首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 551 毫秒
1.
Isothermal solid state experiments on the diffusion of Cu, Fe, Zn and In and related effects have been carried out in sphalerite single crystals. The driving force for the diffusion and corresponding reactions are chemical potential gradients which are established by differences in sulfur fugacity, oxygen fugacity and the chemical activity between sulfide powders as metal sources and receptor crystals.Studies in the system ZnS-CuInS2 show replacement rims in sphalerite produced by the formation of solid solutions between ZnS and CuInS2. These differences reflect the extent of mutual solid solution. The composition profiles of these rims at different temperatures and sulfur fugacities are calculated to diffusion coefficients for the coupled substitution of Cu+ + In3+ versus 2 Zn2+. The interdiffusion coefficients of (Cu + In) in Fe-free sphalerite at the Fe/FeS sulfur fugacity of the sources obey to the relation:  相似文献   

2.
The partitioning of Fe and Zn between coexisting fahlore and sphalerite and fluid inclusions in sphalerite from the Darasun gold deposit have been studied. These data were used to estimate the formation temperature of the minerals by the sphalerite–fahlore geothermometer. The calculated crystallization temperature of 175–355°С is close to the homogenization temperature of fluid inclusions in sphalerite of 225–385°С.The estimated pressure for fluid inclusion trapping ranged from 340 to 1420 bar. The sulfur fugacity obtained from the FeS content in sphalerite associated with pyrite and the calculated temperature ranges from 10–5.5 to 10–11 bar.  相似文献   

3.
The mineral assemblages, mode of occurrence, and chemical compositions of coexisting fahlore and sphalerite from the Darasun gold deposit have been described. Three generations of fahlore and three generations of sphalerite have been recognized. The FeS content in sphalerite coexisting with fahlore ranges from 0.8 to 9.4 mol %. The complete solid solution series Fe-tetrahedrite–Zn-tetrahedrite–Fe-tennantite–Zn-tennantite reflected in Sb/(Sb + As) and Fe/(Fe + Zn) ratios ranging from 0 to 0.97 and from 0.07 to 1.00, respectively, with a predominant negative relationship between these ratios has been identified for the first time at the deposit. Stepped, oscillatory, and combined stepped-oscillatory growth zonings within fahlore grains and heterogeneous aggregates of fahlore have been found. Fahlore is enriched in As with respect to Sb, and Zn-tetrahedrite is followed by Fe- and Zn-tennantite from early to late generation; Zn-tetrahedrite is followed by Fe-tennantite in zoned grains and overgrown rims; sphalerite crystallized at decreased temperature and sulfur fugacity. The evolution of the chemical composition of fahlores was caused by the evolving temperature, fluid salinity, and conditions of metal migration.  相似文献   

4.
A refined set of Mössbauer parameters (isomer shifts, quadrupole splittings, Fe2+/Fe3+ ratios) and lattice parameters were obtained from annites synthesized hydrothermally at pressures between 3 and 5 kbars, temperatures ranging from 250 to 780° C and oxygen fugacities controlled by solid state buffers (NNO, QMF, IM, IQF). Mössbauer spectra showed Fe2+ and Fe3+ on both the M1 and the M2 site. A linear relationship between Fe3+ content and oxygen fugacity was observed. Towards low Fe3+ values this linear relationship ends at ≈10% of total iron showing that the Fe3+ content cannot be reduced further even if more reducing conditions are used. This indicates that in annite at least 10% Fe2+ are substituted by Fe3+ in order to match the larger octahedral layer to the smaller tetrahedral layer. IR spectra indicate that formation of octahedral vacancies plays an important role for charge balance through the substitution 3 Fe2+ → 2 Fe3+ + ?(oct).  相似文献   

