Precise in situ zircon U-Pb dating and Lu-Hf isotopic measurement using an LA-ICP-MS system, whole-rock major and trace element geochemistry and Sr-Nd isotope geochemistry were conducted on the volcanic host rocks of ...Precise in situ zircon U-Pb dating and Lu-Hf isotopic measurement using an LA-ICP-MS system, whole-rock major and trace element geochemistry and Sr-Nd isotope geochemistry were conducted on the volcanic host rocks of the Tongyu copper deposit on the basis of further understanding of its geological characteristics. Three zircon samples from the volcanic host rocks yielded 206Pb/238 U weighted average ages ranging from 436±4 Ma to 440±5 Ma, which are statistically indistinguishable and coeval with the ca. 440 Ma northward subduction event of the Paleo-Qinling oceanic slab. The volcanic host rocks were products of magmatic differentiation that evolved from basalt to andesite to dacite to rhyolite, forming an integrated tholeiitic island arc volcanic rock suite. The primitive mantle-normalized trace element patterns for most samples show characteristics of island arc volcanic rocks, such as relative enrichment of LILE（e.g. Th, U, Pb and La） and depletion of HFSE（e.g. Nb, Ta, Ti, Zr and Hf）. Discrimination diagrams of Ta/Yb vs Th/Yb, Ta vs Th, Yb vs Th/Ta, Ta/Hf vs Th/Hf, Hf/3 vs Th vs Nb/16, La vs La/Nb and Nb vs Nb/Th all suggest that both the volcanic host rocks from the Tongyu copper deposit and the volcanic rocks from the regional Xieyuguan Group were formed in an island arc environment related to subduction of an oceanic slab. Values of ISr（0.703457 to 0.708218） and εNd（t）（-2 to 5.8） indicate that the source materials of volcanic rocks from the Tongyu copper deposit and the Xieyuguan Group originated from the metasomatised mantle wedge with possible crustal material assimilation. Most of the volcanic rock samples show good agreement with the values of typical island arc volcanic rocks in the ISr-εNd（t） diagram. The involvement of crustal-derived material in the magma of the volcanic rocks from the Tongyu copper deposit was also reflected in the zircon εHf（t） values, which range from-3.08 to 10.7, and the existence of inherited ancient xenocrystic zircon cores（2616±39 Ma and 1297±22 Ma）. The mineralization of the Tongyu copper deposit shows syn-volcanic characteristics such as layered orebodies interbedded with the volcanic rock strata, thus, the zircon U-Pb age of the volcanic host rocks can approximately represent the mineralization age of the Tongyu copper deposit. Both the Meigou pluton and the volcanic host rocks were formed during the ca. 440 Ma northward subduction of the Paleo-Qinling Ocean when high oxygen fugacity aqueous hydrothermal fluid released by dehydration of the slab and the overlying sediments fluxed into the mantle wedge, triggered partial melting of the mantle wedge, and activated and extracted Cu and other ore-forming elements. The magma and ore-bearing fluid upwelled and erupted, and consequently formed the island arc volcanic rock suite and the Tongyu VHMS-type copper deposit.展开更多
The Tongyu copper deposit, located in the western part of the North Qinling Orogen, China, is one of several volcanic-hosted massive sulphide（VHMS） deposits with industrial value and is also a typical example of min...The Tongyu copper deposit, located in the western part of the North Qinling Orogen, China, is one of several volcanic-hosted massive sulphide（VHMS） deposits with industrial value and is also a typical example of mineralization related to the subduction and metallogenesis during the Caledonian orogeny. We conducted systematic lead-sulphur isotope geochemical analyses of the Tongyu deposit to understand the possible ore-forming material sources and tectonic settings. Twenty-six sulphide samples yielded clustered δ^34SCDT values of 1.13‰-3.36‰, average 2.22‰, and show a tower-type distribution,implying that the sulphur of the Tongyu copper deposit mainly originated from a mantle source. The Pb isotope compositions of sulphides（^206Pb/^204Pb = 17.59225-18.56354, average 18.32020; ^207Pb/^204Pb =15.51770-15.69381, average 15.66217; ^208Pb/^204Pb= 37.99969-39.06953, average 38.52722） are close to the values of the volcanic host rocks（^206Pb/^204PbPb= 18.10678-18.26293, average 18.21158; ^207Pb/^204PbPb =15.63196-15.68188, average 