Partitioning Behavior Of Trace Elements Research Articles

Trace element partitioning in silica-undersaturated alkaline magmatic systems

Alkaline magmatism is an important chemical end-member of magmatic activity that typically occurs in response to small volume melting of asthenospheric- and/or lithospheric mantle material in intra-continental settings. Understanding trace element partitioning and phase equilibria during alkaline magmatism can therefore provide constraints on intra-continental geodynamic settings. However, the partitioning of trace elements between alkaline melts and their dominant equilibrium mineral phases remains poorly constrained. Feldspathoids in particular have received limited attention with regards to their trace element contents, hampering our ability to interpret geochemical trends in alkaline magmatic systems. In this study, we performed a series of 1 atmosphere experiments in a gas-mixing furnace using a variety of highly alkaline (Na2O + K2O = 4.15–14.97 wt%) and silica-undersaturated (SiO2 = 36.73–45.96 wt%) lava compositions from Nyiragongo, Democratic Republic of Congo, in order to investigate the partitioning behaviour of trace elements in minerals from alkaline magmas. Experimental runs were performed with oxygen fugacity buffered at both QFM (quartz-fayalite-magnetite equilibrium) and QFM + 1 and cover a range of geologically-relevant temperatures (1025–1200 °C). The quenched products of these experiments contained leucite, nepheline, melilite, clinopyroxene, olivine, and rhönite crystals, of which glass-crystal pairs were analysed for rare earth elements, large-ion lithophile elements, and high-field-strength elements. Leucite and nepheline host considerable quantities of large-ion lithophile elements but take up negligible amounts of more highly charged cations. Åkermanitic melilite readily incorporates mono- to trivalent cations with a preference for light over heavy rare earth elements, but incorporates only select divalent cations. Rhönite and clinopyroxene have analogous partitioning behaviours, with a strong preference for heavy over light rare earth elements. Fractionation modelling using the reported partitioning behaviours reproduces the 2021 eruption products of Nyiragongo, with 48% fractionation from an olivine-melilitic parental melt composition. Crystallization of trace-element poor feldspathoid amplifies pre-existing high LREE/MREE ratios of the parental magma and progressively increase trace element abundances for all but monovalent cations.

The use of trace elements in apatite to trace differentiation of a ferrobasaltic melt in the Sept-Iles Intrusive Suite, Quebec, Canada: Implications for provenance discrimination

The Sept Iles Intrusive Suite, Quebec, Canada, comprises one of the world’s largest mafic layered intrusions. It is a natural laboratory to study differentiation processes of a ferrobasaltic melt whereby extreme fractional crystallisation of the mafic melt resulted in residual, felsic magma. Furthermore, liquid immiscibility played a role in forming Fe–Ti–P mineralisation (Fe-Ti oxides and apatite) in the apatite-bearing Critical Zone near the top of the mafic sequence. In this study, we explore and develop the use of trace elements in apatite as a petrogenetic indicator of these magmatic processes. A full suite of 31 trace elements was determined in apatite by LA-ICP-MS and electron microprobe from the mafic Layered Series and felsic Upper Series of the Sept-Iles Intrusive Suite. We show that the trace element content of cumulus apatite records the changing melt composition of the fractionating ferrobasalt from the mafic to the felsic rocks (increase in REE + Y, Th, U, K, Pb and Rb, and decrease in Sr, Ba, V and Mg of apatite), in accordance with the evolution of Sept-Iles liquid line of descent. In the mineralised Critical Zone, the fractionation trend overprints systematic chemical differences in apatite and plagioclase composition between alternating Fe–Ti–P-rich and -poor layers. This is attributed in part to partitioning behaviour of trace elements between immiscible Fe-rich and Si-rich silicate melts and the different cotectic proportions of apatite crystallising from these melts, which was calculated to be 5 to 8 % and 1 % for the Fe–Ti–P-rich and -poor, respectively. Crystal settling and accumulation is then responsible for the elevated proportion of apatite (7 to 36 vol%) observed in Fe–Ti–P-rich layers. Furthermore, a series of new discrimination diagrams is proposed to help identify the provenance of igneous rocks using apatite chemistry. At Sept Iles, apatite from mafic rocks is distinguished from the felsic rocks using REE + Y, Sr and the Eu anomaly. Intercumulus apatite, which crystallised from the interstitial liquid, are readily distinguishable from cumulus apatite by enrichment in highly incompatible elements (higher Cl/F and Th/Lu ratios). This suggests that apatite could be used as an indicator mineral for the exploration of Fe–Ti–P mineralisation in mafic layered intrusions using detrital apatite.

