Geochemical and Sr-Nd-Hf isotopic compositions of granodiorite from the Wushan copper deposit,Jiangxi Province and their implications for petrogenesis

Wushan deposit is a large copper deposit located in the Jiu-Rui mineralization concentrated area in the Middle and Lower Yangtze Reaches,south China.In this study,we report mineral chemistry,major,trace elements,and Sr-Nd-Hf isotopic compositions of the ore-related granodiorite at Wushan.The biotites are Mg-riched and belong to phlogopite,which Fe~(3 +)/Fe~(2 +) ratios indicating a high oxygen fugacity (f_(02)) for the magma.The amphiboles show high Mg/(Mg + Fe) and low Si,and belong to actinolite and magnesiohornblende.The hornblende geobarometer indicates an ultra-shallow emplacement of the granodiorite.The rocks show geochemical characteristics of adakitic affinity with high SiO_2 (64.9% ～ 68.62%,average 66.52%) and Al_2O_3 (14.0% ～ 15.3%, average 14.8%),and high Mg~#(0.53 ～0.71).The trace elements are characterized by enrichment of K,Rb,Ba and Th,depletion of Nb,Ta,and Ti,high Sr,low Y,Sr/Y ratios of 35.0 ～68.2,and higher contents of V,Cr,Co and Ni.The REE characteristics are LREE enriched with (La/Yb) _N ratio of 27.8 ～64.5,and lack any significant negative Eu anomaly.The initial ~(87) Sr/~(86) Sr ratios are low from 0.7067 to 0.7075,and the e_(Nd) (t) values are high at-4.08 to-4.44.The zircon Hf isotope analysis shows e_(Hf) (t) values of-2.1 to-7.0.These data suggested that the Wushan granodiorite was produced by strong crust-mantle interaction with very high proportion of mantle component,and was most likely derived from partial melting of delaminated lower crust at around 145Ma.During its ascent,the magma may possibly have reacted with surrounding mantle peridotites.