The Guanpo pegmatite field in the North Qinling orogenic belt(NQB),China,hosts the most abundant LCT pegmatites.However,their emplacement conditions and structural control remain unexplored.In this contribution,we inv...The Guanpo pegmatite field in the North Qinling orogenic belt(NQB),China,hosts the most abundant LCT pegmatites.However,their emplacement conditions and structural control remain unexplored.In this contribution,we investigated it combining pegmatite orientation measurement with oxygen isotope geothermometry and fluid inclusion study.The orientations of type A1 pegmatites(P_(f)<σ_(2))are predominantly influenced by P-and T-fractures due to simple shearing in Shiziping dextral thrust shear zone during D_(2)deformation,whereas type A2 pegmatites(contemporaneous with D_(4))are governed by hydraulic fractures aligned with S_(0)and S_(0+1)stemming from fluid pressure(P_(f)<σ_(2)).Additionally,type B pegmatites(P_(f)≤σ_(2))exhibit orientations shaped by en echelon extensional fractures in local ductile shear zones(contemporaneous with D_(3)).The albite-quartz oxygen isotope geothermometry and microthermometric analysis of fluid inclusions in elbaites from the latest pegmatites(including types B and A2)suggest that the crystallization P-T for late magmatic and hydrothermal stages are 527.5-559.2℃,320℃,3.1-3.6 kbar and 2.0 kbar,respectively.Our observations along with previous studies suggest that the genesis of the LCT pegmatites was a long-term,multi-stage event during early Paleozoic orogeny(including the collision stage)of the NQB,and was facilitated by various local fractures.展开更多
The North Qinling Orogenic Belt(NQOB)is a composite orogenic belt in central China.It started evolving during the Meso-Neoproterozoic period and underwent multiple stages of plate subduction and collision before enter...The North Qinling Orogenic Belt(NQOB)is a composite orogenic belt in central China.It started evolving during the Meso-Neoproterozoic period and underwent multiple stages of plate subduction and collision before entering intra-continental orogeny in the Late Triassic.The Meso-Cenozoic intra-continental orogeny and tectonic evolution had different responses in various terranes of the belt,with the tectonic evolution of the middle part of the belt being particularly controversial.The granites distributed in the Dayu and Kuyu areas in the middle part of the NQOB can provide an important window for revealing the geodynamic mechanisms of the NQOB.The main lithology of Dayu and Kuyu granites is biotite monzogranite,and the zircon U-Pb dating yielded intrusive ages of 151.3±3.4 Ma and 147.7±1.5 Ma,respectively.The dates suggest that the biotite monzogranite were formed at the end of the Late Jurassic.The whole-rock geochemistry analysis shows that the granites in the study areas are characterized by slightly high SiO_(2)(64.50-68.88 wt%)and high Al_(2)O_(3)(15.12-16.24 wt%)and Na_(2)O(3.55-3.80 wt%)contents.They are also enriched in light rare earth elements,large ion lithophile elements(e.g.,Ba,K,La,Pb and Sr),and depleted in high field strength elements(HFSEs)(e.g.,Ta,Nb,P and Ti).Additionally,the granites have weakly negative-slightly positive Eu anomalies(δEu=0.91-1.19).Zircon Lu-Hf isotopic analysis showedε_(Hf)(t)=-6.1--3.8,and the two-stage model age is T_(2DM(crust))=1.5-1.6 Ga.The granites in the study areas are analyzed as weak peraluminous high-K calc-alkaline I-type granites.They formed by partial melting of the thickened ancient lower crust,accompanied by the addition of minor mantle-derived materials.During magma ascent,they experienced fractional crystallization,with residual garnet and amphibole for a certain proportion in the magma source region.Comprehensive the geotectonic data suggest that the end of the Late Jurassic granite magmatism in the Dayu and Kuyu areas represents a compression-extension transition regime.It may have been a response to multiple tectonic mechanisms,such as the late Mesozoic intra-continental southward subduction of the North China Craton and the remote effect of the Paleo-Pacific Plate subduction.展开更多
