Late Mesozoic post-orogenic granitoids and its metallogenic implications: Constraints from Nantai porphyry Mo deposit, Northern Qinling, China

Abstract Late Mesozoic Nantai porphyry Mo deposit is located in the Northern Qinling terrane, eastern China. The intrusions at Nantai include lamprophyre, quartz porphyry, and granite porphyry. Among them, molybdenum mineralization is associated with quartz porphyry and granite porphyry. The ore-bearing porphyries and ore-barren lamprophyres emplaced at ca. 155–146 Ma and ca. 156–146 Ma, respectively. The calculated zircon ΔFMQ values for Nantai felsic and mafic intrusions are –5.0 to +9.1 (an average of + 2.2) and –6.7 to +5.0 (an average of +1.2), which are similar to those of contemporaneous giant Mo deposits in the south margin of the North China Block. The quartz porphyry and granite porphyry are characterized by relatively high SiO2 (73.39–75.49%), K2O (4.24–9.61%), and Rb (291–552 ppm) contents, but low total Fe2O3 (0.13–0.83 wt%), MgO (0.1–0.3 wt%), P2O5 (0.01–0.04 wt%), Sr (22.4–141.0 ppm) and Ba (79.8–1757 ppm) concentrations. These granitic samples have TDMC ages of 2204–1592 Ma, corresponding to negative eHf(t) values of –15.8 to –6.2. Geochemical and zircon Lu-Hf signatures as well as lead isotopic analyses for Nantai granitoids suggest that they belong to the high-fractionated I-type granites and were derived from partial melting of lower continental crust with coeval mantle-derived magma contribution. The lamprophyres show low SiO2 (47.59–49.08%) and Rb (96–120 ppm) contents, whereas they have high Ba (1598–2236 ppm), and Sr (771–990 ppm) concentrations, as well as a lack of negative Eu anomalies. The concentrated eHf(t) values (–0.6 to + 3.3), high (Hf/Sm)PMN and La/Sm ratios, as well as Pb isotopic features, indicate that they were derived from an enriched lithospheric mantle that had been metasomatized by subducted components with some crustal material contribution. Combined with our datasets and previous studies, we suggest that the Nantai porphyry Mo deposit formed in a post-orogenic setting.