5.
Sulfur K-edge x-ray absorption spectra (XANES and EXAFS) and L-edge XANES of sphalerite (ZnS), chalcopyrite (CuFeS2) and stannite (Cu2FeSnS4) have been recorded using synchrotron radiation. The K- and L-edge XANES features are interpreted using a qualitative MO/energy band structure model. The densities of unoccupied states at the conduction bands of sphalerite, chalcopyrite and stannite are determined using S K- and L-edge XANES features (up to 15 eV above the edge), combined with published metal K-edge XANES. The SK- and L-edge XANES also indicate that, for sphalerite, the Fe2+ 3d band at the fundamental gap has little or no bonding hybridization with S 3p and S 3s orbitals; for chalcopyrite, the Cu+ 3d and Fe3+ 3d bands have strong mixing with S 3p and S 3s states, while for stannite the Cu+ 3d band strongly hybridizes with S 3p and S 3s orbitals, but the Fe2+ 3d band does not. The post-edge XANES features (15–50 eV above the edge) of sphalerite, chalcopyrite and stannite are similar. These features are related to the tetrahedral coordination of sulfur in all these structures, and interpreted by a multiple scattering model. The resonance energies from both the K-edge and L-edge XANES for these minerals are well correlated with reciprocal interatomic distances and lattice spaces. Sulfur K-edge EXAFS analyses using Fourier transform and curve fitting procedures are presented. Comparison of the structural parameters from EXAFS with x-ray structure data shows that the first shell bond distances (BD) from EXAFS are usually accurate to ±0.02 Å, and that coordination numbers (CN) are generally accurate to ±20 percent. For sphalerite, EXAFS analysis yields the structure parameters for the first three neighbour shells around a sulfur atom; the BD and CN even for the third shell are in close agreement with the x-ray structure, and the Debye-Waller term decreases from the first shell to the third shell. It is shown that sphalerite (ZnS) is a good model compound for EXAFS analysis of sulfur in chalcogenide glasses and metalloproteins.  相似文献   

6.
The iron stable isotope compositions (δ56Fe) and iron valence states of ultrahigh‐pressure eclogites from Bixiling in the Dabie orogen belt, China, were measured to trace the changes of geochemical conditions during vertical transportation of earth materials, for example, oxygen fugacity. The bulk Fe3+/ΣFe ratios of retrograde eclogites, determined by Mössbauer spectroscopy, are consistently higher than those of fresh eclogites, suggesting oxidation during retrograde metamorphism and fluid infiltration. The studied eclogites (five samples) display limited mid‐ocean ridge basalts (MORB)‐like (~0.10‰) δ56Fe values, which are indistinguishable from their protoliths, that is, gabbro cumulates formed through differentiation of mantle‐derived basaltic magma. This suggests that Fe isotope fractionation during continental subduction is limited. Garnet separates display limited δ56Fe variation ranging from ?0.08 ± 0.07 ‰ to 0.02 ± 0.07‰, whereas coexisting omphacite displays a large variation of δ56Fe values from 0.15 ± 0.07‰ to 0.47 ± 0.07‰. Omphacite also has highly variable Fe3+/ΣFe ratios from 0.367 ± 0.025 to 0.598 ± 0.024, indicating modification after peak metamorphism. Omphacite from retrograde eclogites has elevated Fe3+/ΣFe ratios (0.54–0.60) compared to that from fresh eclogites (~0.37), whereas garnet displays a narrow range of ferric iron content with Fe3+/ΣFe ratios from 0.039 ± 0.013 to 0.065 ± 0.022. The homogenous δ56Fe values and Fe3+/ΣFe ratios of garnet suggest that it survived the retrograde metamorphism and preserved its Fe‐isotopic features and ferric contents of peak metamorphism. Because of similar diffusion rates of Fe and Mg in garnet and omphacite, and constant Δ26Mgomphacite‐garnet values (1.14 ± 0.04‰), equilibrium iron isotope fractionation between garnet and omphacite was probably achieved during peak metamorphism. Elevated Fe3+/ΣFe ratios of omphacite from retrograde eclogites and variant Δ56Feomphacite‐garnet values of the studied eclogites (0.13 ± 0.10‰ to 0.48 ± 0.10‰) indicate that oxidized geofluid infiltration resulted in the elevation of δ56Fe values of omphacite during retrograde metamorphism.  相似文献   

