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The St. Ignace Island complex in Northern Ontario is a package of dominantly felsic rocks emplaced within the upper portions of the Osler Volcanic rocks of the ~1.1 Ga Midcontinent Rift System. The Osler volcanic rocks are predominantly tholeiitic basalts intercalated with rare interflow sediments and rhyolites. The St. Ignace Island complex is a ~26 km2 stock with a felsic core of quartz-feldspar-phyric rhyolites and dacites and an outer ring of anorthosite and gabbro. Textures at a variety of scales within the rocks of the complex show clear evidence of the mingling and mixing of partially crystallized mafic and felsic liquids. Two multigrain (zircon/baddeleyite) fractions from a sample of the gabbro define a Discordia line with an upper intercept date of 1107±8.9 Ma. The core of the complex consists of dacites and rhyolites with similar REE abundances with negative Nb anomalies whereas the surrounding mafic rocks are gabbros to monzogabbros that are less LREE-enriched than the felsic rocks but with similar HREE. Felsic units have a narrow range of 87Sr/86Sri (0.7032-0.7045) and 143Nd/144Ndi (0.51051-0.51057) whereas the mafic end members have similar 87Sr/86Sri (0.7040-0.7061) but more radiogenic 143Nd/144Ndi (0.51067-0.51085). Very well-preserved silicate melt inclusions (MI), many completely glassy, were observed in quartz, clinopyroxene and some plagioclase phenocrysts from the complex. These represent some of the oldest unrecrystallized silicate melt inclusions described to date. Melt inclusions within quartz from the felsic volcanics are broadly rhyolitic in composition whereas MI from plagioclase in the mafic volcanics range from basalt to basaltic andesite; these felsic and mafic melt compositions are interpreted to represent the end-member liquids in the system and bulk rock analyses affirm mixtures of the two. Concentrations of Cu and Ag (in both mafic and felsic MI), and Mo (in felsic MI), are up to an order of magnitude higher in the mafic and felsic MI than in continental crust. Bulk rock metal concentrations are also significantly lower than in the MI, suggesting that the melt inclusions may preserve pre-eruptive metal tenors that were subsequently modified by sulfide saturation, degassing, or post-solidus hydrothermal alteration. The whole rock and MI geochemistry of the St. Ignace complex are broadly similar to the Central Osler Group and, given the broad similar ages, suggests they may have been derived from a similar mantle source, but distinct from the source of rhyolites in the Black Bay Peninsula. The negative Nb anomalies and negative εNd values for the St. Ignace complex are consistent with mixing with older continental crust during ascent and emplacement. The rocks of the St. Ignace Island complex likely formed as the result of emplacement of a large mafic magma chamber at the base of the Osler volcanic pile that triggered partial melting to generate the rhyolite end members. The felsic melts ascended to shallower levels in the crust where they mixed with mafic magmas derived directly from the deeper chamber. Generally, melt inclusions in the complex have very high Cu and Ag contents, similar to those observed in arc-related and extremely oxidized early rift-related rocks and may account for the world-class volcano-sediment-hosted Cu-(Ag) deposits within the rift and the presence of small porphyry-style deposits.

Oxygen fugacity (fO2) is typically controlled in high P-T experiments by using solid-state redox buffer assemblages. However, these are restricted to impose discrete fO2 values, often with significant gaps between neighboring assemblages. Semi-permeable hydrogen membranes (Shaw 1963) are often used in internally heated pressure vessels for more flexible fO2 control in hydrous experiments; however, their implementation in more widely available externally heated pressure vessels has not yet gained space. We propose a prototype molybdenum-hafnium carbide (MHC) pressure vessel apparatus that simultaneously allows rapid quenching and flexible, precise, and accurate redox control via a custom-designed hydrogen membrane. Test runs with two membranes at a time, one imposing and another one monitoring fH2, demonstrated that 95% of the imposed hydrogen pressure was attained inside the pressure vessel within 2 h at 800–1000 °C, after which a steady state equilibrium was established. Furthermore, experiments comparing redox-dependent Cu solubility in silicate melts at fO2 imposed by the fayalite-magnetite-quartz, Re-ReO2, and MnO-Mn2O3 buffers and identical target fO2 imposed by the hydrogen membrane confirmed consistency between the two methods within 0.25 log units fO2 deviation at T = 900 °C and P = 2000 bar. This powerful yet cost-effective and low-maintenance apparatus may open up new pathways for studying redox reactions in hydrous magmas and magmatic fluids. As a proof of concept, we conducted near-liquidus phase-equilibrium experiments with H2O-saturated calc-alkaline basalt and shoshonite melt compositions at five different fO2 values equally distributed between half log unit below the Ni-NiO buffer (NNO-0.5) and NNO+2.7. Most experiments crystallized olivine, clinopyroxene, and Ti-magnetite. The Mg# of the olivine increased with fO2, and the Fe3+/Fetotal ratios in the silicate melt were determined based on Fe(II)-Mg exchange between olivine and melt. The Fe3+/Fetotal ratios in the shoshonite melt were systematically higher by about 0.06 ± 0.01 than those in the calc alkaline basalt melt at identical fO2. The values determined for the basaltic melt were consistent within 1σ error (

Several field-based studies have proposed that late-stage magmatic aqueous brines may be responsible for the transportation and redistribution of platinum-group elements (PGE) in mafic–ultramafic igneous systems. We experimentally studied the solubility of Pt in high-temperature aqueous brines as a function of oxygen fugacity (ƒO2), temperature (T), pH and total chloride concentration (Cltotal) in a S-free system. Experiments were conducted at 800–1000 °C and 200 MPa in an externally-heated rapid-quench Molybdenum-Hafnium Carbide (MHC) pressure vessel assembly. We employed the synthetic fluid inclusion (SFI) technique to trap and sample pre-equilibrated, high-salinity brines in quartz cylinders subjected to in situ fracturing during experimental run conditions. Platinum solubility was observed to have a positive correlation with ƒO2, temperature, fluid acidity and Cltotal (salinity). A log Pt versus log ƒO2 diagram derives a weighted-error linear regression slope (m) = 0.48 ± 0.04 which demonstrates that Pt is present in the 2+ oxidation state over the studied ƒO2 range. At relatively oxidizing conditions, 1.44 log units above the Ni-NiO oxygen buffer (NNO+1.44), aqueous brines (containing 63 NaCl eq. wt.%) with a mildly acidic fluid composition (pH = 6.03) can dissolve up to ∼100 µg/g Pt at 900 °C and 200 MPa. Aqueous brines with identical fluid compositions yield a solubility of 4–13 µg/g Pt under more reducing conditions (NNO–0.41 to NNO–1.42). Thermodynamic model calculations suggest that both PtCl2 and PtCl3− are the dominant Pt(II)-chloride complexes which facilitate the transport of Pt in high-temperature aqueous vapors and brines. In fluid compositions with Cltotal >32 m (mol/kg H2O), PtCl3− complex is expected to be the dominant Pt species. In natural mafic–ultramafic systems, high-salinity, orthomagmatic aqueous brines may be important transporting agents if such magmatic fluids can participate in the dissolution of Pt-enriched base-metal sulfides or react with discrete insoluble Pt phases imposing a relatively high activity of Pt (i.e., Pt3Fe). Furthermore, precipitation of Pt from aqueous brines is promoted by a decrease in ƒO2, temperature, acidity and Cltotal.

Most of the global Sn resources are from granite-related ore deposits, which form in response to cassiterite precipitation from hydrothermal fluids. However, the physical and chemical controls on the efficiency of Sn extraction from upper crustal plutons by exsolving magmatic fluids are still unclear. In this study, we determine the partition coefficient of Sn between aqueous fluids and granitic melts ( D S n f l u i d / m e l t ) at 800 °C, 150 MPa and the fO2 of the Ni-NiO buffer. To obtain equilibrium partition coefficients, a new experimental method has been used relying on local equilibrium between silicate melt and microscopic-sized fluid bubbles. The latter formed synthetic fluid inclusions in the quenched glasses, which in turn were analyzed by laser ablation inductively coupled plasma mass spectrometry along with the enclosing glass. The results show that at constant aluminum saturation index (ASI = 1.05–1.08) of the silicate melt, D S n f l u i d / m e l t increases from 1.9 to 35.0 as the total Cl concentration ( m C l t o t a l ) in fluid increases from 1.0 to 16.6 mol/kg H2O. At a fixed m C l t o t a l = 2 mol/kg H2O, D S n f l u i d / m e l t increases from 4.3 to 10.6 as the HCl concentration in the solution increases from 0.15 to 0.79 mol/kg H2O, which in turn is a function of the ASI of the melt (ASI = 1.06–1.29). Numerical modeling suggests that Sn is extracted by magmatic fluids from upper crustal plutons most efficiently at the late stage of crystallization and degassing. At a similar degree of crystallization, granitic magma with lower initial water concentration and higher ASI will separate a fluid phase with higher Sn concentration and thus has higher Sn mineralization potential. Due to the relatively high D S n f l u i d / m e l t value, fluids exsolved from highly evolved magmas can sequester enough Sn to form Sn deposits and the sub-solidus remobilization of Sn from granite bodies is not a pre-requisite for ore genesis.

