Abstract: Abstract：Quartz-diorite intrusion is spatially and temporally associated with the REE-Sc mineralization in the Yijiang REE-Sc deposit, Rucheng County, Hunan Province. To constrain the age of the quartz-dioritic pluton related to REE-Sc mineralization, the authors conducted U-Pb analysis of zircon. Hafnium isotope data were also acquired through laser-ablation multi-collector ICPMS analysis of the zircon, with the aim of gaining an insight into the age and nature of the source region of the pluton. The yielded age (424±3 Ma) confirms that this quartz-diorite intrusion belongs to the Caledonian period. Hafnium analysis shows that the Caledonian quartz-diorite has negative and variable εHf values (-1.9 to -7.6) and Palaeo-Mesoproterozoic (1.5 to1.9 Ga) depleted-mantle model ages, which is interpreted to reflect derivation from an isotopically heterogeneous mantle-crust mixed source. The source region of these magmas might have been correlated at least with Palaeo-Mesoproterozoic materials of the South China Block, which has been held to underlie Hunan Province; however, further work is necessary to demonstrate this suggestion.