Trace Element Partitioning Research Articles

Biogeochemistry of macrophytes, sediments and porewaters in thermokarst lakes of permafrost peatlands, western Siberia

The chemical composition of thermokarst lake ecosystem components is a crucial indicator of current climate change and permafrost thaw. Despite high importance of macrophytes in shallow permafrost thaw lakes for control of major and trace nutrients in lake water, the trace element (TE) partitioning between macrophytes and lake water and sediments in the permafrost regions remains virtually unknown. Here we sampled dominant macrophytes in thermokarst lakes of discontinuous and continuous permafrost zones in the Western Siberia Lowland (WSL) and measured major and trace elements in plant biomass, lake water, lake sediments and sediment porewater. All six plant species (Hippuris vulgaris L., Glyceria maxima (Hartm.) Holmb., Comarum palustre L., Ranunculus spitzbergensis Hadac, Carex aquatilis Wahlenb s. str., Menyanthes trifoliata L.) sizably accumulated macronutrients (Na, Mg, Ca), micronutrients (B, Mo, Nu, Cu, Zn, Co) and toxicants (As, Cd). Accumulation of other trace elements, including rare earth elements (REE), in macrophytes relative to pore waters and sediments was highly variable among species. Using miltiparametric statistics, we described the behavior of ТЕ across two permafrost zones and identified several group of elements depending on their sources in the lake ecosystems and their affinity to sediments and macrophytes. Under future climate warming and shifting the permafrost border to the north, we anticipate an increasing uptake of heavy metals and lithogenic low mobile elements such as Ti, Al, Cr, As, Cu, Fe, Ni, Ga, Zr, and REEs by macrophytes in the discontinuous permafrost zone and Ba, Zn, Pb and Cd in the continuous permafrost zone. This may eventually diminish transport of metal micronutrients and geochemical tracers from soils to lakes and rivers and further to the Arctic Ocean.

Mantle–melt partitioning of the highly siderophile elements: New results and application to Mars

AbstractTrace elements and extant and extinct isotopic attributes in Martian meteorites have been used to argue that Mars accreted quickly, differentiated into core and mantle, and established several mantle reservoirs, possibly within 10 Ma of T0. The partitioning of trace elements in the deep mantle has been relatively unstudied, despite the need for such knowledge in understanding magma ocean crystallization and the origin of depleted and enriched mantle reservoirs. The siderophile element composition of the Martian mantle and lithophile isotopic systems such as Sr, Hf, and Nd are thought to record evidence for early metal–silicate equilibrium and deep magma ocean at an intermediate depth and pressure of 800 km or 14 GPa. We have carried out experiments across this pressure range to better understand the mineral/melt partitioning of a wide range of elements. These new data are used to evaluate differentiation models for Mars and to help interpret the available isotopic data. The relatively incompatible nature of Re compared to mildly compatible Os means that the crystallization of a deep magma ocean will lead to residual liquids with superchondritic Re/Os, and solids with subchondritic Re/Os. Such material available in the mantle could be the source of enriched isotopic reservoir that produced shergottites with +γOs values. Slightly subchondritic Re/Os ratios in the crystallizing solids would provide a reservoir that could produce −γOs values. Melting of mixtures of these two enriched and depleted endmembers could explain the Nd‐Os isotopic correlations and systematics of shergottites.

The influence of fractionation of REE-enriched minerals on the zircon partition coefficients

Zircon is widely used to simulate melt generation, migration and evolution within the crust and mantle. The achievable performance of melt modelling generally depends on the availability of reliable trace element partition coefficients (D). However, a large range of DREE values for zircon from natural samples and experimental studies has been reported, with values spanning up to 3 orders of magnitude. Unfortunately, a gap of knowledge on this variability is evident. In this study we model the crystallization processes of common REE-bearing minerals from granitic melts and show that the measured zircon DREE would be elevated if there is crystallization of REE-enriched minerals subsequent to zircon. Nevertheless, compared to zircon DREE values measured from experimental studies, this mechanism appears to have a less significant influence on those from natural granite samples since the quantity of crystallized REE-enriched minerals is very low in natural magmatic systems and/or most of them crystallize prior to zircon. Combined with recently published studies, this work supports that analysis of natural zircon/host groundmass pairs provides more robust DREE values applicable to natural systems than those measured from experimental studies, which can be used to constrain the provenance of detrital zircons.