The Dehe granitic pluton intruded the Xiahe Group which is in the core complex of the North Qinling Orogenic Belt(NQOB).It shows gneissic bedding and possesses typical S-type granite minerals such as muscovite and gar...The Dehe granitic pluton intruded the Xiahe Group which is in the core complex of the North Qinling Orogenic Belt(NQOB).It shows gneissic bedding and possesses typical S-type granite minerals such as muscovite and garnet.LA-ICP-MS U-Pb isotopic dating of the Dehe granite yielded a weighted average age of 925±23 Ma which represents the emplacement age of the pluton.Most of the εHf(t) values are negative,and the two-stage model ages are consistent with the age of the Qinling Group.The isotope data show that the Dehe granite was formed in the following geological setting:in the syn-collision setting of the NQOB in the Neoproterozoic,crustal thickening induced partial melting of materials derived from the Qinling complex,and then the maga upwelled and intruded into the Xiahe Group.The formation of the Dehe S-type granite implied the occurrence of a convergent event in the QOB during the Neoproterozoic.展开更多
A new cerite group mineral species,taipingite-(Ce),ideally(Ce7^3+,Ca2)∑9Mg(SiO4)3[SiO3(OH)]4 F3,has been found in the Taipingzhen rare earth element(REE)deposit in the North Qinling Orogen(NQO),Central China.It forms...A new cerite group mineral species,taipingite-(Ce),ideally(Ce7^3+,Ca2)∑9Mg(SiO4)3[SiO3(OH)]4 F3,has been found in the Taipingzhen rare earth element(REE)deposit in the North Qinling Orogen(NQO),Central China.It forms subhedral grains(up to approximately 100 μm×200 μm)commonly intergrown with the REE mineral assemblages and is closely associated with allanite-(Ce),gatelite-(Ce),tornebohmite-(Ce),fluocerite-(Ce),fluocerite-(La),fluorite,bastnasite-(Ce),parisite-(Ce)and calcite.Taipingite-(Ce)is light red to pinkish brown under a binocular microscope and pale brown to colorless in thin section,and it is translucent to transparent with a grayish-white streak and vitreous luster.This mineral is brittle with conchoidal fracture;has a Mohs hardness value of approximately 51/2 and exhibits no cleavage twinning or parting.The calculated density is 4.900(5)g/cm3.Optically,taipingite-(Ce)is uniaxial(+),withω=1.808(5),ε=1.812(7),c=ε,and a=b=ω.Furthermore,this mineral is insoluble in HCl,HNO3 and H2 SO4.Electron microprobe analysis demonstrated that the sample was relatively pure,yielding the empirical formula(with calculated H2 O):(Ce4.02La1.64Nd1.49Pr0.41Sm0.10Gd0.02Ho0.02Tm0.01Lu0.02Y0.03Ca0.66Mg0.05Th(0.01-0.51∑9(Mg0.75Fe0.253+)∑1(SiO4)3{[SiO3(OH)]3.98[PO3(OH)]0.02}∑4(F1.81OH1.17Cl0.02∑3.Taipingite-(Ce)is trigonal and exhibits space group symmetry R3 c with unit cell parameters a=10.7246(3)Å,c=37.9528(14)Å,V=3780.39(20)Å3 and Z=6.The strongest eight lines in the X-ray diffraction pattern are[d in A(I)(hkl)]:4.518(50)(202),3.455(95)(122),3.297(85)(214),3.098(35)(300),2.941(100)(02,10),2.683(65)(220),1.945(40)(238)and 1.754(40)(30,18).The crystal structure has been refined to a R1 factor of 0.025,calculated for the 2312 unique observed reflections(Fo≥4σ).The mineral is named after its discovery locality and is characterized as the F-dominant analogue of cerite-(Ce).展开更多