We performed experiments to determine the solubility of Au and Pd in magmatic aqueous fluids as a function of oxygen fugacity (ƒO2), temperature (T), pH and total chloride concentration (Cltotal). Experiments were conducted at 800–1000 °C and 200 MPa in an externally-heated rapid-quench Molybdenum-Hafnium Carbide (MHC) cold-seal pressure vessel assembly. We employed a synthetic fluid inclusion (SFI) technique to entrap equilibrated, hydrothermal fluids in response to in situ fracturing of quartz cylinders at experimental run conditions. The solubility of Au and Pd both have positive relationships with ƒO2, temperature, acidity and chlorinity. Concentrated aqueous brines containing 63 wt.% NaCl can dissolve wt.% levels of Au (∼1.2 wt.%) and Pd (∼1.7 wt.%) at metal saturation in relatively oxidized conditions, 1.44 log units above the Ni-NiO oxygen buffer (NNO+1.44), and mildly acidic pH at 900 °C and 200 MPa. Thermodynamic modeling of experimental results suggests that Au is mainly transported as AuCl(aq) at high pH and low Cltotal conditions, whereas HAuCl2(aq) and potentially AuCl2(aq)− predominates at low pH and high Cltotal conditions. Results from thermodynamic modeling also suggest Pd is mobilized in significant contributions by both PdCl2(aq) and PdCl3(aq)− with the latter gaining predominance in response to increasing Cltotal. Calculated fluid/melt partition coefficients for Au and Pd in low-density, magmatic vapors at 1000 °C and 200 MPa suggest that Pd may experience fractionation from Au in porphyry Au-Cu (±Pd, Pt) systems due to the restricted compatibility of Pd in the fluid phase (requiring strongly acidic and substantially high ƒO2 conditions). Moreover, high-density, concentrated aqueous brines facilitate the compatibility of Pd in the fluid phase which may be important with respect to the formation of platinum-group element (PGE)-enriched horizons in layered mafic intrusions (e.g., J-M Reef, Stillwater Complex, U.S.A.). The potential for magmatic, near-neutral pH, high-salinity brines to dissolve significant amounts of Pd as Pd(II)-chloride complexes (∼400 to ∼900 µg/g) well below the NNO buffer suggests that such fluids may be responsible for late-stage hydrothermal remobilization of Pd within mafic-ultramafic igneous environments (e.g., Cu-Ni-PGE footwall deposits and low-sulfide PGE deposits in the Sudbury Igneous Complex, Canada).

Serpentinization, i.e. the hydrothermal alteration of ultramafic rocks, is an important and ubiquitous geologic process that occurs at slow- and ultraslow-spreading mid-ocean ridges, magma-poor passive margins, and subduction zones. While serpentinization occurs over a wide temperature range and involves diverse fluid compositions, few experimental studies systematically examined the effects of temperature and fluid composition on the kinetics of serpentinization of olivine, and published rates diverge greatly. We present results of an experimental study using synthetic fluid inclusions in Mg-rich olivine as micro-batch reactors to monitor the effects of temperature (100–350 °C), fluid composition (H2O-MgCl-NaCl, H2O-NaCl, H2O-MgCl), and total salinity on serpentinization rates of olivine under closed system conditions. Petrographic observations and Raman analyses of the experimental run products revealed the alteration of olivine to produce serpentine minerals, brucite, and magnetite. The salinity of the aqueous fluid in the inclusions increased as H2O was removed from the solution and incorporated into the hydrous product phases and served as a proxy for reaction progress. The fastest serpentinization rates were found at 250 °C in the presence of a seawater-like aqueous solution. This result further suggests that serpentinization of olivine is fastest at lower temperatures (∼250 °C) and shallower depths in the oceanic lithosphere than suggested by previous studies (∼300 °C). Moreover, our experiments show that serpentinization rates decrease by several orders of magnitude as salinity and the concentration of dissolved Mg increase. These effects may reconcile some of the differences observed when comparing results of previously published rates obtained from experiments involving fluids of different compositions. We constructed a quantitative model based on the principle of detailed balance to predict variations in serpentinization rates (J±) from low temperatures to 320 °C. It suggests that at 25 °C, serpentinization rates are 4 to 5 orders of magnitude slower than at 250 °C. Moreover, the temperature dependence model has been coupled with the kinetic effects derived from experiments involving different fluid composition to calculate the amount of time required for serpentinization of olivine having different reactive surface areas. The model shows that between 200 and 300 °C serpentinization is fast on geologic timescales when rocks with large reactive surface areas interact with a seawater-like aqueous solution (complete serpentinization in days to decades).

A genetic link between Sb mineralization and magmatism has previously been proposed, yet little is known about the mobility of Sb during magma degassing. We have carried out a series of experiments to understand the effects of fluid composition, oxygen fugacity (fO2), pressure and temperature on the partitioning of Sb between magmatic fluids and a rhyolitic melt at crustal conditions (T = 850 °C, P = 200 MPa). The experiments were carried out in Molybdenum - Hafnium Carbide (MHC) pressure vessel assemblies at T = 850 to 1000 °C, P = 100 to 200 MPa and logfO2 from 1.64 log units below to 1.78 log units above the Ni-NiO buffer. Antimony partitions into aqueous chloride-bearing fluids weakly, with the fluid/silicate melt partition coefficient of Sb (DSbfluid/melt) increasing from 0.48 ± 0.11 (1σ) to only 0.85 ± 0.17 (1σ) as the total chlorine concentration in the fluid increases from 0.99 to 16.24 m, indicating the lack of significant Sb-chloride species in the fluid. In contrast, DSbfluid/melt increased from 0.89 ± 0.19 to 1.49 ± 0.19 as the aluminum saturation index (ASI) of the melt increased from 1.02 to 1.24. The moderate increase in DSbfluid/melt with increasing ASI of the melt (and HCl/metal chloride in the fluid) most likely relates to decreasing Sb solubility in the melt and further demonstrates the lack of significant chloride complexing of Sb. We also found that DSbfluid/melt is only slightly influenced by fO2 suggesting that Sb does not change oxidation state (Sb3+) at redox conditions typical of arc magmatism. Furthermore, the presence of reduced S species in the fluid phase caused only a minor increase in DSbfluid/melt indicating that Sb-sulfide complexes are not particularly stable in magmatic fluids. Our data also show that pressure and temperature, within the range of 100 to 200 MPa and 850 to 1000 °C, do not significantly influence DSbfluid/melt. Thus it is apparent that at most possible conditions at which rhyolitic melts degas in the upper crust, Sb will only weakly partition into the fluid phase and it is likely that the Sb budget of large epithermal Sb deposits is not directly derived from primary magmatic fluids.

Low-dimensional copper halides with high luminance have attracted increasing interest as heavy-metal-free light emitters. However, the optical mechanisms underpinning their excellent luminescence r...

Metallic sublimates coated by sulfides and chlorides line the vesicle walls of mafic volcanic lava and bombs from Kīlauea, Vesuvius, Etna, and Stromboli. The metallic sublimates were morphologically and compositionally similar among the volcanoes. The highest concentrations of S and Cl occurred on the surface of the sublimates, while internally they had less than 1 wt % S and Cl in most cases, leading us to classify them as alloys. The major components of the alloys were Cu, Sn, Co, and Ag based on electron microprobe analyses and environmental scanning electron microscope element maps. Alloy element maps showed a covariance of Cu-Sn, while Co and Ag concentrations varied independently. Laser ablation-inductively coupled plasma-mass spectrometry analysis of matrix glass and melt inclusions in bombs from Stromboli showed appreciable amounts of Cu, Co, and Sn. We propose a model for the origin of the metallic grains, which involves syneruptive and posteruptive magma degassing and subsequent cooling of the basalt vesicles. During syneruptive vapor phase exsolution, volatile metals (Cu, Co, and Sn) partition into the vapor along with their ligands, S and Cl. The apparent oxygen fugacity (fO2) in these vapor bubbles is low because of the relative enrichment of the exsolved gas phase in H2 relative to H2O in silicate melts, due to the much higher diffusivity of the former in silicate melts. The high fH2 and low fO2 induces the precipitation of metal alloys from the vapor phase. Subsequently, the reducing environment in the vesicle dissipates as the cooling vapor oxidizes and as H2 diffuses away. Then, metal-rich sulfides (and chlorides) condense onto the outer surfaces of the metal alloy grains either due to a decrease in temperature or an increase in fO2. These alloys provide important insights into the partitioning of metals into a magmatic volatile phase at low pressure and high temperature.

