EARLY MESOZOIC VOLCANIC ACTIVITY IN THE ORKHON DEPRESSION SYSTEM (NORTHERN MONGOLIA): INSIGHTS INTO CORRELATION WITH THE ERDENET Cu–Mo DEPOSIT

In the Northern Mongolia major Early Mesozoic magmatic events are the formation of large Cu–Mo Erdenet deposits and volcanic activity in the Orkhon depression system. Even though they are spatially related, their temporal and genetic comparison have not been determined yet. This paper focuses on geochronological and geochemical studies of volcanic rocks of the Mogod Formation from three depressions (Mogod, the Khushig-Und-Er and Bugat) and data correlation with igneous rocks from Cu–Mo Erdenet deposit. The Mogod Formation mainly consists of basaltic trachyandesites and trachyandesites with subordinate trachytes. The age of volcanism was estimated using the U–Pb_CA ID TIMS method on zircon from trachytes of the Bugat depression (236±1 Ma) and the ⁴⁰Ar–³⁹Ar method on amphibole from basaltic trachyandesites of the Khushig-Und-Er (230±6 Ma) and the Mogod (233±4 Ma) depressions. The obtained age interval coincides with the final stage of ore-bearing porphyry magmatism of the Erdenet deposit, located on the edge of the Bugat depression. Geochemical comparison of the Mogod Formation and the porphyry complex revealed common signatures from both basic and acid rocks, such as the depletion of HREE, Nb, Ta and Ti, as well as the significant enrichment of Ba, LREE and Sr. The obtained geological, geochronological and geochemical data allow us to conclude that the Cu–Mo magmatism responsible for ore formation and the widespread volcanism of the Mogod Formation are the result of common magmatic event.

Cu–Mo porphyry deposits, Central Asian fold belt, CA ID TIMS geochronology, ⁴⁰Ar–³⁹Ar geochronology