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The large Yueyang Ag-Au-Cu deposit is commonly regarded as a low-sulfidation epithermal deposit in the Zijinshan orefield, Fujian Province, southeastern China. The Ag-Ag-Cu orebodies hosted in the Zijinshan granitic batholith are mainly stratoid and lens in shape, and controlled by a series of NW-trending listric faults with shallow dip angles. Four mineralization stages are recognized on the basis of mineral assemblage, ore fabrics, and crosscutting relationships of the ore veins, namely: pre-ore (pyrite + sericite + quartz ± chlorite), main Cu (chalcopyrite + pyrite + sericite + quartz ± bornite), main Ag-Au (Ag and Au minerals + pyrite + quartz + adularia ± calcite ± apatite ± chalcopyrite ± galena ± sphalerite) and post-ore (quartz ± chalcedony ± calcite) stages. Fluid inclusions (FIs) in the deposit include aqueous liquid-rich (WL-), aqueous vapor-rich (WV-), and minor carbonic (C-) and daughter mineral-bearing (S-) type ones. WL-subtype is the main inclusion type in the Yueyang deposit, accounting for more than 90% in proportion in each stage. Minor WV-subtype inclusions occur in both the main Cu and Ag stages, while the C-type and S-type ones are only observed in the main Cu stage. Fluid inclusion and H-O isotope study indicated that the ore-forming fluid of the main Cu stage is primarily magmatic vapor, which further underwent fluid boiling and mixing with meteoric water, while the ore-forming fluid of the main Ag stage is meteoric water-dominated, and the precipitation of silver and gold was mainly resulted from fluid boiling and the precipitation of other sulfides. On the basis of the aforementioned geological, fluid inclusion and stable isotope studies, we proposed a two-stage model for the Yueyang deposit, including a magmatic vapor-related porphyry type Cu mineralization and meteoric water-related low-sulfidation epithermal Ag-Au-Cu mineralization, although the porphyry Cu mineralization is very limited in scale. The mineralization and exhumation depths of the Yueyang deposit are estimated to be 448‒527 m and 18‒97 m, respectively. By comparison with the exhumation depths of other deposits in the Zijinshan orefield, it is suggested that more epithermal deposits could be found in the southwest of the orefield due to less uplift and exhumation therein. [ABSTRACT FROM AUTHOR]

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 Luoboling Cu–Mo deposit in the Zijinshan Orefield, Fujian province, southeastern China, is a large porphyry deposit hosted by the Sifang granodiorite and the Luoboling granodiorite porphyry. The largest Cu–Mo orebody is saddle-shaped with various types of hydrothermal veinlets. Intensive hydrothermal alteration in the deposit is characterized by outward zoning from potassic, overprinted by phyllic alteration, to phyllic and alunite–dickite alteration. Based on the mineral assemblages and crosscutting relationships of veins, the ore-forming process can be divided into three stages, namely: an early-stage K-feldspar+quartz±magnetite±molybdenite veins associated with potassic alteration; a middle-stage quartz+molybdenite+chalcopyrite+pyrite veins in phyllic zone; and a late-stage quartz±gypsum veins in the phyllic and alunite–dickite alteration zones. Six molybdenite separates yield a Re−Os isochron age 104.6±1.0Ma, which is identical to the age of emplacement of the Sifang and Luoboling granodiorite porphyries. Three types of fluid inclusions (FIs) were observed at the Luoboling deposit: 1) NaCl–H2O (aqueous), 2) daughter mineral-bearing and 3) CO2–H2O fluid inclusions. FIs of the early and middle stages are predominantly vapor-rich aqueous and daughter mineral-bearing inclusions, together with minor CO2-rich and liquid-rich aqueous inclusions; whereas the late-stage minerals only contain liquid-rich aqueous inclusions. Homogenization temperatures and salinities of FIs trapped in the early-stage minerals range from 420 to 540°C and 0.4 to 62.9wt.% NaCl equiv., respectively. FIs of the middle-stage yield homogenization temperatures of 340 to 480°C and salinities of 0.5 to 56.0wt.% NaCl equiv. CO2 content and the oxygen fugacity (indicated by daughter minerals) of FIs trapped in middle-stage minerals are lower than those in the early stage. The liquid-rich aqueous inclusions of the late-stage homogenize at temperatures of 140 to 280°C, yielding salinities of 0.4 to 8.4wt.% NaCl equiv. The minimum estimated pressures of the three stages are 30–70MPa, 10–40MPa and 1–10MPa, respectively, corresponding to minimum ore-forming depths of 1–2.8km. Fluids trapped in early, middle and late stages yield δD values of −67‰ to −54‰, −54‰ to −70‰, and −62‰, and δ18O values of 5.4‰ to 6.7‰, 2.8‰ to 4.2‰, and −2.1‰, respectively. Fluid boiling, which resulted in the formation of stockworks and the precipitation of sulfides, occurred in the early and middle stages. The fluids subsequently evolved into a low temperature, low salinity system in the late stage, along with an input of meteoric water. The Luoboling porphyry Cu–Mo system was developed in a transition from continental arc to back-arc extension region, which was related to the westward subduction of the paleo-Pacific plate beneath the Huanan Orogen. [ABSTRACT FROM AUTHOR]

