Geochemistry International最新文献

The solubility of vysotskite PdS_(cr) was measured in aqueous sulfide solutions from 4.5 to 490°C at 1–1000 bar as a function of pH. The total reduced sulfur concentrations varied between 0.03 and 106 m [mol (kg H₂O)^–1]. The solubility data were described in terms of the aqueous complexes Pd(HS)_2(aq), ({text{Pd(HS}})_{3}^{ - }), and ({text{PdS(HS}})_{2}^{{2 - }}). The 1st complex dominates in acidic to near-neutral solutions, the 2nd complex in neutral to alkaline pH, and the 3rd one under alkaline pH conditions. The PdS_(cr) solubility constants show a minimum at 200°C (Pd(HS)_2(aq), ({text{PdS(HS}})_{2}^{{2 - }})) and 350°C (({text{Pd(HS}})_{3}^{ - })). The experimental values pooled with reliable literature data, were fitted to the HKF (Helgeson–Kirkham–Flowers) model equation of state (EoS). Literature data on the solubility of cooperite PtS_(cr) were regressed to calculate of the HKF EoS parameters of Pt(HS)_2(aq) and ({text{Pt(HS}})_{3}^{ - }), the 3rd complex was not detected for Pt. The PtS_(cr) solubility constant to form the main Pt hydrosulfide complex, Pt(HS)_2(aq), shows a pronounced minimum at 100°C and then increases sharply, whereas the ({text{Pt(HS}})_{3}^{ - }) formation constant has a maximum at 250°C. At ambient temperature, the solubility of PdS_(cr) exceeds that of PtS_(cr) by 2–3 log units, depending on pH. The temperature of ca. 250°C is a borderline one where the solubilities of Pd and Pt sulfides are equal. At temperature above 300°C, due to the sharp increase in the Pt(HS)_2(aq) formation constant, the dissolved Pt concentration exceeds that of Pd in the whole pH region from acidic to alkaline. At 700°C and 2000 bar, the solubility of PtS_(cr) reaches a few ppm, whereas the solubility of PdS_(cr) comprises about 40 ppb in a solution containing 0.1 m total reduced sulfur. These concentrations are high enough to sustain hydrothermal mobility of these metals in high-temperature magmatic-hydrothermal fluids, whereas the differences in the stability of Pt(HS)_2(aq) and Pd(HS)_2(aq) can result in separation of these metals in hydrothermal systems.

The abundance of sulfide inclusions in diamonds, mantle xenoliths, and meteorites determines the importance of studying the Fe–S system at mantle pressures and temperatures. In the present work, the phase relationships in the Fe–S system were studied at 6 GPa in the range of 450–1500°C using a Kawai-type multianvil press. It was found that in the entered temperature range, the iron metal does not dissolve measurable amounts of sulfur and remains solid. Two intermediate compounds are stable in the system: a monosulfide solid solution (Fe_{1 – x}S, where x = 0–0.036, 50–54 mol % S) and iron disulfide (FeS₂). In coexistence with iron metal or Fe-rich liquid, monosulfide solid solution contains 50 mol % S. The Fe–FeS eutectic is located at 1000°C and 33 mol % S. Sulfur content in Fe_{1 – x}S, coexisting with FeS₂, increases from 52 to 54 mol % as temperature increases from 500 to 1100°C and does not change systematically with further temperature increase. At 1500°C, Fe_{1 – x}S is still crystalline. The Fe_{1 – x}S–FeS₂ eutectic is situated at 1350°C and 63 mol % S. FeS₂ melts congruently at 1375°C. In the range 450–1200°C, the solubility of Fe in sulfur does not exceed the detection limit (<0.5 mol %). At 1300°C, sulfur melt coexisting with FeS₂ contains 10 mol % Fe. At 1400°C in the ranges of 20–43 and 58–100 mol % S, the system undergoes complete melting.

Subsolidus phase relations in the Fe–Ni–S system were studied in a multianvil press at 6 GPa, 450°C, and a duration of 17 h using ceramic capsules. The nine intermediate compounds were established: FeS₂ pyrite (Ni# ≤ 7), NiS₂ vaesite (Ni# ≥ 96), (Fe, Ni)_{1 – x}S (Ni# 0–100), (Ni, Fe)₄S₃ (S# 42–44, Ni# ≥ 60), Ni₃S₂ heazlewoodite (S# 40, Ni# ≥ 97), Ni_{3 – x}S (S# 26, Ni# 100), Ni_3.5Fe_0.5S (S# 21, Ni# 87), and metal phase (Ni# 64–68), where Ni# = Ni/(Ni + Fe) × 100 mol % and S# = S/(S + Ni + Fe) × 100 mol %. A wide solubility gap between disulfides results in two large three-phase fields: (Fe_0.93Ni_0.07)S₂ + S + (Ni_0.96Fe_0.04)S₂ and (Fe_0.93Ni_0.07)S₂ + (Ni_0.96Fe_0.04)_{1 – x}S + (Ni_0.96Fe_0.04)S₂. A narrow field of monosulfide solid-solution is sandwiched between FeS₂ + (Fe, Ni)_{1 – x}S and (Fe, Ni)S + (Ni, Fe)₄S₃ two-phase fields. Large three-phase fields: Fe_0.88Ni_0.12 Fe_0.78Ni_0.22S + Fe_0.65Ni_0.35, Ni₀₆₃Fe_0.37 + Fe_0.78Ni_0.22S + (Ni_0.6Fe_0.4)₄S₃, and Fe_0.32Ni₀₆₈ + (Fe_0.3Ni_0.7)₄S₃ + Fe_0.05Ni_0.95 appear at bulk S# < 50. Stabilization of a new phase, Ni_3.5Fe_0.5S, yields two large three-phase fields: Ni_3.5Fe_0.5S + (Fe_0.3Ni_0.7)₄S₃ + Ni₃S₂ and Ni_3.5Fe_0.5S + Ni₃S₂ + Ni.

