The Early Cambrian Quartet Mountain lamprophyres are volatile-rich ultramafic alkaline dikes that crosscut the Wernecke and Mackenzie mountains supergroups in the Wernecke Mountains of northern Yukon. Their emplacement may have been triggered by Early Paleozoic extension of the Cordilleran miogeocline. Numerous small-volume alkalic igneous rocks that range in age from Cambrian to Devonian occur elsewhere in the miogeocline and may reflect a similar tectonic setting. The Quartet Mountain lamprophyres contain phenocrysts of phlogopite ± diopside ± olivine within a dark-grey aphanitic groundmass and were likely generated by low-percentage melting of mantle at depths >90 km. One of the lamprophyres contains abundant pseudomorphed olivine xenocrysts and xenoliths of inferred crustal and mantle affinities. Although this dike resembles kimberlite because of its abundance of mantle xenoliths and xenocrysts and its ultramafic composition, it differs from kimberlite in its abundance of phlogopite phenocrysts. It is best described as an ultramafic lamprophyre with kimberlitic affinity. The lamprophyres have modest potential to host diamonds.

Paleomagnetic and geobarometric results are reported here for the Early Jurassic Granite Mountain batholith, an ~600 km² granodiorite intrusion in the Yukon-Tanana Terrane. Paleomagnetic analyses of 331 specimens from 24 sites yield magnetite-borne characteristic remanent magnetization (ChRM) directions. Eight northerly and westerly sites display a mean direction A (D=337, I=69°; a 95 =7.6°, k=54). Another 11 sites appear to be lightning-struck, or exhibit unstable remanence, and 3 sites in a fault-bounded block to the southeast carry an anomalous northeast upwards ChRM direction B. Two sites in a Cretaceous andesite porphyry dyke and its contact zone give a westerly, steep-down ChRM direction, C. Aluminum-in-hornblende geobarometry at 10 sites defines emplacement depths of ~16 km in the north and west, and ~19 km in the southeast. The batholith has probably not been significantly tilted since its emplacement, but it may be subdivided into two separate intrusive phases or structural blocks that have experienced differential uplift. Ambient temperatures at 16-19 km were too high for magnetite to record an enduring remanence, so the observed ChRMs likely record uplift of the batholith through ~15 km depth, at 180-170 Ma. Both A and C ChRM directions are similar to those expected for Early Jurassic and Late Cretaceous reference poles, respectively, suggesting that the Yukon-Tanana Terrane is not far-traveled with respect to cratonic North America since Early Jurassic time.

Lime Peak is an Upper Triassic carbonate complex approximately 40 km northeast of Whitehorse. It is one of many carbonate buildups in the Whitehorse Trough which occur as isolated lenses surrounded by Triassic greywacke and volcanic-clast conglomerates derived from an arc to the southwest. The carbonates at Lime Peak are particularly well-exposed and have been shown to be a series of organic reefs which shed debris into surrounding inter-reef areas. Fieldwork at Lime Peak in 1980 established the existence of massive reefal limestones occurring in 3 distinct forms. The variability of both the geometry and the lithology of the massive limestones was observed in 1980 but was not studied in detail. Considerable effort was spent in 1981 mapping lithology in order to establish the nature and extent of organic framework in the reefal bodies and to develop an explanation for the three distinct growth forms.

A copy of this thesis is available at the EMR library – QE993.B73 1981.