Experimental constraints on the long-lived radiogenic isotope evolution of the Moon

This study presents the results of high pressure and temperature experiments to investigate the mineral–melt trace element partitioning behaviour for minerals predicted to have formed during the crystallisation of the Lunar Magma Ocean (LMO). The focus of this work has been particularly on determining partition coefficients for parent–daughter pairs of radiogenic elements, for LMO-relevant temperatures, pressures and compositions. The new experimental data are compared with previous studies for the same minerals and elements in order to establish best estimates for the partition coefficient of each element for evolving compositions of minerals as predicted in recent studies modelling LMO crystallisation. These estimates are used to calculate evolving parent–daughter ratios in the LMO residual melt and crystallising minerals for the four main long-lived radiogenic isotope systems that have been studied in lunar samples (Rb–Sr, Sm–Nd, Lu–Hf and U–Pb). The calculated 87Rb/86Sr, 147Sm/144Nd, and 176Lu/177Hf ratios are consistent with predictions for the mantle sources of lunar basalts and evolved lithologies. In contrast, it is difficult to explain the wide range of 238U/204Pb source ratios predicted from the Pb isotopic compositions of basaltic lunar samples. Potential explanations for this observation are discussed, with the conclusion that the Moon most likely experienced a significant loss of volatiles (including Pb), towards the end of LMO crystallisation, resulting in the dramatic U–Pb fractionation evidenced by recent sample analyses.

Rare elements enrichment in crustal peraluminous magmas: insights from partial melting experiments

Experiments were conducted to explore the behavior of Li, Rb, Nb, Sn, Cs, Ta, W during crustal melting and test the anatectic origin of rare metal-bearing peraluminous granites such as rare metal granites (RMGs). The experiments were performed under fluid-absent conditions at 800 and 850 °C, 400 MPa and moderately reducing fO2 (ΔFMQ = − 0.5 to − 0.8). Starting materials were cores of several millimetres drilled from two natural rocks, a biotite-rich paragneiss (Pg) and a muscovite-rich orthogneiss (Og) enriched in Li, Be, Sn, Cs, W. Both protoliths produced small melt fractions from 8 to 20% vol. Melt distributions were either homogeneously distributed at grain boundaries in the Pg or preferentially associated with muscovite reaction zones in the Og. In the Pg at 800 °C, melting is mainly fluid present, driven by interstitial water at grain boundaries. At 850 °C, biotite dehydration-melting produces peritectic orthopyroxene, hercynitic spinel, ilmenite and alkali feldspar in addition to melt. In the Og, muscovite dehydration-melting generates melt plus peritectic biotite, hercynitic spinel, ilmenite, Al silicates and alkali feldspar. Experimental glasses are nearly homogeneous, silica rich, peraluminous and leucogranitic and their major element compositions differ only little between the two protoliths. In contrast, the trace element concentrations vary as a consequence of chemical and textural heterogeneities in our starting materials. Compared with source rocks, the Og glasses are enriched in Rb, Nb, Ta, W and depleted in Li, Cs and the Pg are enriched in Li, Rb, Cs, W and depleted in Nb, Ta. Mass-balance calculations indicate that during muscovite dehydration-melting, Li, Cs and Rb partition into the melt; whereas Nb, Ta and W are preferentially incorporated in peritectic phases. Li and Cs also partition toward the melt during biotite dehydration-melting. The partitioning behavior of trace elements during crustal melting is a function of the melting reaction and partition coefficients between melt, residual and peritectic phases. Experimental glasses are similar to peraluminous muscovite granites but fail to reproduce RMG compositions. Alternatives to mica dehydration-melting such as fluid-present and residual source melting emphasize the difficulties with an origin of RMGs by purely anatectic processes. Crystallization differentiation might have to be combined with mica dehydration-melting to explain the distinctive geochemical features of RMGs.

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.

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.

