Fe-REE-Nb-Zr mineralization in Chungju area South Korea represent one of the largest resources of zirconium, niobium, and the heavy rare earth elements (HREE) in South Korea. The deposits are located at the northern edge of the Ogcheon Metamorphic belt (OMB), within the 890 to 860 Ma Gyemyeongsan Formation. The Formation comprises bimodal metavolocanic rocks, dominated felsic metatrachyte, and minor mafic rocks (metabasite). Typical minerlas of mafic metavolcanic rocks are amphibole, plagioclase, chlorite, epidote, and quartz, while felsic metatrachyte contain quartz, K-feldspar, Na-plagioclase, magnetite, muscovite, biotite, and zircon with minor apatite and epidote.
Much of the rare metal mineralization occurs in NW dipping sub-tabular layers, which is embedded concordantly to the foliation of the Gyemyoeongsan Formation, and in which Fe is hosted by primarily magnetite, LREE primarily by allanite-(Ce), Nb primarily by fergusonite-(Y), Zr primarily by zircon, and HREE by fergusonite-(Y) and britholite-(Y).
REE-Nb-Zr mineralization in Chungju area occurred not only by magmatic processes but also by hydrothermal alteration. The peralkaline nature of the rock with a supercritical mixed-volatile fluid containing dominantly H2O, CO2, and CH4, with F, Cl, and assorted other species likely generated high concentration of incompatible, high field strength elements (HFSE) in particular the HREE (HREO/TREO= approximately 30%). Following hydrothermal fluid, caused by metamorphic processes and intrusion of Jurassic granite, played an important role in concentrating the REE and HFSE. Formation of F or possibly Cl aqueous complexes in hydrothermal fluids was a significant process. Those complexes inhance the mobility of the metals and enrichment. HFSE containing minerals are replaced by or replaces mostly Ca alteration minerals, such as calcite, fluorite, andradite, epidote, aegirine, and hornblende. Fe containing mineral is mainly magnetite, replaces all other minerals so that Fe mineralization is the last stage. Granite intrusion related hydrothermal fluid assimilate the Fe from the Gyemyeongsan Formation so that Fe orebody is lense shape between those two rocks. As a result, band formed magnetite - zircon - ferro allanite-(Ce) - britholite(Y) - fergusonite-(Y) - K-feldspar - albite - quartz - biotite - fluorite - hematite by an inferred fluorine-enriched magmatic hydrothermal fluid.