Fluid inclusion and H-O-S-Pb isotope systematics of the Chayong Cu-polymetallic deposit,Sanjiang Metallogenic Belt,Qinghai Province,China

The Chayong Cu-polymetallic deposit is a recently discovered Cu-polymetallic deposit hosted in the Sanjiang Metallogenic Belt within the Tibetan Plateau of China to the northeast of the North Qiangtang terrane.The ore body occurs in siltstone and is controlled by a northwest-trending fault structure.According to the associations,assemblages,and cutting relationships between ore veins,the hydrothermal mineralization period can be divided into three mineralization stages:(1)a molybdenite mineralization stage,(2)a Cu-polymetallic sulfide stage,and(3)a quartzcarbonate stage.Two types of fluid inclusions(FIs),namely,liquid and vapor-rich inclusions,are present in quartz as so ciated with sulfide minerals.Early-stage FIs are both iquid and vapor-rich,homogenized at temperatures ranging from 364.1 to 384.2℃,and have salinities ranging from0.70%to 9.60%NaCl equivalent(eqv).The middle-stage FIs are also both liquid-and vapor-rich,homogenized at temperatures ranging from 272.4 to 355.6℃,and have salinities ranging from 0.53%-17.10%NaCl eqv.The late-stage FIs are liquid,homogenized at temperatures ranging from 209.4to 255.3℃,and have salinities ranging from 0.35%-6.87%NaCl eqv.The samples from the deposit haveδ^(34)S values of-21.8‰to-19.2‰and-5.5‰to-6.0‰,suggesting that sulfur was derived from the host sediments and magmatic fluids,respectively.The metallic minerals within the deposit have^(206)Pb/^(204)Pb,^(207)Pb/^(204)Pb,and^(208)Pb/^(204)Pb values of 18.439-18.458,15.656-15.679,and 38.772-38.863,respectively,suggesting that the metals were derived from the upper crust and orogenic belts.The samples from the deposit haveδ^(18)O_(W)values of 2.99‰-7.99‰andδD_(W) values ranging from-84.4‰to-73.9‰,indicating that the pre-forming fluids were magmatic and mixed with minor amounts of meteoric water.The ore-forming fluid of the Chayong copper polymetallic deposit was a high-temperature,medium-to low-salinity H_(2)O-NaCl-CH_(4)-N_(2)±CO_(2)fluid system.The early high-temperature magmatic fluid,due to boiling,decreased in temperature,and via the mixing of meteoric water,gradually evolved towards the later-stage medium-to low-temperature and low-salinity fluid,causing nolybdenite mineralization and forming copper polymetallic sulfide veins and quartz carbonate veins.

Genesis of the Jianbeigou Gold Deposit on the Southern Margin of the North China Craton: Insights from Fluid Inclusions, H-O-S Isotopes, and Pyrite in situ Trace Element Analyses

The Jianbeigou gold deposit is a typical lode gold deposit in the Qinling metallogenic belt, located on the southern margin of the North China Craton. Three stages of the hydrothermal process can be distinguished, including the quartz ± pyrite, quartz-polymetallic sulfide, and quartz-carbonate ± pyrite stages. From the early to late stages, the homogenization temperatures of primary fluid inclusions are 281–362°C, 227–331°C, and 149–261°C, respectively. The corresponding salinities estimated for these fluids are 3.9–9.9 wt%, 0.4–9.4 wt%, and 0.7–7.2 wt% Na Cl equiv. Combined with laser Raman spectroscopy data, the ore-forming fluid belongs to a H_(2)O-CO_(2)-Na Cl ± CH_4 system with medium–low temperature and salinity. The δ~(18)Ofluid and δD values for the quartz veins are-1.0‰ to 6.0‰ and-105‰ to-84‰, respectively, which indicates that the ore-forming fluid is of mixed source, mainly derived from magma, with a contribution from meteoric water. Pyrite has been identified into three generations based on mineral paragenetic sequencing, including Py1, Py2, and Py3. The pyrites have δ~(34)S sulfur isotopic compositions from three stages between 3.7‰ and 8.4‰, indicating that sulfur mainly originated from magma. Te, Bi, Sb, and Cu contents in pyrite were all high and showed a strong correlation with Au concentrations. Native gold and the Au-Ag-Bi telluride minerals were formed concurrently, and the As concentration was low and decoupled from the Au content. Therefore, Te, Bi, Sb and other low-melting point chalcophile elements play an important role for gold mineralization in arsenic-deficient ore-forming fluid. Combined with the geological setting, evolution of pyrite, and ore-fluids geochemistry, we propose that the Jianbeigou deposit can be classified as a magmatic–hydrothermal lode gold deposit. Gold mineralization on the southern margin of the North China Craton is related to Early Cretaceous magmatism and formed in an extensional setting.

