Geological map (1:50,000 scale) of West Lake map area, Hess Mountains, east-central Yukon (NTS 105N/9) including geological cross sections, mineral occurrences, and fossil localities.

Clear Creek map area of central Yukon is underlain by deformed and metamorphosed Proterozoic and Paleozoic rocks of western Selwyn Basin (Hyland Group, unnamed carbonate unit, Road River and Earn groups) and mid-Cretaceous felsic intrusions. Metasedimentary rocks are disposed in a warped northwest to northeast-dipping structural panel with younger, structurally shallow rocks in the north and older, structurally deeper rocks in the south. Younger rocks in the north are deformed into Lost Horses syncline, a southwest-overturned tight to isoclinal syncline with an axial surface trace extending across the northern part of the area. Older rocks at deeper structural levels in the south are deformed by a suite of fabric elements that probably post-date Lost Horses syncline, indicate a top-to-the-northwest sense of tectonic transport, and are probably related to Early Cretaceous displacement on the Tombstone thrust. Subsequent deformation warped the panel into its current orientation. All structures are intruded by mid-Cretaceous felsic intrusions including hornblende-biotite (rare muscovite) granite, quartz monzonite, granodiorite, syenite, and quartz syenite. Mineral occurrences are mainly precious metal, tin, and/or tungsten bearing vein, skarn, and breccias associated with felsic intrusions. Bedded barite occurs in Earn Group strata. New analyses of mineralized samples confirm earlier data reporting significant gold values in veins cutting felsic intrusions and nearby country rock, and correlation of anomalous gold with anomalous bismuth in some veins.

Geological map of Quartet Lakes map area (NTS 106E/1), including a geological cross section and mineral occurrences.

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Thirty-Seven Mile Creek map area, northwest of Whitehorse, straddles the contact between Coast Plutonic Complex and rocks attributed to northern Stikine Terrane. Late Triassic Little River granodiorite and Late Paleocene (57 Ma) Annie Ned granite underlie the western part of the map area. Upper Triassic to Middle Jurassic volcanic and sedimentary rocks of the Lewes River and Laberge groups underlie the eastern part of the map. The contact between Coast Plutonic Complex and Stikine Terrane is marked by the Takhini deformation zone - a region of greenschist, gneiss, mylonite, and amphibolite whose protolith is volcanic rocks of Lewes River Group. Potential mineral deposits in this map area include epithermal and mesothermal quartz veins, and magnetite skarns.

The northeast corner of Grass Lakes map area is underlain by polydeformed metasedimentary, metavolcanic and metaplutonic rocks of Yukon-Tanana Terrane, and ultramafic rocks of unknown affinity. Layered metasedimentary and metavolcanic rocks, about half the area mapped, include a basal unit of quartz-rich schist, psammite, metapelitic schist, and grit with a laterally continuous sandy marble marker high in the unit; a unit made up of a variety of mafic metavolcanic (?) rock types interlayerd with carbonaceous phyllite, grey quartzite, quartzofeldspathic psammite and grit; Devono-Mississippian felsic metavolcanic (?) rocks interlayered with carbonaceous phyllite and grey quartzite, and an upper mafic metavolcanic (?) unit with quartzofeldspathic psammite and grit, and carbonaceous phyllite and quartzite. Metarhyolite of the third unit hosts the Kudz Ze Kayah massive sulphide deposit and underlies numerous gossans. The succession is thought to be upright based on an interpretation of the structure of metarhyolitic rocks at Kudz Ze Kayah. The remainder of the area is underlain by metaplutonic rocks. Quartz-feldspar metaporphyry near Kudz Ze Kayah is thought to be a hypabyssal intrusion coeval with the adjacent metavolcanic pile. Coarse-grained granitic to monozonitic Grass Lakes Orthogneiss of probably Early Mississippian age underlies much of the area; it and its apophyses intrude the layered units. The undated North Lakes Metadiorite is thought to intrude the Grass Lakes Orthogneiss. Three large undated bodies and numerous discordant dykes of weakly foliated biotite-muscovite granite intrude the layered succession. Ultramafic rocks occur in two settings in the eastern part of the area. Discontinuous 10 to 100 metre-scale bodies of ultra-mafic rock occur along the contact between actinolite-chlorite schist and calcareous quartzose psammite (above) near the Pack occurrence. A km-scale body of ultramafic rock also overlies the same calcareous quartzose psammite in the prominent peak along the east side of the map area. An axial surface trace of a recumbent north-closing fold lies between the two localities suggesting that the ultramafic rocks are folded. All rocks except biotite-muscovite granite and ultramafic rocks are strongly foliated and lineated. The prominent foliation transposes an older foliation and bedding and is axial-planar to south-vergent folds mappable at 1:50 000 scale. This deformation occurred after the intrusion of the Grass Lakes Orthogneiss (therefore post-Mississippian) and waned during the emplacement of biotite-muscovite granite. Two weak later phases of deformation comprise sporadically developed north-trending, east-vergent folds of the second-phase foliation and regional arching of the second phase foliation over a southwest-trending hinge in the central part of the map area.

Geological map including geological cross sections and mineral occurrences.

The Quartet Lakes map area is underlain by rocks that range in age from Early Proterozoic to early Paleozoic. Stratified rocks include, from oldest to youngest, the Lower Proterozoic Fairchild Lake and Quartet groups (Wernecke Supergroup), the Middle to Late Proterozoic Tsezotene Formation, Katherine Group, and Little Dal Formation Mackenzie Mountains Supergroup), and the Cambrian Slats Creek Formation. Five igneous units are recognized, including the Early Proterozoic Bonnet Plume River Intrusions, the Middle Proterozoic Bear River dykes, the Late Proterozoic Tsezotene Sills, Late Proterozoic to Cambrian lamprophyre, and Late Proterozoic to early Paleozoic diorite. Older rocks (Wernecke Supergroup, Wernecke Breccia and Bonnet Plume River Intrusions) were thrust northward over the Mackenzie Mountains Supergroup along a portion of the Knorr Fault. This part of the fault may be a restraining bend in an otherwise dextral strike-slip system. Copper-golduranium mineral occurrences in the area include disseminated and vein mineralization associated with zones of Wernecke Breccia.

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The Clark Lakes area is located along the northern boundary of the Selwyn fold belt, and is underlain by the Ediacaran to Cambrian Hyland Group. In the surrounding region, the Hyland Group and Paleozoic platformal carbonate rocks host several Au and polymetallic mineral deposits. The Clark Lakes area is bordered by regional-scale, southeast-striking thrust faults, which include the Dawson thrust to the northeast, and the Tombstone and Robert Service thrusts to the southwest. Based on stratigraphic relationships identified during 1:50000-scale bedrock mapping, Hyland Group rocks in the Clark Lakes area are considered to belong to the Cryogenian–Ediacaran Yusezyu Formation, the Ediacaran Algae Formation and the Ediacaran–Terreneuvian Narchilla Formation. The Yusezyu Formation has been subdivided into five units based on dominant siliciclastic lithofacies, which form a broadly coarsening-upward sequence. The Yusezyu and Narchilla formations host gabbro sills, and quartz monzonite occurs locally in the upper Yusezyu Formation. Rocks in the Clark Lakes area exhibit a steeply northeast-to-southwest-dipping foliation that is axial planar to southeast-trending folds.