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Abstract: A fluid inclusion investigation of the polymetallic mineralization at Yinshan from the Le–De metallogenic belt in Jiangxi Province of China has been carried out using petrographic and microthermometric techniques. The data obtained here indicate that three major types of fluids were involved during the formation of the deposit. They are type I vapor-rich, type II liquid-rich and type III halite-bearing inclusions within the H2O–NaCl system. The high salinity fluids represented by type III inclusions, being unusual to the distal part of an intrusion-centered ore-forming system such as Yinshan, have been interpreted as the product of direct exsolution of a crystallizing magma, rather than a result of fluid immiscibility from a low salinity fluid. Evidence used to support such an interpretation includes the mode of homogenization of type III inclusions exclusively via halite dissolution, spatial separation of type I and type III inclusions on microscopic scale, the consistent phase ratios within the inclusions concerned, and considerable deviation in homogenization temperature for both type I and type III inclusions. Trapping conditions for type I inclusions were estimated to be around 440 °C and 260 bars, while type III inclusions were constrained to be trapped at least above 900 bars and >500 °C. The formation temperatures for type II inclusions range from 270 to 390 °C if a lithostatic pressure of 260 bars is assumed. Pressure fluctuation determined by this fluid inclusion study coupled with decreases in salinity and temperature as result of the potential fluid mixing are supposed to have played an important role in triggering the precipitation of ore minerals from the hydrothermal solution. [Copyright &y& Elsevier]

[Display omitted] • The parental granite formed by significant crustal contamination of partial mantle melts. • The hydrothermal fluids were derived from magmatic sources and gradually mixed with meteoric waters. • The precipitation of Mo was triggered by boiling and fluid-wallrock interactions. The Shiyaogou deposit in Luanchuan County, China, is a large concealed porphyry Mo deposit within the East Qinling metallogenic belt (EQMB). Major and trace element analyses reveal that the host granite is defined by high silica (SiO 2 = 71.56 to 75.25%) and alkali (Na 2 O + K 2 O = 6.91 to 7.88%) contents and has typical I-type characteristics. Zircons derived from the pluton yield U–Pb ages of 133.2 ± 1.1 Ma, indicating an early Cretaceous magmatic event in the EQMB. The ε Hf (t) values and T DM2 ages range from − 15.1 to − 11.2 and from 2.1 to 1.9 Ga, respectively, suggesting that the granite mainly originated from the lower crust melting with the involvement of mantle components. The mineralization process can be divided into three stages: (1) quartz + K-feldspar + pyrite + molybdenite; (2) quartz + pyrite + molybdenite; and (3) quartz + calcite veins. Three different types of fluid inclusions (FIs) are present in quartz veins: NaCl–H 2 O (W-type), CO 2 –H 2 O (C-type), and daughter mineral-bearing (S-type). Hematite is recognized as a daughter mineral in S-type inclusions of stage 1, whereas the daughter sulfide and reducing CH 4 gases can be observed in the stage 2 quartz, suggesting that the ore-forming fluids were initially oxidizing and then evolved to more reducing conditions. The FIs in stages 1 mainly display Th above 428 °C with salinities up to 57.62 wt% NaCl eqv; in stage 2, the FIs display Th of 132–423 °C and salinities of 3.23–50.03 wt% NaCl eqv; in stage 3, the FIs homogenized in the range of 117–247 °C with low salinities of 2.74–8.95 wt% NaCl eqv. The coexisting W-, S- and/or C-type inclusions homogenized at similar temperatures, but contain different salinities during stages 1 and 2, suggesting that the fluids boiled during both stages. Our study reveals that the ore-forming fluids are magmatic in origin. These high-temperature magmatic fluids gradually evolved from high salinities and high CO 2 contents to a mixture of magmatic and meteoric water with lower temperature, lower salinity, and lower CO 2 content. The precipitation of Mo mainly resulted from the decreasing temperature and salinity. Additionally, the changes in pH and CO 2 content due to boiling and the water–rock reaction could have contributed toward the precipitation of Mo. [ABSTRACT FROM AUTHOR]

Reports on advances in the study of fluid inclusions of the Yishan ore deposit in Jiangxi Province, China. Geology of the ore deposit; Different types of fluid inclusions of the deposit; Primary ore zoning; Origin of oil-forming fluid.

The article discusses a study on ore-forming fluid of Shiyaogou porphyry molybdenum deposit in Henan Province, China. Topics discussed include use of fluid inclusions stages and laser Raman technique in the study, types of fluid inclusions containing sodium chloride, water and carbon dioxide, and fluid boiling as dominant factor in formation of molybdenum deposits.

Abstract: This work reports the application of thermodynamic models, including equations of state, to binary (salt-free) CH4–H2O fluid inclusions. A general method is presented to calculate the compositions of CH4–H2O inclusions using the phase volume fractions and dissolution temperatures of CH4 hydrate. To calculate the homogenization pressures and isolines of the CH4–H2O inclusions, an improved activity–fugacity model is developed to predict the vapor–liquid phase equilibrium. The phase equilibrium model can predict methane solubility in the liquid phase and water content in the vapor phase from 273 to 623K and from 1 to 1000bar (up to 2000bar for the liquid phase), within or close to experimental uncertainties. Compared to reliable experimental phase equilibrium data, the average deviation of the water content in the vapor phase and methane solubility in the liquid phase is 4.29% and 3.63%, respectively. In the near-critical region, the predicted composition deviations increase to over 10%. The vapor–liquid phase equilibrium model together with the updated volumetric model of homogenous (single-phase) CH4–H2O fluid mixtures (Mao S., Duan Z., Hu J. and Zhang D. (2010) A model for single-phase PVTx properties of CO2–CH4–C2H6–N2–H2O–NaCl fluid mixtures from 273 to 1273K and from 1 to 5000bar. Chem. Geol. 275, 148–160), is applied to calculate the isolines, homogenization pressures, homogenization volumes, and isochores at specified homogenization temperatures and compositions. Online calculation is on the website: http://www.geochem-model.org/. [Copyright &y& Elsevier]