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1.ObjectiveThe Sepon Au-Cu deposit (Fig.1) is the largest polymetal deposit ever discovered in Laos, of which the resources of gold and copper is 102 t (Au: 1.6 g/t) and 1.96×106 t (TCu:2％) (Zhu HP et al., 2013) respectively.Sepon Au-Cu deposit is one of the most important super large deposits of the Truong Son Fold Belt.The Truong Son Fold Belt, located at the northeaste margin of the Indo-China terrane, is considered to be tectonically linked to the subduction of the Paleotethys Ocean and subsequent collision.The granodiorite porphyry samples from the Sepon deposit belong to Ⅰ-type calc-alkaline series and tectonic settings are continental arc environment (Cromie PW, 2010).LA-ICP MS zircon U-Pb dating results show that granodiorite porphyry samples from the Sepon deposit have ages of 302.1 ± 2.9 Ma.The in situ zircon εHf(t) values range from +4.32 to +9.64, and TDM2(Hf) has an average age of 914 Ma (Wang XY et al., 2018).In this study, the authors present new in situ zircon oxygen isotopic data to identify the source of the magma.