Magmatic-hydrothermal Evolution and Mineralization Mechanisms of the Wangjiazhuang Cu(-Mo)Deposit in the Zouping Volcanic Basin,Shandong Province,China:Constraints from Fluid Inclusions

The Wangjiazhuang Cu(-Mo)deposit,located within the Zouping volcanic basin in western Shandong Province,China,is unique in this area for having an economic value.In order to expound the metallogenetic characteristics of this porphyry-like hydrothermal deposit,a detailed fluid inclusion study has been conducted,employing the techniques of representative sampling,fluid inclusion petrography,microthermometry,Raman spectroscopy,LA-ICP-MS analysis of single fluid inclusions,as well as cathode fluorescence spectrometer analysis of host mineral quartz.The deposit contains mainly two types of orebodies,i.e.veinlet-dissemination-stockwork orebodies in the K-Si alteration zone and pegmatiticquartz sulfide veins above them.In addition,minor breccia ore occurs locally.Four types of fluid inclusions in the deposit and altered quartz monzonite are identified:L-type one-or two-phase aqueous inclusions,V-type vapor-rich inclusions with V/L ratios greater than 50%-90%,D-type multiphase fluid inclusions containing daughter minerals or solids and S-type silicate-bearing fluid inclusions containing mainly muscovite and biotite.Ore petrography and fluid inclusion study has revealed a three-stage mineralization process,driven by magmatic-hydrothermal fluid activity,as follows.Initially,a hydrothermal fluid,separated from the parent magma,infiltrated into the quartz monzonite,resulting in its extensive K-Si alteration,as indicated by silicate-bearing fluid inclusions trapped in altered quartz monzonite.This is followed by the early mineralization,the formation of quartz veinlets and dissemination-stockwork ores.During the main mineralization stage,due to the participation and mixing of meteoric groundwater with magmatic-sourced hydrothermal fluid,the cooling and phase separation caused deposition of metals from the hydrothermal fluids.As a result,the pegmatitic-quartz sulfide-vein ores formed.In the late mineralization stage,decreasing fluid salinity led to the formation of L-type aqueous inclusions and chalcopyrite-sulfosalt ore.Coexistence of V-type and D-type inclusions and their similar homogenization temperatures with different homogenization modes suggest that phase separation or boiling of the ore-forming fluids took place during the early and the main mineralization stages.The formation P-T conditions of S-type inclusions and the early and the main mineralization stages were estimated as ca.156-182 MPa and 450-650℃,350-450℃,18-35 MPa and 280-380℃,8-15 MPa,respectively,based on the microthermometric data of the fluid inclusions formed at the individual stages.

Infrared microthermometry of fluid inclusion in sphalerite:A case study of the Xinqiao deposit in the Middle-Lower Yangtze metallogenic belt

Infrared microthermometry allows direct measurement of fluid inclusions hosted in opaque ore minerals and can provide direct constraints on the evolution of ore-forming fluids.This study presents infrared microthermometry of spherite-hosted fluid inclusions from the Xinqiao deposit in the Middle-Lower Yangtze Metallogenic Belt and sheds new light on the ore genesis of the deposit.Considering that infrared light may lead to non-negligible temperature deviations during microthermometry,some tests were first conducted to ensure the accuracy of the microthermometric measurements.The measurement results indicated that using the lowest light intensity of the microscope and inserting an optical filter were effective in minimizing the possible temperature deviations of infrared microthermometry.All sphalerite-hosted fluid inclusions from the Xinqiao deposit were aqueous.They show homogenization temperature ranging from~200 to 350℃,but have two separate salinity groups(1.0 wt%-10 wt%and 15.1 wt%-19.2 wt%NaCl equivalent).The low-salinity group represents sedimentary exhalative(SEDEX)-associated fluids,whereas the high-salinity group results from modification by later magmatic hydrothermal fluids.Combined with published fluid inclusion data,the four-stage fluid evolution of the Xinqiao deposit was depicted.Furthermore,our data suggest that the Xinqiao deposit was formed by twostage metallogenic events including SEDEX and magmatic-hydrothermal mineralization.

Utility of fluid inclusion paleo-temperature in petroleum system modelling:A case study from western offshore,India

