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1.
The speciation of Nd(III), Sm(III), and Er(III) in sulfate-bearing solutions has been determined spectrophotometrically at temperatures from 25 to 250 °C and a pressure of 100 bars. The data obtained earlier on the speciation of Nd in sulfate-bearing solutions (Migdisov et al., 2006) have been re-evaluated and corrected using a more appropriate activity model and are compared with the corresponding data for Sm(III) and Er(III) and new data for Nd(III). Based on this comparison, the dominant species in the solution are interpreted to be and , with the latter complex increasing in importance at higher temperature. Equilibrium constants were calculated for the following reactions:
2.
3.
Xiaoxian Zhang A. Glyn Bengough John W. Crawford Iain M. Young 《Journal of Hydrology》2002,260(1-4):75-87
The non-linear solvers in numerical solutions of water flow in variably saturated soils are prone to convergence difficulties. Many aspects can give rise to such difficulties and in this paper we address the gravity term and the prescribed-flux boundary in the Picard iteration. The problem of the gravity term in the Picard iteration is iteration-to-iteration oscillation as the gravity term is treated, by analogy with the time-step advance technique, ‘explicitly’ in the iteration. The proposed method for the gravity term is an improvement of the ‘implicit’ approach of Zhang and Ewen [Water Resour. Res. 36 (2000) 2777] by extending it to heterogeneous soil and approximating the inter-nodal hydraulic conductivity in the diffusive term and the gravity term with the same scheme. The prescribed-flux boundary in traditional methods also gives rise to iteration-to-iteration oscillation because there is no feedback to the flux in the solution at the new iteration. To reduce such oscillation, a new method is proposed to provide such a feedback to the flux. Comparison with traditional Picard and Newton iteration methods for a wide range of problems show that a combination of these two proposed methods greatly improves the stability and consequently the computational efficiency, making the use of small time step and/or under-relaxation solely for convergence unnecessary. 相似文献
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5.
Homogenization temperatures and salinity data are presented for fluid inclusions from hydrothermal gangue minerals (quartz and fluorite) associated with porphyry wolframite-molybdenite-arsenopyrite-sphaleritebismuth-chalcopyrite-cassiterite mineralization within the Fire Tower ore zone, Mt Pleasant, New Brunswick. The data indicate that ore mineral precipitation occurred within a temperature range of 260° to 490°C from moderate to high salinity (10–42 wt% NaCl equivalent) aqueous fluids. Two stages of hydrothermal activity characterized by high (>30 wt% NaCl equivalent) salinity fluids are recognized; one which occurred at relatively high temperature (350°–490°C); and one which took place at lower temperature (180°–250°C). The high salinity, high temperature stage is interpreted to be the result of resurgent boiling. Dilution of these early fluids by convecting meteoric water resulted in low to moderate salinity fluids, which dominate the inclusion population. The low temperature, high salinity fluid inclusions are interpreted to represent late residual fluids derived from boiling which occurred as a result of a change in the pressure regime from dominantly lithostatic to hydrostatic conditions. 相似文献
6.
S.M. Archibald A.A. MigdisovA.E. Williams-Jones 《Geochimica et cosmochimica acta》2002,66(9):1611-1619
The solubility of copper chloride in liquid-undersaturated HCl-bearing water vapor was investigated experimentally at temperatures of 280 to 320°C and pressures up to 103 bars. Results of these experiments show that the solubility of copper in the vapor phase is significant and increases with increasing fH2O, but is retrograde with respect to temperature. This solubility is attributed to the formation of hydrated copper-chloride gas species, interpreted to have a copper-chlorine ratio of 1:1 (e.g., CuCl, Cu3Cl3, etc.) and a hydration number varying from 7.6 at 320°C, to 6.0 at 300°C, and 6.1 at 280°C. Complex formation is proposed to have occurred through the reaction:
A1 相似文献
7.