7.
Field and laboratory data are presented that show a soluble FeS species(FeSaq) exists in sulfidic seawater solutions, and is observedwhen the IAP exceeds the Ksp of amorphous FeS. TheFeSaq yields a discrete signal (double peak) using square-wavevoltammetry and two one-electron waves in sampled DC polarographyexperiments at the Hg electrode. The aqueous FeS species reacts irreversiblyat the electrode as a single FeS subunit and not as a polymeric entity. Thepeak potential of FeSaq occurs at -1.1 V whereas the peakpotential of Fe occurs at-1.45 V; the positive shift for Fe2+ reduction inFeSaq indicates a change in geometry for Fe2+from octahedral to tetrahedral. The kinetics of electron transfer at theelectrode are determined to be similar for both Fe2+ andFeSaq. Molecular orbital energy diagrams, further indicatethat Fe(II) does change from octahedral to tetrahedral geometry in solution.First, Fe(II) exists as octahedralFe in solution whichundergoes a substitution reaction of bisulfide for water. The resultingcomplex, Fe(H2O)5(HS)+, thentransforms to a tetrahedral complex on further addition of sulfide. Thisgeometry change is consistent with the formation of amorphous FeS thatconverts to mackinawite which has tetrahedral Fe(II). The process is entropydriven because of the water loss that occurs. The overall sequence can berepresented as: Soluble FeS species are important asreactants in the formation of iron-sulfide minerals including pyrite.  相似文献   

8.
Compounds of Fe, Pb and Zn with mixed and intermediate sulfur valences form ubiquitous inclusions and relics in banded sphalerite, pyrite-melnikovite and galena. Banded sulfides continuously grade into banded compounds with mixed and intermediate sulfur valences, the latter with a fibrous microtexture. A fibrous microtexture is also shown by banded sphalerite and pyrite from Zn-Pb deposits of Belgium and Poland. It is therefore suggested that the fibrous sphalerite inherited such a microtexture, unusual for cubic ZnS, by direct replacement of a fibrous precursor with mixed and/or intermediate sulfur valences. The last band of banded sphalerite is often overgrown by idiomorphic, isometric sphalerite precipitated directly from the solution as ZnS. The following Fe, Pb and Zn compounds with mixed and intermediate sulfur valences were found in carbonate-hosted Zn-Pb deposits of Belgium and Poland: sulfoxylanes (M2+SO2; S2+), subsulfites (M2+S2O4; S3+), sulfites (M2+SO3; S4+), pyrosulfites (M2+S2O5; S4+) and thiosulphates(M2+S2O3; S2– and S6+).  相似文献   

9.
(Mg,Fe)(Si,Al)O3 perovskite samples with varying Fe and Al concentration were synthesised at high pressure and temperature at varying conditions of oxygen fugacity using a multianvil press, and were characterised using ex?situ X-ray diffraction, electron microprobe, Mössbauer spectroscopy and analytical transmission electron microscopy. The Fe3+/ΣFe ratio was determined from Mössbauer spectra recorded at 293 and 80?K, and shows a nearly linear dependence of Fe3+/ΣFe with Al composition of (Mg,Fe)(Si,Al)O3 perovskite. The Fe3+/ΣFe values were obtained for selected samples of (Mg,Fe)(Si,Al)O3 perovskite using electron energy-loss near-edge structure (ELNES) spectroscopy, and are in excellent agreement with Mössbauer data, demonstrating that Fe3+/ΣFe can be determined with a spatial resolution on the order of nm. Oxygen concentrations were determined by combining bulk chemical data with Fe3+/ΣFe data determined by Mössbauer spectroscopy, and show a significant concentration of oxygen vacancies in (Mg,Fe)(Si,Al)O3 perovskite.  相似文献   

