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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]

Abstract: The Qiyugou gold deposits, Henan Province, are hosted in breccia pipes within the Xiong''er terrane (Qinling Orogen), on the southern margin of the North China Craton. In these deposits three paragenetic assemblages have been recognized: an early K-feldspar–epidote–quartz–pyrite; a middle quartz-polymetallic sulfide; and a late quartz–carbonate±adularia. In this paper we review and interpret fluid inclusion and stable and radiogenic isotopic data of host rocks and ores. Fluid inclusions in quartz and calcite include water-rich, CO2-rich, and daughter crystal-bearing. The CO2-rich and daughter mineral-bearing fluid inclusions are common in the early-stage quartz and absent in the late-stage quartz and calcite which only contain water-rich fluid inclusions. Accordingly, the early-stage ore-fluids are magmatic in origin and characterized by high-temperature (>350 °C), high-salinity (>30 wt.% NaCl equiv.), and are CO2-rich. Fluid-boiling in the middle ore stage resulted in CO2-release, decreasing oxygen fugacity and rapid precipitation of ore materials. The late stage fluids, have low-temperature, low-salinity, are CO2-poor and lack daughter minerals. These fluids are probably sourced from meteoric water. H–O–C isotope systematics confirm that, the ore–fluid system evolved from magmatic to meteoric. The carbon and lead isotope ratios indicate that the Meso-Neoproterozoic sequence south of the Xiong''er terrane was the likely source of the ore-forming materials. The Qiyugou breccia-pipes and their associated gold ores were emplaced during an extensional regime following a transition from collision to rifting tectonics, linked to collision and subduction of the Yangtze plate beneath the North China Craton. Geochronological studies show that Mesozoic magmatism in the region occurred between the Triassic and Cretaceous. The Triassic to Jurassic magmas were mostly derived from partial melting of ancient crust, whereas the Cretaceous magmas show juvenile signatures, indicating mantle-derived components. Processes of fragmentation of lithospheric roots, crustal and lithospheric thinning, extension and rifting were probably associated with the subducting Pacific (Izanagi) plate. These crust–mantle geodynamic processes were responsible for the development of anorogenic granitic melts that interacted with the Meso-Neoproterozoic volatile-rich sedimentary successions, producing a flow of gas-rich hydrothermal fluids that resulted in the emplacement of the Qiyugou auriferous breccia pipes. We conclude that the Qiyugou gold deposits are intrusion-related explosive breccia pipe-type that evolved from hypothermal through mesothermal to epithermal. [Copyright &y& Elsevier]

Abstract: The Nannihu Mo–W deposit, located in the Henan Province of China, is a giant porphyry deposit formed in the Qinling Orogen during the Jurassic continental collision between the North China and Yangtze Cratons. Mo–W mineralization is associated with the Nannihu porphyritic monzogranite, occurring as numerous stockwork veinlets in the altered wallrocks and the causative porphyry. Both the porphyry stock and wallrocks underwent intense hydrothermal alteration, ranging outwardly from potassic to phyllic alteration, and to carbonation zones with increasing distance from the intrusion. The hydrothermal ore-forming process can be divided into four stages characterized by veinlets, from early to late: (1) quartz+potassic feldspar±molybdenite±pyrite; (2) quartz+molybdenite veins containing minor pyrite and chalcopyrite; (3) quartz+polymetal sulfide; and (4) quartz+carbonate+fluorite. Most of the ores are formed during stages 2 and 3. Four types of fluid inclusions (FIs) are distinguished in this study based on petrographic and microthermometric criteria, i.e. pure CO2, NaCl–H2O, CO2–H2O and daughter mineral-bearing fluid inclusions. All of the four types of FIs can be observed in the hydrothermal quartz formed in stages 1, 2 and 3; while the stage 4 minerals contain only NaCl–H2O fluid inclusions. Fluid inclusions of stage 1 are mainly homogenized between 350 and 460°C, with salinities ranging from 5.7 to 17.9wt.% NaCl equiv. The stage 2 FIs yield homogeneous temperatures of 300–380°C and salinities of 3.5–16.9wt.% NaCl equiv. FIs of stage 3 are homogenized between 250 and 370°C, with salinities of 1.8–14.3 and 28.6–39.1wt.% NaCl equiv. FIs of stage 4 are homogenized at temperatures of 115 to 265°C, yielding salinities of 0.5 to 1.2wt.% NaCl equiv. Daughter minerals, such as halite, chalcopyrite and some unknown minerals, are frequently present in stage 3 FIs, which probably represent a reducing and oversaturated fluid-system resulting from fluid-boiling. The daughter mineral-bearing FIs coexist with vapor- and liquid-rich NaCl–H2O FIs that have contrasting salinities. These FIs are homogenized in divergent ways at similar temperatures, suggesting that fluid boiling took place in stages 2 and 3. The estimated pressures range from 70 to 270MPa in stage 1, through 30–150MPa in stage 2, to 30–85MPa in stage 3, corresponding to a depth of no less than 3km. In other words, the ore-forming fluids are characterized by high temperature, high salinity, high fO2 and high CO2 content; and fluid-boiling resulted in CO2 release, fO2 decrease and ore mineral precipitation. We suggest that the CO2-rich fluid is a distinctive feature of porphyry systems developed in continental collision setting, in transitional compressional to extensional regime, contrasting to the CO2-poor NaCl–H2O fluids observed in volcanic arcs. [Copyright &y& Elsevier]