N2 Fluids Research Articles

Theoretical investigation of indicated thermal efficiency variation within in-cylinder steam assist cycle under different working fluids

Improving efficiency and reducing emissions are essential to achieving carbon peaking and carbon neutrality in transportation sector. As a carbon neutral fuel, hydrogen is widely considered the most promising fuel for future zero-carbon internal combustion power, while iso-octane, represented by gasoline, symbolizes the current hydrocarbon fuel utilized in modern internal combustion engines. In this study, the maximum indicated thermal efficiency of both hydrogen and iso-octane utilizing air (blending O2 and N2), oxy-fuel (blending O2 and CO2) and argon power cycle (blending O2 and Ar) were investigated theoretically based on in-cylinder steam assist cycle. A theoretical thermodynamic model combining in-cylinder steam assist and exhaust gases waste heat recovery was established to explore the thermodynamic process of in-cylinder steam assist and systematically analyze the effects of different working fluids. Results show that the utilization of in-cylinder steam assist improves thermal efficiency under O2, N2, and CO2 working fluids, but limits the improvement of thermal efficiency under Ar. In addition, the maximum achievable steam temperature and mass are limited by the exhaust gases temperature and heat exchanger efficiency. When running with H2 under 400 K steam temperature, the optimized water-to-gas ratios were 1.58, 1.13, 1.62, and 1.13 for O2, Ar, N2, and CO2, respectively, the maximum thermal efficiencies increased by 35.80 %, 0.28 %, 28.21 %, and 62.79 % compared with baseline condition. Meanwhile, the competition of overall specific heat ratio and working fluid mass under different working fluids leads to different thermal efficiency enhancement, such as Ar, the decrement of overall specific heat ratio under limited steam mass leads to thermal efficiency deterioration, which can be further improved as steam mass increased.

The flow and heat transfer characteristics of supercritical mixed-phase CO2 and N2 in a 3D self-affine rough fracture

Utilizing a three-dimensional self-affine function, we constructed the fracture morphology and established a numerical model considering the thermal-hydraulic coupling (TH) mechanism to simulate the flow and heat transfer processes of CO2 and N2 in a single fracture under supercritical mixed-phase conditions in dry hot rock. The fractal dimension of the fracture was set to 2.5, and the Joint Roughness Coefficient (JRC) roughness coefficient was 13.71. The model accurately simulated the flow and heat transfer processes of supercritical mixed-phase CO2 and N2 fluids within the fracture under the conditions of 50 MPa underground pressure, 200 °C rock exterior temperature, initial temperature of 32 °C for the heat transfer fluid, and inlet velocities ranging from 0.005 to 0.03 m/s. The results revealed that the output thermal power curves for nine different ratios of CO2 and N2 could be classified into three categories.Among the four conventional thermodynamic parameters, specific heat capacity and density significantly impacted output thermal power. The convective heat transfer process between the fluid and the rock wall resulted in temperature fluctuations, primarily influenced by the sharp edges of the fracture wall. As the inlet velocity increased, the outlet-inlet temperature difference monotonically decreased. The fluid with a composition of 45 % N₂ and 55 % CO₂ exhibited the smallest reduction in temperature, with a value of 50.52 °C. Meanwhile, the output thermal power monotonically increased, with the fluid composition of 5 % N2 and 95 % CO2 experiencing the most significant increase, reaching 122.22 W.

Prediction of the volumetric and vapor-liquid equilibrium properties of CO2-N2-O2-Ar fluid mixtures with a general Helmholtz equation of state

A general equation of state (EOS) explicit in the form of Helmholtz free energy has been developed to predict the pressure-volume-temperature-composition (PVTx) and vapor-liquid equilibrium (VLE) properties of the CO2N2O2-Ar fluid mixtures. The EOS, which uses four mixing parameters, is based on highly accurate EOS for pure CO2, N2, O2 and Ar fluids and contains a simple generalized departure function presented by Lemmon and Jacobsen (1999). Four mixing parameters are fitted from the experimental PVTx and VLE data of binary systems available. Comparison with experimental data available indicates that the EOS can reproduce the PVTx and VLE properties of CO2N2O2-Ar fluid mixtures up to 453 K and 1000 bar within or close to experimental uncertainties. The general EOS can be used to evaluate the change of density and VLE composition from impurities N2, O2 and Ar during the CO2 capture and sequestration process.

