The project area, covering 2,142 square kilometres, includes the following three map areas: Colorado Creek (115 J/10), Selwyn River (115 J/9), and Prospector Mountain (115 I/5). Most of the area is in the Dawson Range subdivision of the Yukon Plateau in west-central Yukon Territory. In this study, the bedrock geology of the area was mapped at a scale of 1:50 000.
The oldest rocks in the region are metamorphosed Proterozoic to Paleozoic(?) sedimentary and igneous rocks of the Yukon Metamorphic Complex. They are intruded by batholiths and plutons of hornblende and (or) biotite granodiorite, monzonite, and quartz monzonite of three Mesozoic suites. The older two, which show penetrative metamorphic textures, are the Triassic(?) Klotassin Suite and the Jurassic(?) Big Creek Suite. The third is the unmetamorphosed Dawson Range Suite of Middle Cretaceous age. Slightly younger igneous units consist of felsic to intermediate volcanic and subvolcanic rocks of the Mount Nansen Suite. Early Tertiary igneous rocks include extrusive andesite, basalt, and minor rhyodacite of the Carmacks Suite, and the slightly younger monzonite to quartz monzonite of the Prospector Mountain Suite.
The district contains numerous mineral deposits and occurrences of economic interest. Copper and molybdenum deposits are associated with felsic plutons of at least two ages. Lode gold deposits and one gold-bismuth vein are associated with felsic volcanic rocks and associated subvolcanic intrusions of the Mount Nansen Suite. Placer gold deposits are derived from these rocks. Lead-zinc-silver veins are associated with late-stage intrusions of the Dawson Range and Prospector Mountain Suites. Skarn deposits occur in rocks of the Yukon Metamorphic Complex along borders of younger plutonic rocks.
This Open File includes three 1:50 000-scale bedrock geology maps of the areas, including mineral occurrences.