The Wulong lode deposit contains over 80 tonnes of gold with an average grade of 5.35 g/t.It is one of the largest deposits in Dandong City,Liaoning Province in northeast China.Previous studies on the deposit focused ...The Wulong lode deposit contains over 80 tonnes of gold with an average grade of 5.35 g/t.It is one of the largest deposits in Dandong City,Liaoning Province in northeast China.Previous studies on the deposit focused on its geological characteristics,geochemistry,fluid inclusions,and the timing of gold mineralization.However,controversy remains regarding the origin of the ore-forming fluids and metals,and the genesis of the gold deposit.This paper presents zircon U-Pb and pyrite Rb-Sr ages and S,Pb,He,and Ar isotopic results along with quartz H and O isotopic data for all litho-units associated with the deposit.Laser ablation inductively coupled mass spectrometry measurements yielded zircon U-Pb dates for samples of pre-mineralization rocks like granite porphyry dike,the Sanguliu granodiorite,fine-grained diorite,and syn-mineralization diorite,as well as post-mineralization dolerite,and lamprophyre;their emplacement ages are 126±1 Ma,124±1 Ma,123±1 Ma,120±1 Ma,119±2 Ma,and 115±2 Ma,respectively.The pyrite Rb-Sr isochron age is 119±1 Ma,indicating that both magmatism and mineralization occurred during the Early Cretaceous.The δ18OH2 O values of ore-forming hydrothermal fluids from the quartz-polymetallic sulfide vein stage vary from 4.8‰to 6.5‰,and the δDv-SMOW values are between-67.7‰and-75.9‰,indicating that the ore-forming fluids were primarily magmatic.The noble gas isotope compositions of fluid inclusions hosted in pyrite suggest that the ore-forming fluids were dominantly derived from crustal sources with minor mantle input.Sulfur isotopic values of pyrite vary between 0.2‰and 3.5‰,suggesting that S was derived from a homogeneous magmatic source or possibly from fluids derived from the crust.The Pb isotopic compositions of sulfides（207 Pb/204 Pb=15.51-15.71,206 Pb/204 Pb=17.35-18.75,208 Pb/204 Pb=38.27-40.03） indicate that the Pb of the Wulong gold deposit is a mixture of crust and mantle components.Geochronological and geochemical data,together with the regional geological history,indicate that Early Cretaceous magmatism and mineralization of the Wulong gold deposit occurred during the rollback of the subducting Paleo-Pacific Plate,which resulted in lithospheric thinning and the destruction of the North China Craton（NCC）,which indicates that the deposit is of magmatic-hydrothermal origin.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 Wulong deposit is one of the largest quartz vein-type gold deposits with at least 80 tons of identified gold reserves in the eastern part of the Liaodong Peninsula.Gold orebodies are mainly hosted in the Late Jura...The Wulong deposit is one of the largest quartz vein-type gold deposits with at least 80 tons of identified gold reserves in the eastern part of the Liaodong Peninsula.Gold orebodies are mainly hosted in the Late Jurassic gneissic two-mica granite and Early Cretaceous diorite dykes,and are structurally controlled by the NNE-and NW-trending faults.Gold mineralization mainly occurs as veins with lenticular shapes and is closely associated with sulfides and Bi minerals.Previous studies on the deposit mainly focused on its geological characteristics,fluid inclusions and the timing of gold mineralization.However,the extreme enrichment mechanism of gold,the geodynamic setting and ore source of the gold deposit remain equivocal.Here we present results from geochemical studies of pyrite and pyrrhotite at Wulong to address these issues.Pyrrhotite can be grouped into euhedral(Po1)and anhedral(Po2)varieties based on the textures.Four generations of pyrite were identified based on petrographic studies:Py1 is coarse-grained subhedral to euhedral crystal coexisting with milky quartz,and Au-depleted in composition;Py2 is represented by medium-grained,subhedral to anhedral pyrite coexisting with euhedral Po1,smoky quartz and minor chalcopyrite;Py3 occurs as fined-grained anhedral grains in the quartz-polymetallic sulfide veins;Py4 occurs as veinlets or aggregates in the quartz-calcite veins and contains the lowest Au concentrations.The time-resolved LA-ICP-MS ablation depth profiles of sulfides combined with detailed petrological observations indicate that gold mainly occurs either as invisible solid solution within the crystal lattice of sulfides,to some extent,or as small blebs of native gold and electrum.The close temporal and spatial relationships among native bismuth,native gold and Bi-Te-S minerals suggest that Bi-rich melts may have significantly sequestered gold from the hydrothermal fluids in the Wulong gold deposit.Sulfides from auriferous quartz veins have a restricted D33S range(-0.2‰to+0.2‰)and a mean d34S value of+1.25‰with a feature of the mass-dependent fractionation(MDF)of sulfur isotopes,implying that the ore-forming materials were potentially derived from the mantle lithosphere that was metasomatized and fertilized by subduction-related fluids released from slab during the Early Cretaceous.This study demonstrates the Bi-rich melts as significant gold scavengers in As-deficient ore-forming fluid,and highlights the fundamental role of the metasomatized and fertilized mantle lithosphere in the formation of giant lode gold deposits in the eastern North China Craton at ca.120 Ma.展开更多
