Manganese pyroxenoids and carbonates: Critical phase relations in metamorphic assemblages from the Alps     

Tj. Peters  V. Trommsdorff  J. Sommerauer 《Contributions to Mineralogy and Petrology》1978,66(4):383-388

The compositions of coexisting pyroxmangites, rhodonites, rhodochrosites and manganese calcites in regional metamorphosed manganese cale-silicate marbles from Val Scerscen and Alagna were analysed by microprobe and permit definition of critical tie lines at metamorphic grades appropriate to temperatures between 400 and 450 °C.Variations in composition of coexisting mineral pairs in one and the same locality are attributed to variations in and not to metamorphic temperatures. From the analysed assemblages isothermal plots (with SiO₂ as excess component) were constructed for the system CaO-MnO-SiO₂-CO₂.  相似文献   

Inversions in sub-potassic nephelines     

C. M. B. Henderson  J. Roux 《Contributions to Mineralogy and Petrology》1977,61(3):279-298

Sub-potassic nephelines in the system NaAlSiO₄(Ne)-KAlSiO₄(Ks) were synthesized under a variety of conditions and studied at room temperature and up to 1000 °C using an X-ray powder diffractometer. At low temperatures they do not have the hexagonal structure determined by Hahn and Buerger (1955) for natural nepheline. Samples with 0.7 to 2.5 mole % Ks have an orthorhombic supercell with parameters equivalent to a, 3a, 3c where a and c are Hahn and Buerger structure cell parameters. Nephelines with 0 to 0.7% Ks consist of two phases with different c axes; one of these phases has the orthorhombic supercell.Pure-Na nephelines (NaAlSiO₄) invert to a hexagonal phase with the Hahn and Buerger structure at 190 °±10 °C; this inversion temperature decreases with increasing Ks and a sample with 0.5% Ks inverts at 170 °±5 °C. The inversion is reversible and is displacive. Another reversible inversion begins at 875 °±10 °C in pure-Na nepheline; this inversion increases in temperature with increasing Ks and a sample with 1.8% Ks begins to invert at 960 °±10 °C.Superstructures with anomalous low-temperature cell parameters in sub-potassic nephelines are attributed to reversible collapse of the framework about the larger cation sites which must be occupied by small Na in subpotassic nephelines. Superstructures in natural nephelines are also related to framework collapse at a displacive inversion.  相似文献   

Mg–Fe interdiffusion rates in wadsleyite and the diffusivity jump at the 410-km discontinuity     

T.?KuboEmail author  A.?Shimojuku  E.?Ohtani 《Physics and Chemistry of Minerals》2004,31(7):456-464

Mg–Fe interdiffusion rates have been measured in wadsleyite aggregates at 16.0–17.0 GPa and 1230–1530 °C by the diffusion couple method. Oxygen fugacity was controlled using the NNO buffer, and water contents of wadsleyite were measured by infrared spectroscopy. Measured asymmetric diffusion profiles, analyzed using the Boltzmann–Matano equation, indicate that the diffusion rate increases with increasing iron concentration and decreasing grain size. In the case of wadsleyite containing 50–90 weight ppm H₂O, the Mg–Fe interdiffusion coefficients at compositions of Mg/(Mg + Fe)=0.95 in the coarse-grained region (about 60 m) and 0.90 in the fine-grained region (about 6 m) were determined to be a D_Xmg = 0.95 (m² s^–1)=1.24 × 10^–9 exp[–172 (kJ mol^–1)/RT] and D_Xmg = 0.90 (m² s^–1)=1.77 × 10^–9 exp[–143 (kJ mol^–1)/RT], respectively. Grain-boundary diffusion rates were estimated to be about 4 orders of magnitude faster than the volume diffusion rate. Grain-boundary diffusion dominates when the grain size is less than a few tens of microns. Results for the nominally dry diffusion couple in the present study are roughly consistent with previous studies, taking into account differences in pressure and grain size, although water contents of samples were not clear in previous studies. We observed that the diffusivity is enhanced by about 1 order of magnitude in wadsleyite containing 300–2100 wt. ppm H₂O at 1230 °C, which is almost identical to the enhancement associated with a 300 °C increase in temperature. It is still not conclusive that a jump in diffusivity exists between olivine and wadsleyite because water contents of olivine in previous diffusion studies and effects of water on the olivine diffusivity are uncertain.  相似文献   