10.
Fifteen samples of (Mg,Fe)SiO3 majorite with varying Fe/Mg composition and one sample of (Mg,Fe)(Si,Al)O3 majorite were synthesized at high pressure and temperature under different conditions of oxygen fugacity using a multianvil press, and examined ex situ using X-ray diffraction and Mössbauer and optical absorption spectroscopy. The relative concentration of Fe3+ increases both with total iron content and increasing oxygen fugacity, but not with Al concentration. Optical absorption spectra indicate the presence of Fe2+–Fe3+ charge transfer, where band intensity increases with increasing Fe3+ concentration. Mössbauer data were used in conjunction with electron microprobe analyses to determine the site distribution of all cations. Both Al and Fe3+ substitute on the octahedral site, and charge balance occurs through the removal of Si. The degree of Mg/Si ordering on the octahedral sites in (Mg,Fe)SiO3 majorite, which affects both the c/a ratio and the unit cell volume, is influenced by the thermal history of the sample. The Fe3+ concentration of (Mg,Fe)(Si,Al)O3 majorite in the mantle will reflect prevailing redox conditions, which are believed to be relatively reducing in the transition zone. Exchange of material across the transition boundary to (Mg,Fe) (Si,Al)O3 perovskite would then require a mechanism to oxidize sufficient iron to satisfy crystal-chemical requirements of the lower-mantle perovskite phase.  相似文献   

11.
The Fe3+/ΣFe ratio of 104 MORB glasses from the Pacific, the Atlantic, the Indian, and the Red Sea spreading centers have been determined using wet chemical Fe2+ analyses and electron microprobe FeOtotal measurements. The data provide a new estimate for the MORB oxygen fugacity (fO2) of 0.41 ± 0.43 (1sigma, N = 100) log units below the fayalite-magnetite-quartz buffer (FMQ), equivalent to a Fe3+/ΣFe = 0.12 ± 0.02 (1sigma, N = 104). This new fO2 estimate is 0.8 log units more oxidized than the average fO2 proposed by Christie et al. (1986) (FMQ-1.20 ± 0.44; Fe3+/ΣFe = 0.07 ± 0.01; N = 87). This slight difference may be related in part to the 3.5% underestimation of the Fe2+ concentration determined by Christie et al. (1986) compared with this study. MORB oxygen fugacity does not display any significant difference between the three main oceanic domains, or between enriched and depleted MORB. Yet, the iron red-ox state ratio shows a broad increase during fractional crystallization. Detailed study of magmatic suites highlights the lack of systematic Fe3+/ΣFe ratio fractionation during differentiation. Despite the large variations of inferred partial melting degrees (from 5 to 20%), the present data set does not provide any evidence of Fe3+/ΣFe relationships with partial melting proxies such as Na8.0.Based on the Fe3+ systematics during partial melting, it is suggested that the oxidation state of MORB reflects a “buffered mantle melting process” resulting in the apparent compatible behavior of Fe3+ during partial melting, and in the relatively constant Fe3+/ΣFe ratio irrespective of the extent of melting. This result implies that partial melting processes may be open relative to oxygen. We propose a model where the Fe3+/ΣFe ratio in the melt is buffered during partial melting. The MORB Fe2O3 systematics can be accounted for by using a fO2 of FMQ-1 that is equivalent to the average fO2 reported for abyssal peridotites.  相似文献   

12.
The compositions of coexisting hornblendes and biotites from amphibolite and granulite facies gneisses from the south coast of Western Australia were controlled by host rock composition, paragenesis, metamophic grade, pressure, and oxygen fugacity. The Mg/(Mg + Fe2+) and Mn/Fe2+ ratios in both minerals and possibly the Alvi contents of the hornblendes are related to host rock compositions. Metamorphic grade appears to influence, perhaps only indirectly, the Ti, Mn, and Fe3+ contents of both minerals and possibly the hornblende Ca content. The higher Ti and lower Mn contents of the granulite facies hornblendes and biotites are attributed to their coexistence with pyroxenes, whereas their lower Fe3+/(Fe2+ + Fe3+) ratios are probably due to lower oxygen fugacity in the granulite facies environment. Grade-related colour variations in both minerals were controlled by their Ti/Fe2+ and Fe3+/(Fe2+ + Fe3+ ratios. The relatively low Alvi contents of the hornblendes suggest low- to moderate-pressure metamorphism.Variations in element distribution coefficients are related to variations in mineral compositions rather than metamorphic grade. Thus KD(Aliv ?Si) is related to the Aliv andedenite alkali contents of the hornblendes, KD(Fe2+ ?Mg) to the distributions of Aliv ?Si and Alvi + Ti + Fe3+, KD(Mn) to the Mn contents of both minerals, and KD(Alvi) to the Alvi contents of the biotites.  相似文献   

