The Irvine Lake and Gravel lake map-areas (NTS 105B/10,11) lie within the northern Omineca Belt, west of the Tintina-Northern Rocky Mountain Trench (NRMT) fault. The eastern part of the area is underlain by Proterozoic to early Paleozoic metasedimentary rocks of Cassiar terrane, a fragment of the North American miogeocline which has been displaced northward on the Tintina-NRTM fault. The western part of the area is underlain by basaltic metavolcanics, serpentinized ultramafic rocks, metagabbro, and cherty and calcareous metasediments of the Slide Mountain terrane. Unfoliated to weakly foliated granitic intrusives (Marker Lake and Cassiar batholiths and Cabin Creek and Gravel Creek stocks) occur throughout the area intruding both the Cassiar and Slide Mountain terranes. Slide Mountain and Cassiar terranes are juxtaposed by an east-verging thrust referred to in this area as the Zak fault. Southwest of Irvine Lake, the thrust places serpentine, basaltic meta-volcanics, and an undeformed dioritic intrusion onto a footwall consisting of the Proterozoic Tsaydiz Formation and older units. Northwest of Irvine Lake, near Shootamook Creek, the thrust places cherty metasediments of the allochthon onto marble and quartzite inferred to be lower Cambrian Rosella and Boya Formations, respectively. The northern end of the Cassiar batholith extends into the southwestern corner of Irvine Lake map area. Its northeastern contact with rocks of Slide Mountain terrane is a subvertical, northwest-southeast trending mylonite zone several tens of metres wide. Mesoscopic structures including S-C fabrics and shear bands prove dextral displacement parallel to a variably plunging, but commonly sub-horizontal stretching lineation. The mylonite zone lies along a pronounced topographic lineamnet which extends from the trace of the Cassiar fault south of the Alaska Highway northwestwardly into the Irvine Lake map-area rather than veering to the west as previously mapped. Mineral occurrences in this area are primarily near the contact of granitic intrusions and carbonate rocks. Carbonate rocks hosting the deposits belong to the upper Proterozoic Ingenika Group (Swannell, Tsaydiz and Espee formations) rather than the Lower Cambrian Atan Group as has been inferred for nearby deposits in the Rancheria district. Other, non-carbonate-hosted mineral occurrences include a porphyry Mo prospect and Ag, Pb, Zn veins.

Metasedimentary and meta-igneous rocks in ‘Mendocina Creek’ (NTS 105F/5) and eastern Livingstone Creek (NTS 105E/8) areas are part of three distinct stratigraphic sequences: from east to west, the Sheep Creek, Scurvy Creek and Dycer Creek successions. The Sheep Creek succession contains extensive carbonate horizons and is likely part of the Cassiar terrane. To the west, metaclastic rocks of the Scurvy Creek succession are extensively intruded by sills and dykes composed of augen meta-granite of Early Mississippian age; they are correlated with the Snowcap assemblage of Yukon-Tanana terrane. The overlying Dycer Creek succession in the southwest comprises marble, carbonaceous rocks, greenstone and quartzite of Lower Mississippian (and younger?) age that probably correlate with the Finlayson assemblage of Yukon-Tanana terrane. The ‘Mendocina Creek’ area experienced at least four phases of deformation and greenschist- to amphibolite-facies metamorphism. An east-verging thrust locally imbricates the Scurvy Creek succession and the boundary between the Yukon-Tanana and Cassiar terranes corresponds with a west-verging, brittle-ductile thrust fault in the eastern part of the area. Re-interpretation of the geology in western Quiet Lake map-area indicates that this boundary is located 20 km east of the d’Abbadie fault, the previously inferred terrane boundary.

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The Granite Creek map area includes the southwestern section of the Gustavus Range. This area hosts summits approximately 2000 m in elevation. Granite and Albert creeks drain into Roop Lakes, through the wide, u-shaped lower Granite Creek valley. Keystone Creek flows in a narrow, bedrock-controlled valley. Lower Granite creek flows through the middle of the valley, depositing modern fluvial gravel and a blanket of organic material on the floodplain. Till from four alpine sources, as well as from the Cordilleran Ice Sheet (CIS), blanket the lower valley and intermix with glaciolacustrine sand and silt. Glaciolacustrine sediment can also be found capping moraines, and on valley walls above lateral moraines deposited when the CIS advanced up lower Granite Creek valley. Glaciofluvial gravel forms a proglacial fan where the former Granite Creek alpine glacier terminated and meltwater channels mark most former ice margins of the CIS. Till from the most recent glaciation is found in alpine glacier and Cordilleran Ice Sheet moraines, as well as in cirque valleys as blankets and veneers where preserved. Loess forms blankets on most gentle slopes, which allows for its preservation. Colluvium veneers, blankets, and fans form below steep slopes with active rockfall. Bedrock outcrops along steep cirque headwalls and in cirque valleys, as well as in Keystone Creek where fluvial downcutting processes are active. Stone stripes formed by frost heaving are found on gentle slopes. Flat upland surfaces host weathered bedrock and mud boils.