Melt-vapor solubilities and elemental partitioning in peraluminous granite-pegmatite systems: experimental results with Macusani glass at 200 MPa   总被引：5，自引：1，他引：5  

David London  Richard L. Hervig  George B. Morgan VI 《Contributions to Mineralogy and Petrology》1988,99(3):360-373

Vapor-saturated experiments at 200 MPa with peraluminous, lithophile-element-rich rhyolite obsidian from Macusani, Peru, reveal high miscibility of H₂O and silicate melt components. The H₂O content of melt at saturation (11.5+-0.5 wt.%) is almost twice that predicted by existing melt speciation models. The corresponding solubility of melt components in vapor decreases from 15 wt.% dissolved solids (750°–775° C) to 9 wt.% at 600° C. With regard to major and most minor components, macusanite melt dissolves congruently in vapor. Among the elements studied (B, P, F, Li, Rb, Cs, Be, Sr, Ba, Nb, Zr, Hf, Y, Pb, Th, U, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm), only boron has a vapor/melt partition coefficient (D[B]) consistently 1 at superliquidus temperatures (>645° C). Phosphorus and fluorine behave similarly, with D[P] and D[F]<0.5. Little or no significant vapor/melt fractionation is evident among most periodic groups (alkalis, alkaline earths, Zr/Hf, or the REE). The temperature dependence of vapor/melt partition coefficients is generally greatest for cations with charge +3 (except Nb and U); most vapor/melt partition coefficients for trace elements increase with decreasing temperature to the liquidus. Crystallization proceeds by condensation of crystalline phases from vapor; most coexisting melts are aphyric. Changes in the major element content of melt are dominated by the mineral assemblage crystallized from vapor, which includes subequal proportions of white mica, quartz, albite, and orthoclase. The volumetric proportion of (mica + or-thoclase)/albite increases slightly with decreasing T, creating a sodic, alkaline vapor. Vapor deposition of topaz (T500° C), which consumes F from melt, returns K/Na ratios of melt to near unity with the vapor-deposition of albite. The abundances of most trace elements in residual melt change little with the crystallization of major phases, but in some cases are strongly controlled by the deposition of accessory phases including apatite (T550° C), which depletes the melt in P and REE. Below the liquidus, boron increasingly favors the vapor over melt with decreasing temperatures.  相似文献   

Rare earth element partitioning between clinopyroxene and silicate liquid at moderate to high pressure   总被引：5，自引：0，他引：5  

T. H. Green  N. J. Pearson 《Contributions to Mineralogy and Petrology》1985,91(1):24-36

Experimental determination of over seventy sets of clinopyroxene/silicate liquid (glass) partitition coefficients (D) for four rare earth elements (REE — La, Sm, Ho, Lu) in a range of REE-enriched natural rock compositions (basalt, basaltic andesite, andesite and rhyodacite) demonstrate a convex upward pattern, favouring the heavy REE (Ho, Lu) and markedly discriminating against the light REE (La). These patterns are consistent with previously documented clinopyroxene D values reported from natural phenocryst/matrix pairs and from experimental work using either REE-enriched compositions and electron microprobe analytical techniques (as in the present study) or natural or synthetic undoped compositions and mass spectrometric, ion probe or X-ray autoradiographic analytical techniques. However, the large data base in the present study allows evaluation of the effect of compositional and physical parameters on REE partitioning relationships. Considering D_Ho, it is shown that (1) D increases 6-fold with increasing SiO₂ content of the coexisting liquid from 50 to 70 wt% SiO₂ (2) D increases 4-fold with decreasing temperature from 1,120°C to 900° C (3) D increases 2-fold with increasing pressure from 2.5 to 20 kb. (4) D increases 2-fold fO₂ increases from approximately that of the MW buffer to the HM buffer (5) D remains unchanged within experimental error as the water content of the melt changes from 0.3 to 10% by weight H₂O.The absolute REE content of the clinopyroxene shows no consistent trend with temperature, but decreases slightly with increasing pressure, paralleling an increase in the jadeite component of the pyroxene. Thus the increase in D with increasing pressure is attributed to changes in the silicate liquid structure, which discriminate against accommodation of REE with increasing pressure. The clinopyroxene REE content increases with increasing fO₂, and in this case the increase in D with increasing fO₂ may be attributed mainly to this change in the clinopyroxene composition. Application of the present results to geochemical modelling allows a more appropriate choice of D values, according to the liquid composition and physical conditions applicable in the modelled system. They may also be used to evaluate cognate or xenocrystic relationships between clinopyroxene megacrysts and their host matrix.  相似文献   