The Eastern Qinling, Central China, containing more than 20 Mesozoic porphyry±skarn systems, is the most important Mo province in the world. The Shangfanggou giant Mo deposit, Luanchuan County, Henan Province, is a porphyry-skarn system hosted in a lithologic association comprising carbonaceous sandstone, shale, carbonate and chert within the Neoproterozoic Luanchuan Group. Mo ores are mainly altered porphyry, skarn and hornfels, with minor altered gabbro. The mineralization process includes four stages, potassic alteration of the porphyry and skarnization of dolomite marble in stage 1, stockworks of quartz+molybdenite±sulfide (stage 2), pyrite+quartz±sulfides (stage 3), and carbonate±quartz±fluorite (stage 4), respectively. Mo mineralization was generally associated with strong silicification and/or phyllic alteration. The fluid inclusions in minerals include three compositional types, i.e., CO2-bearing (C-type), aqueous (W-type) and daughter mineral-bearing (S-type). Minerals formed in stages 1 to 3 contain all the three types of FIs, but the stage 4 minerals only contain the W-type FIs. Oxides and Cu-phosphate are recognized as daughter minerals in S-type inclusions in minerals of stage 1, whereas the daughter sulfide and reducing gases such as CO, CH4, H2S and C2H6 can be observed in quartz of stages 2 and 3, suggesting that the ore-forming fluids were initially oxidizing and then evolved to reducing. Boiling fluid inclusion assemblages can be observed in minerals formed in stage 2 or earlier, but not in stage 3 or later. Fluid boiling caused CO2 escape, oxygen fugacity decrease and rapid precipitation of ore minerals, and was a key factor causing Mo-mineralization at Shangfanggou. Data and interpretations presented in this contribution show that the fluids forming the Shangfanggou Mo deposit evolved from CO2-rich, high-salinity hypothermal, to CO2-poor, low-salinity epithermal (low-T). The Mo mineralization at the Shangfanggou deposit mainly occurred at depth of 6.6–7.0km, deeper than the majority of porphyry systems in volcanic arcs, which resulted from a CO2-rich magma–fluid system originating from partial melting of thickened lower crust. The Shangfanggou mineral system developed during 158–134Ma when the Yangtze–North China continental collision began to evolve from compression to extension. Magmatic hydrothermal deposits developed in a continental collision regime are generally formed by CO2-rich, high-salinity fluids. [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]

[Display omitted] • Five ore-forming stages are recognized in the Yechangping porphyry-type orebodies. • Fluid characteristics suggest that Yechangping is a Dabie-type porphyry Mo deposit. • The process of fluid immiscibility, boiling, and mixing cause the mineralization. • Magmatic-hydrothermal system of Yechangping deposit extends to depths of 10 km. Dabie-type porphyry Mo deposits have recently emerged as a distinct subtype of porphyry Mo deposits, but questions remain about the magmatic-hydrothermal fluid evolution in the formation of this type of deposit. Here, well-developed fluid inclusions in quartz phenocrysts, unidirectional solidification textures (UST), and quartz veins in the Yechangping porphyry Mo-W deposit, Qinling Orogen, completely record the magmatic-hydrothermal mineralization process. The characteristics and evolution of the ore-forming fluid in this deposit are investigated through petrography, microthermometry, and laser Raman spectroscopy analysis of fluid inclusions at different stages in order to improve our understanding of the fluid evolution in the genesis of Dabie-type porphyry Mo deposit. The mineralization process in the porphyry-type orebody can be divided into three periods and five stages: (1) magmatic period, including quartz phenocrysts (stage 1); (2) magmatic-hydrothermal transition period, including UST (stage 2); (3) hydrothermal period, including quartz ± K-feldspar veins (stage 3), quartz-molybdenite veins (stage 4), and calcite ± quartz veins (stage 5), where stage 4 is the main ore-forming stage. The fluid inclusions in