15.65345; ^208Pb/^204PbPb= 38.43676-38.56360, average 38.49171）, thus consistent with the Pb in ores and volcanic host rocks having been derived from a common source that was island-arc Pb related to oceanic crust subduction. The northward subduction of the Palaeo-Qinling oceanic crust triggered dehydration of the slab, which generated a large amount of high-oxygen-fugacity aqueous hydrothermal fluid. The fluid rose into the mantle wedge, activated and extracted metallogenic material and promoted partial melting of the mantle wedge. The magma and ore-forming fluid welled up and precipitated, finally forming the Tongyu VHMS copper deposit.展开更多
The Tongyu volcanic-hosted massive sulfide(VHMS) copper deposit is located in the west part of the North Qinling(NQL),Shaanxi Province.Here we report geological features and trace elemental characteristics of ores,min...The Tongyu volcanic-hosted massive sulfide(VHMS) copper deposit is located in the west part of the North Qinling(NQL),Shaanxi Province.Here we report geological features and trace elemental characteristics of ores,mineralized rocks,and volcanic host rocks of this deposit.We also conducted in situ zircon U-Pb and Lu-Hf LA-ICP-MS dating and lithogeochemical study of the Meigou granodiorite,which is intruded in the south of the Tongyu mining district.It is inferred that the volcanic host rocks of the Tongyu Cu deposit belong to calc-alkaline island arc volcanic rocks,and the volcanic host rocks and the ore-forming materials share common material sources.During subduction of the Paleo-Qinling oceanic slab at around 472 Ma,high oxygen-fugacity aqueous fluid released by dehydration reaction of the subducting slab rose into the mantle wedge,leached Cu and other metal elements,and triggered partial melting of the mantle wedge.Associated with the ore-forming materials,the arc calc-alkaline magmas erupted and formed the Tongyu VHMS deposit.The weighted average zircon U-Pb age of the Meigou granodiorite is 439.3±3 Ma,suggesting its genesis is associated with the subduction event of the Paleo-Qinling oceanic plate around 440 Ma.In terms of the granitoid’s geochemical characteristics,the Mg#,Ni,and Cr contents are high.REE show strongly fractionated patterns with unobvious Eu anomalies.Sr contents are high while Y contents are low,resulting in high Sr/Y ratios.Two-stage zircon Hf model ages mostly range between 908 and 723 Ma,with εHf(t)】0.Therefore,we classify Meigou granodiorite as island arc granite with adakitic geochemical features.It was generated by interaction between mantle wedge and melt produced by partial melting of the subducted basaltic slab of the Paleo-Qinling Ocean.The Tongyu VHMS deposit was formed in the island arc tectonic setting during Ordovician-Silurian between 439.3±3 Ma and 472±11 Ma.The volcanic exhalation-sedimentation,which was contemporaneous with the submarine volcanics,produced the primary mineralization of the Tongyu Cu deposit.Afterward,the ore bodies and host rocks were reworked and overprinted intensively by structures corresponding with the overall collisional orogenic process of the Qinling Orogenic Belt during the Indosinian period.In contrast to classic VHMS deposits such as the Kuroko deposit in Japan,the Tongyu Cu deposit possesses the dual characteristics of island arc volcanic exhalation and sedimentation as well as structural reworking and overprinting.Therefore,the Tongyu VHMS Cu deposit is a volcanic exhalation and sedimentation-structural reworking and overprinting type deposit.展开更多
基金jointly supported by the National Natural Science Foundation of China(Grant Nos.41272092,41421002 and 41072068)Program for Changjiang Scholars and Innovative Research Team in University(Grant IRT1281)+1 种基金Natural Science Basic Research Program of Shaanxi Province,China(Grant No.2013JZ013)Graduate Innovation Funds of Northwest University,China(Grant No.YZZ12006)
