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
The orogenic gold deposits in Southeast Guizhou are an important component of the Xuefeng polymetallic ore belt and have significant exploration potential, but geochronology research on these gold deposits is scarce. ...The orogenic gold deposits in Southeast Guizhou are an important component of the Xuefeng polymetallic ore belt and have significant exploration potential, but geochronology research on these gold deposits is scarce. Therefore, the ore genetic models are poorly constrained and remain unclear. In the present study, two important deposits(Pingqiu and Jinjing) are investigated, including combined Re-Os dating and the He-Ar isotope study of auriferous arsenopyrites. It is found that the arsenopyrites from the Pingqiu gold deposit yielded an isochron age of 400 ± 24 Ma,with an initial ^(187)Os/^(188)Os ratio of 1.24 ± 0.57(MSWD = 0.96). An identical isochron age of 400 ± 11 Ma with an initial ^(187)Os/^(188)Os ratio of 1.55 ± 0.14(MSWD = 0.34) was obtained from the Jinjing deposit. These ages correspond to the regional Caledonian orogeny and are interpreted to represent the age of the main stage ore. Both initial ^(187)Os ratios suggest that the Os was derived from crustal rocks. Combined with previous rare earth element(REE), trace elements, Nd-Sr-S-Pb isotope studies on scheelite, inclusion fluids with other residues of gangue quartz, and sulfides from other gold deposits in the region, it is suggested that the ore metals from Pingqiu and Jinjing were sourced from the Xiajiang Group. The He and Ar isotopes of arsenopyrites are characterized by ~3 He/~4 He ratios ranging from 5.3 × 10^(-4) Ra to 2.5 × 10^(-2) Ra(Ra = 1.4 × 10^(-6), the ~3 He/~4 He ratio of air), 40 Ar=/~4 He ratios from 0.64 × 10^(-2) to 15.39×10^(-2), and ^(40)Ar/^(36)Ar ratios from 633.2 to 6582.0. Those noble gas isotopic compositions of fluid inclusions also support a crustal source origin,evidenced by the Os isotope. Meanwhile, recent noble gas studies suggest that the amount of in situ radiogenic ~4 He generated should not be ignored, even when Th and U are present at levels of only a few ppm in host minerals.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
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 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
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
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
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jointly supported by the National Natural Science Foundation of China (Grant Nos. 41303038, 41772070)Open Fund of State Key Laboratory of Ore Deposit Geochemistry (201502)the National Basic Research Program of China (2014CB440904)
文摘The orogenic gold deposits in Southeast Guizhou are an important component of the Xuefeng polymetallic ore belt and have significant exploration potential, but geochronology research on these gold deposits is scarce. Therefore, the ore genetic models are poorly constrained and remain unclear. In the present study, two important deposits(Pingqiu and Jinjing) are investigated, including combined Re-Os dating and the He-Ar isotope study of auriferous arsenopyrites. It is found that the arsenopyrites from the Pingqiu gold deposit yielded an isochron age of 400 ± 24 Ma,with an initial ^(187)Os/^(188)Os ratio of 1.24 ± 0.57(MSWD = 0.96). An identical isochron age of 400 ± 11 Ma with an initial ^(187)Os/^(188)Os ratio of 1.55 ± 0.14(MSWD = 0.34) was obtained from the Jinjing deposit. These ages correspond to the regional Caledonian orogeny and are interpreted to represent the age of the main stage ore. Both initial ^(187)Os ratios suggest that the Os was derived from crustal rocks. Combined with previous rare earth element(REE), trace elements, Nd-Sr-S-Pb isotope studies on scheelite, inclusion fluids with other residues of gangue quartz, and sulfides from other gold deposits in the region, it is suggested that the ore metals from Pingqiu and Jinjing were sourced from the Xiajiang Group. The He and Ar isotopes of arsenopyrites are characterized by ~3 He/~4 He ratios ranging from 5.3 × 10^(-4) Ra to 2.5 × 10^(-2) Ra(Ra = 1.4 × 10^(-6), the ~3 He/~4 He ratio of air), 40 Ar=/~4 He ratios from 0.64 × 10^(-2) to 15.39×10^(-2), and ^(40)Ar/^(36)Ar ratios from 633.2 to 6582.0. Those noble gas isotopic compositions of fluid inclusions also support a crustal source origin,evidenced by the Os isotope. Meanwhile, recent noble gas studies suggest that the amount of in situ radiogenic ~4 He generated should not be ignored, even when Th and U are present at levels of only a few ppm in host minerals.
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 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.
