Geophysical exploration of the giant Bayan Obo REE–Nb–Fe deposit in Inner Mongolia, China: Progress and challenges

Over the past decade, extensive integrated geophysical exploration has been conducted in the giant Bayan Obo REE–Nb–Fe deposit in Inner Mongolia, China. This work primarily includes rock physical property testing, reflection seismic exploration, ambient noise tomography, various electromagnetic soundings, and gravity-magnetic surveys at different scales. These efforts have provided substantial evidence for elucidating the subsurface structure of the Bayan Obo deposit, delineating potential mineralization zones, and understanding the genesis of the deposit. • Recent progress in the geophysical exploration of the Bayan Obo deposit. • Challenges of geophysical exploration in the Bayan Obo deposit. • Future directions for geophysical exploration of the Bayan Obo deposit. The Bayan Obo giant rare earth element (REE)–niobium (Nb)–iron (Fe) deposit, located in Inner Mongolia, is recognized globally as a significant comprehensive deposit and serves as a crucial rare resource base in China. Despite nearly seven decades of mining operations, numerous scientific questions pertaining to the Bayan Obo deposit remain unanswered, underscoring an urgent necessity to assess the quantities of rare resources and to explore alternative sources of iron ore. Addressing these issues is intrinsically connected to geophysical exploration efforts. In the past decade, extensive geophysical investigations have been conducted in the Bayan Obo mining region, resulting in substantial evidence that enhances the understanding of the deposit’s characteristics. However, practical exploration has demonstrated that the complex nature of the exploration targets, coupled with the environmental conditions in the Bayan Obo mining area, poses significant challenges to various geophysical exploration initiatives. This paper primarily reviews the advancements and achievements in geophysical exploration within the Bayan Obo mining area over the past ten years, while also examining the key challenges faced during these exploration efforts. Finally, several critical directions for future geophysical exploration activities are proposed.