Located along the southern part of the West Qinling orogenic belt,the Yangshan gold deposit is one of the largest in China.The major gold ores of Yangshan are disseminated in metasedimentary host rocks with minor nati...Located along the southern part of the West Qinling orogenic belt,the Yangshan gold deposit is one of the largest in China.The major gold ores of Yangshan are disseminated in metasedimentary host rocks with minor native gold amounts in stibnite-gold quartz veins.Pyrite and arsenopyrite are the major Au-bearing minerals.Hydrothermal muscovite from gold-bearing quartz veins was dated using the in situ Rb-Sr method to determine the formation age of the Yangshan gold deposit.The Rb-Sr isochron date of the muscovite yielded 210.1±5.6 Ma(MSWD=1.2).This date is near the lower end of the period of the mineralized granitic dykes(210.49-213.10 Ma).Two stages of gold enriching process are recognized in the gold-bearing pyrite:the first is incorporated with the Co,Cu,As,Ni enrichment;and the second is accompanied by Bi,Co,Ni,Pb,Cu,Sb concentration.The in-situ sulfur isotopic values of pyrites show a restrictedΔ34s range of-1.43‰to 2.86‰with a mean value of 0.43‰.Trace-element mapping and in-situ sulfur isotopic analysis of pyrite suggest that the sulfur deposits are likely derived from a magmatic source and likely assimilated by sulfur from the sedimentary bedrock.Thus,magmatism plays a critical role in the formation of the Yangshan gold deposit.展开更多
Based on the metallogenetic geology conditions, the H, O, C and S isotopic compositions were measured by MAT-251 mass spectrometer, and Pb isotope and Rb-Sr dating were carried with MAT-261 multi-acceptor mass spectro...Based on the metallogenetic geology conditions, the H, O, C and S isotopic compositions were measured by MAT-251 mass spectrometer, and Pb isotope and Rb-Sr dating were carried with MAT-261 multi-acceptor mass spectrometer. The results show that the δ18O values of gold-bearing vein quartz from different levels are 1.19%-1.42%. The calculated δ18O values of ore fluids are 0.55%-0.78%, and δD values are from –8.64% to –6.66%. The calculated values of δ 34 SH2Sby the δ34Spy values in quartz veins display sulfur isotope compositions from -0.053% to +0.413%. Carbon isotope compositions of carbonates are from -0.612% to 0.140%. The mole ratios of 206Pb to 204Pb, 207Pb to 204Pb and 208Pb to 204Pb in auriferous quartz vein are 16.987-17.545, 15.342-15.623, and 38.254-38.744, respectively. The age of the Zhuanghe gold deposit determined by Rb-Sr isochron of the fluid inclusions in quartzes is (143.0±5.8) Ma. These isotopic data suggest that the metallogenetic fluids are generated from magmatic hydrotherm and the origin of ore-forming matters is related to the deep-derived magmatic activities. Meanwhile, the metallogenetic epoch of the Zhuanghe gold deposit is in Yanshanian period.展开更多
1 Introduction
Recent improvements in the precision of Li and B isotope measurements have demonstrated the potential of these elements in tracing a wide range of geological processes. The Li and B isotope sys... 1 Introduction
Recent improvements in the precision of Li and B isotope measurements have demonstrated the potential of these elements in tracing a wide range of geological processes. The Li and B isotope systematics of ultrahigh-pressure (UHP) metamorphic rocks provides a unique opportunity to investigate the behaviour of Li and B during fluid-rock interaction at high temperatures and very high pressures and to constrain the fluid budget and the recycling of subducted crustal materials into the mantle during UHP metamorphism.