13.
Structural and compositional data as well as 57Fe Mössbauer parameters were determined on a natural Mn-rich monoclinic ilvaite crystal (ideal composition CaFe 2 2+ Fe3+Si2O8(OH)) which was used for electrical conductivity and thermopower measurements (part 2 of this paper). A zonar structure was found by electron microprobe analysis with a strong decrease in Mn concentration from the rim to the centre of the crystal in a plane perpendicular to the [001] direction. X-ray powder diffraction analysis of the most Mn-rich composition was performed. Mn2+ cations populate preferentially M2 sites of the ilvaite unit cell (space group P21/a), to a lower extent they reside on M1 and a reduced part is on Ca sites. The monoclinic angle was determined to β=90.178(4)°. The structural results are compared to literature data for other natural Mn-rich as well as low-impurity ilvaites; this concerns in particular the lattice b parameter and the undecided issue of the varying β angle. In the literature, the order parameter σ, which describes the varying degree of ordering of Fe2+–Fe3+ pairs on M11 and M12 sites in chains running parallel to the [001] direction, and structural defects are thought to be related to β. The interrelationship between β and σ with respect to a possible twin domain structure is discussed. Various 57Fe Mössbauer spectra were recorded between 151 K and 327 K. Mössbauer parameters and Fe2+/Fe3+ concentration ratios were determined from the fits to the spectra. Fitting of subspectra was accomplished with the idea to find assignments of Fe2+ and Fe3+ doublets in agreement with X-ray results. The fraction of Mn2+ substituting Fe2+ on M1 sites could be estimated.  相似文献   

14.
云南会泽铅锌矿是中国最重要的富锗铅锌矿床之一,已探明伴生锗金属量525 t,但锗赋存状态研究仍然存在颇大争议。文章以会泽铅锌矿床硫化物为研究对象,开展了锗的赋存状态和元素替代机制研究。通过资料收集、野外调查与室内分析,文章查明该矿床锗主要富集在闪锌矿中;富锗闪锌矿可划分为3个世代,其中第三世代闪锌矿锗的富集程度最高,其次为第一世代闪锌矿,第二世代闪锌矿锗富集程度最低;表明闪锌矿结晶顺序并非控制闪锌矿中Ge元素含量的主导因素。Ge元素的富集受矿物沉淀时温度、硫逸度、流体中Ge的浓度等因素共同制约。具有环带结构的闪锌矿成分分析显示,深色部位锗含量通常高于浅色部位,同时锗含量高的部位铜元素含量也较高,推测深色部位与致色的铜离子含量增加有关。不同世代的闪锌矿及同一闪锌矿不同部位的Cu元素与Ge元素含量均具有高度正相关性,结合元素沉淀时的物理化学条件及Cu+、Ge2+与Zn2+的离子半径相近的特征,文章认为闪锌矿中锗元素替代机制主要为2Cu++Ge2+↔2Zn2+。该认识可为今后研究稀散金属锗超常富集机制奠定基础,也为提高锗综合利用率提供理论依据。  相似文献   

