Geological map (1:50,000 scale) of Sprague Creek area, central Yukon (NTS 115P/15)

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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.

Surficial geology map including marginal notes on physiography, glacial history, placer gold potential, drainage anomalies and terrain hazards.

The study area provides a clear record of the Proterozoic geological evolution of northern and central Yukon Territory. The area lies in the Wernecke Mountains of east-central Yukon, approximately 150 km north-northeast of the town of Mayo, and 20 km west of the Yukon-Northwest Territories border. The rocks record events of sedimentation, magmatism and deformation ranging in age from Early Proterozoic to Tertiary. Rocks of Early Proterozoic age predominate, but strata of Middle Proterozoic, Late Proterozoic, and Early Paleozoic ages are also abundant.

Geological map (1:50,000 scale) of Slats Creek area, Wernecke Mountains, central Yukon (NTS 106D/16) including geological cross sections, mineral occurrences and preliminary isotopic age determinations.

The study area is underlain by four stratigraphic successions ranging in age from Middle Proterozoic to Early Paleozoic. From oldest to youngest, they are: Middle Proterozoic Wernecke Supergroup; Middle to Upper Proterozoic Pinguicula Group; Upper Proterozoic Windermere Supergroup; and Uppermost Proterozoic to Lower Paleozoic sandstone and carbonate. Together, they represent about a billion years of intermittent sedimentation punctuated by processes such as deformation, uplift, erosion, magmatism and mineralization. Rocks in the study area record eight phases of contractional and extensional deformation, some of which may be related to strike-slip faulting. Two phases of southwest-verging folds and thrust faults may be related to dextral transpression on the Snake River Fault. Mineral enrichments occur in two general forms:: breccia-related (Middle Proterozoic), and veins (Mesozoic to Tertiary). The breccia-related occurrences have enrichments of Cu ± U, Co, Au and Ag, as dissemminations and veinlets in and near intrusive breccia zones (Wernecke breccia). The vein occurrences comprise Zn-Pb-Ag ± Cu and Au, in veins and related lenses and irregular replacements of carbonate.

The southern Nash Creek area is located along the northern boundary of the Selwyn basin, and is underlain mainly by the Ediacaran–Cambrian Hyland Group, the Devonian–Mississippian Earn Group and the Mississippian Tsichu Group. Several Au and polymetallic mineral deposits are hosted by the Hyland Group and Paleozoic platformal carbonate rocks in the surrounding region. The southern Nash Creek area is bordered by regional-scale, southeast-striking thrust faults, which include the Dawson thrust to the northeast and the Robert Service thrust to the southwest. Based on stratigraphic relationships identified during 1:50 000-scale bedrock mapping, Hyland Group rocks in the area are considered to belong to the Cryogenian–Ediacaran Yusezyu Formation, the Ediacaran Algae Formation and the Ediacaran–Terreneuvian Narchilla Formation. Earn Group rocks include mainly shale and lesser amounts of interbedded dolostone, sandstone and shale. Tsichu Group rocks mostly comprise quartzite. The Yusezyu and Narchilla formations host (Paleozoic?) gabbro sills, and the Earn and Tsichu groups host gabbro sills that are considered to belong to the Triassic Galena suite. Rocks in the southern Nash Creek area exhibit a northeast-to-southwest dipping foliation that is axial planar to southeast-trending folds.

Geological map (1:50,000 scale) of Slats Creek area, Wernecke Mountains, central Yukon (NTS 106D/16) including geological cross sections and mineral occurrences.