Diagnosing open-system magmatic processes using the Magma Chamber Simulator (MCS): part II\u2014trace elements and isotopes

The Magma Chamber Simulator (MCS) is a thermodynamic model that computes the phase, thermal, and compositional evolution of a multiphase–multicomponent system of a Fractionally Crystallizing resident body of magma (i.e., melt ± solids ± fluid), linked wallrock that may either be assimilated as Anatectic melts or wholesale as Stoped blocks, and multiple Recharge reservoirs (RnASnFC system, where n is the number of user-selected recharge events). MCS calculations occur in two stages; the first utilizes mass and energy balance to produce thermodynamically constrained major element and phase equilibria information for an RnASnFC system; this tool is informally called MCS-PhaseEQ, and is described in a companion paper (Bohrson et al. 2020). The second stage of modeling, called MCS-Traces, calculates the RASFC evolution of up to 48 trace elements and seven radiogenic and one stable isotopic system (Sr, Nd, Hf, 3xPb, Os, and O) for the resident melt. In addition, trace element concentrations are calculated for bulk residual wallrock and each solid (± fluid) phase in the cumulate reservoir and residual wallrock. Input consists of (1) initial trace element concentrations and isotope ratios for the parental melt, wallrock, and recharge magmas/stoped wallrock blocks and (2) solid-melt and solid–fluid partition coefficients (optional temperature-dependence) for stable phases in the resident magma and residual wallrock. Output can be easily read and processed from tabulated worksheets. We provide trace element and isotopic results for the same example cases (FC, R2FC, AFC, S2FC, and R2AFC) presented in the companion paper. These simulations show that recharge processes can be difficult to recognize based on trace element data alone unless there is an independent reference frame of successive recharge events or if serial recharge magmas are sufficiently distinct in composition relative to the parental magma or magmas on the fractionation trend. In contrast, assimilation of wallrock is likely to have a notable effect on incompatible trace element and isotopic compositions of the contaminated resident melt. The magnitude of these effects depends on several factors incorporated into both stages of MCS calculations (e.g., phase equilibria, trace element partitioning, style of assimilation, and geochemistry of the starting materials). Significantly, the effects of assimilation can be counterintuitive and very different from simple scenarios (e.g., bulk mixing of magma and wallrock) that do not take account phase equilibria. Considerable caution should be practiced in ruling out potential assimilation scenarios in natural systems based upon simple geochemical “rules of thumb”. The lack of simplistic responses to open-system processes underscores the need for thermodynamical RASFC models that take into account mass and energy conservation. MCS-Traces provides an unprecedented and detailed framework for utilizing thermodynamic constraints and element partitioning to document trace element and isotopic evolution of igneous systems. Continued development of the Magma Chamber Simulator will focus on easier accessibility and additional capabilities that will allow the tool to better reproduce the documented natural complexities of open-system magmatic processes.

The Role of Blueschist Stored in Shallow Lithosphere in the Generation of Postcollisional Orogenic Magmas

AbstractIn regions with small ocean plates and continental blocks, such as the Mediterranean in the Cenozoic and modern Indonesia, many blueschists may be stored at shallow depth in the mantle lithosphere that is newly formed during the amalgamation of small continental blocks and oceans. Melting of these blueschists at low pressures in the mixed lithosphere of this type during postcollisional relaxation may be involved in the generation of postcollisional orogenic magmas. Here, we have conducted a series of melting experiments on three blueschist samples with differing protoliths at 800–850°C, 2 GPa to investigate phase relations, mineral compositions, and trace element partitioning (using laser ablation‐inductively coupled plasma‐mass spectrometry [LA‐ICP‐MS]/nanoscale secondary ion mass spectrometry [NanoSIMS]), including the first results for clinozoisite. Dacitic/rhyolitic melts (SiO2 60 to 66 wt%) containing ~13 wt% volatiles are produced in all runs. Mn‐rich and Mn‐poor almandine garnets exhibit distinct rare earth element (REE) distribution patterns, while Mn‐rich garnets are effective preconcentrators of heavy REEs (HREEs) for later metamorphic processes. Melts produced from fluid‐affected blueschists of terrigenous origin show the most large‐ion lithophile element (LILE) enrichment, whereas those from terrigenous blueschists with no fluid history exhibit the lowest K/Th and Ba/Th and strongest Ce/Pb and Nb/U fractionations. Melts of blueschists derived from mid‐ocean ridge basalt (MORB) have relatively consistent, MORB‐like Ba/Th and Nb/U (~3) but the lowest Ce/Pb ratios (3.3). V/Sc and Zr/Hf ratios remain constant at ≥850°C regardless of the origin of the blueschist. Dehydration melting in new mantle lithosphere where blueschist is stored at shallow depth will significantly affect trace element behavior and should be considered carefully when examining chemical cycling and magmatism in postcollisional orogenic settings.