Barium partitioning between alkali feldspar and silicate liquid at high temperature and pressure   总被引：2，自引：0，他引：2  

Jingfeng Guo  Trevor H. Green 《Contributions to Mineralogy and Petrology》1989,102(3):328-335

Barium partitioning between alkali feldspar and a natural trachyte liquid, enriched with barium, has been determined as a function of pressure and temperature from 10 to 25 kb and 900°–1100° C. Both long duration experiments and a re-equilibration experiment suggest close approach to equilibrium. Partition coefficients (D _Ba) decrease as both temperature and pressure increase (e.g., D _Ba changes from 8.71 at 10 kb, 900° C to 1.48 at 25 kb, 1100° C). Water activity also controls the barium partitioning with a marked decrease in D _Ba ^af/liq for addition of less than 0.8 wt% H₂O, but with no apparent additional effect for higher water contents in the bulk composition (e.g., from 0.8–4.2 wt% H₂O). The composition of alkali feldspar also has a significant effect on D _Ba ^af/liq , but the data obtained do not allow derivation of a complete D-Or relationship. These new data suggest that Henry's Law is obeyed for most of the barium concentrations examined, and the limit of Henry's Law behaviour for barium in alkali feldspar is as high as 6 wt% BaO in alkali feldspar and 1.2 wt% BaO in the melt, similar to the results of Long (1978). The experimental results broadly overlap with natural data for D _Ba, determined from coexisting alkali feldspar phenocrysts and glass (or groundmass).  相似文献   

Changes in stable isotope ratios of metapelites and marbles during regional metamorphism,Mount Lofty Ranges,South Australia: implications for crustal scale fluid flow     

Ian Cartwright  Julie Vry  Michael Sandiford 《Contributions to Mineralogy and Petrology》1995,120(3-4):292-310

