Daughter Mineral-bearing Inclusions Research Articles

Characteristics and Geological Significance of CO2-Rich Fluid Inclusions in Dakalasu No. 1 Pegmatite Dyke, Altay

The fluids in of pegmatite rare metal deposits are generally rich in rare metal elements and volatiles (B, P, F, H2O, CO2, etc.), and they have a high capacity for dissolving and migrating rare metals. The Dakalasu No. 1 rare metal pegmatite vein is located in northwest China’s Altay orogenic belt. Previous studies have indicated that it is a small- to medium-sized beryllium-niobium-tantalum deposit. It showed significant mineral assemblage zonations from the rim to the core, and the mineralizing fluids define a volatile-rich NaCl-H2O-CO2 ± CH4 system. In this contribution, beryl and quartz, which are widely developed in each mineral association and textural zone, were selected for fluid inclusion research through detailed petrographic investigation, microthermometry, and LA-ICP-MS analysis. Petrographic results show that at least three types of fluid inclusions are developed in each mineral textural zone. They are CO2-rich inclusions (type I), gas-liquid two-phase inclusions (type II), and daughter mineral-bearing inclusions (type III), respectively. Additionally, minor melt inclusions (type IV) are visible in the beryl from the rim zone. Microthermometric measurements showed that the homogenization temperature of fluid inclusions in the rim zone was concentrated between 242 °C and 293 °C, with an average of 267 °C, and the salinity was between 7.2–10.3 wt% NaCleqv, with an average of 8.6 wt% NaCleqv. In comparison, the temperature of the core zone was in the range of 225–278 °C, with an average of 246 °C, and the salinity focused between 6.0–7.7 wt% NaCleqv, with an average of 7.1 wt% NaCleqv. The quantitative analysis of individual inclusions by LA-ICP-MS revealed that Li, B, K, Zn, Rb, Sb, Cs, and As were relatively enriched in the rim zone. In contrast, the core zone showed a decreasing trend in trace elements such as Li, B, K, Rb, and Cs. The CO2 content in the fluid exhibited the same decreasing trend from the rim to the core zone, indicating that volatile components such as CO2 played an essential role in the migration and enrichment of rare metal elements. The melt-fluid immiscibility is likely to be a necessary mechanism for significantly enriching rare metals in the Dakalasu No. 1 pegmatite dyke.

Ages, H[sbnd]O[sbnd]C[sbnd]S[sbnd]Pb isotopes, and fluid inclusion study of the Daolundaba Cu–Sn–W–Ag deposit in Inner Mongolia, NE China

The medium-sized Daolundaba Cu–Sn–W–Ag deposit is located in the southern Great Xing'an Range (SGXR), being one of the representative deposits in this area. The vein orebodies of the deposit occur within the NE-trending fracture zones, which are developed in the Early Permian silty slate and Late Variscan biotite monzogranite. However, its mineralization age remains controversial, which affects the understanding of Sn–polymetallic mineralization in the SGXR. To determine the mineralization age and reveal the sources of fluid and ore-forming material, sericite and monazite dating, fluid inclusion microthermometry, and isotopic analysis were carried out in this study. The ore-forming process at the deposit can be divided into four stages: quartz–fluorite–muscovite–tourmaline–cassiterite–wolframite–arsenopyrite stage (stage I), quartz–fluorite–wolframite–chalcopyrite–arsenopyrite–pyrrhotite stage (stage II), quartz–fluorite–sericite–chalcopyrite–pyrite–pyrrhotite–silver mineral stage (stage III), and quartz–calcite–fluorite–pyrite stage (stage IV). The sericite sample yielded a 40Ar–39Ar plateau age of 138.8 ± 0.7 Ma and an isochronal age of 140.0 ± 1.1 Ma, and the LA-ICP-MS U–Pb age of three monazite samples was 136.0 ± 2.3–134.7 ± 2.8 Ma, indicating that the Daolundaba deposit formed in the Early Cretaceous. Liquid-rich, gas-rich, and daughter mineral-bearing inclusions have been identified in quartz, fluorite, and calcite. Homogenization temperatures and salinities of the fluid inclusions (FIs) in the stage I vary from 309 °C to 389 °C and 6.2 wt% to 46.3 wt% NaCl eqv., respectively. Homogenization temperatures and salinities of the FIs in the stage II vary from 242 °C to 339 °C and 5.3 wt% to 41.4 wt% NaCl eqv., respectively. Homogenization temperatures and salinities of the FIs in the stage III vary from 153 °C to 268 °C and 3.5 wt% to 35.4 wt% NaCl eqv., respectively. There are only liquid-rich inclusions in quartz, fluorite, and calcite of the stage IV; their homogenization temperatures and salinities vary from 114 °C to 188 °C and 2.1 wt% to 7.6 wt% NaCl eqv., respectively. The ore-forming fluids of the Daolundaba deposit are characterized by moderate–high temperature and great fluctuating salinity, belonging to an H2O–NaCl ± CO2 ± CH4 system. The δ18Owater and δD values of the stages I and II vary from 2.5 ‰ to 7.2 ‰ and − 127 ‰ to − 106 ‰, respectively; the δ18Owater and δD values of the stage III vary from − 3.0 ‰ to − 0.3 ‰ and − 126 ‰ to − 94 ‰, respectively; the δ18Owater and δD values of the stage IV vary from − 10.9 ‰ to − 4.7 ‰ and − 102 ‰ to − 81 ‰, respectively; indicating that the ore-forming fluids of the stages I and II mainly consist of magmatic water, that the ore-forming fluid in the stage III is a mixture of magmatic and meteoric water, and that the fluid in the stage IV is meteoric water. The δ13C values for calcite of the stage IV vary from − 9.8 ‰ to − 6.7 ‰, suggesting that the carbon was mainly from a magmatic source. The δ34S values range from − 7.4 ‰ to − 1.3 ‰ with an average of − 4.7 ‰. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of the metallic minerals are in the ranges of 18.293–18.612, 15.519–15.706, and 38.078–38.826, respectively. Both S and Pb isotopic systems indicate that the ore-forming metals primarily came from Mesozoic felsic magma. Fluid boiling and mixing were two main mechanisms for the deposition of ore-forming materials.

