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The pore-throat radius of the shale oil reservoir is extremely small, and it is difficult to accurately obtain the absolute permeability and oil–water two-phase relative permeability of the actual oil reservoir through conventional core experiments. However, these parameters are very important for reservoir numerical simulation. In this paper, a method for characterizing flow parameters based on a pore network model that considers differential pressure flow and diffusion flow is proposed. Firstly, a digital core was reconstructed using focused ion beam scanning electron microscopy (FIB-SEM) from the Gulong shale reservoir in the Songliao Basin, China, and a pore network model was extracted. Secondly, quasi-static single-phase flow and two-phase flow equations considering diffusion were established in the pore network model. Finally, pore-throat parameters, absolute permeability, and oil–water two-phase permeability curves were calculated, respectively. The results show that the pore-throat distribution of the Gulong shale reservoir is mainly concentrated in the nanometer scale; the mean pore radius is 87 nm, the mean throat radius is 41 nm, and the mean coordination number is 3.97. The calculated permeability considering diffusion is 0.000124 mD, which is approximately twice the permeability calculated without considering diffusion. The irreducible water saturation of the Gulong shale reservoir is approximately 0.4, and the residual oil saturation is approximately 0.35. The method proposed in this paper can provide an important approach for characterizing the flow parameters of similar shale oil reservoirs. [ABSTRACT FROM AUTHOR]

Organic matter (OM) in shales occurs as nanometer-sized intercalations with clay minerals that are termed as clay-organic nanocomposites; however, the OM occurrence in nanocomposites at different stages of maturation is still unclear, and the co-evolution process of OM and clay under burial is not well understood. To reveal the variation of OM occurrence and clarify the relationship between petroleum generation of OM & transformation of clay minerals in nanocomposites as a function of maturity, this study investigates the structure and clay-OM association in 44 samples from three leading shales at different maturity stages from two basins in China. A total of 15 samples of lacustrine shale from upper Triassic Yanchang Formation, 15 samples of marine shale from Lower Silurian Longmaxi Formation, and 14 samples of marine shale from Lower Cambrian Niutitang Formation were analyzed based on organic geochemistry, X-ray diffraction (XRD), and field emission-scan electron microscopy (FE-SEM), focused ion beam (FIB) sample preparation and consequent high resolution-transmission electron microscopy (HR-TEM) observations combined with energy dispersive spectroscopy (EDS). The results from this study show that most shale samples are organic-rich, and these three shales represent thermal evolutionary process from oil-window mature to overmature in a sequence of Triassic Yanchang, Silurian Longmaxi, and Cambrian Niutitang formations. Thorough observations indicate that sub-parallel bands of clays and intermingling of detrital minerals (such as quartz) dominate the nanocomposites in the Yanchang samples. While for Longmaxi and Niutitang shales, abundant nanopores and pyrite nanoparticles are observed in nanocomposites with features of layered distributions of OM and clay minerals. The structural investigation of nanocomposites shows that organic carbon between multi-layers dominates the OM occurrence in nanocomposites, which significantly extends the traditional opinion of OM-clay association. At an oil-window mature stage, the fluctuational interlayer spacing and a certain intensity of the carbon peak observed in the EDS spectra for corresponding clays provide a visual evidence of the organic molecules accessing the monolayer spaces of smectite. With the evolutional process of nanocomposites in shale and petroleum generation of OM & mineral transformation (illitization of smectite) running in parallel, it is inferred that the organic molecules migrate from monolayer spaces as gaseous hydrocarbons are generated, and eventually form stable clay-organic nanocomposites at an overmature stage. The results presented here will contribute to an improved understanding of diagenesis and organic-inorganic interactions in OM-rich shales. [ABSTRACT FROM AUTHOR]

