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The Middle-Upper Cambrian Xixiangchi Formation in the Sichuan Basin is regarded as an important reservoir with great potential for hydrocarbon exploration. It is previously indicated that the Xixiangchi carbonates have experienced extensive dolomitization, however, the origin of dolomitizing fluids and the dolomitization mechanism still remain uncertain. In this study, a set of petrographic and geochemical examinations, including rare earth elements (REE) and isotopic (C, O, and Sr) compositions were used to trace the origins of dolomitizing fluids and associated diagenetic processes. The petrographic examination revealed three types of matrix dolomites (D1, D2, D3) and one cement saddle dolomite (SD). These phases have crystal size ranges of less than 30 μm (very fine to fine crystals, D1), 30–100 μm (fine to medium crystals, D2), 100–300 μm (medium to coarsely crystalline dolomite, D3), and 0.3–4 mm (fracture filling cements, SD), respectively. D1 is characterized by non to very weak luminescence, weakly negative Ce anomalies (Ce/Ce* = 0.84 ± 0.02), strongly negative Eu anomalies (Eu/Eu* = 0.65 ± 0.03), and high 87Sr/86Sr ratios (0.71062 ± 0.00122). In combination with δ13C (−1.5‰ ± 0.2‰) and δ18O (−9.7‰ ± 0.5‰) compositions, D1 is interpreted to be formed by penecontemporaneous dolomitization in the near-surface environment with seawater as the dolomitizing fluid. In contrast, D2 is characterized by intercrystalline pores, dirty crystal surfaces, similar δ13C (−1.4‰ ± 0.4‰) compositions but higher δ18O (−8.9‰ ± 0.7‰) compositions, and lower 87Sr/86Sr ratios (0.70992 ± 0.00035), similar Ce anomalies (Ce/Ce* = 0.87 ± 0.04) and higher Eu anomalies (Eu/Eu* = 0.85 ± 0.04). The coarser D2 is regarded to be formed by the post-penecontemporaneous seepage-reflux dolomitization or by recrystallization of D1 dolomite in a near-surface or shallow burial environment. D3 is distinguished by a cloudy core with clear rims, showing slightly higher Eu anomalies (Eu/Eu* = 0.88 ± 0.02) and similar Ce anomalies (Ce/Ce* = 0.88 ± 0.02) than those of D1 and D2. Combined with the δ18O compositions (−10.4‰ ± 0.4‰) and 87Sr/86Sr ratios (0.70989 ± 0.00048), D3 is thought to be formed by the overgrowth or recrystallization of D1 and D2 dolomites in a shallow to moderate burial environment. The fractures filling SD dolomite consists of nonplanar and much coarser crystals with undulatory extinctions and brighter red luminescence. The lower δ18O (−11.1‰ ± 0.3‰) compositions, lower negative Eu anomalies (Eu/Eu* = 0.70 ± 0.01) of SD than the matrix dolomites, and similar Ce anomalies (Ce/Ce* = 0.83 ± 0.01) are indicative of hydrothermal dolomitization, with possible fluids associated with the magma during the period of Emei taphrogenic movement. In addition, the 87Sr/86Sr ratios (0.70941 ± 0.00003) of SD suggest probable origin from the coeval seawater partially. Therefore, SD dolomite is interpreted to be formed by hydrothermal dolomitization with mixed dolomitizing fluid of seawater and hydrothermal fluids. In summary, all the matrix dolomites have almost the same ΣREE concentrations and exhibit similar near-flat REE partition patterns with weak LREE enrichments, weakly negative Ce anomalies, and negative Eu anomalies. Such characteristics of REE compositions are indicative of similar evolved dolomitizing fluid, such as seawater or seawater- derived fluids. By contrast, SD dolomites have a different REE partition pattern with left-leaning characteristics, LREE depletions, and negative Eu anomalies, thus suggesting a different dolomitizing fluid source from the matrix dolomites. In addition, the development of intercrystalline pores associated with D2 dolomite makes it more likely to be a potential reservoir, indicating that the dolomitizing history of carbonate has a strong influence on the quality of potential dolomite reservoirs. [ABSTRACT FROM AUTHOR]