Precision evaluation of nitrogen isotope ratios by Raman spectrometry.

We measured Raman spectra of N2 fluids obtained at 0.1-25MPa at room temperature. The 14N15N peak in the Raman spectrum of a low-pressure N2 fluid is difficult to detect because of the prevalence of a group of peaks attributed to rotational vibration of 14N2. The Raman peaks of 14N15N and 14N2 of N2 fluid at 25MPa were acquired at various exposure times. The mean values and standard deviations of the peak height ratios and peak area ones of 14N15N and 14N2 were examined for each time. The standard deviations of the peak height ratios and peak area ones were 2.2% and 1.9%, respectively, for 20 spectra acquired with peak height of 1 million counts of 14N2. The uncertainties are about two times higher than those predicted from the noise of a CCD. Improvement of the pixel resolution can enhance the precision of the nitrogen isotope ratios by Raman spectroscopy.

Application of bulk fluid volatile chemistry to exploration for metasedimentary rock-hosted orogenic gold deposits: An example from the Meguma terrane, Nova Scotia, Canada

Disseminated gold (Au) deposits hosted in metasedimentary rocks present unique exploration challenges because the Au is generally very fine-grained or refractory, and not vein-hosted. Exploration programs in such settings rely on extensive lithogeochemical surveys, lesser structural analysis, and little emphasis on ore-fluid geochemistry. The Moose River anticline (MRA) in the Lower Paleozoic Meguma terrane (Nova Scotia, Canada) hosts several high-tonnage (~10–20 Mt), low-grade (≤1–4 g/t Au) Au deposits comprised of disseminated ± quartz vein-hosted mineralization in metamudstones. Here, the Touquoy deposit hosted in the MRA is used to evaluate a new approach to geochemical exploration by examining if the volatile chemistry of host rocks preserves a signature related to Au mineralization, using a gas chromatographic (GC) technique that analyzes bulk volatiles released from crushed rock. Since GC is a bulk analytical technique, (i.e., multiple generations of fluid inclusion volatiles yielding a mixed analytical volume), the volatile composition of fluid inclusions were also investigated in-situ using laser Raman microspectroscopy to reconcile bulk analyses with the composition and abundance of different inclusion types. Inclusions in quartz pressure shadows associated with porphyroblasts host N2 ± CH4-dominant vapor phases and represent wall rock-equilibrated fluids. In comparison, fluid inclusion vapor phases in quartz veinlets crosscutting the metamudstones are more complex in composition and show a continuum between CO2-dominant and N2 ± CH4-dominant compositions; the former is interpreted as the fluid responsible for Au mineralization in the Meguma terrane (e.g., H2O-CO2 ± CH4 ± N2 fluids). GC shows statistically significant differences in the compostion of the bulk volatiles released from crushed metamudstones from the Touquoy deposit (n = 21) and barren (n = 24) settings. Whereas the former commonly contain detectable CO2 (50% of samples; LoQ(CO2) ~ 10−10 mol/g), only ~4% of metamudstones from barren settings along the MRA contain CO2, yielding a t-test p-value of 0.0103 between the two sample populations. Whereas the more frequent detection of CO2 in mineralized samples is related to increasing carbonate alteration proximal to Au mineralization, no correlation is observed between bulk CO2 abundance and Au grade. Additionally, anomalous differences in abundances of released C3 (t-test p-value = 0.043) and C4 (t-test p-value = 0.03) hydrocarbons (HC) are recognized between the two populations (LoQ(HC) ca. 10−13 to 10−12 mol/g), with Touquoy metamudstones having higher Σ(C3)/CH4 and Σ(C4)/CH4 ratios compared to barren equivalents. The compositional differences suggest that more aqueous-carbonic fluids infiltrated metamudstone units where locally favorable physical and/or chemical conditions were present, resulting in increased Au endowment. The relative increase in fluid flux, and thus Au grade, resulted in more trapped CO2 (i.e., resulting from more trapped inclusions and/or greater CO2 fluid component) and modification to hydrocarbon signatures through homologation and/or degradation reactions. Rigorous sample preparation ensures these compositional differences are related to paleofluids and not contamination.Tentatively, the results suggest that the bulk analysis of volatiles released from fluid inclusions in metamudstones may be a useful vectoring tool for disseminated Au mineralization in Meguma-type gold systems and similar environments (e.g., Carlin-type). This technique may be appropriately scaled to complement exploration drilling programs and may be more sensitive in determining ore proximity than often ambiguous pathfinder elements.