1 Introduction The North Qinling orogenic belt is characterized by diverse rocks,multi-phase tectonic-magmatic events,which is composed of not only basement rocks of the Qinling Group,but also numerous magmatic rocks in
The Huichizi granite complex is the largest Paleozoic 1-type intrusion located in the North Qinling orogenic belt （NQB）. In this study, we present systematic geochemical element data, zircon U-Pb ages, Ln-Hf isotopi...The Huichizi granite complex is the largest Paleozoic 1-type intrusion located in the North Qinling orogenic belt （NQB）. In this study, we present systematic geochemical element data, zircon U-Pb ages, Ln-Hf isotopic data, and Sr-Nd isotopic data for the Huichizi granites. In terms of mineral and chemical compositions, these granites are biotite monzonitic and alkali-feldspar granites, both of which are characterized by high SiO2 and total alkali contents and low MgO, TiO2, and TFeO contents. These granites are weakly peraluminous （A/CNK values are 1-1.06 for biotite mon- zonitic granites and 1.04-1.09 for alkali-feldspar granites） and possess the geochemical characteristics of adakitic rocks, e.g., high Sr contents （319 ppm-633 ppm）, Sr/Y ratios （18.5-174）, and （La/Yb）N ratios （17.6-57） and low MgO （0.04 wt.%-0.83 wt.%）, Y （3.0 ppm-17.2 ppm）, and heavy rare-earth element （HREE） contents. This indicates that these rocks were most likely derived from the partial melting of a thickened lower crust. In situ zircon U-Pb dating of these granites yields Early Caledonian ages （437 Ma for biotite monzonitic granites and 424 Ma for alkali-feldspar granites）, indicating that the Huichizi granitic complex is the product of multi-periodic magmatism. The positive but varying zircon tHe（t） values （＋0.6 to ＋8.5） suggest that this thickened lower crust was mainly juvenile, i.e., accreted from depleted mantle during the Neo-Mesoproterozoic Period, but involved the ancient recycled crust. Biotite monzonitic granites formed during crust thickening at the extrusion stage, whereas the alkali granites formed during crust thickening at the extension stage （post extrusion）. The Huichizi granite complex witnessed the process of extrusion to extension because of the collision between the NCB and the Qinling microcontinent in the Caledonian.展开更多
The Qinling Orogen is a composite orogenic belt that can be subdivided into the North and South Qinling,broadly separated by the Shangdan suture zone.These two orogenic belts were generated by subduction-collisional p...The Qinling Orogen is a composite orogenic belt that can be subdivided into the North and South Qinling,broadly separated by the Shangdan suture zone.These two orogenic belts were generated by subduction-collisional processes in the Early Paleozoic and Late Triassic,respectively.During the Late Jurassic to Early Cretaceous,the eastern portion of the Qinling Orogen was tectonically reactivated due to westerly subduction of the Izanagi plate underneath the East China continental margin.The Qinling Orogen is well-endowed with numerous Au,Mo,Ag-Pb-Zn deposits that predominantly formed in the Late Triassic to Early Cretaceous,with rare Paleozoic varieties documented.In this study,we present garnet and zircon U-Pb dating results to show that the Huoshenmiao iron skarn deposit in the Tongbai area of North Qinling orogenic belt formed in the Early Silurian and is genetically related to subduction-related magmatism.The Huoshenmiao deposit consists of lenticular and stratiform orebodies