A Transect Across Northern Stikinia: Geology of the Northern Whitehorse Map Area, Southern Yukon Territory (105D/13-16)

Results from the geological mapping of four 1:50 000 map areas (NTS 105D/13-16) north of Whitehorse are presented. The maps form a transect across the northern portion of Stikinia, an accreted terrane of uncertain origin. This bulletin establishes a stratigraphic nomenclature, and provides descriptions of 16 units of layered rocks that constitute Stikinia. Portions of the adjacent Cache Creek Terrane, Yukon-Tanana Terrane and the Coast Plutonic Complex are also represented and described. In addition, biostratigraphic and isotopic age constraints are provided for almost all of the units. Stikinia is composed of several tectonic elements that indicate an episodic depositional history characteristic of an island arc environment. A newly discovered Late Paleozoic package, here call the Takhini assemblage, is defined, and represents the most northerly strata correlated as the Joe Mountain Formation. This enigmatic suite is Middle Triassic to Middle Jurassic sedimentary rocks are the fill of the marginal basin known as the Whitehorse Trough. Strata of the Whitehorse Trough Supergroup include: clasts of deformed Takhini assemblage; deep-water sediments as old as Ladinian; igneous clasts with Permian and Late Triassic isotopic dates; extensive Norian carbonates containing Tethyan faunas and phylloidal algae; Jurassic ammonites that represent almost every ammonite zone as young as Bajocian; and a mixed Tethyan-Boreal Early Jurassic faunal assemblage. Plutonic rocks of the region are voluminous and, with the benefit of isotopic dates, can be divided into five plutonic suites (Long Lake, Teslin, Whitehorse, Mount McIntyre, Nisling Range), which record Early Jurassic, mid-Cretaceous and Early Tertiary magmatic epochs. Post-Triassic volcanic rocks are well dated and include the Early Jurassic Nordenskio dacite, mid-Cretaceous Mount Nansen Group (Bying Creek volcanics), Late Cretaceous Carmacks Group and the Windy-Table suite (Open Creek volcanics). Mineral Occurences include a number of small copper-gold skarns and gold-quartz veins. Mapping identifies several regions of favourable geology for these and other types of deposits, including carbonate (granodiorite intrusive contacts, faulted caldera margins, altered fault breccias and quartz-rich rhyolite dykes.