Feldspar Pb isotopes have been widely used to trace magmatic formation and evolution processes.However,it remains unclear whether post-magmatic thermal events can affect feldspar Pb isotopic ratios.Here,the in situ Pb...Feldspar Pb isotopes have been widely used to trace magmatic formation and evolution processes.However,it remains unclear whether post-magmatic thermal events can affect feldspar Pb isotopic ratios.Here,the in situ Pb isotopic composition of feldspar hosted in granitic rocks(thirteen Archean and one Paleoproterozoic)from the northern Kongling terrane,Yangtze Craton,South China,is analyzed.The samples reveal a substantial variation in their Pb isotopic composition,spanning the gap between the 1.9 Ga and present-day geochrons,which indicates extensive resetting by later tectonothermal events.This resetting was interpreted to have likely resulted from Paleoproterozoic and Neoproterozoic tectonothermal events related to the assembly and breakup of the Columbia and Rodinia supercontinents.These results suggest that Pb isotopes should be used cautiously when tracing magma sources and petrogenesis in magmatic rocks that have experienced post-magmatic reworking.However,the in situ Pb isotopic composition of feldspar in ancient granitoids may also potentially be used to reveal later tectonothermal events.The extensive resetting of the Pb isotopic composition in feldspar by regional thermal events may also provide new insights into our understanding of the Pb isotope paradox.展开更多
The coal metamorphism in Central Hunan pro-vides valuable information about hydrothermal activity and water/rock reactions.Learning how to collect age data on hydrothermal fluid systems is necessary for understanding ...The coal metamorphism in Central Hunan pro-vides valuable information about hydrothermal activity and water/rock reactions.Learning how to collect age data on hydrothermal fluid systems is necessary for understanding the history and genetic mechanisms of large-scale coal-generated graphite deposits.The Shihangli graphite deposit,formed by significant siliceous hydrothermal alteration,is the most distinctive in Central Hunan.Re–Os dating of pyrite from the Shihangli graphite deposit demonstrates that the coal-generated graphite mineraliza-tion age is-127.6±3.8 Ma.Based on in-situ mineral analysis,the hydrothermal pyrite in the Shihangli graphite deposit is mostly enriched in Sb,As,Au,W,Ag,Cu,Pb,and Zn.Based on the pyrite Re–Os isochron,the initial(^(187)Os/^(188)Os)values of pyrite were 1.03±0.24 and the Os(t)values varied from 571.8 to 755.1.Pyrite from the Shihangli graphite deposit comprises a Pb isotope composition similar to that of the Madiyi Formation bulk rock and stibnite from the Xikuangshan Sb deposit.Based on the Re–Os,Sr,S,and Pb isotopic compositions of sul-fides in the graphite and Sb deposits in Central Hunan,the Madiyi Formation was likely the primary source of ore-forming elements(Sb,Au,and As).The Re–Os and Pb isotope compositions of pyrite most likely reflect when large-scale fluid migration and coal-generated graphite mineralization occurred in Central Hunan.展开更多
The Southern Great Xing’an Range (SGXR) which forms part of the eastern segment of the Central Asian Orogenic Belt (CAOB) is known as one of the most important Cu-Mo-Pb-Zn-Ag-Au metallogenic belts in China,hosting a ...The Southern Great Xing’an Range (SGXR) which forms part of the eastern segment of the Central Asian Orogenic Belt (CAOB) is known as one of the most important Cu-Mo-Pb-Zn-Ag-Au metallogenic belts in China,hosting a number of porphyry Mo (Cu),skarn Fe (Sn),epithermal Au-Ag,and hydrothermal veintype Ag-Pb-Zn ore deposits.Here we investigate the Bianjiadayuan hydrothermal vein-type Ag-Pb-Zn ore deposit in the southern part of the SGXR.Porphyry Sn ±Cu ± Mo mineralization is also developed to the west of the Ag-Pb-Zn veins in the ore field.We identify a five-stage mineralization process based on field and petrologic studies including (i) the early porphyry mineralization stage,(ii) main porphyry mineralization stage,(iii) transition mineralization stage,(iv) vein-type mineralization stage and (v) late mineralization stage.Pyrite is the predominant sulfide mineral in all stages except in the late mineralization stage,and we identify corresponding four types of pyrites: Py1 is medium-grained subhedral to euhedral occurring in the early barren quartz vein;Py2 is medium- to fine-grained euhedral pyrite mainly coexisting with molybdenite,chalcopyrite,minor sphalerite and galena;Py3 is fine-grained,subhedral to irregular pyrite and displays cataclastic textures with micro-fractures;Py4 occurs as euhedral microcrystals and forms irregularly shaped aggregate with sphalerite and galena.LA-ICP-MS trace element analyses of pyrite show that Cu,Pb,Zn,Ag,Sn,Cd and Sb are partitioned into pyrite as structurally bound metals or mineral micro/nano-inclusions,whereas Co,Ni,As and Se enter the