Jichengite 3CuIr2S4·(Ni, Fe)9S8, a New Mineral, and Its Crystal Structure

A new mineral, jichengite ideally 3CuIr2S4·(Ni,Fe)9S8, was found as a constituent of placer concentrates at a branch of the Luanhe River, about 220 km NNE of Beijing. Its associated minerals are chromite, magnetite, ilmenite, zircon, native gold, iridium, ferrian platinum and osmium. The placer is distributed at places around ultrabasic rock, which hosts chromite orebodies, from which PGM originated. Jichengite occurs commonly as massive or granular aggregates. No perfect morphology of jichengite was observed. It is steel gray and opaque with metallic luster and black streak. It has a Mohs hardness of 5, VHN (d) μm 21.65, Hm 4.465, Hv = 268.1 N/um2. It is brittle and weakly magnetic. Cleavage {010} is rarely observed. No fracture was observed. Density could not be measured because of its too small grain size. Density (calc.) is 7.003 g/cm3. Reflect light is reddish-brown, without internal reflections. Anisotropism is distinct with grayish or yellowish white in crossed nicols and bluish violet-copper red in uncrossed nicols. Jichengite shows weak pleochroism and strong bireflectance. The reflectance values in air at the Standard Commission on Ore Mineralogy wavelengths are: 38.9, 34.3 at 470 nm, 38.9, 34.5 at 546 nm, 39.1, 35.3 at 590 nm, 39.2, 36.8 at 650 nm, parallel-axial extinction. The six strongest lines in the X-ray powder-diffraction pattern [d in ?, (I), (hkl)] are: 3.00 (100) (116), 2.80 (50) (205), 2.48. (50) (208), 1.916 (40) (2, 1, 10), 1.765 (60) (220), 1.753 (50) (2, 0, 16). Five chemical analyses carried out, yielding the following results: S 25.76 (25.49-5.97), Fe 10.03 (9.78-10.31), Co 0.78 (0.75-0.81), Ni 12.48 (12.32-12.85), Cu 4.77 (4.69-4.83), Ir 46.98(46.14-47.89), sum 100.80wt%, which produced a formula (Cu1.556Fe0.976)2.532(Ir5.063S10.126)·(Fe2.7451Ni4.404Co0.273)7.422S6.517. The ideal formula is X10Ir5S17.5, which was calculated by single crystal structure analyses, where X = Cu(II) + Fe(II) + Ni(II) + Co(II). The single crystal data were collected using a diffractometer with Mo Ka radiation and a graphite monochromate. The crystal system is trigonal with space group R3m and unit cell parameters a=7.0745(14) ?, c=34.267(10) ? (The superstructure not found), and the final R Indices [with 564 observed reflections, I>2sigma (I)] are R1=0.0495, wR2=0.1349. The specimens are deposited in the Geological Museum of China.     

Magnetic structure and cation distribution in (Fe,Mn)2SiO4 (olivine) by neutron diffraction

The cation distribution in the synthetic samples of olivine-type structure with composition (Fe _x Mn_1?x )₂SiO₄ was determined at room temperature and confirms previous Mössbauer results. At low temperature an antiferromagnetic ordering is observed. The magnetic structures can be described in the crystallographic cell (i.e. k=0). They are interpreted on the basis of the irreducible representations (modes) of the symmetry groups which are compatible with Pnma. The dominant modes observed for all compounds, including Fe₂SiO₄ and Mn₂SiO₄, only differ in their direction. The main direction of magnetization is dominated by the Fe²⁺ single-ion anisotropy. At 4.2K, for x=0.29, it is parallel to the c-axis, whereas for x=0.76 the direction is parallel to the b-axis. The anisotropy of the M1-sites dominates in the first case, whereas M2-anisotropy dominates in the second case. The influence of temperature is demonstrated for x=0.50 where c is the main direction at 4.2K, when it is b at 38K.     

