not the major factors limiting the growth of mangroves in this region. Improving the growth environment of mangroves should include expanding the landscape area and reinforcing reserve management. In the rock-soil-plant ecosystem, As, Pb, Cd, and B are significantly rich in the soil, indicating that their contents have a slight correlation with their parent rocks. Ni, Cu, Zn, and K are limited by the parent rock contents, and some elements including P, Mo, and Cr show enrichment capacity in the soil. The BCF >2 of mangroves of the mangrove forests in Dongchong are P and B, indicating that the mangrove trees have a higher absorption capacity for P and B. In contrast, the BCF values of As, Pb, and Cd are relatively low, which, in addition to the weak absorption capacity of the mangrove trees for these elements and combined with the geochemical characteristics of the soils in the study area, are also affected by the high Cd and As contents of the soil. All the data presented in this paper are from the project, "Ecological and Environmental Geological Survey of Shenzhen Nature Reserves," for which we express our sincere gratitude. [ABSTRACT FROM AUTHOR]

Abstract The slab–mantle interface in subduction zones is one of the geological boundaries with the most significant chemical potential gradients, which leads to fluid-mediated metasomatic reactions and chemical transport. As subducting sediment and basaltic crust often contain silica in various forms, the Si-metasomatism of mantle rocks is thought to occur along the subduction zone interface. However, growing evidence from the geochemistry of altered rocks and thermodynamic modelling has revealed the presence of multi-component fluids at the slab interface. Here, we review the laboratory experiments, geochemical models, and natural observations that improve our understanding of mass transport and metasomatic reactions at the crust–mantle interface, focusing on the relative mobility of Mg and Si. Hydrothermal experiments using analogues for the boundary between mantle (olivine) and crust (quartz or plagioclase) under vapor-saturated pressures indicate that Si is preferentially transported from crust to mantle, whereas Mg is immobile. This result is consistent with the distribution of talc rocks in oceanic lithosphere. On the other hand, at the contact between ultramafic (e.g., serpentinite) and crustal (pelitic schist or basaltic rocks) rocks in high-pressure metamorphic terranes, a large volume of chlorite rocks form in the crustal rocks, and the volume of chlorite often exceeds talc in serpentinites. Geochemical modeling reveals that in the shallow part of a subduction zone, the dissolved Si content of fluids in equilibrium with pelitic schist (C Si,crust) is significantly higher than the dissolved Mg content of fluids in equilibrium with mantle peridotite (C Mg,mantle); however, C Mg,mantle becomes dominant at depth, resulting in the Mg-metasomatism of crustal rocks to form chlorite rocks. This Mg-metasomatism is more widespread in warmer subduction zones (e.g., the Nankai and Cascadia subduction zones) than in colder subduction zones (e.g., in Northeast Japan). In addition, the infiltration of CO2-bearing fluid can form talc (along with carbonates) in ultramafic rocks without Si-metasomatism. Variations in the relative mobility of Si and Mg at the subduction zone interface produce variations in the overall solid volume change of mantle (expansion or contraction), the types of sheet silicates (talc versus chlorite), and the fluid budget (dehydration or hydration) during metasomatic reactions, which affects the pore fluid pressure, frictional strength of the subduction megathrust, and the location of seismicity around the mantle wedge corner.

The slab–mantle interface in subduction zones is one of the geological boundaries with the most significant chemical potential gradients, which leads to fluid-mediated metasomatic reactions and chemical transport. As subducting sediment and basaltic crust often contain silica in various forms, the Si-metasomatism of mantle rocks is thought to occur along the subduction zone interface. However, growing evidence from the geochemistry of altered rocks and thermodynamic modelling has revealed the presence of multi-component fluids at the slab interface. Here, we review the laboratory experiments, geochemical models, and natural observations that improve our understanding of mass transport and metasomatic reactions at the crust–mantle interface, focusing on the relative mobility of Mg and Si. Hydrothermal experiments using analogues for the boundary between mantle (olivine) and crust (quartz or plagioclase) under vapor-saturated pressures indicate that Si is preferentially transported from crust to mantle, whereas Mg is immobile. This result is consistent with the distribution of talc rocks in oceanic lithosphere. On the other hand, at the contact between ultramafic (e.g., serpentinite) and crustal (pelitic schist or basaltic rocks) rocks in high-pressure metamorphic terranes, a large volume of chlorite rocks form in the crustal rocks, and the volume of chlorite often exceeds talc in serpentinites. Geochemical modeling reveals that in the shallow part of a subduction zone, the dissolved Si content of fluids in equilibrium with pelitic schist (CSi,crust) is significantly higher than the dissolved Mg content of fluids in equilibrium with mantle peridotite (CMg,mantle); however, CMg,mantle becomes dominant at depth, resulting in the Mg-metasomatism of crustal rocks to form chlorite rocks. This Mg-metasomatism is more widespread in warmer subduction zones (e.g., the Nankai and Cascadia subduction zones) than in colder subduction zones (e.g., in Northeast Japan). In addition, the infiltration of CO2-bearing fluid can form talc (along with carbonates) in ultramafic rocks without Si-metasomatism. Variations in the relative mobility of Si and Mg at the subduction zone interface produce variations in the overall solid volume change of mantle (expansion or contraction), the types of sheet silicates (talc versus chlorite), and the fluid budget (dehydration or hydration) during metasomatic reactions, which affects the pore fluid pressure, frictional strength of the subduction megathrust, and the location of seismicity around the mantle wedge corner. [ABSTRACT FROM AUTHOR]

Serpentinite plays a crucial role in element mobility during seawater hydrothermal alteration of mid-ocean ridge peridotite on the seafloor and fluid metasomatism of peridotite in the subduction zone. However, element mobility and Mg isotope fractionation during serpentinization of peridotites are still uncertain. In order to address this issue, we present a geochemical study of serpentinites and their associated peridotites in the Xigaze ophiolite from southern Tibet. The serpentinites have lower MgO contents and Mg/Si ratios than the peridotites. The low Mg/Si ratios in serpentinites, along with the Isocon calculation results, indicate the Mg loss during serpentinization. In terms of trace elements, the serpentinites have higher contents of Ba, U, Sr and Pb than the peridotites, though both types of ultramafic rocks exhibit similar REE distribution patterns and HFSE contents. The serpentine-magnetite O isotope thermometry yields a relatively low serpentinization temperatures of 200–300 °C. The trace element composition of the serpentinites is distinct from that of forearc serpentinites but consistent with that of mid-ocean ridge ones. The peridotites show mantle-like δ26Mg values of –0.27 to –0.23‰ with an average of –0.25 ± 0.03‰ (2SD, n = 6). In contrast, the serpentinites have systematically higher δ26Mg values of –0.21 to –0.09‰ with an average of –0.16 ± 0.09‰ (2SD, n = 8). The Mg isotope composition of serpentinites shows no correlations with either the chemical weathering proxy or the talc modal content, indicating that the Mg isotope fractionation between serpentinite and peridotite is not caused by chemical weathering of the serpentinites. Instead, it probably resulted from the serpentinization of peridotite on the seafloor. Thus, there is the loss of not only element Mg but also isotopically light Mg during the serpentinization of peridotites. The isotopically heavy Mg serpentinites can be carried to oceanic subduction zones, giving rise to higher δ26Mg mantle sources for various basalts. The isotopically light Mg can be released into the seawater, regulating the Mg isotope composition of seawater in geological history. Taking into account the sources and sinks of Mg in subduction zone fluids, the formation of isotopically heavy Mg serpentinites during seafloor serpentinization can be probably an important process in changing the Mg isotope composition of mantle sources. [ABSTRACT FROM AUTHOR]

Element mobility and chemical mass transfer are evaluated in the formation of Cu—Fe exoskarn deposits and endoskarn and minor porphyry‐style alteration in the Tonglushan quartz monzodiorite (QMD) system, eastern China. Endoskarn formation involved the migration of Ca into the QMD from the exoskarnification of carbonates (now marble) xenoliths and wall rocks, addition of Fe and Mn by magmatic‐hydrothermal fluids emanating from the interior of the QMD, and removal of alkali elements due to the replacement of feldspars and mica by prograde skarn minerals. Zirconium, Hf, U, and rare earth elements (REE) were added by hydrothermal fluids which were able to carry these often poorly mobile high field strength elements (HFSE) due to elevated F activity. Additions of Al were likely from Na‐rich fluids that also caused sodic alteration. Several factors favored mineralization within the exoskarns rather than endoskarns and QMD. The endoskarns were relatively oxidizing, as evidenced by a significant addition of Fe3+, which caused Cu to remain in magmatic‐hydrothermal fluids until they entered and precipitated sulphides in the more reducing environment of the exoskarns. Fluid migration from the QMD through the endoskarns and into the exoskarns was favored due to decarbonation of wall rock carbonates and related upwards migration of CO2 to produce a self‐sustaining chimney effect, which drew further fluids towards the carbonates to form, alter and mineralize the exoskarns. The higher porosity and permeability of the endoskarns compared with the QMD further promoted the lateral flow of Cu‐bearing fluids towards the exoskarns and limited porphyry‐style alteration and mineralization within the QMD. This proposed mechanism is only likely to be relevant for porphyry‐type systems developed predominantly within carbonate host rocks. Its significance for exploration models is that relatively poorly mineralized porphyry stocks in this setting may be associated with more substantive exoskarn deposits on their margins. [ABSTRACT FROM AUTHOR]