The formation of columbite-group mineral phases in peraluminous granite has not been demonstrated to date. Here, a nanoscale study of the columbite-tantalite mineral in the Zhaojinggou Nb-Ta deposit in North China Craton elucidated its formation mechanism and the role of fluids in Nb-Ta mineralization. Transmission electron microscopy (TEM) analysis of a focused ion beam cut of the columbite-tantalite mineral revealed a comparatively well-ordered mineral structure. Energy-dispersive X-ray spectroscopy (EDS) revealed the presence of Nb, Ta, Mn, W, Fe, Sn, and Pb in the columbite-tantalite mineral. Furthermore, detailed TEM images depicted the nanoscale hydrothermal fluid occurring within the columbite-group mineral grain as well as between columbite-tantalite mineral and quartz grains. K, Al, Si, and O were found to be enriched in the hydrothermal fluid that was present between the quartz grains and the columbite-tantalite mineral. It did not react with the mineral grains of the columbite group. The ultrastructure of the columbite-tantalite mineral suggested the columbite-group mineral in the Zhaojinggou Nb-Ta deposit formed during magmatic crystallization rather than from hydrothermal fluids. Furthermore, HR-TEM images provided the first nanoscale observations of the fluid-mediated mineral dissolution and amorphous phase formation. This study also revealed that the mineral dissolution, element transport, and reprecipitation were significantly influenced by the fluid amorphous phase in the Nb-Ta deposits. [ABSTRACT FROM AUTHOR]

Here, we present well-oriented hematite exsolutions in corundum megacrysts from Cenozoic basalt in China. Crystallographic orientation relationships (CORs) and the interface characters between the hematite exsolutions and the corundum host were analyzed by electron backscatter diffraction (EBSD) and high-resolution transmission electron microscope (HRTEM), respectively. The CORs and the regular interface confirm the exsolution and the exsolution was formed under depressurization based on the crystal chemistry theory. There are three groups of exsolutions intersected with ~60°. Two groups of the exsolutions have the same orientation with the host and the other group is twinned to those two groups. Focused ion beam (FIB) for HRTEM foil preparation was carried out. HRTEM photographs show that there are periodic coherency units at (0001) interface. The measured unit lengths are 6.71–6.72 nm, which are in good agreement with every 17- D C r n 01 1 ¯ 2 p r o j e c t i o n or 16- D H e m 01 1 ¯ 2 p r o j e c t i o n . Based on the results, the possibility is that at the interface, the hematite-corundum phases tend to modulate to achieve the maximum coherency in the geological process during exsolution. This research is helpful to understand the interface characters between the exsolution and host. [ABSTRACT FROM AUTHOR]

As one of the most important energy sources in the world today, shale gas has attracted extensive research. Numerous scholars agreed that the organic matter (OM) pores in shale provide the main space which benefits effective gas occurrence. However, the connectivity provided by OM pores is more important in the development process than their reservoir properties. A comprehensive portrayal of the 3D connectivity of the OM pores is elaborated in this study. The Lower Silurian Longmaxi shale samples were selected as the research subject. The shale samples are subjected to focused ion beam scanning electron microscope, helium ion microscope observation experiments, 2D microscopic characterization of OM pores, and 3D segmentation extraction. The results indicate that the connectivity of shale is mainly contributed by OM pores. The OM pores have the advantageous structural characteristics of large number per unit area, evenly distributed, regular pore morphology, and large pore size relative to the mineral matrix pores. The OM pores structure in shale is complex with a network structure of small pores nested in large pores, which can increase the adsorption capacity of gas. Besides, the small pores nested in large pores can act as a throat to significantly improve the connectivity. OM pores in the pyrobitumen are interconnected in 3D space, providing the main channels for gas percolation in the shale reservoir. [ABSTRACT FROM AUTHOR]

