Magmatic and hydrothermal controls on diverse Nb mineralization associated with carbonatite-alkaline complexes in the southern Qinling orogenic belt, Central China

Abstract

Although carbonatite-alkaline complexes are the primary source of the world's Niobium (Nb) supply, the mineralization style is largely variable in these complexes and the processes behind are still poorly understood. Exemplifying with the ~430 Ma Miaoya and Shaxiongdong carbonatite-syenite complexes in the southern Qinling orogenic belt, central China, our new observations show that Nb mineralization in these two deposits is persuasively throughout the entire complexes on both syenite and carbonatite in disseminated form. Both the magmatic and hydrothermal processes have attributed to Nb mineralization in both deposits, despite different in the mineralization style. The Nb-bearing minerals in the mineralized Miaoya syenites include magmatic U-poor pyrochlore, rutile, and ilmenite with minor amounts of columbite, and hydrothermal columbite and rutile, whereas those in the mineralized carbonatites are mainly magmatic U-poor pyrochlore, uranpyrochlore, U-rich betafite, and rutile with minor amounts columbite, and hydrothermal columbite and rutile. On the other hand, the Nb-bearing minerals in the mineralized Shaxiongdong syenites include magmatic U-poor pyrochlore, titanite, rutile, and ilmenite, and hydrothermal fersmite, rutile, and ilmenite, whereas those in the mineralized carbonatites are mainly magmatic U-poor pyrochlore without any hydrothermal Nb-bearing minerals. Field observations, whole-rock chemical and Sr-Nd isotopic compositions strongly constrained that assimilation of U-rich rocks (e.g., the hosting Yaolinghe and Meiziya Groups) and magma differentiation are responsible for diverse magmatic Nb mineralization in the two deposits. On the other hand, the diverse This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.