Oxygen fugacity (fO2) is a fundamental variable affecting phase equilibrium in magmas, and in externally heated pressure vessel experiments it is typically controlled by using redox buffer assemblages. However, these do not allow fine enough resolution; for example, most arc magmas fall between the fO2 imposed by the neighboring Ni–NiO and Re–ReO2 buffers and so does the transition of S2− to S6+ in magmas. Here we propose a new method to quantitatively impose fO2 in hydrous high-P–T experiments in molybdenum hafnium carbide (MHC) pressure vessels by admixing small amounts of hydrogen into the Ar pressure medium. The thermodynamic calculation procedure used to determine the initial amount of hydrogen to be loaded to constrain desired fO2 values was verified by CoPd alloy redox sensor experiments to be accurate within ±0.3 log units for the pressure (P) – temperature (T) range of 940–2060 bar and 800–1100 ∘C. As hydrogen can be slowly lost from the pressure medium due to diffusion through the vessel walls at high T, we also determined the hydrogen permeability of the MHC alloy as a function of T. The such-obtained hydrogen permeability equation for the MHC alloy can be used to determine the rate of fO2 increase for any MHC pressure vessel configuration. As the rate of fO2 increase is slow (e.g., 0.36 log units per day in our setup at T= 1000 ∘C), we propose that H2 addition to the Ar pressure medium is an effective way to accurately impose fO2 in many types of experiments conducted in MHC vessels allowing experimentation up to T= 1200 ∘C and P= 300 MPa.

Ultramafic and mafic rocks are possible targets for CO2 sequestration via mineral carbonation. The determination of reaction kinetics and the factors that control mineralization are important in order to understand and predict how fast injected CO2 will react with host rocks to permanently isolate and store the carbon. Here we present experimental results of olivine carbonation experiments using synthetic fluid inclusions (SFI) as micro-reactors. The micro-reactor technique coupled with non-destructive Raman spectroscopy allows us to monitor the reaction progress in situ and in real time at elevated temperatures (50–200°C) and pressures (several 10's to a few hundred bars), and quantify the amount of CO2 consumed in the reaction using the Raman CO2 densimeter and mass-balance calculations. Results show a measurable decrease of CO2 density in the fluid inclusions as a result of the reaction between the CO2-bearing seawater-like aqueous solution and olivine. Magnesite formation was observed within hours at ≥100°C, while at 50°C magnesite nucleation and precipitation was only observed after a few weeks. Raman mapping and FIB-SEM analysis confirmed the formation of a non-continuous Si-rich layer on the inclusion wall and the presence of ferroan magnesite as a reaction product. Reaction rates [log J (mol/m−2 s−1)] obtained for olivine carbonation range between ~-8.4 at 50°C and −4.7 at 200°C, which is sufficiently rapid to be suitable for commercial CO2 injection projects. Reaction rates involving a seawater-like fluid were similar to rates published for high salinity solutions containing NaHCO3, and were faster compared to rates involving solutions with low salinity. Thus, CO2 injection into submarine environments might offer some advantages over CO2 storage in onshore basalts where the pores are likely to be filled with low salinity meteoric water. The application of the synthetic fluid inclusion technique, combined with non-destructive analytical techniques, is a promising tool to monitor rates of fluid-rock reactions in situ and in real time. Here, we have documented its application to experimentally study carbonation reactions in the olivine-H2O-CO2-NaCl-MgCl2 system.

Major and trace element composition of silicate melt inclusions (SMI) and their rock-forming minerals were studied in mafic garnet granulite xenoliths from the Bakony–Balaton Highland Volcanic Field (Western-Hungary). Primary SMIs occur in clinopyroxene and plagioclase in the plagioclase-rich domains of mafic garnet granulites and in ilmenite in the vicinity of these domains in the wall rock. Based on major and trace elements, we demonstrated that the SMIs have no connection with the xenolith-hosting alkaline basalt as they have rhyodacitic composition with a distinct REE pattern, negative Sr anomaly, and HFSE depletion. The trace element characteristics suggest that the clinopyroxene hosted SMIs are the closest representation of the original melt percolated in the lower crust. In contrast, the plagioclase and ilmenite hosted SMIs are products of interaction between the silicic melt and the wall rock garnet granulite. A further product of this interaction is the clinopyroxene–ilmenite±plagioclase symplectite. Textural observations and mass ­balance calculations reveal that the reaction between titanite and the silicate melt led to the formation of these assemblages. We propose that a tectonic mélange of metapelites and (MOR-related) metabasalts partially melted at 0.3–0.5 GPa to form a dacitic–rhyodacitic melt leaving behind a garnet-free, plagioclase+clinopyroxene+orthopyroxene+ilmenite residuum. The composition of the SMIs (both major and trace elements) is similar to those from the middle Miocene calc-alkaline magmas, widely known from the northern Pannonian Basin (Börzsöny and Visegrád Mts., Cserhát and Mátra volcanic areas and Central Slovakian VF), but the SMIs are probably the result of a later, local process. The study of these SMIs also highlights how crustal contamination changes magma compositions during asthenospheric Miocene ascent.

While the recent decline in the δ13C composition of oceanic dissolved inorganic carbon (DIC) can be attributed to increasing anthropogenic CO2 emissions (13C Suess effect), the causes of natural variability in the δ13C of oceanic DIC (δ13CDIC) are far less understood. Unfortunately, instrumental oceanic DIC measurements are not available prior to the 1970s, prohibiting the observation and study of long-term variability in oceanic carbon isotope dynamics. Thus, in order to identify the main driving forces of changes in oceanic δ13CDIC, multicentury carbon isotope time series that extend from the present into the preindustrial period are required. Such time series may be extracted from the carbonate skeletons of long-lived marine organisms, which have been shown to be robust recorders of fluctuations and trends in oceanic δ13CDIC. In this study, we use an annually-banded coralline alga live-collected from the Labrador shelf to generate a 266-year time series of δ13CDIC changes in the Labrador Sea. Our results indicate that from the 1960s onwards, the rate of δ13CDIC decline in the Labrador Sea slightly exceeds the rate of δ13C decline in the atmosphere, providing support for the enhanced CO2 uptake ability of the Labrador Sea. In addition, the detrended algal δ13C time series displays multidecadal variability with typical Atlantic Multidecadal Oscillation (AMO) frequencies. We show that prior to the late 1980s, algal δ13C compositions significantly correlate with regional sea ice cover (SIC) variability, post-1850 instrumental, reconstructed AMO indices, and solar variability. We speculate that these low-frequency oscillations in δ13C reflect changes in marine primary productivity modulated by a mechanism involving solar changes, the AMO and SIC variability. Our algal carbon isotope time series suggests that while the anthropogenic Suess effect has influenced Labrador Sea δ13CDIC since the 1960s, its influence may have been obscured by the effects of natural climatic variability up until the late 1980s.

Carbon dioxide is one of the most abundant volatile components in magmas after H2O along with S and Cl, which are of great importance to the extraction of trace metals into magmatic-hydrothermal fluids and ore minerals. Yet the effect of CO2 on the partition coefficients of chlorine between water-rich fluid and melt (i.e. the ratio of mass Cl concentrations in the corresponding phase; [ D Cl fluid/melt ]) is still poorly constrained. We conducted a set of experiments to constrain the effect of CO2 on D Cl fluid/melt by equilibrating felsic silicate melts with aqueous NaCl-bearing fluids while varying the concentration of CO2 at pressures between 120 and 300 MPa and temperatures of 850 and 1000 °C. The starting melt was synthetized as a glass in the ternary albite-quartz-Al2O3 system to ensure the only significant metal chloride species in the equilibrium fluid phase was NaCl. The results demonstrate that D Cl fluid/melt values increase with the concentration of Cl in the fluid phase and the silicate melt. The addition of CO2 into aqueous metal chloride-bearing fluids induces a pronounced drop in D Cl fluid/melt , the extent of which is only weakly affected by pressure, temperature and fluid salinity, at least at relatively low Cl concentrations ( D Cl fluid/melt drop by approximately a factor of 3 in response to the addition of 20–25 mol% CO2 to the fluid phase due to the decreased ability of the fluid to hydrate NaCl ion pairs. A new empirical equation describing wt%-based D Cl fluid/melt is derived: l n [ D C l f l u i d / m e l t ] = 1.419 ± 0.048 ∗ l n P + 0.912 ± 0.031 ∗ l n C C l f l u i d + 1.434 ± 0.260 + 4547 ± 443 T - 4.026 ± 0.155 ∗ X C O 2 - 9.790 ± 0.440 which expresses D Cl fluid/melt as a function of pressure (in MPa), temperature (in Kelvins), and the equilibrium concentration of Cl (in wt%) and CO2 (as molar fraction) in the fluid. The average absolute percentage error of the model predictions relative to the experimental data is 7.3%. The equation contains only monotonous functions to allow moderate extrapolation outside the range of the calibration dataset as long as the fluid remains in the single-phase field (e.g. pressure above 100 MPa and up to 500 MPa or even higher). Our model equation represents a reasonable approximation for granitoid magma evolution in the upper and middle crust. The presence of CO2 suppresses fluid salinity at a given chloride content of a granitoid melt, which will also hinder the extraction of chloride-complexed ore metals (e.g. Cu, Pb, Zn, Mo, and Ag) into magmatic fluids, reducing the likelihood of base-metal ore formation (e.g. porphyry copper deposits) from such fluids in the uppermost crust. On the other hand, the highly volatile components, CO2, H2S and SO2, are enriched in magmatic fluids exsolving early during the ascent of hydrous magmas. Chloride suppression by CO2 and enrichment of fluids in sulfur species near the SO2/H2S predominance boundary favors extraction of sulfide-complexed metals, notably Au as Au(HS)0, Au(HS)2−, NaAu(HS)20 or Au(HS)S3− into low-salinity magmatic fluids. Such fluids resemble those forming mid-crustal lode gold deposits that are typically poor in base metals. Our experimental results may therefore be taken as indirect support for a magmatic component in fluids forming orogenic lode gold deposits.

