Stable carbon isotope geochemistry provides important information for the recognition of funda- mental isotope exchange processes related to the movement of carbon in the lithosphere and permits the elab- oration of m...Stable carbon isotope geochemistry provides important information for the recognition of funda- mental isotope exchange processes related to the movement of carbon in the lithosphere and permits the elab- oration of models for the global carbon cycle. Carbon isotope ratios in fluid-deposited graphite are powerful tools for unravelling the ultimate origin of carbon （organic matter, mantle, or carbonates） and help to constrain the fluid history and the mechanisms involved in graphite deposition. Graphite precipitation in fluid-deposited occurrences results from C02- and/or CH4-bearing aqueous fluids. Fluid flow can be considered as both a closed （without replenishment of the fluid） or an open system （with renewal of the fluid by successive fluid batches）. In closed systems, carbon isotope systematics in graphite is mainly governed by Rayleigh precipi- tation and/or by changes in temperature affecting the fractionation factor between fluid and graphite. Such processes result in zoned graphite crystals or in successive graphite generations showing, in both cases, isotopic variation towards progressive 13C or 12C enrichment （depending upon the dominant carbon phase in the fluid, C02 or CH4, respectively）. In open systems, in which carbon is episodically introduced along the fracture systems, the carbon systematics is more complex and individual graphite crystals may display oscillatory zoning because of Rayleigh precipitation or heterogeneous variations of 613C values when mixing of fluids or changes in the composition of the fluids are the mechanisms responsible for graphite precipitation.展开更多
The Jinman deposit is a Ag-bearing copper vein deposit located at the north marginof the Lanping-Simao back-arc basin in West Yunnan. Systematic studies of fluid inclusions andstable isotopes are presented in this pap...The Jinman deposit is a Ag-bearing copper vein deposit located at the north marginof the Lanping-Simao back-arc basin in West Yunnan. Systematic studies of fluid inclusions andstable isotopes are presented in this paper. The filling-replacement stage and the boiling-exhala-tive precipitation stage of mineralization took place at T1 = 140 - 280℃ and T2 = 94 - 204℃under pressure of (600 - 1200) ×105 Pa. The salinity of ore-forming solutions ranges from 5 wt%-20. 8 wt% (NaCl). Sulphide δ34S(CDT) values are in the rang of - 9.6‰ - + 11.03% witha range of 22. 66‰ showing an apparent "pagoda"-shaped distribution in histogram. Mean-while, the δ34S values of the various sulphides are consistent with the characters of isotope equi-librium fractionation, i. e., δ34SPy>δ34 SCp> δ34SBn. The TS/TOC ratios of the ores are widelyvariable between 0.16 and 5. 54 with no correlation of any kind can be established. Accirding to themodel of Ohmoto, the oxidation-reduction ratios of sulfur species in ore-forming solutions at the twomineralization stages were calculated to be R’1 = 2. 16×10(-17) and R’2 = 1. 55×104. δ13CCO2 (PDB)values obtained from fluid inclusions in calcite and quartz are between - 8.12‰ - - 3. 18‰, av-eraging - 5. 26‰, which are comparable with the isotopic composition of mantle-derived CO2.Inclusions in quartz yield δ13CCH4(PDB) between - 32. 11‰ and - 22. 04‰ (averaging- 26. 69‰),similar to that of methane in modern geothermal gases. For the ore-forming soutions, δ18OH2O(SMOW) values are between - 10. 57‰ and + 9. 77‰ and δDH2O(SMOW) are between - 51‰and - 135‰. Considering the effect of isotope exchange during waterrock reactions, most ofthe data are plotted along or close to the line defined by the reaction of meteoric water withclastic rocks, while a small part of the points fall near the reaction line of magmatic water withclastic rocks. In δ13C vs. δ18O diagram, the ore-forming soutions are plotted for the most partinto the mixing area between the meteoric fluid and the deep-seated fluid and partially on themixing line of P = 1.展开更多