Fluid Inclusions and Stable Isotope Geochemistry of Gold Mineralization Associated with Fine-Grained Granite: A Case Study of the Xiawolong Gold Deposit, Jiaodong Peninsula, China

The Xiawolong gold deposit, located in the Muping–Rushan gold metallogenic belt (eastern Jiaodong Peninsula), is a newly discovered deposit that developed in the late Early Cretaceous as fine-grained granite. Gold mineralization, which mainly occurs in the middle of fresh fine-grained granite dikes, consists of stockwork-style and disseminated ores. They are characterized by middle-high-temperature mineral assemblages, such as molybdenite and magnetite, associated with gold-bearing pyrite. Four types of primary fluid inclusions, contained within the quartz grains from the gold-bearing disseminated and stockwork-style fine-grained granitic ores, were identified based on microthermometry and Raman spectroscopy. The types identified were type 1 aqueous inclusions with middle-high temperature (201 to 480 °C) and middle-low salinity of 0.18 to 17.00 wt.% NaCl equiv.; type 2 H2O–CO2 inclusions, which show middle-high temperatures (218 to 385 °C), middle-low salinities (1.23 to 13.26 wt.% equiv. NaCl), and variable XCO2 (0.031 to 0.044); type 3 daughter mineral-bearing inclusions with high temperature (416 to 446 °C) and relatively constant and high salinity (28.59 to 32.87 wt.% NaCl equiv.); and type 4 CO2 fluid inclusions, which possess a bulk density of 0.405 to 0.758 g/cm3 and a constant XCO2 (0.952 to 0.990) (according to the decreasing abundance of fluid inclusions). The δ18Owater range is between 3.4 and 5.9‰, and the range of the δD is from −97.1 to −77.4‰, which indicates that the ore-forming process is of a magmatic water origin. The δ34S values possess a narrow range between 4.5 and 9.3‰, indicating the source of the Mesozoic Kunyushan granitoids. The Pb isotopic compositions of pyrite show that the Mesozoic Kunyushan granitoids are the main lead source for pyrites. Types 1, 2, and 3 fluid inclusions coexist in the same view field of the quartz grain, which are suggested to occur as the result of fluid immiscibility because of the boiling of a single homogeneous NaCl-CaCl2-KCl-CO2-H2O system. The fluid immiscibility, rather the fluid mixing and wall-rock sulfidation, is the mechanism of gold precipitation in the Xiawolong deposit. Compared with both the “Linglong-type” and “Jiaojia-type” gold deposits in the Jiaodong Peninsula in terms of geological–petrographic evidence and all of the available geochemical data, it can be concluded the Xiawolong gold deposit is of magmatic hydrothermal origin, having a genetic relation to the fine-grained granite.

Fluid origin and evolution of the Ruanjiawan W-Cu-(Mo) deposit from the Edong District in the Middle-Lower Yangtze River metallogenic belt of China: Constraints from fluid inclusions and H-O-C-S isotopes

Ruanjiawan W-Cu-(Mo) deposit, located in the Edong District of the Middle-Lower Yangtze River metallogenic belt, is one of the largest W deposits (40348 tons WO3 at an average grade of 0.32 wt%) in this ore district. The orebodies mainly occur in the contact zone between the granitoid and Ordovician carbonate strata. A detailed field geology and petrographic observation indicates four stages of ore formation: (1) prograde skarn stage, (2) retrograde skarn stage, (3) quartz-sulfide stage, and (4) quartz-carbonate stage. The δ18O values of the ore fluids vary from 3.0‰ to 11.2‰, and the δD values vary from −88‰ to −105‰, suggesting a dominant magmatic water origin, with a small amount of meteoric water mixing during the late stages. The δ13C values of fluid inclusions vary from −15.0‰ to −7.1‰, also indicating a major magmatic carbon source but with some mixing of organic carbon component in the sedimentary strata that probably leached by circulated meteoric water. The sulfides show a large δ34S variation from −4.8‰ to +16.3‰, and the sulfur may have two different sources, with a majority magmatic source (with δ34S around 0), and some marine sulphate source (with high positive δ34S value) in sedimentary strata in the region leached by meteoric water. In the prograde skarn stage, garnet shows a fluid inclusion homogenization temperature above 517 °C. The estimated salinity of the vapour-liquid two-phase inclusions ranges from 15.7 to 21.4 wt% NaCl equiv., and the salinity of the daughter mineral-bearing inclusions ranges from 39.8 to 57.1 wt% NaCl equiv. In the retrograde skarn stage, the fluid inclusions in epidote show a homogenization temperature of 385 °C to 463 °C, and the salinity estimated from the vapour-liquid two-phase inclusions ranges from 9.7 to 16.4 wt% NaCl equiv. The fluid inclusions in coarse-grained garnet from the retrograde skarn stage show similar homogenization temperature of 339 °C to 398 °C, and similar salinity of vapour-liquid two-phase inclusions of 7.4 to 15.3 wt% NaCl equiv., however, the salinity estimated from the daughter mineral-bearing inclusions ranges from 35.2 to 42.0 wt% NaCl equiv. In the quartz-sulfide stage, fluid inclusions in quartz show a homogenization temperature of 274 °C to 344 °C. The salinity varies from 6.5 to 14.0 wt% NaCl equiv. for the vapour-liquid two-phase inclusions, from 5.1 to 8.0 wt% NaCl equiv. for the CO2-bearing three phase inclusions, and from 35.3 to 39.8 wt% NaCl equiv. for the daughter-mineral-bearing inclusions. In the quartz-carbonate stage, the fluid inclusions have homogenization temperatures from 137 °C to 261 °C, and the salinity for the vapour-liquid two-phase inclusions shows a range from 3.9 to 1.0 wt% NaCl equiv. Fluid boiling and water-rock reaction in the retrograde skarn stage lead to the first precipitation of scheelite. The precipitation of scheelite, chalcopyrite and molybdenite in the quartz-sulfide stage was mostly triggered by the mixing of meteoric water and magmatic fluids, and fluid immiscibility also plays an important role. According to petrographic evidence and all available geological and geochemical data, we conclude that the Ruanjiawan deposit is an oxidized skarn-type W-Cu-(Mo) deposit.