This study describes the structural and stratigraphic setting of Devonian bedded barite and sedimentary exhalative lead-zinc-silver-barite deposits near MacMillan Pass in eastern Yukon. It shows that the deposits occur within MacMillan Fold Belt, an anomalous west-trending feature made up of three parallel elongate domains called the North, Central and South Blocks. Each is characterized by distinctive styles of deformation and Devonian strata. The North Block is characterized by a thick Early and Middle Devonian chert and shale sequence included in the Lower Earn Group and by an intricate array of southerly directed thrust faults. The Central Block includes unusually thick Early and Middle Devonian silty limestone intercalated with volcanic and volcaniclastic rocks within the upper part of the Road River Group. The Tom and Jason sedimentary exhalative zinc-lead-silver-barite deposits are associated with a thick sequence of coarse clastic rocks thought to belong to a submarine fan complex within the Lower Earn Group. Tight, upright folds, high angle reverse faults and irregularly oriented faults are characteristic. In the South Block, the Lower Earn Group comprises a thin Devonian shale sequence. Open upright folds and few faults are the structural style. The differences in Devonian strata and contrasting style of deformation between blocks may reflect older (Devonian?) fault control to depositional patterns, but structures of that age have not been identified. This report is accompanied by three 1:50 000-scale geological base maps of the MacMillan fold belt, east-central Yukon Territory (NTS map sheets 105 O/1,2,7,8 and parts of NTS map sheets 105 P/4,5 ).

This study describes the structural and stratigraphic setting of Devonian bedded barite and sedimentary exhalative lead-zinc-silver-barite deposits near MacMillan Pass in eastern Yukon. It shows that the deposits occur within MacMillan Fold Belt, an anomalous west-trending feature made up of three parallel elongate domains called the North, Central and South Blocks. Each is characterized by distinctive styles of deformation and Devonian strata. The north Block is characterized by a thick Early and Middle Devonian chert and shale sequence included in the Lower Earn Group and by an intricate array of southerly directed thrust faults. The Central Block includes unusually thick Early and Middle Devonian silty limestone intercalated with volcanic and volcaniclastic rocks within the upper part of the Road River Group. The Tom and Jason sedimentary exhalative zinc-lead-silver-barite deposits are associated with a thick sequence of coarse clastic rocks thought to belong to a submarine fan complex within the Lower Earn Group. Tight upright folds, high angle reverse faults and irregularly oriented faults are characteristic. In the South Block, the Lower Earn Group comprises a thin Devonian shale sequence. Open upright folds and few faults are the structural style. The differences in Devonian strata and contrasting style of deformation between blocks may reflect older (Devonian?) fault control to depositional patterns, but structures of that age have not been identified.

A copy of this thesis is available at the EMR library – QE195.R53 1968. This thesis is available online at https://circle.ubc.ca/handle/2429/36000.

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.

Eight lithofacies types have been identified. These include: 1) Gms - massive, matrix support conglomerate; 2) Gm - massive or crudely bedded, clast supported conglomerate; 3) Sr - rippled sandstone; 4) Sp - planar crossbedded sandstone; 5) Sh - massive sandstone; 6) F1 - laminated sandstone, siltstone and mudstone; 7) Fsc - laminated or massive siltstone and mudstone; and 8) L - limestone. All lithofacies are present in the Sixtymile River area, but only lithofacies Sp, Sh and F1 were observed in the Grayling Creek area. The eight types are grouped into four assemblages and are interpreted as: 1) Scott type braided river deposits; 2) Donjek type braided river deposits; 3) South Saskatchewan type braided river deposits; and 4) lacustrine deposits. Lithofacies assemblages are arranged into at least ten fining-upward and thinning-upward megacycles reflecting a history of pulsed and rapid uplift in the source area.

Most chert-pebble conglomerate units within the Late Jurassic to mid-Cretaceous Tantalus Formation were deposited in shallow, deep and meandering gravel-bed rivers. However, the presence of largescale angle of repose foresets of large- to small-pebble conglomerate, with distinct down-slope termination in laminated mudrocks, indicates that at least some >5 m foresets were formed by episodic flood-controlled progradation of a small river-dominated lobate delta. Architectural analysis of exposures at the Whitehorse Coal deposit, 26 km south-southwest of Whitehorse, indicates periodic rapid progradation into a small lake that was at least 6 m deep. Thinning and downlap of some foreset units indicate shifting location of topset distributary channels. Down-slope transition of gravel foresets into thin sub-horizontal beds of massive and graded sandstone and pebbly sandstone suggests that the foresets were inertia-dominated. Deformation of bottomset beds is directly related to foreset progradation over under-compacted lacustrine clays.