Trace and major element incorporation into amorphous calcium carbonate (ACC) precipitated from seawater

Amorphous calcium carbonate (ACC) has been identified or inferred to exist in many groups of marine organisms that produce biominerals widely used as geochemical archives (e.g. foraminifera, molluscs, echinoderms). However, little is known about trace element incorporation into ACC, and thus it is not understood how precipitation through an ACC precursor might impact the fidelity of climate proxies and biomineralisation models built on the skeletal geochemistry of these marine calcifiers. To address this, we investigated the incorporation of Li, B, Na, Mg, Mn, Sr, Ba, and U into inorganic amorphous calcium magnesium carbonates precipitated from seawater under a variety of different carbonate chemistries, Mg/Ca ratios, and in the presence of aspartic and glutamic acid, two of the most common intracrystalline amino acids found in foraminifera and corals. ACC is highly enriched in most of these trace elements relative to the crystalline carbonates yet similar in some respects in terms of the factors influencing trace element partitioning. For example, ACC B/Ca is sensitive to the carbonate system, whilst Mg/Ca and Sr/Ca are largely a function of their respective ratio in seawater. In general, we find that most of the variance in the distribution coefficients of the other trace elements can be explained by some combination of the seawater carbonate chemistry and the seawater or ACC Mg/Ca ratio.

Trace element partitioning between pyrochlore, microlite, fersmite and silicate melts

We present experimentally determined trace element partition coefficients (D) between pyrochlore-group minerals (Ca2(Nb,Ta)2O6(O,F)), Ca fersmite (CaNb2O6), and silicate melts. Our data indicate that pyrochlores and fersmite are able to strongly fractionate trace elements during the evolution of SiO2-undersaturated magmas. Pyrochlore efficiently fractionates Zr and Hf from Nb and Ta, with DZr and DHf below or equal to unity, and DNb and DTa significantly above unity. We find that DTa pyrochlore-group mineral/silicate melt is always higher than DNb, which agrees with the HFSE partitioning of all other Ti–rich minerals such as perovskite, rutile, ilmenite or Fe-Ti spinel. Our experimental partition coefficients also show that, under oxidizing conditions, DTh is higher than corresponding DU and this implies that pyrochlore-group minerals may fractionate U and Th in silicate magmas. The rare earth element (REE) partition coefficients are around unity, only the light REE are compatible in pyrochlore-group minerals, which explains the high rare earth element concentrations in naturally occurring magmatic pyrochlores.

Modelling garnet-fluid partitioning in H2O-bearing systems: a preliminary statistical attempt to extend the crystal lattice-strain theory to hydrous systems

Accurate geochemical models of magmatic processes require an understanding of crystal-melt partitioning of trace elements. Many major igneous processes at different tectonic environments in Earth occur in the presence of garnet as a residual phase. Since the pioneering crystal lattice-strain model, several attempts have been made to quantify garnet-melt partitioning coefficients over a wide range of conditions. However, high pressure high-temperature experimental data demonstrate distinct differences in partitioning determined at anhydrous conditions and partitioning determined in the presence of H2O. In this study, we present for the first time a constraint on the partitioning of REE, Y, and Sc between garnet and hydrous fluids as a function of the water content in the fluid phase. We analysed published hydrous experimental partitioning data using different statistical methods and modelled key parameters in the crystal lattice strain model (r0, D0, and E). We show a robust correlation between r0, temperature and garnet-fluid partitioning of Mg. We further show that D0 can be predicted using the garnet-fluid partitioning of Fe and that E can be predicted using various parameters describing the fluid phase. We validate and illustrate the ability to predict partitioning of REE in H2O-bearing systems using major element analysis of garnet and fluid only. Consequently, our statistical model paves the way to integrate thermodynamic models based on major element chemical equilibria with trace element studies on hydrous magmatic systems, allowing a description of the transfer of key trace elements in more realistic conditions.

The partitioning behavior of trace elements in subduction zones: Advances and prospects

