Methane Admixture Research Articles

Growth of metal nanoparticles in hydrocarbon atmosphere of arc discharge

A direct current (DC) arc discharge is a widely used method for large-scale production of metal nanoparticles, core–shell particles, and carbon nanotubes. Here, the growth of iron nanoparticles is explored in a modified DC arc discharge. Iron particles are produced by the evaporation of an anode, made from low-carbon steel. Methane admixture into argon gas serves as a carbon source. Electron microscopy and elemental analysis suggest that methane and/or products of its decomposition adhere to iron clusters forming a carbon shell, which inhibits iron particle growth until its full encapsulation, at which point the iron core growth is ceased. Experimental observations are explained using an aerosol growth model. The results demonstrate the path to manipulate metal particle size in a hydrocarbon arc environment.

Methane Admixture Protects Liver Mitochondria and Improves Graft Function after Static Cold Storage and Reperfusion

Mitochondria are targets of cold ischemia-reperfusion (IR), the major cause of cell damage during static cold preservation of liver allografts. The bioactivity of methane (CH4) has recently been recognized in various hypoxic and IR conditions as having influence on many aspects of mitochondrial biology. We therefore hypothesized that cold storage of liver grafts in CH4-enriched preservation solution can provide an increased defence against organ dysfunction in a preclinical rat model of liver transplantation. Livers were preserved for 24 h in cold histidine-tryptophan-ketoglutarate (HTK) or CH4-enriched HTK solution (HTK-CH4) (n = 24 each); then, viability parameters were monitored for 60 min during normothermic isolated reperfusion and perfusate and liver tissue were collected. The oxidative phosphorylation capacity and extramitochondrial Ca2+ movement were measured by high resolution respirometry. Oxygen and glucose consumption increased significantly while hepatocellular damage was decreased in the HTK-CH4 grafts compared to the HTK group. Mitochondrial oxidative phosphorylation capacity was more preserved (128.8 ± 31.5 pmol/s/mL vs 201.3 ± 54.8 pmol/s/mL) and a significantly higher Ca2+ flux was detected in HTK-CH4 storage (2.9 ± 0.1 mV/s) compared to HTK (2.3 ± 0.09 mV/s). These results demonstrate the direct effect of CH4 on hepatic mitochondrial function and extramitochondrial Ca2+ fluxes, which may have contributed to improved graft functions and a preserved histomorphology after cold IR.

Metal Oxide Gas Sensors Signal Shape Processing for Selective Detection of Hydrocarbons in Realistic Air Conditions

Introduction The selective detection with high spatio-temporal resolution of hydrocarbons leakage as a result of pipelines inconsistency is a valid industrial demand [1]. Perspectives are associated with deployment of distributed networks of chemical sensors, transferring data on ambience pollution to the data processing center [2]. Miniature micromachined metal oxide semiconductor gas sensors possess a great perspective of practical use in this regard, however their long term operation in real atmosphere conditions requires improvement [3]. In this work we demonstrate improved selectivity of propane vs. methane detection in low concentrations in the ambient air of highly urbanized location by the SnO2-based semiconductor gas sensors with the modulated working temperature, using statistical analysis of “sensor response/sensor working temperature” shape representation. The obtained results of gases discrimination with artificial neural network (ANN) machine learning algorithm, used such pre-treated data as input samples, demonstrate advantages over similar classification methods without signal pre-processing, or pre-processing with previously reported methods of PCA, wavelet transformation and polynomial curve approximation. Sensor fabrication, data collection and processingThree SnO2-based materials have been used – pure SnO2, gold-modified SnO2 and bimetallic Au and Pd modified SnO2. The gas sensing materials synthesis via single step flame spray pyrolysis technique and sensors fabrication has been reported in a recent paper [4]. A fixed air flow from outside of the building of the Department of Chemistry of Moscow State University through PTFE sensor chamber was used as a background. Methane or propane were admixed to the background air flow through precise mass-flow controllers in three different concentrations from certified gas bottles. Sensors were operated in a working temperature modulation mode between 500 oC and 150 oC with period length of 60 sec. Sensitive layer resistance was measured with the 10 Hz frequency. Collected data was separated in two parts: first, collected in December 2018 was used for data processing algorithms training. Second, collected during January and February 2019, was used for the testing of elaborated data processing models. The total data set of 22440 measurement cycles,11220 of which represent an ambient air, while two data subsets of 5610 measurement cycles represent same air with admixture of methane or propane, were used for processing. The multilayer perceptron ANN-model with 2 hidden dense layers has been used for data processing model development and gases discrimination. The batch normalization and dropout techniques were implemented to avoid model overfitting.According to statistical shape analysis approach, each characteristic point of sensor response is characterized by certain gas sensor working temperature and sensitive layer resistance. All characteristic points of each single measurement cycle during analysis are converted into Kendall’s pre-shape space with removed translation and scaling factor, but with remaining rotation as well as the shape. During further processing the data samples are projected onto the unit-sphere with a pole of mean shape of sensor responses towards air without additives. Later inverse transformation of data samples leads to icon representation of response shape, eliminating possible effects of sensor baseline and response amplitude drift. Results and Conclusions Direct application of collected data to artificial neural network algorithm for methane vs. propane selective detection without any pre-processing gives a decent level of accuracy (Fig.1). However, it can be seen by the rise of discrimination error after normalization of data samples, that the main component of the sensors response, used by algorithm for gases discrimination, is of amplitude nature. It means, that the developed signal processing model may work in unstable manner when any additional gas is involved in the measurements. The use of statistical shape analysis allows to significantly improve the accuracy of discrimination of methane vs. propane in comparison with other pre-processing techniques. The remained error of gases identification is mostly related to the single day of measurements, which is associated with urban air pollution during winter heating season.