The paleo-temperature(Th)data from fluid inclusions are utilized for thermal history modelling using PetroMod software.Generally,bottom hole temperature(BHT)and vitrinite reflectance(Ro)measurements are widely used in petroleum system modelling(PSM)in the oil industry for calibration purposes.Th representing the minimum temperature of fluid entrapment estimated from fluid-inclusion study provides extra support to build the thermal models for PSM.Fluid inclusion parameters along with Rock-Eval pyrolysis analysis have been used to predict the maturity of oil in terms of API gravity as well as the maturity of source rocks respectively.Two exploratory wells RV-1(Mumbai Offshore Basin)and KK4C-A-1(Kerala-Konkan Offshore Basin),India were examined and the T_(h)from most of the fluid inclusions of wells RV-1 and KK4C-A-1 fell in the oil window range of 60-140℃suggesting thermal conditions favourable for oil generation in both of the wells.T_(h)of coeval aqueous inclusions along with the Hydrocarbon Fluid inclusions(HCFIs)was used to calibrate PSM.Vital parameters show that source rocks of well RV-1 are mature and that of well KK4C-A-1 are immature.Two sets of PSM are created in terms of generation and expulsion for the dry wells RV-1 and KK4C-A-1 and calibrated each well using fluid inclusion Th and BHT.From the fluid inclusion analysis method,it is evident that hydrocarbon generation happened in both wells and the paleo-temperature indicates that the formations of both wells were subjected to temperatures in the oil window range,even though it was designated as dry wells in the present scenario.The present study highlights the application of fluid inclusion paleo-temperature(Th)during calibration instead of commonly used methods.We could obtain desirable and accurate data output from PSM using T_(h) calibration.

Fluid inclusion and mineralization of Dafulou tin deposit in Dachang metal district, Guangxi, south China

Based on the study of the petrology, mineralogy, structural geology and fluid inclusion of the Dafulou ore deposit in the Dachang ore field, the ore deposit geology and ore-forming fluids were analyzed. It shows that there are five main hydrothermal alteration types in the Dafulou ore district, namely the silicification, carbonate, sericite, pyrite and pyrrhotite. The mineralization types are composed of the stratiform type, interlayer type and stockwork type. The ore textures present as metasomatic texture, euhedral-subhedral granular texture and solid solution texture. The ore structure consists of massive structure, dissemination structure, fine veined structure, stockwork structure and brecciated structure. Four ore types are recognized, namely the disseminated ore, dense massive ore, veinlet ore and brecciated ore. Six types of fluid inclusions are determined, i.e. the single-phase gaseous fluid inclusions, single-phase salt solution fluid inclusions, two-phase vapour-rich fluid inclusions, two-phase liquid-rich fluid inclusions, three-phase CO2-rich fluid inclusions and solid（s）-bearing fluid inclusions, all of which form in three dominant temperature scopes, 120-150, 230-270, 350-460 °C. But, the majority of them form in the high temperature environment （350-460 °C）. The tectonism plays an important role in the mineralization, which usually controls the scale, occurrence and shape of the Sn orebody. There are four types of hydrothermal fluid systems, H2O-NaCl-CaCl2, H2O-CaCl2, H2O-NaCl-MgCl2 and H2O-MgCl2. Similar to the other ore deposits in the Dachang ore field, there also exists the multiple source of ore-forming fluids. Overall, the Dafulou ore deposit should be the result of the crust-mantle interaction.

Fluid Inclusions of Calcite and Sources of Ore-forming Fluids in the Huize Zn-Pb-(Ag-Ge) District, Yunnan, China

The Huize Zn-Pb- (Ag-Ge) district is a typical representative of the well-known medium-to large-sized carbonate-hosted Zn-Pb- (Ag-Ge) deposits, occurring in the Sichuan-Yunnan-Guizhou Pb-Zn Ore-forming Zone. Generally, fluid inclusions within calcite, one of the major gangue minerals, are dominated by two kinds of small (1-10 um) inclusions including pure-liquid and liquid. The inclusions exist in concentrated groups along the crystal planes of the calcite. The ore-forming fluids containing Pb and Zn, which belong to the Na+-K+-Ca2+-Cl--F--SO42- type, are characterized by temperatures of 164-221℃, medium salinity in 5-10.8 wt% NaCl, and medium pressure at 410×105 to 661×105 Pa. The contents of Na+-K+ and C1--F-, and ratios of Na+/K+-Cl-/F- in fluid inclusions present good linearity. The ratios of Na+/K+ (4.66-6.71) and Cl-/F- (18.21-31.04) in the fluid inclusions of calcite are relatively high, while those of Na+/K+ (0.29-5.69) and Cl-/F- (5.00-26.0) in the inclusions of sphalerite and pyrite are relatively low. The ratio of Na+/K+ increases in accord with those of Cl-/F-, which indicates that ore-forming fluid of deep source participates in the mineralization. The waters of fluid inclusions have δD values from -43.5‰ to -55.4‰ of calcite. The δ18OV-SMOW values of the ore-forming fluids, calculated values, range from 17.09‰ to 18.56‰ of calcite and 17.80‰ to 23.14‰ for dolomite. δ13CV-PDB values range from -1.94‰ to -3.31‰ for calcite and -3.35‰ to 0.85‰ for the ore-bearing dolomite. These data better demonstrate that the ore-forming fluids were mainly derived from metamorphic water and magmatic hot fluid, in relation to the metamorphism of the Kunyang Group in the basement and magmatic hydrothermalism. The deposit itself might have resulted from ascending cycles of ore-forming fluid, enriched in Pb and Zn. The Huize Zn-Pb- (Ag-Ge) deposits related to carbonate-hosted Zn-Pb sulphides.

