We report here the results of U-Pb zircon analyses for samples collected during regional mapping of the northern Whitehorse trough. Three samples of the Nordenskiold formation, a crystal-rich volcaniclastic unit that occurs at several stratigraphic horizons in the Laberge Group, yielded concordant U-Pb zircon ages of 188.1 ± 0.4 Ma, 187.2 ± 0.4 Ma and 186.5 ± 0.3 Ma, respectively. These results clearly indicate multiple eruptive events rather than recycling of the volcaniclastic material. Zircons from a thin layer of ash tuff in the Tanglefoot formation (Laberge Group) yielded a concordant U-Pb age of 187.1 ± 0.7 Ma, confirming correlation with the Nordenskiold formation. A sample of porphyritic granite from the only pluton intruding the northern Whitehorse trough, near Carmacks, yielded a concordant U-Pb zircon age of 112.8 ± 0.2 Ma, whereas a precise age could not be resolved from zircons extracted from a porphyry dyke intruding the Tantalus Formation in the southern Whitehorse trough.