Fluid inclusion and C-O isotopic constrains on the origin and evolution of ore-forming fluids of the Badaguan Cu-Mo deposit, Inner Mongolia

The Badaguan porphyry Cu–Mo deposit is located in the Derbugan metallogenic belt. Aqueous (W-type), CO2-rich (WC-type), vapor-rich (V-type), and daughter mineral–bearing inclusions (S-type) were recognized in the hydrothermal quartz. Fluid inclusions in the early stage show high homogenization temperatures (247–374 ℃) and high pressures (66–191 MPa), with salinities of 0.95–12.15 wt% NaCl equiv. The presence of anhydrite in veins and phenocrysts suggests high oxygen fugacity conditions. The veins in the Mo- and Cu mineralization stages were formed by immiscible fluids at temperatures of 244–366 ℃ and 183–342 ℃, and pressures of 39–137 MPa and 30–98 MPa, respectively. They yielded salinities of 1.69–10.52 and 0.35–6.85 wt% NaCl equiv, respectively. Homogenization temperatures of fluid inclusions in late stage range from 194 to 269 ℃ with a salinity of 0.6–5.88 wt% NaCl equiv. It is concluded that the ore-forming fluids in the early stage were magmatic in origin, then gradually diluted and cooled by meteoric water. During this process, fluid immiscibility and CO2 release induced by pressure drop and oxygen fugacity decrease resulted in Mo mineralization, while temperature drop was the main trigger for the precipitation of chalcopyrite. Laser-Raman analyses suggest that the fluid inclusions of the Badaguan porphyry Cu-Mo deposit in Inner Mongolia are rich in CO2. Minor CH4 occurs in the Mo- and Cu-mineralization stage, which may be generated during water–rock interaction. The hybrid carbon isotope compositions of the fluid inclusions, mainly representing CO2, show a very depleted δ13CPDB (−21‰ to −28.3‰), which can be explained by the joint influence of ~ 0.5% subducted oceanic sedimentary contamination in the mantle and carbon isotope fractionation induced by 35–80% CO2 degassing. Petrographic observation, previous studies on the geochemical and isotopic characteristics of ore-causative rocks rule out the possibility of contamination of ascending magma with reducing wall rocks. The large variations in δ18Owater (−6.6‰ to +2.4‰) for quartz and calcite suggest the participation of meteoric water during water–rock interaction.

Fluid evolution in the Beidabate porphyry Cu-Mo deposit, Xinjiang, northwest China: Evidence from fluid inclusions and H-O-C-S isotopes

• A fluid evolution model for Beidabate deposit is presented. • The model relies on fluid phase separation. • The precipitation mechanism for Mo and Cu is proposed. The Beidabate deposit is a porphyry Cu-Mo deposit located in the West Tianshan Orogenic Belt , Xinjiang Uygur Autonomous Region. The fluid evolution path and Cu-Mo mineralization mechanism remain obscured by multiple hydrothermal pulses. Systematic fluid inclusion and H-O-C-S isotope analyses were performed on five identifiable mineralization stages. Variations in fluid composition, temperature, and pressure record the fluid evolution path: (1) During the formation of barren quartz veins (stage I), fluid inclusions were trapped under single- to two-phase transitional conditions, as evidenced by the presence of intermediate-density inclusions as well as coexisting daughter mineral-bearing inclusions and vapor-rich inclusions (boiling FIAs). Fluid phase separation occurred at temperatures of 387–412 °C and pressures of 180–300 bar. (2) Fluid inclusions in K-feldspar-quartz veins (stage II) and molybdenite-quartz veins (stage III) were trapped under two-phase conditions. Boiling FIAs were also recognized, with homogenization temperatures of 306–368 °C and entrapment pressures of 80–200 bar. Fluid boiling is the main precipitation mechanism of molybdenite . (3) Fluid inclusions in pyrite-chalcopyrite-quartz veins (stage IV) and fluorite-chalcopyrite veins (stage V) are predominantly liquid-rich and CO 2 -bearing inclusions, which represent extraneous fluids. These inclusions homogenized at temperatures of 192° to 285 °C, and minimum entrapment pressures of 40–50 bar. Fluid mixing is the main precipitation mechanism of chalcopyrite . H-O-C-S isotope data (δ 18 O = 3.2 to 15.2‰, δD = −103.6 to −75.1‰, δ 13 C = −24.2 to −9.7‰ and δ 34 S = 4.6 to 7.0‰) indicate that the ore-forming fluids have a predominantly magmatic signature with subsequent dilution by late meteoric water and intense water–rock interaction. We established a genetic model of the Beidabate porphyry Cu-Mo deposit with the aim of providing insight into prospecting at a regional scale.

Fluid Inclusions and S–Pb Isotopes of the Reshui Porphyry Mo Deposit in East Kunlun, Qinghai Province, China

The Reshui porphyry Mo deposit is located in the East Kunlun orogenic belt (EKOB). Molybdenum mineralization is distributed in monzogranite and porphyritic monzogranite rocks, mainly presenting as various types of hydrothermal veinlets in altered wall rocks, and the orebodies are controlled by three groups of fractures. In this paper, we present the results of fluid-inclusion and isotopic (S and Pb) investigations of the Reshui Mo deposit. The ore-forming process of the deposit can be divided into three stages: an early disseminated molybdenite stage (stage 1), a middle quartz–molybdenite stage (stage 2) and a late quartz–polymetallic sulfide stage (stage 3). The alteration was mainly potassic and silicic in stage 1, silicic in stage 2, and sericitic and silicic in stage 3. Five types of fluid inclusions (FIs) can be distinguished in quartz phenocrysts and quartz veins, namely W, PL (pure liquid inclusions), PV (pure gas inclusions), C (CO2 three-phase inclusions), and S (daughter mineral-bearing inclusions). The homogenization temperatures of fluid inclusions belonging to stages 1 to 3 are 282.3–378 °C, 238.7–312.6 °C and 198.3–228 °C, respectively. The fluid salinities at stages 1 to 3 are 4.65–8.14% NaCl eq., 4.34–42.64% NaCl eq., and 3.55–4.65% NaCl eq., respectively. The fluids of this deposit were generally moderate–high temperature and moderate–low salinity and belong to the H2O–NaCl–CO2 ± CH4 system. The temperature and pressure changed considerably between stage 2 (high–medium-temperature) and stage 3 (low-temperature). The evidence for ore-forming fluids containing different types of coexisting inclusions in stage 2 and a decrease in the fluid temperature from stage 2 to stage 3 indicate that fluid boiling and fluid mixing were the main mechanisms of ore precipitation. The sulfide 34SV-CDT values range from 4.90‰ to 5.80‰, which is characteristic of magmatic sulfur. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of the ore minerals are 18.210–18.786, 15.589–15.723, and 38.298–39.126, respectively. These lead isotopic compositions suggest that the ores were mainly sourced from crustally derived magmas, with minor input from the mantle. The fluid inclusions and S–Pb isotopes provide important information on the genesis of the Reshui porphyry Mo deposit and indicate that the Triassic has high metallogenic porphyry potential in the EKOB.