The partitioning behavior of trace elements is of key importance for understanding the geochemical process and material cycle mechanism in subduction zones. This paper focuses on the advances and prospects on the studies of trace element partitioning in subduction zones from the following four aspects. (1) The properties of fluids derived from subducting slabs and their ability in element transport. How slab-derived solute-rich fluids and supercritical fluids are formed and what the roles and key control factors of these fluids are in transferring of elements (especially the high field strength elements) from slab to wedge are discussed. We point out that the detailed investigations of supercritical fluids may provide a new perspective for the element migration mechanism, material cycle process, arc magma genesis and so on. (2) The behavior of transition elements during mantle wedge melting. The behavior of the first row transition elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) in the mantle partial melting process is compatible or incompatible, depending on residual mineral assemblage and physicochemical conditions. The partitioning behavior of the elements such as Sc, Ti, Co, Ni and Zn whose valence states do not change in the melting process mainly depends on the residual mineral assemblage and temperature, whereas the partitioning behavior of the multivalent elements such as V and Fe is also the function of oxygen fugacity (fO2) in addition to mineral assemblage and temperature. Therefore, the partitioning behavior of transition elements has important applications in tracing lithologic inhomogeneity and fO2 of the mantle wedges. (3) The specificity of element partitioning behavior during arc magma evolution. Garnet has Dy/Yb partitioning behavior different from amphibole, and rutile has Nb/Ta partitioning behavior different from amphibole. Dy/Yb and Nb/Ta partitioning differences for these minerals enable to distinguish the specific evolution process of arc magmas. The Dy/Yb and Nb/Ta generally decrease with the increase of SiO2 in arc magmas, indicating that amphibole fractionation should be the most important during arc magma differentiation. (4) The behavior of sulfur and chalcophile elements and porphyry metallogeny. In subduction zones, the behavior of chalcophile elements such as Cu and Au is controlled by sulfide and fluid. Therefore, the stability of sulfide, the time at which the fluid exsolves from the melt relative to sulfide saturation, the fluid/sulfide mass ratio and fluid/melt Cu and Au partition coefficients in intermediate-felsic magma- H2O systems are especially important in understanding Cu and Au enrichment in magma-hydrothermal processes. Intermediate-felsic magmas mainly originate from the differentiation of arc magmas at lower crustal reservoirs, and thus the fluid exsolution from the lower crustal reservoirs and the fluid/melt and fluid/sulfide partition coefficients of Cu and Au should be the keys to understanding quantitatively how Cu and Au are migrated from the deep crust to the shallow site of mineralization.

Highly reduced accretion of the Earth by large impactors? Evidence from elemental partitioning between sulfide liquids and silicate melts at highly reduced conditions

The Earth may have formed at very reducing conditions through the accretion of (a) large reduced and differentiated impactor(s). Segregation of Fe-S liquids within these bodies would have left a geochemical mark on the mantles of reduced impactors and on the proto-Earth’s mantle. Here, we study the geochemical consequences of highly reduced accretion of the Earth by large impactors. New insights into the partitioning of trace elements between Fe-S liquid and silicate melt at (highly) reduced conditions (ΔIW = −5 to +1) were obtained by performing 21 high pressure experiments at 1 GPa and 1683–2283 K. The observed Fe-S liquid-silicate melt partitioning behavior is in agreement with thermodynamic models that predict a significant role for O in Fe-S liquid and S in the silicate melt.The experimental results were combined with literature data to obtain new and/or revised thermodynamic parameterizations that quantify the effects of composition and redox state on the elemental distribution between Fe-S liquids and highly reduced silicate melts. The results were used to assess which elements would most likely retain the geochemical signature of accretion of reduced impactors. Under the assumption of instantaneous core merging, impact delivery to the proto-Earth’s mantle was found to be significant (>10% of present-day BSE concentrations) only for S, Zn, Se, Te and Tl, whereas the abundances of the other elements remain largely unaffected.The results also show that present-day BSE S/Se, Se/Te, Tl/S and potentially In/Zn as well as their absolute abundances are inconsistent with their delivery by (a) large, highly reduced chondritic differentiated impactor(s) during terrestrial accretion. Continued core-mantle equilibration in the proto-Earth, volatility-related loss and/or post-accretion sulfide liquid segregation in the terrestrial magma ocean would further increase or not affect these discrepancies. We conclude that a significant contribution of (a) large (>10% of Earth’s mass) reduced and differentiated chondritic impactor(s) during accretion of the Earth is not reflected in the present-day S, Zn, Se, Te and Tl systematics of the terrestrial mantle. This suggests that significant overprinting of the primordial BSE S/Se, Se/Te and S/Tl signature could have occurred and/or (2) that the S/Se and Se/Te ratios were set by accretion of more oxidised CI-like materials.

On a synthesis of crystal population dynamics and trace element partitioning models: A mechanism for zoning in minerals

