Located in the eastern part of the Baiyinwula-Dong Ujimqin Banner alkali granite belt on the southern edge of the Siberian plate, the Qagan Obo quartz diorite stock has an intimate temporal and spatial relationship with the Qagan Obo Fe-Zn deposit. SHRIMP magmatic zircon U-Pb dating of quartz diorite stock yields an age of 237±6 Ma (1σ), with the MSWD value being 0.63. Based on field geological investigation and laboratory data in combination with the result of zircon dating, it is suggested that the quartz diorite and its associated Fe-Zn ore bodies were formed in Indosinian period. Both of them were formed in a post-collision extensional tectonic setting within the Xing'anling-Mongolia orogenic belt.