LNG 저장탱크 재액화용 LNG Sub-Cooler 및 N2 Pre-Cooler 열전달 특성 및 구조안정성 해석

In this study, the heat transfer characteristics - in accordance with the operating conditions - of the heat exchanger for re-liquefaction of LNG storage tanks is analyzed. The heat transfer characteristics and structural stability were analyzed for each of the sub-cooler and pre-cooler, which uses an LNG fluid and an N2 fluid respectively. The N2 fluid is used in the actual experiment. Considering the efficiency and cost of the calculation, 1/25 and 1/49 reduced models were used for the number of pipes; the temperature difference among pipes at the outlet was less than 5%. Hence it was confirmed that the analysis of the reduced model was reasonable. Comparing with the one-dimensional analysis results, a discrepancy from 2.2% to 7.4% could be confirmed. By visualizing the flow field through the computational fluid cynamics (CFD) analysis, the cause of inefficiency could be identified. The analysis results will be helpful in understanding the exact performance of the heat exchanger by predicting the design variables in the future.

Sound velocity and refractive index of pure N2 fluid and of equimolar N2-CO2 fluid mixture up to 15 GPa.

The sound velocity and refractive index of pure N2 and of the equimolar N2-CO2 mixture are measured up to 15 GPa and 700 K in a resistive heating diamond anvil cell. The refractive index vs pressure is obtained by an interferometric method. The adiabatic sound velocity is then determined from the measurement of the Brillouin frequency shift in the backscattering geometry and the refractive index data. No phase separation of the N2-CO2 fluid mixture is observed. The fluid mixture properties are discussed in terms of ideal mixing.

Porous carbon nanotube networks and pillared graphene materials exhibiting high SF6 adsorption uptake and separation selectivity of SF6/N2 fluid mixtures: A comparative molecular simulation study

Abstract SF6 and SF6–N2 gas mixtures are well known insulators used in industry applications, but SF6 has to be recovered due to its high global warming potential. In this study, the adsorption of the pure SF6 and N2 fluids and the separation of their mixture with SF6:N2 = 1:9 composition, using three-dimensional porous carbon nanotube networks and pillared graphene materials has been studied by employing Monte Carlo and Molecular Dynamics simulations at ambient temperature and pressure up to 20 bar. The results obtained reveal a significant SF6 uptake and high adsorption selectivity for SF6 over N2, compared to the best performing materials in the literature. The selectivity for SF6 decreases in the case of pillared graphene and strongly depends on the nanotube pillar and graphene layer distances. The saturation capacity of the investigated materials is also achieved at very different pressure ranges, as it has been reflected on the calculated adsorption isotherms. Due to this fact, the translational diffusion coefficients of the adsorbed SF6 and N2 molecules in each material are significantly different at ambient conditions. The results obtained might be used as a springboard towards the rational design of carbon-based materials for the capture of the very potent greenhouse gas SF6.

Numerical analysis of the flow dynamics of an N2 cryogenic jet

Injection and mixing of cryogenic propellants are very complex at near-critical and supercritical conditions. The concise description and the reliable measurements on such flows are still questionable. In this work, a RANS study is performed for a pure N2 fluid injection at transcritical conditions on a laboratory scale test rig. An in-depth thermodynamical analysis on the real-gas behavior has allowed N2 density prediction over the experimental range of the injection temperature and for several equations of state. A focus was thrown on the prediction of the density evolution on the chamber centerline and across the injector. The calculations were performed using both adiabatic and constant temperature conditions for the injector wall. The inner heat transfer in the injector had a significant effect on the jet density distribution and therefore, on the overall flow dynamics. Numerical results regarding axial profiles of density and dense core lengths agree fairly well with the experimental data provided by the literature.

