Based on data on the composition of ore-bearing hydrothermal solutions and parameters of ore-forming processes at various antimony and antimony-bearing deposits, which were obtained in studies of fluid inclusions in ore minerals, we investigated the behavior of Sb(III) in the system Sb–Cl–H2S–H2O describing the formation of these deposits.
We also performed thermodynamic modeling of native-antimony and stibnite dissolution in sulfide (mHS− = 0.0001−0.1) and chloride (mCl− = 0.1−5) solutions and the joint dissolution of Sb(s)0 and Sb2S3(s) in sulfide-chloride solution (mHS− = 0.01; mCl− = 1) depending on Eh, pH, and temperature. All thermodynamic calculations were carried out using the Chiller computer program. Under the above conditions, stibnite precipitates in acid, weakly acid to neutral, and medium redox solutions, whereas native antimony precipitates before stibnite under more reducing conditions in neutral to alkaline solutions.
The metal-bearing capacity of hydrothermal solutions (200–250 °C) of different compositions and origins has been predicted. We have established that the highest capacity is specific for acid (pH = 2–3) high-chloride solutions poor in sulfide sulfur and alkaline (pH = 7–8) low-chloride low-sulfide solutions. 相似文献
Infrared absorbance spectra over ∼100 to 1,800 cm−1 were collected from optically thin films of 21 samples with compositions spanning the forsterite–fayalite binary. Polarization
information from previous specular reflectance data on end-members was used in tracing the peaks across the entire binary.
Peak positions (νi) were constrained by Lorentzian decompositions. Fitting also constrained widths for singlet peaks but for doublets and triplets,
variation in νi with composition among the constituent polarizations alters widths from intrinsic. Because film thicknesses of 0.6–1.4 μm
were estimated, our band strengths are approximate; however, relative intensities should be correct. Only for a few peaks
does νi vary smoothly across the entire binary; instead, distinct linear trends exist for Fe- and Mg-rich olivines. Discontinuities
and kinks in νi(X) occur at X = Mg/(Fe + Mg) = 0.7 and are accompanied by a change in intensity patterns. This interesting behavior was not revealed in
previous spectra of powder dispersions. The contrasting character of IR vibrations for Fe- and Mg-rich olivines is inferred
to arise from structural variations because (1) frequency is related to bond length, (2) other factors affecting frequency
(cation mass and probably bonding type) vary linearly across the binary, and (3) available data on unit cell parameters are
consistent with distinct trends for forsterites and fayalites. Vibrational components of heat capacity (CV) and enthalpy (H) calculated from νi, were found to be slightly more negative than linear interpolations between values for forsterite and fayalite. Our computations
give smaller negative excesses from ideality in H than do previous calorimetric measurements, but are equal within experimental uncertainties. 相似文献
An unresolved issue in the study of pressure solution in rock materials is the dependence of grain boundary structure and
diffusive properties on the mutual orientation of neighbouring grain lattices. We report electrical measurements yielding
the diffusivity of differently oriented halite–glass and halite–halite contacts loaded in the presence of brine. The halite–glass
contact experiments show pressure solution of the halite and an effect of halite lattice orientation on grain boundary transport.
Post-mortem observations show an orientation-dependent grain boundary texture controlled by the periodic bond chains in the
halite structure. It is inferred that this texture determines the internal grain boundary structure and properties during
pressure solution. In the halite–halite experiments neck-growth occurred, its rate depending on twist-misorientation. The
results imply that deformation by pressure solution may lead to lattice-preferred orientation development, and that polymineralic
rocks may deform faster at lower stresses than monomineralic rocks. 相似文献
Static lattice energy calculations (SLEC), based on empirical interatomic potentials, have been performed for a set of 800
different structures in a 2 × 2 × 4 supercell of C2/c diopside with compositions between diopside and jadeite, and with different states of order of the exchangeable Na/Ca and
Mg/Al cations. Excess static energies of these structures have been cluster expanded in a basis set of 37 pair-interaction
parameters. These parameters have been used to constrain Monte Carlo simulations of temperature-dependent properties in the
range of 273–2,023 K and to calculate a temperature–composition phase diagram. The simulations predict the order–disorder
transition in omphacite at 1,150 ± 20°C in good agreement with the experimental data of Carpenter (Mineral Petrol 78:433–440,
1981). The stronger ordering of Mg/Al within the M1 site than of Ca/Na in the M2 site is attributed to the shorter M1–M1 nearest-neighbor
distance, and, consequently, the stronger ordering force. The comparison of the simulated relationship between the order parameters
corresponding to M1 and M2 sites with the X-ray refinement data on natural omphacites (Boffa Ballaran et al. in Am Mineral
83:419–433, 1998) suggests that the cation ordering becomes kinetically ineffective at about 600°C. 相似文献