The Mount Lofty Ranges comprises interlayered marbles, metapsammites, and metapelites that underwent regional metamorphism during the Delamarian Orogeny at 470–515 Ma. Peak metamorphic conditions increased from lowermost biotite grade (350–400°C) to migmatite grade (700°C) over 50–55 km parallel to the lithological strike of the rocks. With increasing metamorphic grade, ¹⁸O values of normal metapelites decrease from 14–16 to as low as 9.0, while ¹⁸O values of calcite in normal marbles decrease from 22–24 to as low as 13.2 These isotopic changes are far greater than can be accounted for by devolatilisation, implying widespread fluid-rock interaction. Contact metamorphism appears not to have affected the terrain, suggesting that fluid flow occurred during regional metamorphism. Down-temperature fluid flow from synmetamorphic granite plutons (¹⁸O=8.4–8.6) that occur at the highest metamorphic grades is unlikely to explain the resetting of oxygen isotopes because: (a) there is a paucity of skarns at granite-metasediment contacts; (b) the marbles generally do not contain low-XCO₂ mineral assemblages; (c) there is insufficient granite to provide the required volumes of water; (d) the marbles and metapelites retain a several permil difference in ¹⁸O values, even at high metamorphic grades. The oxygen isotope resetting may be accounted for by along-strike up-temperature fluid flow during regional metamorphism with time-integrated fluid fluxes of up to 5x10⁹ moles/m² (10⁵ m³/m²). If fluid flow occurred over 10⁵–10⁶ years, estimated intrinsic permeabilities are 10^-20 to 10^-16m². Variations in ¹⁸O at individual outcrops suggest that time-integrated fluid fluxes and intrinsic permeabilities may locally have varied by at least an order of magnitude. A general increase in XCO₂ values of marble assemblages with metamorphic grade is also consistent with the up-temperature fluid-flow model. Fluids in the metapelites may have been derived from these rocks by devolatilisation at low metamorphic grades; however, fluids in the marbles were probably derived in part from the surrounding siliceous rocks. The marble-metapelite boundaries preserve steep gradients in both ¹⁸O and XCO₂ values, suggesting that across-strike fluid fluxes were much lower than those parallel to strike. Up-temperature fluid flow may also have formed orthoamphibole rocks and caused melting of the metapelites at high grades.This paper is a contribution to IGCP Project 304 Lower Crustal Processes  相似文献   

A K-Ar and 40Ar/39Ar study on white micas from the Brixen Quartzphyllite,Southern Alps     

K. Hammerschmidt  B. Stöckhert 《Contributions to Mineralogy and Petrology》1987,95(4):393-406

The Brixen Quartzphyllite, basement of the Southern Alps (Italy), consists of metasediments which had suffered progressive deformation and low grade metamorphism (p _max4 kbar, T _max375±25° C) during the Palaeozoic. It has been excavated by pre-Permian erosion, buried again beneath a pile of Permo-mesozoic to Cainozoic sediments (estimated T _max150° C), and is now exposed anew due to late Alpine uplift and erosion. The behavior of the K-Ar system of white micas is investigated, taking advantage of the narrow constraints on their thermal history imposed by the geological/stratigraphic reference systems.The six structurally and petrographically differing samples come from a single outcrop, whose position is roughly two kilometers beneath the Permian land-surface. White mica concentrates from five grain size fractions (<2 , 2–6 , 6–20 , 20–60 , 60–75 ) of each sample have been analyzed by the conventional K-Ar method, four selected concentrates additionally by the ⁴⁰Ar/³⁹Ar stepwise heating technique; furthermore, Ar content and isotopic composition of vein quartz were determined.The conventional ages of the natural grain size fractions (20–60 , 60–75) are in the range 316±8 Ma, which corresponds to the ⁴⁰Ar/³⁹Ar plateau age of 319.0±5.5 Ma within the error limits. The finer grain size fractions yield significantly lower ages, down to 233 Ma for fractions <2 . Likewise low apparent ages (down to 83 Ma) are obtained for the low temperature ⁴⁰Ar/³⁹Ar degassing steps.There is no correlation between microstructural generation of white mica prevailing in the sample and apparent age. This favours an interpretation of the 316±8 Ma values as cooling age; progressive deformation and metamorphism must be respectively older and their timing cannot be resolved by these methods. The data preclude any significant influence of a detrital mica component as well as of excess argon.The lower ages found for the fine grain-size fractions (respectively the low-T degassing steps) correspond to a near-surface period (p-T-minimum); the values are geologically meaningless. The effect is interpreted to result from partial Ar loss due to reheating during Mesozoic-Cainozoic reburial. A model based on diffusion parameters derived from the outgassing experiments and Dodson's (1979) equation yields a closure temperature of 284±40 °C for a cooling rate of 18° C/Ma. Furthermore, this model suggests that the observed argon loss of up to 5% may in fact have been induced by reheating to 150 °C for 50 Ma.  相似文献   

Conditions of diamond growth: a proton microprobe study of inclusions in West Australian diamonds     

W. L. Griffin  A. L. Jaques  S. H. Sie  C. G. Ryan  D. R. Cousens  G. F. Suter 《Contributions to Mineralogy and Petrology》1988,99(2):143-158