The Lower Cambrian Niutitang and Sinian Doushantuo shales are the most important and widespread source rocks and target layers in South China. Reliable data of the thermal maturity of organic matter (OM) is widely used to assess hydrocarbon generation and is a key property used in determining the viability and hydrocarbon potential of these new shales. Nevertheless, traditional thermal maturity indicators are no longer suited to the vitrinite-lack marine shales. This study aims to combine high throughput Raman and infrared spectroscopy analysis to confirm and validate the thermal maturity in comparison with the bitumen reflectance (Rb). Raman parameters such as the differences between the positions of the two bands (VG-VD) are strong parameters for calculating the thermal maturity in a large vitrinite reflectance (Ro) ranging from 1.60% to 3.80%. The infrared spectroscopy analysis indicates that the aromatic C-C bands and CH2/CH3 aliphatic groups both are closely correlated with thermal maturity. The calculated Ro results from Raman and infrared spectroscopy are in strong coincidence with the Rb. The relationships between Rb and pore volumes/surface areas (calculated from N2 adsorption) indicate that the sample with Rb of 3.40% has the lowest pore volumes and surface areas. Focused ion beam scanning electron microscopy (FIB-SEM) observations of OM pores indicate that Ro of approximately 3.60% may be an upper limit for OM porosity development. Obviously, kerogen Raman and infrared spectroscopy can indicate methods for reducing the risk in assessing maturity with practical, low-cost accurate results. Exploration of shale gas in the high maturity (>3.40%–3.60%) region carries huge risks. [ABSTRACT FROM AUTHOR]

Organic pores play an important role in shale reservoirs. Organic pores occur where shale gas was produced and accumulated. However, there is little scientific understanding of the distribution and connectivity of organic pores. Organic pore types and their structural characteristics were studied using a total organic carbon (TOC), thin section, focused ion beam scanning electron microscope (FIB-SEM), and nano-CT. The samples were from the Wufeng Formation in the Upper Ordovician and Longmaxi Formations from the lower Silurian. The results show that organic matter is mainly concentrated in the Wufeng Formation and the bottom of the Longmaxi Formation and that the middle and upper parts of the Longmaxi Formation contain a low amount of organic matter. The shale of the Wufeng-Longmaxi Formation has high maturity, and its organic pores are well developed. There are three types of organic pores: algae, graptolite, and pyrobitumen pores. The pore connectivity of shale with a high organic content is better than that of shale with a low organic content. The volume of the organic pores accounts for more than 50% of the volume of the organic matter. Majority of the organic pores have an aperture smaller than 100 nm and are round, nearly circular, and elliptical in morphology. Most of the organic pores in a shale formation are developed in pyrobitumen, and most of the larger organic pores are concentrated at the center of solid pyrobitumen. The organic pores in pyrobitumen have the best connectivity and are the most favorable reservoir spaces and migration channels for shale gas, which is a crucial point of reference for future research of shale gas. [ABSTRACT FROM AUTHOR]

Recent studies have identified gold nanoparticles in ores in a range of deposit types, but little is known about their formation processes. In this contribution, gold-bearing magnetite from the well-documented, world-class Beiya Au deposit, China, was investigated in terms of microstructure and crystallography at the nanoscale. We present the first three-dimensional (3D) focused ion beam/scanning electron microscopy (FIB/SEM) tomography of the distribution of gold nanoparticles in nanopores in the low-Si magnetite. The porous low-Si magnetite, which overprints an earlier generation of silician magnetite, was formed by a coupled dissolution-reprecipitation reaction (CDRR). The extrinsic changes in thermodynamic conditions (e.g., S content and temperature) of the hydrothermal fluids resulted in the CDRR in magnetite and the disequilibrium of Au-Bi melts. The gold nanoparticles crystallized from Au-supersaturated fluids originating from the disequilibrium of Au-Bi melts and grew in two ways depending on the intrinsic crystal structure and pore textures: (1) heteroepitaxial growth utilizing the (111) lattice planes of magnetite, and (2) randomly oriented nucleation and growth. Therefore, this study unravels how intrinsic and extrinsic factors drove the formation of gold nanoparticles at fluid-mineral interfaces. [ABSTRACT FROM AUTHOR]