The High Energy Cosmic Radiation Detection (HERD) facility will be installed on the China space station, and the critical sub-detector is the homogeneous, isotropic, and finely segmented 3D calorimeter (CALO), composed of 7500 LYSO cubes. In this paper, GEANT4 was used to simulate the optical photon propagation inside a single LYSO crystal including the Wavelength Shifting Fiber (WLSF) and photodiode (PD) and compared with experimental results. The results show that only a tiny fraction of the photons produced in the LYSO can be collected through the WLSF and PD, and the light output can be enhanced by increasing the number of rough surfaces. Additionally, the variability in WLSF and PD light output when particles entered the LYSO crystal from varying positions, known as non-uniformity, was examined through simulation. The simulated non-uniformity using thin X-ray beams is compatible within the experimental errors and can be improved at higher light output. Finally, the non-uniformity is highly sensitive to the polishing condition of the crystal surface, and better polishing conditions are preferred. [ABSTRACT FROM AUTHOR]

The high-content salt rock stratum is a highly water-soluble, corrosive, and expansive stratum, and it is extremely difficult to construct tunnels in the stratum. The China-Laos cross-border railway friendship tunnel, which traverses the high-content salt rock stratum, sustained extremely serious damage during the construction. Therefore, studying the mechanisms by which the salt rock stratum tunnels are damaged is the key to ensuring the long-term service of the tunnel. In this paper, a comprehensive method system was used, such as on-site exploration, laboratory tests, and theoretical analysis, to identify the mechanisms by which the tunnels are damaged in the high-content salt rock stratum. Research has indicated that the main component of the rocks that surround the tunnel in the salt rock stratum is rock salt (NaCl and Na2SO4). Excavation in the salt rock stratum is prone to various catastrophes, such as the precipitation of salt crystals on the lining surface, the formation of a cavity at the bottom of the tunnel, cracking of the concrete lining, bulging and cracking of the inverted arch, and serious corrosion of the steel structure. Tunnels in salt rock stratum will undergo physical erosion and physicochemical erosion of the concrete lining in a water environment, and the precipitation of salt crystals and expansion will eventually damage the lining of the structure. Also, due to the accelerated corrosion effect of water and salt on the structure of the lining, cavities occur in the lining in a short time, and this results in a decrease of the bearing capacity. [ABSTRACT FROM AUTHOR]

The Neolithic jades excavated from southern China often exhibit a serious corrosion phenomenon called "Whitening", where the jade mineral aggregates have lost compact textures and transform into loose white powders, which cause a substantial decline in mechanical strength and the jades cannot remain intact. Meanwhile, a glossy hyaline layer with a more compact and uniform structure can be observed on the surface of some whitened jades, exert great influence in the integral structure strength of the jades and can be considered as highly significant natural reinforcing materials. The recent excavation of a workshop for jade processing in Zhejiang Province provided us with a great opportunity to investigate the deteriorated jades and the taphonomic environmental conditions associated with it. In this study, analyses of morphology and compositions revealed that the glassy layer is a composition of geopolymers with silica-alumina gels as the major components, which can also be found between mineral grains of jade crystals closest to the surface. Notably, some jade fragments with a yellowish infusion were found to be mechanically stronger compared to other jades unearthed from the same context, which may be explained by the consolidate effect of iron ions in the soil. These results have demonstrated the remarkable protective properties of soil colloids, and thus proposed that by using soil colloids as templates, consolidants with the natural compatibility with jades synthesized by chemical precipitations of charged inorganic colloidal particles can be a promising solution for jade conservation. [ABSTRACT FROM AUTHOR]

