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James D. Webster - One of the best experts on this subject based on the ideXlab platform.
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Partitioning Behavior of chlorine and fluorine in felsic melt fluid s apatite systems at 50mpa and 850 950 c
Chemical Geology, 2014Co-Authors: Angela L Doherty, James D. Webster, Beth Goldoff, Philip M PiccoliAbstract:Abstract The Partitioning of Cl between apatite, felsic melts, and aqueous fluids (vapor ± brine), and the Partitioning of F between apatite and felsic melt were investigated experimentally at 50–58 MPa and 850–950 °C. Chlorine Partitioning between apatite, melt, and fluid(s) is a function of the Cl content of the system, melt composition, Cl solubility in the melt, and pressure. For most of the 23 equilibrium experiments, the Cl content of apatite increases as a simple and linear function of the Cl concentration of the melt. The Partitioning Behavior of Cl between apatite and melt (DClapat/mt by wt. fractions of [Cl in apatite/Cl in melt]) ranges from 3 to 32. Furthermore, weight fractions of DClapat/fluid(s) range from 0.07 to 1.3 and most are less than unity. Both DClapat/mt and DClapat/fluid(s) vary with the molar (Al2O3/(Na2O + K2O + CaO)) ratio of the melt at 50 MPa. Chlorine partitions more strongly in favor of melt as the molar (Al2O3/(Na2O + K2O + CaO)) ratio decreases below 0.9, and Cl distribution between apatite and fluid(s) varies non-linearly with the molar (Na2O/(Na2O + K2O)) ratio of the coexisting silicate melts. Weight-based values of DClfluid(s)/mt range from 3 to 31. Chlorine Partitioning exhibits non-Nernstian Behavior; the distribution of Cl between fluid(s) and melt at 50 MPa varies with the Cl concentration of the system and the Cl solubility in the silicate melt. Similar Behavior was observed previously with this rhyodacitic melt composition at 200 MPa ( Webster et al., 2009b ). Comparison with prior research at 200 MPa shows that Cl is distributed increasingly in favor of apatite, relative to felsic melt or vapor ± saline liquid, as pressure decreases from 200 to 50 MPa. The Partitioning of F between apatite and silicate melt is masked by analytical imprecision. No distinct relationships with system composition or pressure are apparent for molar DXFapat/mt ranging from 13 to 219; F partitions in favor of apatite relative to melt at all conditions. We estimate pressures of apatite crystallization and Cl contents of melts and fluid(s) coexisting with apatite by comparing these 50-MPa results with published data involving apatite, rhyodacitic melt, and fluid(s) at 200 MPa. These experimental constraints are applied to prehistoric and recent Cl-enriched apatites and silicate melt inclusions of magmas of Augustine volcano to investigate pre-eruptive Cl concentrations of magma and pressures of apatite crystallization.
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the Partitioning Behavior of cl s and h2o in aqueous vapor saline liquid saturated phonolitic and trachytic melts at 200 mpa
Chemical Geology, 2009Co-Authors: James D. Webster, M F Sintoni, B De VivoAbstract:Abstract Hydrothermal experiments were conducted with molten Mt. Somma–Vesuvius phonolite and mixed-composition fluids comprised of O–H–Cl–S-cations to determine the solubilities and melt-fluid(s) Partitioning Behavior of the dominant volatile components at 896–1022 °C, 200 MPa, and f O2 of NNO +0.54 to NNO + 1.6. The final melt compositions ranged from phonolitic to trachytic due to component exchange between the melt and fluid(s) and limited crystallization of plagioclase and iron–titanium oxides. The Cl concentration of the fluids was measured directly and confirmed by mass-balance calculation, and the S concentration of the fluids was determined by mass-balance computations involving a new technique based on the mass loss of CaSO 4 crystals which served as the primary S source in the starting experimental charges. These experiments determine the apparent molal solubility of CaSO 4 in NaCl-, KCl-, and CaCl 2 -enriched fluids to be: [ m C a S O 4 = 71.52 ( X ( N a , K ) C l C a S O 4 − freefluids ) − 1.61 ] at 200 MPa and ca . 