Investigating the pore structure of shale rocks plays an important role in understanding the mechanism of shale oil accumulation and migration; thus, it has a notable influence on the exploration and development of shale oil resources. In the present study, the microstructure of oil shale samples extracted from the Shahejie Formation in the Dongying Depression was investigated through the joint usage of focused ion beam (FIB) and scanning electron microscopy (SEM). Herein, we selected four representative samples. The SEM images of the sample surfaces milled by FIB indicated that pores were found in both the organic and inorganic matter. Organic pores were less developed in the samples because of the low thermal maturity of the organic matter. Continuous 3D digital rock images of shale samples were generated by FIB grinding and SEM in situ imaging. Based on multithreshold segmentation, the shale rocks were separated into different parts including kerogen, inorganic matter, and pores. The pore connectivity and pore size distributions were analyzed via Avizo software and in‐house developed MATLAB scripts. The pore size and corresponding volume distributions suggested that mesoscale pores (2‐50 nm) were abundant in the samples but they contributed limitedly to the total pore volume. Macropores (>50 nm) accounted for a small proportion but they had a greater contribution to the overall pore space volume. The coordination numbers of the subject four samples were mainly 0 and 1, which means that isolated pores accounted for the vast majority of the pores. These observations are critical to conduct reliable petrophysical simulations in the oil shales and understand their intrinsic properties accurately. [ABSTRACT FROM AUTHOR]

Vacuum is discharge, which is widely used in material surface modification, semiconductor doping and high-energy physics research in particle accelerator injection, the characteristics of vacuum arc discharge plasma, which are of great significance in practical application. Owing to characteristics of time-of-flight mass spectrometry (TOF), it is fast analysis, wide quality range and suitable for transient process, it has great advantage to availability of the information on the composition and charge distribution of the plasma. In our study，a linear time-of-flight mass spectrometer combined with vacuum arc ion source was developed using for diagnosis of high energy ion beam. The TOF analyzer mainly consisted of ion source, ion gate, lens system and MCP detector, the whole system was aligned coaxially with horizontal axis of the drift tube. Ions generated by vacuum arc discharge and accelerated by 30 kV DC high voltage were selectively passed through the ion-gate and then focused by lens system to reach the MCP detector. The effective distance of free-field flight region was 1.5 m. The mass resolution was higher than 90 FWHM by accurate intercepting of short-duration pulse ion gate，and the ion beam focusing effect was investigated by using ICCD high speed camera to improve sensitivity. The instrument could be used to analyze the ion compositions of plasma generated during discharge in various time. Rapid and accurate detection of plasma generated in the discharge process of vacuum arc discharge ion source was realized. Compositions of ionization in the initial stage of discharge (2 μs) were mainly gaseous ions, such as C+, O+, C2+ and O2+, and in the later stage of discharge (6 μs)，metal ion such as Fe+, Cu+ and their isotope peaks could be detected. At the same time, the information such as the species, charged state and relative content of ions produced by vacuum arc ion source discharge could be given, and the accurate diagnosis of the whole discharge process could be realized. Though this instrument was not yet able to achieve the quantitative analysis of the ionic components and the change of the plasma under different discharge voltages in this study, however, in similar studies, the research could be expanded on the basis of the results of the study, and carried out a more in-depth study of the vacuum arc discharge ionization performance by corresponding high-voltage and vacuum design and combining the actual ion source structure, such as the study of different acceleration voltages and different discharge voltages provide a new and reliable method for the research of vacuum arc discharge plasma in China, especially for high energy plasma detection. [ABSTRACT FROM AUTHOR]