Gold (Au) mining area is known to be one of the major sources of toxic elements; however, the potential risks of toxic elements from abandoned Au mines to the surrounding river basin districts and human exposure pathways to toxic elements need to be clarified. In this study, the distribution and mobilities of nine toxic elements (As, Cd, Cu, Pb, Sb, Zn, Cr, Ni and V) in Kesennuma City, Tohoku Region in Japan, a typical Au-mining district with several river basins, were studied through a geochemical survey (including element total concentrations and water-/acid-leaching concentrations determinations, as well as GB calculations), and environmental assessment on these elements in soil, river sediment, and river water samples from the study area. The contamination evaluation by index of geo-accumulation (Igeo) and enrichment factor (EF) suggested that As, Cu, Ni and Sb enrichments were greatly observed in the vicinity of the abandoned Au mines; moreover, calculated GB upper values for Cu in the river sediment surpass that of Tohoku Region. It has been found in this study that each element has particular mobility, which eventually influences its exposure pathway to humans. For instance, As in soil and sediment poses adverse non-carcinogenic risks and unacceptable carcinogenic risks to especially children mainly through groundwater ingestion. To minimize the potential risks associated with exposure to toxic elements in Au-mining districts, effective risk management measures should be implemented around river system by Au-mining companies even after their long-time closures, based on the consideration of each element's mobility. [ABSTRACT FROM AUTHOR]

• This work explores the roles of depositional and diagenetic processes that operated on an Archean carbonate platform. • Micro-analytical techniques (scanning XRF and LA-ICP-MS) were employed to investigate those controls on geochemistry. • Samples with proxies indicating the presence of free oxygen are the least diagenetically altered. • Rare earth elements and minor elements, e.g. Sr, Ba and Mn, were mobile during dolomitization. • The extent of diagenetic alteration was not apparent using only visual and microscopic examination. A plethora of proxies has been developed over the preceding two decades in attempts to investigate the geochemistry of the Archean ocean–atmosphere system, and in particular oxygen levels. Unfortunately the necessary parallel investigations of the effects that localized ocean chemistry and diagenesis can have on Archean sediments have commonly not kept pace. We used micro-analytical techniques (LA-ICP-MS and XRF scanning), to distinguish the effects of changes in water composition during precipitation and diagenesis on marine limestone precipitates at the margin and interior of a 2.8 Ga carbonate platform (Mosher Carbonate, Steep Rock Group) in western Superior Province, Canada. Platform margin meter-scale hybrid giant domes consist of centimetric interlayered couplets of (1) Sr-rich crystal fan fabric and cuspate fenestral microbialite, both with pronounced negative Ce-anomalies, and (2) net-like fenestral microbialite, rich in diagenetic cement with diminished concentrations of Sr and lacking negative Ce anomalies. The elevated Sr in the crystal fan fabric and cuspate fenestral microbialite is a general sign of less diagenetic alteration, as is preservation of millimeter-scale chemical differences. XRF mapping revealed that samples that otherwise appear pristine from a second site on the platform rim, near a zone of alteration in the limestone, have ferroan dolomite-filled micro-fractures with Mn flooding of the surrounding calcite and lack Ce anomalies. Platform interior silicified and ferroan dolomitized columnar stromatolites have some calcite laminae, but exceptionally low Sr contents indicate that they formed by dedolomitization. In several horizons REE patterns identical to those of offshore iron formation, replacement of calcite by iron carbonate, and the presence of iron oxides all suggest that short term flooding of the platform by offshore seawater episodically introduced ferroan dolomitizing fluids. Overall, these data indicate a restricted marine environment subject to periodic flooding by offshore waters that caused seafloor diagenetic alteration and precipitation of iron hydroxides. In this system the least altered limestone was the lithotype most likely to retain evidence of free oxygen. Samples with abundant phreatic cement and/or Mn alteration associated with micro-fractures were liable to have experienced REE mobilization. Detailed studies that integrate both depositional and diagenetic information are critical for the correct interpretation of geochemical data from sedimentary rocks. [ABSTRACT FROM AUTHOR]

The ceramic industry is a production sector that can efficiently recycle its own processing residues, achieving a reuse index of almost 100%. Recently, the range of waste from other industrial sectors that can be used as secondary raw materials in ceramic bodies has expanded. However, such an expansion potentially introduces hazardous components. This study aimed to quantitatively assess the efficiency of inertising hazardous elements (HEs) through ceramisation. The ceramics were characterised through XRPD, SEM-EDS and leaching tests to determine their leaching behaviour and the mechanisms of element immobilisation in neoformation phases during the ceramisation process. The results indicate high immobilisation efficiency for Ba, Co, Cr, Cu, Pb, Sb, Sn and Zn. However, Mo is the main element of concern owing to its poor retention in ceramic bodies. This is likely due to the formation of oxyanionic complexes that are difficult to immobilise in silicate matrices. In addition, the ceramic bodies exhibit substantial differences that appear to be associated with variations in pseudo-structural components and the degree of polymerisation of their vitreous phase. [Display omitted] • Circular economy in ceramic industry: effective recycling of various industrial waste. • Quantitative evaluation of immobilisation efficiency for 11 hazardous elements. • Vitrified ceramics: high immobilisation efficiency, depending on composition. • Poor retention of Mo in ceramic bodies, related to oxyanionic complexes. [ABSTRACT FROM AUTHOR]

Purpose: Kettle holes are small inland water bodies known to be dominated by terrigenous material; however, the processes and structures that drive the enrichment and depletion of specific geochemical elements in the water column and kettle hole sediment remain unclear. We hypothesized that the mobile elements (Ca, Fe, K, P) behave different from each other in their transport, intermediate soil retention, and final accumulation in the kettle hole sediment. Methods: Topsoils from transects spanning topographic positions from erosional to depositional areas, sediment cores, shallow groundwater, and kettle hole water of two glacial kettle holes in NE Germany (Rittgarten (RG) and Kraatz (KR)) were collected. The Fe, Ca, K, and total P (TP) concentrations were quantified and additionally the major anions in shallow groundwater and kettle hole water. The element-specific mobilization, relocation, and, finally, accumulation in the sediment were investigated by enrichment factors. Furthermore, a piper diagram was used to estimate groundwater flow directions and pond-internal processes. Results: At KR only, the upper 10 cm of the kettle hole sediment reflected the relative element composition of the eroded terrestrial soils. The sediment from both kettle holes was enriched in Ca, Fe, K, and P compared to topsoils, indicating several possible processes including the input of clay and silt sized particles enriched in these elements, fertilizer input, and pond-internal processes including biogenic calcite and hydroxyapatite precipitation, Fe–P binding (KR), FeSx formation (RG), and elemental fixation and deposition via floating macrophytes (RG). High Ca concentrations in the kettle hole water indicated a high input of Ca from shallow groundwater inflow, while Ca precipitation in the kettle hole water led to lower Ca concentration in groundwater outflow. Conclusions: The considerable element losses in the surrounding soils and the inputs into the kettle holes should be addressed by comprehensive soil and water protection measures, i.e., avoiding tillage, fertilizing conservatively, and creating buffer zones. [ABSTRACT FROM AUTHOR]

Sediment management is a fundamental part of reservoir operation, but it is often complicated by metal(loid) enrichment in sediments. Knowledge concerning the sources of potential contaminants is therefore of important significance. To address this issue, the concentrations and the mobile fractions of metal(loid)s were determined in the sediments and the respective catchment areas of six reservoirs. The results indicate that reservoirs generally have a high potential for contaminated sediment accumulation due to preferential deposition of fine particles. The median values of the element-specific enrichment factor (EF) demonstrates slight enrichments of arsenic (EF: 3.4), chromium (EF: 2.8), and vanadium (EF: 2.9) for reservoir sediments. The enrichments of cadmium (EF: 8.2), manganese (EF: 3.9), nickel (EF: 4.8), and zinc (EF: 5.0) are significantly higher. This is enabled by a diffuse element release from the soils into the impounded streams, which is particularly favored by soil acidity. Leaching from the catchment soils partially enriches elements in stream sediments before their fine-grained portions in particular are deposited as reservoir sediment. We assume that this effect is of high relevance especially for reservoirs impounding small streams with forested catchments and weakly acid buffering parent material of soil formation. [ABSTRACT FROM AUTHOR]

The Morro do Onça suite is a package of ultramafic rocks in the southern São Francisco Craton, Brazil. Owing to the complete alteration of primary silicate minerals, the Morro do Onça suite has been the subject of diverging interpretations, including: part of a retrogressed eclogite-facies Paleoproterozoic ophiolite/accretionary wedge or an Archean komatiite flow(s). In this paper, we utilize spinel-group mineral chemistry—alongside field mapping, petrography, silicate mineral chemistry and bulk-rock geochemistry—to decipher the magmatic and metamorphic evolution of the Morro do Onça suite. A komatiite origin is supported by the identification of spinifex-textured layers, as well as primary spinel-group mineral compositions (mean Cr-number = 79; mean TiO2 = 0.3 wt%) and chondrite-normalized bulk-rock rare-earth element values ([Sm–Lu]N = 1.2–5.1). Metamorphism reached mid/upper amphibolite-facies and was likely responsible for Al mobility on mineral and bulk-rock scales, demonstrating that the bulk-rock Al/Ti proxy commonly used to classify komatiites is susceptible to alteration. Thus, the Morro do Onça komatiites record variable bulk-rock Al/Ti values (17–47) that overlap with both Munro- (Al/Ti = 22) and Weltevreden-type (Al/Ti = 30) komatiites. Based on immobile trace-element ratios ([Gd/Lu]N = 0.6–2.0) and primary spinel-group mineral compositions, we classify the Morro do Onça komatiites as Weltevreden-type. Mesoarchean komatiites related to mantle plume-magmatism are now recognized throughout the southern São Francisco Craton, potentially suggesting that its precursor lithosphere was continuous during this Era. [ABSTRACT FROM AUTHOR]