Synthesis of Nitrogen Oxides in a Subthreshold Microwave Discharge in Air and in Air Mixtures with Methane

A subthreshold discharge excited by a microwave beam in air at pressures close to atmospheric is studied as a plasmachemical method of nitrogen oxide (NOx) production. It is shown that at the energy expenditure level (2–4) kW h/m3, it is possible to produce a nitrogen oxide concentration in pure air that exceeds the concentration in the initial gas by several orders of magnitude. At the same time, it is shown that it is possible to stop nitrogen oxide production almost completely by adding an admixture of methane (CH4) to the irradiated air, which makes the so-called self-non-self-sustained (SNSS) discharge much more promising for cleaning the gaseous exhausts from urban landfills from harmful admixtures (hydrogen sulfide, mercaptans, etc.).

Dual Separation of Krypton and Argon from Environmental Samples for Radioisotope Dating.

The noble gas radioisotopes 85Kr, 81Kr, and 39Ar are nearly ideal environmental tracers because of their chemical inertness and simple transport mechanisms. Recent advances in Atom Trap Trace Analysis have enabled measurements of 85Kr and 81Kr using 10-20 kg of water or ice, and 39Ar in only a few kilograms, making these tracers available to be applied in the earth sciences on a large-scale. To meet the resulting increase in demand, we have developed an automated process for the dual separation of krypton and argon from environmental samples based on titanium gettering and gas chromatography. 0.5-4 L STP air samples have been purified, demonstrating purities and recoveries of >90% for krypton and >99% for argon within 90-120 min of processing time. Samples of high methane admixtures, a challenge regularly encountered in groundwater applications, have been purified by exploiting the full potential of titanium gettering at high temperatures (>1000 °C). Samples with 0.4-48 L STP of methane admixture are processed in 2-5 h without compromising purity or recovery. The applicability of the purification system is further demonstrated using actual groundwater samples with carbon dioxide and methane content in the extracted gas up to 16 L STP and 42 L STP, respectively.

Complex gas hydrate system in a gas chimney, South China Sea

Abstract Gas hydrates and deep-sea cold seeps are of interest to industry and academia for several reasons, including their implications for offshore geohazards and unconventional resources, and for global climate change and carbon cycling. Guangzhou Marine Geological Survey (GMGS) implemented its fifth gas hydrate drilling expedition in the QiongDongNan Sea Area (QDN-SA) of the northern South China Sea (SCS) from June to September 2018. Multidisciplinary investigations, including Logging While Drilling (LWD), pressure and non-pressure coring, gas composition analyses, in situ temperature and permeability measurements, pore water geochemical analyses, and a regional seismic survey, reveal a complex distribution of gas hydrate within a vertical chimney structure. LWD profiles record high resistivity anomalies and high P-wave velocity variations at 9–174 mbsf, suggesting the coexistence of free gas and gas hydrate in the sediment column throughout the investigated gas chimney. Hydrate-bound and void gas is an admixture of methane (70.1%–98.3%) and heavier hydrocarbons (C2H6: 0.16%–17.59%, C3H8: 0.05%–9.88%, i-C4H10:

On the influence of carbon contamination of reactor parts in active screen plasma nitrocarburizing processes

Compared to conventional plasma nitrocarburizing the active screen plasma nitrocarburizing technology reduces significantly the risk of soot production and cementite precipitation in the compound layer of nitrocarburized materials. However, in long-time treatments, the uncontrollable contamination even up to full saturation of the metallic active screen and of the walls of the used plasma reactor with carbon compounds is still a remaining factor of uncertainty. It may result in an increased carbon concentration or even in an appearance of the cementite phase in the compound layer of the treated steel surface, as in the case of 42CrMo4 (AISI 4140). The absolute concentration of hydrogen cyanide (HCN), in situ monitored by tunable diode laser absorption spectroscopy, and the emission intensity of the CN (0–0) band of the violet system at a wavelength of λ = 388 nm, recorded by optical emission spectroscopy, were found to be reliable parameters to control the carburizing potential of the nitrocarburizing plasma. A close relationship was found between (i) the concentration of HCN and the CN band emission intensity with (ii) the level of the methane admixture in the feed gas and the time-dependent contamination effects of the active screen and other inner reactor surfaces with carbon compounds. Therefore, this relation could serve as a basis for an in-line control of the carburizing activity in plasma nitrocarburizing processes with methane admixture using an active screen.

Mud extrusion and ring-fault gas seepage \u2013 upward branching fluid discharge at a deep-sea mud volcano

Submarine mud volcanoes release sediments and gas-rich fluids at the seafloor via deeply-rooted plumbing systems that remain poorly understood. Here the functioning of Venere mud volcano, on the Calabrian accretionary prism in ~1,600 m water depth is investigated, based on multi-parameter hydroacoustic and visual seafloor data obtained using ship-borne methods, ROVs, and AUVs. Two seepage domains are recognized: mud breccia extrusion from a summit, and hydrocarbon venting from peripheral sites, hosting chemosynthetic ecosystems and authigenic carbonates indicative of long-term seepage. Pore fluids in freshly extruded mud breccia (up to 13 °C warmer than background sediments) contained methane concentrations exceeding saturation by 2.7 times and chloride concentrations up to five times lower than ambient seawater. Gas analyses indicate an underlying thermogenic hydrocarbon source with potential admixture of microbial methane during migration along ring faults to the peripheral sites. The gas and pore water analyses point to fluids sourced deep (>3 km) below Venere mud volcano. An upward-branching plumbing system is proposed to account for co-existing mud breccia extrusion and gas seepage via multiple surface vents that influence the distribution of seafloor ecosystems. This model of mud volcanism implies that methane-rich fluids may be released during prolonged phases of moderate activity.

Biodegradation in the Nkh 3-4 reservoir at Vankor Field (West Siberia Basin, Russia) is strongly controlled by rock properties

The Vankor Field, located in the West Siberia Basin, Russia, contains oils at various levels of biodegradation. A study of reservoir oils and rock extracts from the Lower Cretaceous sandstones in the Nkh 3-4 interval reveals that increasing biodegradation when moving from the gas-oil contact (GOC) towards the oil-water contact (OWC) is strongly controlled by rock properties. Biodegradation is most advanced where the OWC is located in the high permeability reservoir interval. High permeability rocks also allow for more extensive upward mixing of biodegraded oil. Changes in the oil and gas fractions due to biodegradation also affect the gas-oil ratio as dry gas is less soluble in heavy oil. This explains the presence of reservoir oil saturated with gas near the OWC. The latter also can be partly due to the admixture of methane through methanogenic processes at the OWC. Upward movement of microbial gas bubbles enhances the mixing of biodegraded oil in the high permeability reservoir intervals.