Crystalline primary inclusions in diamonds from the Argyle and Ellendale lamproites have been analyzed for Mn, Ni, Cu, Zn, Ga, Pb, Rb, Sr, Y, Zr, Nb, Ta, Ba and Mo by proton microprobe. Eclogite-suite inclusions dominate at Argyle and occur in equal proportions with peridotite-suite inclusions at Ellendale. Eclogitic phases present include garnet, omphacitic clinopyroxene, coesite, rutile, kyanite and sulfide. Eclogitic clinopyroxenes are commonly rich in K and contain 300–1060 ppm Sr and 3–70 ppm Zr: K/Rb increases with K content up to 1400 at 0.7–1.1% K. Rutiles have high Zr and Nb contents with Zr/Nb=1.5–4 and Nb/Ta 16. Of the peridotite-suite inclusions, olivine commonly contains > 10 ppm Sr and Mo; Cr-pyropes are depleted in Sr, Y and Zr, and enriched in Ni, relative to eclogitic garnets.Eclogite-suite diamonds grew in host rocks that were depleted in Mn, Ni and Cr, and enriched in Sr, Zn, Cu, Ga and Ti, relative to Type I eclogite xenoliths from the Roberts Victor Mine. Crystallization temperatures of the eclogite-suite diamonds, as determined by coexisting garnet and clinopyroxene from single diamonds, range from 1085 to 1575° C. Log K _D (C _i ^cpx /C _i ^gnt ) varies linearly with 1/T for Zr, Sr and Ga in most of the same samples. This supports the validity of the temperature estimates; Argyle eclogite-suite diamonds have grown over a T range 400° C. Comparison with data from eclogite xenoliths in kimberlites suggests that K _D ^Sr and K _D ^Zr are mainly T-dependent, while K _D ^Ga may be both temperature-and pressuredependent. K _D ^Ni , K _D ^Cu and K _D ^Zn show no T dependence in these samples.In several cases, significant major-and/or trace-element disequilibrium is observed between different grains of the same mineral, or between pyroxene and garnet, within single diamonds. This implies that these diamonds grew in an open system; inclusions trapped at different stages of growth record changes in major and trace-element composition occurring in the host rock. Diamond growth may have been controlled by a fluid flux which introduced or liberated carbon and modified the composition of the rock. The wide range of equilibration temperatures and the range of composition recorded in the inclusions of single diamonds suggest that a significant time interval was involved in diamond growth.  相似文献   

Late Hercynian U-vein mineralization in the Alps: fluid inclusion and C,O, H isotopic evidence for mixing between two externally derived fluids     

H. S. Negga  S. M. F. Sheppard  J. M. Rosenbaum  M. Cuney 《Contributions to Mineralogy and Petrology》1986,93(2):179-186

Late Hercynian U-bearing carbonate veins within the metamorphic complex of La Lauzière are characterized by two parageneses. The first is dominated by dolomite or ankerite and the second by calcite and pitchblende. Fluids trapped in the dolomites and ankerites at 350–400° C are saline waters (20 to 15 wt % eq. NaCl) with D –34 to –49. In the calcite they are less saline (17 to 8 wt % eq. NaCl) and trapped at 300–350° C with D –50 to –65. All fluids contain trace N₂, CO₂ and probably CH₄. The carbonates have ¹³C –8 to –14. and derived their carbon from organic matter. Evolution of the physico-chemical conditions from dolomite (ankerite) to calcite deposition was progressive.H and O-isotope studies indicate the involvement of two externally derived fluids during vein development. A D-rich ( –35) low fO₂, saline fluid is interpreted to have come from underlying sediments and entered the hotter overlying metamorphic slab and mixed with more oxidizing and less saline U bearing meteoric waters during regional uplift. This evidence for a sedimentary formation water source for the deep fluid implies that the metamorphic complex overthrusted sedimentary formations during the Late-Hercynian.  相似文献   

