Petrogenesis and mineralization of REE-rich granites in Qingxi and Guanxi, Nanling region, South China

Abstract

Mesozoic granites in the Nanling region, South China, are important primary rocks for ion-adsorption rare earth element (REE) deposits. Moreover, metallic deposits of W, Sn, Nb and Ta also develop in these granites, most of which formed in the Late Jurassic. The Qingxi and Guanxi granites in the Nanling region contain abundant REE minerals and have zircon U-Pb ages of 223.0±0.7Ma and 198.8±1.4Ma, respectively. They are of metaluminous to slightly peraluminous in character having a high K calc-alkaline composition, and have high K2O+Na2O and FeOT+MgO contents and a Ga/Al ratio similar to A-type granites. These granites plot into the post-collision field, similar to the A2-type granites. The Qingxi and Guanxi granites indicate a crust-dominant origin by having high levels of Rb and Th relative to Nb and Ta normalized to ocean-ridge granites. They are characterized by LREE enrichment and the majority of REE accumulating in the primary REE minerals include REE-phosphates and fluorocarbonates. The Guanxi rocks have a stronger negative Eu anomaly, but lower REE composition than the Qingxi granites, implying that the basement may have played an important role in the REE mineralization rather than fractional crystallization. This further implies that the basement in South China may have been subjected to different evolutionary geodynamics, resulting in different multi-metallic mineralization of W-Sn-Nb-Ta-REE hosted by large scale Mesozoic granites.