• The Journal of the Petrological Society of Korea
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• v.11 no.2
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• pp.90-102
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• 2002

The studied Fe-REE ore consists of magnetite, ankerite, siderite, magnesite and strontianite as the major constituent, and monazite, columbite, fergusonite, apatite, aegirine-augite, Na-amphibole, pyrite, chalcopyrite, sphalerite, molybdenite and barite as accessaries. Wall rock of ore deposits is replaced to fenite due to Na-metasomatism and mainly consists of sugary albite and Na-amphibole. Monazite $Ce_{0.49}La_{0.31}Pr_{0.14}Nd_{0.03}Gd_{0.03})PO_4$ is the main mineral for REE deposit and shows myrmekitic intergrowth with strontianite $Ca_{0.02-0.16}Sr_{0.84-0.98}CO_3$ and is corroded by carbonate minerals. Mineral forming sequence can be divided into early and late periods by the development of microfractures. The early period minerals such as magnetite, ankerite, magnesite, monazite and apatite show well developed networks of microfractures due to cataclastic deformation caused by enriched $CO_2$ gas in melts during emplacement. The late minerals of columbite, fergusonite, siderite molybdenite, chalcopyrite and sphalerite formed after the brecciation event and have little micro-fractures. Ankerite, magnesite, monazite, strontianite, barite and pyrite seem to be formed continuously from the ealy to the late period since they show textures both with well developed fractures and also with little fractures. Mineral chemistry, mineral assemblages such as various carbonate minerals, magnetite, REE minerals of monazite and fergusonite, Sr mineral of strontianite, and Nb minerals of columbite, myrmekitic texture of monazite and ankerite, and well developed fenite along ore deposits observed from this studied area strongly indicate that this Hongcheon Fe-REE ore deposits are formed from carbonatitic melt and its rock type is late differentiated Fe-carbonatite or ankerite-carbonatite.