Research of the Uranium,Niobium, and Tantalum Behavior in the Granite Melt–Chloride Fluid System at 750°C and 1000 Bar

Geology of Ore Deposits - The major objective of the study investigation was to find the physicochemical conditions for U, Nb, and Ta mobilization into the solution from acidic melts similar in...     

Experimental Study of the Solubility of Natural Tantalite and Pyrochlore and Tantalum and Niobium Oxides in Hydrothermal Fluoride–Chloride Solutions

Doklady Earth Sciences - The concentration and temperature dependences of the solubility of tantalite, pyrochlore, and tantalum and niobium oxides in fluoride–chloride aqueous (mHF + mHCl)...     

Erratum to: Experimental Study of the Solubility of Natural Tantalite and Pyrochlore and Tantalum and Niobium Oxides in Hydrothermal Fluoride–Chloride Solutions

Doklady Earth Sciences - An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X22340025     

Formation of Water-Bearing Defects in Olivine in the Presence of Water–Hydrocarbon Fluid at 6.3 GPa and 1200°C

The main trends of water dissolution in Fe-bearing olivine have been investigated in the olivine–H₂O–hydrocarbon fluid system in experiments at a pressure of 6.3 GPa, a temperature of 1200°C, and hydrogen fugacity ( fH₂) buffered by the Mo–MoO₂ equilibrium. The content and contribution of ОH defects of different types in Fe-bearing olivines depend on the composition of reduced fluids in the system. As the fraction of hydrocarbons in the fluid increases, the H₂O content in olivine crystals decreases from 900 to 160–180 ppm, while the ОН absorption peaks become lower at high frequencies and occupy a larger part of the infrared spectrum in the low-frequency region. According to the experimental results, even the deepest seated mantle olivines with OH defects were not equilibrated with a fluid rich in light alkanes or oxygenated hydrocarbons.     

Melt–Fluid and Fluid–Fluid Immiscibility in a Na2SO4–SiO2–H2O System and Implications for the Formation of Rare Earth Deposits

Liquid–liquid immiscibility has crucial influences on geological processes, such as magma degassing and formation of ore deposits. Sulfate, as an important component, associates with many kinds of deposits. Two types of immiscibility, including (i) fluid–melt immiscibility between an aqueous solution and a sulfate melt, and (ii) fluid–fluid immiscibility between two aqueous fluids with different sulfate concentrations, have been identified for sulfate–water systems. In this study, we investigated the immiscibility behaviors of a sulfate- and quartz-saturated Na2SO4–SiO2–H2O system at elevated temperature, to explore the phase relationships involving both types of immiscibility. The fluid–melt immiscibility appeared first when the Na2SO4–SiO2–H2O sample was heated to ~270°C, and then fluid–fluid immiscibility emerged while the sample was further heated to ~450°C. At this stage, the coexistence of one water-saturated sulfate melt and two aqueous fluids with distinct sulfate concentrations was observed. The three immiscible phases remain stable over a wide pressure–temperature range, and the appearance temperature of the fluid–fluid immiscibility increases with the increased pressure. Considering that sulfate components occur extensively in carbonatite-related deposits, the fluid–fluid immiscibility can result in significant sulfate fractionation and provides implications for understanding the formation of carbonatite-related rare earth deposits.     

Experimental Study of REEs,Ba, and Sr Interphase Partitioning in Fluid–Magmatic Silicate Systems at T = 1250°C and P = 2 kbar

The results of study of the alkaline silicate melt–hydrous saline (carbonate, sulfate, and fluoride) fluid system, as well as partitioning of ore metals (Ba, Sr, and REEs) between coexisting phases at T = 1250°C and P = 2 kbar are reported. It is shown that aqueous solutions with the compositions studied cannot be effective concentrators and transporters of ore elements such as REEs, Sr, and Ba. The sulfate melt accumulates Sr and Ba in the alkaline silicate melt–hydrous sulfate fluid system, which provides evidence for the efficiency of sulfate ore extraction of Sr and Ba from the melt. The results obtained support the important oregenerating role of dense saline phases formed upon the development of liquid heterogeneity in fluid–magmatic systems.

