B. N. Ryzhenko

Titanium complexation in hydrothermal systems

The solubility of rutile in aqueous solutions of HCl, HF, H2SO4, NaOH, and NaF was determined at 500°C, 1000 bar, and hydrogen fugacity from 8 × 10−12 to 10.3 bar (Mn3O4/Mn2O3 and Ni/NiO buffers, dissolution of an Al batch weight). The experimentally determined solubility values were used to calculate the constants of the following equilibria at 500°C and 1 kbar pressure: TiO2(rutile) + H2O + HCl0 = Ti(OH)3Cl0 (pK = 4.89); TiO2(rutile) + 2HCl0 = Ti(OH)2Cl20 (pK = 4.69), TiO2(rutile) + HS O4− + H+ = Ti(OH)2SO40 (pK = 1.98), TiO2(rutile) + 2HSO4− + 2H+ = Ti(SO4)20 + 2H2O (pK = −1.50), TiO2(rutile) + 2H2O + OH− = Ti(OH)5− (pK = 3.17), TiO2(rutile) + 2H2O + 2OH− = Ti(OH)62− (pK = 1.46), TiO2(rutile) + 2H2O + F− = Ti(OH)3F0 + OH− (pK = 5.86), TiO2(rutile) + 2HF0 = Ti(OH)2F20 (pK = 2.99), and TiO2(rutile) + 2H2O + F− = Ti(OH)4F− (pK = 3.69). Based on the results obtained on the composition of volcanic emanations whose Ti concentrations were determined, we evaluated the constants of the equilibria TiO2(rutile) + H2O + HCl0 = Ti(OH)3Cl0 (pK = 2.74) and TiO2(rutile) + HSO4− + H+ = Ti(OH)2SO40 (pK = 3.40) at 25°C. The electrostatic model of electrolyte ionization was used to calculate the ionization constants and the Gibbs free energy values for the following Ti species in aqueous fluids at the parameters of postmagmatic processes: Ti(OH)3+, Ti(OH)40, Ti(OH)5−, Ti(OH)62−, Ti(OH)3F0, Ti(OH)2F20, Ti(OH)4F−, Ti(OH)3Cl0, Ti(OH)2Cl20, Ti(OH)2SO40, and Ti(SO4)20. As follows from our data on Ti complexation with Cl, F, and SO4, fluids the most favorable for Ti migration are aqueous acid F-rich solutions with Ti concentrations of no higher than a few fractions of a milligram per kilogram of water.

Inclusions of silicate and sulfate melts in chrome diposide from the Inagli deposit, Yakutia, Russia

Melt inclusions were studied in chrome diopside from the Inagli deposit of gemstones in the Inagli massif of alkaline ultrabasic rocks of potassic affinity in the northwestern Aldan shield, Yakutia, Russia. The chrome diopside is highly transparent and has an intense green color. Its Cr2O3 content varies from 0.13 to 0.75 wt %. Primary and primary-secondary polyphase inclusions in chrome diopside are dominated by crystal phases (80–90 vol %) and contain aqueous solution and a gas phase. Using electron microprobe analysis and Raman spectroscopy, the following crystalline phases were identified. Silicate minerals are represented by potassium feldspar, pectolite [NaCa2Si3O8(OH)], and phlogopite. The most abundant minerals in the majority of inclusions are sulfates: glaserite (aphthitalite) [K3Na(SO4)2], glauberite [Na2Ca(SO4)2], aluminum sulfate, anhydrite (CaSO4), gypsum (CaSO4 × 2H2O), barite (BaSO4), bloedite [Na2Mg(SO4)2 × 4H2O], thenardite (NaSO4), polyhalite [K2Ca2Mg(SO4)4 × 2H2O], arcanite (K2SO4), and celestite (SrSO4). In addition, apatite was detected in some inclusions. Chlorides are probably present among small crystalline phases, because some analyses of aggregates of silicate and sulfate minerals showed up to 0.19–10.3 wt % Cl. Hydrogen was identified in the gas phase of polyphase inclusions by Raman spectroscopy. The composition of melt from which the chrome diopside crystallized was calculated on the basis of the investigation of silicate melt inclusions. This melt contains 53.5 wt % SiO2, considerable amounts of CaO (16.3 wt %), K2O (7.9 wt %), Na2O (3.5 wt %), and SO3 (1.4 wt %) and moderate amounts of Al2O3 (7.5 wt %), MgO (5.8 wt %), FeO (1.1 wt %), and H2O (0.75 wt %). The content of Cr2O3 in the melt was 0.13 wt %. Many inclusions were homogenized at 770–850°C, when all of the crystals and the gas phase were dissolved. The material of inclusions heated up to the homogenization temperature became heterogeneous even during very fast quenching (two seconds) producing numerous small crystals. This fact implies that most of the inclusions contained a salt (rather than silicate) melt of sulfate-dominated composition. Such inclusions were formed from salt globules (with a density of about 2.5 g/cm3) occurring as an emulsion in the denser (2.6 g/cm3) silicate melt from which the chrome diopside crystallized.

