Genesis of Late Cretaceous granite and its related Nb–Ta–W mineralization in Shangbao, Nanling Range: Insights from geochemistry of whole-rock and Nb–Ta minerals

Abstract

Abstract The Shangbao mining district, located in Nanling Range, South China, includes a series of middle-large scale granite-related W–Sn–Nb–Ta deposits. The genesis for W-Sn-Nb–Ta mineralization in this region is in fact ambiguous. In addition, the research of the latest mineralized granites in Nanling Range may be contributed to further understand the mineralization mechanism. In this study, we report the geochronological, geochemical and isotopic compositions of the Shangbao granite, together with the texture and element of Nb–Ta bearing minerals. LA-MC-ICP-MS U–Pb dating of zircon and columbite in granite from Shangbao Nb–Ta deposit yields weighted mean 206Pb/238U age of 87.3\xa0±\xa00.9\xa0Ma and 86.83\xa0±\xa00.8\xa0Ma, respectively, revealing the emplacement of the granites and their mineralization during Late Cretaceous. The major elements of these granites show high contents of K2O\xa0+\xa0Na2O, Fe2O3, SiO2 and F, low contents of P2O5, CaO, TiO2 and MgO, suggesting high-K calc-alkaline series with slightly peraluminous signature. Besides, they exhibit flat REE pattern and high content of Zr\xa0+\xa0Nb\xa0+\xa0Ce\xa0+\xa0Y, revealing the Shangbao granite affinity of highly fractionated A-type granite. Lu–Hf and Sr–Nd isotopes indicate that the Nb–Ta bearing magma was formed by the mixing crust-mantle materials. Combined with the previous studies, emplacement of Shangbao granite is linked to an expansional geodynamic setting, likely caused by the roll-back of the paleo-Pacific plate subduction. The principal economic Nb–Ta oxides of Shangbao granite are columbite group minerals (CGM). Three major groups are identified given textural and chemical characteristics of CGM, i.e., (i) Group I displays systematic core-rim evolution from columbite to tantalite, and eventually to columbite; (ii) Group II shows that the columbite and tantalite have undergone metasomatism through the wolframoixiolite, and numerous REE-mineral were contained; (iii) Group III is anhedral columbite crystallized together with rutile. As revealed from geochemical characteristics of these three groups, the formation of Nb–Ta oxides within Shangbao granite display three generating stages, supporting the magmatic-hydrothermal origin. The high-degree fractional crystallization of Shangbao granitic magma is the main factor leading to the enrichment of Nb to allow saturation of columbite.