Abstract Background Three stages of basalt weathering are known: early or incipient weathering, intermediate weathering and advanced weathering. The Late Oligocene basalt of Gebel Qatrani in Fayum Depression, Egypt, shows signs of early weathering, particularly exhibited in basalt spheroids found at the top of the basalt flow. The present paper gives the results of detailed petrographical, mineralogical and geochemical study of the weathering of these basalt spheroids. Results The core-stones of the basalt spheroids are composed of phenocrystals of plagioclase feldspars and clinopyroxenes set in a groundmass of tiny feldspars and pyroxenes, relatively altered olivine and opaque minerals. The basalt is subalkali (tholeiitic). The outer weathered shells surrounding the core-stones are composed of partly altered feldspars and pyroxenes. The calculated weathering indices show that there is marked weathering trend from the core-stones of the spheroids to the outer shells. The chemical mobility of the elements shows marked depletion of Mg, Ca, Na and K from the core-stones to the outer shells due to the weathering of olivine, pyroxene and feldspars. The trace elements Rb, Sr, Ni, V, Cr and Zn are also depleted. Conclusions The weathering of basalt spheroids from Gebel Qatrani, Fayum Depression, Egypt, is of the incipient type. The degree of weathering from the core-stones of the basalt spheroids to the corresponding weathered shells indicates that the weathering occurred under predominantly semiarid to arid conditions.

The Ruwai deposit is Indonesia's largest Zn‐Pb‐Ag skarn deposit and is located in Lamandau district, Central Borneo, within the Central Borneo metallogenic belt. This skarn deposit consists of four main zones, namely Gojo, Karim, Ruwai, and Southwest Gossan Zones. The skarn orebodies are mostly hosted by limestone of the Jurassic Ketapang Complex where quartz diorite of the Cretaceous Sukadana Granitoid is the ore‐causative intrusion. Despite the several mineralogical studies carried out in this deposit, there is still a lack of knowledge of its geochemical characteristics. This study evaluates the element mobility during skarn formation on the basis of skarn and ore mineralogy combined with lithogeochemical data of the intrusions, sedimentary wall rocks, and skarn bodies. The skarn mineralogy of the Ruwai skarn complex can be divided into prograde, retrograde and supergene stages. The prograde stage is characterized by the formation of an anhydrous assemblage of garnet‐pyroxene, while the retrograde stage features the replacement of prograde minerals by predominant epidote‐chlorite‐actinolite. The mineralization was first introduced during the late prograde stage, while the formation of massive orebodies attributed to the retrograde stage. The skarn samples show a wide range of major element contents, but both the mineralized skarn and massive orebodies show similar trace and rare‐earth elements patterns in global Phanerozoic limestone‐ and upper crust sedimentary rocks‐normalized spider diagrams. The skarn and orebodies, as well as the metalimestone in this study area, are depleted in REE, although HREE are higher than LREE. Most metals (e.g., Zn, Pb, Ag, Cu, Fe) in skarn and associated orebodies, interpreted to be predominantly magmatic‐sourced, show co‐occurring enrichment or depletion relative to the metalimestone and intrusive rocks. The isocon analysis shows that there was significant mass loss as a consequence of significant volatile loss, such as CO2, during skarn formation. Major oxides and large ion lithophile elements mostly behaved as mobile elements during skarn formation, whereas rare‐earth and high field strength elements tended to be immobile. However, the occurrence of several HFSE‐ and REE‐bearing minerals in Ruwai deposit (i.e., zircon, thorite, cerite, cerianite, monazite, allanite), suggesting minor or local mobility of these elements. Such unexpected behavior can be justified by the occurrence of fluorine‐rich hydrothermal fluid, which could have been responsible for the increasing mobility of these elements. [ABSTRACT FROM AUTHOR]

This contribution deals with new geology, petrography, and bulk-rock/mineral chemistry of the poorly studied ultramafics of Wadi Ibib–Wadi Shani (WI–WS) district, South Eastern Desert, Egypt. These ultramafics are dismembered ophiolitic rocks that can be subdivided into serpentinites and serpentinized peridotites. Primary minerals such as olivine and pyroxene are absent in serpentinites, but relics of them occur in serpentinized peridotites. Pseudomorph after olivine is indicated by common hourglass textures with less mesh, whilst schistose bastites reflect a pyroxene pseudomorph. Chromite can be subdivided into Cr-spinel and Al-spinel. Cr-spinel ranges from chromite to magnesochromite in composition, whereas Al-spinel belongs to the spinel field. Cr-spinel includes YCr (Cr/(Cr+Al+Fe+3), YAl (Al/(Al+Cr+Fe+3), and YFe+3 (Fe+3/(Fe+3+Al+Cr), similar to forearc peridotite, whilst Al-spinel is more similar to abyssal peridotite, and may be formed during inanition of subduction processes in proto forearc environments. The main secondary minerals are tremolite, talc, and chlorite—which is subdivided into pycnochlorite and diabantite—and their temperature ranges from 174 to 224 °C. The examined rocks had undergone high partial melting degrees (>25%), as indicated by the Cr# of their unaltered cores (Cr-spinel, >0.6), whole rocks (Al2O3, SiO2, CaO, and MgO), trace and REEs, depleted Na2O, Al2O3, and Cr2O3 of clinopyroxene, and high forsterite content ((Fo = 100 Mg/Mg + Fe), av. 95.23 mol%), consistent with forearc settings. [ABSTRACT FROM AUTHOR]

The use of strontium isotopes in pre-historic mobility studies requires accurate isoscapes for evaluating whether pre-historic individuals are local to the areas in which they were buried or not. Isoscapes are often based on modern-day samples, commonly surface waters. There is, however, growing evidence that modern-day farming has a significant impact on the strontium isotopic composition of surface waters and farmed soils, mainly due to the use of agricultural lime for soil improvement. In this paper, we investigate the fate of strontium from agricultural lime in an experimentally-manipulated field in central Jutland, Denmark. Agricultural limestone was added to this field at very high rates in 2012 and 2013 to investigate CO2 storage in soils. Strontium was first measured from the site in 2014. In 2019 we reevaluated strontium concentrations and found that 80–100% of the strontium from the agricultural lime had leached out of the organic-rich topsoil, and likely seeped into the underlying groundwater and nearby surface waters. In both the sandy soils of the liming test site and farmed soils and heathland in the adjacent area, Sr exhibits a degree of mobility similar to that of calcium, which is in agreement with data for other soil types and what is predicted by the size of its hydrated ions. Strontium isotopic compositions of unfarmed heathland samples show much higher 87Sr/86Sr ratios, and so are not influenced by carbonates, suggesting that the limestone 87Sr/86Sr signature seen in the farmland and in streams and rivers in contact with this comes from agricultural lime, and not from natural carbonate relicts occasionally found in the area. This suggests that the 87Sr/86Sr signatures of the area were higher in pre-historic times, and that an isoscape map based on samples from modern-day farmland is inappropriate for application to provenance and mobility studies of pre-historic people. Thus, it is critical that the possible impact of farming is evaluated when conducting provenance and mobility studies, especially in areas with Sr-poor soils and where agricultural lime is used for soil improvement. Overlooking this can result in significant overestimation of the degree of pre-historic mobility.

Condensates of vapor-gas streams were collected during field and laboratory experiments for the determination of the volatility of chemical elements in sulfide tailings under ambient conditions. The object of research was the Ursk waste heaps (Kemerovo region, Russia). Field experiments were performed on the top of the heap and in neighboring territories; the elements' concentrations in condensates from the top exceed the background values in 2–3 orders of magnitude. To obtain condensates in the laboratory, the waste material was heated to 60 °С. Laboratory condensate–contended high concentrations Ca, Mg, but Fe, Cd, Mo, Sn, Zr, and W were lower by more than 2 orders of magnitude. Also, chemical elements such as Au, Zr, Cs, U, and Tl were determined in the laboratory condensates at elevated temperatures. Also, solid samples were leached with water at the laboratory. A high positive correlation of condensate compositions with compositions of water extracts obtained from parallel samples was established. The most mobile elements transferred in the steam-gas phase are alkaline (Li, Cs, Na, K), alkaline earth (Ca, Sr), chalcophile metals (Hg, Zn, Cu), and metalloids (As, Sb, Se). The numerical experiment of metal transfer forms using thermodynamic modeling methods has been performed, including those with organic ligands. [ABSTRACT FROM AUTHOR]

