The source of ore\|forming materials has long been a controversial focus both in metallogenic theory and in ore\|searching practice. This study deals with the helium and argon isotopic characteristics of pyrites from ...The source of ore\|forming materials has long been a controversial focus both in metallogenic theory and in ore\|searching practice. This study deals with the helium and argon isotopic characteristics of pyrites from 11 gold deposits and some country rocks in the gold mineralization\|concentrated areas within the three mantle\|branch structures in the region of North Hebei Province. It is indicated that \{\}\+3He/\+4He ratios in the gold deposits are within the range of \{0.93×10\+\{-6\}\}-\{7.3×10\+\{-6\}\}, with an average of \{3.55\} ×10\+\{-6\}; R/Ra=\{0.66\}-\{4.93\}, averaging \{2.53\}; \{\{\}\+\{40\}Ar/\+\{39\}Ar\} ratios vary between 426 and 2073, with the average value of \{\}\+\{40\}Ar being \{8.32\}; and the average of \{\}\+4He/\{\}\+\{40\}Ar ratios is 2.17. \{\}\+3He/ \{\}\+4He ratios in gneiss and granite in the periphery of the mining district are within the range of \{0.001×10\+\{-6\}\}-\{0.55×10\+\{-6\}\}, reflecting significant differences in their sources. \{\}\+3He and \{\}\+4He fall near the mantle, as is shown in the He concentration diagram. Studies have shown that the ore\|forming materials in this region should come from the deep interior of the Earth. With the multi\|stage evolution of mantle plume, ore\|forming fluids in the deep interior were moving upwards to shallow levels (crust). Under such circumstances, there would be inevitably occur crust/mantle fluid mixing, so their noble gas isotopic characteristics are intermediate between the mantle and the crust.展开更多
The barium deposits in Ankang and Xunyang counties,Shaanxi Province,China,occur in the northernmost part of the world-class barium metallogenic belt in south Qinling.The deposits are hosted by the Lower Silurian carbo...The barium deposits in Ankang and Xunyang counties,Shaanxi Province,China,occur in the northernmost part of the world-class barium metallogenic belt in south Qinling.The deposits are hosted by the Lower Silurian carbonaceous siliceous rocks,with a unique combination of barite and witherite.The homogenization temperatures of fluid inclusions in the barite are mainly concentrated between 135 and 155 ℃,whereas those from the witherite have two peaks of 165-175 ℃,and 215-225℃,respectively.Laser Raman analysis of fluid inclusions indicates that the vapor phase of fluid inclusions in barite is dominated by H_2O,although some contains N_2,H_2S,and CH_4.The compositions of the vapor and liquid phases of fluid inclusions in witherite can be divided into two end-members,one dominated by H_2O without other volatiles,and the other containing CH_4,C_2H_6,C_3H_8,C_2H_4,and C_6H_6 in addition to H_2O.CO_2,H_2S,and some CH_4 are interpreted as products of chemical reactions during mineralization.Organic gases（CH_4,C_2H_6,C_3H_8,C_2H_4,and C_6H_6） in the fluids were critical in the formation of barium sulfate versus carbonate.The δ^（34）S values of barite range from 38.26‰ to54.23‰（CDT）,the δ^（34）S values of sulfides coexisting with barium minerals vary from 22.44‰ to25.11‰（CDT）,and those in the wall rock from 11.60‰ to 19.06‰（CDT）.We propose that the SO_4^（2-）generally experienced bacterial sulfate reduction in seawater before mineralization,and some SO_4^（2-）also experienced thermochemical sulfate reduction in hydrothermal system during mineralization.The δ^（13）C values of witherite range from-27.30‰ to-11.80‰（PDB）,suggesting that carbon was sourced from organic substances（like CH_4,C_2H_4,and C_2H_6）.The formation of witherite was possibly associated with thermochemical sulfate reduction,which caused the consumption of the organic gases and SO_4^（2-） in the hydrothermal solutions,consequently inhibiting barite formation.The important conditions for forming witherite include high fluid temperatures,high Ba^（2＋） concentrations,CO_2 in the fluids,low HS^- concentrations,and the subsequent rapid diffusion of H_2S during thermochemical sulfate reduction of the fluids.展开更多