An experimental study of Fe-Mg partitioning between garnet and olivine and its calibration as a geothermometer   总被引：4，自引：0，他引：4  

Hugh St. C. O'Neill  B. J. Wood 《Contributions to Mineralogy and Petrology》1979,70(1):59-70

The partitioning of Fe and Mg between coexisting garnet and olivine has been studied at 30 kb pressure and temperatures of 900 ° to 1,400 °C. The results of both synthesis and reversal experiments demonstrate that K _D (= (Fe/Mg)_gt/(Fe/Mg)_OI) is strongly dependent on Fe/Mg ratio and on the calcium content of the garnet. For example, at 1,000 °C/30 kb, K _D varies from about 1.2 in very iron-rich compositions to 1.9 at the magnesium end of the series. Increasing the mole fraction of calcium in the garnet from 0 to 0.3 at 1,000 ° C increases K _D in magnesian compositions from 1.9 to about 2.5.The observed temperature and composition dependence of K _D has been formulated into an equation suitable for geothermometry by considering the solid solution properties of the olivine and garnet phases. It was found that, within experimental error, the simplest kind of nonideal solution model (Regular Solution) fits the experimental data adequately. The use of more complex models did not markedly improve the fit to the data, so the model with the least number of variables was adopted.Multiple linear regression of the experimental data (72 points) yielded, for the exchange reaction: 3Fe₂SiO₄+2Mg₃Al₂Si₃O₁₂ olivine garnet 2Fe₂Al₂Si₃O₁₂+3Mg₂SiO₄ garnet olivine H ° (30kb) of –10,750 cal and S ° of –4.26 cal deg^–1 mol^–1. Absolute magnitudes of interaction parameters (W _ij ) derived from the regression are subject to considerable uncertainty. The partition coefficient is, however, strongly dependent on the following differences between solution parameters and these differences are fairly well constrained: W _FeMg ^ol -W _FeMg ^gt 800 cal W _CaMg ^gt -W _CaFe ^gt 2,670 cal.The geothermometer is most sensitive in the temperature and composition regions where K _D is substantially greater than 1. Thus, for example, peridotitic compositions at temperatures less than about 1,300 ° C should yield calculated temperatures within 60 °C of the true value. Iron rich compositions (at any temperature) and magnesian compositions at temperatures well above 1,300 °C could not be expected to yield accurate calculated temperatures.For a fixed K _D the influence of pressure is to raise the calculated temperature by between 3 and 6 °C per kbar.  相似文献   

The Černý Důl deposit (Czechoslovakia): An example of Ni-, Fe-, Ag-, Cu-arsenide mineralization with extremely high activity of arsenic; new data on paxite,novakite and kutinaite     

Dr. Z. Johan 《Mineralogy and Petrology》1985,34(3-4):167-182

Summary The erný Dl mineralization (Giant Mts., Czechoslovakia) consists of calcite veins cross-cutting metamorphic rocks and exhibiting a complex paragenesis of Ni-, Fe-, (Co)- and Cu-, Ag-arsenides associated with native arsenic. Several new minerals belonging to Cu–As and Cu–Ag–As systems were described from this deposit (koutekite, novakite, paxite, kutinaite). New data on paxite, novakite and kutinaite were obtained. Paxite, CuAs₂, is monoclinic,P2₁/c,a=5.830,b=5.111,c=8.084 Å, =99.7°,Z=4,D _calc=5.97 g/cm³, polysynthetically twinned along (010). Novakite belongs to the Cu–Ag–As system. It is monoclinic,C2/m,Cm orC2,a=16.269,b=11.711,c=10.007 Å, -112.7°,Z=4,D _calc=8.01 g/cm³. The ideal formula is Cu_20+x Ag_1–x As₁₀,x0.16. New microprobe analyses of kutinaite indicate a cell-content of 4 [Cu₁₄Ag₆As₇],D _calc=8.37 g/cm³.