quartz and calcite can be recognized as pure CO 2 (PC type), CO 2 -H 2 O (C type), daughter minerals-bearing (S type), and H 2 O (WV type and WL type) inclusions. Ore-forming fluid is initially high temperature, high salinity, and CO 2 -rich, belonging to the H 2 O-CO 2 -NaCl (±KCl) system suggested by the fluid inclusions identified in UST. The estimated lithostatic pressures of stage 1 range from 284–362 MPa, corresponding to depths of 10.3 to 13.2 km, which are consistent with the formation depth of the underlying magma chamber. The presence of UST in stage 2 indicates that the magma was saturated with fluid. Due to the fluctuating pressure (123–260 MPa) in UST of stage 2, fluid immiscibility happened soon after the fluid exsolution and is inferred to occur between the CO 2 -rich and aqueous phases. Then, the fluid boiling and mixing occurred in stages 3 and 4, respectively. The estimated pressures of stage 4, which represent the main mineralization stage, range from 45–175 MPa, corresponding to depths of 4.6–6.4 km. The immiscibility of CO 2, along with the fluid mixing-induced cooling and dilution, caused an increase in p H and a decrease in oxygen fugacity, which serves as a crucial mechanism for Mo mineralization at the Yechangping deposit. Stage 5 is characterized by low temperature (185–309 °C) and low salinity (2.9–8.7 wt% NaCl equiv.). The primary high temperature, high salinity, CO 2 -rich fluids, and relatively deep ore-forming depth suggest that the Yechangping deposit is a typical example of a Dabie-type porphyry deposit. The characteristics of fluids and the variation in estimated depth at each stage record the evolutionary process of a magmatic-hydrothermal system extending to depths of nearly 10 km in the Yechangping deposit. [ABSTRACT FROM AUTHOR]

The Keketale Pb–Zn deposit is located in the Devonian volcanic-sedimentary Maizi basin of the Altay orogenic belt. The mineralization at Keketale is hosted in marbles and deformed volcanic tuffs and biotite–garnet–chlorite schists, folded into a series of overturned synclines formed in multiple deformation events. Keketale contains economic amounts of Pb (0.89Mt @ 1.51wt.%), Zn (1.94Mt @ 3.16wt.%) and Ag (650t @ 40g/t). Detailed petrographic studies have defined two main generations of sulfide development. The banded pyrite of the early Stage A is commonly stratiform, with minor galena, sphalerite and chalcopyrite. Stage B is characterized by a large amount of polymetallic sulfides including pyrrhotite, chalcopyrite, sphalerite and galena, with minor pyrite hosted in quartz veins. Three types of fluid inclusions (FIs), including mixed carbonic-aqueous (C-type), pure carbonic (PC-type) and aqueous (W-type), have been recognized in quartz of stage B. The C-type FIs have homogenization temperatures of 150–326°C and salinities of 0.2–16.6wt.% NaCl equivalent. The PC-type FIs are dominated by CO2 with minor CH4 and N2 and have initial ice-melting temperatures of −57.5 to −56.7°C, CO2 homogenization temperatures of 11–14.1°C. The W-type primary FIs were completely homogenized at temperatures of 124–359°C with salinities of 5.0–14.6wt.% NaCl equivalent. Such CO2-rich fluid inclusions are consistent with those discovered in orogenic-type deposits in the Altay area and elsewhere. Muscovite separates from the polymetallic quartz veinlets of stage B yield a well-defined 40Ar/39Ar isotopic plateau age of 259.33±2.56Ma, with an isochron age of 259.62±2.65Ma. This age is coeval with the closure of the Paleo-Asia Ocean and reactivation of the Ertix Fault system. LA-ICP-MS analyses of two generations of pyrite indicate that the banded pyrite of stage A is relatively depleted in metallic elements and contains low contents of Cu (0.39ppm), Ag (0.20ppm), Au (below the detection limits), Pb (17.43ppm) and Zn (14.38ppm); whereas the pyrite in quartz–polymetallic sulfide veinlets of the stage B is relatively rich in metallic elements, e.g., Cu (2.56ppm), Ag (3.07ppm), Au (0.01ppm), Pb (1047ppm) and Zn (1136ppm). The trace amounts of Cu, Pb, Zn, Au and Ag are interpreted to have been initially locked in the lattice of type-A pyrite, and then liberated and precipitated as micromineral inclusions with type-B pyrite during subsequent metamorphism and deformation. Two key factors are considered vital to the formation of economic ores of the Keketale Pb–Zn deposit, namely the original Devonian banded pyrite formed in a VMS system and subsequent Permian deformation and metamorphic processes that liberated Cu, Pb, Zn, Au and Ag from the lattice of type-A pyrite to form galena, sphalerite and chalcopyrite with minor muscovite in quartz veinlets. The model provides a new interpretation of VMS Pb–Zn deposit occurring in back-arc basin environments followed by collision, and new insights into the unique regional Fe–Cu–Pb–Zn–Au mineralization in the Altay orogenic belt. [ABSTRACT FROM AUTHOR]

