The Beiya porphyry-skarn Au deposit is one of the largest gold deposits in China,temporally and spatially associated with Eocene intrusions in a post-collisional setting in western Yunnan,China.In this study,we report new whole-rock geochemistry,Sr-Nd isotope,zircon U-Pb geochronology and in situ zircon Hf-O isotopes of quartz-monzonite and biotite-monzonite porphyries from the Beiya deposit.The porphyry-skarn mineralization at the Beiya deposit is mainly associated with the quartz monzonite porphyry(35.8±0.6 Ma),while the biotite-monzonite porphyry(34.3±0.5 Ma)represents a post-mineralization intrusion crosscutting the main orebodies and the quartz-monzonite porphyry.Both intrusions have high-K and adakitic composition and are characterized by high Sr/Y ratios,high SiO2 and Al2O3 concentrations(SiO2=69.80-73.86 wt％;Al2O3=14.11-15.19 wt％),and low MgO,Cr,and Ni concentrations(MgO=0.2-1.0 wt％;Cr=1.76-11.13 ppm;Ni=2.52-11.72 ppm).Their Sr-Nd isotope compositions(87Sr/86Sr=0.7066-0.7077;eNd(t)=-5.3 to-1.5)are consistent with the lower crustal-derived amphibolite xenoliths(87Sr/86Sr=0.7060-0.7100;εNd(t)=-10.0 to 0.0),indicating that they might be derived from a thickened juvenile lower crust beneath the Yangtze Craton.The biotite-monzonite porphyry has lower zircon δ18O values of+5.3‰ to+6.8‰ and higher εH f(t)values of-2.3 to+5.5 than those of the quartz-monzonite porphyry with δ18O values of+7.1‰ to+8.2‰ and εHf(t)values of-3.8 to+1.5,implying that they were derived from different parts of the lower crust.High Ba/La and Pb/Ce ratios suggest that the quartz-monzonite porphyry is derived from a volatiles-rich reservoir.Relatively higher La/Yb,Sm/Yb and Dy/Yb ratios of the biotite-monzonite porphyry indicate residual garnet in the source,indicating a deeper source than that of the quartz-monzonite porphyry.The hydrous components should be represented by the amphibole-rich lithologies,which has relatively shallower depth than that of the garnet-bearing mafic thickened lower crust.Our data suggest that the mineralized quartz-monzonite porphyry at the Beiya deposit is derived from partial melting of amphibole-rich lithologies in the upper part of the thickened juvenile lower crust beneath the Yangtze Craton,while the post-mineralization biotite-monzonite porphyry is derived from the basal,and volatiles-poor,part of the juvenile lower crust.

WANG Zixuan;ZHENG Yuanchuan;XU Bo;HOU Zengqian;ZHANG Aiping;SHEN Yang;MA Rui;WU Changda;XU Peiyan

State Key Laboratory of Geological Processes and Mineral Resources and School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China;School of Gemmology,China University of Geosciences,Beijing 100083,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;College of Resource Environment and Earth Sciences,Yunnan University,Kunming 650091,China

地质学报（英文版）

[1]WANG Zixuan;ZHENG Yuanchuan;XU Bo;HOU Zengqian;ZHANG Aiping;SHEN Yang;MA Rui;WU Changda;XU Peiyan-.Hydrous Juvenile Lower Crust at the Western Yangtze Craton Margin as the Main Source of the Beiya Porphyry-skarn Au Deposit)[J].地质学报（英文版）,2022(03):972-992

Beiya,Porphyry,monzonite,of+5,to+6,to+5,of+7,to+8,to+1

Hydrous,Juvenile,Lower,Crust,Yangtze,Craton,Margin,Main,Source,skarn,Au,Deposit,porphyry,largest,gold,deposits,China,temporally,spatially,associated,Eocene,intrusions,post,collisional,setting,western,Yunnan,In,this,study,report,new,whole,rock,geochemistry,zircon,Pb,geochronology,situ,Hf,isotopes,quartz,biotite,porphyries,from,mineralization,mainly,while,represents,crosscutting,orebodies,Both,have,adakitic,are,characterized,by,ratios,SiO2,Al2O3,concentrations,wt,MgO,ppm,Their,compositions,87Sr,86Sr,eNd,consistent,crustal,derived,amphibolite,xenoliths,indicating,that,they,might,thickened,juvenile,beneath,has,18O,values,higher,than,those,implying,were,different,parts,High,Ba,La,Ce,suggest,volatiles,rich,reservoir,Relatively,Yb,Sm,Dy,indicate,residual,garnet,source,deeper,hydrous,components,should,represented,amphibole,lithologies,which,relatively,shallower,depth,bearing,mafic,Our,data,mineralized,partial,melting,upper,basal,poor

0.384018