Abstract: The Gejigeyin Ul volcanic edifice consists dominantly of agglomerate, breccia agglomerate lava and alkali olivine basalt. The basalt contains lherzolite xenoliths and belongs to the intracontinental alkali basalt series. It occurs as a horizontal bed overlying the Miocene Tunggalag Formation, so is the basal bed of the Abag basalt. The basalt has a whole rock K Ar dilution age of 12.99 Ma. An integrated analysis indicates that the early eruption of the Abag basalt continued till the Pliocene.