With the advancement of space exploration in China, mass spectrometers are becoming increasingly important in space missions. A miniature Mattauch-Herzog double focusing mass spectrometer was developed for mass analysis. Based on the study of the fringing field of the analyzer, the ion optical lens software SIMION8.1 was used to simulate the focusing performance of the ion beam. The 90° magnetic analyzer with asymmetric structure is adopted, which has a magnetic flux density of 0.85T. The experiment shows that the ion current is actually affected by the fringing field of electrostatic analyzer which is basically consistent with the simulation results. Besides, the performance indicators of the miniature MS are tested, the mass resolution of N 2 is 75.7, the sensitivity of N 2 is 4.13 × 105 V/Pa and the minimum detectable partial pressure of N 2 is 2.81 × 10−7Pa. • Miniaturized design of Mattauch-Herzog Mass Analyzer. • Fringing field optimization design for Mattauch-Herzog mass spectrometer. • The performance indicators research for Instrument. [ABSTRACT FROM AUTHOR]

This paper documents depositional structures and their reservoir characteristics in the Wufeng–Longmaxi shale from outcrops and cores using thin sections, X-ray powder diffraction (XRD) analysis, carbon–sulfur analyzer, helium porosimeter, decay permeameter, and focused ion beam scanning electron microscope (FIB-SEM). In the study area, clayey and silty laminae abound in the shale. Clayey laminae are rich in bedding parallel fractures, microfractures, and organic pore networks. Silty laminae are rich in isolated inorganic pores and limited amounts of bedding non-parallel fractures. Various inter-lamination of clayey and silty laminae form five depositional structure types which are closely related to the ancient hydrodynamics, paleoredox condition, and sedimentation rate and have significant impacts on shale fractures, microfractures, pore types, pore-size distribution, and porosity. For the paper lamination (PL) and grading lamination composed of siltstone and claystone (GL-SC), organic pores account for 71.6% and 61.4% of the total, and dense bedding parallel and non-parallel fractures intersect to form connective networks. In the interlaminated lamination composed of siltstone and claystone (IL), grading lamination composed of claystone (GL-C) and structureless beds (SB), organic pores merely account for 20% to 51.8% of the total and minor isolated bedding parallel fractures occur. Among five depositional structure types, the PL and GL-SC have the highest porosity, permeability, TOC content, siliceous content, organic pore proportions, and ratios of horizontal to vertical permeability, which help them become shale gas exploration and development targets. [ABSTRACT FROM AUTHOR]

• Effects of salt precipitation on the properties of the shale matrix are studied. • The 3D porous structure reconstructions of the shale matrix are conducted. • Petrophysical properties are simulated based on the reconstructed pore networks. • The methane adsorption capacities at different temperatures are predicted. • The method complements laboratory measurements or empirical rock property models. The study of salt precipitation and its effect on the reservoir physical properties and hydrocarbon adsorption capacity is important to the development of the shale reservoir with high salinity brine. In this study, a brine evaporation (static salting-out) is conducted on the shale matrix sample extracted from the Eocene Qianjiang inter-salt hypersaline lacustrine shale formation located in the Qianjiang Depression, Jianghan Basin, mid-eastern China, to prompt the salt precipitation to reach the exacerbation stage. The porous structure reconstruction technology is applied to study the effect of salt precipitation on the petrophysical properties of the shale matrix. The 3D pore networks of the shale matrix before and after brine evaporation are reconstructed based on 2D high-resolution nanoscale focused ion beam scanning electron microscopy (FIB-SEM) images. Pore-throat structural analyses and fluid flow simulations are carried out on the reconstructed pore networks to generate the physical and fluid flow properties. The density function theory (DFT) and the adsorption potential theory (APT) are combined to predict the CH 4 adsorption isotherms of shale matrix with salt precipitation at different temperatures based on the pore size distribution (PSD) obtained from the reconstructed pore networks. The results show that salt precipitation can cause a 23.0% reduction in the porosity and a 47.0% reduction in the absolute permeability of the shale matrix. Salt precipitation has a stronger effect on larger pores and throats, which will cause the destruction of the reservoir fluid flow channels and a large change in the pore size distribution. The CH 4 adsorption isotherms that are predicted based on the pore size distribution by the density function theory and the adsorption potential theory show that salt precipitation could cause a reduction of approximately 20.4% in the adsorption capacity, and the absolute adsorption capacity could be even smaller when the temperature is increased from the lab temperature to higher temperatures. [ABSTRACT FROM AUTHOR]