920 °C . The concentration of Cl in these melts increases with temperature and the Cl, CaO, and FeO concentrations of the system; Cl concentration decreases with increasing S in the system. The fluid(s)/melt partition coefficients for Cl, D Cl , range from ca. 3–50 and vary with the Cl S, and FeO concentrations of the system and the molar (Na 2 O/Na 2 O + K 2 O) of the melt. The concentration of S in the melts increases with temperature, the S content of the system, the CaO content of the melt, the (S 6+ /S total ) melt , and with f O2 . The fluid/melt partition coefficients for S, D S , range from 2 to nearly 1100, but most range from 50–300. D S increases with increasing S in the system just as D Cl increases with increasing Cl in the system, and D S increases with the Larson Index of the melt. The concentration of H 2 O in these melts increases significantly with increasing Cl, S, and cations in the fluids. These new partition coefficients have been integrated with the results of Raleigh fractionation modeling of Mt. Somma–Vesuvius magmas [that underwent plinian to subplinian eruptions in ca. 3550 a.B.P. (Avellino), AD 79 (Pompeii), and AD 472 (Pollena)] to compute the compositions of magmatic fluids exsolved at 200 MPa. The magmas range from phonotephritic to phonolitic compositions. The modeled Somma–Vesuvius fluids contain from 3 to ca. 50 wt.% Cl and 4–17 wt.% S with 1 to 4 wt.% fluid(s) in the evolving magmas. These concentrations vary strongly with the bulk mass of fluid(s) exsolved and the stage of magma evolution as expressed by the Larson Index. The mass (S/Cl) ratio of these fluids was calculated for 1 wt.% fluid(s) in the magmas, and it ranges from ca. 0.4–4.7 for these modeled conditions. These modeled values are strikingly consistent with the (S/Cl) of gases from numerous subduction-related volcanoes.
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Partitioning Behavior of chlorine and fluorine in the system apatite melt fluid ii felsic silicate systems at 200 mpa
Geochimica et Cosmochimica Acta, 2009Co-Authors: James D. Webster, Christine Tappen, Charles W MandevilleAbstract:Abstract Hydrothermal experiments were conducted to determine the Partitioning of Cl between rhyolitic to rhyodacitic melts, apatite, and aqueous fluid(s) and the Partitioning of F between apatite and these melts at ca. 200 MPa and 900–924 °C. The number of fluid phases in our experiments is unknown; they may have involved a single fluid or vapor plus saline liquid. The Partitioning Behavior of Cl between apatite and melt is non-Nernstian and is a complex function of melt composition and the Cl concentration of the system. Values of D Cl apat/melt (wt. fraction of: Cl in apatite/Cl in melt) vary from 1 to 4.5 and are largest when the Cl concentrations of the melt are at or near the Cl-saturation value of the melt. The Cl-saturation concentrations of silicate melts are lowest in evolved, silica-rich melts, so with elevated Cl concentrations in a system and with all else equal, the maximum values of D Cl apat/melt occur with the most felsic melt. In contrast, values of D F apat/melt range from 11 to 40 for these felsic melts, and many of these are an order of magnitude greater than those applying to basaltic melts at 200 MPa and 1066–1150 °C. The Cl concentration of apatite is a simple and linear function of the concentration of Cl in fluid. Values of D Cl fluid/apat for these experiments range from 9 to 43, and some values are an order of magnitude greater than those determined in 200-MPa experiments involving basaltic melts at 1066–1150 °C. In order to determine the concentrations and interpret the Behavior of volatile components in magmas, the experimental data have been applied to the halogen concentrations of apatite grains from chemically evolved rocks of Augustine volcano, Alaska; Krakatau volcano, Indonesia; Mt. Pinatubo, Philippines; Mt. St. Helens, Washington; Mt. Mazama, Oregon; Lascar volcano, Chile; Santorini volcano, Greece, and the Bishop Tuff, California. The F concentrations of these magmas estimated from apatite–melt equilibria range from 0.06 to 0.12 wt% and are generally equivalent to the concentrations of F determined in the melt inclusions. In contrast, the Cl concentrations of the magmas estimated from apatite–melt equilibria (e.g., ca. 0.3–0.9 wt%) greatly exceed those determined in the melt inclusions from all of these volcanic systems except for the Bishop Tuff where the agreement is good. This discrepancy in estimated Cl concentrations of melt could result from several processes, including the hypothesis that the composition of apatite represents a comparatively Cl-enriched stage of magma evolution that precedes melt inclusion entrapment prior to the sequestration of Cl by coexisting magmatic aqueous and/or saline fluid(s).