Optical and electrical properties of boron doped diamond thin conductive films deposited on fused silica glass substrates

This paper presents boron-doped diamond (BDD) film as a conductive coating for optical and electronic purposes. Seeding and growth processes of thin diamond films on fused silica have been investigated. Growth processes of thin diamond films on fused silica were investigated at various boron doping level and methane admixture. Two step pre-treatment procedure of fused silica substrate was applied to achieve high seeding density. First, the substrates undergo the hydrogen plasma treatment then spin-coating seeding using a dispersion consisting of detonation nanodiamond in dimethyl sulfoxide with polyvinyl alcohol was applied. Such an approach results in seeding density of 2×1010cm−2. The scanning electron microscopy images showed homogenous, continuous and polycrystalline surface morphology with minimal grain size of 200nm for highly boron doped films. The sp3/sp2 ratio was calculated using Raman spectra deconvolution method. A high refractive index (range of 2.0–2.4 @550nm) was achieved for BDD films deposited at 500°C. The values of extinction coefficient were below 0.1 at λ=550nm, indicating low absorption of the film. The fabricated BDD thin films displayed resistivity below 48Ohm cm and transmittance over 60% in the visible wavelength range.

Chemical analysis of H2–B2H6 and H2–CH4–B2H6 microwave CVD plasmas used for diamond deposition

This study provides a detailed analysis of the H2/B2H6 chemistry and a first evaluation of H2/CH4/B2H6 plasmas for conditions close to boron doped diamond microwave plasma assisted chemical vapor deposition. A H2/B2H6 chemical scheme composed of 38 reactions has been formulated from the research literature and finalized by an equilibrium approach of the gas composition. 1D thermochemical modeling of the gas phase provides a spatial description of the temperatures and of the mole fractions of the species. A comparison with the mole fractions of atomic boron and diborane measured by optical emission spectroscopy and tunable diode laser absorption spectroscopy in the mid-infrared region, respectively, have been performed on a wide range of operating conditions, i.e. for pressure values of p = 60–300 mbar, power values of P = 0.6–4 kW, diborane admixtures of 30 and 66 ppm and methane admixtures of up to 5% diluted in H2. For the H2/B2H6 plasmas, the agreement between the experiments and the 1D model is satisfactory, especially for high power density conditions. At low power density, the electron processes would appear to be necessary to describe the diborane dissociation. Finally, the effect of methane addition to the H2/B2H6 mixture on the mole fraction of the atomic boron was investigated. At high pressure/power conditions, no significant influence was observed, whereas at low power densities the measured boron atom mole fractions decreased when methane was added.

Ore-forming processes in the Drazhnoe gold–quartz deposit (Eastern Yakutia, Russia)

Themobarogeochemical investigations revealed that quartz from the Drazhnoe deposit was formed in mesothermal conditions at depths of 3–4 km from carbon dioxide–water fluids with wide salinity variations and an admixture of methane. Several types of fluids are distinguishable on the basis of the composition of extracts: hydrocarbonate–sodium, highly diluted, and late sulfate–hydrocarbonate–sodium with elevated salinity. Ore minerals precipitated in the thermostatic environments against the background of fluid heterogenization due to a probably significant pressure drop and mixing of different solutions. Metamorphic processes related to the early collision stage provided no substantial impact on the composition and potential of gold ore mineralization.

Spectroscopic diagnostics of active screen plasma nitriding processes: on the interplay of active screen and model probe plasmas