Trace elements in the estuarine systems of the Gulf of Trieste (northern Adriatic Sea): A chemometric approach to depict partitioning and behaviour of particulate, colloidal and truly dissolved fractions

Estuaries are transitional water systems where the hydrodynamic processes governing water circulation actively influence suspended particle transport and deposition. In the estuarine mixing zone, the strong physico-chemical gradients resulting from the interaction between river freshwater and seawater may affect the distribution, mobility and fate of several potentially toxic compounds, among which trace elements are of major concern. Knowledge regarding the partitioning behaviour of trace elements would provide essential scientific support for the environmental management of estuaries. In this study, trace element occurrence and phase partitioning among suspended particulate matter, colloidal material and the truly dissolved fraction were investigated in the main Italian and Slovenian estuarine environments of the Gulf of Trieste (northern Adriatic Sea). Further information about the water quality at the river mouths was provided and, in addition to the traditional evaluation of single chemical parameters, a multi-way principal component analysis was employed in order to depict disparities among sampling sites, water layers and seasonal conditions with the final aim of evaluating trace element phase partitioning.Results indicated that the suspended particulate matter acts as the main effective vehicle for Cu, Cr, Fe, Ni and Pb, and enhanced adsorption processes resulted in elevated partitioning coefficients, especially for Fe and Pb. Although disparities occurred between sampling sites and seasons, trace elements showing affinity for the solid phase appeared to be partially bound to the colloidal material. Conversely, As and Cs prevailed in the truly dissolved fraction, especially in seawater and showed scarce affinity for both the suspended particles and colloids.

Mineralogical and Environmental Geochemistry of Coal Combustion Products from Shenhuo and Yihua Power Plants in Xinjiang Autonomous Region, Northwest China

The mineralogical and geochemical characteristics of feed coals and coal combustion products (CCPs) from the Shenhuo and Yihua Power Plants in Xinjiang Autonomous Region, were studied by means of proximate analysis, Power X-ray diffraction (XRD), scanning electron microscopy with Energy Dispersive X-ray analyzer (SEM-EDX), inductively coupled plasma atomic emission spectrometry (ICP-MS) and inductively coupled plasma mass spectrometry (ICP-AES). The environmental geochemistry of CCPs was evaluated by Al-normalized enrichment factor as well as European Standard EN-12457 leaching test. Two feed coals have the characteristics of low sulfur content, medium to high volatiles matter yields, medium moisture content, super low to medium ash yield, medium to high calorific value and low mineral content. The main crystalline facies in fly ash and slag are quartz and mullite, with a small amount of calcite, and some unburned carbon. Hematite, SrSO4 and barite also can be observed in fly ashes by SEM. Typical plerophere occurs in fine fly ash rather than the coarse fly ash. The concentration of most trace elements in CCPs falls within the lower concentration range of European fly ashes. With respect to the partitioning behavior of trace elements during coal combustion, S is highly volatile, and Mg, Na, Zn, B, Co, As, Nb, Zr, Cu and K also show certain volatility, which may to some extent emit to the atmosphere. Furthermore, leaching experiments show that leachable concentrations of most of the potentially toxic elements in CCPs are low, and the CCPs fall in the range between inert and nonhazardous landfill material regulated by the 2003/33/EC Decision.

Trace element partitioning between sulfide-, metal- and silicate melts at highly reduced conditions: Insights into the distribution of volatile elements during core formation in reduced bodies