Geology, chronology, fluid inclusions, and H–O–S isotopic compositions of the Hongyuntan magnetite deposit, Eastern Tianshan, NW China

The Hongyuntan magnetite deposit, which is located in the Aqishan–Yamansu belt of Eastern Tianshan, Xinjiang, is hosted within Carboniferous submarine volcanic-sedimentary sequences. The deposit is characterized by five metallogenic stages: Stage I (garnet–diopside), Stage II (magnetite–tremolite–chlorite–pyrite), Stage III (magnetite–quartz–albite–actinolite), Stage IV (pyrite–quartz–epidote) and Stage V (hematite–limonite). Pyrite associated with magnetite formed during the Stage II has a Re-Os isochron age of 324 ± 31 Ma. Four types of fluid inclusions were observed in the mineral assemblages, namely, two-phase liquid and vapor inclusions, multi-phase daughter mineral-bearing inclusions, multi-phase CO2-bearing inclusions, and monophase vapor inclusions. Microthermometry data reveal that the ore-forming fluids evolved from high-temperature (average 532.5 °C) and high-salinity (average 26.9 wt% NaCleqv) fluids to moderate–low-temperature (average 203.6 °C) and low-salinity (5.07 wt% NaCleqv) fluids. Magnetite precipitation may have been greatly assisted by mixing and boiling in Stage II and Stage III, respectively. The hydrogen and oxygen isotopic values of Stage I garnet (δDV-SMOW = −107.9‰ to −76.7‰, δ18Ofluid = 6.4–10.7‰) and Stage III quartz (δDV-SMOW = −85.5‰ to −83.2‰, δ18Ofluid = 3.8–4.7‰) indicate that the ore-forming fluids were dominated by magmatic water, whereas fluid mixing occurred during Stage II (δDV-SMOW = −117.3‰ to −112.6‰, δ18Ofluid = 3.3–5.7‰) and Stage IV (δDV-SMOW = −115.2‰ to −58.5‰, δ18Ofluid = −1.3‰ to 4.5‰). The variable δ34S values of pyrite (−3.8‰ to 4.7‰) and δ18Omgt values of magnetite (−0.6‰ to 4.1‰) suggest that they were not sourced from a single reservoir.The Hongyuntan magnetite deposit is spatially and temporally associated with volcanism and may be genetically related to it. The fluid inclusions and isotopic compositions of this deposit indicate that its ore-forming fluid was derived from the exsolution of deep-seated magmas and that fluid mixing could have effectively triggered the deposition of ore-forming materials. Multiple periods of volcanic activity could have incorporated additional heat and ore metals into the ore-forming system. Based on our data, we conclude that the origin of the Hongyuntan magnetite deposit is related to the volcanism in the Carboniferous period.

Ore genesis of the Saridala gold deposit, Western Tianshan, NW China: Constraints from fluid inclusion, S-Pb isotopes and 40Ar/39Ar dating

The Saridala gold deposit is located in the Western Tianshan (Xinjiang, NW China), southwestern part of the Central Asian Orogenic belt (CAOB). The deposit is mainly hosted in Precambrian metamorphic rocks and Early Paleozoic granites, and is structurally controlled by the Shenglidaban ductile shear zone. The gold orebodies consist of gold-bearing quartz veins and altered mylonite. The mineralization comprises three stages: quartz-pyrite veins (early stage), sulfide-quartz veins (middle stage), and quartz-carbonate veins/veinlets (late stage). Ore minerals and native gold were mainly formed in the middle stage. Four fluid inclusion types in quartz veins were identified: pure CO2 (PC-type), CO2-H2O (C-type), aqueous (W-type) and daughter mineral-bearing (S-type) inclusions. Hydrothermal fluids related to the mineralization are composed of CO2-H2O-NaCl±N2 fluids (115–307MPa) with Th(total) values of 256–475°C (peak at 320–380°C) and salinities <∼11 wt% NaCl equiv. (mostly 4–7 wt% NaCl equiv.). Ore minerals were likely deposited via fluid immiscibility and the subsequent fluid mixing. Except for the two negative outliners (−4.5 and −4.8‰), δ34S‰ values of the ore pyrite range from 11.0 to 17.9‰, suggesting that the ore-forming fluids contained heavier sulfur from marine sulfate-bearing rocks. Lead isotope compositions of the ore sulfides are characterized by being highly radiogenic and their relatively wide ranges: 18.01–19.62 (206Pb/204Pb), 15.58–15.78 (207Pb/204Pb) and 37.95–39.08 (208Pb/204Pb). These data indicate that the lead in the ores may have been derived from an orogenic reservoir with some crustal input. 40Ar/39Ar age dating on the sericite from the syn-mineralized quartz-sericite-sulfide alteration yielded a plateau age of 337.6±1.7Ma, an age coeval with the subduction–collision tectonic transition related to the closure of the North Tianshan Ocean. We concluded that the Saridala gold deposit shares many similarities with typical orogenic gold deposits, and was likely formed in an orogenic environment.

