Age and petrogenesis of the Madi intrusion in the Huashi area, northern margin of the North China Craton: Implications for magma evolution and Nb–Ta mineralization

• The Madi rare metal mineralized intrusion consists of the medium–fine grained granite in the lower part and the alkali-feldspar granite in the upper part, and their LA − ICP − MS columbite U − Pb ages are 182.9 ± 1.7 Ma and 184.7 ± 1.3 Ma, respectively. • The mineralogical and geochemical characteristics point to the Madi intrusion being a highly differentiated I-type granite. • The granitic magma underwent fractional crystallization of various minerals such as plagioclase, K-feldspar, biotite, muscovite, and zircon. • During the early stage of magma evolution, the extremely fractional crystallization of granitic magma leads to the enrichment of Nb and Ta. In the final stage of magma evolution, the fluid − melt interaction plays a crucial role in the large-scale crystallization of columbite, and eventually forming Nb − Ta mineralization. Although the mineralization of rare earth elements (REEs) and rare metals is intimately associated with the extreme fractionation of granitic magmas, the metallogenic intrusions of many granite-hosted Nb–Ta deposits have undergone fluid–melt interaction. Nevertheless, the precise mechanisms by which fluid–melt interaction influences mineralization remain poorly understood. The present investigation examines the issues of the fluid–melt interaction in highly fractionated granites with Nb–Ta mineralization, utilizing data from the newfound Huashi deposit in the northern margin of the North China Craton (NNCC). The Huashi Nb–Ta–Rb–Li deposit hosted in the Madi intrusion consists of two lithologies that have evolved continuously, namely medium–fine grained granite (MGG) in the lower section and alkali-feldspar granite (AG) at the top. The ages of the MGG and AG were determined using LA–ICP–MS columbite U–Pb dating, yielding values of 182.9 ± 1.7 Ma and 184.7 ± 1.3 Ma, respectively. The Madi intrusion has high SiO 2 , Al 2 O 3 , and total alkali contents, along with low CaO, MgO, MnO, and TFe 2 O 3 contents and high Al 2 O 3 / (CaO + Na 2 O + K 2 O) (A/CNK) values, classifying it as highly peraluminous granite with a high-K calc-alkaline affinity. Additionally, the intrusion also exhibits enrichment in Rb, U, Th, and Nb alongside significant depletion in Sr, Ba, Ti, Eu, and P, with a noticeable tetrad effect of REEs. The investigation of mica and feldspar minerals in the Madi intrusion using electron probe microanalysis (EPMA) indicates that the mica is mainly zinnwaldite, while the plagioclase belongs to albite. In summary, the Madi intrusion exhibits a highly I-type fractionated granite affinity. The extreme fractionation, intense fluid–melt interaction, and hydrothermal alteration of the intrusion contribute to the formation of the Huashi deposit.