Determination of cation distribution in (Co,Ni,Zn)2SiO4 olivine by synchrotron X-ray diffraction

 The cation distribution of Co, Ni, and Zn between the M1 and M2 sites of a synthetic olivine was determined with a single-crystal diffraction method. The crystal data are (Co_0.377Ni_0.396Zn_0.227)₂SiO₄, M _r  = 212.692, orthorhombic, Pbnm, a = 475.64(3), b = 1022.83(8), and c = 596.96(6) pm, V = 0.2904(1) nm³, Z = 4, D _x  = 4.864 g cm⁻³, and F(0 0 0) = 408.62. Lattice, positional, and thermal parameters were determined with MoKα radiation; R = 0.025 for 1487 symmetry-independent reflections with F > 4σ(F). The site occupancies of Co, Ni, and Zn were determined with synchrotron radiation employing the anomalous dispersion effect of Co and Ni. The synchrotron radiation data include two sets of intensity data collected at 161.57 and 149.81 pm, which are about 1 pm longer than Co and Ni absorption edges, respectively. The R value was 0.022 for Co K edge data with 174 independent reflections, and 0.034 for Ni K edge data with 169 reflections. The occupancies are 0.334Co + 0.539Ni + 0.127Zn in the M1 sites, and 0.420Co + 0.253Ni + 0.327Zn in the M2 sites. The compilation of the cation distributions in olivines shows that the distributions depend on ionic radii and electronegativities of constituent cations, and that the partition coefficient can be estimated from the equation: ln [(A/B)_M1/(A/B)_M2] = −0.272 (IR _A -IR _B ) + 3.65 (EN _A −EN _B ), where IR (pm) and EN are ionic radius and electronegativity, respectively. Received: 8 April 1999 / Revised, accepted: 7 September 1999     

Al,Ge cation ordering in BaAl2Ge2O8-feldspar: monodomain ordering kinetics

The kinetics of monodomain order-disorder processes in monoclinic (I2/c) BaAl₂Ge₂O₈-feldspar have been investigated by X-ray powder diffraction, Hard Mode IR Spectroscopy, and TEM darkfield imaging on quenched samples. Compared to the behaviour predicted by the TDGL approximation ordering kinetics observed at low temperatures slow down significantly when equilibrium is approached. Such a delay is not observed in disordering experiments starting from essentially ordered cation distributions. The deviation from TDGL behaviour is interpreted in terms of partial order parameter conservation in a non-uniformly ordered phase. Modifications to the uniform TDGL rate equation are tested against the available data. An activation energy of 352 ± 28 kJ/mol is obtained for Al,Ge ordering. The mixing coefficient ξ_c ²/ξ², which describes the degree of order parameter conservation, is obtained as a function of temperature. While this coefficient vanishes in the vicinity of the transformation temperature T _tr, it saturates towards a level of ξ_c ²/ξ²≈0.4 for T→0. ξ _c ²/ξ² determines the kinetic stability of ordered clusters quenched from T≈T _tr. Received: 21 April 1999 / Revised, accepted: 19 July 1999     

Crystal structures and cation distributions in simple spinels from powder XRD structural refinements: MgCr2O4, ZnCr2O4, Fe3O4 and the temperature dependence of the cation distribution in ZnAl2O4