Decrepitation Thermometry and Compositions of Fluid Inclusions of the Damoqujia Gold Deposit,Jiaodong Gold Province,China:Implications for Metallogeny and Exploration

The recently discovered Damoqujia （大磨曲家） gold deposit is a large shear zone-hosted gold deposit of disseminated sulphides located in the north of the Zhaoping （招平） fault zone, Jiaodong （胶东） gold province, China. In order to distinguish the temperature range of cluster inclusions from different mineralization stages and measure their compositions, 16 fluid inclusions and 5 isotopic geochemistry samples were collected for this study. Corresponding to different mineralization stages, the multirange peaks of quartz decrepitation temperature （250-270, 310-360 and 380-430℃） indicate that the activity of ore-forming fluids is characterized by multistage. The ore-forming fluids were predominantly of high-temperature fluid system （HTFS） by CO2-rich, and SO4^2--K^＋ type magmatic fluid during the early stage of mineralization and were subsequently affected by low-temperature fluid system （LTFS） of CH4-rich, and Cl^--Na^＋/Ca^2＋ type meteoric fluid during the late stage of mineralization. Gold is transferred by Au-HS^- complex in the HTFS, and Au-Cl^- complex can be more important in the LTFS. The transition of fluids from deeper to shallow environments results in mixing between the HTFS and LTFS, which might be one of the most key reasons for gold precipitation and large-scale mineralization. The ore-forming fluids are characterized by high-temperature, strong-activity, and superimposed mineralization, so that there is a great probability of forming large and rich ore deposit in the Damoqujia gold deposit. The main bodies are preserved and extend toward deeper parts, thereby suggesting a great potential in future.

Genesis of the Bangbu Orogenic Gold Deposit, Tibet： Evidence from Fluid Inclusion, Stable Isotopes, and Ar-Ar Geochronology

The Bangbu gold deposit is a large orogenic gold deposit in Tibet formed during the AlpineHimalayan collision. Ore bodies（auriferous quartz veins） are controlled by the E-W-trending Qusong-Cuogu-Zhemulang brittle-ductile shear zone. Quartz veins at the deposit can be divided into three types： pre-metallogenic hook-like quartz veins, metallogenic auriferous quartz veins, and postmetallogenic N-S quartz veins. Four stages of mineralization in the auriferous quartz veins have been identified：（1） Stage S1 quartz＋coarse-grained sulfides,（2） Stage S2 gold＋fine-grained sulfides,（3） Stage S3 quartz＋carbonates, and（4） Stage S4 quartz＋ greigite. Fluid inclusions indicate the oreforming fluid was CO_2-N_2-CH_4 rich with homogenization temperatures of 170–261°C, salinities 4.34–7.45 wt% Na Cl equivalent. δ^（18）Ofluid（3.98‰–7.18‰） and low δDV-SMOW（-90‰ to-44‰） for auriferous quartz veins suggest ore-forming fluids were mainly metamorphic in origin, with some addition of organic matter. Quartz vein pyrite has δ^（34）SV-CDT values of 1.2‰–3.6‰（an average of 2.2‰）, whereas pyrite from phyllite has δ^（34）SV-CDT 5.7‰–9.9‰（an average of 7.4‰）. Quartz vein pyrites yield 206Pb/204 Pb ratios of 18.662–18.764, 207Pb/204 Pb 15.650–15.683, and ^（208）Pb/204 Pb 38.901–39.079. These isotopic data indicate Bangbu ore-forming materials were probably derived from the Langjiexue accretionary wedge. 40Ar/39 Ar ages for sericite from auriferous sulfide-quartz veins yield a plateau age of 49.52 ± 0.52 Ma, an isochron age of 50.3 ± 0.31 Ma, suggesting that auriferous veins were formed during the main collisional period of the Tibet-Himalayan orogen（-65–41 Ma）.

He-Ar Isotopic Systematics of Fluid Inclusions in Pyrites from PGEpolymetallic Deposits in Lower Cambrian Black Rock Series, South China

He-Ar isotopic compositions of fluid inclusions trapped in pyrites from some representative PGE-polymetallic deposits in Lower Cambrian black rock series in South China were analyzed by using an inert gas isotopic mass spectrometer. The results show that the ore-forming fluids possess a low 3He/4He ratio, varying from 0.43×10-8 to 26.39×10-8, with corresponding R/Ra value of 0.003-0.189. The 40Ar/36Ar ratios are 258-287, close to those of air saturated water (ASW). He-Ar isotopic indicator studies show that the ore-forming fluids were mainly derived from the formation water or basinal hot brine and sea water, while the content of mantle-derived fluid or deep-derived magmatic water might be negligible. The PGE-polymetallic mineralization might be related to the evolution of the Caledonian miogeosynclines distributed along the southern margin of the Yangtze Craton. During the Early Cambrian, the formation water or basinal hot brine trapped in Caledonian basins which accumulated giant thick sediments was expelled and migrated laterally along strata because of the pressure generated by overlying sediments. The basinal hot brine ascended along faults, mixed with sea water and finally deposited ore minerals.