……展开更多
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 mas...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.展开更多
On the basis of detailed geological studies of the Wulong gold deposit, three metallogenic stages can be identified. With quartz fluid inclusions as an object of study, the authors investigated phase characteristics, ...On the basis of detailed geological studies of the Wulong gold deposit, three metallogenic stages can be identified. With quartz fluid inclusions as an object of study, the authors investigated phase characteristics, compositional variations, temperature and pressure changes, fluid evolution, Pb isotope tracing and Rb-Sr isotopic dating of fluid inclusions entrapped in the above three metallogenic stages. The results show that Na+ is decreased obviously with metallogenic evolution, while K+ and other cations and gas compositions (H2, CO, CH4 and CO2) are increased slightly, and that the temperature and salinity vary in a pulsating manner along with the metallogenic evolution. Inverse calculation of hydrogen and oxygen isotopes indicate that at the first metallogenic stage the fluids were magmatic water, at the second stage they were dominated by magmatic water with a minor amount of meteoric water involved, and at the third stage, i.e., the final stage of metallogenesis, the fluids were composed completely of meteoric water. Its Pb isotopic composition implicates that the ore lead has some affinities with the lead in the Sanguliu granite, but the linear array of the ore-lead isotopic data reflects a mixing source of two end members. It can be deduced that the ore-forming materials and magma were both derived mainly from the same magma source region at depths. The Rb-Sr isotopic ages of the fluid inclusions are 112.2±3.2 Ma, indicating that the Wulong gold deposit was formed during the Yanshanian period.展开更多
The subduction factories in convergent plate margins exert crucial control on recycling terrestrial components and returning to the overlying crust. The Nd and Hf isotopic systems provide potential tracers to evaluate...The subduction factories in convergent plate margins exert crucial control on recycling terrestrial components and returning to the overlying crust. The Nd and Hf isotopic systems provide potential tracers to evaluate these processes. Here we present a case where these isotopic systems are decoupled in a suite of granites from the Chinese Altai, showing a wide range of εHf(t) values(from -4.7 to +10.8) in contrast to a limited range of εNd(t) values(from -5.8 to -1.9). The zircon xenocrysts occurring frequently in these rocks show markedly negative εHf(t) values(from -34.3 to -6.5) and positive d7 Li values(from +12.5 to +18.2). We propose a model to explain the observed relationship between residual zircon and Nde Hf isotope decoupling. We suggest that the Altai granites originated from partial melting of subducted slab components under relatively low temperature conditions which aided the residual zircon from oceanic sediments to inherit and retain a significant amount of177 Hf in the source, thereby elevating the^(176) Hf/^(177) Hf ratio of the melt, and decoupling from the^(143) Nd/^(144) Nd ratio during the subsequent magmatic processes. Our study illustrates a case where sediment recycling in subduction zone contributes to decoupling of Nd and Hf isotopic systems, with former providing a more reliable estimate of the source characteristics of granitic magmas.展开更多
Rb -Sr isotopic isochron dating of the volcanic rock samples from the Upper Cretaceous Half Three Point Formation on the King George Island is 71. 33±0. 3 Ma. Correlative study of εND(T)-147Sm/144Nd, 143Nd/144Nd...Rb -Sr isotopic isochron dating of the volcanic rock samples from the Upper Cretaceous Half Three Point Formation on the King George Island is 71. 33±0. 3 Ma. Correlative study of εND(T)-147Sm/144Nd, 143Nd/144Nd-87Sr/86Sr, 87Sr/86Sr-Sr and 87Sr/86Sr-K2O/(K2O+Na2O) indicated that the volcanic rocks were chiefly derived from the depleted mantle source and generally were not mixed crust materials. Of the samples 6 were given the mean Sm -Nd model age (TDM) of 443. 3±20. 6 Ma possibly indicating the age of chemical variation event in the magma source of the study area. Features of the trace elements indicated that the rocks from the Half Three Point Formation are of typical calc-alkaline volcanic suite and similar to those from the Tertiary volcanic rocks of the Fildes Peninsula, being the same products of the island-arc volcanic activity.展开更多