Experimental determination of zirconium speciation in hydrothermal solutions

The solubility of ZrO2(baddeleyite) in HCl, HF, H2SO4, NaOH, and Na2CO3 solutions was determined by the capsule method at 500°C and 1000 bar. Baddeleyite is the only solid phase detected in the experimental products. Based on the ZrO2(baddeleyite) solubility measurements, the values of equilibrium constants at 500°C and 1000 bar (consistent with the Gibbs free energies of all the reactants) were obtained for the following reactions: ZrO2(cr) + H2SO40 = Zr(OH)2OH40 (pKo = 4.95), ZrO2(cr) + 2H2SO40 = Zr(SO4)20) + 2H2O (pKo = 3.74), ZrO2(cr) + H2O + HF0 = Zr(OH)3F0 (pKo = 3.35), ZrO2(cr) + 2HF0 = Zr(OH)2F20 (pKo = 2.37), and ZrO2(cr) + 2H2O + OH− = Zr(OH)5− (pKo = 4.39). Ionization constants were estimated for the chloride, fluoride, sulfate, and hydroxo complexes of zirconium. Using the experimental data and thermodynamic information derived from experiments and the electrostatic model of the ionization of electrolytes, it was shown that no more than n mg zirconium per one kilogram H2O can be accumulated in high-temperature fluids at 500°C and 1000 bar.

Chemical composition of natural waters and brines as a result of hydrogeochemical processes in water-rock-gas systems

AbstractThermodynamic computer modeling was carried out to evaluate the formation of the chemical composition of main geochemical types of groundwaters. An explanation was proposed for the geochemical evolution of underground saline waters and brines along the calcic and sodic trends, the inversion of groundwater in the deep horizons of sedimentation structures, and the geochemical diversity of CO2-rich waters in crystalline rocks.The occurrence of hydrogeochemical processes is controlled by the physicochemical conditions of the state of the water-rock-gas system. The following parameters (boundary conditions) are critical in natural hydrogeologic environments: the mass ratio of interacting rock and water (R/W), the openness (closeness) of hydrogeochemical systems with respect to CO2 and O2, the chemical and mineral composition of rocks, and temperature-pressure conditions. The estimation of boundary conditions showed the following. (1)The petrochemical type of rock affects the composition of the aqueous phase through the dissolution rates of minerals, especially volatile-bearing ones. A decrease in water exchange and an increase in R/W (10−6→102) are accompanied by an increase in the salinity of the aqueous phase and an increase in the fraction of Cl, Na, and Ca (in a closed system) or HCO3, Cl, and Na (in a system open to CO2).(2)The composition of the aqueous phase of water-rock systems is most strongly affected by the abundance in the rock of extractable Cl and reactive organic matter, which controls the geochemical type of the aqueous phase and its position in the Hardie-Eugster diagram.(3)The composition of the aqueous phase is shifted into the calcic field of the Hardie-Eugster diagram at the closure of the water-rock system and into the carbonate field at the opening of the water-rock system to CO2. Waters showing pH ≈ 8.5 are formed in feldspathic rocks with low contents of extractable volatiles. Alkaline waters with pH > 9 are formed in water-rock systems (a) under the influence of organic matter and (b) by the evaporative concentration waters under surface conditions.(4)The higher the degree of seawater concentration and the lower the R/W value, the more significant the effect of seawater composition on the aqueous phase chemistry of the water-rock system. With increasing degree of seawater concentration, the composition of the aqueous phase changes in the sequence Cl-SO4-Na-Mg- → Cl-SO4-Mg-Na→ Cl-Mg (at low R/W) and Cl-Na → Cl-Na-Mg (at high R/W). The influence of the petrochemical type of rock and CO2 partial pressure, on the geochemical type of the aqueous phase in the seawater-rock system is more significant at high R/W.(5)A temperature increase shifts the acid-base state of the aqueous phase into the alkaline region and its redox state into the reducing region.