Background: Three stages of basalt weathering are known: early or incipient weathering, intermediate weathering and advanced weathering. The Late Oligocene basalt of Gebel Qatrani in Fayum Depression, Egypt, shows signs of early weathering, particularly exhibited in basalt spheroids found at the top of the basalt flow. The present paper gives the results of detailed petrographical, mineralogical and geochemical study of the weathering of these basalt spheroids. Results: The core-stones of the basalt spheroids are composed of phenocrystals of plagioclase feldspars and clinopyroxenes set in a groundmass of tiny feldspars and pyroxenes, relatively altered olivine and opaque minerals. The basalt is subalkali (tholeiitic). The outer weathered shells surrounding the core-stones are composed of partly altered feldspars and pyroxenes. The calculated weathering indices show that there is marked weathering trend from the core-stones of the spheroids to the outer shells. The chemical mobility of the elements shows marked depletion of Mg, Ca, Na and K from the core-stones to the outer shells due to the weathering of olivine, pyroxene and feldspars. The trace elements Rb, Sr, Ni, V, Cr and Zn are also depleted. Conclusions: The weathering of basalt spheroids from Gebel Qatrani, Fayum Depression, Egypt, is of the incipient type. The degree of weathering from the core-stones of the basalt spheroids to the corresponding weathered shells indicates that the weathering occurred under predominantly semiarid to arid conditions. [ABSTRACT FROM AUTHOR]

This contribution deals with new geology, petrography, and bulk-rock/mineral chemistry of the poorly studied ultramafics of Wadi Ibib–Wadi Shani (WI–WS) district, South Eastern Desert, Egypt. These ultramafics are dismembered ophiolitic rocks that can be subdivided into serpentinites and serpentinized peridotites. Primary minerals such as olivine and pyroxene are absent in serpentinites, but relics of them occur in serpentinized peridotites. Pseudomorph after olivine is indicated by common hourglass textures with less mesh, whilst schistose bastites reflect a pyroxene pseudomorph. Chromite can be subdivided into Cr-spinel and Al-spinel. Cr-spinel ranges from chromite to magnesochromite in composition, whereas Al-spinel belongs to the spinel field. Cr-spinel includes YCr (Cr/(Cr+Al+Fe+3), YAl (Al/(Al+Cr+Fe+3), and YFe+3 (Fe+3/(Fe+3+Al+Cr), similar to forearc peridotite, whilst Al-spinel is more similar to abyssal peridotite, and may be formed during inanition of subduction processes in proto forearc environments. The main secondary minerals are tremolite, talc, and chlorite—which is subdivided into pycnochlorite and diabantite—and their temperature ranges from 174 to 224 °C. The examined rocks had undergone high partial melting degrees (>25%), as indicated by the Cr# of their unaltered cores (Cr-spinel, >0.6), whole rocks (Al2O3, SiO2, CaO, and MgO), trace and REEs, depleted Na2O, Al2O3, and Cr2O3 of clinopyroxene, and high forsterite content ((Fo = 100 Mg/Mg + Fe), av. 95.23 mol%), consistent with forearc settings.

Physical and geochemical properties of six soils developed on tephra from Mts. Kupe and Manengouba were studied in order to assess the degree of weathering of the tephric parent materials. Physico-chemical properties were determined following standard procedures. Total elemental contents and selective extracted contents of Al and Fe by acid ammonium oxalate, dithionite-citrate-bicarbonate (DCB) and pyrophosphate were determined using inductively coupled plasma optical emission spectroscopy (ICP-OES) after being brought into solution. Parent rocks were chemically classified as hawaiite, tephricfoidite, and basanites, while soils were classified as Andosols and Cambisols. Both the soils and parent rocks have high concentrations in SiO2, Al2O3, and Fe2O3. Texture and the evaluated related weathering indices correlate with horizon development and are important in capturing the differences between the two Reference Soil Groups. Mobility of major elements showed erratic trends in conformity with the stratigraphic breaks indicating variability of parent materials with depth. Enrichment and depletion of major elements to a certain degree explains the ongoing andosolization process in the Andosols. Physical and geochemical data can both be used concomitantly for assessment of weathering trends in these soils. Total reserve in bases (TRB) is very high in the Andosols indicating the presence of large quantities of weatherable minerals and thus the high potential of these soils for agricultural production. [ABSTRACT FROM AUTHOR]

Assimilation serves as a significant part during magma's evolution. Because of rapid cooling of mafic–ultramafic magma, assimilation between mantle‐derived magma and crustal rocks (wall rocks) is often neglected. The Beidaihe diabase dyke in North China Craton suggests that assimilation of the rapidly cooled mantle‐derived magma cannot be ignored. The diabase dyke is very thin (~1 m in width) with chilled margin. The dyke centre is porphyritic texture while the chilled margin is aphanitic texture, suggesting a rapid crystallization process. From the centre to margin of the dyke, contents of SiO2 (from 48.12–49.94 wt.% to 38.29–46.63 wt.%), MgO (from 7.46–9.17 wt.% to 3.39–4.71 wt.%), Ni (from 91.5–118 ppm to 6.5–45.8 ppm), and Cr (from 243–306 ppm to 1.7–80.5 ppm) are obviously decreased, but contents of Fe2O3T (from 8.71–9.39 wt.% to 9.21–12.30 wt.%), CaO (from 5.67–7.08 wt.% to 6.91–10.26 wt.%), and CO2 (from 0.25–1.92 wt.% to 4.52–6.58 wt.%) are distinctly increased. The dyke intruded discordantly into Ordovician limestone. Limestone far away from the dyke mainly consists of micro calcites with low MgO (0.55–0.77 wt.%) and FeO (0.07–0.09 wt.%) but high CaO (53.82–55.51 wt.%) and CO2 (44.46–45.02 wt.%) contents. Limestone close to the dyke metamorphosed into marble, which mainly comprises of recrystallized calcite/dolomite and diopside, with high MgO (1.85–2.35 wt.%) and FeO (0.17–1.36 wt.%) but relatively low CaO (52.30–54.15 wt.%) and CO2 (38.77–41.04 wt.%). All these suggest an assimilation process of the mantle‐derived magma with wall rocks limestone. Based on the chemical balance at the interface between the diabase and limestone, CO2 exchange model is used to estimate the degree of assimilation. The calculated assimilation degree is about 8–12% at the dyke margin. There is obvious elements exchange between magma and wall rocks, and the transfer ability of Mg is greater than that of Ca. Meanwhile, Fe oxides quickly precipitated at the margins of the dyke for the increase of fO2. Therefore, even for mantle‐derived magma which chilled rapidly, it may also be obviously influenced by assimilation, especially when wall rocks are carbonate sediments. Simultaneously, this study provides a possible explanation for some mantle‐derived rocks in carbonate areas with high LOI. [ABSTRACT FROM AUTHOR]

Mining in the Bolivian Altiplano is important and has historically provided much of the world's Ag, Sn, and Sb. This study aims to better understand the effects of important recent increases in Bolivian mining on the deposition of metals and metalloids in sediment near Oruro, Bolivia's fifth largest city, with special attention to natural and anthropogenic factors as well as early diagenesis, which could have broader implications in other high-elevation environments that have or will be affected by increased mining activities. To better assess the depositional trends of elements in sediments, five sedimentary cores collected in Lake Uru Uru and the Cala Cala Lagoon (nearby Oruro) were studied and analysis of the physicochemical variables coupled with radiometric dating indicate that (a) sediment deposited in Lake Uru Uru was likely sourced from local outcrops of Tertiary volcanics, Paleozoic shales, and ore and waste piles from mining activities material; (b) sedimentation rates in Lake Uru Uru were close to 3 mm·year−1, 1 mm higher than the ancient Tauca paleolake (~11,000–30,000 years ago); (c) early diagenetic effects have affected the distribution of Mn, As, and Cd in the sedimentary archive; and (d) the deposition of Ag, Sb, and Pb in the studied sediment has largely been related to historical trends in Bolivian Sn mining methods and production. [ABSTRACT FROM AUTHOR]

Despite recent advances, diagenetic processes in fine‐grained sediments are still relatively poorly understood. Key questions still to be resolved include the types of diagenetic minerals present in mudstones and the extent of element mobility in these low permeability systems. This study utilizes data from the Haynesville‐Bossier Shale, USA, to analyze lithologies, discriminate authigenic phases and identify mobile elements during diagenesis. It has implications for understanding how authigenic minerals develop and the sources of those authigenic minerals in fine‐grained sediments. On the basis of grain‐size and mineralogy five lithologies are designated: (i) silica‐rich argillaceous mudstones; (ii) argillaceous siliceous mudstones; (iii) mixed siliceous mudstones; (iv) mixed mudstones; and (v) authigenically‐dominated mudstones. The diagenetic development of the Haynesville‐Bossier Shale can be divided into early and late diagenesis. Ferroan and non‐ferroan dolomite, framboidal pyrite and bioclast pore‐filling kaolinite and calcite grain replacements and cements all formed during early diagenesis. Late diagenetic mineral phases include illite formed by the illitization of smectite, replacive and displacive chlorite, calcite‐replacive albite, quartz‐replacive calcite and replacive and/or displacive quartz. The presence of extensive late diagenetic mineral precipitates indicates that there was a degree of element mobility on at least the local scale. Aluminium present in albite is most likely to have resulted from the illitization of smectite. Quartz overgrowths probably resulted from illitization and the pressure dissolution at quartz silt grain boundaries. Externally, hydrothermal fluids resulting from regional‐scale igneous activity appear to have played a role in the formation of chlorite and possibly albite. The work indicates that extensive mineral development and element mobility occurred during late diagenesis. [ABSTRACT FROM AUTHOR]

