Geological map (1:125,000 scale) of the Lansing Range map area (NTS 105N), east half, Hess Mountains, Yukon, including geological cross sections, mineral occurrences, fossil age determinations, isotopic age determinations and marginal notes on regional setting.

Between the Cretaceous granitic rocks (Hake Batholith on the west; Cassiar Batholith to the east) are three belts of metamorphic rocks, collectively part of Yukon-Tanana terrane. These are remnants of oceanic and continental volcanic arcs, and marginal basin sediments of Early to mid-Paleozoic age. At the head of Borden Creek are thick carbonate and andesitic volcanic rocks correlated with Klinkit Group. The Ram Creek fault and Hidden Lake fault are not exposed but deduced to be steeply dipping brittle structures with northeastward thrust or transpressional offset, based upon more complete exposure to the southeast in 105B/3 map area. The former is likely of Cretaceous age; the latter was active between mid-Permian and Early Jurassic time.

The Southwest McQuesten-northern Carmacks area is primarily underlain by rocks of the Yukon-Tanana terrane which is divided into two distinct belts separated by the Willow Creek fault: 1) a central belt of polydeformed, upper greenschist-amphibolite facies metasedimentary and metaplutonic rocks of Permian and older ages; and 2) a northeastern belt of generally undeformed and unmetamorphosed volcano-plutonic rocks of the Early Mississippian Reid Lakes complex. The southern part of the area is underlain mainly by rocks of Quesnellia and Stikinia, including: 1) Paleozoic retrogressed metamorphic rocks of the Boswell assemblage; 2) Upper Triassic augite-phyric volcanic rocks; and 3) Early Jurassic granitoids of the Aishihik plutonic suite. These rocks are dissected by a series of dextral strike-slip faults, probably related to the Teslin fault system. Post-accretion rocks include: 1) mid-Cretaceous biotite monzogranite plutons; 2) dacite and minor basalt of the Upper Cretaceous Carmacks Group; and 3) Quaternary basalt of the Selkirk volcanics. The southwest McQuesten-northern Carmacks area is under-explored, but shares many geological attributes with nearby, highly prospective districts such as the Dawson Range mineral belt, the recently discovered White Gold area and the producing Minto Mine.

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The NTS 106B/04 map area straddles the upper reaches of the Stewart River in east-central Yukon. The area north of the Stewart River is underlain by Ediacaran clastic and carbonate continental slope deposits of the uppermost Windermere Supergroup, and by Ediacaran-Cambrian rocks of the Hyland Group (Selwyn basin). The area south of the Stewart River is dominated by the Cambrian Gull Lake Formation and Cambrian (-Silurian?) volcanic rocks of the Old Cabin Formation. The main structures in 106B/04 define an arcuate pattern; they are oriented NW-SE in most of the area, but are approximately E-W in the westernmost part of the map area. These structures include upright, gently-plunging folds and steeply-dipping, axial-planar cleavage. Folding was locally accompanied by thrusting. Late structures include a steeply-dipping sinistral fault that transects the central part of the map area and a number of NW-WNW-striking normal (± dextral) faults. Stratigraphic relationships suggest correlation of the upper Yusezyu, Algae, and Narchilla formations of the Hyland Group (Selwyn basin) with the upper Blueflower, Risky, and Ingta formations of the Windermere Supergroup (Ogilvie and Mackenzie platforms). Gold mineralization has recently been discovered in the Algae Formation, which has also been explored for Mississippi Valley-type lead-zinc-silver mineralization elsewhere in the area.

Granodiorite of the Coast Plutonic Complex intruded metasedimentary rocks in the Dezadeash Range of the northern Coast Belt in the late Mesozoic. Graphitic staurolite-biotite schist, associated with the Kluane Metamorphic Assemblage, underlies the western Dezadeash Range, whereas cordierite-biotite gneiss, previously correlated with the Late Proterozoic - Paleozoic Nisling Assemblage, is exposed in the eastern and southern regions. A terrane boundary was placed in the central Dezadeash Range. Recent petrographic studies reveal a southeastward increase in metamorphic grade. Prograde appearance of cordierite partly obliterated an older schistosity and caused a fabric change near the postulated terrane boundary. Furthermore, typical continental margin rocks, such as marble and quartzite, are not observed. This suggests that all metamorphic rocks in the Dezadeash Range can be correlated with the Kluane Metamorphic Assemblage, whereas Nisling Assemblage rocks occur in the Coast Mountains to the east. Therefore, the terrane boundary is located in the Dezadeash River valley, further southeast than previously thought.

The map area spans the western edge of the old North American continent and the terranes that accreted to it in Mesozoic time, which together form a generally west-dipping structural stack, separated by layer-parallel thrust faults. Three major elements are represented: 1) tilted strata of the ancient North American margin (Cassiar Terrane), 2) overthrust rocks that originated as volcanic arcs and off-shore sediments (Yukon-Tanana Terrane), and 3) granitic bodes injected into this thickened crust after the Cordilleran orogeny.

Mafic volcanic and clastic strata of the Middle Triassic Joe Mountain Formation, east of Lake Laberge, Yukon, represent a juvenile volcanic arc sequence. Mafic volcanic rocks of the Upper Triassic Lewes River Group were formed in the spatial and temporal continuity of Joe Mountain volcanism. Carbonate sedimentation took place in shallow oceanic subbasins adjacent to the arc from the Carnian to Rhaetian; these subbasins were separated by physiographic boundaries inherent to the arc, resulting in lateral stratigraphic variations. Polymictic conglomerate and turbiditic sequences of the Lower-Middle Jurassic Laberge Group unconformably overlie Triassic rocks. Two north-northwest strike-slip faults, the Laurier Creek and the Goddard, control the distribution of units. Joe Mountain Formation rocks are characterized by an east-west structural trend, whereas the Upper Triassic and Jurassic sequences are characterized by north-northwest trending tight folds and thrust faults. At least five post-accretion igneous suites intrude or overlie older stratigraphy, including the Late Cretaceous Open Creek volcanic complex.

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