滇西维西县铜厂箐铜矿床赋存于中侏罗统花开佐组二段粉砂质泥岩、粉砂岩夹泥灰岩中,受断裂构造控制呈脉状产出。本次通过研究与该矿床铜矿化关系密切的石英及方解石C-H-O同位素组成特征,揭示其成矿流体来源,进而探讨该矿床成因。研究发...滇西维西县铜厂箐铜矿床赋存于中侏罗统花开佐组二段粉砂质泥岩、粉砂岩夹泥灰岩中,受断裂构造控制呈脉状产出。本次通过研究与该矿床铜矿化关系密切的石英及方解石C-H-O同位素组成特征,揭示其成矿流体来源,进而探讨该矿床成因。研究发现,该矿床中主成矿阶段与铜矿共生的方解石样品的δ13 C V-PDB值变化于-6.93‰~-6.16‰,均值为-6.69‰,δ18 O V-SMOW值变化于10.88‰~13.07‰,均值为11.98‰;与铜矿共生的石英样品的δ18 O V-SMOW值变化于14.22‰~16.88‰,均值为15.93‰,δD V-SMOW值介于-87.0‰~-61.7‰,均值为-75.99‰,表明成矿流体主要源自岩浆水。结合区域地质背景,认为在喜马拉雅期印度-欧亚大陆碰撞背景下,由于澜沧江深大断裂和雪龙山断裂长期活动,伴有深部岩浆含矿热液沿构造裂隙充填,形成铜厂箐脉状铜矿床。展开更多
Using the secondary spinel standard, the authors have precisely measured theFe^(3+)/SIGMA Fe values of spinels in mantle xenoliths from Cenozoic basalts in eastern China, andestimated the oxygen fugacities recorded by...Using the secondary spinel standard, the authors have precisely measured theFe^(3+)/SIGMA Fe values of spinels in mantle xenoliths from Cenozoic basalts in eastern China, andestimated the oxygen fugacities recorded by 63 mantle xenoliths through olivine-orthopyroxene-spineloxygen barometry. The results indicate that the oxygen fugacities of the lithospheric mantle ineastern China are higher in the south than in the north. Among them, the oxygen fugacity of theNorth China craton lithospheric mantle is the lowest, similar to that of the oceanic mantle, whilethat of Northeast and South China are the same as that of the global continental mantle. Thevariations of mantle redox state in eastern China are mainly controlled by the C-O-H fluids derivedfrom the asthenospheric mantle. According to the mantle oxidation state, it can be concluded thatthe C-O-H fluids in the lithospheric mantle of eastern China consist mainly of CO_2 and minor H_2O,but CH_4-rich fluids should come from the asthenosphere where the oxidation state is lower.展开更多
基金contribution from project CGL2010-16008 (Spanish Ministry for Science and Innovation)
文摘Stable carbon isotope geochemistry provides important information for the recognition of funda- mental isotope exchange processes related to the movement of carbon in the lithosphere and permits the elab- oration of models for the global carbon cycle. Carbon isotope ratios in fluid-deposited graphite are powerful tools for unravelling the ultimate origin of carbon （organic matter, mantle, or carbonates） and help to constrain the fluid history and the mechanisms involved in graphite deposition. Graphite precipitation in fluid-deposited occurrences results from C02- and/or CH4-bearing aqueous fluids. Fluid flow can be considered as both a closed （without replenishment of the fluid） or an open system （with renewal of the fluid by successive fluid batches）. In closed systems, carbon isotope systematics in graphite is mainly governed by Rayleigh precipi- tation and/or by changes in temperature affecting the fractionation factor between fluid and graphite. Such processes result in zoned graphite crystals or in successive graphite generations showing, in both cases, isotopic variation towards progressive 13C or 12C enrichment （depending upon the dominant carbon phase in the fluid, C02 or CH4, respectively）. In open systems, in which carbon is episodically introduced along the fracture systems, the carbon systematics is more complex and individual graphite crystals may display oscillatory zoning because of Rayleigh precipitation or heterogeneous variations of 613C values when mixing of fluids or changes in the composition of the fluids are the mechanisms responsible for graphite precipitation.