     

Characteristics and Applications of Fluid Inclusions in the Eogene System of the Biyang Depression—I.A Fluid Inclusion Study

Presented in this paper are the rypes,salinities,homogenization temperatures and organic components of fluid inclusions formed at the four stages of diagenetic authigenesis in the Eogene of the Biyang Depression.The results of cooling experiments on fluid inclusions were used to determine the fluid system and composition of saline aqueous solution in each of the stages .The homogenization temperatures of saline aqueous solution inclusions and hydrocarbon organic inclu-sions have been corrected by two approaches ,and the trapping temperatures and pressures of fluid inclusions at each of the stages have been obtained.This strdy has shed light on the physicochemistry and evolution of diagenetic fluids.The diagentic fluid system is a system which was transformed from a chloride-bearing to a carbonate-bearing system along with the diagenic evolu-tion.The decrease of diagenetic temperature at Stage III of diagenetic authigenesis suggests that the depression would have experiences uplifting at that time.The fluorescent characteristics of fluid inclusions indicate the varieties of organic components in fluid inclusions both in time and in space.     

Phase Relations in the Harzburgite–Hydrous Carbonate Melt at 5.5–7.5 GPa and 1200–1350°С

Phase relations are studied experimentally in the harzburgite–hydrous carbonate melt system, the bulk composition of which represents primary kimberlite. Experiments were carried out at 5.5 and 7.5 GPa, 1200–1350°С, and \({{X}_{{{\text{C}}{{{\text{O}}}_{2}}}}}\) = 0.39–0.57, and lasted 60 hours. It is established that olivine–orthopyroxene–garnet–magnesite–melt assemblage is stable within the entire range of the studied parameters. With increase of temperature and \({{X}_{{{\text{C}}{{{\text{O}}}_{2}}}}}\) in the system, Ca# in the melt and the olivine fraction in the peridotite matrix significantly decrease. The composition of silicate phases in run products is close to those of high-temperature mantle peridotite. Analysis of obtained data suggest that magnesite at the base of subcontinental lithosphere could be derived by metasomatic alteration of peridotite by asthenospheric hydrous carbonate melts. The process is possible in the temperature range typical of heat flux of 40–45 mW/m², which corresponds to the conditions of formation of the deepest peridotite xenoliths. Crystallization of magnesite during interaction with peridotite matrix can be considered as experimentally substantiated mechanism of CO₂ accumulation in subcratonic lithosphere.     

Phase Distribution of Rare and Rare-Earth Elements in the Silicate–Fluoride Systems at Т = 800–1200°С and Р = 1–2 kbar (Experimental Investigations)

Doklady Earth Sciences - The melt in the alumosilicate (granite) melt–molten fluoride salt system is experimentally studied at Т = 800–1200°С and Р = 1–2...     

Pyrochlore Solubility in NaF Solutions at 800°C and p = 170–230 MPa

Doklady Earth Sciences - The solubility of pyrochlore (NaCa)Nb2O6F was studied experimentally in the NaF–H2O system covering both the homogeneous region of hydrothermal solutions and the...     

Phase Relations in the Fe–S–C System at P = 0.5 GPa,T = 1100–1250°C: Fe–S–C Liquation and Its Role in the Formation of Magmatic Sulfide Deposits

Doklady Earth Sciences - The liquid phases are represented by immiscible Fe–S and Fe–C melts under partial melting of the graphite-saturated Fe–S–C system at P = 0.5 GPa and...     

Experimental Study of the SiO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O–KF–KCl–NaF System at 700–800°C and 1–2 kbar Based on Synthetic Fluid Inclusions in Quartz

The phase state of the fluid in the H₂O–KF ± KCl ± NaF system is studied in the presence of quartz for an experimental assay of the mutual influence of various salts of the fluid-forming mixture on heterogeneous fluid equilibria. The fluid inclusions were synthesized in quartz by the fracture healing method from solutions with KF + KCl and KF + NaF mixtures at 1 or 2 kbar and 700, 750, or 800°C. The results of the fluid inclusion study indicate a heterogeneous state of the fluid and variation in the fluid composition during experiments as a result of its interaction with quartz. The increase in temperature and pressure, as well as variation in the proportions of the salt contents in the fluid-forming mixture, changed the course of chemical reactions. After all the experiments, a glassy phase was observed in some types of inclusions. It is known that aqueous KF or KCl solutions, the solubility of which increases during heating, are characterized by phase equilibria of systems of the first type (Valyashko, 1990), when liquid and vapor are equilibrated for a heterogeneous state of the fluid. In this case, some inclusions should homogenize to vapor. However, no similar inclusions were observed in contrast to denser fluid phases (liquids), which are typical of the upper heterogeneous area of systems of the second (P–Q) type. Some inclusions host solid phases, the solubility of which decreases as the temperature increases. The results of experiments in the presence of KF + NaF solutions showed that the amount of inclusions of heterogeneous entrapment increases at higher temperatures simultaneously with a decrease in the H₂O content of the glassy phase.     

