Research on the enrichment and mineralization of Nb–Ta elements in alkaline rhyolite of the Early Cretaceous Toudaoqiao deposit, the Great Xing'an Range

The Toudaoqiao niobium–tantalum (Nb–Ta) deposit is the largest magmatic rock-type rare metal deposit discovered in the Great Xing'an Range. The ore body is hosted in alkaline rhyolite, and Nb–Ta primarily hosted by columbite, magnetite-(Nb), and ilmenite-(Nb). In this study, we present U–Pb zircon ages, Hf isotope date, and whole-rock geochemistry to elucidate Toudaoqiao alkaline rhyolite evolution. Magmatic zircon ages suggest the mineralization occurred in the Early Cretaceous. The positive ε Hf (t) (zircon) values range from 5.50 to 9.61 with T DM2 of 836–574 Ma, as well as the geochemical characteristics of K 2 O/Na 2 O > 1 and Mg # <<40, indicate that the magma originated from the partial melting of Neoproterozoic–Paleozoic newly accreted potassium-rich intermediate-mafic lower crust. During extension of the Great Xing'an Range in the Early Cretaceous, roll-back of the subducting Paleo-Pacific plate triggered upwelling of asthenosphere mantle material to heat and partially melt the lower crust. The parental magma became highly fractionated by the action of F and other volatiles, resulting in enrichment of Nb–Ta in the residual melt, culminating in precipitation of Nb–Ta minerals. A magma source characterized by significant rare element enrichment is the key factor for Nb–Ta mineralization of the Toudaoqiao.