Molybdenite Re–Os age, H–O–C–S–Pb isotopes, and fluid inclusion study of the Caosiyao porphyry Mo deposit in Inner Mongolia, China

The giant Caosiyao porphyry Mo deposit, located in the northern margin of the North China Craton, is a newly discovered Mo deposit in the Yan–Liao molybdenum belt. Orebodies of the deposit are mainly hosted in metamorphic rocks of the Mesoarchean Jining Group with a small amount of orebodies in the Late Jurassic syenogranite porphyry. The ore-forming process of the deposit can be divided into three stages: an early quartz–molybdenite±magnetite±pyrite stage, a middle quartz–molybdenite–pyrite±pyrrhotite±chalcopyrite stage, and a late quartz–carbonate–pyrite±fluorite±pyrrhotite stage. Molybdenite Re–Os dating indicates that the Caosiyao deposit formed at ca. 150Ma. Four types of fluid inclusions (FIs) have been distinguished in quartz phenocryst and various quartz veins including liquid-rich, gas-rich, H2O–CO2, and daughter mineral-bearing inclusions. The FIs in the quartz phenocrysts of the syenogranite porphyry contain liquid-rich, gas-rich, H2O–CO2, and daughter mineral-bearing types; their homogenization temperatures and salinities vary from 385°C to >550°C and 6.5wt% to 65.0wt% NaCl eqv., respectively. The FIs in the quartz of the early stage are also mainly liquid-rich, gas-rich, H2O–CO2, and daughter mineral-bearing types; their homogenization temperatures and salinities vary from 243°C to 401°C and 6.0wt% to 39.8wt% NaCl eqv., respectively. The FIs in the quartz of the middle stage are mainly liquid-rich, H2O–CO2, and daughter mineral-bearing types; their homogenization temperatures and salinities vary from 208°C to 336°C and 1.2wt% to 34.1wt% NaCl eqv., respectively. The FIs in the quartz of the late stage are only liquid-rich type; their homogenization temperatures and salinities vary from 124°C to 196°C and 3.9wt% to 13.2wt% NaCl eqv., respectively. The ore-forming fluids of the Caosiyao deposit are characterized by moderate–high temperature and great fluctuating salinity, belonging to an H2O–NaCl–KCl–MgCl2–CO2±CH4 system. The δ18OH2O and δDH2O values of the early and middle stages vary from 3.5‰ to 7.4‰ and −96‰ to −77‰, respectively; the δ18OH2O and δDH2O values of the late stage vary from −2.9‰ to −0.6‰ and −112‰ to −77‰, respectively; indicating that the ore-forming fluids of the early and middle stages mainly consist of magmatic water and that the fluid in late stage is a mixture of magmatic and meteoric water. The δ13C values vary from −16.5‰ to −8.8‰ for the early and middle stages and −11.4‰ to −5.3‰ for the late stage, suggesting that the carbon of the early and middle stages consists of a mixture of organic and magmatic sources and that the carbon in the late stage was mainly from a magmatic source. The δ34S values range from 4.0‰ to 6.1‰ with an average of 4.8‰. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of the metallic minerals are in the ranges of 15.962–17.832, 15.200–15.511, and 35.918–37.927, respectively. Both S and Pb isotopic systems indicate that the ore-forming metals came primarily from Mesozoic intermediate–felsic magma. The multi-stage boiling or immiscibility of the ore-forming fluids was the dominant mechanism for the deposition of ore-forming materials.

Fluid inclusion characteristics and geological significance of the Dajinshan W–Sn polymetallic deposit in Yunfu, Guangdong Province

The Dajinshan tungsten–tin polymetallic deposit is a quartz-vein-type ore deposit located in Western Guangdong Province. The ore bodies show a fairly simple shape and mainly occur as tungsten–tin polymetallic-bearing sulfide quartz veins, including quartz vein, quartz-greisens, and sulfide quartz veins, and their distribution is spatially related to Dajinshan granitoids. The formation of the deposit experienced three stages: a wolframite–molybdenite–quartz stage, a wolframite–cassiterite–sulfide–quartz stage, and a fluorite–calcite–carbonate stage. Based on detailed petrographic observations, we conducted microthermometric and Raman microspectroscopic studies of fluid inclusions formed at different ore-forming stages in the Dajinshan tungsten–tin polymetallic deposit, identifying four dominant types of fluid inclusions: aqueous two-phase inclusions, CO2-bearing inclusions, solid or daughter mineral-bearing inclusions, and gas-rich inclusions. The gas compositions of ore-forming fluids in the Dajinshan tungsten–tin polymetallic deposit are mostly CO2, CH4, and H2O. The hydrogen, oxygen, and sulfur isotopic data imply that the ore-forming fluids in the Dajinshan tungsten–tin polymetallic deposit were mainly derived from magmatic fluids, mixed with meteoric water in the ore-formation process. These results indicate that the fluid mixing and boiling led to the decomposition of the metal complex in ore-forming fluids and ore deposition.

Fluid inclusions and isotopic characteristics of the Jiawula Pb–Zn–Ag deposit, Inner Mongolia, China

The large Jiawula Pb–Zn–Ag deposit is located in the Derbugan metallogenic belt of the northern Great Xing’an Range. The vein style orebodies of the deposit occur along NWW- to NNW-trending fault zones. The ore-forming process at the deposit can be divided into three stages: an early quartz–pyrite–pyrrhotite–chalcopyrite stage, a middle quartz–carbonate–pyrite–galena–sphalerite stage, and a late quartz–carbonate–pyrite stage. Sulfide Rb–Sr dating indicates that the Jiawula deposit formed at ca. 143–142Ma. Four types of fluid inclusions have been distinguished in quartz veins including liquid-rich, gas-rich, H2O–CO2, and daughter mineral-bearing inclusions. The fluid inclusions of the early stage are mainly liquid-rich, gas-rich, and H2O–CO2 types, with a small number containing daughter minerals. Cumulatively, the types have homogenization temperatures, densities, and salinities of 304–438°C, 0.35–1.37g/cm3, and 0.8–44.6wt.% NaCl eqv., respectively. Inclusions of the middle stage are mainly liquid-rich and gas-rich types, with a small amount of H2O–CO2 and daughter mineral-bearing types; their homogenization temperatures, densities, and salinities vary from 242°C to 297°C, 0.71 to 1.44g/cm3, and 0.4wt.% to 36.8wt.% NaCl eqv., respectively. The late stage only comprises liquid-rich inclusions with homogenization temperatures, densities, and salinities of 181–238°C, 0.81–0.90g/cm3, and 0.2–1.9wt.% NaCl eqv., respectively. The ore-forming fluids of the Jiawula deposit are generally characterized by moderate temperature and low salinity and density, and belong to an H2O–NaCl–CO2±CH4 system. The δ18Owater values calculated for ore-bearing quartz vary from −13.4‰ to −9.1‰, and the δDV-SMOW values from bulk extraction of fluid inclusion waters vary from −166‰ to −133‰, suggesting that the ore-forming fluids mainly consist of meteoric water with a small amount of magmatic water. The δ34SV-CDT values range from 1.2‰ to 8.4‰. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of the ore minerals are in the ranges of 18.319–18.377, 15.499–15.596, and 38.094–38.314, respectively. Initial 87Sr/86Sr ratios of sulfides range from 0.712381 to 0.712770. The data for the S, Pb, and Sr isotopic systems indicate that the ore-forming metals and sulfur came from Mesozoic magma. The Jiawula deposit is a low-sulfidation epithermal Pb–Zn–Ag deposit, and fluid boiling is the dominant mechanism for the deposition of ore-forming materials.