In a reactor used for active screen plasma nitriding (ASPN) the interplay of two plasma types, (i) the plasma of the cylindrical active screen driven in a pulsed dc mode (f = 1 kHz, 60% duty cycle) and (ii) the plasma at an internal model probe driven in a cw dc mode, ignited in a low pressure H2–N2 gas mixture (p = 3 mbar) containing small amounts of CH4 and CO2 have been studied by tunable diode laser infrared absorption (TDLAS) and optical emission spectroscopy (OES) techniques. Applying in situ TDLAS the evolution of the carbon containing precursors, CH4 and CO2, and of the reaction products, NH3, HCN, CO and H2O, has been monitored. The degree of dissociation of the carbon containing precursor molecules varied between 70% and 92%. The concentrations of the reaction products were found to be in the range 1012…1015 molecules cm−3. By analyzing the development of the molecular concentrations at changes of gas mixtures and plasma power values, it was found that (i) HCN and NH3 are the main products of plasma conversion in the case of methane admixture and (ii) CO, HCN and NH3 in the carbon dioxide case. The fragmentation efficiencies of methane and carbon dioxide (RF(CH4) ≈ 1…2 × 1015 molecules J−1, RF(CO2) ≈ 0.5…1.0 × 1016 molecules J−1) and the respective conversion efficiencies to the product molecules (RC(product) ≈ 1013–1015 molecules J−1) have been determined for different gas mixtures and plasma power values, while the influence of probe and screen plasmas, i.e. the phenomena caused by the interplay of both plasma sources, was analyzed. The additional usage of the plasma at the model probe has a sensitive influence on the generation of the reaction products, in particular that of NH3 and HCN. With the help of OES the rotational temperature of the screen plasma could be determined, which increases with power from 770 K to 950 K. Also with power the ionic component of nitrogen molecules, i.e. the intensity of the -(0-0) band of the first negative system, increases strongly in relation to the intensity of the neutral component, represented by the N2-(0-0) band of the second positive system. In addition, the behavior of the emission of the plasma at the model probe has been studied during the off phase of the plasma of the active screen leading to a direct comparison of the emission characteristics of both plasma sources.

Influence of the carbon isotopic composition of methane and the proportion of methane-derived bicarbonate on the 13C/12C ratio of dissolved inorganic carbon at the sulfate–methane transition in the Joetsu Basin area, eastern margin of the Sea of Japan

The geochemistry of interstitial waters associated with active marine hydrocarbon seepage provides insight into the source and ongoing dynamics of such systems. In this investigation of interstitial waters obtained from sediments in a gas hydrate region of the Sea of Japan, we compare carbon isotopic composition (δ13C) of dissolved inorganic carbon (DIC) at the sulfate–methane transition (SMT) with δ13C of deeply sourced methane (as inferred from the deepest samples obtained beneath the SMT). Based on this comparison, we distinguish two causes for lower values of δ13CDIC at the SMT. In Group A (17 piston cores), δ13CDIC values at the SMT (−30.0 to −9.7‰ VPDB) correlate positively with δ13C of deep methane (−90.7 to −61.4‰ VPDB). Lowering of these δ13CDIC values was independent of methane flux, which controls the generation rate of methane-derived bicarbonate by anaerobic oxidation of methane, owing to the influence of a high alkalinity flux from depth. In the Group B core samples, δ13CDIC at the SMT (−41.6 to −14.2‰ VPDB) relative to δ13C of deep methane (−68.2 to −40.5‰ VPDB) is lower than that of Group A, implying a greater contribution of methane-derived HCO3−. With only two exceptions, the Group B core sites were located at areas of active gas seepage. The admixture of methane from migrating methane bubbles with deep methane in the interstitial waters of sediments has the potential to significantly increase the overall methane flux at gas seep sites. Although the admixture may reflect higher δ13C values of deep methane, the increase in methane flux results in a higher proportion of methane-derived HCO3− and lower δ13CDIC at the SMT. Recovery of two group B cores adjacent a dormant pockmark suggests that the depression with seismic blanking beneath it, similar to that of the gas seep sites, is a previous gas seepage site.

Study of a Continuous Microwave Discharge in Two Crossed Wave Beams of the Millimeter Wavelength Band

We present the results of studying a microwave discharge produced by continuous-wave gyrotron radiation with a frequency of 30 GHz in a mixture of argon and hydrogen with an admixture of methane in the region of crossing of two wave beams. The discharge wave maintained over a substrate and had the form of a thin plasma layer. The gas temperature and electron density in the plasma were measured by the methods of optical spectroscopy of radiation. Features of determining Stark broadening of spectral lines of atomic hydrogen at a relatively low (of about 1013 cm−3) electron density are discussed. Dependences of the electron density and gas temperature on the pressure and gas composition, as well as the power of the incident microwave radiation are presented. The prospects of using the discharge under consideration for plasmochemical deposition of diamond films from the gaseous phase are considered.