that contain massive or densely disseminated magnetite variably associated with garnet,diopside,epidote,hornblende,and actinolite.Garnets from iron ores are andradite and grossular in composition(Ad_(83.1)Gr_(13.3)-Ad_(86.5)Gr_(10.2))and characterized by enrichment in light rare earth elements(ΣLREE=57.85-103.82 ppm)and depletion in heavy rare earth elements(ΣHREE=5.50-11.34 ppm),with significantly positive Eu and Ce anomalies(δEu of 1.09-1.89 andδCe of 1.39-1.69).These compositional signatures are distinctly different from those of garnets in the ore-hosting metamorphic rocks that are typically dominated by almandine,spessartine and grossular(Al_(47.4)Sp_(30.4)Gr_(13.8)-Al_(51.9)Sp_(24.8)Gr_(17.6)),depleted in LREE(0.14-0.69 ppm),enriched in HREE(95.68-841.60 ppm)and have pronounced negative Eu anomalies(δEu=0.24-0.51).In addition,garnets from iron ores of the Huoshenmiao deposit contain abundant daughter mineral-bearing,multiphase fluid inclusions,further confirming their hydrothermal origin.Two samples of those hydrothermal garnets yield U-Pb dates of 437±9 Ma and 437±10 Ma(2σ),revealing a Paleozoic mineralization event that has long been ignored and rarely documented.These garnet dates agree well with zircon U-Pb dates of 438±4 Ma to 436±3 Ma for a gabbroic diorite and 430±4 Ma for a granite intrusion in close proximity of the mine,supporting a possible genetic link between the iron mineralization and Early Silurian magmatism.The Paleozoic intrusions are enriched in large ion lithophile elements(LILEs:Ba,K,Sr)and LREEs,depleted in high field strength elements(HFSEs:Nb,Ta,P,Ti),have whole-rock(^(87)Sr/^(86)Sr)i,ε_(Nd)(t),and zirconεHf(t)values of 0.7039-0.7042,3.32-4.33,and 13.0-14.9,respectively.These geochemical and isotopic characteristics suggest that the Paleozoic intrusions were affiliated with arc magmatism triggered by subduction of the Shangdan oceanic plate in the Early Paleozoic.Recognition of the Silurian Huoshenmiao iron skarn deposit opens a new window for exploration of Paleozoic mineral resources in the Tongbai area and other portions of the North Qinling Orogen.展开更多
基金supported by the National Key R&D Program of China(Grant Nos.2021YFC2901902 and 2019YFC0605202)。
文摘The Guanpo pegmatite field in the North Qinling orogenic belt(NQB),China,hosts the most abundant LCT pegmatites.However,their emplacement conditions and structural control remain unexplored.In this contribution,we investigated it combining pegmatite orientation measurement with oxygen isotope geothermometry and fluid inclusion study.The orientations of type A1 pegmatites(P_(f)<σ_(2))are predominantly influenced by P-and T-fractures due to simple shearing in Shiziping dextral thrust shear zone during D_(2)deformation,whereas type A2 pegmatites(contemporaneous with D_(4))are governed by hydraulic fractures aligned with S_(0)and S_(0+1)stemming from fluid pressure(P_(f)<σ_(2)).Additionally,type B pegmatites(P_(f)≤σ_(2))exhibit orientations shaped by en echelon extensional fractures in local ductile shear zones(contemporaneous with D_(3)).The albite-quartz oxygen isotope geothermometry and microthermometric analysis of fluid inclusions in elbaites from the latest pegmatites(including types B and A2)suggest that the crystallization P-T for late magmatic and hydrothermal stages are 527.5-559.2℃,320℃,3.1-3.6 kbar and 2.0 kbar,respectively.Our observations along with previous studies suggest that the genesis of the LCT pegmatites was a long-term,multi-stage event during early Paleozoic orogeny(including the collision stage)of the NQB,and was facilitated by various local fractures.