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Partitioning Behavior of chlorine and fluorine in the system apatite-silicate melt-fluid
Geochimica et Cosmochimica Acta, 2005Co-Authors: E. A. Mathez, James D. WebsterAbstract:The Partitioning Behavior of Cl among apatite, mafic silicate melt, and aqueous fluid and of F between apatite and melt have been determined in experiments conducted at 1066 to 1150 °C and 199–205 MPa. The value of DClapatite/melt (wt. fraction of Cl in apatite/Cl in melt) ≈0.8 for silicate melt containing less than ∼3.8 wt.% Cl. At higher melt Cl contents, small increases in melt Cl concentration are accompanied by large increases in apatite Cl concentration, forcing DClapatite/melt to increase as well. Melt containing less than 3.8% Cl coexists with water-rich vapor; that containing more Cl coexists with saline fluid, the salinity of which increases rapidly with small increases in melt Cl content, analogous to the dependency of apatite composition on melt Cl content. This Behavior is due to the fact that the solubility of Cl in silicate melt depends strongly on the composition of the melt, particularly its Mg, Ca, Fe, and Si contents. Once the melt becomes “saturated” in Cl, additional Cl must be accommodated by coexisting fluid, apatite, or other phases rather than the melt itself. Because Cl solubility depends on composition, the Cl concentration at which DClapatite/melt and DClfluid/melt begin to increase also depends on composition. The experiments reveal that DFapatite/melt ≈3.4. In contrast to Cl, the concentration of F in silicate melt is only weakly dependent on composition (mainly on melt Ca contents), so DFapatite/melt is constant for a wide range of composition. The experimental data demonstrate that the fluids present in the waning stages of the solidification of the Stillwater and Bushveld complexes were highly saline. The Cl-rich apatite in these bodies crystallized from interstitial melt with high Cl/(F + OH) ratio. The latter was generated by the combined processes of fractional crystallization and dehydration by its reaction with the relatively large mass of initially anhydrous pyroxene through which it percolated.
Yang Liu - One of the best experts on this subject based on the ideXlab platform.
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distribution Partitioning Behavior and ecological risk assessment of phthalate esters in sediment particle pore water systems from the main stream of the haihe river northern china
Science of The Total Environment, 2020Co-Authors: Yang Liu, Jiaodi Zhang, Chuanyang Cai, Florian Breider, Shu Tao, Wenxin LiuAbstract:Abstract The distribution, Partitioning Behavior and risk assessment of phthalate esters (PAEs) in the surface sediment-pore water system of the Haihe River were investigated. The total cumulative concentrations of 21 PAE species (Σ21PAEs) in the surface sediment ranged from 45.9 to 1474.1 ng·g−1 dry weight (dw) and were from 17.9 to 2628.8 ng·mL−1 in the pore water. Di (2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), and diisobutyl phthalate (DIBP) were the dominant components, and their sum accounted, on average, for 88.4% and 72.0% of Σ21PAEs in the surface sediment and pore water, respectively. The spatial distributions of Σ21PAEs in the surface sediment and pore water indicated that large amounts of the consumed products contained plasticizers in the urban and nearshore areas and increased the discharge of PAEs into the Haihe River. The river dam also affected PAEs distributions. The organic carbon normalized Partitioning coefficient (logKOC) followed a sequence as dry season (2.47 ± 0.35 mL·g−1) > wet season (2.02 ± 0.45 mL·g−1) > normal season (1.98 ± 0.42 mL·g−1). The risk quotient (RQ) method was employed to assess the potential ecological risk from specific species. High ecological risks of DEHP to the sensitive algae, crustacean, and fish species along with high ecological risks of DIBP to sensitive fish species were found in the surface sediment and pore water for all sampling seasons. In addition, DBP in the surface sediment and pore water exhibited moderate and high ecological risks to sensitive aquatic species. The highest RQ values for PAEs were found in the surface sediment and pore water in suburban and urban areas, respectively, and indicated that anthropogenic activities may cause severe river pollution and high risk to the local aquatic ecosystem. Capsule High levels and ecological risks from PAEs were found in the urban river, and the Partitioning Behaviors of PAEs between the surface sediment and pore water were not significantly affected by their hydrophobicity, especially for species with low KOW.