基金supported by the National Key Research and Development Program (Grand Nos. 2018YFC0603804, 2016YFC0600108-09)the National Natural Science Foundation of China (41502093)the Geological Investigation Project of the China Geological Survey (DD20160049)
文摘The Wulong lode deposit contains over 80 tonnes of gold with an average grade of 5.35 g/t.It is one of the largest deposits in Dandong City,Liaoning Province in northeast China.Previous studies on the deposit focused on its geological characteristics,geochemistry,fluid inclusions,and the timing of gold mineralization.However,controversy remains regarding the origin of the ore-forming fluids and metals,and the genesis of the gold deposit.This paper presents zircon U-Pb and pyrite Rb-Sr ages and S,Pb,He,and Ar isotopic results along with quartz H and O isotopic data for all litho-units associated with the deposit.Laser ablation inductively coupled mass spectrometry measurements yielded zircon U-Pb dates for samples of pre-mineralization rocks like granite porphyry dike,the Sanguliu granodiorite,fine-grained diorite,and syn-mineralization diorite,as well as post-mineralization dolerite,and lamprophyre;their emplacement ages are 126±1 Ma,124±1 Ma,123±1 Ma,120±1 Ma,119±2 Ma,and 115±2 Ma,respectively.The pyrite Rb-Sr isochron age is 119±1 Ma,indicating that both magmatism and mineralization occurred during the Early Cretaceous.The δ18OH2 O values of ore-forming hydrothermal fluids from the quartz-polymetallic sulfide vein stage vary from 4.8‰to 6.5‰,and the δDv-SMOW values are between-67.7‰and-75.9‰,indicating that the ore-forming fluids were primarily magmatic.The noble gas isotope compositions of fluid inclusions hosted in pyrite suggest that the ore-forming fluids were dominantly derived from crustal sources with minor mantle input.Sulfur isotopic values of pyrite vary between 0.2‰and 3.5‰,suggesting that S was derived from a homogeneous magmatic source or possibly from fluids derived from the crust.The Pb isotopic compositions of sulfides（207 Pb/204 Pb=15.51-15.71,206 Pb/204 Pb=17.35-18.75,208 Pb/204 Pb=38.27-40.03） indicate that the Pb of the Wulong gold deposit is a mixture of crust and mantle components.Geochronological and geochemical data,together with the regional geological history,indicate that Early Cretaceous magmatism and mineralization of the Wulong gold deposit occurred during the rollback of the subducting Paleo-Pacific Plate,which resulted in lithospheric thinning and the destruction of the North China Craton（NCC）,which indicates that the deposit is of magmatic-hydrothermal origin.
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supported by the National Nature Science Foundation of China(Grant No.41730426)。
文摘The Wulong deposit is one of the largest quartz vein-type gold deposits with at least 80 tons of identified gold reserves in the eastern part of the Liaodong Peninsula.Gold orebodies are mainly hosted in the Late Jurassic gneissic two-mica granite and Early Cretaceous diorite dykes,and are structurally controlled by the NNE-and NW-trending faults.Gold mineralization mainly occurs as veins with lenticular shapes and is closely associated with sulfides and Bi minerals.Previous studies on the deposit mainly focused on its geological characteristics,fluid inclusions and the timing of gold mineralization.However,the extreme enrichment mechanism of gold,the geodynamic setting and ore source of the gold deposit remain equivocal.Here we present results from geochemical studies of pyrite and pyrrhotite at Wulong to address these issues.Pyrrhotite can be grouped into euhedral(Po1)and anhedral(Po2)varieties based on the textures.Four generations of pyrite were identified based on petrographic studies:Py1 is coarse-grained subhedral to euhedral crystal coexisting with milky quartz,and Au-depleted in composition;Py2 is represented by medium-grained,subhedral to anhedral pyrite coexisting with euhedral Po1,smoky quartz and minor chalcopyrite;Py3 occurs as fined-grained anhedral grains in the quartz-polymetallic sulfide veins;Py4 occurs as veinlets or aggregates in the quartz-calcite veins and contains the lowest Au concentrations.The time-resolved LA-ICP-MS ablation depth profiles of sulfides combined with detailed petrological observations indicate that gold mainly occurs either as invisible solid solution within the crystal lattice of sulfides,to some extent,or as small blebs of native gold and electrum.The close temporal and spatial relationships among native bismuth,native gold and Bi-Te-S minerals suggest that Bi-rich melts may have significantly sequestered gold from the hydrothermal fluids in the Wulong gold deposit.Sulfides from auriferous quartz veins have a restricted D33S range(-0.2‰to+0.2‰)and a mean d34S value of+1.25‰with a feature of the mass-dependent fractionation(MDF)of sulfur isotopes,implying that the ore-forming materials were potentially derived from the mantle lithosphere that was metasomatized and fertilized by subduction-related fluids released from slab during the Early Cretaceous.This study demonstrates the Bi-rich melts as significant gold scavengers in As-deficient ore-forming fluid,and highlights the fundamental role of the metasomatized and fertilized mantle lithosphere in the formation of giant lode gold deposits in the eastern North China Craton at ca.120 Ma.
