Characteristics and geological significance of geochronologic results from the Bayan Obo deposit, Inner Mongolia

Abstract

Objective The Bayan Obo deposit in Inner Mongolia is a rare superlarge REE-Nb-Fe polymetallic deposit worldwide. There are still controversies on the timing of REE mineralization in the deposit due to the complex geological evolution in the region. Methods Based on previous isotopic dating results, in combination with geological characteristics of the deposit, this paper re-evaluates potentially multiple episodes of REE mineralization. Results The Bayan Obo deposit has experienced the Precambrian tectonic evolution of the North China Craton between 2.5-1.8 Ga. The major REE mineralization was formed in the Bayan Obo rift at ~1.3 Ga during the final stage of the breakup of the Columbia supercontinent, coeval with carbonate dike in the region. Hydrothermal metasomatism or overprints occurred throughout the Bayan Obo area, which is related to the late Paleo-Asian Ocean subduction-collision orogeny in the northern margin of the North China Craton, producing the late REE veins and recrystallization of original REE minerals. Such a hydrothermal modification event has variably disturbed the isotopic system of the H8 ore-bearing dolomite, resulting in multiple periods of isotopic ages (1.0-0.2 Ga) with peaks at 440 Ma and 270 Ma. Conclusion In summary, the Bayan Obo deposit primarily formed from the ~1.3 Ga rift metallogenic event, superposed by Caledonian and Hercynian tectonothermal events.

Keywords

• bayan obo deposit
• isotopic age
• rare earth metallogenic epoch
• north china craton