The Turpan-Hami Basin in eastern Xinjiang is one of the driest regions on Earth and a premier environment to form and preserve nitrate.A large nitrate ore field in this basin was found recently.It is estimated there a...The Turpan-Hami Basin in eastern Xinjiang is one of the driest regions on Earth and a premier environment to form and preserve nitrate.A large nitrate ore field in this basin was found recently.It is estimated there are about 2.5 billion tons of resources of nitrate,and the amount is as much as the Atacama Desert super-scale nitrate deposit in Chile.Nitrate is one of a few minerals with mass-independent fractionation（MIF）,and the oxygen isotope MIF is an effective method to determine the source of nitrate.Theδ^（17）O,δ^（18）O of nitrate were measured by fluorination and thermal decomposition method.The date indicated that this is the first time that oxygen isotope MIF has been located in inland nitrate minerals.The results obtained by two methods are similar,⊿^（17）=δ^（17）O-0.52×δ^（18）O=12‰-17‰.The experiment and observation data proved that oxygen isotope MIF of nitrate are the result of photochemical reactions in the troposphere and stratosphere.Thus, evidence from MIF oxygen isotopic compositions indicate that long term atmospheric deposition of nitrate aerosol particles produced by photochemical reactions is the source of the deposits.展开更多
Experiments for oxygen isotope exchange between ferberite and water were carried out and the followingequation on oxygen isotope fractionation between ferberite and water against temperature was obtained:Combining thi...Experiments for oxygen isotope exchange between ferberite and water were carried out and the followingequation on oxygen isotope fractionation between ferberite and water against temperature was obtained:Combining this equation with the equation of Clayton et al. (1972) on oxygen isotope fractionation be-tween quartz and water, an equation on oxygen isotope fractionation between quartz and ferberite was ob-tained:The Bigeleison-Mayer function method was used to calculate the oxygen isotope fractionation betweenquartz and ferberite. The theoretical curve obtained agrees with the experimental calibration results quite wellin the temperature range of study.The above calibrated equation has been used in 5 world famous tungsten deposits to determine their tem-peratures of formation. The results show that the temperature range for an idividual deposit determined by thisgeothermometer agrees with those obtained from fluid inclusion determination and other isotopegeothermometers.展开更多
The Archean atmospheric oxygen concentration and sulfur cycle was long debated.The banded iron formation(BIF)is a special type of the sedimentary formation,which has truly recorded the atmospheric and oceanic conditio...The Archean atmospheric oxygen concentration and sulfur cycle was long debated.The banded iron formation(BIF)is a special type of the sedimentary formation,which has truly recorded the atmospheric and oceanic conditions at that time.In this study,the composition of multiple sulfur isotope(δ34S/δ33S/δ32S)for sulfides bedded in the Archean(~2.7 Ga)BIFs,in Anshan-Benxi area of Liaoning Province has been measured.The value of△33S varies from-0.89‰to+1.21‰,which shows very obvious mass-independent fractionation(MIF)signatures.These non-zero△33S values indicate that the Archean sulfur cycles are different from what it is today,which have been deeply influenced by gas phase photochemical reactions.Algoma-type BIFs which are closely related to the volcanic activity have negative△33S value,however,Superior-type BIFs which are far away from the volcanic center have positive△33S value.Theδ34S varies in a large range from-22.0‰to+11.8‰,which indicates that the bacteria reduction activity has already existed at that time,and that the oceanic sulfate concentration has at least reached 1 mmol/L in local areas.Combined with the contemporaneous existence of the hematite,magnetite and the occurrence and preservation of the sulfur MIF,it can be inferred that the Archean atmospheric oxygen level must be at 10-2―10-3 of the present atmospheric level(PAL).展开更多
The recently discovered nitrate ore field in the Turpan-Hami Basin of western China represents an estimated resource of 2.5 billion tons, and is comparable in scale to the Atacama Desert super-scale nitrate deposit in...The recently discovered nitrate ore field in the Turpan-Hami Basin of western China represents an estimated resource of 2.5 billion tons, and is comparable in scale to the Atacama Desert super-scale nitrate deposit in Chile. The research on this area is rarely carried out, and the origin of the deposits remains uncertain. In this study, new methods were used to systematically analyze N and O isotopes in nitrate minerals collected from the Kumutage, Xiaocaohu, Wuzongbulak, Dawadi, Tuyugou, and Shaer ore deposits in the Turpan-Hami Basin. The data showed that the δ15NAir value ranges from 0.7‰ to 27.6‰, but mostly between 2‰ and 6‰, which was similar to atmospheric NO3-. The 18O was highly enriched with δ18OV-SMOW varying from 30.2‰ to 46.7‰. This differs from levels in deposits derived from microbial nitrogen fixation, but is similar to those in atmospheric nitrates. N and O isotopes data indicated that nitrate deposits in Turpan-Hami Basin must be the result of deposition of atmospheric nitrate particles. Although atmospheric nitrate particles are common, the nitrate deposits could form only under the condition of long-term extreme drought climate and very limited biological activity. This paper summarized the ore-forming mechanism of different types nitrate deposits based on their geological setting.展开更多
基金supported by the National Science Foundation of China(No:40543013, 40873003)and Key Laboratory of Isotope Geology, Ministry of Land and Resources
文摘The Turpan-Hami Basin in eastern Xinjiang is one of the driest regions on Earth and a premier environment to form and preserve nitrate.A large nitrate ore field in this basin was found recently.It is estimated there are about 2.5 billion tons of resources of nitrate,and the amount is as much as the Atacama Desert super-scale nitrate deposit in Chile.Nitrate is one of a few minerals with mass-independent fractionation（MIF）,and the oxygen isotope MIF is an effective method to determine the source of nitrate.Theδ^（17）O,δ^（18）O of nitrate were measured by fluorination and thermal decomposition method.The date indicated that this is the first time that oxygen isotope MIF has been located in inland nitrate minerals.The results obtained by two methods are similar,⊿^（17）=δ^（17）O-0.52×δ^（18）O=12‰-17‰.The experiment and observation data proved that oxygen isotope MIF of nitrate are the result of photochemical reactions in the troposphere and stratosphere.Thus, evidence from MIF oxygen isotopic compositions indicate that long term atmospheric deposition of nitrate aerosol particles produced by photochemical reactions is the source of the deposits.