Chalcophile and siderophile element abundances are used to provide important constraints on the interior compositions of planetary bodies as well as the pressure (P) - temperature (T) conditions that prevailed during core formation. The oxygen fugacity (fO2) during core formation varied considerably between the various terrestrial planets and asteroidal bodies in our solar system. Mercury, the aubrite parent body (AuPB) and some terrestrial precursor bodies may have differentiated at highly reduced conditions.At present knowledge about how the metal liquid-silicate melt and sulfide liquid-silicate melt partitioning behavior of major and trace elements are affected by high S concentrations in the silicate melt at highly reducing conditions is incomplete. Here, we experimentally study the metal-silicate and sulfide-silicate partitioning behavior of trace elements in reduced silicate melts over a wide range of S contents as a function of redox state at 1 GPa and 1833–1883 K. Silicate melt S contents ranged between ~0.5 and ~20 wt%, with a corresponding silicate FeO range of ~0.4 to ~17.5 wt%, in a fO2 range between 1 and 9 log units below the iron-wüstite buffer. Our results reproduce the decrease of the S concentration at sulfide saturation (SCSS) with decreasing FeO contents down to ~3 wt%, as well as its strong increase at <3 wt% FeO. At S contents exceeding >6–9 wt% S, the FeO contents increase again.Results show that most elements (Mg, Ti, V, Cr, Mn, Cu, Zn, Se, Nb, Cd, Sb, Te, Ta, Tl, Pb and Bi) are more chalcophile than siderophile at reducing conditions, whereas Si, Co, Ni, Ga, Ge, Mo and W preferentially partition into Fe-rich melts instead of sulfide liquids. Silicon, Ti, Se, and Te preferentially partition into Fe-S over (Fe,Mg,Ca)-S liquids, whereas Mn, Zn and Cd are more compatible in the latter. As proposed by Wood and Kiseeva (2015), chalcophile elements such as Cu, Se and Te behave less chalcophile with increasing S concentrations of the silicate melt, whereas the opposite is observed for nominally lithophile elements such as Mg, Ca and Ti.The results can be used to improve interpretations of the observed trace element systematics of aubrites and other reduced achondrites. All of the volatile elements considered here behave chalcophile at the reducing conditions inferred for differentiation of the AuPB. A significant degree of the observed volatile element depletions in aubrites may therefore reflect their preferential partitioning into sulfide liquids, rather than degassing during or after differentiation of the AuPB. These results suggest that, depending of the extent of core merging, precursor body differentiation and the efficiency of sulfide liquid segregation, reduced precursor bodies that were incorporated in the early Earth were likely more rich in volatile elements than currently assumed.

Crystals from the Powellite-Scheelite Series at the Nanoscale: A Case Study from the Zhibula Cu Skarn, Gangdese Belt, Tibet

Scheelite (CaWO4) and powellite (CaMoO4) are isostructural minerals considered as a non-ideal solid solution series. Micron- to nanoscale investigation of a specimen of skarnoid from Zhibula, Gangdese Belt, Tibet, China, was carried out to assess the identity of the phases within a broad scheelite-powellite (Sch-Pow) compositional range, and to place additional constraints on redox changes during ore formation. An electron probe microanalysis shows that Mo-rich domains within complex oscillatory-zoned single crystals, and as thin sliver-like domains, have a compositional range from 20 mol.% to 80 mol.% Pow. These occur within a matrix of unzoned, close-to-end-member scheelite aggregates (87 mol.%–95 mol.% Sch). Laser-ablation inductively coupled plasma mass spectrometry spot analysis and element mapping reveal systematic partitioning behaviour of trace elements in skarn minerals (grossular50, diopside80, anorthite, and retrograde clinozoisite) and scheelite-powellite aggregates. The Mo-rich domains feature higher concentrations of As, Nb, and light rare earth elements LREE, whereas W-rich domains are comparatively enriched in Y and Sr. Transmission electron microscopy (TEM) was carried out on focused-ion-beam-prepared foils extracted in situ from domains with oscillatory zoning occurring as slivers of 20 mol.%–40 mol.% Pow and 48 mol.%–80 mol.% Pow composition within an unzoned low-Mo matrix (20 mol.% Pow). Electron diffractions, high-angular annular dark field (HAADF) scanning-TEM (STEM) imaging, and energy-dispersive spectroscopy STEM mapping show chemical oscillatory zoning with interfaces that have continuity in crystal orientation throughout each defined structure, zoned grain or sliver. Non-linear thermodynamics likely govern the patterning and presence of compositionally and texturally distinct domains, in agreement with a non-ideal solid solution. We show that the sharpest compositional contrasts are also recognisable by variation in growth direction. Atomic-scale resolution imaging and STEM simulation confirm the presence of scheelite-powellite within the analysed range (20 mol.%–80 mol.% Pow). Xenotime-(Y) inclusions occur as nm-wide needles with epitaxial orientation to the host scheelite-powellite matrix throughout both types of patterns, but no discrete Mo- or W-bearing inclusions are observed. The observed geochemical and petrographic features can be reconciled with a redox model involving prograde deposition of a scheelite+molybdenite assemblage (reduced), followed by interaction with low-T fluids, leading to molybdenite dissolution and reprecipitation of Mo as powellite-rich domains (retrograde stage, oxidised). The observation of nanoscale inclusions of xenotime-(Y) within scheelite carries implications for the meaningful interpretation of petrogenesis based on rare earth element (REE) concentrations and fractionation patterns. This research demonstrates that HAADF-STEM is a versatile technique to address issues of solid solution and compositional heterogeneity.

