The Huangjinshan pyroxene diorite intruded Paleoproterozoic Hutuo Group, and was cut and penetrated by late Paleoproterozoic dolerite in Wutai Mountains area. SHRIMP zircon dating of pyroxene diorite yielded a ²⁰⁷Pb/²⁰⁶Pb age of 1 755±12 Ma, which is similar to ages of the widely distributed Paleoproterozoic mafic dyke swarms in the North China Craton. The pyroxene diorite sample contains high TiO₂, Fe₂O₃, P₂O₅, K₂O and Na₂O, and low MgO (Mg^#, 36～39). The sample has high concentration of REE (365.75×10^-6～411.97×10^-6), with strong LREE fractionation and slight fractionation of HREE, and slightly negative Eu anomaly. The rock samples are enriched in Rb, Ba, Sr, Zr and Hf, and are depleted in Cr and Ni. The variation of (⁸⁷Sr/⁸⁶Sr)_i and (¹⁴³Nd/¹⁴⁴Nd)_i ratios is small, and εNd(t=1.76 Ga)values vary from -6.08 to -4.81. Based on a comprehensive analysis of all evidence, the authors hold that Huangjinshan pyroxene diorite was partially melted from enriched upper lithosphere mantle related to the mantle plume and was fractionally crystallized with the same magmatic source of mafic dyke swarms widely distributed in North China Craton, thus representing a different stage of the same magmatic cycle. Zircons in pyroxene diorite samples show the same characteristics as basic-intermediate rocks, but their Th/U ratios are very low, similar to features of the metamorphic zircon. Generally speaking, Th/U ratios are high in pyroxene diorite whereas the partition coefficients of Th and U are very low in plagioclase, clinopyroxene and hornblende. It is thus inferred that the Th/U ratios in zircon are independent of the source magma and major diagenetic minerals, and are probably related to crystallization of Th-rich accessory minerals. The zircons with very low Th/U ratios in pyroxene diorite indicate that we should be very careful in explanation of the genesis of zircon by Th/U ratios.