The geology and geochemistry of Jinchangyu gold deposit, North China Craton: Implications for metallogenesis and geodynamic setting

The Jinchangyu Au deposits contained an original resource of 50t of gold and is located close to the northeastern margin of the North China Craton (NCC). The orebodies are controlled by structures in the amphibolite units of the Archaean Zunhua Group. Mineralization is generally associated with albite and hematite which is indicative of Na–Al–Si–Fe alteration. The most common styles of mineralization are subdivided based on the cross-cutting relationships of mineral assemblages as follows: (i) quartz–albite–hematite; (ii) quartz–albite–polymetallic sulfides with gold and molybdenite; (iii) quartz–pyrite; and (iv) quartz–carbonate. Quartz samples from the second (Stage II) and third (Stage III) assemblages contain two-phase fluid inclusion types; these are: (i) CO2–H2O fluid inclusions, and (ii) daughter mineral-bearing inclusions, which have homogenization temperatures of 270°–350°C (for assemblage Stage II) and 180°–240°C (for Stage III), and salinities of ≤13wt.% NaCl equiv. A few S-type fluid inclusions suggesting salinities of 27.6–28.3wt.% NaCl equiv. The S isotope composition of pyrite and molybdenite from Stage II (δ34S=–4.4 to 1.9‰) indicates that the mineralizing fluid originated predominantly from a magmatic source. The H–O isotope signatures from Stage II indicate a magmatic-dominated source for the mineralizing fluid with some addition of meteoric fluids. Previously published Pb and C isotope data indicate that ore and magma in the eastern part of the Hebei Province of China interacted with Precambrian country rocks, and so the fluids moved from the lower crust to shallower level during mineralization. The red quartz–albite–hematite veins from Jinchangyu were generated under strongly oxidizing alkaline conditions that were favorable for the incorporation of gold into the fluid and the crystallization of albite during the early stage of gold deposition.Seven molybdenite samples from Jinchangyu yield Re–Os model ages of ca. 233 to 219Ma with a weighted mean age of 225±4Ma and an isochron age of 223±5Ma. This indicates that at least some of the gold associated with molybdenite is Late Triassic in age, and could be associated with buried intrusions that are part of the Late Triassic Dushan granites in the eastern portion of the NCC. This mineralization was formed after the closure of the Paleo-Asian Ocean. These results indicate that the intrusion-related Jinchangyu deposit is the far-field structural product of the collision of the NCC with the Siberian Craton to the north along the northern margin of the NCC.

Ore genesis and fluid evolution of the Daheishan giant porphyry molybdenum deposit, NE China

The Daheishan giant porphyry Mo deposit is located at the eastern segment of the CAOB, NE China. The ore-bearing intrusion of Daheishan deposit is a Jurassic granitic complex that includes Changgangling biotite granodiorite, Qiancuoluo seriate granodiorite, and Qiancuoluo granodioritic porphyry. Mineralization consists of disseminated, breccia and veined types. The hydrothermal fluids show significant magmatic signatures, as evidenced by the hydrogen and oxygen isotopic compositions of quartz and sulfur isotopic characteristics of ores. Consistence of lead isotopic compositions of the sulfides and the Daheishan intrusive complex further indicate a close relationship between the mineralization and magma. The fluid inclusions in quartz comprise of predominant aqueous two-phase as well as gas-rich fluid inclusions and a small number of daughter mineral-bearing inclusions. The gas species in the fluid inclusions are H2O, CO2, N2, CH4, C2H6, Ar∗ and minor H2S; the liquid compositions are SO42−, Cl−, Na+, K+, Ca2+ and Mg2+. Raman spectroscopy on individual fluid inclusions reveals a main gaseous composition of H2O, minor H2S and CO2. The fluid system in Daheishan Mo deposit can be described as NaCl–KCl–H2O type. Fluid inclusion microthermometry reveals subsolidus homogenization temperatures for fluid inclusions in the magmatic quartz phenocrysts (Th=400–450°C, salinities=∼21eq. wt.%), suggesting an obliteration of higher temperature history of the porphyry system by the superimposed processes. Most of the mineralization occurred at temperature range of 220–360°C, or higher. The temperature and salinity decreased to 100–170°C and 0–15eq. wt.%, respectively, when the hydrothermal fluid activities were gradually ending. No distinct evolution pattern based on the homogenization temperature or stable isotopic analyses is observed among the different mineralization stages. Mineralization was supposed to be related to the multi-phased boiling of fluids, instead of the gradual cooling of fluids. Pressure may be more critical than temperature in controlling the precipitation of molybdenite.

Fluid evolution of the Tongkuangyu porphyry copper deposit in the Zhongtiaoshan region: Evidence from fluid inclusions