lattice via isomorphism in all types of pyrite.The Cu,Zn,Ag,Cd concentrations gradually increase from Py1 to Py4,which we correlate with cooling and mixing of ore-forming fluid with meteoric water.Py2 contains the highest contents of Co,Ni,Se,Te and Bi,suggesting high temperature conditions for the porphyry mineralization stage.Ratios of Co/Ni (0.03-10.79,average 2.13) and sulphur isotope composition of sulfide indicate typical hydrothermal origin for pyrites.The δ^34SCDT values of Py1 (0.42‰-1.61‰,average 1.16‰),Py2 (-1.23‰ to 0.82‰,average 0.35‰),Py3 (-0.36‰ to 2.47‰,average 0.97‰),Py4 (2.51‰-3.72‰,average 3.06‰),and other sulfides are consistent with those of typical porphyry deposit (-5‰ to 5‰),indicating that the Pb-Zn polymetallic mineralization in the Bianjiadayuan deposit is genetically linked to the Yanshanian (JurassiceCretaceous) magmatic-hydrothermal events.Variations of d34S values are ascribed to the changes in physical and chemical conditions during the evolution and migration of the ore-forming fluid.We propose that the high Sn content of pyrite in the Bianjiadayuan hydrothermal vein-type PbeZn polymetallic deposit can be used as a possible pathfinder to prospect for Sn mineralization in the surrounding area or deeper level of the ore field in this region.展开更多
1 Introduction Hetai district,which is a mountainous area,situated on Guangning and Zhaoqing city,west Guangdong Province.Hetai district is generally located on southwest of South China Caledonian fold belt,east margi...1 Introduction Hetai district,which is a mountainous area,situated on Guangning and Zhaoqing city,west Guangdong Province.Hetai district is generally located on southwest of South China Caledonian fold belt,east margin of Yunkai post-Caledonian uplift.Multiple type granites are widely distributed in Hetai district,including Caledonian,Indosinian and Yanshanian granites.Based on展开更多
Detrital zircon U-Pb geochronology has become the gold standard in evaluating source to sink relationships in sedimentary basins. However, the physical and chemical robustness of zircon, which make it such a useful mi...Detrital zircon U-Pb geochronology has become the gold standard in evaluating source to sink relationships in sedimentary basins. However, the physical and chemical robustness of zircon, which make it such a useful mineral for provenance studies, is also a hindrance as zircon can be recycled through numerous sedimentary basins, thus obscuring the first cycle source to sink relationship. An elegant approach to addressing this potential issue is to compare the Pb isotope composition of detrital K-feldspar, a mineral which is unlikely to survive more than one erosion-transport-deposition cycle, with that of magmatic K-feldspar from potential basement source terranes. Here we present new in situ Pb isotope data on detrital K-feldspar from two Proterozoic arkosic sandstones from Western Australia, and magmatic K-feldspar grains from potential igneous source rocks, as inferred by the age and Hf isotope composition of detrital zircon grains. The data indicate that the detrital zircon and K-feldspar grains could not have been liberated from the same source rocks, and that the zircon has most likely been recycled through older sedimentary basins. These results provide a more complete understanding of apparently simple source to sink relationships in this part of Proterozoic Western Australia.展开更多
The authors measured Pb isotope compositions of seven USGS rock reference standards, i.e. AGV-1, AGV-2, BHVO-1, BHVO-2, BCR-2, BIR-1/1 and W-2, together with NBS 981 using a micromass isoprobe multi-collector inductiv...The authors measured Pb isotope compositions of seven USGS rock reference standards, i.e. AGV-1, AGV-2, BHVO-1, BHVO-2, BCR-2, BIR-1/1 and W-2, together with NBS 981 using a micromass isoprobe multi-collector inductively-coupled plasma mass spectrometer(MC-ICP-MS) at the University of Queensland. 203Tl-205Tl isotopes were used as an internal standard to correct for mass-dependant isotopic fractionation. The results for both NBS 981 and USGS rock standards AGV-1 and BHVO-1 are comparable to or better than double- and triple-spike TIMS (thermal ionization mass spectrometry) data in precision. The data for BHVO-2 and, to a lesser extent, AGV-2 and BCR-2 are reproducibly higher for 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb than double-spike TIMS data in the literature. The authors also obtained the Pb isotope data for BIR-1/1 and W-2, which may be used as reference values in future studies. It is found that linear correction for Pb isotopic fractionation is adequate with the results identical to those corrected following an exponential law or a power law. Precise 207Pb/206Pb, 208Pb/206Pb and 208Pb/207Pb ratios can be acquired for sample solutions with Pb≥1 ppb. However, Pb isotope ratios involving 204Pb (i.e., 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb) are reliable