Jiama is a giant,high-grade porphyry copper system in the Gangdese metallogenic belt,Xizang.Multistage intermediate-felsic porphyries intruded in this deposit,some of which are strongly associated with copper-polymeta...Jiama is a giant,high-grade porphyry copper system in the Gangdese metallogenic belt,Xizang.Multistage intermediate-felsic porphyries intruded in this deposit,some of which are strongly associated with copper-polymetallic mineralization.These ore-bearing porphyries include monzogranite,granodiorite,and quartz diorite porphyries.A new granite aplite dyke was found in the south of Jiama.Its age,genesis,and relationship with ore-related magmatism are obscure.Here,its emplacement age and petrogenesis were determined using mineralogy,zircon U-Pb dating,geochemistry,and Sr-Nd-Pb isotope studies.The zircon LA-ICP-MS U-Pb age of the aplite dyke is 16.66±0.21 Ma(n=14,MSWD=0.66),earlier than that of the ore-bearing porphyries(~15 Ma)in Jiama.Furthermore,the aplite exhibits high amounts of silicon(SiO_(2)=73.39%-74.74%),potassium(K_(2)O=5.12%-6.61%),aluminum(Al_(2)O_(3)=14.25%-14.69%),and light/heavy rare earth elements(LREE/HREE=12.12-16.19)as well as negative europium(δEu=0.47-0.72)and weak negative cerium anomalies(δCe=0.84-0.93).The aplite dyke is characteristic of metaluminous-peraluminous I-type granite,which is rich in large-ion lithophile elements(Rb,Ba,Th and U)and depleted in high-field-strength elements(Nb,P and Ti).The aplite dyke and ore-bearing porphyries in the Jiama deposit are the results of a partial melting of the juvenile lower crust,according to whole-rock geochemistry and Sr-Nd-Pb isotope data,but the dyke and ore-bearing porphyries were emplaced from the same magma chamber at different times.Thus,the aplite dyke shows the composition of the early evolution stage of shallow magma in the Jiama deposit and is the product of rapid condensation and crystallization.展开更多
Leucogranite,pegmatite,and aplite from selected areas in the Wadi El Gemal area in the southern Eastern Desert of Egypt were investigated geochemically for their petrogenesis.These rocks represent a significant episod...Leucogranite,pegmatite,and aplite from selected areas in the Wadi El Gemal area in the southern Eastern Desert of Egypt were investigated geochemically for their petrogenesis.These rocks represent a significant episode of felsic magmatism during the late stage of the Pan-African orogeny in the evolution of the Arabian–Nubian Shield(ANS)during the Late Neoproterozoic.On a petrographic basis,the leucogranite is sometimes garnetiferous and can be distinguished into monzogranite,syenogranite,and alkali feldspar granite.The analyses of muscovite,biotite,garnet,and apatite reveal the magmatic nature of the studied leucogranite.The investigated leucogranite,pegmatite,and aplite are alkali-calcic,calc-alkaline,and peraluminous.The peraluminous nature of these rocks is evidenced by using the chemical analyses of biotite.These studied rocks show a slight enrichment in light rare-earth elements(LREEs)and large-ion lithophile elements(LILE,especially Rb and Th),with an insignificant depletion of heavy rareearth elements(HREEs).On a geochemical basis,the leucogranite,pegmatite,and aplite in the study area crystallized from multiple-sourced melts that include mafic,metagraywake,and pelitic.They were derived from melts generated at crystallization temperatures around 568-900℃ for leucogranite,553-781℃ for pegmatite,and 639-779℃ for aplite based on the Zr saturation geothermometers,and at a pressure around 0.39-0.48 GPa,i.e.shallow depth intrusions.The studied felsic rocks have strong negative Eu anomalies,which are very consistent with an upper crust composition,indicating fractionation of feldspar cumulates.Also,they show a moderate La/Sm ratio indicating combined magmatic processes represented by partial melting and fractional crystallization.Integration of whole-rock chemical composition and mineral microanalysis suggests that felsic magmatism in the west Wadi El Gemal area produced voluminous masses of syn-to post-collisional granite,pegmatite,and aplite.An evolutionary three-stage model is presented to understand late magmatism in the ANS in terms of a geodynamic model.Such a model discusses the propagation of felsic magmatism in the ANS during syn-collisional to post-collisional stages.展开更多