A petrological study was performed on an eclogite‐vein system from the Dabie ultrahigh‐pressure terrane by focusing on high‐pressure (HP) fluid‐rock interaction and mass transfer during exhumation. The veins comprise mainly garnet and quartz and resulted from a HP leaching process along fractures in the eclogite during exhumation. Relict peak garnet, phengite, and apatite in this rock system were altered by HP fluids forming characteristic compositional zonings. Zoned garnet in the eclogite records an isothermal exhumation from 3.3 GPa and 665–680 °C. Partial dissolution of garnet and a back incorporation of Mn‐heavy rare earth element (REE)‐Y increased the content of these elements in the altered garnet zone in the veins. Altered phengite is characterized by a Ba‐rich rim. Fluid‐aided alteration reduced the light REE (LREE) contents and produced oriented monazite, calcite, and pyrrhotite inclusions within apatite, reflecting mobilization and redistribution of LREEs, CO32−, Fe, and S between these minerals. The active HP fluid is proposed to have been a Si‐Al‐Na‐Ba‐rich aqueous fluid, as indicated by sodic plagioclase rims around various eclogitic minerals and by the altered phengite composition. Mass balance calculations reveal that LREEs, middle REEs, and Zr‐Hf‐Th‐U were added to and Li, large ion lithophile elements, and Ti‐Nb were removed from the quartz‐garnet veins, requiring a high fluid flux. These findings shed new light on the nature and behavior of HP fluids and highlight their key role in resetting mineral chemistry and mass transfer in subduction zone metamorphic environments. Key Points: Garnet, phengite, and apatite record HP fluid‐aided alteration in an eclogite‐vein system from the Dabie UHP terraneThe active HP fluid is a Si‐Al‐Na‐Ba‐rich aqueous fluid formed closed to the wet solidusA high fluid flux caused considerable element mobility during the vein formation [ABSTRACT FROM AUTHOR]

The mobility of redox sensitive elements such as iron, carbon and sulfur in subduction zone fluids is important for redox transfer between the subducting slab and mantle wedge. However, the speciation of Fe during its mobility in subduction zone fluids at forearc depths is still unclear. Here, we studied the Fe isotope compositions of high-pressure (HP) fluid-metasomatized rocks (Mg-rich leucophyllite and gneiss, which is mineralogically transitional between leucophyllite and metagranite) from the Eastern Alps and found evidence for two distinct types of Fe species during Fe mobility in subduction zone fluids. The protolith of both types of rocks is metagranite, which shows δ56Fe values of 0.12–0.25‰. Compared to the metagranite, the transitional gneiss shows slightly higher Fe 2 O 3t contents, lower Fe3+/∑Fe ratios and significantly lower δ56Fe values of −0.03–0.16‰, whereas the leucophyllite exhibits much lower Fe 2 O 3t contents, comparable or slightly lower Fe3+/∑Fe ratios and generally higher δ56Fe values of up to 0.55‰. These observations indicate that the granitic protolith has experienced two types of fluid metasomatism. Combined with previous results, we infer the mobility of Fe in subduction zone fluids at forearc depths via two kinds of Fe species, Fe2+-(CO 3), and Fe2+-(HS) or Fe2+-Cl. The Fe mobility was dominant in the form of the Fe2+-(CO 3) complex in a carbonate-rich fluid during the formation of transitional gneiss, consistent with reported radiogenic Sr and isotopically light Mg isotope compositions, whereas Fe loss in the form of Fe2+-(HS) or Fe2+-Cl complexes via dissolution of biotite and phlogopite can account for the formation of leucophyllites. According to the tectonic evolution of the Eastern Alps, both types of fluids possibly originated from the dehydration of the sediment-serpentinite mélange produced by the subducting oceanic slab of the Alpine Penninic unit. The diversity of ferrous iron species in the subduction zone fluids at forearc depths probably reflects the variation in the redox properties of fluids derived from carbonate-rich sediment and serpentinite under such conditions. Our results provide an excellent example of tracing Fe mobility with distinct Fe species in subduction zone fluids. [ABSTRACT FROM AUTHOR]

[Display omitted] • Weathering of tetrahedrite-(Hg) ores releases priority pollutant elements. • The genesis and weathering of tetrahedrite-(Hg) in meta -carbonate rocks are studied. • Four stages of supergene weathering of tetrahedrite-(Hg) have been recognized. • Mercury sequestration in cinnabar limits its dispersion into the environment. The Cu-Sb-Hg mineralization of San Giuliano Terme (Monti Pisani, Tuscany, Italy) is characterized by the widespread occurrence of deeply altered tetrahedrite-(Hg) hosted within joints and faults in the Liassic "Calcari ceroidi" Formation. Through a multi-technique approach (optical and scanning electron microscopy, electron microprobe analysis, single-crystal and powder X-ray diffraction, micro-Raman spectroscopy, X-ray fluorescence, fluid inclusion analysis), tetrahedrite-(Hg) and its alteration products have been characterized and data about its genesis and successive supergene weathering have been collected. Tetrahedrite-(Hg) from San Giuliano Terme has the empirical formula Cu 9.92 Ag 0.02 (Hg 1.64 Fe 0.30 Zn 0.04) Σ1.98 (Sb 3.53 As 0.56) Σ4.09 S 12.95 , and is found with scarce gangue minerals represented by calcite, baryte, and very rare fluorite. The mineralization formed from hydrothermal fluids with moderately high salinity (∼17.5 wt% NaCl equiv.) of dominantly metamorphic origin at T ∼ 285 °C. Tetrahedrite-(Hg) is usually fully replaced by a mixture of cinnabar, roméite-group minerals, malachite, and rarely azurite. Based on the modal abundance of the mineralogical constituents and their micro-textures, four stages of supergene weathering of tetrahedrite-(Hg) have been recognized. The alteration stages reflect the progressive ingression of meteoric water into the system, with consequent oxidation of tetrahedrite-(Hg) and the introduction of Ca2+, HCO 3 – and H 2 O, as well as the progressive removal of S, Sb, and Cu. The relative proportions of the supergene minerals in the four alteration stages can be taken as a proxy for the mobility of the main chemical constituents of tetrahedrite-(Hg), three of which (Hg, Sb, and Cu) are priority pollutant metals. Mercury was found to be the least mobile element in the reconstructed geochemical process. In fact, the widespread precipitation of cinnabar in the space formerly occupied by tetrahedrite-(Hg) hinders the dispersion of Hg in the environment, sequestering it in a solid matrix. [ABSTRACT FROM AUTHOR]

In this manuscript, samples of Kupa River sediments were examined using three different extraction agents. The aim of this study was to evaluate the applicability of single extraction procedures to investigate the bioavailability and mobility of major and trace elements (Al, As, Ba, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Pb, S, Si, Sr, Ti, V, and Zn) from river sediment. Two forms of studied elements were evaluated: mobile, the most toxic element form (extraction with 1 M CH3COONH4 and 0.01 M CaCl2) and potentially mobilized form (2 M HNO3 extraction). The estimation of the ecological risk, with the application of the probability distribution of RI (potential ecological risk index) values, is yielded with the help of the Monte Carlo simulation (MCS). Ammonium acetate is proved to be a better extraction agent than calcium chloride. A positive correlation between the content of all extracted elements with nitric acid and the total element content indicates that 2 M HNO3 efficiently extracts all studied elements. Results showed anthropogenic sources of cadmium and copper and high barium mobility. The MCS suggests that risk of Cr, Cu, Ni, Pb, and Zn was low; As and Cd posed a lower and median ecological risk in the studied areas.

The Campiglia Marittima magmatic-hydrothermal system includes a peraluminous granite, its carbonatic host, and skarn. The system evolved generating a time-transgressive exchange of major and trace elements between granite, metasomatic fluids, and host rock. The process resulted in partial metasomatic replacement of the granite and severe replacement of the carbonate host rocks. The fluid activity started during a late-magmatic stage, followed by a potassic–calcic metasomatism, ending with a lower temperature acidic metasomatism. During the late-magmatic stage, B-rich residual fluids led to the formation of disseminated tourmaline–quartz orbicules. High-temperature metasomatic fluids generated a pervasive potassic–calcic metasomatism of the granite, with replacement of plagioclase, biotite, ilmenite, and apatite by K-feldspar, phlogopite–chlorite–titanite, titanite–rutile, and significant mobilization of Fe, Na, P, Ti, and minor HFSE/REE. The metasomatized granite is enriched in Mg, K, Rb, Ba, and Sr, and depleted in Fe and Na. Ca metasomatism is characterized by crystallization of a variety of calc-silicates, focusing along joints into the granite (endoskarn) and at the marble/pluton contact (exoskarn), and exchange of HFSE and LREE with hydrothermal fluids. Upon cooling, fluids became more acidic and fluorine activity increased, with widespread crystallization of fluorite from disequilibrium of former calc-silicates. At the pluton-host boundary, fluids were accumulated, and pH buffered to low values as temperature decreased, leading to the formation of a metasomatic front triggering the increasing mobilization of REE and HFSE and the late crystallization of REE–HFSE minerals. [ABSTRACT FROM AUTHOR]

