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The Jintingling gold deposit, located in the Jiaodong peninsula, north China, contains vein-, dissemination- and stockwork-style ores hosted in the Jurassic Linglong granitic pluton. Hydrothermal activities in this deposit are divided into seven stages, including pre-ore massive K-feldspar alteration, specularite-quartz vein (V1), milky quartz ± sulfide vein (V2), quartz-pyrite vein (V3), massive quartz-sericite-pyrite alteration and gold mineralization, quartz-polymetallic sulfide vein (V4), and quartz-calcite vein (V5). Rhenium-Osmium dating was conducted on molybdenite from V2, yielding an isochron age of 123.3 ± 3.6 Ma. LA-ICP-MS zircon U-Pb dating yielded 121.5 ± 1.5 Ma (1σ, MSWD = 0.010) for a pre-ore diorite porphyrite dyke and 117.6 ± 1.2 Ma (1σ, MSWD = 0.018) for a post-ore diorite porphyry dyke, respectively. Thus, gold mineralization occurred at 122–118 Ma. Four types of fluid inclusions were identified in quartz veins, including CO2-H2O ± CH4 inclusions (type I), pure CO2 inclusions (type II), mineral-bearing inclusions (type III) and aqueous inclusions (type IV). Fluid inclusion studies demonstrate that the primary ore-forming fluids contain CO2-rich vapor (357–420 °C, 7.2–11.3 wt% NaCl equivalent) and critical fluids (368–400 °C). The two phases were likely formed by immiscibility of magmatic-hydrothermal fluids. Later on, the fluids evolved to a H2O-CO2-NaCl ± CH4 system which had temperatures of 300–364 °C and salinities of 2.0–9.7 wt% NaCl equivalent. The H2O-CO2-NaCl ± CH4 fluid system may experience phase separation, forming coexisted CO2-H2O ± CH4 inclusions (homogenized to vapor or liquid at temperature of 265–309 °C and 265–287 °C, salinities of 3.1–7.1 wt% and 4.3–7.1 wt% NaCl equivalent, respectively) and aqueous inclusions (homogenized to liquid at temperature of 255–294 °C and 3.7–7.6 wt% NaCl equivalent). Along with further evolution, the fluids shifted to a H2O-NaCl system, with temperatures of 163–258 °C and salinities of 0.5–9.0 wt% NaCl equivalent. Pyrite from the Jintingling deposit has δ34S values (5.5‰–6.1‰) similar to those of pyrite from other gold deposits in the Jiaodong district, indicating that they were related to the same hydrothermal ore-forming system. The δ13CPDB values of calcite (−4.5‰ to −5.4‰) in V5 are generally located in the range of magmatic-derived carbon. Fluids of V2, V3, V4 have δD from −64.4‰ to −87.1‰, and δ18O from 8.4‰ to 0.2‰, located in the compositional fields between magmatic water and meteoric water. Collectively, microthermonetric results and isotopic data indicate that the primary ore-forming fluids were most probably magmatic in origin, with incorporation of meteoric water in the later ore-forming stage. Precipitation of gold was triggered by cooling of fluids, fluid immiscibility and decrease of sulfur in the fluids.

An experimental system consisting of a spherical vessel with a horizontal pipe was established. By changing the pipe length, the effect that the ignition position has on methane explosion in an airtight spherical vessel with a pipe was studied, and the regularities of Pmax, (dP/dt)max and flame transmission were analyzed in detail. The results show that different ignition position leading to different propagation of flame and pressure wave. As the ignition position moved from the wall of vessel to the end of pipe, the Pmax in the apparatus first increased, then decreased when ignition occurs behind the center of vessel, and finally increased when ignition occurs behind the middle of pipe. The same trend was observed for (dP/dt)max. When ignited near the end of pipe, the Pmax and (dP/dt)max were large, and the explosion was the most dangerous. In addition, gas oscillation was observed during the explosion process in the pipe, and it was more serious when igniting at the wall of vessel, the center of vessel and the end of pipe. Furthermore, the influence that structure effect had on the gas explosion was determined. With ignition in spherical vessel, the longer the pipe is, the weaker the explosion intensity in vessel is, but the greater the explosion intensity in pipe is. With ignition in the pipe, the longer the pipe is, the greater the explosion intensities are in both the vessel and pipe. The influence that the ignition position has on a gas explosion was revealed, and the reason was analyzed. This research has great theoretical value and practical significance for preventing and controlling potentially disastrous accidents in complex units. The research results provide a theoretical foundation for antiknock and explosion venting in technical vessels and pipes.