Three allochthonous terranes, igneous rocks of the Cretaceous and Tertiary Coast Plutonic Complex and associated volcanic complexes comprise the geology between Whitehorse and the Yukon-BC border. The Paleozoic and older(?) Nisling Terrane is composed of the quartz-rich Nisling assemblage, the carbonaceous Nasina assemblage and orthogneiss assumed to be Devono-Mississippian in age. The Nakina sub-terrane of the northern Cache Creek Terrane is composed of Mississippian to Permian spilitized basalt, ultramafite, chert and limestone characterized by Tethyan faunal assemblages and dramatic facies variations. The northern Stikine Terrane is composed of the Upper Triassic Lewes River arc and its plutonic roots. Upper Triassic to Middle Jurassic sedimentary rocks of the Lewes River and Laberge groups collectively comprise the Whitehorse Trough overlap assemblage. Basal augite-phyric volcanic rocks of the Lewes River Group (Povoas Fm) are unconformably overlain by sedimentary debris derived from the eroding arc (Aksala Fm). These rocks are disconformably overlain by Laberge Group coarse clastics (Takwahoni Fm) deposited in laterally discontinuous submarine fans and conformably overlain by distal fine-grained equivalents (Inklin Fm). Siliciclastic rocks of the Tantalus Formation were deposited in a variety of marine environments in a successor basin to the Whitehorse Trough during Upper Jurassic and Late Cretaceous(?) times. Plutonic rocks cover approximately 40% of the project area and comprise over 30 individual bodies with a wide range of compositions. Plutonic rocks have been divided into six chrono-lithologically distinct suites: Late Triassic batholiths of the Klotassin plutonic suite; Early Jurassic syn-tectonic(?) foliated diorite; mid-Cretaceous granodiorite of the Whitehorse plutonic suite; mid-Cretaceous granophyric quartz monzonite of the Mount McIntyre plutonic suite; a poorly defined suite of Late Cretaceous intrusions with associated volcanism; and quartz-rich high-level Late Paleocene/Early Eocene intrusions of the Nisling Range Plutonic Suite which form the plutonic roots to Skukum Group volcanism. The Klotassin suite is assumed to form the plutonic roots to the Lewes River arc, but are isotopically dissimilar. The Bennett Granite provides a Late Triassic link between Nisling Terrane and Lewes River arc. Cretaceous and Tertiary intrusions are peraluminous and comprise the Coast Plutonic Complex. Isolated but widespread accumulations of intermediate mid- and Late Cretaceous volcanic rocks form the Mt. Nansen and Carmacks groups. Four Late Paleocene/Early Eocene volcanic complexes of the Skukum Group are aligned in a northerly trend and represent deeper levels of erosion to the north. Skukum Group activity is also represented by numerous northeast-trending rhyolite dyke swarms representative of a transtensional regime. Strata of the Whitehorse Trough were deformed into a set of open to tight, northwest-trending folds during Middle and(?) Latest Jurassic/Early Cretaceous compressional event(s). In northern Cache Creek Terrane, much of the deformation took place during Middle Jurassic terrane accretion, but Late Cretaceous southerly verging thrust faults are documented. Nisling Terrane metasedimentary rocks were metamorphosed prior to the intrusion of the Late Triassic Bennett Granite. The Tally Ho shear zone is a narrow domain of penetrative, ductile deformation with evidence of Late Triassic, sinistral strike-slip displacement. It strikes northwest and dips steeply and marks the easternmost limit of Nisling Terrane exposures. It may represent a terrane boundary between the Lewes River arc and the Nisling Terrane; alternatively it may be a transpressional structure within the arc itself.

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Geological map including geological cross sections, mineral occurrences and preliminary isotopic age determinations.

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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.

Map presents an interpretation of the bedrock geology of the northern Whitehorse trough as extrapolated from field observations and a reflection seismic survey.