The widespread W-(Mo)-Sn-Nb-Ta polymetallic mineralization in Southeast(SE)China is genetically associated with Mesozoic highly fractionated granitic rocks.Such rocks have enigmatic mineralogical and geochemical featu...The widespread W-(Mo)-Sn-Nb-Ta polymetallic mineralization in Southeast(SE)China is genetically associated with Mesozoic highly fractionated granitic rocks.Such rocks have enigmatic mineralogical and geochemical features,making its petrogenesis an intensely debated topic.To better understand the underlying magma evolution processes,petrography,garnet chemistry and whole-rock major and trace element data are reported for Jurassic highly fractionated granitic rocks and associated microgranite and aplitepegmatite dikes from Macao and compared with coeval similar granitic rocks from nearby areas in SE China.Despite the fact that the most evolved rocks in Macao are garnet-bearing aplite-pegmatite dikes,the existence of coeval two-mica and garnet-bearing biotite and muscovite granites displaying more evolved compositions(e.g.,lower Zr/Hf ratios)indicates that the differentiation sequence reached higher degrees of fractionation at a regional scale.Although crystal fractionation played an important role,late-stage fluid/melt interactions,involving F-rich fluids,imparted specific geochemical characteristics to Macao and SE China highly fractionated granitic rocks such as the non-CHARAC(CHArge-and-RAdius-Controlled)behavior of trace elements,leading,for example,to non-chondritic Zr/Hf ratios,Rare Earth Elements(REE)tetrad effects and Nb-Ta enrichment and fractionation.Such process contributed to the late-stage crystallization of accessory phases only found in these highly evolved facies.Among the latter,two populations of garnet were identified in MGI(Macao GroupⅠ)highly fractionated granitic rocks:small grossular-poor euhedral grains and large grossular-rich skeletal garnet grains with quartz inclusions.The first group was mainly formed through precipitation from highly evolved Mn-rich slightly peraluminous melts under low-pressure and relatively low temperature(~700℃)conditions.Assimilation of upper crust metasedimentary materials may have contributed as a source of Mn and Al to the formation of garnet.The second group has a metasomatic origin related to the interaction of magmatic fluids with previously crystallized mineral phases and,possibly,with assimilated metasedimentary enclaves or surrounding metasedimentary strata.The highly fractionated granitic rocks in Macao represent the first stage in the development of granite-related W-(Mo)-Sn-Nb-Ta mineralization associated with coeval more evolved lithotypes in SE China.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2022YFC2905001)National Natural Science Foundation of China(Grant Nos.42272093 and 42230813)+2 种基金Basic Research Fund of Chinese Academy of Geological Sciences(Grant Nos.JKYZD202316,KJ2102,KK2116,and JKY202208)Geological Survey Project(Grant No.DD20221684)China Scholarship Council(Grant No.CSC202206400059)。
文摘Jiama is a giant,high-grade porphyry copper system in the Gangdese metallogenic belt,Xizang.Multistage intermediate-felsic porphyries intruded in this deposit,some of which are strongly associated with copper-polymetallic mineralization.These ore-bearing porphyries include monzogranite,granodiorite,and quartz diorite porphyries.A new granite aplite dyke was found in the south of Jiama.Its age,genesis,and relationship with ore-related magmatism are obscure.Here,its emplacement age and petrogenesis were determined using mineralogy,zircon U-Pb dating,geochemistry,and Sr-Nd-Pb isotope studies.The zircon LA-ICP-MS U-Pb age of the aplite dyke is 16.66±0.21 Ma(n=14,MSWD=0.66),earlier than that of the ore-bearing porphyries(~15 Ma)in Jiama.Furthermore,the aplite exhibits high amounts of silicon(SiO_(2)=73.39%-74.74%),potassium(K_(2)O=5.12%-6.61%),aluminum(Al_(2)O_(3)=14.25%-14.69%),and light/heavy rare earth elements(LREE/HREE=12.12-16.19)as well as negative europium(δEu=0.47-0.72)and weak negative cerium anomalies(δCe=0.84-0.93).The aplite dyke is characteristic of metaluminous-peraluminous I-type granite,which is rich in large-ion lithophile elements(Rb,Ba,Th and U)and depleted in high-field-strength elements(Nb,P and Ti).The aplite dyke and ore-bearing porphyries in the Jiama deposit are the results of a partial melting of the juvenile lower crust,according to whole-rock geochemistry and Sr-Nd-Pb isotope data,but the dyke and ore-bearing porphyries were emplaced from the same magma chamber at different times.Thus,the aplite dyke shows the composition of the early evolution stage of shallow magma in the Jiama deposit and is the product of rapid condensation and crystallization.