for solutions with Pb≥40 ppb. The errors for Pb isotope ratio analysis using the MC-ICP-MS are dominated by errors in the analysis of 204Pb, which is commonly ascribed to the difficulty and imprecise correction for a 204Hg isobaric interference. It is found however that the major errors on 204Pb come from the tailings of mass 203Tl and mass 205Tl. These mass tailings lead to over-subtraction of the baseline for 204Pb, which is measured at -0.5 amu on both sides of mass-204 (i.e., at amu 203.5 and 204.5 respectively). Such errors are insignificant for Pb-rich sample solutions (i.e., high Pb/Tl ratios), but can be severe for low-Pb sample solutions when over-'spiked' with Tl. Experiments in this study suggest that a minimum concentration ratio of Pb/Tl>5 in Tl-'spiked' solutions be required to ensure reliable 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb isotopic ratios. The tailings of 203Tl and 205Tl can also lead to over-subtraction of baselines for 202Hg (at amu 202.5) and 206Pb (at amu 205.5). Therefore, the elegance of using 203Tl and 205Tl isotopes for mass fractionation correction becomes a severe problem in low-Pb rock solutions-caution is required. Alternative internal standards for mass fractionation correction may be considered. Of course, significant instrumental refinement in abundance sensitivity is in demand.展开更多
The Liziyuan gold deposit, situated on the south side of the Shangdan suture zone, West Qinling Orogen, occurs in metamorphic volcanic rocks(greenschist facies) of the early Paleozoic Liziyuan Group and in Indosinian ...The Liziyuan gold deposit, situated on the south side of the Shangdan suture zone, West Qinling Orogen, occurs in metamorphic volcanic rocks(greenschist facies) of the early Paleozoic Liziyuan Group and in Indosinian Tianzishan monzogranite. Orebodies in the Liziyuan gold field are controlled by the ductile-brittle shear zone, and by thrusting nappe faults related to the Indosinian orogeny. In detail, this paper analyzed the geological characteristics of the Liziyuan gold field, and the Pb isotopes of the Lziyuan host rocks, granitoids(Tianzishan monzogranite and Jiancaowan syenite porphyry), sulfides, and auriferous quartz veins by multiple-collector inductively coupled plasma mass spectrometry(MC-ICPMS). In addition, previous data on the sulfur, hydrogen, and oxygen isotopes were employed to discuss the possible sources of the ore-forming fluids and materials, and to further understand the tectonic setting of the Liziyuan gold deposit. The sulfides and their host rocks(Lziyuan Group), Tianzishan monzogranite and Jiancaowan syenite porphyry, and auriferous quartz veins have similar Pb isotopic compositions.Zartman's plumbotectonic model diagram shows that most of the data for the deposit fall near the orogenic Pb evolutionary curve or within the area between the orogenic and mantle Pb evolutionary curves. In the△β-△γ diagram, which genetically classifies the lead isotopes, most of the data fall within the range of the subduction-zone lead mixed with upper crust and mantle. This indicates that a complex source of the ore lead formed in the orogenic environment. The δ^(34)S values of the sulfides range from 3.90 to 8.50‰(average6.80‰), with a pronounced mode at 5.00‰-8.00‰. These values are consistent with that of orogenic gold deposits worldwide, indicating that the sulfur sourced mainly from reduced metamorphic fluids. The isotopic hydrogen and oxygen compositions support a predominantly metamorphic origin of the oreforming fluids, with possible mixing of minor magmatic fluids, but the late stage was dominated by meteoric water. The characteristics of the Liziyuan gold deposit formed in the Indosinian orogenic environment of the Qinling Orogen are consistent with those of orogenic gold deposits found worldwide.展开更多
Zircon U–Pb and Hf isotope data integrated in this study for magmatic and metamorphic rocks fromthe Hida Belt,southwest Japan,lead to a new understanding of the evolution of the Cordilleran arc system along the ances...Zircon U–Pb and Hf isotope data integrated in this study for magmatic and metamorphic rocks fromthe Hida Belt,southwest Japan,lead to a new understanding of the evolution of the Cordilleran arc system along the ancestral margins of present-day Northeast Asia.Ion microprobe data for magmatic zircon domains from eight mafic tointermediate orthogneisses in the Tateyama and Tsunogawa areas yielded weighted mean 206Pb/238U ages spanning the entire Permian period(302–254 Ma).Under cathodoluminescence,primary magmatic growth zones in the zircon crystals were observed to be partially or completely replaced by inward-penetrating,irregularly curved featureless or weakly zoned secondary domains that mostly yielded U–Pb ages of 250–240 Ma and relatively high Th/U ratios(>0.2).These secondary domains are considered to have been formed by solid-state recrystallization during thermal overprints associated