15.
Iron-57 resonant absorption Mössbauer spectroscopy was used to describe the redox relations and structural roles of Fe3+ and Fe2+ in meta-aluminosilicate glasses. Melts were formed at 1500 °C in equilibrium with air and quenched to glass in liquid H2O with quenching rates exceeding 200 °C/s. The aluminosilicate compositions were NaAlSi2O6, Ca0.5AlSi2O6, and Mg0.5AlSi2O6. Iron oxide was added in the form of Fe2O3, NaFeO2, CaFe2O4, and MgFe2O4 with total iron oxide content in the range ∼0.9 to ∼5.6 mol% as Fe2O3. The Mössbauer spectra, which were deconvoluted by assuming Gaussian distributions of the hyperfine field, are consistent with one absorption doublet of Fe2+ and one of Fe3+. From the area ratios of the Fe2+ and Fe3+ absorption doublets, with corrections for differences in recoil-fractions of Fe3+ and Fe2+, the Fe3+/ΣFe is positively correlated with increasing total iron content and with decreasing ionization potential of the alkali and alkaline earth cation. There is a distribution of hyperfine parameters from the Mössbauer spectra of these glasses. The maximum in the isomer shift distribution function of Fe3+, δFe3+, ranges from about 0.25 to 0.49 mm/s (at 298 K relative to Fe metal) with the quadrupole splitting maximum, ΔFe3+, ranging from ∼1.2 to ∼1.6 mm/s. Both δFe3+ and δFe2+ are negatively correlated with total iron oxide content and Fe3+/ΣFe. The dominant oxygen coordination number Fe3+ changes from 4 to 6 with decreasing Fe3+/ΣFe. The distortion of the Fe3+-O polyhedra of the quenched melts (glasses) decreases as the Fe3+/ΣFe increases. These polyhedra do, however, coexist with lesser proportions of polyhedra with different oxygen coordination numbers. The δFe2+ and ΔFe2+ distribution maxima at 298 K range from ∼0.95 to 1.15 mm/s and 1.9 to 2.0 mm/s, respectively, and decrease with increasing Fe3+/ΣFe. We suggest that these hyperfine parameter values for the most part are more consistent with Fe2+ in a range of coordination states from 4- to 6-fold. The lower δFe2+-values for the most oxidized melts are consistent with a larger proportion of Fe2+ in 4-fold coordination compared with more reduced glasses and melts.  相似文献   

16.
A Raman spectroscopic study of Fe-rich sphalerite (Zn1 − x Fe x S) has been carried out for six samples with 0.10 ≤ x ≤ 0.24. Both the intensities and frequencies of the TO and LO modes of sphalerite are approximately independent of Fe concentration. However, the substitution of Zn by Fe results in five additional bands with frequencies between the TO (271 cm−1) and LO (350 cm−1) modes. Three of these bands are attributed to resonance modes (i.e. Y 1, Y 2 and Y 3 modes). The fourth band (B mode) is assigned to a breathing mode of the nearest-neighbor sulfur atoms around the Fe atoms. The band at 337 cm−1 is attributed to the presence of Fe3+. The excellent correlations between the normalized intensities of these five different modes and x Fe show that these modes depend on Fe-content. Another extra mode at 287 cm−1 is assigned to the presence of Cd in sphalerite.  相似文献   

17.
Assessing the ferric-ferrous ratio in magmas prior to eruption remains a challenging task. X-ray absorption near-edge structure (μXANES) spectra were collected at the iron K-edge in water-rich peralkaline silicic melt/glass inclusions trapped in quartz. These experiments were carried out between 800 and 20 °C. The chemical environment of iron was also determined in the naturally quenched samples (glass inclusions and matrix glass) and in the peralkaline rhyolitic reference glasses, with variable [Fe3+ / ∑Fe] ratios.In the reference glasses, both the intensity of the pre-peaks (Fe2+, Fe3+) and site geometry of iron change as the oxidation state increases. Fourfold-coordinated Fe3+ prevails in highly oxidised peralkaline silicic glasses, using alkalis for charge balance. The position of the pre-edge centroid of the 1s-3d transition correlates with the Fe3+ / ΣFe ratios that allowed calibration of the redox state of iron of our natural samples.At high temperatures, Fe2+ dominates in the pre-edge structure of melt inclusions. Upon cooling down to 20 °C, the intensity of the Fe3+ peak increases, the centroid position of the pre-edge features shifts by nearly 0.5 eV and the main edge moves slightly towards higher energies. The slower the cooling rate, the higher the ferric iron contribution. Iterative μXANES experiments performed on the same samples show that the process is reversible. However, this apparent oxidation of iron upon cooling is an artefact of changes in Fe coordination. It implies that the [Fe3+ / ΣFe] ratio of glassy samples, measured at 20 °C, may be overestimated by a factor > 1.7, and that this ratio cannot be reliably retrieved by probing naturally cooled glass inclusions, and most silicate glasses. High temperature μXANES experiments led first to an assessment of the ferric-ferrous ratio in the water-rich peralkaline melt in pre-eruptive magmatic conditions and second to the determination of the corresponding oxygen fugacity at 740 °C.  相似文献   