Liquid immiscibility in the CaF2-granite system and trace element partitioning between the immiscible liquids

The recent discoveries of Ca-fluoride melt in magmatic systems, especially in peralkaline granites with rare earth element enrichment, has raised questions about the presence and nature of liquid immiscibility in CaF2-granite systems, as well as the partitioning behavior of trace elements between such immiscible liquids. We have experimentally explored the immiscibility in this system using natural granite-fluorite starting materials at fast-and slow-cooling rates, temperatures from 500 °C to 1200 °C and 1 atmosphere pressure. Our experiments confirm the presence of a miscibility gap in the CaF2-granite system over a wide range of temperatures. The two immiscible liquids are a mafic fluorosilicate melt (fm) with high CaO and F and a felsic oxysilicate melt (sm) with high SiO2 and alkalis. Immiscibility is encountered when the bulk F-content exceeds approximately 4.4 wt% at 1200 °C and then rapidly decreases to only 0.75 wt% at low temperature (below 900 °C). This indicates that calcic magmas are able to evolve to the liquid immiscibility domain by the residual enrichment of fluorine resulting from fractional crystallization, and that liquid immiscibility should be common. The peritectic reaction fm = sm + fluorite removes the fluorosilicate liquid around 600 °C and could explain the absence of fluorosilicate observations in natural granites. The compositions of the liquids in fast-cooling experiments show a significantly larger miscibility gap which is characterized by, compared to slow-cooling runs, similar sm compositions but higher Ca and F content in fm. This difference is caused by suppression of fluorite nucleation and is interpreted as a metastable extension of the high temperature liquid immiscibility. Immiscibility results in strong fractionation of trace elements which is primarily governed by melt structure and the ionic potential (Z/r) of the elements. The behavior of trace elements can be categorized into three groups: 1. Network formers (Si, Al, Ga, Pb, B) partition into the oxysilicate melt; 2. The partitioning of the alkalis and alkali earths is strongly dependent on the ionic potential, with the partitioning coefficients (D fm/sm) in the order DCs < DRb < DK < DNa < DLi < DBa < DSr < DCa ≤ DMg; 3. High field strength elements (Ti, Zr, Hf, Nb, Ta, Th, U) and rare earth elements (REE) strongly partition into the fluorosilicate melt. The D values vary with the size of the miscibility gap, which is in turn controlled by temperature with more pronounced fractionation as the miscibility gap widens. The fluorosilicate melt effectively sequesters the REE especially at the lower temperatures relevant for granite magmatism and, given its higher density and lower viscosity compared to the coexisting oxysilicate melt, fractionates the REE from the host silicate melt, suggesting a potential REE-mineralising process.

Modes of occurrence and partitioning behavior of trace elements during coal preparation—A case study in Guizhou Province, China

Coal preparation technology is expected to play an important role in trace elements removal before coal combustion. The modes of occurrence of five trace elements (As, Se, Pb, Be, and Hg) in two coal cleaning plants in Guizhou, China, designated WJZ and ZZC, were studied using screening and float-and-sink tests. The behaviors of these trace elements when coal was cleaned were also investigated via sampling and analysis of raw coal, coal products, fresh water, and circulating water in two coal cleaning plants. Screening tests show that the content of trace elements is highest in 3–1 mm or 1–0.5 mm size fraction and they distributed mainly (more than 50%) in the +0.5 mm size fractions. Float-and-sink tests indicate that trace elements have a strong inorganic affinity and are significantly enriched, distributed in high-density fraction (+1.8 g/cm3). Over 50% of trace elements could be removed when pre-gangue removal is done with separation density of 1.8 g/cm3. The analysis of solid samples (raw coal, coal products) demonstrates that trace elements migrated mainly into gangue, and slime, enrichment of trace elements in middlings was also observed in ZZC plant. Results of water samples analysis suggest that Se, and As in coal are more likely to be released into water during coal cleaning while Be and Hg are present in a highly insoluble form in coal.