The Middle Permian Lucaogou Formation in the Junggar Basin, China is a typical tight oil reservoir. Thin sections, helium porosity and permeability, X-ray diffraction, X-ray computed tomography, and focused ion beam scanning electron microscopy were used to analyze 11 core samples with different oiliness from the Lucaogou Formation. Muddy siltstone, tuffaceous siltstone, dolomitic siltstone, and sandy dolarenite are the primary rock types in the Lucaogou tight oil reservoirs with different oil saturations. The dolomite content of the Lucaogou tight reservoir is positively correlated with porosity and permeability, suggesting that dolomite has an important influence on reservoir quality. Sandy dolarenite and dolomitic siltstone are characterized by a high dolomite content with the largest pore and throat radii and have a higher pore-throat network connection ratio with higher permeability and better oiliness. Thus, the quality of the Lucaogou tight reservoir is primarily controlled by the dolomite content. • Sandy dolarenite and dolomitic siltstone have the largest radius of pores and throats. • Dolomite content has the positive correlations with porosity and permeability, respectively. • The quality of Lucaogou tight reservoir is mainly controlled by dolomite content. [ABSTRACT FROM AUTHOR]

Success has been achieved in the exploration and development of marine shales of the Lower Silurian Longmaxi Formation in southern China, but there has been almost no commercial shale gas produced from the Lower Cambrian Niutitang Formation in much of the same area. Breakthroughs have been made with shale gas in the Niutitang Formation in Yichang City, south China, by the China Geological Survey (CGS). How to evaluate and exploit the Niutitang shale more quickly, accurately and efficiently remains a major question. This paper proposed that the key reservoir parameter for effective exploration and development of marine shales is based on the thermal maturity. Shale samples from Chongqing City of both the Longmaxi Formation and the Niutitang Formation were selected for the analysis of total organic carbon (TOC) content, mineral composition and equivalent vitrinite reflectance (Eq- R o), as well as for the characterization of organic matter pores (OM pores) using focused ion beam scanning electron microscopy (FIB-SEM). Selected shale samples from Yichang City of the Niutitang Formation were also studied for comparison. Results show that shale samples from Chongqing present a large number of OM pores in the Longmaxi Formation, but almost no OM pores in the Niutitang Formation. While shale samples from Yichang present a large number of OM pores in the Niutitang Formation. Commercial gas has been produced from shale reservoirs with abundant OM pores, such as the Longmaxi shale in Chongqing and the Niutitang shale in Yichang. By contrast, there is no gas production from shale reservoirs with no OM pores as is the case for the Niutitang shale in Chongqing. Thus OM pores is an indicator for the evaluation of marine shale gas potential. Because these shales have similar TOC content, mineral composition and kerogen type, but different thermal maturity, OM porosity is mainly controlled by the thermal maturity and the key geological parameter for shale reservoir potential is thus a suitable thermal maturity. Marine shale reservoirs favorable for gas production generally have an Eq- R o ranging from 2.0% to 3.0%, which is mainly controlled by ancient burial depth of reservoirs. This means exploration and development of highly over matured marine shales should be focused on less buried areas such as the edge of paleo-uplift. • OM pores are mainly controlled by thermal maturity. • Key shale reservoir parameter refers to the R o. • The most favorable shale reservoir has an Eq- R o <3.0%. • Marine shales distributed in paleo-uplift edge should be focused on. [ABSTRACT FROM AUTHOR]

