Intrusive style, three-dimensional morphology of carbonatite and REE potential resources in the Bayan Obo giant deposit, Inner Mongolia

Rare earth elements ( REE) have been considered as critical metals in modern society. China is dominated in world REE resources, with most of the REE concentrated in the Bayan Obo deposit. Despite its economic importance, the mechanism of REE mineralization, the spatial distribution of orebodies, and REE potential resources have long been contentious in the Bayan Obo deposit, which hinders further exploration and utilization of REE. Combining geological, geochemical and geophysical investigations, this paper studies the intrusive style, evolution process and three-dimensional morphology of ore-related carbonatite, and the enrichment mechanism of REE. In addition, the REE potential resources are estimated. In the Bayan Obo district, the Paleo-to Mesoproterozoic sedimentary rocks experienced compression. As a result, the primary horizontal rocks have been changed to E-W trending, steeply inclined strata, which provides suitable channels for ore-related carbonatitic melts. The ore-related carbonatite was intruded at ca. 1. 3Ga, and evolved from ferric carbonatite, to magnesian carbonatite, and further to calcic carbonatite. The ore -related carbonatite contains high contents of REE, and thus it can be taken as REE orebody. The deposit experienced hydrothermal overprint in the Paleozoic time, during which the REE were mobilized but the REE resources were not enhanced. According to high magnetic and low resistance anomaly, the shape of the ore -related carbonatite is defined, i. e., the intruding center is located between the East Pit and Main Pit, and the melts moved toward west and east along the tectonic foliation. According to the volume, density and REE contents of ore -related carbonatite, the RE2O3 potential resources is estimated to reach 333 million tons. This number is much larger than previously thought. It is proposed that further exploration is highly required to accurately determine the real REE reserve of the Bayan Obo deposit.