Partitioning of trace elements, As, Ba, Cd, Cr, Cu, Mn and Pb, in a 2.5 MWth pilot-scale circulating fluidised bed combustor burning an anthracite and a bituminous coal

Coal combustion introduces large amounts of pollutants into the atmosphere, including trace elements originally bonded in the coal matrix. The emission of these elements raises considerable environmental and human health concerns. To optimise process parameters and reduce gaseous trace element emissions, it is of significant importance to investigate the solid–gas partitioning behaviour of trace elements during combustion processes. To date, limited numbers of experimental studies have been carried out, especially using pilot circulating fluidised bed (CFB) combustion plants. This paper discusses the partitioning behaviour of seven elements (As, Ba, Cd, Cr, Cu, Mn and Pb) in different product streams during combustion tests on anthracite and bituminous coal. The combustion tests were carried out in a 2.5MWth CFB unit equipped with multi-stage control of solids, which is well suited for trace element partitioning studies. The mass balance ratio of the elements studied ranged from 56%–137%, which is, considering their concentrations, both satisfactory and reasonable. Most of the elements were found in the bottom ash and fly ash during CFB combustion, while small amounts of As, Cd and Pb were emitted to the atmosphere along with fine particulates. The trace elements are more likely to be retained in the bottom ash from the bituminous coal but not in the case of anthracite. For the volatile elements, the enrichment in solid streams follows the trend of: bag filter ash > cyclone ash > IBHX (in-bed heat exchanger) solids > bottom ash, indicating that the volatile elements tend to be enriched in fine particles. Anthracite, when compared to bituminous coal, shows lower emission factors for all monitored elements, except for Pb. This study can serve as a good reference for trace element control strategies in coal-fired CFB boilers.

An Experimental Study of Trace Element Fluxes from Subducted Oceanic Crust

We have determined experimentally the hydrous phase relations and trace element partitioning behaviour of ocean floor basalt protoliths at pressures and temperatures (3 GPa, 750‐1000 � C) relevant to melting in subduction zones. To avoid potential complexities associated with trace element doping of starting materials we have used natural, pristine mid-ocean ridge basalt (MORB from Kolbeinsey Ridge) and altered oceanic crust (AOC from Deep Sea Drilling Project leg 46, � 20 � N Atlantic). Approximately 15 wt % water was added to starting materials to simulate fluid fluxing from dehydrating serpentinite underlying the oceanic crust. The vapour-saturated solidus is sensitive to basalt K2O content, decreasing from 825 6 25 � C in MORB (� 0� 04 wt % K2O) to � 750 � Ci n AOC (� 0� 25 wt % K2O). Textural evidence indicates that near-solidus fluids are sub-critical in nature. The residual solid assemblage in both MORB and AOC experiments is dominated by garnet and clinopyroxene, with accessory kyanite, epidote, Fe‐Ti oxide and rutile (plus quartz‐coesite, phengite and apatite below the solidus). Trace element analyses of quenched silica-rich melts show a strong temperature dependence of key trace elements. In contrast to the trace elementdoped starting materials of previous studies, we do not observe residual allanite. Instead, abundant residual epidote provides the host for thorium and light rare earth elements (LREE), preventing LREE from being released (RLREE 1500 and La/ SmPUM (where PUM indicates primitive upper mantle) � 1, most closely matching the geochemical signal of arc lavas worldwide, were generated from AOC at 800‐850 � C.

Hydrous Phase Relations and Trace Element Partitioning Behaviour in Calcareous Sediments at Subduction-Zone Conditions

We report the results of experiments on two natural marine sediments with different carbonate contents (calcareous clay: CO2 ¼ 6� 1 wt %; marl: CO2 ¼ 16� 2 wt %) at subduction-zone conditions (3 GPa, 750–1200 � C). Water (7–15 wt %) was added to the starting materials to simulate the effects of external water addition from within the subducting slab. The onset of melting is at 760 � Ci n water-rich experiments; melt becomes abundant by 800 � C. In contrast, the onset of melting in published, water-poor experiments occurs at variable temperatures with the production of significant melt fractions being restricted to more than 900 � C (phengite-out). The different solidus temperatures (Tsolidus) can be ascribed to variable fluid XH2O [H2O/(CO2 þ H2O)], which, in turn, depends on bulk K2O, H2O and CO2. Partial melts in equilibrium with residual garnet, carbonate, quartz/coesite, epidote, rutile, kyanite, phengite, and clinopyroxene are granitic in composition, with substantial dissolved volatiles. Supersolidus runs always contain both silicate melt and solute-rich fluid, indicating that experimental conditions lie below the second critical endpoint in the granite–H2O–CO2 system. Carbonatite melt coexists with silicate melt and solute-rich fluid above 1100 � C in the marl. The persistence of carbonate to high temperature, in equilibrium with CO2-rich hydrous melts, provides a mechanism to both supply CO2 to arc magmas and recycle carbon into the deep Earth. The trace element compositions of the experimental glasses constrain the potential contribution of calcareous sediment to arc magmas. The presence of residual epidote and carbonate confers different trace element characteristics when compared with the trace element signal of Ca-poor marine sediments (e.g. pelagic clays). Notably, epidote retains Th and light rare earth elements, such that some melts derived from calcareous sediments have elevated Ba/Th and U/Th, and low La/SmPUM, thereby resembling fluids conventionally ascribed to altered oceanic crust. Our results emphasize the importance of residual mineralogy, rather than source lithology, in controlling the trace element characteristics of slab-derived fluids.