The combined petrographic,petrological,geochemical and geochronological study of the Neoproterozoic gneisses of the Sarychabyn and Baskan complexes of the Junggar Alataw of South Kazakhstan elucidate the Precambrian t...The combined petrographic,petrological,geochemical and geochronological study of the Neoproterozoic gneisses of the Sarychabyn and Baskan complexes of the Junggar Alataw of South Kazakhstan elucidate the Precambrian tectonic evolution of the Aktau–Yili terrane.It is one of the largest Precambrian crustal blocks in the western Central Asian orogenic belt.The U-Pb single-grain zircon ages indicate that granite-gneisses formed from the same source and crystallised in the early Neoproterozoic ca.930–920 Ma.The chemical composition of gneisses corresponds to A2-type granites.The whole-rock Nd isotopic characteristics(εNd(t)=−4.9 to−1.0 and TNd(DM-2st)=1.9 to 1.7 Ga)indicate the involvement of Paleoproterozoic crustal rocks in magma generation.Early Neoproterozoic ca.930–920 Ma A-type granitoids in the Aktau–Yili terrane of South and Central Kazakhstan might reflect within-plate magmatism adjacent to the collisional belt or a local extension setting in back-arc areas of the continental arc.展开更多
The Meng’entaolegai Ag-Pb-Zn vein-type deposit in Inner Mongolia,NE China is hosted in biotite/muscovite granite.This deposit includes the western(Zn-rich,deepest),middle(Zn-Pb rich)and eastern(Pb-Ag-rich,shallowest)...The Meng’entaolegai Ag-Pb-Zn vein-type deposit in Inner Mongolia,NE China is hosted in biotite/muscovite granite.This deposit includes the western(Zn-rich,deepest),middle(Zn-Pb rich)and eastern(Pb-Ag-rich,shallowest)ore-blocks.To better understand the metallogenic processes in ore district,we have undertaken a series of studies including fluid inclusion microthermometry,H-O-S-Pb isotope compositions and thermodynamic modeling.Based on fluid inclusion petrography,microthermometry results and HO isotope compositions,the ore-forming H2O-NaCl fluid inclusions are characterized by medium temperature and medium salinity.And two kinds of fluid processes(boiling in western and middle ore-block and fluid mixing in the eastern ore-block)were identified to explain the ore fluid evolution.More importantly,log ?O2-pH diagrams of δ^34S contours with the stability fields of Fe-and Cu-,Zn-,Pb-,and Ag-bearing minerals were constructed to restore the physicochemical conditions of ore-forming fluid in the western(270℃ and 80 bars),middle(250℃ and 70 bars),and eastern(230℃ and 50 bars)ore-blocks.As a result,the ore-forming conditions in the western and middle ore-block were similar.In the eastern ore-block,the fluids may have changed from acidic,S-poor and δ^34S(ΣS)≈2.8 to neutral,S-richer and δ^34S(ΣS)≈0.5,which imply that neutral S-rich meteoric water was mixed with the magmatic fluid.Meanwhile,the activity of Ag+was estimated to be about 10 ppm–9 ppm in the middle ore-block,but in the eastern ore-block it was about^10 ppm–12 ppm.We proposed that the key for Ag ore deposition was likely to be neutralization led by fluid mixing.展开更多
The extensive tracing of Nd, Sr and Pb isotopes has revealed that there exist high-degree heterogeneities in suboceanic mantle and mantle anomalies of the Southern Hemisphere on a large scale (DUPAL, high <sup>8...The extensive tracing of Nd, Sr and Pb isotopes has revealed that there exist high-degree heterogeneities in suboceanic mantle and mantle anomalies of the Southern Hemisphere on a large scale (DUPAL, high <sup>87</sup>Sr/<sup>86</sup>Sr, and HIMU, high μ value, i. e. <sup>238</sup> U/<sup>204</sup>pb). Recently, the isotopic tracing of the Cenozoic Volcanics from the continent of China has confirmed that there exists a general tendency that the subcontinental mantle of eastern China was en-展开更多