Mineralization Styles and Genesis of the Yinkeng Au-Ag-Pb-Zn-Cu-Mn Polymetallic Orefield, Southern Jiangxi Province, SE China: Evidence from Geology, Fluid Inclusions, Isotopes and Chronology

The Yinkeng orefield in Yudu County,Jiangxi Province,SE China,is a zone of concentrated Au-Ag-Pb-Zn-Cu-Mn polymetallic ores.Based on summing up basic geology and ore geology of the orefieid,the polymetallic deposits in the orefield have been divided into seven major substyles according to their occurring positions and control factors.The ore-forming fluid inclusion styles in the orefield include those of two-phase fluid,liquid CO2-bearing three-phase and daughter mineral-bearing multi-phase.The homogenization temperatures range from 382° to 122℃,falling into five clusters of 370° to 390°,300° to 360°,230° to 300°,210° to 290° and 120° to 200°,and the clusters of 300° to 360°,230° to 300° and 120° to 200° are three major mineralization stages,with fluid salinity peaks from 4.14% to 7.31%,2.07% to 7.31% and 0.53% to 3.90%,respectively.The ore-forming fluids are mainly type of NaCl-H2O with medium to high density （0.74-1.02 g/cm3）,or CO2-bearing NaCl-H2O with medium to low density （0.18-0.79 g/cm3）.The fluid salinity and density both show a decline tendency with decreasing temperature.According to the measurement and calculation of Hand O-isotopic compositions in the quartz of the quartz-sulfide veins,δDV-SMOW of the ore-forming fluid is from-84‰ to-54‰,and δ18OV-SMOW of that is from 6.75‰ to 9.21‰,indicating a magmatic fluid.The δ34SV-CDT of sulfides in the ores fall into two groups,one is from-4.4‰ to 2.2‰ with average of-1.42‰,and the other from 18.8‰ to 21.6‰ with average of 19.8‰.The S-isotopic data shows one peak at-4.4‰ to 2.2‰ （meaning-1.42‰） suggesting a simple magmatic sulfur source.The ore Pbisotopic ratios are 206pb/204pb from 17.817 to 17.983,207pb/204pb from 15.470 to 15.620 and 208pb/204pb from 38.072 to 38.481,indicating characteristics of mantle-derived lead.The data show that the major ore deposits in the orefield have a magmatic-hydrothermal genesis and that the SHRIMP zircon age of the granodiorite porphyry,closely related to the mineralization,is 151.2±4.2 Ma （MSWD =1.3）,which can represent the formation ages of the ores and intrusion rocks.The study aids understanding of the ore-forming processes of the major metallic ore deposits in the orefield.

Degree of Brine Evaporation and Origin of the Mengyejing Potash Deposit：Evidence from Fluid Inclusions in Halite

The Mengyejing potash deposit is located in the southern port of the Simao Basin, Yunnan Province, and is hosted in mid-Cretaceous strata. The chemical compositions of fluid inclusions in halite crystals, collected from the level-610 adit in the deposit, were analysed by laser ablation inductively coupled plasma mass spectrometry（LA-ICP-MS）. The results show that the brine is of the Na-K-Mg-Ca-Cl type and has K concentrations that are distinctly higher than those of Mg and Ca, unlike normal brines associated with Cretaceous halite. The high K concentrations indicate that the degree of evaporation of the ancient Mengyejing saline lake was very high, reaching the sylvite deposition stage but rarely reaching the carnallite deposition stage. The trajectory of the H and O isotopic compositions of the brines in the halite-hosted fluid inclusions corresponds to intense evaporation, indicating that the net evaporation exceeded the net inflow of brines. These brine compositions in halite-hosted fluid inclusions were likely formed by the dissolution of previously deposited K-bearing minerals by fresh continental and/or seawater, forming a type of modified seawater, with deep hydrothermal fluids potentially supplying additional potassium. The basin likely experienced multiple seawater incursion, dissolution and redeposition events in a high-temperature environment with high evaporation rates.

Discovery and Significance of High CH_4 Primary Fluid Inclusions in Reservoir Volcanic Rocks of the Songliao Basin,NE China

Comparing compositions of the fluid inclusions in volcanic rocks to the contents and isotopes of the gases in corresponding volcanic reservoirs using microthermometry, Raman microspectroscopy and mass spectrum analysis, we found that： （1） up to 82 mole% methane exists in the primary inclusions hosted in the reservoir volcanic rocks; （2） high CH4 inclusions recognized in the volcanic rocks correspond to CH4-bcaring CO2 reservoirs that are rich in helium and with a high ^3He/^4He ratio and which show reversed order of 813C in alkane; （3） in gas reservoirs of such abiotic methane （〉80%） and a mix of CH4 and CO2, the enclosed content of CH4 in the volcanic inclusions is usually below 42 mole%, and the reversed order of δ^13C in alkane is sometimes irregular in the corresponding gas pools; （4） a glassy inclusion with a homogeneous temperature over 900℃ also contains a small portion of CH4 although predominantly CO2. This affinity between gas pool and content of inclusion in the same volcanic reservoirs demonstrates that magma-originated gases, both CH4 and CO2, have contributed significantly to the corresponding gas pools and that the assumed hydrocarbon budget of the bulk earth might be much larger than conventionally supposed.