The crystal structure and cation distributions in the spinels MgCr₂O₄, ZnCr₂O₄, Fe₃O₄ and a suite of ZnAl₂O₄ samples annealed at 900 to 1400° C and then rapidly quenched, have been determined by powder X-ray diffraction, using several different X-ray procedures and both conventional structure-factor refinement and whole-pattern (or Rietveld) refinement methods. The chromite spinels are expected from crystal chemical considerations to have an almost completely normal cation distribution (inversion parameter, x, equal to zero). In agreement with this expectation, three samples of MgCr₂O₄ annealed at 900, 1100 and 1300° C, and ZnCr₂O₄ were all found to have x=0 within two estimated standard deviations (esd), suggesting that the accuracy with which cation distributions in spinels may be determined by powder XRD is close to the estimated precision. Slightly better results are obtained assuming neutral-atom scattering curves rather than half-ionized or fully ionized, but the differences are small (within the esd). The results from the Rietveld refinements are similarly in good agreement with those using the conventional structure factor refinement approach (agreement within the combined esd's), although in detail the Rietveld procedure sometimes produces small systematic differences in refined parameters. The suite of ZnAl₂O₄ spinels show a smooth increase in x from 0.01 at 900° C to 0.05 at 1300° C, and this behaviour is well described by the simple thermodynamic model for disordering in spinels with α_Zn-Al=89 kJ/mol, assuming β=?20 kJ/mol. The oxygen positional parameters for Fe₃O₄ are similar to those from published single crystal studies, indicating that the powder method also yields accurate interatomic distances in spinels.     

Influence of oxygen partial pressure on the Mg/Fe distribution in olivines

The dependence of Mg/Fe ordering on oxygen partial pressure in natural olivine crystals of volcanic origin has been studied by X-ray diffraction. Two natural crystals with 10% and 12% fayalite have been investigated and the atomic positions, anisotropic temperature factors, extinction coefficients and site occupancies have been refined, reaching R-values of 2.2%. After subjecting the crystals to oxygen partial pressures of 10^?16 bar and 10^?21 bar the crystals were studied again. In total six crystals were studied and the distribution coefficients K _D determined. The natural untreated crystals had K _D=1.09 and 1.06, e.g., a slight preference of Fe in (M1). p(O₂) of 10^?16 bar increased the ordering of Fe in (M1) to K _D=1.2, while p(O₂)=10^?21 bar reversed K _D to 0.8 with ordering of Fe in (M2). These experiments suggest that Mg/Fe ordering in olivines is primarily determined by the prevailing oxygen partial pressure.     

Cation partitioning versus temperature in (Mg0.70Fe0.23)Al1.97O4 synthetic spinel by in situ neutron powder diffraction

Neutron powder diffraction experiments in the temperature range 300–1770 K were performed at BENSC, Berlin, Germany, on synthetic (Mg_0.70Fe_0.23) Al_1.97O₄. The cation partitioning over the crystallographic tetrahedral and octahedral sites was determined as a function of temperature through joint Rietveld refinements and advanced minimization techniques. The thermal expansion coefficients of the lattice parameter and inter-atomic bond lengths were also obtained from the full-profile structure refinements. The behaviour of the polyhedral bond-lengths, especially the T−O distances, and of the cell constant upon heating, clearly indicate that the interdiffusion of tetrahedral and octahedral Mg/Al cations starts at about 950 K. This result is straightforwardly supported by the direct analysis of the neutron site scattering factors: Fe always retains tetrahedral coordination at all temperatures, and the cation rearrangement is entirely due to Mg and Al diffusion. Received: 18 November 1997 / Revised, accepted: 23 August 1998     

The influence of Fe(II) competition on the sorption and migration of Ni(II) in MX-80 bentonite