Phase Chemistry Study of the Zabuye Salt Lake Brine: Isothermal Evaporation at 15°C and 25°C

Zabuye Salt Lake in Tibet, China is a carbonate-type salt lake, which has some unique characteristics that make it different from other types of salt lakes. The lake is at the latter period in its evolution and contains liquid and solid resources. Its brine is rich in Li, B, K and other useful minor elements that are of great economic value. We studied the concentration behavior of these elements and the crystallization paths of salts during isothermal evaporation of brine at 15°C and 25°C. The crystallization sequence of the primary salts from the brine at 25°C is halite (NaCl) → aphthitalite (3K2SO4·Na2SO4) → zabuyelite (Li2CO3)→ trona (Na2CO3·NaHCO3·2H2O) → thermonatrite (Na2CO3·H2O) → sylvite (KCl), while the sequence is halite (NaCl) → sylvite (KCl) → trona (Na2CO3·NaHCO3·2H2O) → zabuyelite (Li2CO3) → thermonatrite (Na2CO3·H2O) → aphthitalite (3K2SO4·Na2SO4) at 15°C. They are in accordance with the metastable phase diagram of the Na+, K+-Cl?, CO32?, SO42?-H2O quinary system at 25°C, except for Na2CO3·7H2O which is replaced by trona and thermonatrite. In the 25°C experiment, zabuyelite (Li2CO3) was precipitated in the early stage because Li2CO3 is supersaturated in the brine at 25°C, in contrast with that at 15°C, it precipitated in the later stage. Potash was precipitated in the middle and late stages in both experiments, while boron was concentrated in the early and middle stages and precipitated in the late stage.     

Dehydration melting of amphibolite at 1.5 GPa and 800–950
C:Implications for the Mesozoic potassium-rich adakite in the eastern North China Craton

Mesozoic intermediate-felsic magmatic rocks in the eastern North China Craton commonly show geochemical similarity to adakites.However,the lack of direct constraints from partial melting experiments at high pressures and temperatures fuels a debate over the origin of these rocks.In this work,we performed partial melting experiments at 1.5 GPa and 800–950℃on amphibolite samples collected from the vicinity of the Mesozoic potassium-rich adakitic rocks in the Zhangjiakou area,northern margin of the North China Craton.The experimental melts range from granitic to granodioritic compositions,with SiO₂=56.4–72.6 wt.%,Al₂O₃=16.1–19.3 wt.%,FeO^*=2.4–9.6 wt.%,MgO=0.3–2.0 wt.%,CaO=0.6–3.8 wt.%,Na₂O=4.7–5.3 wt.%,and K₂O=2.6–3.9 wt.%,which are in the ranges of the surrounding Mesozoic potassium-rich adakitic rocks,except for the higher Al₂O₃contents and the data point at 1.5 GPa and 800℃.Trace element compositions of the melts measured by LA-ICP-MS are rich in Sr(849–1067 ppm)and light rare earth elements(LREEs)and poor in Y(<10.4 ppm)and Yb(<0.88 ppm),and have high Sr/Y(102–221)and(La/Yb)n(27–41)ratios and strongly fractionated rare earth element(REE)patterns,whereas no obvious negative Eu anomalies are observed.The geochemical characteristics show overall similarity to the Mesozoic potassium-rich adakitic rocks in the area,especially adakites with low Mg#,again except for the data point at 1.5 GPa and 800℃.The results suggest that partial melting of amphibolite can produce potassium-rich adakitic rocks with low Mg#in the eastern North China Craton under the experimental conditions of 1.5 GPa and 850–950℃.The experimental restites consist of hornblende(Hbl)+plagioclase(Pl)+garnet(Grt)±clinopyroxene(Cpx),a mineral assemblage significantly different from that of the nearby Hannuoba mafic granulite xenoliths which consist of Cpx+orthopyroxene(Opx)+Pl±Grt.Chemically,the experimental restites contain higher Al₂O₃but lower MgO and CaO than the Hannuoba mafic granulite xenoliths.We therefore argue that the Hannuoba mafic granulite xenoliths cannot represent the direct products of partial melting of the experimental amphibolite.     