Genesis of the Zhaokalong Fe-Cu Polymetallic Deposit at Yushu, China: Evidence from Ore Geochemistry and Fluid Inclusions

The ore types of the Zhaokalong Fe-Cu deposit are divided into two categories： sulfide-type and oxide-type. The sulfide-type ore include siderite ore, galena-sphalerite ore and chalcopyrite ore, whereas the oxide-type ore include magnetite ore and hematite ore. The ore textures and structures indicate that the Zhaokalong deposit is of the sedimentary-exhalative mineralization type. Geochemical analyses show that the two ore types have a high As, Sb, Mn, Co and Ni content. The REE patterns reveal an enrichment of the LREE compared to the HREE. Isotopic analysis of siderite ore reveal that the j13CpDB ranges from -2.01 to 3.34 （%0） whereas the JISOsMow ranges from 6.96 to 18.95 （%0）. The fluid inclusion microthermometry results indicate that homogenization temperatures of fluid inclusions in quartz range from 131 to 181~C, with salinity values of 1.06 to 8.04 wt% NaCI eq. The mineralizing fluid therefore belongs to the low temperature - low salinity system, with a mineralizing solution of a CO2-Ca2＋（Na＋, K＋）-SO42- （F-, CI--H20 system. The geochemical results and fluid inclusion data provide additional evidence that the Zhaokalong deposit is a sedex-type deposit that experienced two stages of mineralization. The sulfide mineralization probably occurred first, during the sedimentary exhalative process, as exhibited by the abundance of marine materials associated with the sulfide ores, indicating a higher temperature and relatively deoxidized oceanic depositional environment. After the main exhalative stage, hydrothermal activity was superimposed to the sulfide mineralization. The later stage oxide mineralization occurred in a low temperature and relatively oxidized environment, in which magmatic fluid circulation was dominant.

China's First Independent Cobalt Deposit and its Metallogenic Mechanism:Evidence from Fluid Inclusions and Isotopic Geochemistry

The Tuolugou cobalt deposit is the first independent large-scale Co- and Au-bearing deposit discovered in northwestern China. It is located in the eastern Kunlun orogenic belt in Qinghai Province, and occurs conformably in low-grade metamorphic volcano-sedimentary rock series with well-developed Na-rich hydrothermal sedimentary rocks and typical hydrothermal sedimentary ore fabrics. Fluid inclusions and isotopic geochemistry studies suggest that cobalt mineralizing fluid is dominated by NaCI-H20 system, accompanied by NaCI-CO2-H20-N2 system responsible for gold mineralization. Massive, banded and disseminated pyrite ores have similar compositions of He and Ar isotopes from the mineralizing fluid, with 3He/4He range between 0.10 to 0.31Ra （averaging 0.21Ra）, and 4~Ar/36Ar between 302 and 569 （averaging 373）, which reflects that Co mineralizing fluids derived dominantly from meteoric water deeply circulating. ~34S values of pyrite approaches to zero （~34S ranging from -4.5%o to ＋1.5%o, centering around -1.8%o to -0.2%o）, reflecting its deep source. Ore lead is characterized by distinctly high radiogenesis, with 2~6pb/2~4pb〉19.279, 2~7pb/2~4pb〉15.691 and 2~spb/2~4pb〉39.627, and its values show an increase trend from country rocks, regional Paleozoic volcanic rocks to ores. This may have suggested that high radiogentic ore Pb derived mainly from country rocks by leaching meteoric water-dominated hydrothermal fluid during its circulation at depth. Cobalt occurs mainly in sulfide phase （such as pyrite）, but cobalt enrichment, and presence and increasing contents of Co-bearing minerals have a positive correlation with metamorphic degree. The Tuolugou deposit and other typical strata-bound Co-Cu-Au deposits have striking similarities in the geological features and metallogenic pattern of primary cobalt. All of them are syngenetic hydrothermal exhalative sedimentation in origin.