Crystal zoning is considered in the context of the evolution of a population of crystals. Crystal size distribution (CSD) theory provides an important framework and constraints that are applied in a numerical model of crystal nucleation and growth in an infinite half-sheet which proxies for a sill. The CSD/crystal population approach is combined with a relatively simple principle of trace element (TE) partitioning for batch crystallization. A model of crystal nucleation and growth that is applied to a constrained volume of magma is modified by the addition of a co-precipitating phase and TE modeling. The coprecipitating phase does not consume the TE and so the TE's concentration in the residual liquid increases. Thus the primary phase for which the TE is compatible incorporates more as it grows. A single partition coefficient value is used and is held constant. One crystal in the much larger, evolving population of crystals is tracked and TE concentration in the crystal vs. time is recorded as the crystal grows. In general, TE concentration within the crystal initially decreases while only the primary phase is present and then begins to increase in that crystal when the second/coprecipitating phase appears. For the relatively short solidification interval utilized in the modeling, one half-cycle of oscillation: high concentration to low to high, or normal to reverse zoning, is demonstrated. Beyond the TE's partition coefficient, the presence and magnitude of zoning is dependent upon the time the second phase begins within the solidification interval and the mass proportion of crystallization of primary phase to second phase—which is held constant throughout the remainder of solidification once the second phase appears. The model, as currently implemented, is based solely on thermal and mass balances. A multi-faceted crystallization history, one involving, e.g., more complicated phase equilibria, crystal fractionation, convection, and magma mixing would expose the tracked crystal to changing surroundings such that the mass balance mechanism that yielded the half-cycle of zoning obtained here would perhaps continue to yield oscillatory zoning.

Isotopic analyses of clinopyroxenes demonstrate the effects of kimberlite melt metasomatism upon the lithospheric mantle

The trace element and radiogenic isotope systematics of clinopyroxene have frequently been used to characterise mantle metasomatic processes, because it is the main host of most lithophile elements in the lithospheric mantle. To further our understanding of mantle metasomatism, both solution-mode Sr-Nd-Hf-Pb and in situ trace element and Sr isotopic data have been acquired for clinopyroxene grains from a suite of peridotite (lherzolites and wehrlites), MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside), and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks from the Kimberley kimberlites (South Africa). The studied mantle samples can be divided into two groups on the basis of their clinopyroxene trace element compositions, and this subdivision is reinforced by their isotopic ratios. Type 1 clinopyroxene, which comprises PIC, wehrlite, and some sheared lherzolite samples, is characterised by low Sr (~100–200 ppm) and LREE concentrations, moderate HFSE contents (e.g., ~40–75 ppm Zr; La/Zr < 0.04), and restricted isotopic compositions (e.g., 87Sr/86Sri = 0.70369–0.70383; εNdi = +3.1 to +3.6) resembling those of their host kimberlite magmas. Available trace element partition coefficients can be used to show that Type 1 clinopyroxenes are close to being in equilibrium with kimberlite melt compositions, supporting a genetic link between kimberlites and these metasomatised lithologies. Thermobarometric estimates for Type 1 samples in this study indicate equilibration depths of 135–160 km within the lithosphere, thus showing that kimberlite melt metasomatism is prevalent in the deeper part of the lithosphere beneath Kimberley. In contrast, Type 2 clinopyroxenes occur in MARID rocks and coarse granular lherzolites in this study, which derive from shallower depths (<135 km), and have higher Sr (~350–1000 ppm) and LREE contents, corresponding to higher La/Zr of > ~ 0.05. The isotopic compositions of Type 2 clinopyroxenes are more variable and extend from compositions resembling the “enriched mantle” towards those of Type 1 rocks (e.g., εNdi = −12.7 to −4.4). To constrain the source of these variations, in situ Sr isotope analyses of clinopyroxene were undertaken, including zoned grains in Type 2 samples. MARID and lherzolite clinopyroxene cores display generally radiogenic but variable 87Sr/86Sri values (0.70526–0.71177), which are correlated with Sr contents and La/Zr ratios, and which might be explained by the interaction between peridotite and melts from different enriched sources within the lithospheric mantle. Most notably, the rims of these Type 2 clinopyroxenes trend towards compositions similar to those of the host kimberlite and Type 1 clinopyroxene from PIC and wehrlites. These results are interpreted to represent clinopyroxene overgrowth during late-stage (shortly before/during entrainment) metasomatism by kimberlite magmas. Our study shows that a pervasive, alkaline metasomatic event caused MARID to be generated and harzburgites to be converted to lherzolite in the lithospheric mantle beneath the Kimberley area, which was followed by kimberlite metasomatism during Cretaceous magmatism. This latter event is the time at which discrete PIC, wehrlite, and sheared lherzolite lithologies were formed, and MARID and granular lherzolites were partly modified.