Chemical composition of the primary aqueous phase of the earth and origin of life

Prokaryotes and cytoplasm of eukaryotes are dominated by K+, whereas the extracellular fluid of most species of multicellular organisms is dominated by Na+. It was substantiated that the K+/Na+ ratio in the salt constituent of the cells of modern organisms qualitatively reflects the proportions between these elements in the aqueous phase, in which the first forms of life and the protocell originated. The same conclusion is done by Armen Y. Mulkidjanian et al. (PNAS 13, 2012, E821-830). The chemical composition of primary aqueous phase of the Earth was reconstructed using thermodynamic numerical simulation of the equilibrium composition of the “carbonaceous chondrite material-water”, “primitive mantle material-water”, “ultramafic rock-water”, “mafic rocks-water” systems that are open with respect to CO2 and CH4.It was shown that at 25°C, total pressure of 1 bar, and partial pressures of CO2 and CH4 10−5–10−8 and 10−2–10−8 bar, respectively, the aqueous phase of the systems with carbonaceous chondrite and primitive mantle has K+/Na+ > 1, which corresponds to the proportions of these elements in the intracellular solution. The aqueous phase is characterized by pH = 8–9, Eh = −450 ± 50 mV, the presence of ammonium nitrogen, and concentrations of K, Na, and Mg close to those in the inferred intracellular fluid. The interaction of water with ultramafic and mafic rocks provides K+/Na+ < 1 in aqueous solution, which corresponds to the chemical composition of the modern natural waters of the Earth’s crust.Simulation results show that the protocell could arise in the primary aqueous phase of the Earth during differentiation of chondritic material into the Earth’s core and mantle, after the formation of the nitrogen atmosphere containing CH4, CO2, NH3, H2, H2S, CO and other gases, but prior to the formation of the modern rocks of the Earth’s crust (first billion years of the planet’s lifetime).

Zn and Pb Solubility and Speciation in Aqueous Chloride Fluids at T-P Parameters Corresponding to Granitoid Magma Degassing and Crystallization

The solubility of all possible Zn and Pb species in aqueous chloride fluids was evaluated by means of thermodynamic simulations in systems ZnO(PbO)-aqueous solution of NaCl (KCl, NaCl + HCl) within broad ranges of temperature (600–900°C), pressure (0.7–5 kbar), and chloride concentrations, under parameters corresponding to the crystallization and degassing of granitoid magmas in the Earth’s crust. Our simulation results demonstrate that the addition of Cl to the fluid phase in the form of Na(K)Cl and HCl significantly increases the concentrations of Cl-bearing Zn and Pb complexes and the total concentration of the metals in the solutions in equilibrium with the solid oxides. In Zn-bearing fluids, the Zn(OH)20, ZnOH+, and Zn(OH)3−—hydroxyl complexes and the ZnCl20, and ZnCl+ chlorocomplexes, which are predominant at low Cl concentrations (CCl < 0.05–0.1 m) give way to ZnCl42− with increasing CCl, which becomes the predominant Zn species of the fluid at CCl > 0.1–0.5 m throughout the whole temperature range in question and pressures higher than 1 kbar. For Pb-bearing fluids, the T-P-X region dominated by the Pb(OH)20, and Pb(OH)3− hydroxyl complexes is remarkably wider than the analogous region for Zn, particularly at elevated temperatures (≥700°C) in alkaline solutions. An increase in CCl is associated with an increase in the concentration and changes in the speciation of Pb chlorocomplexes: PbCl20 → PbCl3− → PbCl42−. The concentrations of Zn and Pb chlorocomplexes increase with increasing pressure, decreasing temperature, and decrease pH with the addition of HCl to the system. It is demonstrated that the solubility of ZnO at any given T-P-X in alkaline solutions with low chloride concentrations are lower than the solubility of PbO. The Zn concentration increases more significantly than with the Pb concentration with increasing CCl and decreasing pH, so that the Zn concentration in acidic solutions is higher than the Pb concentration over broad ranges of temperature, pressure, and Cl concentration. Chloride complexes of Zn (ZnCl20, and ZnCl42−) and Pb (PbCl20, and PbCl3− are proved to be predominant within broad T-P-X-pH ranges corresponding to the parameters under which magmatic fluid are generated. Our simulation results confirm the hypothesis that chlorocomplexes play a leading role in Zn and Pb distribution between aqueous chloride fluids and granitic melts. These simulation results are consistent with experimental data on the Zn and Pb distribution coefficients (D(Zn)f/m and D(Pb)f/m, respectively) between aqueous chloride fluids and granitic melts that demonstrated that (1) D(Zn)f/m and D(Pb)f/m increase with increasing Na and K chloride concentrations in the aqueous fluid, (2) both D(Zn)f/m and D(Pb)f/m drastically increase when HCl is added to the fluid, and (3) (D(Zn)f/m is higher than D(Pb)f/m at any given T-P-X parameters. The experimentally established decrease in D(Zn)f/m and D(Pb)f/m with increasing pressure (at unchanging temperature and Cl concentration) is likely explained by an increase in the alkalinity of the aqueous chloride fluid in equilibrium with granite melt and, correspondingly, a decrease in the Zn and Pb solubility in this fluid.