The results from batch sorption experiments on montmorillonite systems have demonstrated that bivalent transition metals compete with one another for sorption sites. For safety analysis studies of high level radioactive waste repositories with compacted bentonite near fields, the importance of competitive sorption on the migration of radionuclides needs to be evaluated. Under reducing conditions, the bentonite porewater chosen has a Fe(II) concentration of ∼5.3 × 10⁻⁵ M through saturation with siderite. The purpose of this paper is to assess the influence of such high Fe(II) concentrations on the transport of Ni(II) through compacted bentonite, Ni(II) was chosen as an example of a bivalent transition metal. The one-dimensional calculations were carried out at different Ni(II) equilibrium concentrations at the boundary (Ni(II)_EQBM) with the reactive transport code MCOTAC incorporating the two site protolysis non electrostatic surface complexation/cation exchange sorption model, MCOTAC-sorb. At a Ni(II)_EQBM level of 10⁻⁷ M without Fe(II) competition, the reactive transport calculations using a constant K_d approach and the MCOTAC-sorb calculation yielded the same breakthrough curves. At higher Ni(II)_EQBM (10⁻⁵ M), the model calculations with MCOTAC-sorb indicated a breakthrough which was shifted to later times by a factor of ∼5 compared with the use of the constant K_d approach.When sorption competition was included in the calculations, the magnitude of the influence depended on the sorption characteristics of the two competing sorbates and their respective concentrations. At background Fe(II) concentrations of 5.3 × 10⁻⁵ M, and a Ni(II)_EQBM level of 10⁻⁷ M, the Ni(II) breakthrough time was ∼15 times earlier than in the absence of competition. At such Fe(II) concentrations the Ni(II) breakthrough curves at all source concentrations less than 3.5 × 10⁻⁵ M (fixed by the NiCO_3,S solubility limit) are the same i.e. Ni(II) exhibits linear (low) sorption.Competitive sorption effects can have significant influences on the transport of radionuclides through compacted bentonite i.e. reduce the migration rates. Since, for the case considered here, the Fe(II) concentration in the near field of a high-level radioactive waste repository may change in time and space, the transport of bivalent transition metal radionuclides can only be properly modelled using a multi-species reactive transport code which includes a sorption model.     

The effect of garnet cell volume on the distribution of Mg and Fe in garnet exchange equilibria

The distribution of Mg in garnet exchange equilibria has been examined in three regional metamorphic and four eclogitic parageneses. Garnet cell volume has been found to have a significant effect on the distribution of Mg between garnet and coexisting ferromagnesian minerals. When the activity of Mg is corrected for the variation in cell volume, the range in variation of the distribution coefficients is strongly reduced within each group. Also the relative positions of the different groups in the distribution diagrams are in better accordance with geological evidence of crystallization temperatures. It is proposed that the effect of the garnet cell volume on the Mg distribution may be used as a geobarometer. The distribution of Ca between garnet and plagioclase is also discussed and it is found that the Ca partitioning is not suitable for geobarometry, as this partioning is dependent on the Mg/Fe ratio of the garnet.     

Iron-water reaction at high pressure and temperature, and hydrogen transport into the core

We observed a direct reaction of metallic iron with water to form iron hydride and iron oxide, 3Fe + H₂O–>2FeH_x + FeO, at pressures from 6 GPa to 84 GPa and temperatures above 1,000 K in diamond anvil cell (DAC). Iron hydride is dhcpFeH_x or -FeH_x, and iron oxide has the rhombohedral or B1 structure at pressures at least up to 37 GPa. The formation of an assembly composed of dhcpFeH_x and FeO with the B8 structure was observed at 84 GPa. In primordial Earth, water formed by dehydration of the low temperature primitive materials reacts with metallic iron in the high temperature component to form iron hydride FeH_x and iron oxide FeO. The former would be incorporated in the iron forming the core. Thus hydrogen could be an important element of the Earths core. This reaction would be essential for transport of hydrogen into the core in the accretion stage of the Earth.     

Chemistry and distribution of accessory Ni, Co, Fe arsenic minerals in the Pechenga Ni-Cu deposits, Kola Peninsula, Russia