文摘Precise in situ zircon U-Pb dating and Lu-Hf isotopic measurement using an LA-ICP-MS system, whole-rock major and trace element geochemistry and Sr-Nd isotope geochemistry were conducted on the volcanic host rocks of the Tongyu copper deposit on the basis of further understanding of its geological characteristics. Three zircon samples from the volcanic host rocks yielded 206Pb/238 U weighted average ages ranging from 436±4 Ma to 440±5 Ma, which are statistically indistinguishable and coeval with the ca. 440 Ma northward subduction event of the Paleo-Qinling oceanic slab. The volcanic host rocks were products of magmatic differentiation that evolved from basalt to andesite to dacite to rhyolite, forming an integrated tholeiitic island arc volcanic rock suite. The primitive mantle-normalized trace element patterns for most samples show characteristics of island arc volcanic rocks, such as relative enrichment of LILE（e.g. Th, U, Pb and La） and depletion of HFSE（e.g. Nb, Ta, Ti, Zr and Hf）. Discrimination diagrams of Ta/Yb vs Th/Yb, Ta vs Th, Yb vs Th/Ta, Ta/Hf vs Th/Hf, Hf/3 vs Th vs Nb/16, La vs La/Nb and Nb vs Nb/Th all suggest that both the volcanic host rocks from the Tongyu copper deposit and the volcanic rocks from the regional Xieyuguan Group were formed in an island arc environment related to subduction of an oceanic slab. Values of ISr（0.703457 to 0.708218） and εNd（t）（-2 to 5.8） indicate that the source materials of volcanic rocks from the Tongyu copper deposit and the Xieyuguan Group originated from the metasomatised mantle wedge with possible crustal material assimilation. Most of the volcanic rock samples show good agreement with the values of typical island arc volcanic rocks in the ISr-εNd（t） diagram. The involvement of crustal-derived material in the magma of the volcanic rocks from the Tongyu copper deposit was also reflected in the zircon εHf（t） values, which range from-3.08 to 10.7, and the existence of inherited ancient xenocrystic zircon cores（2616±39 Ma and 1297±22 Ma）. The mineralization of the Tongyu copper deposit shows syn-volcanic characteristics such as layered orebodies interbedded with the volcanic rock strata, thus, the zircon U-Pb age of the volcanic host rocks can approximately represent the mineralization age of the Tongyu copper deposit. Both the Meigou pluton and the volcanic host rocks were formed during the ca. 440 Ma northward subduction of the Paleo-Qinling Ocean when high oxygen fugacity aqueous hydrothermal fluid released by dehydration of the slab and the overlying sediments fluxed into the mantle wedge, triggered partial melting of the mantle wedge, and activated and extracted Cu and other ore-forming elements. The magma and ore-bearing fluid upwelled and erupted, and consequently formed the island arc volcanic rock suite and the Tongyu VHMS-type copper deposit.
基金jointly supported by National Natural Science Foundation of China(Grant Nos.41421002,41272092,and 41030423)MOST Special Fund from the State Key Laboratory of Continental Dynamics,Northwest University,China
文摘The Tongyu copper deposit, located in the western part of the North Qinling Orogen, China, is one of several volcanic-hosted massive sulphide（VHMS） deposits with industrial value and is also a typical example of mineralization related to the subduction and metallogenesis during the Caledonian orogeny. We conducted systematic lead-sulphur isotope geochemical analyses of the Tongyu deposit to understand the possible ore-forming material sources and tectonic settings. Twenty-six sulphide samples yielded clustered δ^34SCDT values of 1.13‰-3.36‰, average 2.22‰, and show a tower-type distribution,implying that the sulphur of the Tongyu copper deposit mainly originated from a mantle source. The Pb isotope compositions of sulphides（^206Pb/^204Pb = 17.59225-18.56354, average 18.32020; ^207Pb/^204Pb =15.51770-15.69381, average 15.66217; ^208Pb/^204Pb= 37.99969-39.06953, average 38.52722） are close to the values of the volcanic host rocks（^206Pb/^204PbPb= 18.10678-18.26293, average 18.21158; ^207Pb/^204PbPb =15.63196-15.68188, average 15.65345; ^208Pb/^204PbPb= 38.43676-38.56360, average 38.49171）, thus consistent with the Pb in ores and volcanic host rocks having been derived from a common source that was island-arc Pb related to oceanic crust subduction. The northward subduction of the Palaeo-Qinling oceanic crust triggered dehydration of the slab, which generated a large amount of high-oxygen-fugacity aqueous hydrothermal fluid. The fluid rose into the mantle wedge, activated and extracted metallogenic material and promoted partial melting of the mantle wedge. The magma and ore-forming fluid welled up and precipitated, finally forming the Tongyu VHMS copper deposit.