Mayumi Ojima - One of the best experts on this subject based on the ideXlab platform.
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stress Partitioning Behavior of multilayered steels during tensile deformation measured by in situ neutron diffraction
Scripta Materialia, 2012Co-Authors: Mayumi Ojima, Junya Inoue, Shoichi Nambu, Pingguang Xu, Koichi Akita, Hiroshi Suzuki, Toshihiko KosekiAbstract:Stress Partitioning in multilayered steels consisting of martensitic and austenitic layers was measured during tensile deformation by in situ neutron diffraction measurements to investigate the mechanism of the improved strength–elongation balance. The deformation mode can be classified into three stages, and the results indicate that the applied stress is effectively transferred to the martensitic phase, because no stress concentration sites exist, owing to the multilayered structure. Hence, even as-quenched martensite deformed uniformly, resulting in improved strength–elongation balance in multilayered steels.
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stress Partitioning Behavior in an fcc alloy evaluated by the in situ ex situ ebsd wilkinson method
Acta Materialia, 2011Co-Authors: Mayumi Ojima, Yoshitaka Adachi, Seiichi Suzuki, Yo TomotaAbstract:Hierarchical stress Partitioning Behavior among grains in the elasto-plastic region of a polycrystalline material was studied by a combined technique of in situ/ex situ electron backscattering diffraction based on local strain measurements (the EBSD-Wilkinson method) and neutron diffraction measurements during tensile deformation. Elastic strains parallel to the tensile direction both during loading (e11) and after unloading (e′11) were measured. The volume-averaged stress Partitioning among [hkl] family grains measured by the EBSD-Wilkinson method was in good agreement with that measured by neutron diffraction measurements, but a more complicated strain distribution occurred microscopically because of restriction from the surrounding grains.
Philip M Piccoli - One of the best experts on this subject based on the ideXlab platform.
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Partitioning Behavior of chlorine and fluorine in felsic melt fluid s apatite systems at 50mpa and 850 950 c
Chemical Geology, 2014Co-Authors: Angela L Doherty, James D. Webster, Beth Goldoff, Philip M PiccoliAbstract:Abstract The Partitioning of Cl between apatite, felsic melts, and aqueous fluids (vapor ± brine), and the Partitioning of F between apatite and felsic melt were investigated experimentally at 50–58 MPa and 850–950 °C. Chlorine Partitioning between apatite, melt, and fluid(s) is a function of the Cl content of the system, melt composition, Cl solubility in the melt, and pressure. For most of the 23 equilibrium experiments, the Cl content of apatite increases as a simple and linear function of the Cl concentration of the melt. The Partitioning Behavior of Cl between apatite and melt (DClapat/mt by wt. fractions of [Cl in apatite/Cl in melt]) ranges from 3 to 32. Furthermore, weight fractions of DClapat/fluid(s) range from 0.07 to 1.3 and most are less than unity. Both DClapat/mt and DClapat/fluid(s) vary with the molar (Al2O3/(Na2O + K2O + CaO)) ratio of the melt at 50 MPa. Chlorine partitions more strongly in favor of melt as the molar (Al2O3/(Na2O + K2O + CaO)) ratio decreases below 0.9, and Cl distribution between apatite and fluid(s) varies non-linearly with the molar (Na2O/(Na2O + K2O)) ratio of the coexisting silicate melts. Weight-based values of DClfluid(s)/mt range from 3 to 31. Chlorine Partitioning exhibits non-Nernstian Behavior; the distribution of Cl between fluid(s) and melt at 50 MPa varies with the Cl concentration of the system and the Cl solubility in the silicate melt. Similar Behavior was observed previously with this rhyodacitic melt composition at 200 MPa ( Webster et al., 2009b ). Comparison with prior research at 200 MPa shows that Cl is distributed increasingly in favor of apatite, relative to felsic melt or vapor ± saline liquid, as pressure decreases from 200 to 50 MPa. The Partitioning of F between apatite and silicate melt is masked by analytical imprecision. No distinct relationships with system composition or pressure are apparent for molar DXFapat/mt ranging from 13 to 219; F partitions in favor of apatite relative to melt at all conditions. We estimate pressures of apatite crystallization and Cl contents of melts and fluid(s) coexisting with apatite by comparing these 50-MPa results with published data involving apatite, rhyodacitic melt, and fluid(s) at 200 MPa. These experimental constraints are applied to prehistoric and recent Cl-enriched apatites and silicate melt inclusions of magmas of Augustine volcano to investigate pre-eruptive Cl concentrations of magma and pressures of apatite crystallization.