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Résumé La minéralisation du gisement de erný Dl (Monts des Géants, Tchécoslovaquie) se distingue par une paragenèse complexe d'arséniures de Ni, Fe, (Co), Cu et Ag associés à l'arsenic natif, et apparaissant dans des filons de calcite qui recoupent une série de roches métamorphiques. Plusieurs minéraux nouveaux appartenant aux systèmes Cu–As et Cu–Ag–As ont été découverts dans ce gisement (koutekite, novakite, paxite, kutinaïte). De nouvelles données sur la paxite, la novakite et la kutinaïte ont été obtenues. La paxite, CuAs₂, est monoclinique,P2₁/c,a=5,830,b=5,111,c=8,084 Å, =99,7°,Z=4,D _calc=5,97 g/cm³; elle est polysythétiquement maclée suivant (010). La novakite est une phase du système Cu–Ag–As. Elle est monoclinique,C2/m,Cm ouC2,a=16,269,b=11,711,c=10,007 Å, =112,7°,Z=4,D _calc=8,01 g/cm³. Saformule idéale s'écrit Cu_20+x Ag_1–x As₁₀,x0,16. Des analyses de la kutinaïte conduisent à 4 [Cu₁₄Ag₆As₇] par maille,D _calc=8,37 g/cm³.L'étude paragénétique a permis de voir que le système hydrothermal à erný Dl couvre un interval de température large, s'étalant de500° à 100°C environ. Une très forte activité d'arsenic au cours des épisodes minéralisants tardifs a abouti à la cristallisation des arséniures de Cu riches en arsenic, stables à basse température. Cinq épisodes minéralisants ont été reconnus: le dépôt des arséniures de Ni, Fe, (Co) (löllingite, nickéline, pararammelsbergite, chloentite) était suivi de: kutinaïte, koutekite, arsenic natif et arséniures de cuivre riches en arsenic (novakite, Cu₂As, paxite). L'abondance des carbonates laisse entrevoir un rôle de composés ou de complexes de carbone dans l'évolution de ce système hydrothermal fortement réducteur.The study of mineral associations showed that the erný Dl hydrothermal system extended over a large temperature interval from 500° to 100°C. An extremely high arsenic activity during the late mineralization periods lead to the precipitation of low-temperature, As-rich copper arsenides. Five mineralization periods were distinguished: the precipitation of Ni-, Fe-, (Co)-arsenides (löllingite, nickeline, pararammelsbergite, chloanthite) was followed by kutinaite, koutekite, native arsenic and As-rich copper arsenides (novakite, Cu₂As, paxite). The abundance of carbonates suggests a possible role of carbon compounds or complexes in the evolution of this highly reducing hydrothermal system.

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With 2 Figures  相似文献   

1Tc-Strontiohilgardit (Ca,Sr)2[B5O8(OH)2Cl] und seine Stellung in der Hilgarditgruppe X2/II[B5O8(OH)2Cl]     

Dr. Otto Braitsch 《Contributions to Mineralogy and Petrology》1959,6(4):233-247

Zusammenfassung 1Tc-Strontiohilgardit (Ca, Sr)₂ [B₅O₈(OH)₂,Cl] mit Ca : Sr etwa 1 : 1 ist ein neues Mineral der Hilgarditgruppe. Fundpunkt: Reyersbausen (9° 59,7 E, 51° 36,6 N), Grube Königshall-Hindenburg, Flöz Staßfurt in sylvinitischer Ausbildung.Konstanten : triklin-pedial,a ₀=6,38 Å,b ₀=6,480 Å,c ₀=6,608 Å, =75,4°,=61,2°, =60,5°; tafelige-gestreckte Links- und Re chtskristalle, farblos, wasserunlöslich, piezoelektrisch. Härte 5–7, Dichte 2,99 g cm^–3;n =1,638,n =1,639,n =1,670; 2V =19°.Neue Daten für die Hilgarditgruppe : 2 M (Cc)-Calciumhilgardit (=Hilgardit) =4 Ca₂[B₅O₃(OH)₂Cl], Raumgruppe Cc.3Tc-Calciumhilgardit (=Parahilgardit) = 3 Ca₂[B₅O₃(OH)₂Cl]; trinklin-pedial, ₀=6,31 Å,b =6,484 Å,c ₀=17,50 Å; =84,0°,=79,6°, =60,9°.Die Polymorphiebeziehungen sind geometrisch deutbar durch eine spezielle Art der Polytropie (Stapelung von Links- und Rechtskristallen im Elementarbereich).  相似文献   