An improved equation of state of binary CO2–N2 fluid mixture and its application in the studies of fluid inclusions

An equation of state (EOS) in the form of Helmholtz free energy for fluid mixtures was improved by using four mixing parameters. It can calculate the pressure-volume-temperature-composition (PVTx) and vapor-liquid equilibrium (VLE) properties of the CO2–N2 fluid mixture. This EOS is based on highly accurate EOSs of pure CO2 and N2 fluids and contains a simple generalized departure function of Lemmon and Jacobsen (1999). This EOS can reproduce experimental PVTx and VLE data available up to 673 K and 1000 bar, with an accuracy within or close to experimental uncertainties. The EOS of CO2–N2 fluid mixture and an updated Gibbs free energy model of solid CO2, can be combined to determine the compositions and molar volumes of CO2–N2 fluid inclusions with the melting temperature of solid CO2 and the vapor-liquid homogenization temperature which can be directly obtained from experimental microthermometric analysis. Isochores of CO2–N2 inclusions can be easily calculated from this EOS.

Reaction between Forsterite and Nitrogen Fluid at High Pressure and High Temperature

Behavior of nitrogen in the deep Earth still remains unrevealed. Geochemical data suggest that substantial amount of nitrogen could be stored in the deep Earth. In this study, reactions between forsterite (Mg2SiO4) and molecular nitrogen (N2) were investigated at high pressure and high temperature using laser-heating diamond anvil cells (DACs). Pressure in the DAC was estimated from Raman spectra of nitrogen before heating and the initial pressure was set at 5 GPa. Pelleted sample of powder forsterite or a single crystal of forsterite was loaded in the DAC with N2 fluid. A carbon dioxide laser (λ = 10.64 μm, <100 W) and a fiber laser (λ = 1.019 μm, <100 W) were used to heat forsterite in the temperature range from 1300 to 3500 K. An SEM image on the surface of the recovered forsterite crystal after the laser heating showed a stepwise texture which strongly suggests the dissolution of forsterite into the N2 fluid. The EDS chemical mapping showed that Mg-rich area and Si-poor area overlapping each other, which suggests the preferential dissolution of MgO component and its precipitation from the N2 fluid. X-ray diffraction patterns of the powder and single crystal forsterite samples after the reaction showed reflections assignable to orthopyroxene (MgSiO3) and periclase (MgO). The present experimental results indicate that Mg2SiO4 incongruently melts into MgSiO3 and MgO in N2 fluid. Moreover, N1s XPS spectra collected from a single crystal of forsterite after the reaction with N2 fluid revealed three components assignable to $${\text{NH}}_{4}^{ + },$$ N2, and N3–. The present study provides a new clue to the reaction between forsterite and molecular nitrogen under the upper mantle condition.

N2-rich fluid in the vein-type Yangjingou scheelite deposit, Yanbian, NE China

Nearly pure N2 fluid inclusions (Th (L) = −151~−168 °C; Th (V) = ~150.3 °C) were identified in W-mineralized quartz veins from the Yangjingou scheelite deposit, in the eastern Yanbian area, NE China. Other fluid inclusion populations include N2-CO2, NaCl-H2O ± N2 and CO2 ± N2-NaCl-H2O, but no hydrocarbons were detected. The host rocks are part of the Wudaogou Group metamorphic series, which mainly consist of Ca-rich mica schist. Subhedral sulfide minerals occur in early disseminated W-mineralized quartz veins, or have partially replaced early scheelite. ThN2 and ThN2-H2O indicate N2 fluid-trapping from 315 °C to 410 °C and from 80 MPa to 350 MPa. Oxygen and hydrogen isotopic data (δD = −74.9‰~−77‰, δ18O = 9.6‰~12‰, V-SMOW) suggest that the mineralizing fluids were composed of mixed magmatic and metamorphic water, N2-rich inclusions (δ15N = −0.5‰ to 1.4‰) indicate fluid-rock interaction with metamorphic rocks. The N2-rich fluid was closely associated with scheelite precipitation. During thermal decomposition under high oxygen fugacity conditions, which occurred synchronously with metamorphism and magmatic activity, large amounts of N2 were liberated from NH4+-micas, which then accumulated in the parent fluid of the quartz scheelite veins.