with intrusions of Hida granitoids.Available whole-rock geochemical and Sr–Nd isotope data as well as zircon age spectra corroborate that the Hida Belt comprises the Paleozoic–Mesozoic Cordilleran arc system built upon the margin of the North China Craton,together with the YeongnamMassif in southern Korea.The arcmagmatismalong this systemwas commenced in the Carboniferous and culminated in the Permian–Triassic transition period.Highly positiveεHf(t)values(>+12)of late Carboniferous to early Permian detrital zircons in the Hida paragneisses indicate that there was significant input from the depleted asthenospheric mantle and/or its crustal derivatives in the early stage of arc magmatism.On the other hand,near-chondriticεHf(t)values(+5 to−2)of magmatic zircons from late Permian Hida orthogneisses suggest a lithospheric mantle origin.Hf isotopic differences between magmatic zircon cores and the secondary rims observed in some orthogneiss samples clearly indicate that the zircons were chemically open to fluids or melts during thermal overprints.Resumed highly positive zirconεHf(t)values(>+9)shared by Early Jurassic granitoids in the Hida Belt and Yeongnam Massif may reflect reworking of the Paleozoic arc crust.展开更多
Mesozoic granitic intrusions are widely distributed in the Nanling region,South China.Yanshanian granites are closely connected with the formation of tungsten deposits.The Xihuashan granite is a typical representative...Mesozoic granitic intrusions are widely distributed in the Nanling region,South China.Yanshanian granites are closely connected with the formation of tungsten deposits.The Xihuashan granite is a typical representative of tungsten-bearing granite.The Xihuashan granite consists mainly of medium-grained porphyritic biotite granite,medium-grained biotite granite and fine-grained two-mica granite,which correspond to LA-ICP-MS zircon U-Pb ages of 155.5±0.4 Ma,153.0±0.6 Ma and 152.8±0.9 Ma,respectively.Rocks from the Xihuashan mining area displays high SiO2(73.85% to 76.49%) and Na2O+K2O contents(8.09% to 9.43%),belonging to high-K calc-alkaline series.They are metaluminous to weakly peraluminous with A/CNK values ranging from 0.96 to 1.06.All granites in this study area are rich in Rb,Th,U and Pb,and depleted in Ba,Sr,P,Ti,Nb and Eu,especially depleted in medium-grained biotite granite and fine-grained two-mica granite.The medium-grained porphyritic biotite granites usually have high LREE concentrations,whereas medium-grained biotite granite and fine-grained two-mica granite displays high HREE contents.Our geochemical data reveal that the studied rocks are highly fractionated I-type granite.The magma underwent strong magma differentiation with decreasing temperature and increasing oxygen fugacity,which may explain the formation of three types of distinct granites.Variations of Rb,Sr and Ba concentrations in different type granites were controlled by fractional crystallization of biotite and feldspar.Fractional crystallization of monazite,allanite and apatite resulted in LREE changes in granite,and formation of garnet mainly caused HREE changes.Granites from the Xihuashan mining area have relatively high εNd(t) values(-9.77 to -11.46),indicating that they were probably generated by partial melting of underlying Proterozoic metasedimentary rocks with minor addition of juvenile crust or mantle-derived magmas.展开更多
基金supported by the Key Laboratory of Gold Mineralization Processes and Resource Utilization,MNRShandong Provincial Key Laboratory of Metallogenic Geological Process and Resource Utilization(Grant No.KFKT202103)National Natural Science Foundation of China(Grant No.41876037)。
文摘Feldspar Pb isotopes have been widely used to trace magmatic formation and evolution processes.However,it remains unclear whether post-magmatic thermal events can affect feldspar Pb isotopic ratios.Here,the in situ Pb isotopic composition of feldspar hosted in granitic rocks(thirteen Archean and one Paleoproterozoic)from the northern Kongling terrane,Yangtze Craton,South China,is analyzed.The samples reveal a substantial variation in their Pb isotopic composition,spanning the gap between the 1.9 Ga and present-day geochrons,which indicates extensive resetting by later tectonothermal events.This resetting was interpreted to have likely resulted from Paleoproterozoic and Neoproterozoic tectonothermal events related to the assembly and breakup of the Columbia and Rodinia supercontinents.These results suggest that Pb isotopes should be used cautiously when tracing magma sources and petrogenesis in magmatic rocks that have experienced post-magmatic reworking.However,the in situ Pb isotopic composition of feldspar in ancient granitoids may also potentially be used to reveal later tectonothermal events.The extensive resetting of the Pb isotopic composition in feldspar by regional thermal events may also provide new insights into our understanding of the Pb isotope paradox.
