The Xiaoqinling gold field in central China is the second largest orogenic Au province in China. In the Xiaoqinling area, the Dahu Au–Mo deposit is typical because it is one of the five early‐discovered large gold deposits, but also unique for its northernmost location and Mo‐association. This study shows that the deposit is a fault‐controlled lode system formed by a three‐stage hydrothermal process. The early‐stage pyrite–quartz veins are structurally deformed and broken. The middle‐stage molybdenite–pyrite–quartz stockworks (mostly coaxial) infill the cracks of the early‐stage veins and minerals. The late‐stage open‐space filling quartz–carbonate veinlets show a comb‐like texture. The early‐ and late‐stage quartz only contains the fluid inclusions of CO₂–H₂O and H₂O–NaCl types, respectively, suggesting an evolution from CO₂‐rich to CO₂‐poor; whereas the middle‐stage quartz contains fluid inclusions of CO₂–H₂O, H₂O–NaCl, pure CO₂ and daughter mineral‐bearing types, supporting a boiling fluid system, because they can occur in a microscopic domain of a single crystal, homogenize divergently at similar temperatures clustering between 293 and 410 °C, and show contrasting salinities of 26.3 wt.% NaCl equiv. The inclusions in early‐stage quartz are homogenized at 402–503 °C, with salinities of 4.5–10.4 wt.% NaCl equiv.; and those in late‐stage quartz are homogenized at temperatures of 11 km and ~7.8 km, respectively. Hydrogen and oxygen isotope signatures indicate that the fluids originated from metamorphic devolatilization in the early stage, then mixed with meteoric water in the middle stage, and finally replaced by meteoric water in the late stage. Hence, it is concluded, that metal precipitation at the Dahu deposit was mainly caused by fluid boiling, followed by fluid mixing, along with a trans‐compressing at the transitional zone from a magmatic arc to back‐arc basin, which resulted from the Triassic northward subduction of the Mian‐Lue oceanic slab. © 2014 The Authors. Geological Journal published by John Wiley & Sons Ltd.

Natural gas of organic origin is primarily biogenic or thermogenic; however, the formation of natural gas is occasionally attributed to hydrothermal activity. The Precambrian dolomite reservoir of the Anyue gas field is divided into three stages. Dolomite-quartz veins were precipitated after two earlier stages of dolomite deposition. Fluid inclusions in the dolomite and quartz are divided into pure methane (P-type), methane-bearing (M-type), aqueous (W-type), and solid bitumen-bearing (S-type) inclusions. The W-type inclusions within the quartz and buried dolomite homogenized between 107 °C and 223 °C. Furthermore, the trapping temperatures and pressures of the fluid (249 °C to 319 °C and 1619 bar to 2300 bar, respectively) are obtained from the intersections of the isochores of the P-type and the coeval W-type inclusions in the quartz. However, the burial history of the reservoir indicates that the maximum burial temperature did not exceed 230 °C. Thus, the generation of the natural gas was not caused solely by the burial of the dolomite reservoir. The results are also supported by the presence of paragenetic pyrobitumen and MVT lead-zinc ore. A coupled system of occasional invasion by hydrothermal fluids and burial of the reservoir may represent a new genetic model for natural gas accumulation in this gas field.