The Xiadian gold deposit, located in the Zhaoyuan–Laizhou belt of the Jiaodong gold province, is a typical Jiaojia-type gold deposit, which is characterized by disseminated and stockwork ores enclosed by hydrothermally altered wall rocks. The exact age and the genesis of the gold deposit remain controversial. Here, we present precise in-situ monazite U-Pb dating to constrain the age of the gold mineralization, which we integrate with published geochronological work on the associated geological events to understand the genesis of the gold deposit. The Linglong granite represents the earliest magmatic event at Xiadian, and yielded a zircon LA–ICPMS U-Pb age of 159.5 ± 0.9 Ma (2σ, MSWD = 0.63). Subsequent geologic events were recorded by minor amounts of quartz–pyrite–molybdenite veins which are dated at 124.8 ± 2.1 Ma (2σ, MSWD = 0.01) by molybdenite Re–Os dating in a granitic pegmatite. The formation of such veins was close to the emplacement of adjacent Guojialing granodiorite (~130 Ma), and thus may be considered as a product of post–magmatic hydrothermal activity. It is proposed that the molybdenum–bearing hydrothermal fluids acted as a prelude to gold mineralization and participated in the formation of the latter ore fluids. Gold mineralization took place at 120.0 ± 1.4 Ma (2σ, MSWD = 0.59), determined by LA–ICPMS U–Pb dating on hydrothermal monazite from quartz–polymetallic sulfide veins. Prior to and post mineralization, voluminous hydrothermally altered porphyritic diorite and fresh quartz diorite porphyry dykes were emplaced, which yielded U–Pb ages of 121.3 ± 1.4 Ma (2σ, MSWD = 0.28) and 115.8 ± 1.9 Ma (2σ, MSWD = 0.71), respectively. Based on these geochronological data, we have established a comprehensive geochronologic framework, which suggests that the genesis of the Xiadian deposit might be related to the craton destruction and lithosphere thinning in the North China Craton.

The material source, fluid evolution and mineralizing mechanism in the Jiaodong gold province have been hotly debated for several decades. The Sizhuang gold deposit provides an excellent object for studying these issues. Gold in this deposit mainly precipitated in the quartz–Au–pyrite (stage II) and quartz–Au–polymetallic (stage III) stages. Stage III can be further subdivided into the early stage III (chalcopyrite, galena with minor amounts of electrum, pyrrhotite, pyrite, siderite and sphalerite) and the late stage III (chalcopyrite, magnetite, siderite with a little pyrrhotite). Pyrite from stage II and stage III contains consistent δ34S signatures (8.1‰–9.6‰ and 7.5‰–9.8‰, respectively) as well as trace elements (e.g. Co: 8.19 vs. 2.63 ppm, Ni: 3.54 vs. 0.74 ppm, As: 29.95 vs. 5.78 ppm, and Bi: 3.18 vs. 7.81 ppm). These consistent geochemical features combined with previous fluid inclusion and C-H-O isotope studies argue for a common source for ore-forming materials and fluids of the stage II and III at Sizhuang deposit. During the stage II and III, reduced sulfur species may have been lost from ore-forming fluids in response to pyrite precipitation (HS- being scavenged by pyrite) and fluid immiscibility (H2S entering vapor phase), which led to the total sulfur concentration (∑Stotal) decrease in the ore-forming fluids. Thermodynamic calculations at different ∑Stotal and constant pressure (2000 bar) and temperature (300 °C) in Fe-Cu-O-S-H system reveal that ∑Stotal decrease can lead to first enlargement and then shrinkage of pyrrhotite stability field with magnetite stability field being broadened to more acidic field; that sulfur species is dominated by H2S (>90 mol%) under the bornite–pyrite phase boundaries in the acidic ore-forming fluids; and that decreases in H2S concentration can efficiently cause gold precipitation by reducing gold bisulfide solubility up to 2–3 orders of magnitude while ∑Stotal just decreases ~50 times. Pyrrhotite and magnetite precipitated due to enlarged stability field during this physicochemical process, which is in line with geologic observations. It is proposed that the two-stage gold deposition by H2S loss from a single ore-forming fluid could account for gold precipitation coupling with occurrence of pyrrhotite and magnetite in the mineral assemblage at Sizhuang deposit.