基金the National Key Research and Development Program of China(2016YFC0600207,2014CB440904)National Natural Science Foundation of China(Nos.42062006,41962007)the Integrated Exploration Project of China Geological Survey(No.12120114034501).
文摘The coal metamorphism in Central Hunan pro-vides valuable information about hydrothermal activity and water/rock reactions.Learning how to collect age data on hydrothermal fluid systems is necessary for understanding the history and genetic mechanisms of large-scale coal-generated graphite deposits.The Shihangli graphite deposit,formed by significant siliceous hydrothermal alteration,is the most distinctive in Central Hunan.Re–Os dating of pyrite from the Shihangli graphite deposit demonstrates that the coal-generated graphite mineraliza-tion age is-127.6±3.8 Ma.Based on in-situ mineral analysis,the hydrothermal pyrite in the Shihangli graphite deposit is mostly enriched in Sb,As,Au,W,Ag,Cu,Pb,and Zn.Based on the pyrite Re–Os isochron,the initial(^(187)Os/^(188)Os)values of pyrite were 1.03±0.24 and the Os(t)values varied from 571.8 to 755.1.Pyrite from the Shihangli graphite deposit comprises a Pb isotope composition similar to that of the Madiyi Formation bulk rock and stibnite from the Xikuangshan Sb deposit.Based on the Re–Os,Sr,S,and Pb isotopic compositions of sul-fides in the graphite and Sb deposits in Central Hunan,the Madiyi Formation was likely the primary source of ore-forming elements(Sb,Au,and As).The Re–Os and Pb isotope compositions of pyrite most likely reflect when large-scale fluid migration and coal-generated graphite mineralization occurred in Central Hunan.
基金financially supported by National Key Research and Development Program of China (2016YFC0600504)Fundamental Research Funds for the Central Universities (2652017218)
文摘The Southern Great Xing’an Range (SGXR) which forms part of the eastern segment of the Central Asian Orogenic Belt (CAOB) is known as one of the most important Cu-Mo-Pb-Zn-Ag-Au metallogenic belts in China,hosting a number of porphyry Mo (Cu),skarn Fe (Sn),epithermal Au-Ag,and hydrothermal veintype Ag-Pb-Zn ore deposits.Here we investigate the Bianjiadayuan hydrothermal vein-type Ag-Pb-Zn ore deposit in the southern part of the SGXR.Porphyry Sn ±Cu ± Mo mineralization is also developed to the west of the Ag-Pb-Zn veins in the ore field.We identify a five-stage mineralization process based on field and petrologic studies including (i) the early porphyry mineralization stage,(ii) main porphyry mineralization stage,(iii) transition mineralization stage,(iv) vein-type mineralization stage and (v) late mineralization stage.Pyrite is the predominant sulfide mineral in all stages except in the late mineralization stage,and we identify corresponding four types of pyrites: Py1 is medium-grained subhedral to euhedral occurring in the early barren quartz vein;Py2 is medium- to fine-grained euhedral pyrite mainly coexisting with molybdenite,chalcopyrite,minor sphalerite and galena;Py3 is fine-grained,subhedral to irregular pyrite and displays cataclastic textures with micro-fractures;Py4 occurs as euhedral microcrystals and forms irregularly shaped aggregate with sphalerite and galena.LA-ICP-MS trace element analyses of pyrite show that Cu,Pb,Zn,Ag,Sn,Cd and Sb are partitioned into pyrite as structurally bound metals or mineral