文摘The Jinman deposit is a Ag-bearing copper vein deposit located at the north marginof the Lanping-Simao back-arc basin in West Yunnan. Systematic studies of fluid inclusions andstable isotopes are presented in this paper. The filling-replacement stage and the boiling-exhala-tive precipitation stage of mineralization took place at T1 = 140 - 280℃ and T2 = 94 - 204℃under pressure of (600 - 1200) ×105 Pa. The salinity of ore-forming solutions ranges from 5 wt%-20. 8 wt% (NaCl). Sulphide δ34S(CDT) values are in the rang of - 9.6‰ - + 11.03% witha range of 22. 66‰ showing an apparent "pagoda"-shaped distribution in histogram. Mean-while, the δ34S values of the various sulphides are consistent with the characters of isotope equi-librium fractionation, i. e., δ34SPy>δ34 SCp> δ34SBn. The TS/TOC ratios of the ores are widelyvariable between 0.16 and 5. 54 with no correlation of any kind can be established. Accirding to themodel of Ohmoto, the oxidation-reduction ratios of sulfur species in ore-forming solutions at the twomineralization stages were calculated to be R’1 = 2. 16×10(-17) and R’2 = 1. 55×104. δ13CCO2 (PDB)values obtained from fluid inclusions in calcite and quartz are between - 8.12‰ - - 3. 18‰, av-eraging - 5. 26‰, which are comparable with the isotopic composition of mantle-derived CO2.Inclusions in quartz yield δ13CCH4(PDB) between - 32. 11‰ and - 22. 04‰ (averaging- 26. 69‰),similar to that of methane in modern geothermal gases. For the ore-forming soutions, δ18OH2O(SMOW) values are between - 10. 57‰ and + 9. 77‰ and δDH2O(SMOW) are between - 51‰and - 135‰. Considering the effect of isotope exchange during waterrock reactions, most ofthe data are plotted along or close to the line defined by the reaction of meteoric water withclastic rocks, while a small part of the points fall near the reaction line of magmatic water withclastic rocks. In δ13C vs. δ18O diagram, the ore-forming soutions are plotted for the most partinto the mixing area between the meteoric fluid and the deep-seated fluid and partially on themixing line of P = 1.
文摘滇西维西县铜厂箐铜矿床赋存于中侏罗统花开佐组二段粉砂质泥岩、粉砂岩夹泥灰岩中,受断裂构造控制呈脉状产出。本次通过研究与该矿床铜矿化关系密切的石英及方解石C-H-O同位素组成特征,揭示其成矿流体来源,进而探讨该矿床成因。研究发现,该矿床中主成矿阶段与铜矿共生的方解石样品的δ13 C V-PDB值变化于-6.93‰~-6.16‰,均值为-6.69‰,δ18 O V-SMOW值变化于10.88‰~13.07‰,均值为11.98‰;与铜矿共生的石英样品的δ18 O V-SMOW值变化于14.22‰~16.88‰,均值为15.93‰,δD V-SMOW值介于-87.0‰~-61.7‰,均值为-75.99‰,表明成矿流体主要源自岩浆水。结合区域地质背景,认为在喜马拉雅期印度-欧亚大陆碰撞背景下,由于澜沧江深大断裂和雪龙山断裂长期活动,伴有深部岩浆含矿热液沿构造裂隙充填,形成铜厂箐脉状铜矿床。
基金the Nationa1 Natural Science Foundation(Grant No.49673185)the Ministry of Science and Technology of China(Grant No.95-Pre-39).
文摘Using the secondary spinel standard, the authors have precisely measured theFe^(3+)/SIGMA Fe values of spinels in mantle xenoliths from Cenozoic basalts in eastern China, andestimated the oxygen fugacities recorded by 63 mantle xenoliths through olivine-orthopyroxene-spineloxygen barometry. The results indicate that the oxygen fugacities of the lithospheric mantle ineastern China are higher in the south than in the north. Among them, the oxygen fugacity of theNorth China craton lithospheric mantle is the lowest, similar to that of the oceanic mantle, whilethat of Northeast and South China are the same as that of the global continental mantle. Thevariations of mantle redox state in eastern China are mainly controlled by the C-O-H fluids derivedfrom the asthenospheric mantle. According to the mantle oxidation state, it can be concluded thatthe C-O-H fluids in the lithospheric mantle of eastern China consist mainly of CO_2 and minor H_2O,but CH_4-rich fluids should come from the asthenosphere where the oxidation state is lower.