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solubility and Partitioning Behavior of au cu ag and reduced s in magmas
Geochimica et Cosmochimica Acta, 2013Co-Authors: Zoltan Zajacz, Philip M Piccoli, Philip A Candela, Carmen Sanchezvalle, Markus WalleAbstract:Abstract 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.
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the Partitioning Behavior of silver in a vapor brine rhyolite melt assemblage
Geochimica et Cosmochimica Acta, 2008Co-Authors: Adam C Simon, Thomas Pettke, Philip A Candela, Philip M PiccoliAbstract:Abstract The Partitioning of silver in a sulfur-free rhyolite melt–vapor–brine assemblage has been quantified at 800 °C, pressures of 100 and 140 MPa and f O 2 ≈ NNO (nickel–nickel oxide). Silver solubility (±2σ) in rhyolite increases 5-fold from 105 ± 21 to 675 ± 98 μg/g as pressure increases from 100 to 140 MPa. Nernst-type partition coefficients ( D Ag i , j ± 2 σ ) describing the mass transfer of silver at 100 MPa between vapor and melt, brine and melt and vapor and brine are 32 ± 30, 1151 ± 238 and 0.026 ± 0.004, respectively. At 140 MPa, values for D Ag i , j ( ± 2 σ ) for vapor and melt, brine and melt, and vapor and brine are 32 ± 10, 413 ± 172 and 0.06 ± 0.03, respectively. Apparent equilibrium constant values (±2σ) describing the exchange of silver and sodium between vapor and melt, K Ag , Na v / m , at 100 and 140 MPa are 105 ± 68 and 14 ± 6. The average values (±2σ) for silver and sodium exchange between brine and melt, K Ag , Na b / m , at 100 and 140 MPa are 313 ± 288 and 65 ± 12. These data indicate that the mass transfer of silver from rhyolite melt to an exsolved volatile phase(s) is enhanced at 100 MPa relative to 140 MPa, suggesting that decompression increases the silver ore-generative potential of an evolving silicate magma. Model calculations using the new data suggest that the evolution of low-density, aqueous fluid (i.e., vapor) may be responsible for the the silver tonnage of many porphyry-type and perhaps epithermal-type ore deposits. For example, Halter et al. (Halter W. E., Pettke T. and Heinrich C. A. (2002) The origin of Cu/Au ratios in porphyry-type ore deposits. Science 296, 1842–1844) used detailed silicate and sulfide melt inclusion and vapor and brine fluid inclusions analyses to estimate a melt volume on the order of 15 km3 to satisfy the copper budget at the Bajo de la Alumbrera copper-, gold-, silver-ore deposit. Using their melt volume estimate with the data presented here, model calculations for a 15-km3 felsic melt, saturated with pyrrhotite and magnetite, suggest that a low-salinity magmatic vapor may scavenge on the order of 7 × 1012 g of silver from the melt. This quantity of silver exceeds the discovered 2 × 109 g of Ag at Alumbrera. Calculated tonnages for numerous other deposits yield similar results. The excess silver in the vapor, remaining after porphyry formation, is then available to precipitate at lower PTconditions in the stratigraphically higher epithermal environment. These data suggest that silver, and perhaps other ore metals, in the porphyry-epithermal continuum may be derived solely from the time-integrated flux of dominantly low-salinity vapor exsolved from a series of sequential magma batches.