Fluid Inclusions and Metallization of the Kendekeke Polymetallic Deposit in Qinghai Province, China

The Kendekeke polymetallic deposit,located in the middle part of the magmatic arc belt of Qimantag on the southwestern margin of the Qaidam Basin,is a polygenetic compound deposit in the Qimantag metallogenic belt of Qinghai Province.Multi-periodic ore-forming processes occurred in this deposit,including early-stage iron mineralization and lead-zinc-gold-polymetallic mineralization which was controlled by later hydrothermal process.The characteristics of the ore-forming fluids and mineralization were discussed by using the fluid inclusion petrography,Laser Raman Spectrum and micro-thermometry methods.Three stages,namely,S1-stage （copper-iron-sulfide stage）,S2-stage （lead-zinc-sulfide stage） and C-stage （carbonate stage） were included in the hydrothermal process as indicated by the results of this study.The fluid inclusions are in three types：aqueous inclusion （type I）,CO2-aqueous inclusion （type Ⅱ） and pure CO2 inclusion （type Ⅲ）.Type Ⅰ inclusions were observed in the S1-stage,having homogenization temperature at 240-320℃,and salinities ranging from 19.8％ to 25.0％ （wt％ NaCl equiv.）.All three types of inclusions,existing as immiscible inclusion assemblages,were presented in the S2-stage,with the lowest homogenization temperature ranging from 175 ℃ to 295℃,which represents the metallogenic temperature of the S2-stage.The salinities of these inclusions are in the range of 1.5％ to 16％.The fluid inclusions in the C-stage belong to types Ⅰ,Ⅱ and Ⅲ,having homogenization temperatures at 120-210℃,and salinities ranging from 0.9％ to 14.5％.These observations indicate that the ore-forming fluids evolved from high-temperature to low-temperature,from high-salinity to low-salinity,from homogenization to immiscible separation.Results of Laser Raman Spectroscopy show that high density of CO2 and CH4 were found as gas compositions in the inclusions.CO2,worked as the pH buffer of ore-forming fluids,together with reduction of organic gases （i.e.CH4,etc）,affected the transport and sediment of the minerals.The fluid system alternated between open and close systems,namely,between lithostatic pressure and hydrostatic pressure systems.The calculated metallogenic pressures are in the range of 30 to 87 Mpa corresponding to 3 km mineralization depth.Under the influence of tectonic movements,immiscible separation occurred in the original ore-forming fluids,which were derived from the previous high-salinity,high-temperature magmatic fluids.The separation of CO2 changed the physicochemical properties and composition of the original fluids,and then diluted by mixing with extraneous fluids such as meteoric water and groundwater,and metallogenic materials in the fluids such as lead,zinc and gold were precipitated.

Geological and Fluid Inclusion Constraints on Gold Deposition Processes of the Dayingezhuang Gold Deposit, Jiaodong Peninsula, China

The Dayingezhuang gold deposit,hosted mainly by Late Jurassic granitoids on Jiaodong Peninsula in eastern China,contains an estimated 170 t of gold and is one of the largest deposits within the Zhaoping fracture zone.The orebodies consist of auriferous altered pyrite–sericite–quartz granites that show Jiaojia-type(i.e.,disseminated and veinlet)mineralization.Mineralization and alteration are structurally controlled by the NE-to NNE-striking Linglong detachment fault.The mineralization can be divided into four stages:(K-feldspar)–pyrite–sericite–quartz,quartz–gold–pyrite,quartz–gold–polymetallic sulfide,and quartz–carbonate,with the majority of the gold being produced in the second and third stages.Based on a combination of petrography,microthermometry,and laser Raman spectroscopy,three types of fluid inclusion were identified in the vein minerals:NaCl–H2 O(A-type),CO2–H2 O–NaCl(AC-type),and pure CO2(PC-type).Quartz crystals in veinlets that formed during the first stage contain mainly AC-type fluid inclusions,with rare PC-type inclusions.These fluid inclusions homogenize at temperatures of 251°C–403°C and have low salinities of 2.2–9.4 wt%NaCl equivalent.Quartz crystals that formed in the second and third stages contain all three types of fluid inclusions,with total homogenization temperatures of 216°C–339°C and salinities of 1.8–13.8 wt%NaCl equivalent for the second stage and homogenization temperatures of 195°C–321°C and salinities of 1.4–13.3 wt%NaCl equivalent for the third stage.In contrast,quartz crystals that formed in the fourth stage contains mainly A-type fluid inclusions,with minor occurrences of AC-type inclusions;these inclusions have homogenization temperatures of 106°C–287°C and salinities of 0.5–7.7 wt%NaCl equivalent.Gold in the ore-forming fluids may have changed from Au(HS)0 as the dominant species under acidic conditions and at relatively high temperatures and f O2 in the early stages,to Au(HS)2–under neutral-pH conditions at lower temperatures and f O2 in the later stages.The precipitation of gold and other metals is inferred to be caused by a combination of fluid immiscibility and water–rock interaction.