• The methane in Weiyuan area comes from different hydrocarbon generation materials. • Nitrogen in Xiuwu basin is derived from atmosphere and deep crust-upper mantle. • The sealing capacity and the anticline are the reason for the high methane content. • The detachment layers, faults and volcanism are the reasons for the high nitrogen. Marine shale gas exploration in southern China has successes and failures. Under the condition of great hydrocarbon generation material basis, shale gas wells drilled from some shale gas blocks are rich in methane, while the wells in other shale gas blocks with high nitrogen and low hydrocarbon gas, which indicates that they have different accumulation mechanisms. Therefore, the study of gas composition in shale will help us to figure out the mechanism of shale gas accumulation and loss. In this paper, the Lower Cambrian shale from Wei-201 well in Upper Yangtze Weiyuan Block and Jiangye-1 well from Lower Yangtze Xiuwu Basin are selected as research object, and shale samples are used for tests and experiments including analysis of gas composition and nitrogen isotope, test of porosity and TOC content, overburden permeability test, permeability test before and after methane adsorption under different osmotic pressure, permeability test parallel and vertical to the bedding surface, FIB-SEM (Focus Ion Beam Scanning Electron Microscope) and FIB-HIM (Focused Ion Beam Helium Ion Microscope). Finally, the reasons for the difference in the gas components of the Lower Cambrian shale gas in Weiyuan Block and Xiuwu Basin are studied by means of seismic interpretation, core description and outcrop observation besides the tests and experiments. The results show that the gas components of the Lower Cambrian shale in Weiyuan Block, the Upper Yangtze, mainly consist of methane, derived from liquid hydrocarbon cracking. The sealing capacity of roof and floor, the great self-sealing of shale and the flat anticline structure contribute to the high methane content in shale gas. The Lower Cambrian shale gas in Xiuwu Basin, the Lower Yangtze, is mostly nitrogen, which is derived both from atmosphere and deep crust-upper mantle. The detachment layer at the bottom of the Lower Cambrian, the widely developed deep faults and the Jurassic volcanic activity are the reasons for the high nitrogen and low hydrocarbon of shale gas. Based on the above analysis, the patterns are summarized for shale gas accumulation in the simple anticline background and reservoir destruction in the complex syncline background. [ABSTRACT FROM AUTHOR]

• The Laozuoshan gold deposit is a reduced gold skarn deposit. • The mineralogical and compositional evolution of the sulfides constrain the physicochemical conditions of multi-stage ore-forming fluids. • Assemblage and chemical composition of sulfides reveal the gold mineralization occurred under low f O 2 and low f S 2 conditions. • The pyrrhotite replaced by marcasite and pyrite indicates the fluids changed from the weakly acidic and reducing to more neutral and weakly oxidizing. The Laozuoshan gold deposit is a large gold deposit which experienced the early hydrothermal mineralization and the late hydrothermal mineralization in Jiamusi Massif, Northeast China. The Jiamusi Massif hosts numerous gold deposits that are commonly considered as products of the metamorphic hydrothermal process during two oceanic subductions episodes. In this study, we report detailed textures observations, identify the sulfides phases by the laser Raman spectroscopy, and obtain in situ composition data with electron probe micro analysis to further understand the formation and metasomatism of multi-stage sulfides deposition in the Laozuoshan gold deposit. The paragenetic relationship between pyrite and marcasite at the nanoscale was also clarified by focused ion beam scanning electron microscopy and transmission electron microscopy. According to the observed textural relationships among ore and gangue minerals, the early hydrothermal mineralization period can be divided into three stages (Stage I to Stage III), and the late hydrothermal mineralization period into four stages (Stage IV to Stage VII). The sulfides are mainly pyrrhotite (Po-1) in Stage I , with minor chalcopyrite, arsenopyrite, and pyrite. The Ag-rich (averaging 15.44 wt%) electrum (Au-1) is hosted in arsenopyrite, which is also rich in cobalt (averaging 2.69 wt%). Pyrite (Py-2) is the main sulfide in Stage II , with minor chalcedony and calcite. The mineral stability relationships in both Stage I and Stage II confirm that there was an increase in sulfur and oxygen fugacities and a decrease in temperature. The sulfides are mainly arsenopyrite (Apy-2) in Stage III , with minor native golds and tellurbismuth. The native golds (Au-2) average 8.02 wt% silver. Arsenopyrite geothermometers indicate precipitation temperatures between 420 and 390 °C for Stage III. The sulfur and oxygen fugacities of the ore-related fluids were below the pyrite-pyrrhotite buffer during Stage III , revealing a reduced fluids system. In the late hydrothermal mineralization period, multiple magmatic activities caused multi-stage hydrothermal fluids events. In Stage VI , the pyrrhotite replaced by marcasite and pyrite through the dissolution-reprecipitation mechanism, indicating the increase in pH and oxygen fugacity of the fluids, and alteration from weakly acidic and weakly reduced conditions to neutral and weakly oxidizing conditions. The mineralogical and compositional evolution of the sulfides in the Laozuoshan gold deposit constrain the physicochemical conditions of multi-stage ore-forming fluids, which is of considerable significance in understanding the metamorphic-hydrothermal superimposed gold-bearing fluids evolved in the Jiamusi Massif. [ABSTRACT FROM AUTHOR]