This study reports the sphalerite Rb-Sr age and LA-MC-ICP-MS in situ sulfur isotope analysis results of the Daliangzi Lead-Zinc Deposit in the Sichuan-Yunnan-Guizhou (SYG) triangle. Sphalerite Rb-Sr dating yields a ...This study reports the sphalerite Rb-Sr age and LA-MC-ICP-MS in situ sulfur isotope analysis results of the Daliangzi Lead-Zinc Deposit in the Sichuan-Yunnan-Guizhou (SYG) triangle. Sphalerite Rb-Sr dating yields a Mississippian age of 345.2±3.6 Ma (MSWD=I.4), which is older than the published Late Triassic mineralization ages (230-200 Ma) of some other deposits. This indicates that at least two stages of lead-zinc mineralization have occurred in the SYG lead-zinc triangle. The first stage occurred in the Mississippian under an extensional environment, while the second stage occurred in the Late Triassic under a compressional environment. In situ sulfur isotope analysis of sphalerite growth zoning presents relatively large δ^34S values of 11.3‰-15.2‰ with small variations. The large δ^34S values indicate a reduced sulfur source of thermochemical reduction of seawater sulfates. Abundant organic matter in the black fracture zone possibly supplied reductants for thermochemical sulfate reduction (TSR) at the mineralization site. The small variation of δ^34S values suggests a slow and stable TSR process that could prevent the sudden supersaturation of sphalerite in the fluid and the resulting of fast participation. This is consistent with the well-crystallized characteristic of the sphalerite of the Daliangzi Deposit.展开更多
THE Dajiangping pyrite ore deposit located in the Yunfu County of Guangdong Province is asuper-large pyrite ore deposit. Its age has not been defined so far because of the absence of fos-sil. This note is to use Rb-Sr...THE Dajiangping pyrite ore deposit located in the Yunfu County of Guangdong Province is asuper-large pyrite ore deposit. Its age has not been defined so far because of the absence of fos-sil. This note is to use Rb-Sr isotope dating of silicalite to constrain the age of the ore depositand place special emphasis on its geological significance.展开更多
Geologists are paying more attention to studies on genesis of granitoids and their metallogenetic characteristics through tracing their source materials and geological evolution by means of strontium, neodymium and le...Geologists are paying more attention to studies on genesis of granitoids and their metallogenetic characteristics through tracing their source materials and geological evolution by means of strontium, neodymium and lead isotopes. However, using Sm-Nd isotopes to study source rocks of young granites, especially of the Mesozoic granites is not as effective as using Rb-Sr isotopes. In order to explain geological significance of isotopic studies, this note only makes use of Rb-Sr and Pb isotopes to investigate the source rocks of Guposhan granite complex which is a very important granite pluton of the Mesozoic era in South China.展开更多
基金financially supported by China Geological Survey Project(Grant No.DD20220971)。
文摘Located along the southern part of the West Qinling orogenic belt,the Yangshan gold deposit is one of the largest in China.The major gold ores of Yangshan are disseminated in metasedimentary host rocks with minor native gold amounts in stibnite-gold quartz veins.Pyrite and arsenopyrite are the major Au-bearing minerals.Hydrothermal muscovite from gold-bearing quartz veins was dated using the in situ Rb-Sr method to determine the formation age of the Yangshan gold deposit.The Rb-Sr isochron date of the muscovite yielded 210.1±5.6 Ma(MSWD=1.2).This date is near the lower end of the period of the mineralized granitic dykes(210.49-213.10 Ma).Two stages of gold enriching process are recognized in the gold-bearing pyrite:the first is incorporated with the Co,Cu,As,Ni enrichment;and the second is accompanied by Bi,Co,Ni,Pb,Cu,Sb concentration.The in-situ sulfur isotopic values of pyrites show a restrictedΔ34s range of-1.43‰to 2.86‰with a mean value of 0.43‰.Trace-element mapping and in-situ sulfur isotopic analysis of pyrite suggest that the sulfur deposits are likely derived from a magmatic source and likely assimilated by sulfur from the sedimentary bedrock.Thus,magmatism plays a critical role in the formation of the Yangshan gold deposit.