基金substantially supported by the National Nature Science Foundation of China(Grant No.41872220)。
文摘The North Qinling Orogenic Belt(NQOB)is a composite orogenic belt in central China.It started evolving during the Meso-Neoproterozoic period and underwent multiple stages of plate subduction and collision before entering intra-continental orogeny in the Late Triassic.The Meso-Cenozoic intra-continental orogeny and tectonic evolution had different responses in various terranes of the belt,with the tectonic evolution of the middle part of the belt being particularly controversial.The granites distributed in the Dayu and Kuyu areas in the middle part of the NQOB can provide an important window for revealing the geodynamic mechanisms of the NQOB.The main lithology of Dayu and Kuyu granites is biotite monzogranite,and the zircon U-Pb dating yielded intrusive ages of 151.3±3.4 Ma and 147.7±1.5 Ma,respectively.The dates suggest that the biotite monzogranite were formed at the end of the Late Jurassic.The whole-rock geochemistry analysis shows that the granites in the study areas are characterized by slightly high SiO_(2)(64.50-68.88 wt%)and high Al_(2)O_(3)(15.12-16.24 wt%)and Na_(2)O(3.55-3.80 wt%)contents.They are also enriched in light rare earth elements,large ion lithophile elements(e.g.,Ba,K,La,Pb and Sr),and depleted in high field strength elements(HFSEs)(e.g.,Ta,Nb,P and Ti).Additionally,the granites have weakly negative-slightly positive Eu anomalies(δEu=0.91-1.19).Zircon Lu-Hf isotopic analysis showedε_(Hf)(t)=-6.1--3.8,and the two-stage model age is T_(2DM(crust))=1.5-1.6 Ga.The granites in the study areas are analyzed as weak peraluminous high-K calc-alkaline I-type granites.They formed by partial melting of the thickened ancient lower crust,accompanied by the addition of minor mantle-derived materials.During magma ascent,they experienced fractional crystallization,with residual garnet and amphibole for a certain proportion in the magma source region.Comprehensive the geotectonic data suggest that the end of the Late Jurassic granite magmatism in the Dayu and Kuyu areas represents a compression-extension transition regime.It may have been a response to multiple tectonic mechanisms,such as the late Mesozoic intra-continental southward subduction of the North China Craton and the remote effect of the Paleo-Pacific Plate subduction.
基金supported jointly by the National Natural Science Foundation of China (Grant Nos. 41030423,41072068 and 40872071)National Basic Research Program of China (Grant No. 2006CB403502)+2 种基金MOST Special Fund from the State Key Laboratory of Continental Dynamics, Northwest University (Grant No. BJ091349)National Found for Fostering Talents of Basic Sciences (Grant No. J0830519)Graduate Innovation and Creativity Funds of Northwest University,China (Grant No. 10YZZ24)
文摘The Dehe granitic pluton intruded the Xiahe Group which is in the core complex of the North Qinling Orogenic Belt(NQOB).It shows gneissic bedding and possesses typical S-type granite minerals such as muscovite and garnet.LA-ICP-MS U-Pb isotopic dating of the Dehe granite yielded a weighted average age of 925±23 Ma which represents the emplacement age of the pluton.Most of the εHf(t) values are negative,and the two-stage model ages are consistent with the age of the Qinling Group.The isotope data show that the Dehe granite was formed in the following geological setting:in the syn-collision setting of the NQOB in the Neoproterozoic,crustal thickening induced partial melting of materials derived from the Qinling complex,and then the maga upwelled and intruded into the Xiahe Group.The formation of the Dehe S-type granite implied the occurrence of a convergent event in the QOB during the Neoproterozoic.
