Genesis of the Paleoproterozoic Heiyuting Fe deposit in the Jiao-Liao-Ji Belt, North China Craton: Constraints from geochronology and geochemistry

• The Heiyuting Fe deposit in the JLJB formed at 1848 ± 5 Ma. • Fe derived from Li’eryu Formation and 2.2–2.1 Ga volcanism • Partial melting promoted migmatization, which subsequently led to iron enrichment. • Regional metamorphism-anatexis activity led to polymetallic mineralization in JLJB. Paleoproterozoic metamorphic rock series is widely distributed and hosts several iron deposits. The Heiyuting iron (Fe) deposit is hosted by typical Paleoproterozoic leptite of the Li’eryu Formation and represents a key example for constraining the mineralization process of Paleoproterozoic iron deposits within the Liaohe Group. This type of deposit has great exploration potential, but the precise timing of iron mineralization, the sources of ore-forming materials, and iron mineralization processes remain unclear. We conducted zircon and monazite U-Pb geochronology together with monazite electron probe microanalysis (EPMA) to constrain iron mineralization. Zircon cores from the migmatitic granite yield an age of 2174 ± 23 Ma, representing protolith formation, whereas the rims yield 1892 ± 14 Ma, consistent with ∼ 1900 Ma granulite-facies metamorphism. Monazite grains associated with magnetite yielded an age of 1848 ± 5 Ma, constraining Fe mineralization and coinciding with regional partial melting (1870–1840 Ma). Monazites observed under back-scattered electron (BSE) imaging show embayed structures and concentric coronas composed of apatite, allanite, and epidote. Based on the major-, trace-, and REE-element compositions of monazite, a metamorphic-hydrothermal origin is suggested. We propose that the apatite-allanite-epidote coronas developed on early-formed monazite through disequilibrium reactions with F-Ca-Fe-Si-Al-rich fluids during the retrograde metamorphic stage. The Li’eryu Formation and the 2.2–2.1 Ga magmatism provided the primary sources of iron. The iron was subsequently concentrated by hydrothermal activity during late metamorphism-anatexis at ∼ 1850 Ma. Our results refine the age, source, and mechanisms of iron mineralization in the Heiyuting Fe deposit, provide geochronological and geochemical constraints for similar deposits, and highlight the role of regional metamorphism-anatexis in polymetallic enrichment.