基金Project(20040491502) supported by the Doctoral Education Program Fund of Ministry of Education, China
文摘Based on the metallogenetic geology conditions, the H, O, C and S isotopic compositions were measured by MAT-251 mass spectrometer, and Pb isotope and Rb-Sr dating were carried with MAT-261 multi-acceptor mass spectrometer. The results show that the δ18O values of gold-bearing vein quartz from different levels are 1.19%-1.42%. The calculated δ18O values of ore fluids are 0.55%-0.78%, and δD values are from –8.64% to –6.66%. The calculated values of δ 34 SH2Sby the δ34Spy values in quartz veins display sulfur isotope compositions from -0.053% to +0.413%. Carbon isotope compositions of carbonates are from -0.612% to 0.140%. The mole ratios of 206Pb to 204Pb, 207Pb to 204Pb and 208Pb to 204Pb in auriferous quartz vein are 16.987-17.545, 15.342-15.623, and 38.254-38.744, respectively. The age of the Zhuanghe gold deposit determined by Rb-Sr isochron of the fluid inclusions in quartzes is (143.0±5.8) Ma. These isotopic data suggest that the metallogenetic fluids are generated from magmatic hydrotherm and the origin of ore-forming matters is related to the deep-derived magmatic activities. Meanwhile, the metallogenetic epoch of the Zhuanghe gold deposit is in Yanshanian period.
文摘 1 Introduction
Recent improvements in the precision of Li and B isotope measurements have demonstrated the potential of these elements in tracing a wide range of geological processes. The Li and B isotope systematics of ultrahigh-pressure (UHP) metamorphic rocks provides a unique opportunity to investigate the behaviour of Li and B during fluid-rock interaction at high temperatures and very high pressures and to constrain the fluid budget and the recycling of subducted crustal materials into the mantle during UHP metamorphism.
……
基金the National Natural Sciences Foundation of China(grants40173025,49928201)Trans-century Training Program Foundation for the Talents by the Ministry of Education the Visiting Scholar Foundation of Labs in Universities.
文摘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.
基金This research project was supported by the Outstanding Young Scientists Foundation(Grant No 49625304)the Ministry of Sciences and Technology of China(Grant No 95-pre-39).
文摘On the basis of detailed geological studies of the Wulong gold deposit, three metallogenic stages can be identified. With quartz fluid inclusions as an object of study, the authors investigated phase characteristics, compositional variations, temperature and pressure changes, fluid evolution, Pb isotope tracing and Rb-Sr isotopic dating of fluid inclusions entrapped in the above three metallogenic stages. The results show that Na+ is decreased obviously with metallogenic evolution, while K+ and other cations and gas compositions (H2, CO, CH4 and CO2) are increased slightly, and that the temperature and salinity vary in a pulsating manner along with the metallogenic evolution. Inverse calculation of hydrogen and oxygen isotopes indicate that at the first metallogenic stage the fluids were magmatic water, at the second stage they were dominated by magmatic water with a minor amount of meteoric water involved, and at the third stage, i.e., the final stage of metallogenesis, the fluids were composed completely of meteoric water. Its Pb isotopic composition implicates that the ore lead has some affinities with the lead in the Sanguliu granite, but the linear array of the ore-lead isotopic data reflects a mixing source of two end members. It can be deduced that the ore-forming materials and magma were both derived mainly from the same magma source region at depths. The Rb-Sr isotopic ages of the fluid inclusions are 112.2±3.2 Ma, indicating that the Wulong gold deposit was formed during the Yanshanian period.