micro/nano-inclusions,whereas Co,Ni,As and Se enter the lattice via isomorphism in all types of pyrite.The Cu,Zn,Ag,Cd concentrations gradually increase from Py1 to Py4,which we correlate with cooling and mixing of ore-forming fluid with meteoric water.Py2 contains the highest contents of Co,Ni,Se,Te and Bi,suggesting high temperature conditions for the porphyry mineralization stage.Ratios of Co/Ni (0.03-10.79,average 2.13) and sulphur isotope composition of sulfide indicate typical hydrothermal origin for pyrites.The δ^34SCDT values of Py1 (0.42‰-1.61‰,average 1.16‰),Py2 (-1.23‰ to 0.82‰,average 0.35‰),Py3 (-0.36‰ to 2.47‰,average 0.97‰),Py4 (2.51‰-3.72‰,average 3.06‰),and other sulfides are consistent with those of typical porphyry deposit (-5‰ to 5‰),indicating that the Pb-Zn polymetallic mineralization in the Bianjiadayuan deposit is genetically linked to the Yanshanian (JurassiceCretaceous) magmatic-hydrothermal events.Variations of d34S values are ascribed to the changes in physical and chemical conditions during the evolution and migration of the ore-forming fluid.We propose that the high Sn content of pyrite in the Bianjiadayuan hydrothermal vein-type PbeZn polymetallic deposit can be used as a possible pathfinder to prospect for Sn mineralization in the surrounding area or deeper level of the ore field in this region.
基金co-funded by the China Geological Survey (No.12120114052801)the DREAM project of MOST, China (NO. 2016YFC0600401)
文摘1 Introduction Hetai district,which is a mountainous area,situated on Guangning and Zhaoqing city,west Guangdong Province.Hetai district is generally located on southwest of South China Caledonian fold belt,east margin of Yunkai post-Caledonian uplift.Multiple type granites are widely distributed in Hetai district,including Caledonian,Indosinian and Yanshanian granites.Based on
基金funded via an Australian Geophysical Observing System grant provided to Au Scope Pty Ltd.the AQ44 Australian Education Investment Fund programpartly funded by the Western Australian Exploration Incentive Scheme
文摘Detrital zircon U-Pb geochronology has become the gold standard in evaluating source to sink relationships in sedimentary basins. However, the physical and chemical robustness of zircon, which make it such a useful mineral for provenance studies, is also a hindrance as zircon can be recycled through numerous sedimentary basins, thus obscuring the first cycle source to sink relationship. An elegant approach to addressing this potential issue is to compare the Pb isotope composition of detrital K-feldspar, a mineral which is unlikely to survive more than one erosion-transport-deposition cycle, with that of magmatic K-feldspar from potential basement source terranes. Here we present new in situ Pb isotope data on detrital K-feldspar from two Proterozoic arkosic sandstones from Western Australia, and magmatic K-feldspar grains from potential igneous source rocks, as inferred by the age and Hf isotope composition of detrital zircon grains. The data indicate that the detrital zircon and K-feldspar grains could not have been liberated from the same source rocks, and that the zircon has most likely been recycled through older sedimentary basins. These results provide a more complete understanding of apparently simple source to sink relationships in this part of Proterozoic Western Australia.