The Tongkuangyu porphyry copper deposit is located in the Zhongtiaoshan region, southern margin of the North China Craton. More than 2.8million tons of Cu (Average Cu grade: 0.68%) is hosted in the Paleoproterozoic quartz-monzonite porphyry (2122±10Ma). The ore-forming processes of the Tongkuangyu porphyry Cu deposit are divided into three mineralization stages, namely the early-, main- and late mineralization stages. The majority of Cu ores were formed in the main stage, which is characterized by veinlets and disseminated chalcopyrite and minor molybdenite, pyrite, magnetite and hematite. Quartz is the major gangue mineral, which occurs as veinlets and associates with metallic minerals.Through systematic petrographic observation, the ore-bearing quartz veins (A-type quartz) and the quartz hosted in chalcopyrite (B-type quartz) were studied in detail to investigate the fluid evolution of the Tongkuangyu porphyry Cu deposit. Four types of fluid inclusions were recognized in the A-type quartz, which include (1) pure vapor or vapor-rich (V-type) inclusions, (2) CO2–H2O (C-type) inclusions, (3) liquid-rich (L-type) inclusions, and (4) daughter mineral-bearing (S-type) inclusions. S-type inclusions in the main stage A-type quartz contain mainly halite and minor sylvite, calcite, hematite, chalcopyrite and anhydrite, with homogenization temperatures of 233–450°C. V-type inclusions (coexisting with the S-type inclusions) homogenize to vapor phase at 282–375°C, suggesting that the ore-forming fluids may have experienced boiling in the main mineralization stage. The late stage S-type inclusions have homogenization temperatures of 186–245°C and contain largely halite with minor sylvite. Fluid inclusions in the B-type quartz (intergrown with chalcopyrite) are closely associated with the ore-forming processes. The main stage B-type quartz contains predominantly S-type inclusions with homogenization temperatures of 250–412°C and minor V-type inclusions. On the other hand, the late stage B-type quartz contains abundant S-type inclusions with homogenization temperatures of 195–230°C and less L-type inclusions. Our results show that the S-type inclusions in both the A- and B-type quartz (of the same ore stage) have very similar homogenization temperatures. Therefore, fluid boiling may have promoted the Cu enrichment in the high salinity fluids and the brine phase is the main metal transport medium in the Tongkuangyu porphyry Cu deposit.The common occurrence of hematite and anhydrite daughter minerals in the S-type inclusions further suggests that ferrous ion oxidization may have caused sulfate reduction. This process may have played an important role during the Cu precipitation event. The progressive cooling of fluids and the incorporation of meteoric water in the late mineralization stage possibly resulted in the small-scale vein-type mineralization.

Geochronology and fluid inclusion study of the Yinjiagou porphyry–skarn Mo–Cu–pyrite deposit in the East Qinling orogenic belt, China

The Yinjiagou Mo–Cu–pyrite deposit of Henan Province is located in the Huaxiong block on the southern margin of the North China craton. It differs from other Mo deposits in the East Qingling area because of its large pyrite resource and complex associated elements. The deposit’s mineralization process can be divided into skarn, sulfide, and supergene episodes with five stages, marking formation of magnetite in the skarn episode, quartz–molybdenite, quartz–calcite–pyrite–chalcopyrite–bornite–sphalerite, and calcite–galena–sphalerite in the sulfide episode, and chalcedony–limonite in the supergene episode. Re–Os and 40Ar–39Ar dating indicates that both the skarn-type and porphyry-type orebodies of the Yinjiagou deposit formed approximately 143Ma ago during the Early Cretaceous. Four types of fluid inclusions (FIs) have been distinguished in quartz phenocryst, various quartz veins, and calcite vein. Based on petrographic observations and microthermometric criteria the FIs include liquid-rich, gas-rich, H2O–CO2, and daughter mineral-bearing inclusions. The homogenization temperature of FIs in quartz phenocrysts of K-feldspar granite porphyry ranges from 341°C to >550°C, and the salinity is 0.4–44.0wt% NaCl eqv. The homogenization temperature of FIs in quartz–molybdenite veins is 382–416°C, and the salinity is 3.6–40.8wt% NaCl eqv. The homogenization temperature of FIs in quartz–calcite–pyrite–chalcopyrite–bornite–sphalerite ranges from 318°C to 436°C, and the salinity is 5.6–42.4wt% NaCl eqv. The homogenization temperature of FIs in quartz–molybdenite stockworks is in a range of 321–411°C, and the salinity is 6.3–16.4wt% NaCl eqv. The homogenization temperature of FIs in quartz–sericite–pyrite is in a range of 326–419°C, and the salinity is 4.7–49.4wt% NaCl eqv. The ore-forming fluids of the Yinjiagou deposit are mainly high-temperature, high-salinity fluids, generally with affinities to an H2O–NaCl–KCl±CO2 system. The δ18OH2O values of ore-forming hydrothermal fluids are 4.0–8.6‰, and the δDV-SMOW values are between −64‰ and −52‰, indicating that the ore-forming fluids were primarily magmatic. The δ34SV-CDT values of sulfides range between −0.2‰ and 6.3‰ with a mean of 1.6‰, sharing similar features with deeply sourced sulfur, implying that the sulfur mainly came from the lower crust composed of poorly differentiated igneous materials, but part of the heavy sulfur came from the Guandaokou Group dolostone. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of sulfides are in the range of 17.331–18.043, 15.444–15.575, and 37.783–38.236, respectively, which is generally consistent with the Pb isotopic signature of the Yinjiagou intrusion, suggesting that the Pb chiefly originated from the felsic–intermediate intrusive rocks in the mine area, with a small amount of lead from strata. The Yinjiagou deposit is a porphyry–skarn deposit formed during the Mesozoic transition of a tectonic regime that is EW-trending to NNE-trending, and the multiepisode boiling of ore-forming fluids was the primary mechanism for mineral deposition.

Geology, geochronology, fluid inclusion and H–O isotope geochemistry of the Luoboling Porphyry Cu–Mo deposit, Zijinshan Orefield, Fujian Province, China

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.

The Jiguanshan porphyry Mo deposit in the Xilamulun metallogenic belt, northern margin of the North China Craton, U–Pb geochronology, isotope systematics, geochemistry and fluid inclusion studies: Implications for a genetic model