The Laowan deposit is a large gold deposit in the Qinling-Dabie orogenic belt where pyrite is the main Au-bearing mineral phase.We present results from the occurrences of gold,trace elements and sulfur isotopes of pyr...The Laowan deposit is a large gold deposit in the Qinling-Dabie orogenic belt where pyrite is the main Au-bearing mineral phase.We present results from the occurrences of gold,trace elements and sulfur isotopes of pyrite,and hydrogen and oxygen isotopes of quartz and calcite to elucidate the sources of ore-forming fluid;the genesis of pyrite and the ore-forming process.From field observations,five generations of pyrite are identified;one formed in a metamorphic-diagenetic epoch(PyI),and the others during four mineralization stages:1)the coarse-grained pyrite-quartz stage(PyII),2)the quartz and medium-to fine-grained pyrite stage(PyIII),3)the polymetallic sulfide stage(PyIV),and 4)the carbonate-quartz stage(PyV).Gold mainly occurs in PyIII and PyIV.We find that Au,Ag,Pb,and Cu are incorporated into pyrite as micro-/nano-inclusions and that Co,Ni,As,and Se enter the pyrite lattice via isomorphous replacement.The Co/Ni values and Se concentrations indicate that PyI formed from metamorphic hydrothermal fluids and that pyrites(PyII,PyIII,and PyIV)from the ore-forming stages typically reflect a hydrothermal genesis involving magmatic fluid.Theδ^34S values of PyI(1.45‰-2.09‰)are similar to that of plagioclase amphibole schist,indicating that S was primarily derived from wall rock,while those of PyII,PyIII,and PyIV(3.10‰-5.55‰)suggest that S was derived from the Guishanyan Formation and the Laowan granite.The four mineralization stages show a systematic decrease inδD(from−77.1‰to−82.8‰,−84.7‰,and−102.7‰),while theδ^18OH2O values showed a gradual decrease from 5.7 to 2.7‰,1.0‰,and−1.3‰.These data show that the ore-forming fluid was similar to a mixture of magmatic and meteoric waters.Thus,we conclude that the Laowan gold deposit is related to magmatic-hydrothermal fluid.展开更多
Investigation of isotope shift（IS） of optical transition is a very important method to obtain the nuclear parameters of an atom. The previous reports on investigation of isotope shifts of Hg were principally focused...Investigation of isotope shift（IS） of optical transition is a very important method to obtain the nuclear parameters of an atom. The previous reports on investigation of isotope shifts of Hg were principally focused on the strong transitions, such as 6<sup>1</sup>S<sub>0</sub>—6<sup>3</sup>P<sub>1</sub>（2537） and 6<sup>3</sup>P<sub>2</sub>—7<sup>3</sup>S<sub>1</sub>（5461）. And in the analysis of the isotope shift, the contribution of p electron was completely ignored due to the contribution of s electron being greatly larger than that ofp electron. These led to the ignorance of the information on p electron.展开更多
文摘The source of ore\|forming materials has long been a controversial focus both in metallogenic theory and in ore\|searching practice. This study deals with the helium and argon isotopic characteristics of pyrites from 11 gold deposits and some country rocks in the gold mineralization\|concentrated areas within the three mantle\|branch structures in the region of North Hebei Province. It is indicated that \{\}\+3He/\+4He ratios in the gold deposits are within the range of \{0.93×10\+\{-6\}\}-\{7.3×10\+\{-6\}\}, with an average of \{3.55\} ×10\+\{-6\}; R/Ra=\{0.66\}-\{4.93\}, averaging \{2.53\}; \{\{\}\+\{40\}Ar/\+\{39\}Ar\} ratios vary between 426 and 2073, with the average value of \{\}\+\{40\}Ar being \{8.32\}; and the average of \{\}\+4He/\{\}\+\{40\}Ar ratios is 2.17. \{\}\+3He/ \{\}\+4He ratios in gneiss and granite in the periphery of the mining district are within the range of \{0.001×10\+\{-6\}\}-\{0.55×10\+\{-6\}\}, reflecting significant differences in their sources. \{\}\+3He and \{\}\+4He fall near the mantle, as is shown in the He concentration diagram. Studies have shown that the ore\|forming materials in this region should come from the deep interior of the Earth. With the multi\|stage evolution of mantle plume, ore\|forming fluids in the deep interior were moving upwards to shallow levels (crust). Under such circumstances, there would be inevitably occur crust/mantle fluid mixing, so their noble gas isotopic characteristics are intermediate between the mantle and the crust.