The Lower Sinian Doushantuo Shale comprises the oldest Neoproterozoic shale gas reservoir in the Middle Yangtze Yichang area of China, which makes the study of their pore characteristics critical to future shale gas exploration and exploitation. Geochemical, petrographical, and pore characteristics are studied in detail, with focused ion beam scanning electron microscopy (FIB-SEM) image analysis to further support and confirm the interpretations of the nano-scale pore structure characteristics. High total organic carbon (TOC) content, high thermal maturity, and considerable brittle mineral content indicate promising potential of the Doushantuo shale. High TOC samples suggest elevated micro-meso porosity, and H2(b) and H3 type hysteresis loops indicate inkbottle, slit-like, and flake-like pore types. Significant inorganic pores are commonly observed in dolomite, pyrite, and apatite, which are characterized by diamond or irregular shapes, with pore diameters ranging from 5 nm to 1000 nm as a result of the interaction between the minerals and the acidic organic fluids. Clustering organic matter (OM) pores are observed with pore diameters ranging from 5 nm to 50 nm; they are characterized by sponge-like, elliptical, and alveolate shapes, which indicate minor organic matter (OM) pores. More substantial organic matter (OM) pores can also be found around or between the pyrite and apatite. Fractures can be clearly observed between the organic matter and minerals with lengths of approximately 10 μm and 50 nm in width, which serve as conduits for shale gas migration. The pores in the Doushantuo Shale are dominated by inorganic pores and minor organic matter (OM) pores, which are different from the pore structure of the Wufeng-Longmaxi Shales in the Sichuan Basin. The Doushantuo Shale organic matter (OM) pores are much smaller and more densely distributed than those in the Wufeng-Longmaxi Shales. The different organic matter origins of these two shales have caused distinct organic matter (OM) pore-development mechanisms. Organic matter (OM) pores and inorganic pores could contribute to the volume of the adsorbed gas and free gas, respectively, which provide significant reservoir space in the Lower Sinian Doushantuo Shale in the Yichang area. • The oldest Neoproterozoic Sinian Doushantuo shale gas reservoir isanalyzed for pore characteristics. • Multiple methods (CO2 and N2 sorption and FIB-SEM) indicate theexistence of µm-nm pore size spectrum. • Inorganic pores are dominated in this dolomite-rich Sinian shale.Pore development is different with typical shales in US. • Although this shale is not as good as the typical shales, it still beascribed as a new promising shale layer in worldwide. [ABSTRACT FROM AUTHOR]