The Metallogenic Age of the Ovor Bayan Molybdenum Deposit in Southeastern Mongolia: Constraints from SHRIMP Zircon U-Pb and Molybdenite Re-Os Geochronology

The Ovor Bayan molybdenum deposit in Mongolia is located within the western segment of the Nukhetdavaa–Erlianhot–Dongwuzhumuqin–Aershan Mo–Pb–Zn–W–Cu–Sn–Cr–Fe metallogenic belt in the Mongolia–Daxing’anling Metallogenic Province. This metallogenic belt lies in the Sino-Mongolian border region, where over ten large-sized deposits have been discovered on the Chinese side in the past two decades. However, the discovered deposits in Mongolia side are relatively small in scale, primarily medium to small-sized, with no large deposits identified to date. Therefore, strengthening research on typical deposits and summarizing metallogenic patterns in this area are the optimal approaches to achieving breakthroughs in prospecting. This study focuses on the Ovor Bayan deposit, a newly identified deposit of molybdenum mineralization within the western segment of the belt. We examine the deposit’s zircon U-Pb geochronology and Re-Os isotopic data. The SHRIMP zircon U–Pb dating of the ore-bearing granite indicates crystallization ages of 183.3 ± 1.9 Ma, which closely align with the mean Re-Os age of 183.1 ± 2.3 MaMa for the Ovor Bayan molybdenum deposit, suggesting an Early Jurassic magmatic event marked by Mo-dominated mineralization coinciding with the extensional tectonic setting following the southeastward subduction-collision of the Mongol–Okhotsk Plate. Regional data indicate that the Nukhetdavaa–Erlian–Dongwuqi–Aershan metallogenic belt experienced concentrated Mo-W mineralization between 240 and 131 Ma. The formation of Mo-dominated deposits, such as Ovor Bayan and Aryn nuur in the western segment of the belt, is at least 50 Ma earlier, which underscores the presence of a significant Mo metallogenic event during this critical post-collision to extensional mineralization period. The molybdenite sample exhibits Re contents ranging from (969.2–1209) × 10−6, suggesting a mantle-derived source for the molybdenum mineralization.