Trace elements in magnetite as petrogenetic indicators

We have characterized the distribution of 25 trace elements in magnetite (Mg, Al, Si, P, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb), using laser ablation ICP-MS and electron microprobe, from a variety of magmatic and hydrothermal ore-forming environments and compared them with data from the literature. We propose a new multielement diagram, normalized to bulk continental crust, designed to emphasize the partitioning behavior of trace elements between magnetite, the melt/fluid, and co-crystallizing phases. The normalized pattern of magnetite reflects the composition of the melt/fluid, which in both magmatic and hydrothermal systems varies with temperature. Thus, it is possible to distinguish magnetite formed at different degrees of crystal fractionation in both silicate and sulfide melts. The crystallization of ilmenite or sulfide before magnetite is recorded as a marked depletion in Ti or Cu, respectively. The chemical signature of hydrothermal magnetite is distinct being depleted in elements that are relatively immobile during alteration and commonly enriched in elements that are highly incompatible into magnetite (e.g., Si and Ca). Magnetite formed from low-temperature fluids has the lowest overall abundance of trace elements due to their lower solubility. Chemical zonation of magnetite is rare but occurs in some hydrothermal deposits where laser mapping reveals oscillatory zoning, which records the changing conditions and composition of the fluid during magnetite growth. This new way of plotting all 25 trace elements on 1 diagram, normalized to bulk continental crust and elements in order of compatibility into magnetite, provides a tool to help understand the processes that control partitioning of a full suit of trace elements in magnetite and aid discrimination of magnetite formed in different environments. It has applications in both petrogenetic and provenance studies, such as in the exploration of ore deposits and in sedimentology.

Preliminary experimental data on trace-element partitioning between tourmaline and silicate melt

Tourmaline is a ubiquitous accessory mineral in magmatic deposits, especially those of evolved compositions. It displays a high compositional sensitivity to the composition of its host environment, as well as pressure, temperature and f (O 2 ). These characteristics make tourmaline an ideal monitor of the physical and chemical conditions in its host silicate melt. Of particular interest is its potential to record the trace-element signature of the melt. However, to read this record requires knowledge of the partitioning behavior of trace elements between tourmaline and melt. Here, I present preliminary results of a partitioning experiment between tourmaline and a H 2 O- and borosilicate-saturated melt at 800°C and 7.5 kbar, in the presence of B-bearing olivine, hercynitic spinel and ilmenite. Calculated partition-coefficients are invariably close to unity, which shows that tourmaline is unable to significantly fractionate trace elements. Partitioning is systematic and agrees with predictions based on lattice-strain theory, which allows element valence and element site-occupancy to be determined from partitioning data. I conclude that the limited range in partition coefficients results from the diversity of lattice sites in the tourmaline structure, which accommodates trace elements of widely different charge and radius. The composition of tourmaline thus can directly record the compositional signature of its host melt.

Partitioning behavior of trace elements between dacitic melt and plagioclase, orthopyroxene, and clinopyroxene based on laser ablation ICPMS analysis of silicate melt inclusions