Crustal recycling at convergent plate boundaries is essential to mantle heterogeneity. However, crustal signatures in the mantle source of basaltic rocks above subduction zones were primarily incorporated in the form of liquid rather than solid phases. The physicochemical property of liquid phases is determined by the dehydration behavior of crustal rocks at the slab-mantle interface in subduction channels. Because of the significant fractionation in incompatible trace elements but the full inheritance in radiogenic isotopes relative to their crustal sources, the production of liquid phases is crucial to the geochemical transfer from the subducting crust into the mantle. In this process, the stability of specific minerals in subducting crustal rocks exerts a primary control on the enrichment of given trace elements in the liquid phases. For this reason, geochemically enriched oceanic basalts can be categorized into two types in terms of their trace element distribution patterns in the primitive mantle-normalized diagram. One is island arc basalts (IAB), showing enrichment in LILE, Pb and LREE but depletion in HFSE such as Nb and Ta relative to HREE. The other is ocean island basalts (OIB), exhibiting enrichment in LILE and LREE, enrichment or non-depletion in HFSE but depletion in Pb relative to HREE. In either types, these basalts show the enhanced enrichment of LILE and LREE with increasing their incompatibility relative to normal mid-ocean ridge basalts (MORB). The thermal regime of subduction zones can be categorized into two stages in both time and space. The first stage is characterized by compressional tectonism at low thermal gradients. As a consequence, metamorphic dehydration of the subducting crust prevails at forearc to subarc depths due to the breakdown of hydrous minerals such as mica and amphibole in the stability field of garnet and rutile, resulting in the liberation of aqueous solutions with the trace element composition that is considerably enriched in LILE, Pb and LREE but depleted in HFSE and HREE relative to normal MORB. This provides the crustal signature for the mantle sources of IAB. The second stage is indicated by extensional tectonism at high thermal gradients, leading to the partial melting of metamorphically dehydrated crustal rocks at subarc to postarc depths. This involves not only the breakdown of hydrous minerals such as amphibole, phengite and allanite in the stability field of garnet but also the dissolution of rutile into hydrous melts. As such, the hydrous melts can acquire the trace element composition that is significantly enriched in LILE, HFSE and LREE but depleted in Pb and HREE relative to normal MORB, providing the crustal signature for the mantle sources of OIB. In either case, these liquid phases would metasomatize the overlying mantle wedge peridotite at different depths, generating ultramafic metasomatites such as serpentinized and chloritized peridotites, and olivine-poor pyroxenites and hornblendites. As a consequence, the crustal signatures are transferred by the liquid phases from the subducting slab into the mantle. Image 1 • The thermal structure of subduction zones changes in both time and space at different depths. • The fractionation of incompatible trace elements is significant during dehydration and melting of crustal rocks. • Crustal signatures are transferred by liquid phases into the mantle source of basaltic rocks. • The geochemical composition of liquid phases is central to that of metasomatites in the mantle wedge. • Crustal metasomatism is the physicochemical mechanism for the geochemical transfer at subduction zones. [ABSTRACT FROM AUTHOR]

Abstract Weathering, as an important process in the earth surface system, can be significantly influenced by tectonics and climates over long time scales. Here, we use mineralogical, petrographic and geochemical data of a paleoweathering profile developed on basement granodioritic rocks of northern Qaidam basin, northern Tibet, to reconstruct early Eocene weathering conditions and to discuss how paleoclimates and tectonics dominated the weathering process. The results indicate that neoformed mineral phases in weathering products are dominated by smectite, and the profile has overwhelmingly low chemical index of alteration values (ca. 51–59) and significantly decreasing micropetrographic index values (from 25.0 to 0.2) from bottom to top. These findings suggest that the basement rocks experienced mild chemical weathering but relatively intensive physical weathering. We favor that non-steady-state weathering, in which mechanical erosion rates compare favorably with rates of chemical weathering, prevailed in northern Tibet during the early Eocene. The weathering conditions were likely an integrated response to active tectonism and dry climates at that time. Furthermore, chemical element mobility evaluation demonstrates that most of large ion lithophile elements and light rare earth elements (LREEs) of granodioritic rocks are quite active during weathering and can be easily leached even under mild chemical weathering conditions. Significant mass loss of Al and LREEs in upper weathered samples probably reflects acidic weathering conditions, which were likely due to extremely high atmospheric CO 2 level during the early Eocene. This study, from the unique perspective of weathering process, suggests that intensive deformation and rapid tectonic erosion occurred in northern Tibet during the early Eocene, as a far-field response to the India-Eurasia collision. It also agrees with warm and relatively dry climates, which were likely attributed to the global greenhouse climates and the Paleogene planetary-wind-dominant climate system in Asia, respectively. Highlights • Mild-chemical, intensive-physical weathering prevailed during the early Eocene. • Smectite dominates the neoformed mineral phase in weathering products. • LILEs and LREEs are greatly leached under mild chemical weathering. • Intense tectonic erosion and dry climates dominated the weathering process. • High atmospheric CO 2 level resulted in acidic weathering conditions. [ABSTRACT FROM AUTHOR]

Highlights • Leaves of an introduced tree species decomposed at a high rate. • Most macroelements decreased in concentration and quantity, nitrogen excepted. • Microelements increased in both concentration and quantity through decomposition. • Macroelements were more mobile than microelements, which tended to be immobilized. Abstract One of the challenges in the restoration of degraded lands is the re-establishment of soil structure and fertility. Novel forests that regenerate on recently abandoned and degraded agricultural lands are among the first biotic systems that begin the process of soil rehabilitation. The rate of litter decomposition and associated element mobility is one of many processes that contribute to the understanding of how ecosystem-level processes restore eroded soils. We studied the stoichiometry of Spathodea campanulata leaves decomposing in novel subtropical moist forests. We found that the speed of leaf decomposition was high (annual decomposition constant of 5.0 to 2.6 or half-life of 51 to 98 days). Spathodea leaf mass loss was particularly fast during the first 16 days of decomposition (half-life of 33 days). Leaf litter was characterized by high chemical quality with low C/N, C/P, and N/P. During the leaf decomposition process, macroelements (N, P, K, Ca, and Mg) were more mobile than microelements (Al, Mn, Fe, and Na). As leaf litter decomposed, nitrogen increased in concentration, the quantity of all macroelements decreased, and microelements tended to increase in both concentration and quantity. Because of the rapid rate of decomposition and high chemical quality of Spathodea leaf litter, it appears that the potential for yielding residual soil organic matter from its leaves is reduced, but this is a tradeoff with the rapid release of elements, which contributes to the high juvenile tree density and primary productivity observed in novel Spathodea forests. [ABSTRACT FROM AUTHOR]

Syros is part of the Attic–Cycladic blueschist belt and consists principally of marbles, schists, and metabasites that have been metamorphosed to the blueschist- to eclogite-facies at about 52 Ma, with a greenschist-facies overprint beginning at about 25 Ma. Distinct, whitish clusters of sub-millimeter-sized grains organized into orthorhombic polyhedral shapes occur in a variety of the blueschists. These clusters are interpreted to be pseudomorphs after lawsonite based on their shape, chemistry, and the presence of rare relict lawsonite in a few of the clusters. A considerable range in observed pseudomorph modes reflects both variety in rock compositions and the extent of greenschist overprinting. Most pseudomorphs contain epidote-group minerals (clinozoisite/epidote), similar to the composition of ideal lawsonite, except for added Fe and lost water. Many contain white mica (phengite, paragonite, muscovite), which requires the addition of K and/or Na to the original lawsonite. In some cases, the pseudomorph is largely mica, so that Ca must have been lost to an epidote mineral, amphibole, or calcite in the matrix. Phengite in the pseudomorphs typically has a lower celadonite content than phengite in the matrix. It appears that the mica has changed its composition by breakdown in the matrix, K diffusion, and regrowth in the pseudomorph. We propose that lawsonite breakdown must be in part driven by the reaction of lawsonite with the celadonite content of phengitic mica in the matrix, to form celadonite-poor (muscovite-rich) white mica in the pseudomorph. The preservation of the lawsonite shape in the pseudomorphs in weakly deformed rocks appears to be due to the relative immobility of Al during the pseudomorphing reactions, with K, Na, and Fe moving to the pseudomorphs and Ca and H2O leaving. The only source of K in these rocks is phengite, which should become less rich in celadonite with an increase in temperature, needed to drive lawsonite breakdown. [ABSTRACT FROM AUTHOR]

Abstract We present a combined mineralogical, chemical, and Sr-Nd isotopic study of hydrothermal alteration effects in near-surface Pleistocene rhyolite sampled at two distinct localities from the Los Azufres geothermal field (LAGF), Mexico. The alteration mineralogy of the near-surface rocks is dominated by silica polymorph minerals (cristobalite, tridymite, opal, and quartz), and kaolinite, showing an intense silicification in most altered samples. In some samples, alteration minerals berlinite, alunite, opal, and wollastonite, are also present. Sulfur (80–28, 300 μg/g) and LOI (1.36–12.18%) contents were used to indicate the intensity of alteration for the LAGF rock samples. The changes were considered as significant when they exceeded the analytical errors. Two main types of chemical and isotopic effects were documented: (1) small loss of both SiO 2 and alkalis represented by one pair of samples, which did not show significant changes in the most major elements, REEs, Nb and Ta negative anomalies, nor in the normalized multiple-element LILE/REE, LILE/HFSE, and REE/HFSE ratio parameters, but indicated significant increase in Al, Fe, Ba, Ga, and Pb; and (2) significant gain of SiO 2 accompanied by loss of alkalis for the rest of the rock samples collected from a different site showed significant decrease of most major elements, all REE concentrations and normalized multiple-element ratio parameters as well as changes in numerous trace element concentrations. During this alteration, the size of the Nb and Ta negative anomalies became smaller as a result of the alteration of the second type. Both types of alteration showed significant changes in 87Sr/86Sr, but generally not in 143Nd/144Nd, probably related to the involvement of highly heterogeneous crust in terms of 87Sr/86Sr. Highlights • The first extensive hydrothermal alteration study of near-surface rhyolite • Significant hydrothermal alteration changes of major and trace elements • Changes in multiple element LILE/REE, LILE/HFSE, and REE/HFSE ratio parameters • Opposite changes in 87Sr/86Sr [ABSTRACT FROM AUTHOR]