Magmatic sulfur is an essential constituent for the genesis of porphyry-type ore deposits and also significantly affects the Earth’s climate when emitted into the atmosphere. As an increasing number of studies indicate that anhydrite commonly occurs as primary igneous mineral in arc magmas, any quantitative model aiming to assess the efficiency of sulfur degassing from magmas must take the potential presence of anhydrite into account. To facilitate this, we present a new empirical model to predict the solubility of anhydrite in silicate melts as a function of pressure (P), temperature (T) and silicate melt composition. The model is based on 189 experimental data points, encompassing T from 750 to 1325 °C, P from 30 to 3000 MPa and basaltic to rhyolitic melt compositions. Fifteen of these experiments were conducted as part of this study in rapid-quench Molybdenum – Hafnium Carbide pressure vessel assemblies to obtain tighter constraints on the effect of water concentration, P and T on anhydrite solubility. These experiments show that anhydrite solubility in the silicate melt rapidly increases with increasing T following Arrhenius relationship. The solubility of anhydrite also increases with increasing dissolved water concentration, with the relative increase being the most significant for felsic melt compositions. The new model predicts sulfur concentration at anhydrite saturation (SCAS) in the silicate melt with median and mean absolute percentage errors of 19 and 25 relative%, respectively. The model is equally successful over the entire P, T and compositional space included in its calibration. This is a significant improvement over most previously published models, which were calibrated based on a more limited P, T and compositional range, and predict SCAS with significantly larger errors when applied to the entire dataset utilized in this study. The implementation of the new anhydrite saturation model in an example scenario of the crystallization of a hydrous andesite magma at P = 200 MPa suggests that anhydrite saturation may severely limit the amount of S that can be transferred into the exsolving magmatic volatile phase during crystallization-driven degassing of upper crustal magma reservoirs.

The fast decline of Arctic sea ice is a leading indicator of ongoing global climate change and is receiving substantial public and scientific attention. Projections suggest that Arctic summer sea ice may virtually disappear within the course of the next 50 or even 30 yr with rapid Arctic warming. However, limited observational records and lack of annual-resolution marine sea-ice proxies hamper the assessment of long-term changes in sea ice, leading to large uncertainties in predictions of its future evolution under global warming. Here, we use long-lived encrusting coralline algae that strongly depend on light availability as a new in situ proxy to reconstruct past variability in the duration of seasonal sea-ice cover. Our data represent the northernmost annual-resolution marine sea-ice reconstruction to date, extending to the early 19th century off Svalbard. Algal records show that the decreasing trend in sea-ice cover in the high Arctic had already started at the beginning of the 20th century, earlier than previously reported from sea-ice reconstructions based on terrestrial archives. Our data further suggest that, although sea-ice extent varies on multidecadal time scales, the lowest sea-ice values within the past 200 yr occurred at the end of the 20th century.

The Hamburg meteorite fell on January 16, 2018, near Hamburg, Michigan, after a fireball event widely observed in the U.S. Midwest and in Ontario, Canada. Several fragments fell onto frozen surfaces of lakes and, thanks to weather radar data, were recovered days after the fall. The studied rock fragments show no or little signs of terrestrial weathering. Here, we present the initial results from an international consortium study to describe the fall, characterize the meteorite, and probe the collision history of Hamburg. About 1kg of recovered meteorites was initially reported. Petrology, mineral chemistry, trace element and organic chemistry, and O and Cr isotopic compositions are characteristic of H4 chondrites. Cosmic ray exposure ages based on cosmogenic 3He, 21Ne, and 38Ar are ~12Ma, and roughly agree with each other. Noble gas data as well as the cosmogenic 10Be concentration point to a small 40-60cm diameter meteoroid. An 40Ar-39Ar age of 4532±24Ma indicates no major impact event occurring later in its evolutionary history, consistent with data of other H4 chondrites. Microanalyses of phosphates with LA-ICPMS give an average Pb-Pb age of 4549±36Ma. This is in good agreement with the average SIMS Pb-Pb phosphate age of 4535.3±9.5Ma and U-Pb Concordia age of 4535±10Ma. The weighted average age of 4541.6±9.5Ma reflects the metamorphic phosphate crystallization age after parent body formation in the early solar system.

Continental arc magmas supply the ore-forming element budget of most globally important porphyry-type ore deposits. However, the processes enabling certain arc segments to preferentially generate giant porphyry deposits remain highly debated. Here we evaluate the large-scale covariation of key ore-forming constituents in this setting by studying silicate melt inclusions in volcanic rocks from a fertile-to-barren segment of the Andean Southern Volcanic Zone (33–40 °S). We show that the north-to-south, fertile-to-barren gradient is characterized by a northward increase in S and Cl concentrations and a simultaneous decrease in Cu. Consequently, we suggest that the concentration of S and Cl rather than the concentration of ore metals regulates magmatic-hydrothermal ore fertility, and that the loss of volatiles prior to arrival in the upper crust impacts ore-forming potential more than magmatic sulfide saturation-related ore metal scavenging.

Low-dimensional copper halides with high luminance have attracted increasing interest as heavy-metal-free light emitters. However, the optical mechanisms underpinning their excellent luminescence remain underexplored. Here, we report multiple self-trapped emissions in Cs

The Arctic cryosphere is changing at a rapid pace due to global warming and the large-scale changes observed in the Arctic during the past decades exert a strong influence throughout the global climate system. The warming of Arctic surface air temperatures is more than twice as large as the global average over the last two decades and recent events indicate new extremes in the Arctic climate system, e.g. for the last five years Arctic annual surface air temperature exceeded that of any year since 1900 AD. Northern Spitsbergen, Svalbard, located in the High Arctic at 80°N, is a warming hotspot with an observed temperature rise of ~6°C over the last three decades indicating major global warming impacts. However, even the longest available datasets on Svalbard climatic conditions do not extend beyond the 1950s, inhibiting the study of long-term natural variability before anthropogenic influence. Ongoing climate trends strongly affect the state of both glaciers and seasonal snow in Svalbard. Modeled data suggest a marked increase in glacier runoff during recent decades in northern Svalbard. However, observational data are sparse and short and the potential effects on the surface ocean are unclear.This study focuses on the ultra-high-resolution analysis of calcified coralline algal buildups growing attached to the shallow seafloor along Arctic coastlines. Analysis of these new annually-layered climate archives is based on the long-lived encrusting coralline algae Clathromorphum compactum, providing a historic perspective on recently observed changes. Here, we present a 200-year record of past surface ocean variability from Mosselbukta, Spitsbergen, northern Svalbard. By using algal Ba/Ca ratios as a proxy for past glacier-derived meltwater input, we investigate past multi-decadal-scale fluctuations in land-based freshwater contributions to the ocean surface layer. Our records, based on multiple coralline algal specimens, show a strong and statistically significant increasing trend in algal Ba/Ca ratios from the 1990s onwards, suggesting a drastic increase in land-based runoff at Mosselbukta. The drastic rate of increase is unprecedented during the last two centuries, directly capturing the impact of amplified surface air temperature warming on coastal high Arctic surface ocean environments.

Evidence of secondary gold enrichment due to the addition of new gold into an earlier orogenic quartz-carbonate vein deposit by magmatic-hydrothermal fluids is strongly suggested for the Madrid Deposit, hosted in the Hope Bay Greenstone Belt in Nunavut, Canada. The conclusion is based on an extensive in situ microanalytical protocol (SEM, confocal Raman microspectroscopy, microthermometry, decrepitate mound analysis, LA-ICP-MS, cathodoluminescence, SIMS) not previously applied to gold systems. This approach was used to characterize the mineralogy and fluid inclusion systematics associated with the upgrading event. Mineralization comprised of only Ag-bearing gold (“electrum”; 89.8 at. % Au avg.; n = 8) is present throughout all investigated laminated and brecciated orogenic quartz veins. However, in high-grade vein intersections where gold grades are locally elevated (up to 122 g/t), assemblages containing tennantite-tetrahedrite + chalcopyrite + electrum (80.7 at. % Au avg.; n = 15) ± Ag Pb Au tellurides occur that are texturally late-stage relative to electrum-only mineralization. Subdomains of quartz coeval with this later assemblage are optically- and texturally-distinct from earlier orogenic quartz. This late mineral assemblage is absent in all low-grade vein intersections (∼1 g/t Au avg.) examined where only electrum is identified. Quartz-hosted fluid inclusions (H2O NaCl ± CO2) of intermediate salinity (16.7 ± 1.2 wt.% NaCl equiv.; n = 93) were identified only in the high-grade vein samples and are present along healed planes associated with tennantite-tetrahedrite + chalcopyrite + electrum ± Ag Pb Au telluride assemblages. In situ SIMS δ18O analyses of quartz, combined with temperature constraints from mineral equilibria, show that early orogenic vein quartz and late quartz subdomains associated with gold upgrading precipitated from fluids with similar δ18OH2O values of 4.5–12.4‰ (n = 10) and −5.5 to 11.8‰ (n = 13), respectively. Isotopic data suggests that meteoric water was a negligible component in fluids responsible for gold precipitation. Microthermometry and Raman spectroscopy show that upgrading fluids were distinct in composition compared to the earlier metamorphic fluids (H2O NaCl CO2 ± CH4 ± N2; 4.6 ± 1.6 wt.% NaCl equiv., n = 33) and later Canadian Shield basement brines (H2O NaCl; 22.4 ± 1.2 wt.% NaCl equiv., n = 12) which have also been identified in the fluid inclusion record at Madrid. Laser ablation ICP-MS analyses indicate the gold upgrading fluids are enriched in As Sb Zn Pb and LILE (Cs Ba Rb Sr); these data are consistent with late fluids derived from an evolved magmatic-hydrothermal system. Trace element mapping of pyrite, coupled with principle component analysis of the data, confirms a strong correlation between Au and Ag Te Sb Bi W( As) in upgraded veins, whereas only Au and As strongly correlate in low-grade veins. The study suggests that gold upgrading, either involving newly introduced gold or remobilization of existing gold, can be linked to the incursion of a late magmatic-hydrothermal fluid that post-dated formation of the main orogenic-type auriferous quartz vein system. The geological setting and mineral-chemical features suggest an intrusion-related (i.e., porphyry), or intermediate-sulfidation epithermal mineralization style for the later event. This work provides another example of the importance of compositionally distinct cumulative hydrothermal events in the development of high-grade gold deposits in orogenic settings.