18.
Micas of the composition K(Fe3–x Mg x )AlSi3 O10(OH)2 (x=0.6, 1.2, 1.8, 2.4 and 3.0, corresponding to ann80phl20, ann60phl40, ann40phl60, ann20phl80 and ann0phl100) were synthesized hydrothermally under controlled oxygen fugacity conditions. Lattice parameters a 0 and b 0 show a distinct linear decrease with increasing Mg content. With increasing ferric iron content a deviation from this linear trend is observed especially within iron rich samples. The tetrahedral rotation angle increases smoothly from 0° in annite to 9.1° in phlogopite. Mössbauer spectra show Fe2+ and Fe3+ on the octahedral M1 and M2 sites and partially also Fe3+ on the tetrahedral site. There is a smooth increase of the quadrupole splitting on both the M1 and the M2 site going from annite to phlogopite, probably due to changes in the lattice contribution to the electric field gradient, assuming a positive correlation between quadrupole splitting and distortion. Fe3+ contents, as determined by Mössbauer spectroscopy, versus oxygen fugacity shows that, depending on the composition of the micas, minimum amounts of Fe3+ are present. For ann80phl20 this minimum amount of Fe3+ is about 8% decreasing to about 1–2% Fe3+ for ann20phl80.The molar volume of each solid solution member has been estimated from the determined relations of the molar volume versus % Fe3+ contents, extrapolated back to 0% Fe3+. Plotting these volumes as a function of Xphl shows that negative excess volume occur in the annitephlogopite join, with the maximum deviation from ideality around X phl=0.3. Margules volume parameters have been constrained as: Wv, AnnPhl=0.018±0.016 J/(bar.mol) and Wv, PhlAnn=-0.391±0.025 J(bar.mol) (three site basis).  相似文献   

19.
Olivine/melt partitioning of ΣFe, Fe2+, Mg2+, Ca2+, Mn2+, Co2+, and Ni2+ has been determined in the systems CaO-MgO-FeO-Fe2O3-SiO2 (FD) and CaO-MgO-FeO-Fe2O3-Al2O3-SiO2 (FDA3) as a function of oxygen fugacity (fO2) at 0.1 MPa pressure. Total iron oxide content of the starting materials was ∼20 wt%. The fO2 was to used to control the Fe3+/ΣFe (ΣFe: total iron) of the melts. The Fe3+/ΣFe and structural roles of Fe2+ and Fe3+ were determined with 57Fe resonant absorption Mössbauer spectroscopy. Changes in melt polymerization, NBO/T, as a function of fO2 was estimated from the Mössbauer data and existing melt structure information. It varies by ∼100% in melts coexisting with olivine in the FDA3 system and by about 300% in the FD system in the Fe3+/ΣFe range of the experiments (0.805-0.092). The partition coefficients ( in olivine/wt% in melt) are systematic functions of fO2 and, therefore, NBO/T of the melt. There is a -minimum in the FDA3 system at NBO/T-values corresponding to intermediate Fe3+/ΣFe (0.34-0.44). In the Al-free system, FD, where the NBO/T values of melts range between ∼1 and ∼2.9, the partition coefficients are positively correlated with NBO/T (decreasing Fe3+/ΣFe). These relationships are explained by consideration of solution behavior in the melts governed by Qn-unit distribution and structural changes of the divalent cations in the melts (coordination number, complexing with Fe3+, and distortion of the polyhedra).  相似文献   

20.
A. A. Borisov 《Petrology》2012,20(4):391-398
Using published experimental data an expression was derived for the Ti4+/Ti3+ ratio as a function of temperature, oxygen fugacity, and melt composition. The equation can be used to estimate Ti3+ content in lunar basaltic melts. It was shown that the Ti3+ content in melts is probably no higher than the Fe3+ content even under the reduced conditions typical of lunar magmas. Trivalent Ti can lead to some decrease in $f_{O_2 }$ during melt cooling under closed-system conditions, but it cannot reduce Fe2+ in melt to metal, because it will be completely consumed by Fe3+ reduction to Fe2+. The presence of additional reducers, such as Cr2+, can be favorable for the formation of metal during melt cooling.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号