Abstract The tennantite-tetrahedrite solid-solution series [called fahlore; (Cu,Ag) 6 Cu 4 (Fe,Zn,Cu,Hg,Cd) 2 (Sb,As,Bi,Te) 4 (S,Se) 13 ] is widespread in many geological environments. Since it incorporates heavy metals and toxic elements, a better understanding of its weathering behaviour and details of its weathering process is important to evaluate environmental risks (emerging mainly from the mobilization of As-Sb-Bi) and local and global metal fluxes in stream waters and oceans. In this study, weathering of Bi-rich members of this mineral group was investigated using microscopy, EMPA, SEM, TEM, LA-ICP-MS, Raman, μXRD, and MLA. Observations reveal a succession of four distinct stages of weathering: During stage 1, irregular tubes within fahlore show an assemblage of nm- to μm-sized roméite group minerals, tripuhyite, crystalline Cu-oxides and Cu-sulfides. Stage 1 textures and secondary sulfides indicate a low redox-potential and a low fluid/rock ratio, typical of cementation zones. Mass balance calculations show that during this stage all Zn and the majority of As and S are released to the weathering fluids. Bismuth is immobile in this stage and Sb and Fe are immobile, if Bi is sufficiently available from fahlore, but both are partly released, if the fahlore did not contain sufficient Bi. During stage 2, amorphous and nano-crystalline arsenates replace fahlore as weathering fronts. Such assemblages indicate a higher redox-potential than in stage 1, typical for oxidation zones. Mass balance calculations reveal that Zn, Sb, S and partially Cu are lost. Arsenic and Bi are immobile. Stage 3 occurs only locally, dissolving former weathering stages and/or precipitating amorphous Cu-arsenates/silicates reflecting processes in micro-compartments, not characteristic for the general weathering process. Stage 4 is characterized by the formation of crystalline Bi-, Cu-, Ba-, Ca- or Al-bearing arsenates and Cu-carbonates, spatially independent of the precursor fahlore. Copper and As originate from older weathering assemblages, whereas many other elements are derived externally (Ca, Ba, Al). This stage reflects the increasing importance of the local host rock and gangue mineralogy, as it is typical in near-surface environments of oxidation zones or on mine dumps, where elements are highly mobile and a high fluid/rock ratio prevails (gossan mineralization). The temporal evolution of fahlore weathering textures reflects the transition from fresh ore to cementation zone, oxidation zone and gossan assemblages in one hand specimen. Thus, one fahlore grain can record the uplift and erosion and the increasing fluid/rock interaction of a weathered ore deposit with time. Tube-like textures similar to the ones observed in stage 1 have been reported from other weathering environments and from a variety of element, oxide, arsenide, and sulfide phases. They also were produced during experimental work in ilmenite. This is clear evidence, that the diffusive process during the first contact with alteration fluids is a basic physical process and that it is not only valid for fahlore. The importance of Bi to stabilize Sb-bearing supergene phases (and thereby for the immobilization of toxic Sb) shown in the present work, may stimulate further investigations on the environmental immobilization of toxic elements by "companion metals" during weathering processes. [ABSTRACT FROM AUTHOR]

The presence of impurities in medicinal products have to be controlled within safety limits from a pharmaceutical quality perspective. This matter is of special significance for those countries and regions where the directives, guidelines, or legislations, which prescribe the rules for the application of some products is quite selective or incomplete. Clay-based hydrogels are quite an example of this matter since they are topically administered, but, in some regions, they are not subjected to well-defined legal regulations. Since hydrogels establish an intimate contact with the skin, hazardous elements present in the ingredients could potentially be bioavailable and compromise their safety. The elemental composition and mobility of elements present in two hydrogels have been assessed. Sepiolite, palygorskite, and natural spring water were used as ingredients. The release of a particular element mainly depends on its position in the structure of the hydrogels, not only on its concentration in each ingredient. As a general trend, elements’ mobility reduced with time. Among the most dangerous elements, whose presence in cosmetics is strictly forbidden by European legal regulations, As and Cd were mobile, although in very low amounts (0.1 and 0.2 μg/100 g of hydrogel, respectively). That is, assuming 100% bioavailability, the studied hydrogels would be completely safe at normal doses. Although there is no sufficient evidence to confirm that their presence is detrimental to hydrogels safety, legally speaking, their mobility could hinder the authorization of these hydrogels as medicines or cosmetics. In conclusion, the present study demonstrates that hydrogels prepared with sepiolite, palygorskite, and Alicún spring water could be topically applied without major intoxication risks.

The relative depletion of high field strength elements (HFSE), such as Nb, Ta and Ti, on normalised trace-element plots is a geochemical proxy routinely used to fingerprint magmatic processes linked to Phanerozoic subduction. This proxy has increasingly been applied to ultramafic-mafic units in Archaean cratons, but as these assemblages have commonly been affected by high-grade metamorphism and hydrothermal alteration/metasomatism, the likelihood of element mobility is high relative to Phanerozoic examples. To assess the validity of HFSE anomalies as a reliable proxy for Archaean subduction, we here investigate their origin in ultramafic rocks from the Ben Strome Complex, which is a 7 km² ultramafic-mafic complex in the Lewisian Gneiss Complex of NW Scotland. Recently interpreted as a deformed layered intrusion, the Ben Strome Complex has been subject to multiple phases of high-grade metamorphism, including separate granuliteand amphibolite-facies deformation events. Additional to bulk-rock geochemistry, we present detailed petrography, and major- and trace-element mineral chemistry for 35 ultramafic samples, of which 15 display negative HFSE anomalies. Our data indicate that the magnitude of HFSE anomalies in the Ben Strome Complex are correlated with light rare earth-element (LREE) enrichment likely generated during interaction with H2O and CO2-rich hydrothermal fluids associated with amphibolitisation, rather than primary magmatic (subduction-related) processes. Consequently, we consider bulk-rock HFSE anomalies alone to be an unreliable proxy for Archaean subduction in Archaean terranes that have experienced multiple phases of high-grade metamorphism, with a comprehensive assessment of element mobility and petrography a minimum requirement prior to assigning geodynamic interpretations to bulk-rock geochemical data. [ABSTRACT FROM AUTHOR]

This study aimed to shed further light on the capacity of macrophytes to translocate, accumulate and bioindicate the levels of trace elements present in contaminated water and sediments. Specifically, this study aimed to find evidence whether translocation, accumulation and bioindication are dependent on the kind of trace element and plant species. To investigate the correlation between trace elements in plants and in the environment, the concentrations of As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, and Zn were analyzed in twenty different wetland plants, and in water and sediments from a wetland area affected by urban and industrial pollutants. Results showed that wetland plants share some common characteristics such as high tolerance to toxic element levels, capacity of phytostabilization and different element concentrations in the various organs. Moreover, element translocation from sediments to roots seems more influenced by the kind of plant species and trace element, whereas translocation across the various organs seems mainly species-specific. No clear patterns of trace element translocation were identified according to plant life forms. [ABSTRACT FROM AUTHOR]

The attenuation of climate changes through substitution of coal with GHG-neutral or low-emission fuels, a replacement of non-renewable resources with renewable ones and reuse of waste materials is being achieved among others by partial or total substitution of coal in power plants with alternative fuels that may affect the composition and leaching behavior of coal fly ash (CFA), and therefore its environmental impact in disposal/reuse sites. A comparison of the most widespread primary alkaline Class F CFA of Sialic type from coal combustion with fly ash from co-combustion of the same coal with process off gas in powerplant boilers (CGFA – coal/gas fly ash) revealed certain reduction of pH, CaO, MgO and Fe 2 O 3, and simultaneous increase of other major and minor constituents, but in particular of almost all trace element contents (by 35% - 2-fold). However, comparative tests of the leaching behavior of both materials as a function of L/S (Liquid/Solid ratio) and extract pH with the use of recently developed US EPA, SW-846 Methods 1316 and 1313 (2012) showed that the mobility of both major and trace elements in both residuals (apart from their properties as cations, oxyanions and amphoteric species) was governed by several factors, among them availability and equilibria constraints, and followed predominantly a similar pattern. Liquid-solid partitioning as a function of L/S showed higher release of Ca, OH, As, Ba, Br, I, Co, Ni, Sb, Pb and W from CFA, and of Al, Na, K, SO 4 , Si, B, Cd, Cr, Hg, Li, Mo, Ti and V from CGFA, Se and Sr showed similar leachability, while Ag, Be, Cu, Fe, Mg, Mn, Tl, Zn, Zr were equally immobile. The decisive factor in element release from CFA and CGFA as a function of pH was the pattern of acid/base neutralization capacity (ANC/BNC) of both materials that in CFA and CGFA appeared to be basically different. Due to the gradual reduction of ANC in CGFA opposite to its sharp depletion in CFA, the majority of elements unstable at acidic pH (Ag, Al, As, Ba, Be, Cd, Cu, Fe, Mn, Ni, Pb, Sb, Si, Ti, Tl, V, W, Zn, Zr) were less susceptible to mobilization from CGFA than from CFA. Along with the lower mobility of a number of elements in the entire (Ca, Mg, Cl, Br, Cr), or neutral/acidic (Fe, Mn, Ni, Sb, PO 4 ), or alkaline range (I, Se, CO 3 ), and similar release of K, SO 4 , Co and Hg, at less developed active surface and interconnected micro-porosity, this makes CGFA from process off gas co-combustion environmentally safer than CFA. [ABSTRACT FROM AUTHOR]