文摘Experiments for oxygen isotope exchange between ferberite and water were carried out and the followingequation on oxygen isotope fractionation between ferberite and water against temperature was obtained:Combining this equation with the equation of Clayton et al. (1972) on oxygen isotope fractionation be-tween quartz and water, an equation on oxygen isotope fractionation between quartz and ferberite was ob-tained:The Bigeleison-Mayer function method was used to calculate the oxygen isotope fractionation betweenquartz and ferberite. The theoretical curve obtained agrees with the experimental calibration results quite wellin the temperature range of study.The above calibrated equation has been used in 5 world famous tungsten deposits to determine their tem-peratures of formation. The results show that the temperature range for an idividual deposit determined by thisgeothermometer agrees with those obtained from fluid inclusion determination and other isotopegeothermometers.
基金National Natural Science Foundation of China(Grant No.40273008)
文摘The Archean atmospheric oxygen concentration and sulfur cycle was long debated.The banded iron formation(BIF)is a special type of the sedimentary formation,which has truly recorded the atmospheric and oceanic conditions at that time.In this study,the composition of multiple sulfur isotope(δ34S/δ33S/δ32S)for sulfides bedded in the Archean(~2.7 Ga)BIFs,in Anshan-Benxi area of Liaoning Province has been measured.The value of△33S varies from-0.89‰to+1.21‰,which shows very obvious mass-independent fractionation(MIF)signatures.These non-zero△33S values indicate that the Archean sulfur cycles are different from what it is today,which have been deeply influenced by gas phase photochemical reactions.Algoma-type BIFs which are closely related to the volcanic activity have negative△33S value,however,Superior-type BIFs which are far away from the volcanic center have positive△33S value.Theδ34S varies in a large range from-22.0‰to+11.8‰,which indicates that the bacteria reduction activity has already existed at that time,and that the oceanic sulfate concentration has at least reached 1 mmol/L in local areas.Combined with the contemporaneous existence of the hematite,magnetite and the occurrence and preservation of the sulfur MIF,it can be inferred that the Archean atmospheric oxygen level must be at 10-2―10-3 of the present atmospheric level(PAL).
基金supported by Basic Scientific Research Operation Cost of State-Leveled Public Welfare Scientific Research Courtyard (Grant No. K0926)National Natural Science Foundation of China (Grant Nos. 40543013, 40873003)Key Laboratory of Isotope Geology, Ministry of Land and Resources
文摘The recently discovered nitrate ore field in the Turpan-Hami Basin of western China represents an estimated resource of 2.5 billion tons, and is comparable in scale to the Atacama Desert super-scale nitrate deposit in Chile. The research on this area is rarely carried out, and the origin of the deposits remains uncertain. In this study, new methods were used to systematically analyze N and O isotopes in nitrate minerals collected from the Kumutage, Xiaocaohu, Wuzongbulak, Dawadi, Tuyugou, and Shaer ore deposits in the Turpan-Hami Basin. The data showed that the δ15NAir value ranges from 0.7‰ to 27.6‰, but mostly between 2‰ and 6‰, which was similar to atmospheric NO3-. The 18O was highly enriched with δ18OV-SMOW varying from 30.2‰ to 46.7‰. This differs from levels in deposits derived from microbial nitrogen fixation, but is similar to those in atmospheric nitrates. N and O isotopes data indicated that nitrate deposits in Turpan-Hami Basin must be the result of deposition of atmospheric nitrate particles. Although atmospheric nitrate particles are common, the nitrate deposits could form only under the condition of long-term extreme drought climate and very limited biological activity. This paper summarized the ore-forming mechanism of different types nitrate deposits based on their geological setting.