Characterization of Optical and Electrical Properties of Transparent Conductive Boron-Doped Diamond thin Films Grown on Fused Silica

Abstract A conductive boron-doped diamond (BDD) grown on a fused silica/quartz has been investigated. Diamond thin films were deposited by the microwave plasma enhanced chemical vapor deposition (MW PECVD). The main parameters of the BDD synthesis, i.e. the methane admixture and the substrate temperature were investigated in detail. Preliminary studies of optical properties were performed to qualify an optimal CVD synthesis and film parameters for optical sensing applications. The SEM micro-images showed the homogenous, continuous and polycrystalline surface morphology; the mean grain size was within the range of 100-250 nm. The fabricated conductive boron-doped diamond thin films displayed the resistivity below 500 mOhm cm-1 and the transmittance over 50% in the VIS-NIR wavelength range. The studies of optical constants were performed using the spectroscopic ellipsometry for the wavelength range between 260 and 820 nm. A detailed error analysis of the ellipsometric system and optical modelling estimation has been provided. The refractive index values at the 550 nm wavelength were high and varied between 2.24 and 2.35 depending on the percentage content of methane and the temperature of deposition.

Spectroscopic study of H2 microwave plasmas with small admixtures of CH4 and B2H6 used for doped diamond deposition

Microwave (MW) H2 plasmas with small admixtures of CH4 and/or B2H6 used for doped diamond deposition have been studied by infrared absorption and optical emission spectroscopy (OES) techniques. The experiments were carried out in order to analyze the dependence of the plasma chemistry on several parameters in the MW discharges, such as power, pressure and gas mixture, at relatively high pressures, i.e. up to 300 mbar, and power values, i.e. up to 4 kW. The evolution of the concentrations of five stable molecules, CH4, C2H2, C2H4, C2H6 and B2H6, was monitored in the plasma processes by in situ infrared tunable diode laser absorption spectroscopy. OES was used simultaneously to gather complementary information about the concentration of the boron atom. One target was the determination of the precursors' fragmentation rates and the conversion rates to the molecular reaction products. The analysis of correlations between the power and pressure of the plasma and molecular concentrations, and the differences found with CH4 and B2H6 admixtures were another focus of interest. The degree of dissociation of the carbon containing precursor molecule CH4 varied between 35% and 75%, while the decomposition of diborane, the boron precursor, varied between 85% and 97%. By analyzing the development of the molecular concentrations with changes of gas mixtures, pressure and plasma power values, it was found that (i) C2H2 is the most abundant reaction product in the plasma in the case of methane admixture and (ii) the boron atom concentration depends strongly on the presence of hydrocarbons in the plasma. The fragmentation efficiencies of methane and of diborane (RF(CH4) ≈ (1–2) × 1015 molecules J−1, RF(B2H6) ≈ (0.4–1.4) × 1013 molecules J−1) and the conversion efficiencies to the molecular products (RC(product) ≈ 1013–1015 molecules J−1) have been determined for different gas mixtures and plasma power, and pressure values. The boron atom balance, in relation to the dissociated B2H6 molecules was found to vary between 10% and 40% depending on the discharge conditions.

Spectroscopic studies of conventional and active screen N2–H2 plasma nitriding processes with admixtures of CH4 or CO2

Low-pressure pulsed dc H2–N2 plasmas with admixtures of CH4 or CO2 used for conventional (CPN) and active screen plasma nitriding (ASPN) were studied by infrared absorption and optical emission spectroscopy (OES) techniques. The experiments were performed in two modes: (i) the plasma at an internal model probe, driven by a bias voltage operated only, representing a CPN approach, and (ii) the screen plasma operated only, which corresponds to an ASPN experiment. Combining in situ tunable diode laser absorption spectroscopy with ex situ Fourier transform infrared spectroscopy the evolution of the concentrations of the methyl radical and of eight stable molecules, C2H2, CH4, C2H4, CO, CO2, NH3, HCN and H2O was monitored. The degree of dissociation of the carbon-containing precursor molecules varied between 40% and 98%. The methyl radical concentration was found to be in the range 1011–1012 molecules cm−3. By analysing the development of molecular concentrations with changes in gas mixtures and plasma power values, it was found that (i) C2H2, HCN and NH3 were the main products of plasma conversion in the case of methane admixture and (ii) CO, HCN and NH3 in the carbon dioxide case. The fragmentation efficiencies of methane and carbon dioxide (RF (CH4) ≈ (0.5–4) × 1016 molecules J−1, RF (CO2) ≈ (0.5–3.4) × 1016 molecules J−1) and the respective conversion efficiencies to the product molecules (RC (product) ≈ 1013–1015 molecules J−1) were determined for different gas mixtures and plasma power values. With the help of OES the rotational temperature of the screen plasma could be determined, which increased with power from 600 to 850 K. Also with power the ionic component of nitrogen molecules, i.e. the intensity of the -(0–0)-band, increased strongly in relation to the intensity of the neutral component, represented by the N2-(0–2)-band.

