One hundred and two new K-Ar age determinations, largely from granitoid rocks, are reported from the Saint Elias Mountains of southwest Yukon, northwest British Columbia, and closely adjacent parts of Alaska. Six new K-Ar dates are also presented for rocks in the northern part of the Coast Plutonic Camplex. New and previously published K-Ar age data from the Saint Elias Mountains aid in defining at least six plutonic episodes in this region: latest Pennsylvanian to Early Permian (270-290 Ma); Late Jurassic to earliest Cretaceous (130-160 Ma); late Early Cretaceous (106-117 Ma); Eocene (41-52 Ma); Oligocene (23-33 Ma); and mid- to Late-Miocene (6-16 Ma) time. Ali can be correlated with plutons or plutonic belts previously outlined in adjoining Alaska. ln the Saint Elias Mountains the plutonic episodes, except for the fast two, are apparently confined to certain terranes, whereas equivalent plutons or plutonic belts in Alaska mostly are not. These six distinct episodes of mainly calc-alkaline plutonism in structurally camplex Saint Elias Mountains and in contiguous Alaska, may be, but are not necessarily, related to periods of plate convergence and subduction.
McBride map-area, about 5,800 square miles in east-central British Columbia, includes parts of the Interior Plateau, Cariboo Mountains, Rocky Mountain Trench, Rocky Mountains, and Foothills. About 25,000 feet of Proterozoic (Windermere) and Lower Cambrian strata can be correlated in some detail from Rocky to Cariboo Mountains. The precision of the correlation, based partly on lithologic similarities, depends primarily on the obvious equivalence of the fossiliferous Lower Cambrian carbonate (Mural Formation) in each sequence. The stratigraphy above the Lower Cambrian differs sharply from one side of the Trench to the other. In Rocky Mountains carbonate-shale Cambro-Ordovician sequence, much like that at Mount Robson, becomes shaly near the Trench where overlying Silurian strata include volcanic rocks. The Upper Devonian to Permian and Mesozoic sedimentary rocks of the Front Range and Foothills are similar to those of the well-known Jasper-Banff region. West of the Trench Lower Cambrian beds pass upward to a Middle (?) and Upper Cambrian shale sequence that is unconformably overlain by Lower Devon ion and (?) younger sedimentary rocks which in turn lie discordantly below conglomerate and basaltic pillow lava at least partly of Lower Mississippian age. These are followed by unconformably overlying Upper Triassic (?) phyllite and shale. The Upper Triassic and Lower Jurassic volcanic rocks of the Interior Plateau are just west of the map-area. Minor dykes and sills and a small body of serpentinite are the only known intrusive rocks in the map-area. Typical Rocky Mountain thrust faults are confined to the eastern Main Ranges, Front Ranges, and Foothills. Farther west in Rocky Mountains and also west of the Trench folding is prominent and recognizable faults are steeply dipping. In Cariboo Mountains folds in structurally deep beds apparently upward to a highly faulted and little folded terrain. To date the only significant mineral production was from the gold placer and lode deposits near Barkerville. The Bowron River coal deposits have been extensively explored. SmalI copper showings are known near Dome Creek.
Glenlyon map-area covers about 4,900 square miles in south-central Yukon Territory. Though mountainous the area is within the Yukon Plateau. Tintina Trench, the locus of a major fault, trends northwesterly across the map-area. Northeast of the Trench, Proterozoic sedimentary rocks apparently are unconformably overlain by a sedimentary Carboniferous sequence, which in turn is succeeded by a volcanic and sedimentary unit of probable Permo-Triassic age. The section southwest of the Trench is different from that to the northeast though some of the strata are of the same age. Ages are tentative because of lack of fossils, but by correlation with the rocks of nearby areas ages may be assigned with some certainty. Strata representing all periods from Cambrian to Mississippian and a Permo-Triassic sequence are thought to be present. The Devono Mississippian and Permo-Triassic sections contain volcanic rocks. Older units are sedimentary, In the extreme southwest corner of the map-area are mainly sedimentary Upper Triassic and Jurassic rocks. Cretaceous and/ or Tertiary terrestrial deposits and Tertiary volcanic rocks underlie small areas. Extensive granitic batholiths are probably late Mesozoic in age. Ultramafic rocks, believed to be Palaeozoic, are restricted to the area near Little Salmon Lake. Folds vary in trend from east to northwesterly. Several inferred northwesterly trending faults bound blocks geologically distinct from adjoining blocks. A lead-zinc-silver deposit east of Little Salmon Lake is the only mineral deposit of importance within the map-area.
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