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The Qiangma gold deposit is hosted in the > 1.9 Ga Taihua Supergroup metamorphic rocks in the Xiaoqinling terrane, Qinling Orogen, on the southern margin of the North China Craton. The mineralization can be divided as follows: quartz-pyrite veins early, quartz-polymetallic sulfide veinlets middle, and carbonate-quartz veinlets late stages, with gold being mainly introduced in the middle stage. Three types of fluid inclusions were identified based on petrography and laser Raman spectroscopy, i.e., pure carbonic, carbonic-aqueous (CO 2 –H 2 O) and aqueous inclusions. The early-stage quartz contains pure carbonic and CO 2 –H 2 O inclusions with salinities up to 12.7 wt.% NaCl equiv., bulk densities of 0.67 to 0.86 g/cm 3 , and homogenization temperatures of 280−365 °C. The early-stage is related to H 2 O–CO 2 ± N 2 ± CH 4 fluids with isotopic signatures consistent with a metamorphic origin (δ 18 O water = 3.1 to 5.2‰, δD = − 37 to − 73‰). The middle-stage quartz contains all three types of fluid inclusions, of which the CO 2 –H 2 O and aqueous inclusions yield homogenization temperatures of 249−346 °C and 230−345 °C, respectively. The CO 2 –H 2 O inclusions have salinities up to 10.9 wt.% NaCl equiv. and bulk densities of 0.70 to 0.98 g/cm 3 , with vapor bubbles composed of CO 2 and N 2 . The isotopic ratios (δ 18 O water = 2.2 to 3.6‰, δD = − 47 to − 79‰) suggest that the middle-stage fluids were mixed by metamorphic and meteoric fluids. In the late-stage quartz only the aqueous inclusions are observed, which have low salinities (0.9−9.9 wt.% NaCl equiv.) and low homogenization temperatures (145−223 °C). The isotopic composition (δ 18 O water = − 1.9 to 0.5‰, δD = − 55 to − 66‰) indicates the late-stage fluids were mainly meteoric water. Trapping pressures estimated from CO 2 –H 2 O inclusions are 100−285 MPa for the middle stage, suggesting that gold mineralization mainly occurred at depths of 10 km. Fluid boiling and mixing caused rapid precipitation of sulfides and native Au. Through boiling and inflow of meteoric water, the ore-forming fluid system evolved from CO 2 -rich to CO 2 -poor in composition, and from metamorphic to meteoric, as indicated by decreasing δ 18 O water values from early to late. The carbon, sulfur and lead isotope compositions suggest the hostrocks within the Taihua Supergroup to be a significant source of ore metals. Integrating the data obtained from the studies including regional geology, ore geology, and fluid inclusion and C–H–O–S–Pb isotope geochemistry, we conclude that the Qiangma gold deposit was an orogenic-type system formed in the tectonic transition from compression to extension during the Jurassic−Early Cretaceous continental collision between the North China and Yangtze cratons. [ABSTRACT FROM AUTHOR]

The Donggou Mo deposit in the eastern Qinling area, China, is a giant porphyry system discovered based on a targeting concept by using the tectonic model for collisional orogeny, metallogeny and fluid flow (CMF model). Mo mineralization is associated with the Donggou aluminous A-type granite porphyry and was formed during the Early Cretaceous in a tectonic regime of continental extension. The orebodies mainly occur as numerous veinlets in the host-rocks. Hydrothermal ore-forming processes include at least three stages, characterized by veinlets of (1) quartz + K-feldspar + minor molybdenite, (2) quartz + molybdenite ± beryl and (3) quartz + carbonate + fluorite. Three types of fluid inclusions (FIs) are distinguished in quartz and beryl in stages 1 and 2, i.e., aqueous (W-type), carbonic–aqueous (C-type) and solid-bearing (S-type), with only aqueous FIs observed in stage 3 minerals. S-type FIs contain variable daughter minerals including halite, chalcopyrite, calcite and an unidentified transparent crystal, but only halite can dissolve during heating. Halite-bearing S-type FIs are mainly homogenized by halite dissolution at 182–416 °C, corresponding to salinities of 30.9–49.2 wt.% NaCl equiv.; minor halite-bearing S-type FIs are homogenized to liquid at 190–360 °C via vapor disappearance, with salinities of 29.1–36.2 wt.% NaCl equiv. Other FIs in minerals of stages 1, 2 and 3 are homogenized at temperatures of 341–550 °C, 220–440 °C and 125–225 °C, with salinities of 8.0–18.3, 5.3–16.8 and 0.5–7.3 wt.% NaCl equiv., respectively. The estimated minimum trapping pressures are up to 141 MPa in stage 1 and up to 81 MPa in stage 2, respectively, corresponding to an initial mineralization depth of no less than 5 km. The quartz in veinlets yields δ 18 O values of 8.5–10.0‰, corresponding to δ 18 O H 2 O values of − 2.9 to 5.9‰, while the δD H 2 O values of fluid inclusions range from − 59 to − 82‰. These data suggest that the ore fluids forming the Donggou deposit changed from high-temperature, high-salinity, CO 2 -rich magmatic to low-temperature, low-salinity and CO 2 -poor meteoritic fluids via boiling and mixing, resembling those of other magmatic–hydrothermal systems in Qinling Orogen and Dabie Shan. This supports the notion that the porphyry systems generated in a post-collisional tectonic setting were initially CO 2 -rich, as indicated by abundant C-type and CO 2 -bearing S-type fluid inclusions. [ABSTRACT FROM AUTHOR]

The Xunyang Hg-Sb orefield, Shaanxi Province, containing two large (Gongguan and Qingtonggou) and tens of small to medium Hg-Sb deposits, is located in the southern Qinling Orogen. Ore bodies of the deposits are hosted in Devonian dolomite and controlled by a fault system. Ores are mainly present as massive veins, disseminations, breccias and fine veinlets, with cinnabar (Hg) and stibnite (Sb) being the dominant ore minerals. Gangue minerals include quartz, calcite and dolomite. Hydrothermal minerals (quartz and calcite) only contain aqueous fluid inclusions with low homogenization temperature (135-274 °C) and salinity (1.23-12.3 wt.% NaCl equiv.), supporting an epizonogenic hydrothermal origin. The carbon, oxygen and hydrogen isotope data indicate that the ore-forming fluids were mainly sourced from epizonogenic to metamorphic devolatilization of the Sinian−Triassic strata that possibly underthrusted beneath the orefield, with inflow of the circulating meteoric water. Sulphur isotope ratios of stibnite and cinnabar range from 2‰ to 12‰, suggesting a contribution from sedimentary sulphate or sulphate-bearing fluids potted in strata, which is coincident with the δ34S values (3.4-8.6‰) of diagenetic pyrite in the strata. The conclusion drawn from sulphur isotopes is fully supported by the Pb isotope signatures. In addition, the 87Sr/86Sr ratios gradationally increase from ore-hosting dolostones, through ore-barren calcite or low-grade ores, to high-grade ores, indicating that a portion of the fluids originated from a source with higher 87Sr/86Sr values than the host-rocks, which is possibly composed of the Neoproterozoic−Lower Palaeozoic basement of the Xunyang Basin. Integrating the data from ore geology, fluid inclusion microthermometry and stable, radioactive isotope geochemistry, it can be concluded that the deposits in the Xunyang Hg-Sb orefield were formed by epizonogenic hydrothermal fluids mainly sourced from the strata via structural deformation during the North China−Yangtze continental collision. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]