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Keywords:

  • Bayan-Obo;
  • carbonatites;
  • iron-oxide Cu-Au;
  • ore genesis;
  • rare earths

Abstract

The Bayan Obo Fe-REE-Nb deposit is the world’s largest rare earth element (REE) resource and its genesis has been the subject of much debate for many years. The most popular are the carbonatite-related and hydrothermal Fe oxide-Cu-Au-(REE-U) genetic models. Comparisons of geologic setting, lithology, mineral assemblages, metal associations, geochemistry (particularly REE and light REE/heavy REE ratios), fluid chemistry and isotopics indicate that the Bayan Obo deposit shares features of both types, which are classified differently; that is, the carbonatites model is host-rock based, while the Fe oxide-Cu-Au-(REE-U) model is essentially mineral assemblage and metal association based. A speculative classification scheme is tentatively put forward to link the two models, but many questions remain for further studies.