Skarn alteration occurs over a wide range of temperatures and geological settings, and hydrothermal magnetite (a common mineral in skarn) represents a potentially useful temperature and tectonic indicator. Here we describe a new 2D/3D quantitative element mapping approach to evaluate the element mobility of magnetite during skarn alteration/mineralization. Magnetite grains from the giant Beiya Fe-Au skarn deposit (Yunnan, SW China) are either coarse-grained euhedral (hexagonal) with core-rim zoning (type I) or subhedral unzoned (type II) coexisting with (some enclosing) garnet. Concentrations of Na, Mg, Al, Si, Ca, Sr, Cr and Mn in the type I magnetite core and rims are drastically different, which are high in the core and outer rim and low in the inner rim. This suggests fluid geochemical fluctuations, probably led by multiple phases of ore fluid incursions that are common in many world-class skarn deposits. Concentrations of Mg, Al, Si, Ca, Mn and Sr in the garnet are higher than those in type II magnetite. This is likely because the earlier garnet crystallization (during the prograde skarn alteration) had depleted these elements in the later magnetite ore fluids. Both the garnet and the magnetite core are characterized by high Ti concentration. The high Ti concentration in the garnet is governed by the crystal structure, while that of Ti in hydrothermal magnetite is governed by Ti mobility. The 3D-mapping and simulation modeling have shown clear element variation patterns in some magnetite grains that were previously determined to be compositionally homogeneous by spot analysis. Our new 2D/3D-mapping have revealed the presence of mineral inclusions such as garnet and calcite as constrained by the trace element mobility during the replacement of garnet by magnetite, as shown in the euhedral zoned magnetite in garnet pseudomorph. [ABSTRACT FROM AUTHOR]

This paper proposes a simple volume (mass) balancing technique as a means to assess the volume loss and tectonic flattening of mylonitic shear zones. The method involves counting the number of zircon crystals in oriented polished thin sections, analyzed subsequently in the electron microprobe, using the BSEI mode, and a spectrometer setup for detection of the element Zr. Here we present an application to the Roffna gneiss (Eastern Switzerland), a porphyritic granite of Permian origin, which has been metamorphosed and transformed into a phengitic schist under low-grade metamorphic conditions. Mass balances for this material have produced controversial interpretations, in that a first analysis of chemical data of wall rock and mylonite suggested an isochoric mylonitic transition event, while a dramatic volume loss of some 50% in the course this process was inferred after a re-evaluation of the same data. Electron-microscopy of zircon crystals that were retrieved from rocks which had undergone different degrees of deformation revealed only minor alterations and mechanical damage of single grains. This stability of zircon justified the use of single crystals, and in consequence of the element Zr, as passive markers in determining volume (mass) changes during deformation. Results obtained by this method allow us to confirm that the deformation of the Roffna gneiss involved a volume loss of 29 ± 6%, accompanied by chemical alterations. Deformation-induced mobility changes of various elements lead to small gains in Mg and Cr but significant losses Si, Al, Na, Ca, and Sr during the metamorphic event. All other elements, including the REE, underwent no substantial long-range transport. [ABSTRACT FROM AUTHOR]

Chromite deposits associated with layered anorthosite complexes in the Archaean high-grade terranes are rare in the world. The late Archaean Sittampundi Layered Magmatic Complex, Tamil Nadu, India is one of the few such deposits in the world where layers of Fe-Al rich chromites are associated with extremely calcic (An>95) anorthosite. ‘Frozen in’ magmatic mineralogy of the chromitite and the enclosing anorthosite suggest successive crystallization of chromite + clinopyroxene and chromite + clinopyroxene + anorthite from a hydrous Al-rich basaltic melt that was emplaced in a suprasubduction zone setting. Intense deformation and upper amphibolite facies metamorphism at ∼2.45 Ga converted the magmatic assemblages to hitherto unreported hornblende + gedrite + Mg-Al rich spinel ± chlorite bearing assemblages. During metamorphic reconstitution, chromite was pseudomorphically replaced by green spinel in the domains rich in secondary amphiboles. Mass-balance calculation and algebraic analyses of the observed mineralogy suggest that a number of chemical species including chromium became mobile during the formation of spinel pseudomorph in response to infiltration driven metamorphism. Aluminium became mobile in the length scale of chromite grain but remained immobile in the length scale of a thin section. [ABSTRACT FROM AUTHOR]

Permian karstic bauxite and its Quaternary derivative, in western Guangxi, southwestern, South China Block, possess a total tonnage greater than 0.5 billion tons. The primary late Permian karstic bauxite formed in reduced environment in the background of Tethyan accretionary orogenesis. And as one consequence of Cenozoic convergence of the Indian and Eurasia continents, the primary orebody was uplifted, eroded and re-sedimented within Quaternary laterite. The geochemical variation and its controls during the ore transformation from Permian to Quaternary remain poorly understood. Quaternary ore blocks comprise an inner zone of fresh ore, and then it gradually transited through a middle zone to a margin with extensive weathering. One such bauxite block was selected and further subdivided into twenty-three samples for geochemical and mineralogical analysis. The inner and middle zones contain similar mineralogical compositions, dominated by diaspore and amesite, with minor illite, anatase, goethite, pyrite, zircon, and rutile. The margin is composed of diaspore, with small amounts of amesite, boehmite, illite, goethite, anatase, kaolinite, zircon, rutile, and barite. Bauxite in all three zones is composed of mainly Al, Si, Fe, and Ti, and high contents of Zr, Cr, Li, F, S, Zn, V, Sr, Nb, Ba, and REE. Variations in Fe 2+ and Fe 3+ between the three zones were observed. The elements Si, Al, Fe 2+ , Mg, Ba, Cr, F, Li, Ni, Zn, and REE decrease from the core of the ore block outwards, corresponding to an increase in S and Fe 3+ . Depletions in Si, Al, Fe 2+ , Mg, Ba, and Cr were caused by the dissolution of amesite. Most of the Al and Si in amesite were lost during the weathering, and minor retained to form kaolinite. Depletions in Li, Ni, and Zn resulted from changes in the depositional environment between the late Permian and Quaternary. Dissolution of REE-bearing fluorocarbonates resulted in depletions of REE and F. The enrichment of Fe 3+ and S was related to the precipitation of goethite, hematite, and barite in an oxidizing environment, while local enrichment of Ce resulted from the redox change of Ce 3+ → Ce 4+ under the same condition. This shows that the chemical composition of laterite enwrapping the bauxite also took part in Quaternary bauxite transformation. This study shows that the elements migrations during bauxite transformation were influenced by multiple independent factors except for the elemental attributes. [ABSTRACT FROM AUTHOR]

Lateritic bauxite deposits in Suriname rest on a variety of metamorphic, igneous and sedimentary parent rocks. Remnants of multiple planation surfaces with duricrusts that mark the tropical landscape are associated with recurrent episodes of bauxite formation since Late Cretaceous times. Plateau-type bauxites at the highest topographic levels developed on a range of Proterozoic crystalline bedrocks on the northern edge of the Guiana Shield in the country's interior. Weathering profiles of the Bakhuis Mountains, Nassau Mountains, Lely Mountains and Brownsberg largely correspond to the classical sequence of an iron-rich cap on top of a bauxite layer that covers a clay-rich saprolite interval grading into weathered and fresh bedrock. All of the investigated profiles are consistent with in-situ formation of the bauxite and are marked by Si-Al-Fe relationships indicative of medium to strong lateritization, with fresh bedrock being poorly exposed. The bauxite deposits contain gibbsite as the dominant Al-bearing phase, whereas boehmite is locally present in subordinate quantities. Their ferruginous character is expressed by relatively abundant goethite and hematite in the top layers. Kaolinite is the main mineral in the saprolite. Anatase and zircon are the most detected minor phases. The investigated bauxite deposits are generally of a medium-grade (average Al 2 O 3 contents 33–49 wt%) but have variable chemical compositions according to exploration drilling results. Average Fe 2 O 3 contents (13–34 wt%) show inverse relationships with Al 2 O 3 . Despite this overall conformity of the deposits, their thicknesses, textures, mineralogy and geochemistry are distinct in detail, reflecting contrasts in the nature of the parent rock and weathering history. Inter-element relationships show conspicuous differences between SiO 2 -poor (< 5 wt%) upper parts and SiO 2 -richer (> 5 wt%) lower parts of profiles in the Bakhuis Mountains, which developed on high-grade metamorphic pyroxene amphibolites and gneissic granulites. The bauxites of the Nassau Mountains and the other areas in eastern Suriname are marked by higher TiO 2 contents (average > 3.9 wt%) and dissimilar profiles that reflect their development on variety of a low-grade metamorphic volcanic parent rocks. Weathering-induced redistribution of rare-earth and other trace elements affected even the least mobile elements. Differences in distribution patterns between individual profiles can be attributed to a combination of primary compositional differences of parent rocks, the nature and content of accessory mineral phases, and unequal responses to multiple bauxitization cycles. [ABSTRACT FROM AUTHOR]