基金finational supported by the Foundation of Science,Technology and Innovation Funding Authority(STDF)(Award Number:47106Recipient:Mokhles K K.Azer)。
文摘Leucogranite,pegmatite,and aplite from selected areas in the Wadi El Gemal area in the southern Eastern Desert of Egypt were investigated geochemically for their petrogenesis.These rocks represent a significant episode of felsic magmatism during the late stage of the Pan-African orogeny in the evolution of the Arabian–Nubian Shield(ANS)during the Late Neoproterozoic.On a petrographic basis,the leucogranite is sometimes garnetiferous and can be distinguished into monzogranite,syenogranite,and alkali feldspar granite.The analyses of muscovite,biotite,garnet,and apatite reveal the magmatic nature of the studied leucogranite.The investigated leucogranite,pegmatite,and aplite are alkali-calcic,calc-alkaline,and peraluminous.The peraluminous nature of these rocks is evidenced by using the chemical analyses of biotite.These studied rocks show a slight enrichment in light rare-earth elements(LREEs)and large-ion lithophile elements(LILE,especially Rb and Th),with an insignificant depletion of heavy rareearth elements(HREEs).On a geochemical basis,the leucogranite,pegmatite,and aplite in the study area crystallized from multiple-sourced melts that include mafic,metagraywake,and pelitic.They were derived from melts generated at crystallization temperatures around 568-900℃ for leucogranite,553-781℃ for pegmatite,and 639-779℃ for aplite based on the Zr saturation geothermometers,and at a pressure around 0.39-0.48 GPa,i.e.shallow depth intrusions.The studied felsic rocks have strong negative Eu anomalies,which are very consistent with an upper crust composition,indicating fractionation of feldspar cumulates.Also,they show a moderate La/Sm ratio indicating combined magmatic processes represented by partial melting and fractional crystallization.Integration of whole-rock chemical composition and mineral microanalysis suggests that felsic magmatism in the west Wadi El Gemal area produced voluminous masses of syn-to post-collisional granite,pegmatite,and aplite.An evolutionary three-stage model is presented to understand late magmatism in the ANS in terms of a geodynamic model.Such a model discusses the propagation of felsic magmatism in the ANS during syn-collisional to post-collisional stages.
基金supported by the Macao Science and Technology Development Fund(No.FDCT 043/2014/A1)the financial FCT support(No.UIDB/50019/2020–IDL)。
文摘The widespread W-(Mo)-Sn-Nb-Ta polymetallic mineralization in Southeast(SE)China is genetically associated with Mesozoic highly fractionated granitic rocks.Such rocks have enigmatic mineralogical and geochemical features,making its petrogenesis an intensely debated topic.To better understand the underlying magma evolution processes,petrography,garnet chemistry and whole-rock major and trace element data are reported for Jurassic highly fractionated granitic rocks and associated microgranite and aplitepegmatite dikes from Macao and compared with coeval similar granitic rocks from nearby areas in SE China.Despite the fact that the most evolved rocks in Macao are garnet-bearing aplite-pegmatite dikes,the existence of coeval two-mica and garnet-bearing biotite and muscovite granites displaying more evolved compositions(e.g.,lower Zr/Hf ratios)indicates that the differentiation sequence reached higher degrees of fractionation at a regional scale.Although crystal fractionation played an important role,late-stage fluid/melt interactions,involving F-rich fluids,imparted specific geochemical characteristics to Macao and SE China highly fractionated granitic rocks such as the non-CHARAC(CHArge-and-RAdius-Controlled)behavior of trace elements,leading,for example,to non-chondritic Zr/Hf ratios,Rare Earth Elements(REE)tetrad effects and Nb-Ta enrichment and fractionation.Such process contributed to the late-stage crystallization of accessory phases only found in these highly evolved facies.Among the latter,two populations of garnet were identified in MGI(Macao GroupⅠ)highly fractionated granitic rocks:small grossular-poor euhedral grains and large grossular-rich skeletal garnet grains with quartz inclusions.The first group was mainly formed through precipitation from highly evolved Mn-rich slightly peraluminous melts under low-pressure and relatively low temperature(~700℃)conditions.Assimilation of upper crust metasedimentary materials may have contributed as a source of Mn and Al to the formation of garnet.The second group has a metasomatic origin related to the interaction of magmatic fluids with previously crystallized mineral phases and,possibly,with assimilated metasedimentary enclaves or surrounding metasedimentary strata.The highly fractionated granitic rocks in Macao represent the first stage in the development of granite-related W-(Mo)-Sn-Nb-Ta mineralization associated with coeval more evolved lithotypes in SE China.