Phase relations along the FeS₂–NiS₂ and Fe_0.36S_0.64–S joins were studied at 6 GPa in ceramics capsules using a multianvil Osugi-type press. The FeS₂–NiS₂ system has an eutectic type of T–X diagram with limited solid solutions. The solubility of NiS₂ in pyrite increases with temperature from 1–6 mol % at 450–700°С, to 7–8 mol % at 800–1100°С, and achieves a maximum of 25 mol % at 1250°С. The FeS₂ content in vaesite increases from 2–4 mol % at 450–600°С, to 5–20 mol % at 650–900°С, and achieves the maximum, 64 mol %, at 1250°С. The pyrite-vaesite eutectic is situated near 1260°C and has Ni# 42 mol %, where Ni# = Ni/(Ni + Fe) × 100 mol %. At 6 GPa, FeS₂ and NiS₂ melt congruently near 1380 and 1410°C, respectively. In the range of 1000–1200°C, the solubility of Fe in liquid sulfur does not exceed the detection limit (<0.5 mol %). At 1300°C, liquid sulfur coexisting with pyrite contains 10 mol % Fe. At 1400°C, a continuous transition from a sulfur melt to a sulfide melt is observed. Thus, FeS₂ and NiS₂ are thermodynamically stable over the entire range of geothermal conditions of subduction zones and the subcontinental lithospheric mantle at a depth of about 180 km and experience congruent melting at temperatures corresponding to the thermal anomalies at the cratonic roots (kinked geotherms) and geothermal conditions of the convective mantle.

In response to the systematic uncertainty of geochemical anomaly detection related to Fe-mineralization in the Hunjiang area in Jilin Province, China, this paper synthesizes nine geochemical elements (Fe₂O₃, Al₂O₃, etc.) and a geological constraint to construct a characteristic dataset and then proposes a method based on the Stacking framework for using Gaussian Naive Bayes to integrate three anomaly detectors of Support Vector Classification, Random Forest, and K-Means-SMOTE-Boost model. The results indicate that: (1) The single model has limitations and high uncertainty: the high anomaly areas detected by Support Vector Classification, Random Forest, and K-Means-SMOTE-Boost model only captured 33.3, 33.3, and 28.6% of known iron deposits. This shows that the accuracy of anomaly detection is not high, presenting a high degree of uncertainty. (2) Multi models averaging effectively reduces uncertainty: by integrating Support Vector Classification, Random Forest, and K-Means-SMOTE-Boost with Gaussian Naive Bayes, the spatial correlation between the high anomaly areas and known Fe-mineralization deposits is significantly enhanced, capturing 85.7% of known iron deposits. This shows that the accuracy has been improved and uncertainty has been reduced. (3) Stacking framework demonstrated clear advantages: compared with a single model, the model designed based on the Stacking framework converges faster and is close to the level of an ideal anomaly detector, effectively improving the accuracy and generalization ability. In summary, the method based on the Stacking framework for using Gaussian Naive Bayes to integrate and average Support Vector Classification, Random Forest, and K-Means-SMOTE-Boost model provides new ideas for reducing the uncertainty of geochemical anomaly detection, and lays a better support foundation for geochemical exploration work and mineral resource prospecting.

The present work aims to study the phase relations along the CaСO₃–CaF₂ join at 6 GPa. The experiments were performed using a multianvil press in graphite capsules. The system has one intermediate compound, Ca₂CO₃F₂, identified as brenkite by Raman spectroscopy. At 900–1000°C, the presence of brenkite splits the system into two partial binaries: aragonite + brenkite and brenkite + fluorite. An aragonite-brenkite eutectic is situated near 1080°C. An eutectic melt contains 40 mol% CaF₂. Brenkite melts incongruently at 1100°C, producing fluorite and peritectic liquid containing 48 mol% CaF₂. The presence of fluorine lowers the melting temperature of the calcium carbonate by almost 600°C to a temperature corresponding to a continental geotherm with a surface heat flow of 35 mW/m². Thus, under mantle conditions, fluorine enable a calcium carbonate-rich melt to remain liquid at a much lower temperature (1080°C) than would be possible without the presence of fluorine (1660°C).

The paper examines coal from the Kaa-Khem field from the viewpoint of its oil and gas generation potential. Coal from the Kaa-Khem field was subjected to hydrothermal treatment at 350°C/24 h to simulate the maturation of its organic matter. The kinetic characteristics of the organic matter of Kaa-Khem coal were assessed from the results of Rock-Eval pyrolysis at three heating rates. The kinetic characteristics of individual C₁–C₅ hydrocarbons were additionally studied by dry stepwise pyrolysis. Changes in the composition of hydrocarbon biomarkers before and after hydrous pyrolysis were also analyzed, and the hydrothermal treatment was found out to have affected mainly the distribution of n-alkanes and aromatic hydrocarbons, whereas the composition of the sterane and hopane biomarkers have not been modified any significantly. The study of the coal composition by pyrolytic gas chromatography–mass spectrometry made it possible to record the loss of long alkyl chains in the studied range of thermal maturity. Although the studies led us to estimate the hydrocarbon potential of Kaa-Khem coal as high, the possibility of its conversion and the prediction of the phase composition of the fluids remain uncertain and require further studies.