基金financially supported by the National Natural Science Foundation of China(Grant No.41502033)the China Geological Survey(DD20160129-3,1212011120771,DD20190813)。
文摘A new cerite group mineral species,taipingite-(Ce),ideally(Ce7^3+,Ca2)∑9Mg(SiO4)3[SiO3(OH)]4 F3,has been found in the Taipingzhen rare earth element(REE)deposit in the North Qinling Orogen(NQO),Central China.It forms subhedral grains(up to approximately 100 μm×200 μm)commonly intergrown with the REE mineral assemblages and is closely associated with allanite-(Ce),gatelite-(Ce),tornebohmite-(Ce),fluocerite-(Ce),fluocerite-(La),fluorite,bastnasite-(Ce),parisite-(Ce)and calcite.Taipingite-(Ce)is light red to pinkish brown under a binocular microscope and pale brown to colorless in thin section,and it is translucent to transparent with a grayish-white streak and vitreous luster.This mineral is brittle with conchoidal fracture;has a Mohs hardness value of approximately 51/2 and exhibits no cleavage twinning or parting.The calculated density is 4.900(5)g/cm3.Optically,taipingite-(Ce)is uniaxial(+),withω=1.808(5),ε=1.812(7),c=ε,and a=b=ω.Furthermore,this mineral is insoluble in HCl,HNO3 and H2 SO4.Electron microprobe analysis demonstrated that the sample was relatively pure,yielding the empirical formula(with calculated H2 O):(Ce4.02La1.64Nd1.49Pr0.41Sm0.10Gd0.02Ho0.02Tm0.01Lu0.02Y0.03Ca0.66Mg0.05Th(0.01-0.51∑9(Mg0.75Fe0.253+)∑1(SiO4)3{[SiO3(OH)]3.98[PO3(OH)]0.02}∑4(F1.81OH1.17Cl0.02∑3.Taipingite-(Ce)is trigonal and exhibits space group symmetry R3 c with unit cell parameters a=10.7246(3)Å,c=37.9528(14)Å,V=3780.39(20)Å3 and Z=6.The strongest eight lines in the X-ray diffraction pattern are[d in A(I)(hkl)]:4.518(50)(202),3.455(95)(122),3.297(85)(214),3.098(35)(300),2.941(100)(02,10),2.683(65)(220),1.945(40)(238)and 1.754(40)(30,18).The crystal structure has been refined to a R1 factor of 0.025,calculated for the 2312 unique observed reflections(Fo≥4σ).The mineral is named after its discovery locality and is characterized as the F-dominant analogue of cerite-(Ce).
基金financially supported by National Natural Science Foundation of China (41372072)Natural Science Foundation of Education Department of Anhui province (KJ2016A025)+1 种基金Dr. Startup Foundation, Anhui university (J10113190090)the State Key Laboratory of Geodynamics, Northwest University
文摘1 Introduction The North Qinling orogenic belt is characterized by diverse rocks,multi-phase tectonic-magmatic events,which is composed of not only basement rocks of the Qinling Group,but also numerous magmatic rocks in
基金financially supported by the National Basic Research Program of China (No. 2014CB440906)the Strateic Priority Research Program (B) of Chinese Academy of Sciences (No. XDB18030200)the National Natural Sciences Foundation of China (Nos. 41473049, 41103027)
文摘The Huichizi granite complex is the largest Paleozoic 1-type intrusion located in the North Qinling orogenic belt （NQB）. In this study, we present systematic geochemical element data, zircon U-Pb ages, Ln-Hf isotopic data, and Sr-Nd isotopic data for the Huichizi granites. In terms of mineral and chemical compositions, these granites are biotite monzonitic and alkali-feldspar granites, both of which are characterized by high SiO2 and total alkali contents and low MgO, TiO2, and TFeO contents. These granites are weakly peraluminous （A/CNK values are 1-1.06 for biotite mon- zonitic granites and 1.04-1.09 for alkali-feldspar granites） and possess the geochemical characteristics of adakitic rocks, e.g., high Sr contents （319 ppm-633 ppm）, Sr/Y ratios （18.5-174）, and （La/Yb）N ratios （17.6-57） and low MgO （0.04 wt.%-0.83 wt.%）, Y （3.0 ppm-17.2 ppm）, and heavy rare-earth element （HREE） contents. This indicates that these rocks were most likely derived from the partial melting of a thickened lower crust. In situ zircon U-Pb dating of these granites yields Early Caledonian ages （437 Ma for biotite monzonitic granites and 424 Ma for alkali-feldspar granites）, indicating that the Huichizi granitic complex is the product of multi-periodic magmatism. The positive but varying zircon tHe（t） values （＋0.6 to ＋8.5） suggest that this thickened lower crust was mainly juvenile, i.e., accreted from depleted mantle during the Neo-Mesoproterozoic Period, but involved the ancient recycled crust. Biotite monzonitic granites formed during crust thickening at the extrusion stage, whereas the alkali granites formed during crust thickening at the extension stage （post extrusion）. The Huichizi granite complex witnessed the process of extrusion to extension because of the collision between the NCB and the Qinling microcontinent in the Caledonian.