Fluid evolution and ore genesis of the Dalingshang deposit, Dahutang W-Cu ore field, northern Jiangxi Province, South China

The Dalingshang W-Cu deposit is located in the North section of the Dahutang ore field, northern Jiangxi Province, South China. Vein- and breccia-style tungsten-copper mineralization is genetically associated with Mesozoic S-type granitic rocks. Infrared and conventional microthermometric studies of both gangue and ore minerals show that the homogenization temperatures for primary fluid inclusions in wolframite (~ 340 °C) are similar to those in scheelite (~ 330 °C), but about 40 °C higher than those of apatite (~ 300 °C) and generally 70 °C higher than those in coexisting quartz (~ 270 °C). Laser Raman analysis identifies CH4 and N2 without CO2 in fluid inclusions in scheelite and coexisting quartz, while fluid inclusions in quartz of the sulfide stage have variable CO2 content. The ore-forming fluids overall are characterized by high- to medium-temperature, low-salinity, CH4, N2, and/or CO2-bearing aqueous fluids. Chalcopyrite, muscovite, and sphalerite are the most abundant solids recognized in fluid inclusions from different ores. The H-O-S-Pb isotope compositions favor a dominantly magmatic origin for ores and fluids, while some depleted δ34S values (− 14.4 to − 0.9‰) of sulfides from the sulfide stage are most likely produced by an increase of oxygen fugacity, possibly caused by inflow of oxidized meteoric waters. The microthermometric data also indicate that a simple cooling process formed early scheelite and wolframite. However, increasing involvement of meteoric waters and fluid mixing may trigger a successive deposition of base metal sulfides. Fluid-rock interaction was critical for scheelite mineralization as indicated by in-situ LA-ICP-MS analysis of trace elements in scheelite.

Accurate non-asymptotic thermodynamic properties of near-critical N2 and O2 computed from molecular dynamics simulations

Four thermodynamic properties of pure N2 and O2 fluids were calculated over a continuous temperature range in the near-critical region employing molecular dynamics combined with the multistate Bennett acceptance ratio (MBAR) technique. The non-asymptotic critical anomalies of the isothermal compressibility, the thermal expansion coefficient and the heat capacities at constant pressure and constant volume were determined in the 0.80Tc–1.20Tc temperature range along the 1.00Pc and 1.15Pc isobars. A single-site united-atom model and a two-site rigid rotor force fields were used in the simulations. The results show that effective force fields developed to describe accurately the behavior of liquids and dense gases in general can be used to obtain near-critical anomalies of the thermodynamic properties. Furthermore, the computed values are in very good agreement with NIST data when available. The results fill existing gaps of the NIST database in the near-critical vicinity of the critical temperature along the critical isobar, especially for the heat capacities. The MBAR technique was crucial to describe the continuous and sharp peak of each property as functions of the temperature. The results indicated that even with a simple force field such as the united-atom one-site approach, very good results could be obtained for the non-asymptotic critical anomalies of thermodynamic properties without using renormalization group techniques. The computation of accurate results was possible due to the availability of precise critical constants especially for the simpler one-site force field. The inclusion of the anisotropy in the force field does not necessarily improve the computed thermodynamic properties in the near critical region.

Seeking an accurate generalized-gradient approximation functional for high pressure molecular fluids

We propose to assess the performance of density functional theory calculations to predict the properties of CO2, H2O, and N2 fluids under high pressure (up to 40 GPa), which are representatives of not only detonation products but also giant planet interiors. Twenty-two generalized-gradient approximation functionals, presently in the ABINIT code, have been compared to molecular data and experimental equations of state of supercritical fluids. We found that the Perdew, Burke, and Ernzerhof (PBE) functional with Grimme's dispersion correction (D3) gives the best results. The residual error of PBE-D3 on pressure is estimated around 15%.

