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Capsule sealing has always been a key procedure in hydrothermal experiments to explore the composition and properties of geo-fluids and their influence on various geological processes. Previously reported capsule sealing techniques have primarily focused on either weld-sealing or cold-sealing methods, which have some disadvantages and limitations. Here, we report on a newly developed, simple, and effective capsule sealing technique incorporating operations from the cold-sealing and weld-sealing techniques. The technique includes three steps: first, preparing inner and outer tubes, both with a flat bottom at one end; subsequently, reverse-buckling the tubes to form a preliminary seal; and finally, welding shut the tiny slit at one end of the tubes. The new capsule sealing technique was tested in experiments for fluid inclusion synthesis. Fluid inclusions were successfully synthesized in 10 runs over a range of conditions (800~900 °C, 1~1.5 GPa). Considering the insignificant mass changes recorded and the occurrence of free fluid from the recovered capsules, the new capsule sealing technique was proven to be reliable. The simple and effective capsule sealing technique has the following advantages over the previous techniques. First, the capsule sealing technique is simple, effective, and easy to operate. The technique does not require a capsule body and lid with a complex structure, nor does it require dies or special tools. The critical weld-sealing operation is easier to complete due to the narrow and uniform slit surrounded by more metal, during which loss of volatilization is prevented by the preliminary seal. Second, the capsules can be sealed with uniform thickness and regular shape, prechecked for leakage in an oven, and annealed under high temperature and high pressure with less deformation, which could improve the success rate of experiments. Third, the theoretically required capsule materials can be changed (such as precious metals, alloys, etc.), as can the dimensions required to construct a capsule with the desired size and wall thickness (large volume or thick wall). Thus, sealed capsules are suitable not only for piston cylinders but also for multi-anvil presses and other gas-media or hydrothermal-media apparatus, such as autoclaves and pressure vessels, which means a wider range of temperatures and pressures are accessible and thus more fields of application.

In this study, petrographic, microthermometric, and synchrotron radiation X-ray fluorescence (SRXRF) analyses of fluid inclusions were conducted to shed light on the mineralization mechanism of the Dongtongyu deposit and provide some evidence of the relationship among CO2, Au, and other ore elements (e.g., Cu, Fe, Zn, and Pb) in ore-forming fluids. The ore-forming fluid is characterized as the H2O–CO2–NaCl system with medium–high temperatures and low salinities. Four structural mineralization stages are distinguished: Pyrite-quartz (Stage 1), gold-quartz-pyrite (Stage 2), gold-quartz-polymetallic sulfide (Stage 3), and quartz-calcite (Stage 4). Fluid inclusions in Stages 1–3 are dominated by the H2O–CO2 type, and most of them contain liquid H2O and liquid CO2 at room temperature. The melting temperatures (Tm-CO2 = −82.1°C to −57.5°C) of solid CO2 in Stage 1 are relatively low. The values of Tm-CO2 in Stages 2–3 are quite close, with ranges of −60.5°C to −56.5°C and −59.2°C to −58.6°C, respectively. The melting temperatures of clathrate in Stages 1–3 are −2.7°C to +7.8°C, −5.5°C to +7.8°C, and +3.7°C to +7.2°C. The homogenization temperatures of the CO2 phase in the H2O–CO2 inclusions of the three stages are measured as −7.5°C to +31.7°C, −7.5°C to +29.3°C, and 7.1°C to +24.1°C. The total homogenization temperatures in Stages 1–3 are 180°C–394°C, 202°C–305°C, and 224°C–271°C, with salinities of 4.3 wt.%–18.2 wt% NaCl, 4.3 wt.%–20.0 wt% NaCl, and 5.3 wt.%–11.0 wt% NaCl, respectively. The laser Raman spectroscopy results show that the CO2–H2O inclusions in the quartz veins contain abundant CO2 and CH4. The SRXFR results show that most of the elements, especially As, Te, and Cu, are more enriched in liquid CO2 than in liquid H2O. The elements of Au, Fe, Ni, Cu, and Pb have higher concentrations in H2O–CO2-type fluid inclusions in Stage 2 than other fluid inclusions in Stages 1–2, suggesting that gold mineralization is closely related to CO2-rich fluids. During the fluid evolution process, fluid immiscibility is an important mineralization mechanism of gold. The increase in CO2 and CH4 and the decrease in the fluid temperature might promote fluid immiscibility.

Several Late Viséan-Serpukhovian coral reefs were identified in Langping, Tianlin. To further understand of environment that was suitable for the development of reef-building communities and the construction of coral reefs in Langping, in this paper, part of the reef-building environmental and the ecological characteristics of coral reefs then were recovered by analyzing the development settings, palaeogeography, sedimentation of reefs, the response to hydrodynamic conditions of reef-building corals, effects of disturbance and non-reef-building organism on reef communities, and the influence of coral morphology on reef development. The sedimentary environment of Langping in Late Viséan-Serpukhovian is considered to be suitable for the development of benthic communities. The current appearance of reefs is determined by both coral populations ecological characteristics and reef-building environment.

High-temperature and high-pressure (HTHP) fluids are one of the most extensive participants in geological events. The representative in situ sampling of the HTHP fluids, which is an essential prerequisite for precisely characterizing the HTHP fluids (including compositional and volumetric properties), has been a vital challenge. The technique of fluid inclusion synthesis (FIS) in quartz is one of the only options. It has experienced an almost 40-year development since the standard fracture healing method was invented. Considerable advances in our understanding of physicochemical properties of geological fluids and their roles in many geological processes have been achieved by the use of the FIS techniques. A set of methodologies for fluid inclusion synthesis have been established. Great progresses have also been made, which includes the various pretreatment FIS techniques, the in situ fracturing FIS technique closely associated with the HTHP apparatus, the in situ fracturing refilled FIS technique for large fluid inclusion synthesis at controlled time under unfavorable conditions, and the novel fluid inclusion synthesis by fused silica capillary. Such great many progresses of the quartz FIS techniques have been scattered in the geochemists’ individual research work, and systematic collection and objective evaluation are missing. Consequently, we synthesize existing research, describe and identify the basic operations, discuss the methodological issues like pros and cons, and highlight the problems and prospects of the quartz FIS techniques. Furthermore, it is suggested that in situ and (or) large volume fluid inclusion synthesis will be an important future direction in view of the growing applications of the FIS techniques in combination with microanalytical techniques, especially the Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). Our review would provide technical guidance to those who wish to investigate HTHP fluids and be beneficial to the future development and applications of the FIS techniques.