基金This work was supported by the National Natural Science Foundation of China(Grant No.41772081).
文摘The Qinling Orogen is a composite orogenic belt that can be subdivided into the North and South Qinling,broadly separated by the Shangdan suture zone.These two orogenic belts were generated by subduction-collisional processes in the Early Paleozoic and Late Triassic,respectively.During the Late Jurassic to Early Cretaceous,the eastern portion of the Qinling Orogen was tectonically reactivated due to westerly subduction of the Izanagi plate underneath the East China continental margin.The Qinling Orogen is well-endowed with numerous Au,Mo,Ag-Pb-Zn deposits that predominantly formed in the Late Triassic to Early Cretaceous,with rare Paleozoic varieties documented.In this study,we present garnet and zircon U-Pb dating results to show that the Huoshenmiao iron skarn deposit in the Tongbai area of North Qinling orogenic belt formed in the Early Silurian and is genetically related to subduction-related magmatism.The Huoshenmiao deposit consists of lenticular and stratiform orebodies that contain massive or densely disseminated magnetite variably associated with garnet,diopside,epidote,hornblende,and actinolite.Garnets from iron ores are andradite and grossular in composition(Ad_(83.1)Gr_(13.3)-Ad_(86.5)Gr_(10.2))and characterized by enrichment in light rare earth elements(ΣLREE=57.85-103.82 ppm)and depletion in heavy rare earth elements(ΣHREE=5.50-11.34 ppm),with significantly positive Eu and Ce anomalies(δEu of 1.09-1.89 andδCe of 1.39-1.69).These compositional signatures are distinctly different from those of garnets in the ore-hosting metamorphic rocks that are typically dominated by almandine,spessartine and grossular(Al_(47.4)Sp_(30.4)Gr_(13.8)-Al_(51.9)Sp_(24.8)Gr_(17.6)),depleted in LREE(0.14-0.69 ppm),enriched in HREE(95.68-841.60 ppm)and have pronounced negative Eu anomalies(δEu=0.24-0.51).In addition,garnets from iron ores of the Huoshenmiao deposit contain abundant daughter mineral-bearing,multiphase fluid inclusions,further confirming their hydrothermal origin.Two samples of those hydrothermal garnets yield U-Pb dates of 437±9 Ma and 437±10 Ma(2σ),revealing a Paleozoic mineralization event that has long been ignored and rarely documented.These garnet dates agree well with zircon U-Pb dates of 438±4 Ma to 436±3 Ma for a gabbroic diorite and 430±4 Ma for a granite intrusion in close proximity of the mine,supporting a possible genetic link between the iron mineralization and Early Silurian magmatism.The Paleozoic intrusions are enriched in large ion lithophile elements(LILEs:Ba,K,Sr)and LREEs,depleted in high field strength elements(HFSEs:Nb,Ta,P,Ti),have whole-rock(^(87)Sr/^(86)Sr)i,ε_(Nd)(t),and zirconεHf(t)values of 0.7039-0.7042,3.32-4.33,and 13.0-14.9,respectively.These geochemical and isotopic characteristics suggest that the Paleozoic intrusions were affiliated with arc magmatism triggered by subduction of the Shangdan oceanic plate in the Early Paleozoic.Recognition of the Silurian Huoshenmiao iron skarn deposit opens a new window for exploration of Paleozoic mineral resources in the Tongbai area and other portions of the North Qinling Orogen.