Summary Ni, Co, Fe arsenic minerals are common accessory phases associated with both the Ni-Cu mineralization and country rock sulphides of the Pechenga complex. The majority of the arsenic minerals fall in the cobaltite-gersdorffite series, with minor arsenopyrite, nickeline and maucherite. These minerals are regularly distributed between different types of mineralization. Nickeline, maucherite and gersdorffite occur mainly in hydrothermally altered Ni-Cu sulphide ores, in particular stringer zone sulphides and mineralized talc-carbonate rocks. Arsenopyrite occurs only in pentlandite-free assemblages of the host shales, mainly in remobilized iron sulphide mineralization. The concentrations of Ni and Co in arsenopyrite decrease with the distance from the Ni-Cu bearing intrusions. Cobaltite is an ubiquitous mineral, but Ni-rich cobaltite occurs mainly in the Ni-Cu ores. In general, the transition from Ni-Cu ores to country rocks is marked by the change from Ni-arsenides to Ni-Co sulpharsenides and, finally, to Fe sulpharsenides.Sedimentary pyrite in sulphidic shales contains up to 1.8 wt.% As and was initially enriched in arsenic during sedimentation and diagenesis. Metamorphic recrystallization of authigenic As-bearing pyrite to As-free pyrrhotite led to significant liberation of arsenic during metamorphism. The mobilized arsenic could have been carried by associated metamorphic fluids and then participated in the low-grade alteration of the ultramafic rocks and associated Ni-Cu sulphide ores.

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Zusammensetzung und Verteilung der akzessorischen Ni-, Co und Fe-Arsenminerale in den Nickel-Kupferlagerstätten von Pechenga, Kola-Halbinsel, Rußland

Zusammenfassung Ni-, Co- und Fe-Arsenminerale sind verbreitete akzessorische Phasen, sowohl in den Nickel-Kupfer-Vererzungen, als auch in den Sulfiden der Nebengesteine des PechengaKomplexes. Der Großteil der Arsenminerale ist zur Cobaltit-Gersdorffit-Serie zu stellen. Arsenkies, Nickelin und Maucherit sind in geringeren Mengen vorhanden. Diese Minerale sind zwischen den verschiedenen Vererzungstypen gleichmäßig verteilt. Nickelin, Maucherit und Gersdorffit kommen hauptsächlich in hydrothermal veränderten Ni-Cu-Sulfiderzen vor, besonders in Sulfiden der Stringer-Zone und in mineralisierten Talk-Karbonat-Gesteinen. Arsenkies kommt nur in Pentlandit-freien Paragenesen in den schiefrigen Nebengesteinen, vor allem in einer remobilisierten Eisensulfidvererzung, vor. Die Konzentrationen von Ni, Fe und Co in Arsenkies nehmen mit zunehmender Entfernung von den Ni-Cu-führenden Intrusionen ab. Cobaltit ist ein verbreitetes Mineral, wobei nickelreicher Cobaltit jedoch hauptsächlich in den Nickel-Kupfererzen vorkommt. Im allgemeinen wird der übergang von NickelKupfererzen zu Nebengesteinen durch den übergang von Nickelarseniden zu NickelKobalt-Sulpharseniden und schließlich zu Eisensulpharseniden markiert.Sedimentärer Pyrit in den schiefrigen Nebengesteinen enthält bis zu 1,8 Gew% As, wobei die Arsenanreicherung während der Sedimentation und Diagenese erfolgten. Metamorphe Rekristallisation authigener As-führenden Pyrite zu As-freiem Magnetkies führte zu signifikanter Freisetzung von Arsen während der Metamorphose. Das mobilisierte Arsen dürfte durch metamorphe Fluide transportiert worden sein, die an der niedriggradigen Alteration der ultramafischen Gesteine und der assoziierten NickelKupfererze beteiligt waren.

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With 8 Figures     

新显色剂5-(3-羟基苯偶氮)-8-羟基喹啉与镍显色反应的研究与应用

本文研究了新显色剂５－（３－羟基苯偶氮）－８－羟基喹啉（５－ＨＡＨＱ）在十六烷基三甲基溴化铵（ＣＴＭＡＢ）存在下,ｐＨ４．４～５．６范围内与镍（ＩＩ）的显色反应,并拟定了光度法测镍的方法。镍与显色剂形成１∶４的稳定的红色配合物,ε４９５＝８．３６×１０４Ｌ·ｍｏｌ－４·ｃｍ－１,镍在０～０．７２μｇ／ｍｌ范围内遵循比耳定律。用于测定钢铁中微量镍,结果满意。     