Pit crater structure and processes governing persistent activity at Masaya Volcano, Nicaragua 总被引:1,自引:1,他引:0
Hazel Rymer Benjamin van Wyk de Vries John Stix Glyn Williams-Jones 《Bulletin of Volcanology》1998,59(5):345-355
Persistent activity at Masaya Volcano, Nicaragua, is characterised by cycles of intense degassing, lava lake development
and pit crater formation. It provides a useful site to study the processes which govern such activity, because of its easy
accessibility and relatively short cycles (years to decades). An understanding of the present activity is important because
Masaya is visited by large numbers of tourists, is located close to major cities and has produced voluminous lavas, plinian
eruptions and ignimbrites in the recent past. We provide structural and geophysical data that characterise the "normal" present
state of activity. These indicate that the ongoing degassing phase (1993 to present) was not caused by fresh magma intrusion.
It was associated with shallow density changes within the active Santiago pit crater. The activity appears to be associated
predominantly with shallow changes in the pit crater structure. More hazardous activity will occur only if there are significant
departures from the present gravity, deformation and seismic signatures.
Received: 16 May 1997 / Accepted: 29 October 1997 相似文献
8.
9.
Art. A. Migdisov A.E. Williams-Jones T. Wagner 《Geochimica et cosmochimica acta》2009,73(23):7087-7109
The solubility of REE(III) fluoride solids was determined in fluoride- and chloride-bearing solutions at 150, 200 and 250 °C and saturated water vapor pressure. These experimental data, together with experimental data from previously published studies, were used to evaluate formation constants for chloride- and fluoride-bearing aqueous species of the entire REE(III) group at temperatures up to 300 °C. The data show that the stability of these species differs significantly from that predicted theoretically. For example, contrary to the theoretical predictions, LREEF2+ species are more stable than HREEF2+ species at elevated temperature. The behavior of the chloride-bearing species is similar. Parameters for the Helgeson–Kirkham–Flowers (HKF) equation of state were determined for REEF2+, REECl2+ and REECl2+ complexes using these experimental data and permit calculation of formation constants of these species at conditions not investigated experimentally. These data now permit the mobility of all REE in fluoride- and chloride-bearing hydrothermal systems to be reliably evaluated at intermediate temperatures and pressures. 相似文献
10.
Factors controlling copper solubility and chalcopyrite deposition in the Sungun porphyry copper deposit, Iran 总被引:14,自引:0,他引:14
The Sungun porphyry copper deposit is hosted in a Diorite/granodioritic to quartz-monzonitic stock that intruded Eocene volcanosedimentary
and Cretaceous carbonate rocks. Copper mineralization is associated mainly with potassic alteration and to a lesser extent
with sericitic alteration. Based on previously published fluid inclusion and isotopic data by Hezarkhani and Williams-Jones
most of the copper is interpreted to have deposited during the waning stages of orthomagmatic hydrothermal activity at temperatures
of 400 to 300 °C. These data also indicate that the hydrothermal system involved meteoric waters, and boiled extensively.
In this work, thermodynamic data are used to delineate the stability fields of alteration and ore assemblages as a function
of fS2, fO2 and pH. The solubility of chalcopyrite was evaluated in this range of conditions using recently published experimental data.
During early potassic alteration (>450 °C), Copper solubility is calculated to have been >50 000 ppm, whereas the copper content
of the initial fluid responsible for ore deposition is estimated, from fluid inclusion data, to have been 1200–3800 ppm. This
indicates that initially the fluid was highly undersaturated with respect to chalcopyrite, which agrees with the observation
that veins formed at T > 400 °C contain molybdenite but rarely chalcopyrite. Copper solubility drops rapidly with decreasing temperature, and at
400 °C is approximately 1000 ppm, within the range estimated from fluid inclusion data, whereas at 350 °C it is only 25 ppm.
These calculations are consistent with observations that the bulk of the chalcopyrite deposited at Sungun is hosted by veins
formed at temperatures of 360 ± 60 °C. Other factors that, in principle, may reduce chalcopyrite solubility are increases
in pH, and decreases in fO2 and aCl−. Our analysis shows, however, that most of the change in pH occurred at high temperature when chalcopyrite was grossly undersaturated
in the fluid, and that the direction of change in fO2 increased chalcopyrite solubility. We propose that the Sungun deposit formed mainly in response to the sharp temperature
decrease that accompanied boiling, and partly as a result of the additional heat loss and decrease in aCl−, which occurred as a result of mixing of acidic Cu-bearing magmatic waters with cooler meteoric waters of lower salinity.
Received: 8 July 1998 / Accepted: 8 April 1999 相似文献