[Display omitted] • With the decrease of temperature, the order degree of the system is strengthened and the fluidity is weakened. • The diffusion coefficient of the H 2 O molecule is greater than that of the n C 5 H 12 molecule by a factor of ∼2. • At the same temperature, the diffusion coefficient of the n C 24 H 50 molecule in n C 5 H 12 is greater than that in H 2 O. • At temperatures of 50–20 °C, n C 24 H 50 molecules precipitate from the oil and gather on the pipe wall surface. Wax deposition on the inner wall of oil pipes, sucker rods, oil- and gas-gathering pipelines and equipment caused by wax crystals has been a challenging problem in the petroleum industry. At present, most of the marine terrestrial transitional facies and continental shale oil and gas being explored and developed in China have high-wax-content volatile oil or condensate, and many shale oil and gas wells have been seriously blocked by wax deposition. In this work, the wax deposition behavior of the binary alkane mixture n C 5 H 12 – n C 24 H 50 at different temperatures under the condition of water wetting of a pipe wall was studied through molecular dynamics simulation. When the temperature is 130–70 °C, the wax molecules are loosely distributed without obvious aggregation, and the pipe wall is mainly occupied by water molecules, exhibiting a water-wetting state. With the decrease in temperature, the distance between n C 24 H 50 molecules decreases correspondingly, which enhances the interaction between wax molecules and increases the probability of mutual aggregation. When the temperature is 50 °C, a small amount of n C 24 H 50 molecules pass through the water molecular layer and gather on the pipe wall. When the temperature is <50 °C, the binding energy between the crystal surface of the pipe wall and the molecule n C 24 H 50 exhibits a first-order phase transition, and the molecule n C 24 H 50 can more easily bind to the pipe wall than the molecule H 2 O. When the temperature is 40–20 °C, the aggregation amount of n C 24 H 50 molecules on the pipe wall further increases, exhibiting an obvious crystallization tendency, and a small amount of n C 5 H 12 molecules begin to aggregate with n C 24 H 50 molecules through the water molecular layer on the pipe wall. At the same temperature, the diffusion speed of n C 24 H 50 molecules in n C 5 H 12 is faster than that in H 2 O. [ABSTRACT FROM AUTHOR]

High-resolution transmission electron microscopy observations of bastnäsite from the Maoniuping rare earth element (REE) deposit at Panxi, SW China, revealed the presence of nanoparticles in the surface of bastnäsite crystal. The nanoparticles are identified as the bastnäsite nanocrystals, with 5–30 nm in length, by energy-dispersive spectrometry and fast fourier transform patterns. This represents the first observation of bastnäsite nanoparticle in nature, confirming a new form of migration and precipitation of La and Ce in the hydrothermal fluids. Meanwhile, we herein reveal that random attachment of small bastnäsite nanoparticles during aggregation-based growth initially produces large bastnäsite nanoparticles, driven by the tectonic stress. Subsequent evolution of the random aggregation and orientation of large bastnäsite nanoparticles result in bastnäsite crystal formation, driven by the tectonic stress and inherent surface stress. This underlines the bastnäsite crystallization by random aggregation and the significant role of tectonic stress in forming the bastnäsite crystal in REE deposit. • Bastnäsite nanoparticles occurred in the Maoniuping REE deposit. • La and Ce can migrate and precipitate as the form of nanoparticle. • Tectonic stress has significant role in forming the bastnäsite crystal in REE deposit. [ABSTRACT FROM AUTHOR]

Recycling phosphogypsum (PG) for cemented paste backfill (CPB) has been widely used at phosphate mines in China. However, the impurities in PG prolong the setting time and reduce the uniaxial compressive strength (UCS), limiting the engineering application of PG. This paper aims to investigate the feasibility of treated PG (TPG) washed repeatedly using deionised water (DW) for CPB. A water-washing pre-experiment was first conducted to find the proportion with the least DW demand and the effects of water-washing on ordinary PG (OPG). Then, based on the PG:DW ratio obtained from the pre-experiment, the properties of the OPG-based CPB (OCPB) and TPG-based CPB (TCPB) were tested using slump tests, UCS tests, and microstructural analysis. The results show that (1) after 11 water-washings at the PG:DW ratio of 1:1.75, the pH of the supernatant (pH = 6.328) meets the requirements of Chinese standard GB 8978-1996. (2) Water-washing improves the particle gradation quality of PG and removes the soluble impurities adsorbed at the surface of PG crystals. (3) The initial slump values of TCPB are 0.19–1.15 cm higher than that of OCPB, furthermore, the diffusivity values of TCPB are better than the performance of OCPB, with 0.61–1.68 cm of superiority. (4) The UCS values of TCPB are up to 0.838 MPa, 1.953 MPa, and 2.531 MPa, after curing for 7, 14, and 28 days. These are 0.283 MPa, 0.823 MPa, and 0.881 MPa higher than that of OCPB, respectively. It can be concluded that water-washing pre-treatment greatly improves the workability and mechanical property of PG-based CPB. These results are of great value for creating a reliable and environmentally superior alternative for the recycling of PG and for safer mining production. [ABSTRACT FROM AUTHOR]