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the Partitioning Behavior of as and au in s free and s bearing magmatic assemblages
Geochimica et Cosmochimica Acta, 2007Co-Authors: Adam C Simon, Philip M Piccoli, Thomas Pettke, Philip A Candela, Christoph A HeinrichAbstract:Abstract The Partitioning of As and Au between rhyolite melt and low-salinity vapor (2 wt% NaCl eq.) in a melt–vapor–Au metal ± magnetite ± pyrrhotite assemblage has been quantified at 800 °C, 120 MPa and f O 2 = NNO . The S-bearing runs have calculated values for the fugacities of H2S, SO2 and S2 of log f H 2 S = 1.1 , log f SO 2 = - 1.5 , and log f S 2 = - 3.0 . The ratio of H2S to SO2 is on the order of 400. The experiments constrain the effect of S on the Partitioning Behavior of As and Au at magmatic conditions. Calculated average Nernst-type partition coefficients (±1σ) for As between vapor and melt, D As v / m , are 1.0 ± 0.1 and 2.5 ± 0.3 in the S-free and S-bearing assemblages, respectively. These results suggest that sulfur has a small, but statistically meaningful, effect on the mass transfer of As between silicate melt and low-salinity vapor at the experimental conditions. Efficiencies of removal, calculated following Candela and Holland (1986) , suggest that the S-free and S-bearing low-salinity vapor can scavenge approximately 41% and 63% As from water-saturated rhyolite melt, respectively, during devolatilization assuming that As is partitioned into magnetite and pyrrhotite during second boiling. The S-free data are consistent with the presence of arsenous acid, As(OH)3 in the vapor phase. However, the S-bearing data suggest the presence of both arsenous acid and a As–S complex in S-bearing magmatic vapor. Apparent equilibrium constants, log K As ′ ( ± 1 σ ) , describing the Partitioning of As between melt and vapor are −1.3 (0.1) and −1.1 (0.1) for the S-free and S-bearing runs, respectively. The increase in the value of K As ′ with the addition of S suggests a role for S in complexing and scavenging As from the melt during degassing. The calculated vapor/melt partition coefficients (±1σ) for Au between vapor and melt, D Au v / m , in S-free and S-bearing assemblages are 15 ± 2.5 and 12 ± 0.3, respectively. Efficiencies of removal ( Candela and Holland, 1986 ) for the S-free melt, calculated assuming that magnetite is the dominant Au-sequestering solid phase during crystallization ( Simon et al., 2003 ), suggest that magmatic vapor may scavenge on the order of 72% Au from a water-saturated melt. Efficiencies of removal calculated for the S-bearing assemblage, assuming pyrrhotite and magnetite are the dominant Au-sequestering solid phases, indicate that vapor may scavenge on the order of 60% Au from the melt. These model calculations suggest that the loss of pyrrhotite and magnetite from a melt, owing to punctuated differentiation during ascent and emplacement, does not prohibit the ability of a rhyolite melt to generate a large-tonnage Au deposit. Apparent equilibrium constants describing the Partitioning of Au between melt and vapor were calculated using the mean D Au v / m values for the S-free and S-bearing assemblages; only S-bearing data from runs longer than 400 h were used as shorter runs may not have reached equilibrium with respect only to vapor/melt Partitioning of Au. The values for log K Au ′ ( ± 1 σ ) are −4.4 (0.1) and −4.2 (0.2) for the S-free and S-bearing runs, respectively. These data suggest that the presence of S does not affect the mass transfer of Au from degassing silicate melt to an exsolved, low-salinity vapor in a low- f S 2 assemblage (i.e., pyrrhotite–magnetite at NNO) at the experimental conditions reported here. Efficiencies of removal are calculated and used to model the mass transfer of Au from a crystallizing silicate melt to an exsolved, low-salinity vapor phase. The calculations suggest that the model, absolute tonnage of Au scavenged and transported by S-free and S-bearing vapors, from a crystallizing melt, would be comparable and that the time-integrated flux of low-salinity vapor could be responsible for a significant quantity of the Au in magmatic-hydrothermal ore deposits.
Toshihiko Koseki - One of the best experts on this subject based on the ideXlab platform.
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stress Partitioning Behavior of multilayered steels during tensile deformation measured by in situ neutron diffraction
Scripta Materialia, 2012Co-Authors: Mayumi Ojima, Junya Inoue, Shoichi Nambu, Pingguang Xu, Koichi Akita, Hiroshi Suzuki, Toshihiko KosekiAbstract:Stress Partitioning in multilayered steels consisting of martensitic and austenitic layers was measured during tensile deformation by in situ neutron diffraction measurements to investigate the mechanism of the improved strength–elongation balance. The deformation mode can be classified into three stages, and the results indicate that the applied stress is effectively transferred to the martensitic phase, because no stress concentration sites exist, owing to the multilayered structure. Hence, even as-quenched martensite deformed uniformly, resulting in improved strength–elongation balance in multilayered steels.