Zircon U-Pb ages and Lu-Hf isotopic compositions of the Nb-Ta-Zrbearing syenitic dikes in the Emeishan large igneous province

Both Nb-Ta-Zr-bearing and Nb-Ta-Zr-barren syenitic dikes of the Luku and Baicao ore districts in the Panxi region( SW China) are spatially associated with basalts,gabbroic and felsic( granitic and syenitic) intrusions of the ~ 260Ma Emeishan large igneous province( ELIP). The syenitic plutons,barren and mineralized dikes at Luku were dated to be 255. 6 ± 2. 0Ma,255. 6 ± 1. 5Ma and 256. 7 ± 4. 4Ma,respectively. The syenitic pluton and mineralized dikes at Baicao were dated to be 257. 9 ± 2. 3Ma and 257. 8 ± 1. 3Ma,respectively. These age data indicated that the Nb-Ta-Zr mineralization hosted in the syenitic dikes are part of the ELIP. Mineralized dikes at Luku and Baicao have zircon e Hf( t) values ranging mostly from + 2 to + 6 and- 0. 2 ~ + 7. 7, comparable to those of the spatially closely associated syenitic plutons( + 1. 0 ~ + 6. 6 in Luku and + 2. 1 ~ + 6. 2 in Baicao), implying that the mineralized dikes may have evolved from the syenitic magma. This is important for regional exploration of Nb-Ta-Zr deposits. We consider that the syenitic plutons and dikes may be the products of partial melting of underplated mafic cumulates.