Silver is a common and economically important constituent of many magmatic-hydrothermal ore deposits, yet little is known about its mobility during magma degassing. We performed experiments to determine the effect of various chemical components (NaCl, KCl, LiCl, HCl, CaCl2, H2S) on the solubility and speciation of Ag in high-temperature, low-density fluids (≈0.38–0.54 g/cm3). The experiments were conducted at T = 900 °C, P = 2000 bar and oxygen fugacity (fO2) of 0.5 log units below Ni-NiO buffer (NNO-0.5) in rapid-quench Molybdenum-Hafnium Carbide externally-heated pressure vessel assemblies. The fluid phase was sampled at run conditions by the entrapment of synthetic fluid inclusions (SFI) in in situ fractured quartz chips. As capsule material, Au97Ag2Cu1 alloy was used, which imposed an Ag activity of 0.005. The apparent Ag solubility, defined as the equilibrium concentration of Ag in the fluid phase at an Ag activity of 0.005, exponentially increases as a function of total chloride concentration in the NaCl-H2O and NaCl-HCl-H2O systems. In the mixed NaCl-HCl system, at a fixed total Cl concentration of 1 mol/kg (1 m) H2O and varying NaCl/HCl ratios, the apparent solubility of Ag reaches a maximum (432 ± 123 μg/g) at equal NaCl and HCl concentration (0.5 m each) and then decreases towards both end-members (1 m for NaCl or HCl) following a parabolic function. Apparent silver solubilities predicted using the HKF model and thermodynamic properties for traditional Ag-chloride and bisulfide complexes greatly underestimate the measured values. Model calculations suggest that instead of charged AgCl2−, a neutral NaAgCl2 species is the dominant dissolved Ag species in S-free, chloride-bearing fluids with the additional presence of NaAgHSCl in S-bearing fluids. Comparison of the solubility data in high-temperature fluids to measured Ag solubilities in silicate melts suggests that efficient Ag partitioning into magmatic fluids will only take place when the composition of the silicate melt is felsic enough (rhyodacitic to rhyolitic), similarly to the behavior of Cu but in contrast to that of Au.

The solubilities of Pd and Au in a hydrous trachyandesitic melt were experimentally determined at 1000 °C and 200 MPa at oxygen fugacity (ƒO2) from 0.45 log units below to 6.55 log units above the Ni-NiO buffer (NNO). The effect of adding metal-binding ligands (i.e. Cl and S) to the silicate melt was also studied. The solubility of Au increases from 0.15 ± 0.1 to 3.85 ± 1.48 ppm in Cl- and S-free melts with ƒO2 increasing from NNO−0.45 to NNO+6.55 with a slope that suggests that it is present in 1+ oxidation state over the entire studied ƒO2 range. On the other hand, Pd solubility, shows a more moderate increase with ƒO2, especially in the lower half of the studied range, increasing from 2.66 ± 0.25 ppm at NNO−0.45 to only 3.62 ± 0.38 ppm at NNO+1.72 in Cl- and S-free melts. Overall, the variation in Pd solubility as a function of ƒO2 indicates Pd being dissolved in the silicate melt in both zero and 1+ oxidation state, with the former being dominant below NNO+4.5. At NNO−0.45 to +3.48, the addition of 3170–4060 ppm Cl to the silicate melt increased the solubility of Au by an average factor of 1.5, in comparison to Cl-free melts. However, at NNO+6.55, Au solubility increased by a factor of 2.5. The addition of Cl had a negligible effect on the solubility of Pd except for a large increase (factor of 2.4) at NNO+6.55. At reducing conditions (NNO−0.45), the addition of 170 ppm S to the silicate melt increased the solubility of Au by a factor of ∼4 but did not change the solubility of Pd in comparison to S-free melts. The observation that Pd is dominantly present as Pd0 at NNO

The diffusivity of S in a hydrous dacitic melt (4.5–6.0 wt.% H2O) has been investigated in the temperature (T) and pressure (P) range of 950 °C to 1100 °C and 200 to 250 MPa, respectively. Three series of experiments were conducted at relatively low oxygen fugacity (fO2) conditions [0.8 log units below fayalite-magnetite-quartz equilibrium (FMQ −0.8); referred to as “low fO2”] and high fO2 conditions (FMQ +2.5; referred to as “high fO2”) to determine if the diffusivity of S is affected by its oxidation state and speciation. Sulfur concentration profiles were measured by electron microprobe and the diffusion coefficient (D) was calculated by fitting these profiles. Sulfur diffusion is approximately one order of magnitude faster when S is dominantly present as sulfide species (low fO2) in comparison to the sulfate dominated experiments (high fO2). The following Arrhenian equations were obtained for high and low fO2 conditions at 200 MPa: high fO 2 : D = 10 - 5.92 ± 0.86 ∗ exp - 137.3 ± 21.5 kJ / mol RT low fO 2 : D = 10 - 5.18 ± 1.39 ∗ exp - 125.7 ± 34.4 kJ / mol RT where D is the average diffusion coefficient in m2 s−1, R is the gas constant in 8.3144 J mol−1 K−1 and T is the temperature in K. Our results demonstrate for the first time in natural melts that S diffusion is strongly sensitive to fO2. Our S diffusivities under low fO2 conditions are only slightly slower of those found for H2O, suggesting that S can be rather efficiently purged from reduced dacitic melts during volcanic eruptions. However, for more oxidized systems (e.g. subduction zones), S diffusion will be much slower and will hinder equilibrium syn-eruptive degassing during rapid decompression. Therefore, we conclude that the “excess S” measured during many explosive volcanic eruptions in arcs is dominantly derived from S-rich bubble accumulation in the eruptible portion of the magma reservoir.

Bingham Canyon is one of the world's largest porphyry Cu–Mo–Au deposits and was previously used as an example to emphasize the role of magma mixing and magmatic sulphide saturation in the enhancement of ore fertility of magmatic systems. We analyzed whole rocks, minerals, and silicate melt inclusions (SMI) from the co-genetic, ore-contemporaneous volcanic package (∼38 Ma). As opposed to previous propositions, whole-rock trace element signatures preclude shoshonite–latite genesis via mixing of melanephelinite and trachyte or rhyolite, whereas core to rim compositional profiles of large clinopyroxene phenocrysts suggests the amalgamation of the ore-related magma reservoir by episodic recharge of shoshonitic to latitic magmas with various degrees of differentiation. Major and trace element and Sr and Nd isotopic signatures indicate that the ore-related shoshonite–latite series were generated by low-degree partial melting of an ancient metasomatized mantle source yielding volatile and ore metal rich magmas. Latite and SMI compositions can be reproduced by MELTS modeling assuming 2-step lower and upper crustal fractionation of a primary shoshonite with minimal country rock assimilation. High oxygen fugacities ( ≈ NNO + 1 ) are prevalent as evidenced by olivine-spinel oxybarometry, high SO3 in apatite, and anhydrite saturation. The magma could therefore carry significantly more S than would have been possible at more reducing conditions, and the extent of ore metal sequestration by magmatic sulphide saturation was minimal. The SMI data show that the latites were Cu rich, with Cu concentrations in the silicate melt reaching up to 300–400 ppm at about 60 wt% SiO2. The Au and Ag concentrations are also high (1.5–4 and 50–200 ppb, respectively), but show less variation with SiO2. A sudden drop in Cu and S concentrations in the silicate melt at around 65 wt% SiO2 in the presence of high Cl, Mo, Ag, and Au shows that the onset of effective metal extraction by fluid exsolution occurred at a relatively late stage of magma evolution. Overall, our results show that fluid exsolution during simple magmatic differentiation of oxidized alkaline magmas is capable of producing giant porphyry Cu deposits.