The effects of crystallographic orientation,interface type and growth kinetics on Ni distribution between olivine and its melt

The effective distribution coefficient K _eff of Ni between solid and liquid has been experimentally determined as a function of growth rates and crystallographic orientations for (Mg, Ni)₂SiO₄ crystals grown by the floating-zone method. Crystals were grown by the continuous mechanism at slow rates, but were faceted at high rates, which enables us to determine the dependence of K _eff on orientations and on smooth versus rough interfaces. It has been verified that K _eff of Ni becomes larger than the equilibrium value K _o as the growth rate increases and that K _eff of faceted «110» directions is larger than that of non-faceted higher index directions. The results can be qualitatively explained by the theories which treat the distribution of elements in relation to growth kinetics. Element distribution during the recovery process from rounded to faceted morphology is also analysed in detail.     

Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization

Crystal-size in crystalline rocks is a fundamental measure of growth rate and age. And if nucleation spawns crystals over a span of time, a broad range of crystal sizes is possible during crystallization. A population balance based on the number density of crystals of each size generally predicts a log-linear distribution with increasing size. The negative slope of such a distribution is a measure of the product of overall population growth rate and mean age and the zero size intercept is nucleation density. Crystal size distributions (CSDs) observed for many lavas are smooth and regular, if not actually linear, when so plotted and can be interpreted using the theory of CSDs developed in chemical engineering by Randolph and Larson (1971). Nucleation density, nucleation and growth rates, and orders of kinetic reactions can be estimated from such data, and physical processes affecting the CSD (e.g. crystal fractionation and accumulation, mixing of populations, annealing in metamorphic and plutonic rocks, and nuclei destruction) can be gauged through analytical modeling. CSD theory provides a formalism for the macroscopic study of kinetic and physical processes affecting crystallization, within which the explicit affect of chemical and physical processes on the CSD can be analytically tested. It is a means by which petrographic information can be quantitatively linked to the kinetics of crystallization, and on these grounds CSDs furnish essential information supplemental to laboratory kinetic studies. In this three part series of papers, Part I provides the general CSD theory in a geological context, while applications to igneous and metamorphic rocks are given, respectively, in Parts II and III.     

The effect of pressure,temperature and composition on the distribution of Fe and Mg between olivine,orthopyroxene and liquid; an appraisal of the reversal in the normal fractionation trend in the Bushveld Complex

The coefficient for iron and magnesium exchange between olivine and liquid is modelled as a function of temperature in the simple system MgO-FeO-SiO₂, and is found to be temperature insensitive in the range 1,200–1,400° C, but temperature sensitive at higher temperatures. In natural systems silica and the alkalis have a strong effect on the exchange coefficient. This effect is approximated by a simple mixture model for the silicate liquid.The influence of pressure is theoretically estimated by the Clapeyron equation, and accord between predicted and observed values is found in experimental melts formed at 20 to 30 kbar. The equation for the exchange coefficient as a function of temperature, pressure and composition is used to test models for the reversal in the normal fractionation trend in the eastern and western Bushveld Complex. Multiple magma intrusion is the only satisfactory hypothesis for this feature.     

Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization

Crystal size distributions (CSDs) measured in metamorphic rocks yield quantitative information about crystal nucleation and growth rates, growth times, and the degree of overstepping (T) of reactions during metamorphism. CSDs are described through use of a population density function n=dN/dL, where N is the cumulative number of crystals per unit volume and L is a linear crystal size. Plots of ln (n) vs. L for olivine+pyroxene and magnetite in high-temperature (1000° C) basalt hornfelses from the Isle of Skye define linear arrays, indicating continuous nucleation and growth of crystals during metamorphism. Using the slope and intercept of these linear plots in conjunction with growth rate estimates we infer minimum mineral growth times of less than 100 years at T<10° C, and nucleation rates between 10^–4 and 10^–1/cm³/s. Garnet and magnetite in regionally metamorphosed pelitic schists from south-central Maine have CSDs which are bell-shaped. We interpret this form to be the result of two processes: 1) initial continuous nucleation and growth of crystals, and 2) later loss of small crystals due to annealing. The large crystals in regional metamorphic rocks retain the original size frequency distribution and may be used to obtain quantitative information on the original conditions of crystal nucleation and growth. The extent of annealing increases with increasing metamorphic grade and could be used to estimate the duration of annealing conditions if the value of a rate constant were known. Finally, the different forms of crystal size distributions directly reflect differences in the thermal histories of regional vs. contact metamorphosed rocks: because contact metamorphism involves high temperatures for short durations, resulting CSDs are linear and unaffected by annealing, similar to those produced by crystallization from a melt; because regional metamorphism involves prolonged cooling from high temperatures, primary linear CSDs are later modified by annealing to bell shapes.     

Fe(III) mobilisation by carbonate in low temperature environments: Study of the solubility of ferrihydrite in carbonate media and the formation of Fe(III) carbonate complexes

The linkage between the iron and the carbon cycles is of paramount importance to understand and quantify the effect of increased CO₂ concentrations in natural waters on the mobility of iron and associated trace elements. In this context, we have quantified the thermodynamic stability of mixed Fe(III) hydroxo-carbonate complexes and their effect on the solubility of Fe(III) oxihydroxides. We present the results of carefully performed solubility measurements of 2-line ferrihydrite in the slightly acidic to neutral–alkaline pH ranges (3.8–8.7) under constant pCO₂ varying between (0.982–98.154 kPa) at 25 °C.The outcome of the work indicates the predominance of two Fe(III) hydroxo carbonate complexes FeOHCO₃ and Fe(CO₃)₃³⁻, with formation constants log^*β°_1,1,1 = 10.76 ± 0.38 and log β°_1,0,3 = 24.24 ± 0.42, respectively.The solubility constant for the ferrihydrite used in this study was determined in acid conditions (pH: 1.8–3.2) in the absence of CO₂ and at T = (25 ± 1) °C, as log^*K_s,0 = 1.19 ± 0.41.The relative stability of the Fe(III)-carbonate complexes in alkaline pH conditions has implications for the solubility of Fe(III) in CO₂-rich environments and the subsequent mobilisation of associated trace metals that will be explored in subsequent papers.     

Effect of pressure, temperature, and oxygen fugacity on the metal-silicate partitioning of Te, Se, and S: Implications for earth differentiation

We have measured liquid Fe metal-liquid silicate partitioning (D_i) of tellurium, selenium, and sulfur over a range of pressure, temperature, and oxygen fugacity (1-19 GPa, 2023-2693 K, fO₂ −0.4 to −5.5 log units relative to the iron-wüstite buffer) to better assess the role of metallic melts in fractionating these elements during mantle melting and early Earth evolution. We find that metal-silicate partitioning of all three elements decreases with falling FeO activity in the silicate melt, and that the addition of 5-10 wt% S in the metal phase results in a 3-fold enhancement of both D_Te and D_Se. In general, Te, Se, and S all become more siderophile with increasing pressure, and less siderophile with increasing temperature, in agreement with previous work. In all sulfur-bearing experiments, D_Te is greater than D_Se or D_S, with the latter two being similar over a range of P and T. Parameterized results are used to estimate metal-silicate partitioning at the base of a magma ocean which deepens as accretion progresses, with the equilibration temperature fixed at the peridotite liquidus. We show that during accretion, Te behaves like a highly siderophile element, with expected core/mantle partitioning of >10⁵, in contrast to the observed core/mantle ratio of ∼100. Less extreme differences are observed for Se and S, which yielded core/mantle partitioning 100- to 10 times higher, respectively, than the observed value. Addition of ∼0.5 wt% of a meteorite component (H, EH or EL ordinary chondrite) is sufficient to raise mantle abundances to their current level and erase the original interelement fractionation of metal-silicate equilibrium.