Constraints on the origin and the genesis of graphite-bearing rocks from the variegated sequence of the Bohemian Massif (Austria)     

M. Schrauder  A. Beran  S. Hoernes  W. Richter 《Mineralogy and Petrology》1993,49(3-4):175-188

Summary Transitions between graphitic gneisses, graphite-bearing calcsilicate rocks and marbles of the Variegated Sequence (Bunte Serie) in the Moldanubian zone of the Bohemian massif were examined for their primary sedimentary signatures. The bulk chemistry of the graphitic gneisses is similar to those of common black shales. Chondrite-normalized rare earth element (REE) distribution patterns of graphite-bearing rocks resemble those of average pelitic sediments. Graphite ¹³C-values around –22%o (PDB) show primary organic isotopic characteristics in the silicate rocks and confirm their organogenic origin. Traces of metasomatic mobilizations were found for a number of elements such as Ba, Rb, Cs, the REEs and Mn.Carbon isotope thermometry using the calibration ofScheele andHoefs (1992) suggests a peak-temperature of 640–780°C for the graphite-bearing calcsilicates and marbles. Small scale isotopic studies at the interface between gneisses and marbles argue against a pervasive streaming CO₂-rich fluid derived from an external source and imply that the fluid was controlled more locally by lithology. Ore petrographic investigations showed iron-rich alabandite as an abundant phase within the calcsilicate rocks and marbles. The occurrence and metamorphic origin of alabandite within these rocks indicates high S- and low CO₂-, O₂-fugacities in local layers of the Variegated Sequence.

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Herkunft und Genese von graphitführenden Gesteinen der Bunten Serie aus der Böhmischen Masse (Österreich)

Zusammenfassung Übergänge zwischen Graphitgneisen, Kalksilikatgesteinen und Marmoren der Bunten Serie im Moldanubikum der Böhmischen Masse wurden auf primäre sedimentäre Merkmale hin untersucht. Die Gesamtzusammensetzung der Graphitgneise gleicht der von durchschnittlichen Schwarzschiefern. Chondrit-normierte Verteilungsmuster der Seltenen Erdelemente (SEE) der graphitführenden Gesteine spiegeln pelitische Sedimente wider. Kohlenstoffisotopenzusammensetzungen der Graphite mit ¹³C-Werten um –22 (PDB) aus den Graphitgneisen lassen eindeutig auf einen organogenen Ursprung der Graphite schließen. Hinweise auf metasomatische Mobilisierungen finden sich bei den Elementen Ba, Rb, Cs, den SEE und Mn.Graphit-Kalzit Isotopenthermometrie nachScheele undHoefs (1992) ergibt eine Peak-Temperatur zwischen 640–780°C für das prägende Metamorphoseereignis. Isotopengeochelnische Kleinbereichsuntersuchungen erlauben es, ein während der prägenden Metamorphose lithologische Grenzen pervasiv durchströmendes CO₂-reiches Fluid, das von einer externen Quelle abgeleitet wird, auszuschließen und weisen auf eine eher lokale, von der Lithologie abhängige, Prägung des Fluids hin. Im Zuge der erzpetrographischen Untersuchung wurde Alabandin in den Kalksilikatgesteinen und Marmoren gefunden. Die Gegenwart von Alabandin, der in diesen Gesteinen als metamorphe Bildung angesehen wird, kann als Anzeiger für bereichsweise höhere S- und niedere CO₂- bzw. O₂-Fugazitäten in lokalen Bereichen der Bunten Serie gewertet werden.

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