The Guodian Fe deposit is representative of the newly discovered Qihe–Yucheng high-grade Fe skarn ore cluster, Luxi Block, eastern North China Craton (NCC). The age of the Pandian Fe deposit remains elusive, which hinders the understanding of its metallogenic tectonic background. Phlogopites are recognized in syn-ore stages, and they are closely associated with magnetite in the Guodian skarn Fe deposit. Here, we carried out ⁴⁰Ar/³⁹Ar dating of phlogopite, which can place a tight constraint on the timing of Guodian iron mineralization and shed light on the geodynamic framework under which the Guodian Fe deposit formed. Ore-related phlogopite ⁴⁰Ar/³⁹Ar dating yielded ⁴⁰Ar/³⁹Ar plateau ages of 131.6 ± 1.7 Ma at 890–1400 °C, with the corresponding isochron age being 131.1 ± 2.6 Ma. These two ages are consistent within the error, indicating that they can represent the formation age of the Guodian iron deposit. The mineralization age overlaps the zircon U-Pb age of 124.4 Ma for ore-related Pandian pluton. This age consistency confirms that the iron skarn mineralization is temporally and likely genetically related to Pandian diorite. The present results, coupled with existing isotopic age data, indicate the Guodian skarn Fe deposit formed contemporaneously with large-scale skarn iron mineralization over the Luxi Block in the Late Mesozoic. The available data demonstrated that the eastern NCC was “destructed” in the Late Mesozoic, as marked by voluminous igneous rocks, faulted-basin formation, high crustal heat flow, and widespread metamorphic core complexes in the eastern part of the NCC. It is thus suggested that the Guodian Fe skarn deposits, together with other deposits of similar ages in the Luxi Block and even in the eastern NCC, were products of this craton destruction. Lithospheric extension and extensive magmatism related to the craton destruction may have provided sufficient heat energy, fluid, chlorine, and Fe for the formation of the Fe deposit.

The Sanchahe iron-gold deposit in western Shandong province is located in the southeast of the North China Craton. The skarn type of iron-gold deposit (without copper) is located in the contact belt between pyroxene diorites and Ordovician limestone xenoliths. The zircon U-Pb age of pyroxene diorites is 138.4 ± 1.2 Ma belonging to the Early Cretaceous. Pyroxene diorites (Rittmann index σ = 2.2~2.5) belong to the calc-alkaline series and the SiO₂ content is 55~59%. Furthermore, pyroxene diorites are characterized by high Mg and Na contents and high contents of Sc, Cr, Co, and Ni, indicating that it has a geochemical affinity with mantle-derived magma. All of the samples are enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs), with a weak Eu-negative anomaly. They are also enriched in Cs, Ba and Sr and depleted in high field strength elements (HFSEs) (Nb, Ta, Zr), indicating the involvement of some crustal materials. The whole-rock (⁸⁷Sr/⁸⁶Sr)_I values are 0.70824~0.70891, and the ε_Nd(_t) values are from −8.1 to −12.5. Two-stage model ages of T_DM2 are 1591~1928 Ma. The εHf(t) values range from −7.0 to −17.4, and the two-stage model ages of T_DM2 range from 1629 to 2297 Ma, indicating that the magma was derived from Mesoproterozoic to Neoarchean crusts. Combined with Pb isotopic characteristics, pyroxene diorites may be generated by the partial melting of the enriched lithospheric mantle, which had been metasomatized by the ancient lower crust materials of the North China Craton and formed in the strong extensional tectonic setting linked with lithospheric thinning, which may be caused by the rollback of the Pacific plate after subduction.