基金supported by National Basic Research Program of China (Grant No.2006CB403502)National Natural Science Foundation of China (Grant No.40872071)+3 种基金Program of Chinese Ministry of Science and Technology for State Key Laboratory of Continental Dynamics (Grant No.BJ091349)Foundation of the State Key Laboratory for Mineral Deposits Research,Nanjing University (Grant No.14-08-1)Foundation of the Educational Bureau of Shaanxi Province Foundation (Grant No.07JK414)Graduate Innovation and Creativity Funds of Northwest University,China (Grant No.08YZZ53)
文摘The Tongyu volcanic-hosted massive sulfide(VHMS) copper deposit is located in the west part of the North Qinling(NQL),Shaanxi Province.Here we report geological features and trace elemental characteristics of ores,mineralized rocks,and volcanic host rocks of this deposit.We also conducted in situ zircon U-Pb and Lu-Hf LA-ICP-MS dating and lithogeochemical study of the Meigou granodiorite,which is intruded in the south of the Tongyu mining district.It is inferred that the volcanic host rocks of the Tongyu Cu deposit belong to calc-alkaline island arc volcanic rocks,and the volcanic host rocks and the ore-forming materials share common material sources.During subduction of the Paleo-Qinling oceanic slab at around 472 Ma,high oxygen-fugacity aqueous fluid released by dehydration reaction of the subducting slab rose into the mantle wedge,leached Cu and other metal elements,and triggered partial melting of the mantle wedge.Associated with the ore-forming materials,the arc calc-alkaline magmas erupted and formed the Tongyu VHMS deposit.The weighted average zircon U-Pb age of the Meigou granodiorite is 439.3±3 Ma,suggesting its genesis is associated with the subduction event of the Paleo-Qinling oceanic plate around 440 Ma.In terms of the granitoid’s geochemical characteristics,the Mg#,Ni,and Cr contents are high.REE show strongly fractionated patterns with unobvious Eu anomalies.Sr contents are high while Y contents are low,resulting in high Sr/Y ratios.Two-stage zircon Hf model ages mostly range between 908 and 723 Ma,with εHf(t)】0.Therefore,we classify Meigou granodiorite as island arc granite with adakitic geochemical features.It was generated by interaction between mantle wedge and melt produced by partial melting of the subducted basaltic slab of the Paleo-Qinling Ocean.The Tongyu VHMS deposit was formed in the island arc tectonic setting during Ordovician-Silurian between 439.3±3 Ma and 472±11 Ma.The volcanic exhalation-sedimentation,which was contemporaneous with the submarine volcanics,produced the primary mineralization of the Tongyu Cu deposit.Afterward,the ore bodies and host rocks were reworked and overprinted intensively by structures corresponding with the overall collisional orogenic process of the Qinling Orogenic Belt during the Indosinian period.In contrast to classic VHMS deposits such as the Kuroko deposit in Japan,the Tongyu Cu deposit possesses the dual characteristics of island arc volcanic exhalation and sedimentation as well as structural reworking and overprinting.Therefore,the Tongyu VHMS Cu deposit is a volcanic exhalation and sedimentation-structural reworking and overprinting type deposit.