Abstract: The Wulasigou Cu deposit occurs as veins controlled by a NW-trending structure in a Devonian volcano-sedimentary basin of the Altay orogenic belt, Xinjiang, China. Igneous and sedimentary rocks exposed in the area have undergone greenschist-facies metamorphism. The ore-forming process can be divided into early, middle, and late stages, represented by, respectively, pyrite-quartz, polymetallic sulfide-quartz, and carbonate–quartz veins, veinlets, and/or replacement bodies. The early veins were deformed and brecciated during a compressional or transpressional event. The middle-stage veinlets filled fractures in the early-stage vein and alteration assemblages, and are undeformed, suggesting a tensional shear setting. The late-stage veinlets are mainly open-space fissure fillings that cut veins and replacement bodies formed in the earlier stages. Four types of fluid inclusions (FIs), including aqueous (W-type), mixed carbonic-aqueous (M-type), purely carbonic (C-type) and daughter mineral-bearing (S-type), have been identified in copper-related quartz and calcite from the Wulasigou deposit. The early-stage quartz contains M- and W-type primary FIs that completely homogenized at temperatures of 322–412°C with low salinities of 0.9–6.5wt.% NaCl equiv. In contrast, the late-stage quartz or calcite contains only the W-type FIs with homogenization temperatures of 101–234°C, and salinities of 0.9–2.9wt.% NaCl equiv. This indicates that the metallogenic system evolved from CO2-rich, metamorphic to CO2-poor, through input of meteoric fluids. All four types of FIs can only be observed in the middle-stage minerals, where they show evidence of vein formation during an episode of fluid immiscibility. These FIs homogenized at temperatures ranging mainly from 230 to 347°C, with salinities clustering 2.7–10.2wt.% NaCl equiv for the W-, M- and C-types, and 34.7–38.2wt.% NaCl equiv for the S-type, respectively. The metal precipitation resulted from a decrease in copper solubility during the fluid immiscibility episode. The estimated trapping pressures for the middle-stage fluids are 1.55–3.55kbar, suggesting an alternating lithostatic-hydrostatic fluid-system, controlled by fault-valve activity at a depth of 13–15.5km. Muscovite separates from the middle-stage polymetallic-quartz veinlets yield a well-defined 40Ar/39Ar isotopic plateau age of 219.41±2.10Ma, and an 39Ar/36Ar - 40Ar/36Ar isochron age of 219.73±2.17Ma. This age postdates the final Paleo-Asia Ocean closure (at ca. 250Ma) by about 30Ma, and indicates that the Cu mineralization at Wulasigou has occurred in the Triassic continental collision setting. Hence, the Wulasigou Cu deposit may be the first example of orogenic lode Cu deposits formed in accretionary orogeny or continental collision. [Copyright &y& Elsevier]

Abstract: The Yuchiling Mo deposit, East Qinling, China, belongs to a typical porphyry Mo system associated with high-K calc-alkaline intrusions. The pure CO2 (PC), CO2-bearing (C), aqueous H2O-NaCl (W), and daughter mineral-bearing (S) fluid inclusions were observed in the hydrothermal quartz. Based on field investigations, petrographic, microthermometric and LA-ICP-MS studies of fluid inclusions, we develop a five-stage fluid evolution model to understand the ore-forming processes of the Yuchiling deposit. The earliest barren quartz±potassic feldspar veins, developed in intensively potassic alteration, were crystallized from carbonic-dominant fluids at high temperature (>416°C) and high pressure (>133MPa). Following the barren quartz±potassic feldspar veins are quartz-pyrite veins occasionally containing minor K-feldspar and molybdenite, which were formed by immiscible fluids at pressures of 47–159MPa and temperatures of 360–400°C. The fluids were characterized by high CO2 contents (approximately 8mol%) and variable salinities, as well as the highest Mo contents that resulted in the development of quartz-molybdenite veins. The quartz-molybdenite veins, accounting for >90% Mo in the orebody, were also formed by immiscible fluids with lower salinity and lower CO2 content of 7mol%, at temperatures of 340–380°C and pressures of 39–137MPa, as constrained by fluid inclusion assemblages. After the main Mo-mineralization, the uneconomic Cu-Pb-Zn mineralization occurred, as represented by quartz-polymetallic sulfides veins consisting of pyrite, molybdenite, chalcopyrite, digenite, galena, sphalerite and quartz. The quartz-polymetallic sulfide veins were formed by fluids containing 5mol% CO2, with minimum pressures of 32–110MPa and temperatures of 260–300°C. Finally, the fluids became dilute (5wt.