Paleoproterozoic volcanism and plutonism in the Wernecke Mountains, Yukon

The Paleoproterozoic Slab volcanics occur in three localities in the Wernecke Mountains. The largest exposure is at Slab Mountain and consists of a 0.6 x 0.25 km block of thin, steeply dipping mafic to intermediate lava flows. A zone of Wernecke Breccia (1.60 Ga), which crops out along the exposed margin of this volcanic block suggests that the megaclast foundered into the breccia zone from a higher crustal level. The volcanic rocks are typically aphyric. The groundmass consists mainly of laths of plagioclase (commonly altered to scapolite), anhedral biotite and magnetite. The scapolite, and possibly the biotite and magnetite, likely grew during hydrothermal alteration associated with Wernecke Breccia emplacement. Primary igneous mineralogy is uncertain. The Slab volcanics appear geochemically similar and are probably comagmatic with some of the 1.71 Ga Bonnet Plume River Intrusions. No correlative volcanic strata have been found in the Wernecke Mountains or in the neighbouring Ogilvie Mountains.