The partition coefficients of Cu, Au and Mo between liquid and vapor were determined at P = 130 MPa and T = 900 °C, and P = 90 MPa and T = 650 °C and redox conditions favoring the dominance of reduced S species in the fluid. The experiments at 900 °C were conducted in rapid-quench Molybdenum-Hafnium Carbide externally-heated pressure vessel assemblies, whereas those at 650 °C were run in Rene41 pressure vessels. The fluids were sampled at run conditions using the synthetic fluid inclusion technique. The host quartz was fractured in situ during the experiments ensuring the entrapment of equilibrium fluids. A new method was developed to quantify the composition of the vapor inclusions from LA-ICPMS analyses relying on the use of boron as an internal standard, an element that fractionates between vapor and liquid to a very small degree. The bulk starting fluid compositions closely represented those expected to exsolve from felsic silicate melts in upper crustal magma reservoirs (0.64 m NaCl, 0.32 m KCl, ±0.2 m HCl and/or 4 wt% S). The experiments were conducted in Au 97 Cu 3 alloy capsules allowing the simultaneous determination of apparent Au and Cu solubilities in the liquid and the vapor phase. Though the apparent metal solubilities were strongly affected by the addition of HCl and S in both phases, all three elements were found to preferentially partition to a liquid phase at all studied conditions with an increasing degree of preference for the liquid in the following order Au K i - Na liq / vap = D i liq / vap / D Na liq / vap ) fall in the following ranges respectively for each studied metal: K Au - Na liq / vap = 0.20 ± 0.07–0.50 ± 0.19 (1 σ ); K Cu - Na liq / vap = 0.36 ± 0.12–0.76 ± 0.22; K Mo - Na liq / vap = 0.67 ± 0.15–2.5 ± 0.8. Decreasing T from 900 °C to 650 °C slightly shifted K Au - Na liq / vap and K Cu - Na liq / vap to the lower end of the reported ranges. A consequence of K Au - Na liq / vap and K Cu - Na liq / vap being significantly smaller than 1 is that much of the Au and a significant fraction of Cu may be carried to shallower levels of magmatic-hydrothermal systems by residual vapors despite potentially extensive brine condensation.

The equilibrium between aqueous fluids and allanite-bearing eclogite has been investigated to constrain the effect of temperature ( T ) and fluid composition on the stability of allanite and on the mobility of major and trace elements during the dehydration of eclogites. The experiments were performed at 590–800 °C and 2.4–2.6 GPa, and fluids were sampled as synthetic fluid inclusions in quartz using an improved entrapment technique. The concentrations and bulk partition coefficients were determined for a range of major (Mg, Ca, Na, Fe, Al, Ti) and 16 trace elements as a function of T and fluid composition. The results reveal a significant effect of T on element partitioning between the fluids and the solid mineral assemblage. The partition coefficients increase by more than an order of magnitude for most of the major and trace elements, and several orders of magnitude for light rare-earth elements (LREE) from 590 to 800 °C. The addition of various ligand species into the fluid at 700 °C results in distinctive trends on element partitioning. The concentrations and corresponding partition coefficients of most of the elements are enhanced upon addition of NaF to the fluid. In contrast, NaCl displays a nearly opposite effect by suppressing the solubilities of major elements and consequently affecting the mobility of trace elements that form stable complexes with alkali-(alumino)-silicate clusters in the fluid, e.g. high field strength elements (HFSE). The results further suggest that fluids in equilibrium with orthopyroxene and/or diopsidic clinopyroxene are peralkaline (ASI ∼0.1–0.7), whereas fluids in equilibrium with omphacitic pyroxene are more peraluminous (ASI ∼1.15). Therefore, natural aqueous fluids in equilibrium with eclogite at about 90 km depth will be slightly peraluminous in composition. Another important finding of this study is the relatively high capacity of aqueous fluids to mobilize LREE, which may be even higher than that of hydrous melts.

A series of piston cylinder experiments were conducted to determine the partition coefficient of Cu between amphibole and andesitic to rhyolitic silicate melts. The experiments were run at T = 740–990 °C, P = 0.7 GPa, oxygen fugacity ( f O 2 ) ranging from that of the Ni-NiO buffer (NNO) to 2.3 log units higher (NNO + 2.3 and dissolved water in variable concentrations (under-saturated to saturated conditions). Fixed metal activities were imposed by using Au 97 Cu 3 and Au 92 Cu 8 alloy capsules, which allowed simultaneously determination of Cu solubility. Our data demonstrate that Cu solubilities in both the silicate melt and amphibole decrease with decreasing temperature. The solubility of Cu decreases by a factor of 6 from 990 to 740 °C in equilibrium with andesitic to rhyolitic melt compositions. The average amphibole/silicate melt partition coefficient of Cu [D Cu (amph/melt)] is 0.066 ± 0.006, and is essentially constant without showing any correlation with silicate melt composition, dissolved water concentration, temperature or f O 2 . The low D Cu (amph/melt) value suggests that amphibole crystallizing at any stage of calc-alkaline magma evolution is unable to scavenge a significant fraction of the initially available Cu from the melt. However, D Cu (amph/melt) is high enough to yield precisely measurable Cu concentrations in natural amphiboles. As D Cu (amph/melt) remains constant along the liquid line of descent of calc-alkaline magmas, amphibole compositions may thus be used as a proxy to monitor the evolution of the Cu concentration in the silicate melt (not the bulk magma if sulfide is present). This may be useful for understanding the metallogenic evolution of intrusive rocks, in which silicate melt inclusions in minerals are generally absent. As most porphyry-type Cu ore deposits are associated with upper crustal intrusions, in-situ microanalysis of inclusion-free amphiboles in such rocks may help understand ore genesis and might also be used in mineral exploration to assess the fertility of prospective magmatic systems.

In the past three years, machine learning (ML) in combination with density functional theory (DFT) has enabled computational screening of compounds with the goal of accelerated materials discovery. Unfortunately, DFT+ML has, until now, either relied on knowledge of the atomic positions at DFT energy minima, which are a priori unknown, or been limited to chemical spaces of modest size. Here we report a strategy that we term learning-in-templates (LiT), wherein we first define a series of space group and stoichiometry templates corresponding to hypothesized compounds and, orthogonally, we allow any list of atoms to take on any template. The LiT approach is deployed in combination with previously established position-dependent representations and performs best with the representations that rely least on the atomic positions. Since the positions of the atoms in templates are known and do not change, LiT enables us to infer the properties of interest directly; additionally, LiT allows working with increased chemical spaces, since the same elements can take on a large number of templates. Only by using LiT were we able to span 5 × 10

The release of large amounts of sulfur to the stratosphere during explosive eruptions affects the radiative balance in the atmosphere and consequentially impacts climate for up to several years after the event. Providing quantitative estimates for the processes that control the mass balance of sulfur between melt, crystals and vapor bubbles is needed to better understand the potential sulfur yield of individual eruption events and the conditions that favor large sulfur outputs to the atmosphere.The processes that control sulfur partitioning in magmas are (1) exsolution of volatiles (dominantly H2O) during decompression (first boiling) and during isobaric crystallization (second boiling), (2) the crystallization and breakdown of sulfide or sulfate phases in the magma and (3) the transport of sulfur-rich vapor transport (gas influx) from deeper unerupted regions of the magma reservoir. Vapor exsolution and the formation/breakdown of sulfur-rich phases can all be considered as closed system process where mass balance arguments are generally easier to constrain, whereas the contribution of sulfur by vapor transport (open system process) is more difficult to quantify. The ubiquitous “Excess Sulfur”, which refers to the much higher sulfur mass released during eruptions than what can be accounted for by the melt inclusion data (petrologic estimate), reflects the challenges in closing the sulfur mass balance between crystals, melt and vapor before and during a volcanic eruption. In this work, we try to quantify the relative importance of closed and open system processes for silicic arc volcanoes using kinetic models of sulfur partitioning during exsolution. Our calculations show that crystallization-induced exsolution (second boiling) can generate a significant fraction of the “Excess Sulfur” observed in crystal-rich arc magmas. This result does not preclude vapor migration to play an important role in the sulfur mass balance, but rather points out that second boiling (in-situ exsolution) can provide the necessary yield to drive the excess sulfur to the levels observed for these eruptions. In contrast, recharges of magma releasing sulfur-rich bubbles are necessary and most likely the primary contributor to the sulfur mass balance in silicic crystal-poor units. Finally, we apply our model to account for the effect of sulfur partitioning during second boiling and its impact on sulfur released during the Cerro Galan super-eruption in Argentina (2.08 Ma), and show the importance of second boiling in releasing a large amount of sulfur to the atmosphere during the eruption of large crystal-rich ignimbrites.

Brine and vapor inclusions were synthesized to study Cl/Br fractionation during magmatic–hydrothermal fluid phase separation at 900 °C and pressures of 90, 120, and 150 MPa in Li/Na/K halide salt–H2O systems. Laser ablation ICP-MS microanalysis of high-density brine inclusions show an elevated Cl/Br ratio compared to the coexisting low-density vapor inclusions. The degree of Cl/Br fractionation between vapor and brine is significantly dependent on the identity of the alkali metal in the system: stronger vapor partitioning of Br occurs in the Li halide–H2O system compared to the systems of K and Na halide–H2O. The effect of the identity of alkali-metals in the system is stronger compared to the effect of vapor–brine density contrast. We infer that competition between alkali-halide and alkali-OH complexes in high-temperature fluids might cause the Cl/Br fractionation, consistent with the observed molar imbalances of alkali metals compared to halides in the analyzed brine inclusions. Our experiments show that the identity of alkali metals controls the degrees of Cl/Br fractionation between the separating aqueous fluid phases at 900 °C, and suggest that a significant variability in the Cl/Br ratios of magmatic fluids can arise in Li-rich systems.