% NaCl equiv) and CO2-poor, which caused the formation of late barren quartz±carbonate±fluorite veins at 140–180°C and 18–82MPa. It is clear that the fluids became more dilute, CO2-poor, and less fertile, with decreasing temperature and pressure from quartz-pyrite to late barren veins. Molybdenite and other sulfides can only be observed in the middle three stages, i.e., quartz-pyrite, quartz-molybdenite and quartz-polymetallic sulfide veins. These three kinds of veins are generally hosted in potassic altered rocks with remarkable K-feldspathization, but always partly overprinted by phyllic alteration. The traditional porphyry-style potassic–phyllic–propylitic alteration zoning is not conspicuous at Yuchiling, which may be related to, and characteristic of, the CO2-rich fluids derived from the magmas generated in intercontinental collision orogens. Among the fluid inclusions at Yuchiling, only the C-type contains maximum detectable Mo that gradationally decreases from 73ppm in quartz-pyrite veins, through 19ppm in quartz-molybdenite veins, and to 13ppm in quartz-polymetallic sulfide veins, coinciding well with the decreasing CO2 contents from 8mol%, through 7mol%, to 5mol%, respectively. Hence it is suggested that decreasing CO2 possibly results in decreasing Mo concentration in the fluids, as well as the precipitation of molybdenite from the fluids. This direct relationship might be a common characteristic for other porphyry Mo systems in the world. The Yuchiling Mo deposit represents a new type Mo mineralization, with features of collision-related setting, high-K calc-alkaline intrusion, CO2-rich fluid, and unique wall-rock alterations characterized by strong K-feldspathization and fluoritization. [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]

Graphical abstract Highlights • The Kuruer Cu-Au deposit is hosted by volcanic and volcano-sedimentary rocks. • It displays porphyry-type hydrothermal alteration and mineralization. • The ore-forming fluids are magmatic water mixed with meteoric water. • The deposit is a transition from high sulfidation epithermal to porphyry system. Abstract Western Tianshan along the southwestern margin of the Central Asian Orogenic Belt is well-endowed with epithermal and porphyry Au deposits. The Kuruer Cu-Au deposit, recently discovered in the eastern part of Western Tianshan, was considered as a high sulfidation epithermal deposit. However, our geological, fluid inclusion and stable isotopic studies indicate that it actually formed in transition from high sulfidation to porphyry. The host rocks include the Dahalajunshan Formation volcanic and volcano-sedimentary rocks such as andesite, rhyolite, ignimbrite and tuff. Cu-Au mineralization mainly occurs as quartz-dominated stockworks or disseminations, with abundant pyrite and chalcopyrite and minor galena and sphalerite. Gold occurs as invisible phase in sulfides. Hydrothermal alteration includes a silicic core, surrounded by phyllic alteration and peripheral propylitic alteration. Based on field observations, paragenetic and crosscutting relationship, the mineralization process can be roughly divided into three stages. The early stage is characterized by the assemblage of quartz + pyrite + chalcopyrite while the middle stage contains quartz and chalcopyrite at absence of pyrite. The late stage is characterized by calcite ± quartz ± chlorite ± chalcopyrite veins. Fluid inclusions at the early stage are mainly liquid-rich aqueous and CO 2 -rich inclusions and minor vapor-rich aqueous and solid-bearing inclusions. Their homogenization temperatures and salinities can be up to 420 °C and 39 wt.% NaCl eq., respectively, indicating that the initial ore-forming fluids are high temperature, high salinity, H 2 O-CO 2 -NaCl systems. In the middle stage, there are only liquid-rich aqueous inclusions, with homogenization temperatures and salinities of 130–190 °C and 0.18 to 10.7 wt.% NaCl eq., respectively. Liquid-rich aqueous inclusions in the late stage display much lower temperatures and salinities, ranging from 110 to 130 °C and 0.18–2.7 wt.% NaCl eq., respectively. Obtained δD H2O and δ18O H2O values of quartz from the middle stage are −98 to −107‰ and −2.1 to 0.74‰, respectively. The δ34S values of 9 chalcopyrite samples range from −10.2 to −2.4‰, with an average of −4.1‰. We conclude that the initial ore-forming fluids are magmatic in origin, and further cooled and diluted by mixing with meteoric water. Intensive fluid boiling and mixing facilitated hydrothermal alteration and mineralization. [ABSTRACT FROM AUTHOR]