Prediction of the PVTx and VLE properties of natural gases with a general Helmholtz equation of state. Part I: Application to the CH4–C2H6–C3H8–CO2–N2 system

A general equation of state (EOS) explicit in Helmholtz free energy has been developed to predict the pressure–volume-temperature-composition (PVTx) and vapor-liquid equilibrium (VLE) properties of the CH4–C2H6–C3H8–CO2–N2 fluid mixtures (main components of natural gases). This EOS, which is a function of temperature, density and composition, with four mixing parameters used, is based on the improved EOS of Sun and Ely (2004) for the pure components (CH4, C2H6, C3H8, CO2 and N2) and contains a simple generalized departure function presented by Lemmon and Jacobsen (1999). Comparison with the experimental data available indicates that the EOS can calculate the PVTx and VLE properties of the CH4–C2H6–C3H8–CO2–N2 fluid mixtures within or close to experimental uncertainties up to 623K and 1000bar within full range of composition. Isochores of the CH4–C2H6–C3H8–CO2–N2 system can be directly calculated from this EOS to interpret the corresponding microthermometric and Raman analysis data of fluid inclusions. The general EOS can calculate other thermodynamic properties if the ideal Helmholtz free energy of fluids is combined, and can also be extended to the multi-component natural gases including the secondary alkanes (carbon number above three) and none-alkane components such as H2S, SO2, O2, CO, Ar and H2O. This part of work will be finished in the near future.

Ore genesis of the Saridala gold deposit, Western Tianshan, NW China: Constraints from fluid inclusion, S-Pb isotopes and 40Ar/39Ar dating

The Saridala gold deposit is located in the Western Tianshan (Xinjiang, NW China), southwestern part of the Central Asian Orogenic belt (CAOB). The deposit is mainly hosted in Precambrian metamorphic rocks and Early Paleozoic granites, and is structurally controlled by the Shenglidaban ductile shear zone. The gold orebodies consist of gold-bearing quartz veins and altered mylonite. The mineralization comprises three stages: quartz-pyrite veins (early stage), sulfide-quartz veins (middle stage), and quartz-carbonate veins/veinlets (late stage). Ore minerals and native gold were mainly formed in the middle stage. Four fluid inclusion types in quartz veins were identified: pure CO2 (PC-type), CO2-H2O (C-type), aqueous (W-type) and daughter mineral-bearing (S-type) inclusions. Hydrothermal fluids related to the mineralization are composed of CO2-H2O-NaCl±N2 fluids (115–307MPa) with Th(total) values of 256–475°C (peak at 320–380°C) and salinities <∼11 wt% NaCl equiv. (mostly 4–7 wt% NaCl equiv.). Ore minerals were likely deposited via fluid immiscibility and the subsequent fluid mixing. Except for the two negative outliners (−4.5 and −4.8‰), δ34S‰ values of the ore pyrite range from 11.0 to 17.9‰, suggesting that the ore-forming fluids contained heavier sulfur from marine sulfate-bearing rocks. Lead isotope compositions of the ore sulfides are characterized by being highly radiogenic and their relatively wide ranges: 18.01–19.62 (206Pb/204Pb), 15.58–15.78 (207Pb/204Pb) and 37.95–39.08 (208Pb/204Pb). These data indicate that the lead in the ores may have been derived from an orogenic reservoir with some crustal input. 40Ar/39Ar age dating on the sericite from the syn-mineralized quartz-sericite-sulfide alteration yielded a plateau age of 337.6±1.7Ma, an age coeval with the subduction–collision tectonic transition related to the closure of the North Tianshan Ocean. We concluded that the Saridala gold deposit shares many similarities with typical orogenic gold deposits, and was likely formed in an orogenic environment.