Model for the formation of arsenic contamination in groundwater. 1. Datong Basin, China

Mineral equilibria were analyzed in the system As-bearing rock-meteoric water. It was shown that carbonate rocks are the most probable source of As and Sr in the waters of the Datong Basin (Peoples Republic of China). The reason for groundwater enrichment in As is the shift of the equilibrium FeCO3 (siderite) + H2O = FeOOH(goethite) + CO2(g) + H2(g) to the left (toward siderite formation) owing to organic matter oxidation by atmospheric oxygen and an increase in the equilibrium partial pressure of CO2, while the Eh of the system remains below −0.30 ± 0.06 V.

V.I. Vernadsky and main research avenues in modern hydrogeochemistry

The main research directions in modern hydrogeochemistry were analyzed in connection with the 75th anniversary of its foundation. It was shown that hydrogeochemistry has fruitfully developed on the basis of the scientific concepts of its founder, V.I. Vernadsky. Among these concepts are the mineralogy of water, evolution of the system of water-rock-gas-organic matter, dynamics of hydrogeochemical processes, isotopic and environmental hydrogeochemistry, geochemistry of free and capillary waters, ocean geochemistry, geological and biological role of water, physicochemical modeling, etc.

Mineralogical and geochemical zoning of sediments at the Semenov cluster of hydrothermal fields, 13°31′-13°30′ N, Mid-Atlantic Ridge

New material from eight columns recovered during Cruise 32 of the R/V Professor Logachev in 2009 was used to explore the lithological facies, biostratigraphy, mineralogy, and geochemistry of sediments from the northwestern (active) and eastern (inactive) hydrothermal vent fields of the Semenov cluster. Mineral types of sediments were distinguished, and a general scheme was proposed for the vertical structure of the hydrothermal-sedimentary sequence overlying massive sulfide ores. It was found that the ore-bearing sediments exhibit a vertical zoning in the distribution of mineral assemblages, which are controlled by oxygen activity. The mechanisms of the formation of atacamite, CuCl2 · 3Cu(OH)2, which is a widespread mineral in red iron-oxide bodies replacing sulfides (gossans), were evaluated.

Estimation of the composition of the Earth’s primary aqueous phase. 2. Synthesis from the mantle and igneous rock material. Comparison with synthesis from the carbonaceous chondrite material

Simulation results of the equilibrium state of systems water-carbonaceous chondrite material, water-primary mantle material, water-ultramafic rock material, and water-mafic rock material open with respect to carbon dioxide and methane at 25°C, 1 bar indicate that highly alkaline reduced aqueous solutions with K/Na > 1 can be formed only if water is in equilibrium with compositions close to those of continental crust and primitive mantle. Yu.V. Natochin’s hypothesis that the living cell can be formed only in an aqueous environment with K/Na > 1 leads to the conclusion that terrestrial life could arise and further evolve on the Earth during the differentiation of primary chondritic material into the Earth’s core and mantle (during the first few million years of the planet’s lifetime) in an alkaline (pH 9–10) reduced (Eh = −400–500 mV) aqueous solution at a temperature of 50–60°C, in equilibrium with an N2-bearing atmosphere, which also contained CH4 (partial pressure from 10−2 to 10−8 bar), CO2 (partial pressure from 10−5 to 10−8 bar), NH3, H2, H2S, CO, and other gases.