Paleozoic carbonatites controlled rare-earth-elements mineralization at Bayan Obo

Area of Science:

• Geology
• Economic Geology
• Geochemistry

Background:

• The increasing demand for rare-earth elements (REE) necessitates understanding the formation of major deposits like Bayan Obo.
• Despite extensive research, the precise origin and mineralization processes of the Bayan Obo deposit remain subjects of debate.

Purpose of the Study:

• To elucidate the multi-stage emplacement and mineralization history of the Bayan Obo carbonatites.
• To identify the key factors controlling the formation of this giant REE deposit.

Main Methods:

• Geological mapping and petrographic analysis of carbonatite occurrences.
• Geochronological dating to establish emplacement timelines (1320 Ma and 430 Ma).
• Fluid inclusion studies and geochemical analyses to characterize mineralization fluids and processes.

Main Results:

• Two distinct carbonatite emplacement events were identified at 1320 Ma and 430 Ma.
• The earlier 1320 Ma carbonatite, though effusive, provided a deformed substrate for later alteration.
• The 430 Ma carbonatites exsolved significant volumes of REE-rich fluids, driving metasomatic mineralization along structures and bedding planes, contributing over 70% of the REE.

Conclusions:

• Multistage carbonatite emplacement in a single locality is a critical factor for forming giant REE deposits.
• The interplay between early carbonatite emplacement, subsequent deformation, and later fluid exsolution explains the formation and scarcity of world-class REE deposits like Bayan Obo.