Organic geochemical study of source rocks and natural gas and their genetic correlation in the central part of the Polish Outer Carpathians

Geochemical characteristics of organic matter (quantity, genetic type, maturity and petroleum potential) were determined in profiles of Lower Cretaceous–Miocene strata of the Dukla and Silesian units of the Polish Outer Carpathians in the Tarnów-Dębica-Nowy Sącz-Gorlice-Jasło area. This determination was based on Rock-Eval, isotopic, and biomarker analyses of 159 rock samples. Oligocene Menilite beds reveal the best hydrocarbon potential within the investigated formations (depositional units of the so-called flysch strata) and can be considered as primary source rock in the study area. Marine and mixed marine–terrestrial kerogen present in these rocks is immature in Silesian Unit and mature (oil window) in Dukla Unit, respectively. The Lower Cretaceous–Eocene formations (Veřovice, Lgota, Godula and Istebna beds, Variegated Shales, and Ciężkowice beds) of the Silesian Unit reveal variable amounts of mostly gas-prone kerogen and can be considered as additional source of hydrocarbons. The Upper Oligocene–Lower Miocene Krosno beds and Miocene Chaotic beds have a variable organic matter content, usually over 1 wt%, but very low maturity and low hydrocarbon potential predispose them as a source of microbial methane. Ten natural gas samples from sandstone reservoirs of the Upper Cretaceous–Lower Miocene strata in the Silesian Unit of the Outer Carpathians were analysed for molecular and isotopic compositions in order to establish their origin and role of thermogenic and microbial processes. Thermogenic gases without the admixture of microbial methane were encountered only in one well (Bystra-4) in the block A of Szalowa-Heddy-Bystra gas deposit. Thermogenic gas component was generated at a maturity level of 0.7 to 1.0% of vitrinite reflectance (Ro) scale from mixed Type II/III kerogen dispersed in the Oligocene Menilite beds from a few fields within the Silesian Unit. Microbial methane had been generated earlier from the same organic matter, during microbial carbon dioxide reduction process. A significantly high microbial component occurs mainly in the gases from Kobylanka (gas horizon), Gorlice-Glinik, and blocks C and B of the Szalowa-Heddy-Bystra fields. The microbial gases were generated within the Oligocene Menilite beds and/or Miocene Chaotic beds within local zones in the study area. Carbon dioxide originated both from thermogenic and microbial processes.

Gold-bearing quartz veins of the Bělčice ore district, Bohemian Massif: evidence for incursion of metamorphic fluids into a granodiorite body and for isothermal mixing between two types of metamorphic fluids

Gold-bearing quartz veins of the Bělcice ore district are hosted by I-type Variscan Blatna granodiorite of the Central Bohemian Plutonic Complex. The quartz gangue precipitated from aqueous-carbonic fluids (3–7 wt. % NaCl eq.) with significant methane admixture (up to 15 mol. % of CH4) at c. 350–400 °C and 200–400 MPa. The ore stage including gold precipitation occurred at lower temperatures (300 to 250 °C) and pressures (~ 100 MPa) from aqueous fluids. The isotope composition of the quartz and carbonate gangue indicates progressively heavier oxygen of the parental fluid (δOfluid from ~ 9–10 ‰ to 10–14 ‰ SMOW). This suggests ingress of metamorphic fluids equilibrated with metasedimentary country rocks into an environment dominated by I-type granitoids. Invasion of external metamorphic fluids is also supported by nearly isothermal mixing trends in aqueous fluids as documented by salinity variations (from 5.5 to 0 wt. % NaCl eq.).