基金financially supported by the National Natural Science Foundation of China(Grant No. 41502209)the Chinese State 973 Project (Grant No.2015CB250901)the Science Foundation of China University ofPetroleum, Beijing (Grant No. 2462014YJRC031)
文摘The subduction factories in convergent plate margins exert crucial control on recycling terrestrial components and returning to the overlying crust. The Nd and Hf isotopic systems provide potential tracers to evaluate these processes. Here we present a case where these isotopic systems are decoupled in a suite of granites from the Chinese Altai, showing a wide range of εHf(t) values(from -4.7 to +10.8) in contrast to a limited range of εNd(t) values(from -5.8 to -1.9). The zircon xenocrysts occurring frequently in these rocks show markedly negative εHf(t) values(from -34.3 to -6.5) and positive d7 Li values(from +12.5 to +18.2). We propose a model to explain the observed relationship between residual zircon and Nde Hf isotope decoupling. We suggest that the Altai granites originated from partial melting of subducted slab components under relatively low temperature conditions which aided the residual zircon from oceanic sediments to inherit and retain a significant amount of177 Hf in the source, thereby elevating the^(176) Hf/^(177) Hf ratio of the melt, and decoupling from the^(143) Nd/^(144) Nd ratio during the subsequent magmatic processes. Our study illustrates a case where sediment recycling in subduction zone contributes to decoupling of Nd and Hf isotopic systems, with former providing a more reliable estimate of the source characteristics of granitic magmas.
基金The project supported by the State Antarctic Committeethe National Natural Science Foundation of China
文摘Rb -Sr isotopic isochron dating of the volcanic rock samples from the Upper Cretaceous Half Three Point Formation on the King George Island is 71. 33±0. 3 Ma. Correlative study of εND(T)-147Sm/144Nd, 143Nd/144Nd-87Sr/86Sr, 87Sr/86Sr-Sr and 87Sr/86Sr-K2O/(K2O+Na2O) indicated that the volcanic rocks were chiefly derived from the depleted mantle source and generally were not mixed crust materials. Of the samples 6 were given the mean Sm -Nd model age (TDM) of 443. 3±20. 6 Ma possibly indicating the age of chemical variation event in the magma source of the study area. Features of the trace elements indicated that the rocks from the Half Three Point Formation are of typical calc-alkaline volcanic suite and similar to those from the Tertiary volcanic rocks of the Fildes Peninsula, being the same products of the island-arc volcanic activity.
基金financially supported by the Russian Science Foundation (RSF) (Grant No. 22-77-00082)financially supported of grant 075-15-2021-680 of the Ministry of Science and Higher Education of the Russian Federation
文摘The combined petrographic,petrological,geochemical and geochronological study of the Neoproterozoic gneisses of the Sarychabyn and Baskan complexes of the Junggar Alataw of South Kazakhstan elucidate the Precambrian tectonic evolution of the Aktau–Yili terrane.It is one of the largest Precambrian crustal blocks in the western Central Asian orogenic belt.The U-Pb single-grain zircon ages indicate that granite-gneisses formed from the same source and crystallised in the early Neoproterozoic ca.930–920 Ma.The chemical composition of gneisses corresponds to A2-type granites.The whole-rock Nd isotopic characteristics(εNd(t)=−4.9 to−1.0 and TNd(DM-2st)=1.9 to 1.7 Ga)indicate the involvement of Paleoproterozoic crustal rocks in magma generation.Early Neoproterozoic ca.930–920 Ma A-type granitoids in the Aktau–Yili terrane of South and Central Kazakhstan might reflect within-plate magmatism adjacent to the collisional belt or a local extension setting in back-arc areas of the continental arc.
基金We are grateful to the staff of the Analytical Laboratory in Beijing Research Institute of Uranium Geology,China National Nuclear Corporation(CNNC)for their advice and assistance in the isotope analysisThis work was financially supported by the Open Foundation of Key Laboratory of Mineral Resources Evaluation in Northeast Asiathe Ministry of Natural Resources of China.
