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Geochemical Characteristics and Metallogenic Mechanism of the Porphyry Cu-Mo Deposits in the Yulong Ore Belt, Eastern Tibet: A Case Study of the Yulong and Duoxiasongduo Porphyries

WU Weizhong;XIA Bin;ZHANG Yuquan;DONG Binghua;XIA Zhongxi;Guangzhou Institute of Geochemistry,Chinese Academy of Sciences;University of Chinese Academy of Sciences;School of Marine Sciences, Sun Yat-Sen University;  
The Yulong porphyry copper belt,located in the middle of the Sanjiang tectonic zone of the eastern Tethys-Himalayan tectonic domain,is an ideal area to study the petrogenesis and mineralization of the Himalayan alkali-rich porphyries.This paper takes the Yulong and Duoxiasongduo as the study areas,presenting detailed dating on the porphyries and associated Cu-Mo mineralization as well as their geological and geochemical characteristics.Combined with Sr-Nd-Pb and S-H-O isotopic analysis,we discussed the difference of ore-bearing magma source,tectonic controls on mineralization,and dynamic mechanism between the Yulong and Gangdese ore-bearing porphyries.The results show that the ore-bearing porphyries which are of potassic alkali-granite and characterized by rich alkali,high potassium and high aluminum.In the Yulong area,the rocks mainly consist of quartz monzonite porphyry in the early stage,the granodiorite and quartz monzonite porphyry in the late stage.While in the Duoxiasongduo area,the rocks mainly consist of monzogranite and granodiorite porphyries,and less K-feldspar granite porphyry.Both of them are rich in light rare earth elements(LREE),large ion lithophile elements(LILE,e.g.,Rb,Th,U and Pb),and depleted relatively in HFSE(e.g.,Nb,Ta and Yb) without significant Eu and Ce negative anomalies.The slightly higher than modern primitive mantle initial~(87)Sr/~(86)Sr ratios,lower ε_(Nd)(t) values,relatively uniform~(206)Pb/~(204)Pb ratios of the porphyries in the studying area,indicate that they were probably generated from partial melting of the garnet amphibolite and/or amphibolite eclogite,followed by a low degree of crystal fractionation and crustal contamination during the magma ascending and intrusion.We suggest that the formation of the Yulong large porphyry copper deposit belt is related to the Toba-Mangkang sinistral strike-slip fault(TBF) in the Red River-Ailaoshan fracture system caused by the India-Asia continental collision in middle Eocene of early Tertiary(37~38 Ma).
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