The Jiguanshan porphyry Mo deposit is located in the southern part of Xilamulun metallogenic belt at the northern margin of the North China Craton (NCC). In the Jiguanshan mining district, two stages of granitoids intrusions have been recognized: a pre-ore granite porphyry with stockworks and veins of Mo mineralization, and a granite porphyry with disseminated Mo mineralization. Zircon U–Pb data and Hf isotope analyses show that the dissemination-mineralized granite porphyry yielded a weighted mean 206Pb/238U age of 156.0±1.3Ma, with a crustal εHf(t) values from −5.6 to +0.2, and that the main group of magmatic zircons from the pre-ore granite porphyry have a weighted mean 206Pb/238U age of 167.7±1.7Ma with εHf(t) values from −3.2 to +1.0. Combined with groundmass Ar–Ar age data of the granite porphyry and molybdenite Re–Os age, it is suggested that the Mo mineralization of Jiguanshan deposit was formed in the late Jurassic (153~155Ma) during tectonic and magmatic events that affected northeast China. The Mo mineralization was a little bit later than the host granite porphyry. Besides disseminated in the host granite porphyry, Mo mineralization also presents in middle Jurassic pre-ore granite porphyry, Jurassic fine-grained diabase, Triassic quartz porphyry, and in rhyolitic volcanic rocks as well as syenite of Devonian age.The Jiguanshan mining district was affected by the tectonic events associated with the Paleo-Asian Ocean closure, and later by far-field tectonism, related to subduction of the Paleo-Pacific plate (Izanagi) in the Jurassic-Cretaceous. The tectonic and thermal events linked with the latter are commonly referred to as Yanshanian tectono-thermal event, and consists of a series of geodynamic, magmatic and ore-forming processes, which in the mining district area included the intrusion of the pre-ore granite porphyry, the host granite porphyry, Mo mineralization, and fine-grained diabase. Major and trace element analyses show that the host granite porphyry is characterized by high silica abundances (SiO2=77.16 to 77.51%), high Rb/Sr ratios (13.57 to 14.83), high oxidation (Fe2O3/FeO=34.25 to 62.00) and high alkalies (Na2O+K2O=8.21 to 8.38%). Petrographic and microthermometry studies of the fluid inclusions from Mo mineralized veins, characterized by plenty of daughter mineral-bearing inclusions, showed that the predominant homogenization temperatures range from 250 to 440°C. Combined with Laser Raman analysis of the fluid inclusions, it is indicated that Mo mineralization is related to a high-temperature, hypersaline and high-oxygen fugacity H2O–NaCl fluid system, with high F contents.Based on geology, geochronology, isotope systematics, geochemistry and fluid inclusion studies as well as regional geology, we propose, for the first time, a genetic model for the Jiguanshan porphyry Mo deposit. During the Jurassic geodynamic evolution of northeast China, high silicic, high oxidized and alkaline-rich granitic magma probably derived from partial melting of the lower crust, episodically intruded along faults into the country rocks. This fluid system, fractionating from the highly differentiated granitic magma and bearing Mo with minor Cu metals, migrated upwards and interacted with the older wall rocks and associated fractures, in which the ore minerals precipitated, resulting in the development of what we refer to as the “Jiguanshan-type” porphyry Mo deposit.

Geology and fluid evolution of the Wangfeng orogenic-type gold deposit, Western Tian Shan, China

The Wangfeng gold deposit is located in Western Tian Shan and the central section of the Central Asian Orogenic Belt (CAOB). The deposit is mainly hosted in Precambrian metamorphic rocks and Caledonian granites and is structurally controlled by the Shenglidaban ductile shear zone. The gold orebodies consist of gold-bearing quartz veins and altered mylonite. The mineralization can be divided into three stages: quartz–pyrite veins in the early stage, sulfide–quartz veins in the middle stage, and quartz–carbonate veins or veinlets in the late stage. Ore minerals and native gold mainly formed in the middle stage. Four types of fluid inclusions were identified based on petrography and laser Raman spectroscopy: CO2–H2O inclusions (C-type), pure CO2 inclusions (PC-type), NaCl–H2O inclusions (W-type), and daughter mineral-bearing inclusions (S-type). The early-stage quartz contains only primary CO2–H2O fluid inclusions with salinities of 1.62 to 8.03wt.% NaCl equivalent, bulk densities of 0.73 to 0.89g/cm3, and homogenization temperatures of 256°C–390°C. Vapor bubbles are composed of CO2. The middle-stage quartz contains all four types of fluid inclusions, of which the CO2–H2O and NaCl–H2O types yield homogenization temperatures of 210°C–340°C and 230°C–300°C, respectively. The CO2–H2O fluid inclusions have salinities of 0.83 to 9.59wt.% NaCl equivalent and bulk densities of 0.77 to 0.95g/cm3, with vapor bubbles composed of CO2, CH4, and N2. Fluid inclusions in the late-stage quartz are NaCl–H2O solution with low salinities (0.35–3.87wt.% NaCl equivalent) and low homogenization temperatures (122°C–214°C). The coexistence of inclusions of these four types in middle-stage quartz suggests that fluid boiling occurred in the middle-stage mineralization. Trapping pressures estimated from CO2–H2O inclusions are 110–300MPa and 90–250MPa for the early and middle stages, respectively, suggesting that gold mineralization mainly occurred at depths of about 10km. In general, the Wangfeng gold deposit originated from a metamorphic fluid system characterized by low salinity, low density, and enrichment of CO2. Depressurized fluid boiling caused gold precipitation. Given the regional geology, ore geology, fluid-inclusion features, and ore-forming age, the Wangfeng gold deposit can be classified as a hypozonal orogenic gold deposit.

Genesis of the 1.76 Ga Zhaiwa Mo–Cu and its link with the Xiong’er volcanics in the North China Craton: Implications for accretionary growth along the margin of the Columbia supercontinent

The East Qinling molybdenum belt, hosting numerous Mesozoic magmatic-hydrothermal Mo deposits, is one of the largest molybdenum provinces in the world. The recently discovered Zhaiwa Mo–Cu deposit, Luoning County, Henan Province, occurs within the Xiong’er Terrane of the East Qinling orogenic belt. The Mo–Cu mineralization is associated with widespread stockworks or veinlets occurring within altered amphibolite. Here we investigate the characteristics of the ore mineralization through systematic fluid inclusion petrography, microthermometry and laser Raman spectroscopy. The typical inclusions in the veins and stockworks are aqueous daughter mineral-bearing, and a subordinate CO2-rich type. The homogenization temperatures of the aqueous inclusions in quartz–molybdenite veins are up to 370°C, which, together with some daughter mineral-bearing inclusions homogenized by dissolution of halite at >500°C, indicates that the ore-forming fluids were derived from a hypothermal fluid system. The daughter mineral-bearing inclusions assign high salinities for the ore-forming fluids, correlating the ore deposit to a magmatic-hydrothermal system. We also present H–O isotope systematics which support this interpretation. The recently reported Re–Os molybdenite age of 1.76±0.03Ga from this deposit is coeval to the Xiong’er Group andesite-dominated volcanic sequence (1.8–1.45Ga), based on which we propose that the Zhaiwa deposit represents the upper domain of a porphyry system developed within a subduction-related setting with accretion to the southern margin of the North China Craton. Our study provides new constraints on the outgrowth of the Columbia supercontinent during Paleoproterozoic.