文摘The Meng’entaolegai Ag-Pb-Zn vein-type deposit in Inner Mongolia,NE China is hosted in biotite/muscovite granite.This deposit includes the western(Zn-rich,deepest),middle(Zn-Pb rich)and eastern(Pb-Ag-rich,shallowest)ore-blocks.To better understand the metallogenic processes in ore district,we have undertaken a series of studies including fluid inclusion microthermometry,H-O-S-Pb isotope compositions and thermodynamic modeling.Based on fluid inclusion petrography,microthermometry results and HO isotope compositions,the ore-forming H2O-NaCl fluid inclusions are characterized by medium temperature and medium salinity.And two kinds of fluid processes(boiling in western and middle ore-block and fluid mixing in the eastern ore-block)were identified to explain the ore fluid evolution.More importantly,log ?O2-pH diagrams of δ^34S contours with the stability fields of Fe-and Cu-,Zn-,Pb-,and Ag-bearing minerals were constructed to restore the physicochemical conditions of ore-forming fluid in the western(270℃ and 80 bars),middle(250℃ and 70 bars),and eastern(230℃ and 50 bars)ore-blocks.As a result,the ore-forming conditions in the western and middle ore-block were similar.In the eastern ore-block,the fluids may have changed from acidic,S-poor and δ^34S(ΣS)≈2.8 to neutral,S-richer and δ^34S(ΣS)≈0.5,which imply that neutral S-rich meteoric water was mixed with the magmatic fluid.Meanwhile,the activity of Ag+was estimated to be about 10 ppm–9 ppm in the middle ore-block,but in the eastern ore-block it was about^10 ppm–12 ppm.We proposed that the key for Ag ore deposition was likely to be neutralization led by fluid mixing.
基金Project supported by the National Natural Science Foundation of China.
文摘The extensive tracing of Nd, Sr and Pb isotopes has revealed that there exist high-degree heterogeneities in suboceanic mantle and mantle anomalies of the Southern Hemisphere on a large scale (DUPAL, high <sup>87</sup>Sr/<sup>86</sup>Sr, and HIMU, high μ value, i. e. <sup>238</sup> U/<sup>204</sup>pb). Recently, the isotopic tracing of the Cenozoic Volcanics from the continent of China has confirmed that there exists a general tendency that the subcontinental mantle of eastern China was en-
基金financially supported by the China Geological Survey (No. 12120114019701)the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan)
文摘This study reports the sphalerite Rb-Sr age and LA-MC-ICP-MS in situ sulfur isotope analysis results of the Daliangzi Lead-Zinc Deposit in the Sichuan-Yunnan-Guizhou (SYG) triangle. Sphalerite Rb-Sr dating yields a Mississippian age of 345.2±3.6 Ma (MSWD=I.4), which is older than the published Late Triassic mineralization ages (230-200 Ma) of some other deposits. This indicates that at least two stages of lead-zinc mineralization have occurred in the SYG lead-zinc triangle. The first stage occurred in the Mississippian under an extensional environment, while the second stage occurred in the Late Triassic under a compressional environment. In situ sulfur isotope analysis of sphalerite growth zoning presents relatively large δ^34S values of 11.3‰-15.2‰ with small variations. The large δ^34S values indicate a reduced sulfur source of thermochemical reduction of seawater sulfates. Abundant organic matter in the black fracture zone possibly supplied reductants for thermochemical sulfate reduction (TSR) at the mineralization site. The small variation of δ^34S values suggests a slow and stable TSR process that could prevent the sudden supersaturation of sphalerite in the fluid and the resulting of fast participation. This is consistent with the well-crystallized characteristic of the sphalerite of the Daliangzi Deposit.
文摘THE Dajiangping pyrite ore deposit located in the Yunfu County of Guangdong Province is asuper-large pyrite ore deposit. Its age has not been defined so far because of the absence of fos-sil. This note is to use Rb-Sr isotope dating of silicalite to constrain the age of the ore depositand place special emphasis on its geological significance.
基金Project supported by the National Natural Science Foundation of China.
文摘Geologists are paying more attention to studies on genesis of granitoids and their metallogenetic characteristics through tracing their source materials and geological evolution by means of strontium, neodymium and lead isotopes. However, using Sm-Nd isotopes to study source rocks of young granites, especially of the Mesozoic granites is not as effective as using Rb-Sr isotopes. In order to explain geological significance of isotopic studies, this note only makes use of Rb-Sr and Pb isotopes to investigate the source rocks of Guposhan granite complex which is a very important granite pluton of the Mesozoic era in South China.