Evidence for Granitoid Magmatism and the Composition of the Silicic Melt in the Gabbroid Assemblage of the Mid-Atlantic Ridge at 13° N: New Data on Melt Inclusions

Doklady Earth Sciences - Despite the local occurrence of silicic magmatism during the formation of the oceanic crust, the nature of felsic granitoid veins (“oceanic plagiogranite”)...     

Experimental Study of the Formation of Ba–Cr Titanates in the Fluid-Bearing Chromite–Rutile/Ilmenite System at Т = 1000–1200°С and Р = 1.8–5.0 GPa

Doklady Earth Sciences - The results of experimental study of crystallization of chromium-bearing Ba-titanates (redlegeite, lindsleyite, and hawthorneite) in the chromite–rutile/ilmenite...     

Experimental determination of coexisting iron–titanium oxides in the systems FeTiAlO, FeTiAlMgO, FeTiAlMnO, and FeTiAlMgMnO at 800 and 900°C, 1–4 kbar, and relatively high oxygen fugacity

A synthetic, low-melting rhyolite composition containing TiO₂ and iron oxide, with further separate additions of MgO, MnO, and MgO + MnO, was used in hydrothermal experiments to crystallize Ilm-Hem and Usp-Mt solid solutions at 800 and 900°C under redox conditions slightly below nickel–nickel oxide (NNO) to $\approx 3\,\log_{10} f_{{{\text{O}}_{2}}}A synthetic, low-melting rhyolite composition containing TiO₂ and iron oxide, with further separate additions of MgO, MnO, and MgO + MnO, was used in hydrothermal experiments to crystallize Ilm-Hem and Usp-Mt solid solutions at 800 and 900°C under redox conditions slightly below nickel–nickel oxide (NNO) to units above the NNO oxygen buffer. These experiments provide calibration of the FeTi-oxide thermometer + oxygen barometer at conditions of temperature and oxygen fugacity poorly covered by previous equilibrium experiments. Isotherms for our data in Roozeboom diagrams of projected %usp vs. %ilm show a change in slope at ≈ 60% ilm, consistent with the second-order transition from FeTi-ordered Ilm to FeTi-disordered Ilm-Hem. This feature of the system accounts for some, but not all, of the differences from earlier thermodynamic calibrations of the thermobarometer. In rhyolite containing 1.0 wt.% MgO, 0.8 wt.% MnO, or MgO + MnO, Usp-Mt crystallized with up to 14% of aluminate components, and Ilm-Hem crystallized with up to 13% geikielite component and 17% pyrophanite component. Relative to the FeTiAlO system, these components displace the ferrite components in Usp-Mt, and the hematite component in Ilm-Hem. As a result, projected contents of ulv?spinel and ilmenite are increased. These changes are attributed to increased non-ideality along joins from end-member hematite and magnetite to their respective Mg- and Mn-bearing titanate and aluminate end-members. The compositional shifts are most pronounced in Ilm-Hem in the range Ilm_50–80, a solvus region where the chemical potentials of the hematite and ilmenite components are nearly independent of composition. The solvus gap widens with addition of Mg and even further with Mn. The Bacon–Hirschmann correlation of Mg/Mn in Usp-Mt and coexisting Ilm-Hem is displaced toward increasing Mg/Mn in ilmenite with passage from ordered ilmenite to disordered hematite. Orthopyroxene and biotite crystallized in experiments with added MgO and MgO + MnO; their X _Fe varies with and T consistent with equilibria among ferrosilite, annite, and ferrite components, and the chemical potentials of SiO₂ and orthoclase in the liquid. Experimental equilibration rates increased in the order: Opx < Bt < Ilm-Hem < Usp-Mag.     

Stability of methane in reduced C–O–H fluid at 6.3 GPa and 1300–1400°C

The composition of a reduced C–O–H fluid was studied by the method of chromatography–mass spectrometry under the conditions of 6.3 GPa, 1300–1400°C, and fO₂ typical of the base of the subcratonic lithosphere. Fluids containing water (4.4–96.3 rel. %), methane (37.6–0.06 rel. %), and variable concentrations of ethane, propane, and butane were obtained in experiments. With increasing fO₂, the proportion of the CH₄/C₂H₆ peak areas on chromatograms first increases and then decreases, whereas the CH₄/C₃H₈ and CH₄/C₄H₁₀ ratios continually decrease. The new data show that ethane and heavier HCs may be more stable to oxidation, than previously thought. Therefore, when reduced fluids pass the “redox-front,” carbon is not completely released from the fluid and may be involved in diamond formation.