文摘The authors measured Pb isotope compositions of seven USGS rock reference standards, i.e. AGV-1, AGV-2, BHVO-1, BHVO-2, BCR-2, BIR-1/1 and W-2, together with NBS 981 using a micromass isoprobe multi-collector inductively-coupled plasma mass spectrometer(MC-ICP-MS) at the University of Queensland. 203Tl-205Tl isotopes were used as an internal standard to correct for mass-dependant isotopic fractionation. The results for both NBS 981 and USGS rock standards AGV-1 and BHVO-1 are comparable to or better than double- and triple-spike TIMS (thermal ionization mass spectrometry) data in precision. The data for BHVO-2 and, to a lesser extent, AGV-2 and BCR-2 are reproducibly higher for 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb than double-spike TIMS data in the literature. The authors also obtained the Pb isotope data for BIR-1/1 and W-2, which may be used as reference values in future studies. It is found that linear correction for Pb isotopic fractionation is adequate with the results identical to those corrected following an exponential law or a power law. Precise 207Pb/206Pb, 208Pb/206Pb and 208Pb/207Pb ratios can be acquired for sample solutions with Pb≥1 ppb. However, Pb isotope ratios involving 204Pb (i.e., 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb) are reliable for solutions with Pb≥40 ppb. The errors for Pb isotope ratio analysis using the MC-ICP-MS are dominated by errors in the analysis of 204Pb, which is commonly ascribed to the difficulty and imprecise correction for a 204Hg isobaric interference. It is found however that the major errors on 204Pb come from the tailings of mass 203Tl and mass 205Tl. These mass tailings lead to over-subtraction of the baseline for 204Pb, which is measured at -0.5 amu on both sides of mass-204 (i.e., at amu 203.5 and 204.5 respectively). Such errors are insignificant for Pb-rich sample solutions (i.e., high Pb/Tl ratios), but can be severe for low-Pb sample solutions when over-'spiked' with Tl. Experiments in this study suggest that a minimum concentration ratio of Pb/Tl>5 in Tl-'spiked' solutions be required to ensure reliable 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb isotopic ratios. The tailings of 203Tl and 205Tl can also lead to over-subtraction of baselines for 202Hg (at amu 202.5) and 206Pb (at amu 205.5). Therefore, the elegance of using 203Tl and 205Tl isotopes for mass fractionation correction becomes a severe problem in low-Pb rock solutions-caution is required. Alternative internal standards for mass fractionation correction may be considered. Of course, significant instrumental refinement in abundance sensitivity is in demand.
基金jointly provided by the National Natural Science Foundation of China (Grant Nos. 41421002, 41730426, 41272092, and 41030423)MOST Special Fund from the State Key Laboratory of Continental Dynamics, Northwest UniversityNorthwest University Graduate Innovation and Creativity Fund (YZZ17190)
文摘The Liziyuan gold deposit, situated on the south side of the Shangdan suture zone, West Qinling Orogen, occurs in metamorphic volcanic rocks(greenschist facies) of the early Paleozoic Liziyuan Group and in Indosinian Tianzishan monzogranite. Orebodies in the Liziyuan gold field are controlled by the ductile-brittle shear zone, and by thrusting nappe faults related to the Indosinian orogeny. In detail, this paper analyzed the geological characteristics of the Liziyuan gold field, and the Pb isotopes of the Lziyuan host rocks, granitoids(Tianzishan monzogranite and Jiancaowan syenite porphyry), sulfides, and auriferous quartz veins by multiple-collector inductively coupled plasma mass spectrometry(MC-ICPMS). In addition, previous data on the sulfur, hydrogen, and oxygen isotopes were employed to discuss the possible sources of the ore-forming fluids and materials, and to further understand the tectonic setting of the Liziyuan gold deposit. The sulfides and their host rocks(Lziyuan Group), Tianzishan monzogranite and Jiancaowan syenite porphyry, and auriferous quartz veins have similar Pb isotopic compositions.Zartman's plumbotectonic model diagram shows that most of the data for the deposit fall near the orogenic Pb evolutionary curve or within the area between the orogenic and mantle Pb evolutionary curves. In the△β-△γ diagram, which genetically classifies the lead isotopes, most of the data fall within the range of the subduction-zone lead mixed with upper crust and mantle. This indicates that a complex source of the ore lead formed in the orogenic environment. The δ^(34)S values of the sulfides range from 3.90 to 8.50‰(average6.80‰), with a pronounced mode at 5.00‰-8.00‰. These values are consistent with that of orogenic gold deposits worldwide, indicating that the sulfur sourced mainly from reduced metamorphic fluids. The isotopic hydrogen and oxygen compositions support a predominantly metamorphic origin of the oreforming fluids, with possible mixing of minor magmatic fluids, but the late stage was dominated by meteoric water. The characteristics of the Liziyuan gold deposit formed in the Indosinian orogenic environment of the Qinling Orogen are consistent with those of orogenic gold deposits found worldwide.
基金jointly supported by a Basic Research Project(20-3111-1:Geological survey in the Korean Peninsula and publication of the geological maps)of the Korea Institute of Geoscience and Mineral Resources,funded by the Ministry of Science and ICT,Korearesearch grants from the Korea Basic Science Institute(C070110,C030120).