Halogens, mainly F and Cl, play key roles in the evolution and rheology of silicic magmas, magmatic-hydrothermal transition, partitioning of metals into aqueous fluids, and formation of ore deposits. Similarity of ionic radii of O, hydroxyl, and F, and a much greater size of Cl are responsible for (i) higher solubility, hence compatibility of F in silicate melts, (ii) greater lattice energies of fluorides, therefore their more refractory character and lower solubilities in fluids, and (iii) higher hardness of F as ligand for complexing, leading to a distinct spectrum of metal-fluoride versus metal-chloride complexes. In the F-rich systems, the interaction of F with rock-forming aluminosilicates corresponds to progressive fluorination by the thermodynamic component F2O−1. Formation of F-bearing minerals first occurs in peralkaline and silica-undersaturated systems that buffer F concentrations at very low levels (villiaumite, fluorite). The highest concentrations of F are reached in peraluminous silica-saturated systems, where fluorite or topaz are stable. Coordination differences and short-range order effects between [NaAl]–F, Na–F versus Si–O lead to the fluoride-silicate liquid immiscibility, which extends from the silica–cryolite binary to the peralkaline albite–silica–cryolite ternary and to peraluminous topaz-bearing systems, where it may propagate to solidus temperatures in the presence of other components such as Li. Differentiation paths of silicic magmas diverge, depending on the Ca-F proportions. In the Ca-rich systems, the F enrichment is severely limited by fluorite crystallization, whereas the Ca-poor magmas evolve to the high F concentrations and saturate with topaz, cryolite, or immiscible multicomponent fluoride melts (brines). These liquids preferentially partition and decouple high-field strength elements and rare-earth elements (REE), and are responsible for the appearance of non-chondritic element ratios and/or lanthanide tetrad effects. Continuous transition from volatile-rich silicate melts to hydrothermal fluids is unlikely, although two fluids—hydrous halide melts and solute-poor aqueous fluids—may often exsolve simultaneously. The fluoride ligand is responsible for the effective sequestration of hard cations, mainly REE, Th, U, and Zr, into the hydrothermal fluids. In the Cl-dominated systems, the maximum concentrations in silicate melts are significantly lower than those of F due to the absence of bonding between Cl and network-forming cations in the melt structure. The typical Cl-rich phase in felsic magmas is an aqueous ± carbonic fluid phase; the saturation of which limits the attainable concentration of Cl in the silicate melt. The more depolymerized the structure of the silicate melt is, the more easily metal-chloride species are accommodated. Therefore, metaluminous rhyolites are characterized by the highest fluid/melt partition coefficients for Cl as well as the lowest maximum dissolved Cl concentration. Chlorine is dominantly present as NaCl, KCl, CaCl2, FeCl2, and HCl species in aqueous magmatic fluids; their relative proportions are strongly influenced by silicate melt composition, pressure and total dissolved chloride concentration. The activity coefficients of metal-chloride species in the aqueous fluid are strongly dependent on pressure and total chloride concentration, and so is the volatile/melt partition coefficient of Cl. The increase of pressure strongly promotes Cl partitioning into the fluid phase, whereas increased chloride concentrations in the fluid work against it, especially if vapor-brine immiscibility occurs anchoring the activity of major chloride species in the system. Chloride ions are dominant, or at least take the form of significant complex forming ligands for a broad range of economically important elements found in magmatic-hydrothermal ore deposits such as Cu, Au, Mo, Pb, Zn, Sn, and W. Therefore, Cl has significant effect on the volatile/melt and vapor/brine partition coefficients of these elements, and at least partially controls the likelihood of the formation of economic ore mineralization.

The platinum-group elements (PGEs; Os, Ir, Ru, Rh, Pt, Pd), along with rhenium and gold, are grouped together as the highly siderophile elements (HSEs), defined by their extreme partitioning into the metallic, relative to the oxide phase (> 104). The HSEs are highly refractory, as gauged by their high melting and condensation temperatures, and were therefore relatively concentrated in the feedstock for the terrestrial planets, as defined by the composition of chondritic meteorites (e.g., Anders and Ebihara 1982; Horan et al. 2003; Fischer-Godde et al. 2010). However, the planetary formation and differentiation process has since acted on this chemical group to produce a rich variety of absolute and relative inter-element fractionations. For example, analysis of iron meteorites suggests a significant decoupling of the HSE in the cores of planetesimals, and likely Earth’s core, with Os, Ir, Ru (IPGE-group) and Re concentrated in the metal phase, and Pt, Rh, Pd (PPGE-group) plus Au usually concentrated in the residual liquid (Goldstein et al. 2009). In terms of the silicate Earth, analysis of mantle rocks reveals very low levels of the HSE, but relative abundances similar to chondrites (see review by Day et al. 2016, this volume), in part reflecting HSE segregation into core-forming iron (Ringwood 1966; Ganapathy et al. 1970). This is in contrast to mantle-derived melts, whose HSE abundances are highly fractionated, with relative depletions in the IPGE-group compared to PPGE-group, as well as Re and Au (Barnes et al. 1985). Resulting Re/Os and Pt/Os fractionation also influence the long-term evolution of the 187Re to 187Os and 190Pt to 186Os decay systems, and, hence, the development of distinctive Os-isotope reservoirs (Walker et al. 1997; Shirey and Walker 1998; Day 2013). The emplacement of mantle-derived magmas into Earth’s crust results in …

Experiments were conducted at 500 MPa and 1240 °C in a piston cylinder apparatus to assess the effect of melt composition on the melt/volatile partition coefficient of sulfur ( D S melt / volatile ) , which was used as a measure of the silicate melt’s capacity to dissolve oxidized sulfur species. Iron-free, three- and four-component silicate melts were equilibrated with H2O–S fluids with sulfur concentrations ⩽2 mol% at an oxygen fugacity imposed by the Re–ReO2 buffer (1.4 log units above the Ni–NiO buffer). At these conditions, SO2 (S4+) is predicted to be the dominant sulfur species in the volatile phase and sulfate (S6+) is the dominant sulfur species in the silicate melt. The values of D S melt / volatile were calculated by mass balance. The results show that D S melt / volatile values increase exponentially with decreasing the degree of polymerization of the silicate melt structure. For example, in calcium-aluminosilicate melts, D S melt / volatile changes from 0.005 to 0.3 as the degree of melt polymerization changes from the equivalent of a rhyolite to the equivalent of a basalt. At a constant degree of melt polymerization, D S melt / volatile in equilibrium with sodium-aluminosilicate (NAS) melts is more than an order of magnitude higher than in equilibrium with calcium-aluminosilicate (CAS) melts, and more than two orders of magnitude higher than in equilibrium with magnesium-aluminosilicate (MAS) melts. The value of D S melt / volatile changes from 0.014 in MAS glasses to 3.4 in NAS glasses for the most depolymerized compositions in each series. Potassium has a similar effect on sulfate dissolution to that of Na. The variation of D S melt / volatile in equilibrium with various calcium–sodium aluminosilicate (CNAS), magnesium–sodium aluminosilicate (MNAS) and magnesium–potassium aluminosilicate (MKAS) melts indicates that alkalis are only available for sulfate complexation when they are present in excess compared to the required amount to charge balance for the Si4+ to Al3+ substitution in the melt structure. Calcium has a moderate, Mg has a very minor affinity to replace alkalis in this charge balancing role. Apparent equilibrium constants are provided to predict the available amount of various network modifiers for sulfate complexation and, therefore, the presented data can be used to predict D S melt / volatile for geologically relevant melt compositions.