Trace element partitioning between clinopyroxene and alkaline magmas: parametrization and role of M1 site on HREE enrichment in clinopyroxenes

Trace element partitioning between minerals and liquids provides crucial constraints on igneous processes. We quantified trace element concentrations in clinopyroxene (Cpx) phenocrysts and their phonolite melt inclusions from the 2007–08 eruption of Oldoinyo Lengai (Tanzania), and report Cpx-melt partition coefficients (D) and corresponding partitioning equations for rare earth elements (REE) and high field strength elements (HFSE) in alkaline magmas. Heavy REE (HREE: Er, Tm, Yb, Lu) are enriched relative to middle REE in alkaline Cpx and display a specific partitioning behavior that is characteristic of alkaline systems. HFSE (Ti, Zr, Hf) and HREE have similar D values (DHf = 0.25; DLu = 0.4) that are significantly higher than MREE (DSm = 0.06). High DHREE/DMREE are strongly correlated with the high values of DZr and DHf relative to the low DMREE values. In this study, REE partitioning between phonolite melt and Cpx is not consistent with standard models assuming incorporation of all REE in the Cpx M2 site, but rather highlights HREE substitution in both the M1 and M2 sites. Here we highlight the preferential incorporation of HREE in the VI-coordinated M1 site, whereas light REE and MREE remain mostly distributed in the VIII-coordinated M2 site. REE partitioning is strongly dependent on Cpx chemistry: the ideal ionic radius and HREE incorporation in the M1 site increase with increasing Fe3+ content and decrease with increasing Mg2+ and AlVI content. In our study, we focus on alkaline evolved magmas, and update existing models to obtain adequate DHREE for alkaline evolved melts. We provide equations to quantify REE and HFSE partitioning, and HREE enrichment in Cpx that are based on Cpx major element composition and temperature. We propose a new model based on the lattice strain approach that predicts HREE partitioning between Cpx and alkaline magmas. The knowledge of the melt composition or of the trace element contents is not required to obtain DREE from the new model. An improved parameterization of HFSE partitioning between Cpx and phonolite and trachy–phonolite melts is also provided herein. We discuss the potential implications of the new data on our understanding of REE deposits that are commonly associated with igneous alkaline complexes.

Partitioning and mixing behaviour of trace elements at the Isonzo/Soča River mouth (Gulf of Trieste, northern Adriatic Sea)

Estuaries are unique water systems and represent a vital link between land and sea. River transported contaminants, among which trace elements are of major concern, are subjected to a variety of physical, chemical and biogeochemical processes in the estuarine mixing zone.The Isonzo/Soča River is the main source of freshwater into the Gulf of Trieste (northern Adriatic Sea) and is known as the primary source of Hg due to long-term cinnabar (HgS) extraction from the Idrija mining district (Slovenia). Mercury distribution, cycling and speciation have been intensively studied at the Isonzo/Soča River mouth. Still, little information is currently available regarding other trace elements (As, Co, Cu, Cs, Cr, Fe, Ni, Mn, Pb and Zn). Indeed, this research aims to evaluate trace element occurrence and partitioning behaviour among suspended particulate matter (>0.45 μm), colloidal material (0.45 μm – 10 kDa) and the truly dissolved fraction (<10 kDa) at the mouth of the Isonzo/Soča River.Generally, trace elements are mainly associated with suspended particulate matter, which represents their main effective vehicle to coastal environments. In addition, dilution effects between riverine and marine particles are responsible for the decrease in particulate trace element concentrations along the water column. Mercury was notably present in winter in the freshwater, as expected under conditions of high river discharge. As opposed to other trace elements, particulate Mn was found to be high in the marine water, particularly in summer when high water temperatures could promote oxidation and precipitation processes. The Isonzo/Soča River mouth is characterised by a strong salinity gradient and geochemical processes appear to affect trace element partitioning behaviour. In this context, Fe, Mn and Cu were found to be mainly associated with the suspended particles and displayed the highest concentration in the colloidal material. Conversely, the truly dissolved fraction prevailed for As and Cs, which are often present in ionic dissolved forms in natural water systems.

Major and trace element partitioning between majoritic garnet, clinopyroxene, and carbon dioxide-rich liquid in model carbonated peridotite at 10 GPa and interpretations of the element chemistry of majoritic garnet inclusions in diamonds from the subcontinental mantle of Brazil and Guinea

Experimentally determined major and trace element partition coefficients between majoritic garnet, clinopyroxene, and carbon dioxide-rich liquid are reported at 10 GPa and 1800 °C in a model carbonated peridotite composition in the system CaO-MgO-Al2O3-SiO2-CO2. Besides majoritic garnet, the liquid coexists with forsterite, orthopyroxene, and clinopyroxene, making melting phase relations invariant at fixed pressure and temperature conditions. Partition coefficients span a wide range of values - for instance, Sr, Nb, Ba, La, and Ce are highly incompatible in majoritic garnet, while Ca, Y, Nb, and Ho are moderately incompatible, and Lu, Si, Al, and Mg are compatible. Strong fractionation of light rare earth elements (e.g., La, Ce, Nd, Sm) and high field strength elements (e.g., Nb, Ta, Zr, Hf, Th) is seen between majoritic garnet and liquid. The experimentally determined partitioning values are used to calculate compositions of melts in equilibrium with majoritic garnet inclusions in diamonds from select localities in Brazil and Guinea. The calculated melts largely straddle those between documented carbonatites, kimberlites, and alkali basalts, low-degree mantle melting products from carbonated peridotite. This resemblance firmly suggests that majoritic garnet inclusions in diamonds from Brazil and Guinea can simply be interpreted as precipitates from such melts, thereby offering an alternative to the hypothesis that the element chemistry of such inclusions in diamonds can largely, and sometimes only, be ascribed to subducted oceanic crust, and further that, fusion of this crust may limit the terrestrial 'carbon recycling' at depths much beyond corresponding to those of Earth's transition zone.