Partitioning behavior of Sc, Ti, V, Mn, Sr, Y, Zr, Nb, Ba, La, Nd, Sm, Eu, Gd, Dy, Ho, Yb, Hf, and Pb between dacitic silicate melt and clinopyroxene, orthopyroxene, and plagioclase has been determined based on laser ablation-inductively coupled plasma mass spectrometric (LA-ICPMS) analysis of melt inclusions and the immediately adjacent host mineral. Samples from the 1988 eruption of White Island, New Zealand were selected because petrographic evidence suggests that all three mineral phases are in equilibrium with each other and with the melt inclusions. All three phenocryst types are found as mineral inclusions within each of the other phases, and mineral inclusions often coexist with melt inclusions in growth-zone assemblages. Compositions of melt inclusions do not vary between the different host minerals, suggesting that boundary layer processes did not affect compositions of melt inclusions and that post-trapping modifications have not occurred. Partition coefficients were calculated from the host and melt inclusion compositions and results were compared to published values. All trace elements examined in this study except Sr are incompatible in plagioclase, and all measured trace elements except for Mn are incompatible in orthopyroxene. In clinopyroxene, Sc, V, and Mn are compatible, and Y, Ti, HREE, and the MREE are only slightly incompatible. Most partition coefficients overlap the wide range of values reported in the literature, but the White Island data are consistently at the lower end of the range in published values. Results from the literature obtained using modern microanalytical techniques such as secondary ion mass spectrometry (SIMS) or proton induced X-ray emission spectroscopy (PIXE) also fall at the lower end of the published values, whereas partition coefficients determined from bulk analysis of glass and crystals separated from volcanic rocks typically extend to higher values. Rapid crystal growth-rates, crystal zonation, or the presence of accessory mineral inclusions in phenocrysts likely accounts for the wide range and generally higher partition coefficients obtained using bulk sampling techniques. The results for 3+ cations from this study are consistent with theoretical predictions based on a lattice strain model for site occupancy. The results also confirm that the melt inclusion-mineral (MIM) technique is a reliable method for determining partition coefficients, as long as the melt inclusions have not experienced post-entrapment reequilibration.

Trace-Element Partitioning Between Amphibole and Silicate Melt

Knowledge of the partitioning behavior of trace elements between solid and liquid is a prerequisite for modern igneous and mantle petrology. Most of the mathematical models simulating melt generation, migration and evolution within the mantle and/or the crust require the availability of reliable solid/liquid partition coefficients for the mineral phases involved in the process. Calcic amphiboles are extremely important for the understanding of lithospheric processes because of both their common occurrence in a variety of igneous and metamorphic rocks types and their capability of hosting a large number of geochemically important trace elements. A series of studies on the partitioning behavior of trace elements between calcic amphibole and silicate melt have therefore been carried out at different pressures, temperatures and system compositions during the last 15 years. However, due to the complex crystal chemistry of amphiboles, only few studies focused on the role of crystal structure and composition on amphibole-liquid partition coefficients (Amph/LD). In this chapter, present knowledge of the solid/ liquid trace element partitioning between calcic amphiboles and silicate melt is summarized and the role played by the crystal structure and melt composition on Amph/LD variations is highlighted in addition to the effects of pressure and temperature. The dataset used in this chapter includes only the results of experimental studies performed under well constrained P - T conditions for which trace element determinations were carried out with highly sensitive in situ microanalytical techniques. The available dataset considered in this work are listed in Table 1⇓. Although far less common than the calcic amphiboles, potassic-richterites are potentially important in the generation of potassic magmatic rocks and in re-enrichment processes occurring in the subcontinental mantle lithosphere sampled as xenoliths in kimberlites. A comprehensive experimental study of trace element partitioning between synthetic potassic richterites and silicate melts has …

Using LA-ICPMS Mapping and Sector Zonation to Understand Growth and Trace-Element Partitioning in Sector-Zoned Clinopyroxene Oikocrysts from the Norra Ulvö Gabbro, Sweden

Petrographic analysis and geochemical mapping are used to characterize sector-zoned clinopyroxene oikocrysts from the Norra Ulvö Gabbro, Sweden. The sector zones are distinguished optically and by differences in TiO2 , Al2O3 , and incompatible trace elements. The oikocrysts grew with a branching morphology as evidenced by numerous triple points in a single oikocryst. Oikocrysts grew from the center of domains outward and the growth within individual domains did not completely fill the space until the oikocryst had reached its full size. In some domains sector zones are overgrown by growth zones that lack sectors. The last crystallization infilled channels that allowed late-stage liquids to move through the oikocryst at the contacts with chadacrysts. Calculation of partitioning behavior of trace elements between adjacent sectors shows it to be regular and consistent with experimental results. The data show that the CaTiAl2O6 component greatly enhances the solubility of most incompatible elements in clinopyroxene.