MAPPING THE CONTACT BETWEEN THE SNOWCAP ASSEMBLAGE-RUBY RANGE BATHOLITH IN THE YUKON TANANA TERRANE, SOUTHWEST YUKON TERRITORY

The Giltana Lake map project is a 1.8 km² area situated in SW Yukon, between Aishihik Lake and Giltana Lake; it is located within the Yukon Tanana Terrane (YTT) at the contact between the Ruby Range Batholith (ca. 64-57) and the Yukon Tanana’s basement, the Snowcap Assemblage (pre-late Devonian). The YTT is a peri-Laurentian terrane formed proximal to the craton’s rifted margin during the Paleozoic, and is composed of sedimentary input from western Laurentia and superimposed magmatic arcs. This mapping project clarifies the contact between the Tertiary Ruby Range Batholith and the Snowcap Assemblage, and aims to uncover the metamorphic and deformational history of the map area while determining the area’s structural geology and lithological relationships. The field area is characterized by NW striking metasedimentary layers of quartz biotite schist, marble and garnet bearing gneiss, with thinner layers of quartzite and skarnified calc-silicate dipping between 45˚ and 75˚. Cross-cutting these are quartz pegmatite veins and a set of NNW striking dikes that draw parallels to the dike systems at the nearby Hopper Pluton skarn and porphyry style mineral deposit showings. This mapping project, supported outside the map area by regional mapping by Israel (2015) shows the contact between the Ruby Range Batholith and the metasediments as C-shaped, with two arms extending to the north and south approximately strike-parallel. It is thought to occur along schist and marble layers, and the main NNW trending feldspar porphyry dike in the north, and along a gneiss layer to the south. The southern contact is complicated by the presence of a NE striking normal fault, of which the extent of displacement is uncertain. Research on the field area’s metamorphic grade and deformation history is ongoing, but preliminary thin section analysis shows the area lies within the amphibolite facies, and micro and macro evidence show multiple deformation events; both findings are congruent with previous studies of regional structure and metamorphic facies.