Flue Gas Desulfurization Wastewater Composition and Implications for Regulatory and Treatment Train Design.

The U.S. Environmental Protection Agency is currently revising its regulations on trace element discharges from flue gas desulfurization (FGD) wastewater. In this work, we expand a predictive model of trace element behavior at coal-fired power plants (CFPPs) to estimate the trace element concentration of FGD wastewater at the plant level. We demonstrate that variation in trace element concentrations in FGD wastewater can span several orders of magnitude and is a function of both coal rank and installed air pollution control devices. This conclusion suggests that the benefits and costs of FGD wastewater treatment for the median plant will poorly describe the actual benefits and costs over the full range of existing CFPPs. Our model can be used to identify different "classes" of CFPPs for future regulatory and technology development efforts and to evaluate the robustness of proposed treatment technologies in light of large intraplant variability. The model can also elucidate new compliance pathways that exploit empirical and mechanistic relationships between coal concentration, trace element partitioning, and FGD wastewater composition.

Experimental Partitioning of Trace Elements into Schreibersite with Applications to IIG Iron Meteorites.

Some of the defining characteristics of the IIG iron meteorite group are their high bulk P contents and massive, coarse schreibersite, which have been calculated to make up roughly 11-14 wt% of each specimen. In this study, we produced two datasets to investigate the formation of schreibersites in IIG irons: measurements of trace elements in the IIG iron meteorite Twannberg and experimental determinations of trace element partitioning into schreibersite. The schreibersite-bearing experiments were conducted with schreibersite in equilibrium with a P-rich melt and with bulk Ni contents ranging from 0-40 wt%. The partitioning behavior for the 20 elements measured in this study did not vary with Ni content. Comparison of the Twannberg measurements with the experimental results required a correction factor to account for the fact that the experiments were conducted in a simplified system that did not contain a solid metal phase. Previously determined solid metal/P-rich melt partition coefficients were applied to infer schreibersite/solid metal partitioning behavior from the experiments, and once this correction was applied, the two datasets showed broad similarities between the schreibersite/solid metal distribution of elements. However, there were also differences noted, in particular between the Ni and P contents of the solid metal relative to the schreibersite inferred from the experiments compared to that measured in the Twannberg sample. These differences support previous interpretations that subsolidus schreibersite evolution has strongly influenced the Ni and P content now present in the solid metal phase of IIG irons. Quantitative attempts to match the IIG solid metal composition to that of late-stage IIAB irons through subsolidus schreibersite growth were not successful, but qualitatively, this study corroborates the striking similarities between the IIAB and IIG groups, which are highly suggestive of a possible genetic link between the groups as has been previously proposed.

Partitioning of V and 19 other trace elements between rutile and silicate melt as a function of oxygen fugacity and melt composition: Implications for subduction zones

AbstractVanadium is a multivalent element that can speciate as V2+, V3+, V4+, and V5+ over a range of geologically relevant oxygen fugacities (fO2). The abundance of V in planetary materials can be exploited as a proxy for fO2 when its partitioning behavior is known. The mineral rutile (TiO2) is an important carrier of the high field strength elements Nb and Ta in the solid Earth, but it can also incorporate substantial quantities of vanadium (up to ~2000 ppm; e.g., Zack et al. 2002). However, little work has been done to systematically investigate how the partitioning of V in rutile-bearing systems changes as a function of both fO2 and composition. We measured the partitioning of V and 19 other trace elements (Sc, Cr, Y, Zr, Nb, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, Lu, Hf, and Ta) between rutile and three silicate melt compositions equilibrated at 1 atm pressure, 1300 °C and fO2 values from two log units below the quartz-fayalite-magnetite oxygen buffer (QFM-2) to air (QFM+6.5). Rutile/melt partition coefficients (DVrt/melt) change dynamically over an eight-log unit range of fO2 and are greatest at fO2 = QFM-2 in all compositions. Vanadium solubility in rutile declines continuously as fO2 increases from QFM-2 and approaches unity in air. Trace-element partitioning between rutile and melt is also correlated with melt composition, with the greatest values of Drt/melt measured in the most polymerized melt systems containing the least TiO2. We do not find any circumstances where V becomes incompatible in rutile. Our results indicate that rutile is a considerable sink for V at terrestrial fO2 values and will contribute to the retention of V in refractory slab residues in subduction zones. In agreement with previous work, we find that DTart/melt&amp;gt;DNbrt/melt under all conditions investigated, suggesting that rutile fractionation does not lead to low Nb/Ta ratios in Earth's continental crust.