Geochronology,Fluid Inclusions and Isotopic Characteristics of the Dongjun Pb-Zn-Ag Deposit,Inner Mongolia,NE China

The Dongjun Pb-Zn-Ag deposit in the northern part of the Great Xing’an Range(NE China)consists of quartzsulfide vein-type and breccia-type mineralization,related to granite porphyry.Hydrothermal alteration is well-developed and includes potassic-silicic-sericitic alteration,phyllic alteration and propylitic alteration.Three stages of mineralization are recognized on the basis of field evidence and petrographic observation,demarcated by assemblages of quartz-pyritearsenopyrite(early stage),quartz-polymetallic sulfide(intermediate stage)and quartz-carbonate-pyrite(late stage).Zircon LA-ICP-MS U-Pb dating indicates that the granite porphyry was emplaced at 146.7±1.2 Ma(Late Jurassic).Microthermometry and laser Raman spectroscopy shows that ore minerals were deposited in conditions of intermediate temperatures(175-359℃),low salinity(0.5-9.3 wt% Na Cl eqv.)and low density(0.60-0.91 g/cm^(3)).Ore-forming fluids were derived largely from magmatic hydrothermal processes,with late-stage addition of meteoric water,belonging to a H_(2)O-NaCl-CO_(2)±CH_(4) system.The δ^(34)SV-CDT values range from 0.75‰ to 4.70‰.The ^(206)Pb/^(204)Pb,^(207)Pb/^(204)Pb,and ^(208)Pb/^(204)Pb values of the ore minerals are in the ranges of 18.240-18.371,15.542-15.570,and 38.100-38.178,respectively.Data for the S and Pb isotopic systems indicate that the ore-forming metals and sulfur were derived from Mesozoic magma.Based on the geological characteristics and geochemical signatures documented in this study,we conclude that the Dongjun deposit is a mesothermal magmatic hydrothermal vein-type Pb-Zn-Ag deposit controlled by fractures and related to granite porphyry,in response to Late Jurassic tectonic-magmatic-hydrothermal activity.We further conclude that fluid immiscibility,fluid mixing and fluid-rock interactions were the dominant mechanisms for deposition of the ore-forming materials.

Determination of Hydrocarbon Charging History by Diagenetic Sequence and Fluid Inclusions:A Case Study of the Kongquehe Area in the Tarim Basin

Petrographic analysis of hydrocarbon inclusions in reservoirs is the basis and prerequisite for study of hydrocarbon charge history using fluid inclusion analysis.Samples from Silurian reservoirs in the Kongquehe area were studied with microscopy,cathode luminescence and scanning electron microscopy,and the paragenetic sequence of diagenetic events was established.Aqueous and oil inclusions were found in four different occurrences,i.e.,① in healed cracks in detrital quartz grains,② in quartz overgrowths that were formed relatively early in diagenesis,③ in healed cracks crosscutting quartz overgrowths and detrital quartz,and ④ in paragenetically late calcite cements.Solid bitumens were found in intergranular pores and in late fractures,whereas gas inclusions occur in healed cracks crosscutting quartz overgrowths and detrital quartz.The homogenization temperatures of aqueous（Th_（aq）） and oil incluisons（Th_0） within individual fluid inclusion assemblages are very consistent,suggesting that the microthermometric data are reliable.The Th_（aq） values are generally larger than Th_0,indicating the oil charging events took place at significant depths.The results suggest that there were at least two episodes of hydrocarbon charging in the Kongquehe area：the early hydrocarbon charging occurred in late Caledonian,dominated by oil,and the late hydrocarbon charging occurred in the Yanshan-Himalayan,first by oil and then gases.In addition,two episodes of hydrocarbon reservoir adjustment and destruction occurred in the Hercynian and Himalayan,respectively,forming solid bitumen.

Thermodynamic Modeling of Fluid-Bearing Natural Gas Inclusions for Geothermometer and Geobarometer of Overpressured Environments in Qiongdongnan Basin, South China Sea

It is a very difficult problem to directly determine fluid pressure duringhydrocarbon migration and accumulation in sedimentary basins. pVt modeling of coupling hydrocarbonfluid inclusion of its coeval aqueous fluid inclusion provides a powerful tool for establishing therelationship of formation pressure evolution with time. Homogenization temperature of fluidinclusion can routinely be measured under microthermometric microscopy. Crushing technique has beenemployed to obtain the composition of fluid inclusions, and the commercial software VTFLINC easilyand rapidly completes the construction of p-t phase diagram. The minimum trapping pressure ofhydrocarbon fluid inclusion would be then determined in the p-t space. In this paper, three samplesof YC21-1-1 and YC21-1-4 wells at YC21-1 structural closure, Qiongdongnan basin, South China Sea,were selected for the pVt modeling practice, and the formation pressure coefficient (equals to fluidpressure/hydrostatic pressure) changing trend with time has primarily been established. Themodeling results also indicate that the reservoirs of Ling-shui and Yacheng formations in YC21-1structure are within a very high potential system and would have undergone a discharging of thermalfluids through top seal rupture, which depicts that there is a very high risk for natural gasexploration in this area.