The Yaochang and Sishanling iron deposits are located respectively in southern and northwestern margin of North China block. A systematic study of chemical composition, pyroelectricity and oxygen isotope components of magnetite samples revealed some important information. The magnetite samples are all characterized by high values of Ni and low values of Co, indicating that the mineralization was related to deep materials. They have similar PAAS-normalized REY distribution patterns and are enriched in light REE, with moderately positive Eu anomalies and lightly negative Ce anomalies; nevertheless, the magnetite in the Sishanling iron deposit has a more obvious Eu positive anomaly. The average δ¹⁸O values and thermoelectric coefficients of magnetites from these two deposits are 7.1‰ and 2.3‰, -59.05 μV/℃ and -57.18 μV/℃ respectively. Based on chemical analyses and other typomorphic peculiarities of magnetite, the authors hold that the magnetite is of the volcanic-sedimentary metamorphic origin, but magnetite samples from the Sishanling iron deposit have relatively low isomorphic extent and a more homogeneous structure. A systematic comparison with the main terrains in North China block in such aspects as oxygen isotope and REE compositions indicates that the oxygen isotope components of rich and poor ores show regularity related to different mechanisms of mineralization and enrichment. The values of δ¹⁸O in poor ores are related to the metamorphic grade of different terrains, consistent with oxygen isotope fractionation. Systematic investigation of the Ce/Ce^* and Eu/Eu^* ratios of BIFs from Archean-Peleoproterozoic strata in North China block indicates relatively low redox levels in the seawater, but with the growth of North China block, the oxygen-free environment exerted less effect on the formation of BIFs, which was unfavorable for the generation of banded iron formation.