Peridotite xenoliths from the Nógrád–Gömör Volcanic Field (NGVF) record the geochemical evolution of the subcontinental lithospheric mantle beneath the northern margin of the Pannonian Basin. This study is focused on spinel lherzolites and presents petrography, and major and trace element geochemistry for 51 xenoliths selected from all xenolith-bearing localities of the NGVF. The xenoliths consist of olivine, orthopyroxene, clinopyroxene and spinel ± amphibole. No correlations between modal composition and textures were recognized; however, major and trace element geochemistry reveals several processes, which allow the distinction of xenolith groups with different geochemical evolution. The xenoliths have undergone varying degrees (∼7–25%) of partial melting with overprinting by different metasomatic processes. Based on their Mg#, the xenoliths can be subdivided into two major groups. Group I has olivine Mg# between 89 and 91, whereas Group II has Mg#, Journal of Petrology, 58 (6), ISSN:0022-3530, ISSN:1460-2415

Sulfur is an important volatile element involved in magmatic systems. Its quantification in silicate glasses relies on state-of-the-art techniques such as electronprobe microanalyses (EPMA) or X-ray absorption spectroscopy but is often complicated by the fact that S dissolved in silicate glasses can adopt several oxidation states (S6+for sulfates or S2-for sulfides). In the present work, we use micro-Raman spectroscopy on a series of silicate glasses to quantify the S content. The database is constituted by 47 silicate glasses of various compositions (natural and synthetic) with S content ranging from 1179 to 13 180 ppm. Most of the investigated glasses have been synthesized at high pressure and high temperature and under fully oxidizing conditions. The obtained Raman spectra are consistent with these fO2conditions and only S6+is present and shows a characteristic peak located at ∼1000 cm-1corresponding to the symmetric stretch of the sulfate molecular group (ν1SO42-SO42-). The intensity of the ν1SO42-SO42-peak is linearly correlated to the parts per million of S6+determined by EPMA. Using subsequent deconvolution of the Raman spectra, we established an equation using the ratio between the areas of the ν1SO42-SO42-peak and the silicate network species (Qn) in the high-frequency region: ppm S6+=34371ASO42-AQn±609. ppm S6+=34371 ASO42-A Qnpm609. We tested our calibration on several silicate glasses equilibrated under moderately reducing conditions (QFM+0.8 ≤fO2≤ QFM+1.4) in which S is dissolved as both SO42-SO42-and S2-. We also analyzed several olivine-hosted melt inclusions collected from Etna for which the fO2and S speciation are unknown. For these samples, the S content estimated by the Raman calibration is systematically lower than the total S measured by EPMA. We combined both methods to estimate the S2-content not accounted for by Raman and derive the S speciation and fO2conditions. The derived fO2is consistent with the imposed fO2for synthesized glasses and with current assumed fO2conditions for basaltic melt inclusions from Etna.

The characteristic REE fractionation pattern in arc magmas compared to MOR-basalts results from the selective mobilization of light rare-earth elements (LREE) by slab-derived mobile components. However, the nature and composition of the slab flux, and the actual mechanisms responsible for the transfer of rare-earth elements (REE) from the slab to the mantle wedge remain unclear. We present experimental data on the solubility of selected REE in ligand-bearing aqueous fluids and a hydrous haplogranitic melt at 2.6 GPa and 600–800 °C, spanning the conditions relevant to slab dehydration and melting. The solubilities of REE in aqueous fluids increase more than an order of magnitude with temperature increasing from 600 to 800 °C. Addition of ligands such as Cl−, F−, CO 3 2 − , SO 4 2 − in relatively small concentrations (0.3–1.5 m [mol/kg H2O]) has a pronounced effect further enhancing REE solubilities. Each ligand yields a characteristic REE pattern by preferential dissolution of either the light or the heavy REE. For example, the addition of NaCl to the aqueous fluids yields highly elevated LREE/HREE ratios ( La/Yb = 17.4 ± 4.3 ), whereas the addition of fluoride and sulfate ligands significantly increases the solubility of all REE with moderate LREE/HREE fractionation ( La/Yb ∼ 4 ). The addition of Na2CO3 results in preferential increase of HREE solubilities, and yields La/Yb ratio of 1.6 ± 0.5 by flattening the moderately fractionated REE pattern seen in pure aqueous fluids. The solubilities in hydrous haplogranite melt are moderate in comparison to those observed in aqueous fluids and do not lead to pronounced REE fractionation. Therefore, REE can be effectively mobilized and fractionated by aqueous fluids, compared to felsic hydrous melts. Furthermore, the aqueous fluid chemistry has a major role in determining REE mobilities and fractionation upon slab dehydration in addition to the significant control exerted by temperature. Our results show that chloride-bearing slab-derived aqueous fluids have a significant contribution to the formation of REE-signatures in arc-magmas, especially at lower slab surface temperatures.

Microanalysis of individual fluid inclusions by laser ablation inductively coupled mass spectrometry (LA-ICP-MS) is a powerful tool for reconstructing the composition of hydrothermal fluids, but it demands a sample quality that is unattainable in many cases. In orogenic gold deposits, the need for direct fluid microanalysis has been present for several decades, but due to the high fluid flux and prolonged hydrothermal and tectonic history that typifies these systems, most samples do not meet the criteria of fluid inclusion size and distribution that allow LA-ICP-MS analysis of individual isolated fluid inclusions. To overcome this difficulty, a method has been developed and tested, whereby areas of quartz densely populated with fluid inclusions (e.g., growth zones, secondary planes) are analyzed along a single continuous laser ablation profile; the generated signals are subsequently converted to time-slice datasets and plotted as element ratios in ternary diagrams to reconstruct specific major- and trace-element ratios. The estimated fluid compositions are in good agreement with previous analytical results of the same material (microthermometry, evaporate mound and conventional LA-ICP-MS) and are shown to be geologically viable on a boarder scale when compared to literature data from similar ore environments. The method has high spatial and chemical resolution, which allows the reconstruction of micro-scale fluid chemical changes, such as significant fluctuation in the relative element concentration (e.g., K, Rb, Ba, Sr and V versus Na, Li and As) during crystal growth, as observed in one of the test samples. The significance of this bulk LA protocol is that it allows the quick, easy and cost-effective microanalysis of samples that are typically inundated with fluid inclusions, such as those in orogenic and epithermal systems, which would otherwise not be amenable for further quantitative analysis to constrain fluid chemistry.

Experiments have been conducted at 200 MPa, 800–1030 °C, and fO2 0.8 log units below the Ni–NiO buffer to determine the solubility of Au, Cu and Ag in silicate melts and pyrrhotite. The metal activities were imposed by using Au965Ag020Cu015 alloy capsules. Sulfur-free and sulfur-bearing systems were studied with otherwise identical melt compositions to assess the relative effect of S on the solubility of these metals. The data show that the major element composition of the silicate melt only moderately affects the solubility of Au, Ag and Cu between basalt and dacite, yielding solubilities identical within 50% relative. In comparison, solubilities in the rhyolite melts are lower by a factor of 1.5–2.5 for Cu and higher by up to a factor of 5 for Ag, depending on the aluminum saturation index of the melt. The solubilitiy of Ag significantly increases with increasing peraluminousity above an aluminum saturation index of 1. The effect of melt composition is significant on the solubility of Au in S-bearing melts, in part due to its effect on the sulfur concentration at sulfide saturation. The effect of S is the most pronounced in peralkaline rhyolites and mafic melts, and minimal in peraluminous rhyolites. The solubilities of all three metals significantly decrease with decreasing temperature. The concentration of sulfur in the melt at sulfide saturation and its volatile/melt partition coefficient are primarily determined by the FeO activity in the melt and the activity coefficients of dissolved FeS species, which appear to correlate with the degree of melt polymerization. The volatile/melt partition coefficient of reduced S increases from 79 ± 4 (1σ) to 635 ± 80 as the melt composition changes from basalt to slightly peraluminous rhyolite, and from 225 ± 13 to 776 ± 148 as the aluminium saturation index increases from 0.7 to 1.1 in rhyolites. At 1000 °C, pyrrhotite/silicate melt partition coefficients for Cu increase from 540 ± 30 (1σ) to 1140 ± 110 from basalt to dacite, whereas the partition coefficients for Ag are nearly constant at 50 ± 10. The partition coefficients of Au increase from 180 ± 20 to 900 ± 210 from basalt to dacite. Pyrrhotite/rhyolite melt partition coefficients for Cu, Ag and Au increase by about an order of magnitude as temperature drops from 1000 °C to 800 °C. At typical S concentrations for arc magmas (500–2000 μg/g), the budget of Ag in the magma will not be controlled by pyrrhotite, whereas primary control on the Au and Cu budget by pyrrhotite may only be relevant in intermediate to felsic magmas.

The aim of this study was to determine both ‘water’ contents (as OH− and H2O) and δD values of several clinopyroxene samples from alkaline basalts. These parameters were first obtained from five clinopyroxene samples using both the classical ‘off-line’ vacuum extraction technique and the ‘on-line’ high-temperature pyrolysis technique. Blanks measured with the ‘on-line’ gas extraction techniques were low enough to prevent any contamination by atmospheric water vapour. The comparison of data has revealed that our ‘on-line’ procedure is more effective for the extraction of ‘water’ from clinopyroxenes and, consequently, this ‘on-line’ technique was applied to ten additional clinopyroxene samples. Sample δD values cover a similar range from −95 to −45 ‰ (VSMOW) regardless of the studied locations, whereas the total ‘water’ content varies from ~115 to ~2570 ppm. The structural hydroxyl content of clinopyroxene samples measured by micro-FTIR spectrometry varies from ~0 to 476 ppm expressed in molecular water equivalent. The total ‘water’ concentrations determined by mass spectrometry differ considerably from structural hydroxyl contents constrained by micro-FTIR, thus indicating that considerable proportion of the ‘water’ may be present in (nano)-inclusions. The structural hydroxyl concentration—apart from clinopyroxenes separated from amphibole clinopyroxenite xenoliths—correlates positively with the δD values of clinopyroxene megacrysts for each locality, indicating that structurally bond hydrogen in clinopyroxenes may have δD values higher than molecular water in inclusions. This implies that there may be a significant hydrogen isotope fractionation for structural hydroxyl during crystallization of clinopyroxene, while for molecular water there may be no or only negligible isotope fractionation.