基金jointly supported by the National Natural Science Foundation of China(grant nos. 41173062 and 40573032)the 111 project under the Ministry of Education and the State Administration of Foreign Experts Affairs,China(grant no.B07011)
文摘The barium deposits in Ankang and Xunyang counties,Shaanxi Province,China,occur in the northernmost part of the world-class barium metallogenic belt in south Qinling.The deposits are hosted by the Lower Silurian carbonaceous siliceous rocks,with a unique combination of barite and witherite.The homogenization temperatures of fluid inclusions in the barite are mainly concentrated between 135 and 155 ℃,whereas those from the witherite have two peaks of 165-175 ℃,and 215-225℃,respectively.Laser Raman analysis of fluid inclusions indicates that the vapor phase of fluid inclusions in barite is dominated by H_2O,although some contains N_2,H_2S,and CH_4.The compositions of the vapor and liquid phases of fluid inclusions in witherite can be divided into two end-members,one dominated by H_2O without other volatiles,and the other containing CH_4,C_2H_6,C_3H_8,C_2H_4,and C_6H_6 in addition to H_2O.CO_2,H_2S,and some CH_4 are interpreted as products of chemical reactions during mineralization.Organic gases（CH_4,C_2H_6,C_3H_8,C_2H_4,and C_6H_6） in the fluids were critical in the formation of barium sulfate versus carbonate.The δ^（34）S values of barite range from 38.26‰ to54.23‰（CDT）,the δ^（34）S values of sulfides coexisting with barium minerals vary from 22.44‰ to25.11‰（CDT）,and those in the wall rock from 11.60‰ to 19.06‰（CDT）.We propose that the SO_4^（2-）generally experienced bacterial sulfate reduction in seawater before mineralization,and some SO_4^（2-）also experienced thermochemical sulfate reduction in hydrothermal system during mineralization.The δ^（13）C values of witherite range from-27.30‰ to-11.80‰（PDB）,suggesting that carbon was sourced from organic substances（like CH_4,C_2H_4,and C_2H_6）.The formation of witherite was possibly associated with thermochemical sulfate reduction,which caused the consumption of the organic gases and SO_4^（2-） in the hydrothermal solutions,consequently inhibiting barite formation.The important conditions for forming witherite include high fluid temperatures,high Ba^（2＋） concentrations,CO_2 in the fluids,low HS^- concentrations,and the subsequent rapid diffusion of H_2S during thermochemical sulfate reduction of the fluids.
基金This research was supported by the Project of the Nanyang Basin and Orogenic Belt Metallogenic Diversity Research(No.2014-49)supported by No.1 Geological Exploration Institute,Henan Bureau of Geo-exploration and Mineral Development.
文摘The Laowan deposit is a large gold deposit in the Qinling-Dabie orogenic belt where pyrite is the main Au-bearing mineral phase.We present results from the occurrences of gold,trace elements and sulfur isotopes of pyrite,and hydrogen and oxygen isotopes of quartz and calcite to elucidate the sources of ore-forming fluid;the genesis of pyrite and the ore-forming process.From field observations,five generations of pyrite are identified;one formed in a metamorphic-diagenetic epoch(PyI),and the others during four mineralization stages:1)the coarse-grained pyrite-quartz stage(PyII),2)the quartz and medium-to fine-grained pyrite stage(PyIII),3)the polymetallic sulfide stage(PyIV),and 4)the carbonate-quartz stage(PyV).Gold mainly occurs in PyIII and PyIV.We find that Au,Ag,Pb,and Cu are incorporated into pyrite as micro-/nano-inclusions and that Co,Ni,As,and Se enter the pyrite lattice via isomorphous replacement.The Co/Ni values and Se concentrations indicate that PyI formed from metamorphic hydrothermal fluids and that pyrites(PyII,PyIII,and PyIV)from the ore-forming stages typically reflect a hydrothermal genesis involving magmatic fluid.Theδ^34S values of PyI(1.45‰-2.09‰)are similar to that of plagioclase amphibole schist,indicating that S was primarily derived from wall rock,while those of PyII,PyIII,and PyIV(3.10‰-5.55‰)suggest that S was derived from the Guishanyan Formation and the Laowan granite.The four mineralization stages show a systematic decrease inδD(from−77.1‰to−82.8‰,−84.7‰,and−102.7‰),while theδ^18OH2O values showed a gradual decrease from 5.7 to 2.7‰,1.0‰,and−1.3‰.These data show that the ore-forming fluid was similar to a mixture of magmatic and meteoric waters.Thus,we conclude that the Laowan gold deposit is related to magmatic-hydrothermal fluid.
基金Project supported by the National Natural Science Foundation of China
文摘Investigation of isotope shift（IS） of optical transition is a very important method to obtain the nuclear parameters of an atom. The previous reports on investigation of isotope shifts of Hg were principally focused on the strong transitions, such as 6<sup>1</sup>S<sub>0</sub>—6<sup>3</sup>P<sub>1</sub>（2537） and 6<sup>3</sup>P<sub>2</sub>—7<sup>3</sup>S<sub>1</sub>（5461）. And in the analysis of the isotope shift, the contribution of p electron was completely ignored due to the contribution of s electron being greatly larger than that ofp electron. These led to the ignorance of the information on p electron.