文摘Zircon U–Pb and Hf isotope data integrated in this study for magmatic and metamorphic rocks fromthe Hida Belt,southwest Japan,lead to a new understanding of the evolution of the Cordilleran arc system along the ancestral margins of present-day Northeast Asia.Ion microprobe data for magmatic zircon domains from eight mafic tointermediate orthogneisses in the Tateyama and Tsunogawa areas yielded weighted mean 206Pb/238U ages spanning the entire Permian period(302–254 Ma).Under cathodoluminescence,primary magmatic growth zones in the zircon crystals were observed to be partially or completely replaced by inward-penetrating,irregularly curved featureless or weakly zoned secondary domains that mostly yielded U–Pb ages of 250–240 Ma and relatively high Th/U ratios(>0.2).These secondary domains are considered to have been formed by solid-state recrystallization during thermal overprints associated with intrusions of Hida granitoids.Available whole-rock geochemical and Sr–Nd isotope data as well as zircon age spectra corroborate that the Hida Belt comprises the Paleozoic–Mesozoic Cordilleran arc system built upon the margin of the North China Craton,together with the YeongnamMassif in southern Korea.The arcmagmatismalong this systemwas commenced in the Carboniferous and culminated in the Permian–Triassic transition period.Highly positiveεHf(t)values(>+12)of late Carboniferous to early Permian detrital zircons in the Hida paragneisses indicate that there was significant input from the depleted asthenospheric mantle and/or its crustal derivatives in the early stage of arc magmatism.On the other hand,near-chondriticεHf(t)values(+5 to−2)of magmatic zircons from late Permian Hida orthogneisses suggest a lithospheric mantle origin.Hf isotopic differences between magmatic zircon cores and the secondary rims observed in some orthogneiss samples clearly indicate that the zircons were chemically open to fluids or melts during thermal overprints.Resumed highly positive zirconεHf(t)values(>+9)shared by Early Jurassic granitoids in the Hida Belt and Yeongnam Massif may reflect reworking of the Paleozoic arc crust.
基金supported by the Chinese Ministry of Science and Technology(Sinoprobe-05-03)Doctoral Fund of Ministry of Education of China(20110022120003)+1 种基金the Fundamental Research Funds for the Central UniversitiesOpen Fund of State Key Laboratory of Geological Processes and Mineral Resources(GPMR2011)
基金supported by the National Natural Science Foundation of China(Grant Nos.90814008,40634023 and 40973043)the National Basic Research Program of China (Grant No.2009CB825002)
基金supported by the National Key Basic Research Program(2012CB416700,2007CB411408),a special fund managed by the State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,and the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences in Wuhan
文摘Mesozoic granitic intrusions are widely distributed in the Nanling region,South China.Yanshanian granites are closely connected with the formation of tungsten deposits.The Xihuashan granite is a typical representative of tungsten-bearing granite.The Xihuashan granite consists mainly of medium-grained porphyritic biotite granite,medium-grained biotite granite and fine-grained two-mica granite,which correspond to LA-ICP-MS zircon U-Pb ages of 155.5±0.4 Ma,153.0±0.6 Ma and 152.8±0.9 Ma,respectively.Rocks from the Xihuashan mining area displays high SiO2(73.85% to 76.49%) and Na2O+K2O contents(8.09% to 9.43%),belonging to high-K calc-alkaline series.They are metaluminous to weakly peraluminous with A/CNK values ranging from 0.96 to 1.06.All granites in this study area are rich in Rb,Th,U and Pb,and depleted in Ba,Sr,P,Ti,Nb and Eu,especially depleted in medium-grained biotite granite and fine-grained two-mica granite.The medium-grained porphyritic biotite granites usually have high LREE concentrations,whereas medium-grained biotite granite and fine-grained two-mica granite displays high HREE contents.Our geochemical data reveal that the studied rocks are highly fractionated I-type granite.The magma underwent strong magma differentiation with decreasing temperature and increasing oxygen fugacity,which may explain the formation of three types of distinct granites.Variations of Rb,Sr and Ba concentrations in different type granites were controlled by fractional crystallization of biotite and feldspar.Fractional crystallization of monazite,allanite and apatite resulted in LREE changes in granite,and formation of garnet mainly caused HREE changes.Granites from the Xihuashan mining area have relatively high εNd(t) values(-9.77 to -11.46),indicating that they were probably generated by partial melting of underlying Proterozoic metasedimentary rocks with minor addition of juvenile crust or mantle-derived magmas.