Polybaric/polythermal magma transport and trace element partitioning recorded in single crystals: A case study of a zoned clinopyroxene from Mt. Etna

We present elemental maps and intra-crystal compositional profiles conducted on a representative clinopyroxene phenocryst from the 1974 eccentric lava flows at Mt. Etna volcano (Sicily, Italy). The eruption was fed by deep-seated and primitive magmas ascending through pathways bypassing the central volcanic conduits. These magmas show MgO and Cr contents higher (and REE + Y lower) than those characterizing younger and more evolved eruptions, albeit the bulk rock compositions of both primitive and more evolved products are invariably classified as trachybasalts in the TAS (total alkali vs. silica) diagram. Mafic recharge episodes are recorded by the complex textural features of the clinopyroxene, with a subrounded core enclosed within a concentrically zoned mantle. The core is enriched in Mg + Fe2++Na and depleted in Fe3++Ca relative to the mantle. The jadeite (Jd) component decreases from core to mantle and is counterbalanced by higher Ca-Tschermak (CaTs) contents, as the number of TAl cations in tetrahedral coordination increases. The Jd-rich core incorporates high proportions of rare earth elements and Y (REE + Y) and low concentrations of high field strength elements (HFSE) and transition elements (TE, such as Ni, Cr and Sc), whereas the opposite occurs for the CaTs-rich mantle. The decoupling of REE + Y and HFSE argues against simple changes in melt composition and indicates an additional mechanism driving trace element zonations. Thermobarometric calculations indicate that the early-formed Jd-rich core equilibrated with the host magma at mantle depths (750–950 MPa and 1190–1210 °C), whereas the later CaTs-rich mantle formed at shallower crustal levels (400–700 MPa and 1150–1180 °C) after magma recharge. Quantitative modeling of apparent cation partitioning between clinopyroxene and melt (Di) indicates that DHFSE increase from the Jd-rich core to the CaTs-rich mantle. In contrast, DREE+Y increase up to one order of magnitude at the Jd-rich core due to the enhanced stability of an Na0.5REE + Y0.5MgSiO6 end-member. We infer that compositional changes in clinopyroxene due to the different P-T conditions of the plumbing system may control the concentrations of REE + Y in residual melts derived after partial crystallization and differentiation of primitive magmas, such as those feeding the 1974 eccentric eruption. On this basis, we use DREE+Y measured across the core-mantle interface to constrain the geochemical evolution of recent 2000–2013 magmas at Mt. Etna volcano by Rayleigh fractional crystallization. Results indicate that magma dynamics proceed via a stepwise polybaric-polythermal process accounting for 1) crystallization of Jd-rich clinopyroxenes at high-P, high-T conditions, 2) upward migration of crystal-bearing magmas due to replenishment phenomena with input of fresh magmas and 3) crystallization of CaTs-rich clinopyroxene in low-P, low-T reservoirs. The resulting total amount (~40 vol%) of clinopyroxene fractionated agrees with geophysical data suggesting the presence of highly crystalline magmatic bodies at shallow to intermediate crustal levels below Mt. Etna.

Indium in polymetallic mineralisation at the Gierczyn mine, Karkonosze-Izera Massif, Poland: results of EPMA and LA-ICP-MS investigations

Cassiterite and base-metal mineralisation from the Gierczyn mine on the Karkonosze-Izera Massif, Poland has been studied using electron microprobe and LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) techniques in order to determine the content of indium in the ore minerals. The main carriers of this element are sphalerite (up to 433 µg/g of In), chalcopyrite (up to 117 µg/g of In) and cassiterite (up to 0.02 wt.% In). Trace element contents of sulphides, especially Ga in chalcopyrite intergrown with sphalerite in comparison with chalcopyrite without sphalerite, may indicate metamorphic re-equlibration and suggests that the ore minerals might recrystallized and underwent metamorphism in conditions of greenschist/amphibolite facies. Although the deposits in the Stara Kamienica Schist Belt are not of economic value, they can contribute to better understanding of the relations between trace element partitioning and the formation of ore minerals.