Detailed mapping of bedrock in the northern Wellesley basin adjacent to the Donjek River revealed a coherent sequence of cumulus-textured gabbros, sheeted dykes, and a large massif of spinel harzburgite. The coarse-textured harzburgite tectonite covers an area of ~75 km2, and is generally well preserved, making it one of the largest and most exceptional mantle tectonite bodies yet recognized in Yukon. Together with regional aeromagnetic data the new fi eld observations are interpreted as part of a large ophiolite complex with a strike length extending ~100 km throughout the Wellesley basin. No age data are available, but correlation with identical ultramafi c bodies to the northwest in Alaska suggests that the ophiolite in Wellesley basin may represent a klippe of Slide Mountain Terrane overlying rocks of the Yukon-Tanana Terrane.