Conditions of sulfide formation in the metasomatized mantle beneath East Antarctica

Garnet–spinel lherzolites from Antarctica and peridotites from Mongolia were fluid saturated, which is indicated by the presence of fluid inclusions in their minerals. Flows of reactive fluids caused extensive metasomatic alteration of mantle materials. The cryometric and Raman spectroscopic investigation of the Antarctic xenoliths showed that their fluid was a complex mixture of CO2, N2, H2S, and H2O with a density of up to 1.23 g/cm3. The entrapment of fluids was accompanied by the formation of clusters of numerous sulfide inclusions. The compositions of these inclusions correspond to a Ni-rich sulfide melt and a monosulfide solid solution. The partition coefficient of Ni between them (DNimss/melt) ranges from 0.99 to 3.23, which suggests that the two-phase sulfide assemblages in the partly decrepitated inclusions equilibrated at 920–1060°C. In order to refine the initial P-T conditions of the development of the Antarctic peridotites, the results of our investigation were evaluated in the light of experimental data on (1) the stability field of the two-phase assemblage mss + sulfide melt, (2) the solidus of peridotite + 0.9CO2 + 0.1 H2O, and (3) isochores of 0.8CO2 + 0.2N2 fluid. The obtained parameters are close to 1270–1280°C and 2.2 GPa and lie near the Sp–Gar boundary. The temperature of the existence of sulfide melt at a pressure of 2.2 GPa must be near 1300°C and corresponds to the boundary between the occurrence of carbon as CO2 fluid and carbonate (carbonate melt).

Geology, fluid inclusion and age constraints on the genesis of the Sarekuobu gold deposit in Altay, NW China

The Sarekuobu gold deposit was discovered in the 1990s and is located in the Kelan Basin on the southern margin of the Chinese Altay Orogen. Orebodies are hosted in the Early Devonian metamorphosed volcanic‐sedimentary sequence and controlled by the NW‐trending Abagong Fault. Mineralization can be divided into early, middle and late stages, characterized by quartz–pyrite, polymetallic quartz–sulphides and carbonate–quartz, respectively. Four types of fluid inclusions were identified in quartz veins, i.e. pure CO2 (PC‐type), CO2–H2O (C‐type), aqueous (W‐type) and daughter mineral‐bearing inclusions (S‐type). Hydrothermal fluids related to the mineralization are composed of CO2–H2O–NaCl ± CH4 ± N2 fluids with Th values of 236–374 °C and salinities of 4.8–15.0 wt.% NaCl eqv. (in general 8.0–15.0 wt.% NaCl eqv.), combined with trapping pressures of 90–330 MPa, suggesting that the mineralization resulted from a metamorphic fluid system. One biotite sample from the polymetallic quartz lodes yields a 40Ar/39Ar isotopic plateau age of 213.5 ± 2.3 Ma, marking the time of mineralization as Triassic. This mineralization age is broadly comparable with the mineralization age reported from the Tiemurt Pb–Zn deposit and Wulasigou Cu deposit located near the Sarekuobu gold deposit, indicating that the deposit was possibly related to the Permian–Triassic continental collision at the southern margin of the Altay Orogen. Our results show that the Sarekuobu gold deposit is not syngenetic, but an epigenetic orogenic gold deposit. Copyright © 2014 John Wiley &amp; Sons, Ltd.

In-reservoir mixing of mantle-derived CO2 and metasedimentary CH4–N2 fluids – Noble gas and stable isotope study of two multistacked fields (Pannonian Basin System, W-Hungary)

Several multistacked gas fields, located in very different parts of Hungary, display a large variation in their gas composition. The shallow position of the mantle beneath the basement of the PBS is responsible for the high heat flux. It facilitates that the CO2 – intensely released from the ascending upper-mantle derived melts – could reach the basin system. In this work the results of a geochemical study of the main components and noble gases of the multistacked Répcelak (CO2–HC–N2) and Mihályi (CO2) fields are presented and discussed. The vertical variations of gas composition in the Répcelak and Mihályi fields fit well with in-reservoir mixing of two end-members, a mantle-related magmatic CO2 fluid and a N2-rich HC-gas fluid of crustal origin. However, it is very likely that other processes modified to some extent the gas composition of the two fields. Carbon isotopic composition of the CO2 of the samples studied agrees with both the carbonate decomposition and mantle degassing origins. It is very likely that the marked difference in helium isotopic composition between the neighbouring Répcelak and Mihályi fields also reflects this heterogeneity.