The nature and extent of past glaciations are depicted on the glacial limits map of Yukon (1:1,000,000 scale). This compilation depicts the maximum extent of each glaciation and the general direction of ice movement, including the provenance of flows. This map also includes marginal notes on mapping criteria, as well as a list of references.

A regional till geochemistry project was completed in conjunction with bedrock mapping across rocks of Yukon-Tanana Terrane and North American affinity in central Yukon. The high mineral potential of the area is based on recent discoveries in the Finlayson Lake area to the southeast, an area thought to juxtapose the Glenlyon area prior to displacement on the Tintina Fault. The study area lies at the limit of the Late Wisconsinan McConnell glaciation. Ice flow was largely directed by topography. Soil profiles reveal a veneer of White River ash and loess over most till deposits. Geochemical results from 285 till samples highlight new anomalies in gold, gold/arsenic (intrusive- and fault-related), copper (veins), copper/nickel (ultramafic rocks) and zinc (sedimentary-exhalative (SEDEX) and epithermal). An orientation survey was completed at the Clear Lake SEDEX deposit to evaluate the extent of glacial dispersion down-ice from mineralization.

A comprehensive stable isotope study of basal ice and debris layers in two Yukon surging glaciers suggests an isotopically variable basal freezing cycle. Trapridge and Backe glaciers, St. Elias Range, Yukon, have parallel basal debris layers that extend for hundreds of metres along marginal ice faces and in meltwater tunnels. Both glaciers are subpolar surging glaciers that surge on a cycle of 40-50 years. They are approximately 5 km long and 1 km wide with a lower ablation zone that is frozen to the bed and an upper accumulation zone that has basal ice at the pressure melting temperature.

Yukon Territory has been glaciated by Cordilleran and montane glaciers at various times throughout the Pleistocene, as well as by continental ice, the Laurentine Ice Sheet in the Late Pleistocene. Throughout the Late Cenozoic, each successive glaciation appears to have been less extensive than the previous one. In west-central Yukon the earliest glaciation occurred between 2.6 and 2.9 Ma. ago (Duk-Rodkin and Barendregt, 1997). This glaciation was the most extensive and formed a continuous carapace of ice covering all the mountain ranges, except for a small area of Dawson Range and a more extensive area in northern Yukon. The Mid Pleistocene Cordilleran glaciation was less extensive than older glaciations but it formed an extensive ice sheet covering most of the northern Cordillera. The Late Pleistocene glaciation was the most restrictive and formed a continuous carapace of ice from the continental divide to the Saint Elias Mountains, but only restricted ice caps formed on the Ogilvie Mountains. During the last glaciation, the Laurentide Ice Sheet, flowing from the east, reached the northeast part of the Yukon Territory ca. 30 ka ago. Distributed from [GeoYukon](https://yukon.ca/geoyukon) by the [Government of Yukon](https://yukon.ca/maps) . Discover more digital map data and interactive maps from Yukon's digital map data collection. For more information: [geomatics.help@yukon.ca](mailto:geomatics.help@yukon.ca)

for a copy of this paper please contact the Yukon Geological Survey; geology@gov.yk.ca.

Ice accumulations in the Coast Mountains of southwestern Yukon and the Cassiar Mountains of south-central Yukon during the late Wisconsinan were responsible for glaciation of the Whitehorse area. Cirques in the Coast Mountains likely supported the first glaciers that advanced out of the mountain valleys ahead of the more distal Cassiar accumulation. Glacial maximum is characterized by topographically unconstrained ice flow trending northwesterly over most of the map area. Ice thickness over the city of Whitehorse exceeded 1350 m during full glacial conditions. Deglaciation is characterized by frontal retreat punctuated by periods of dynamic equilibrium and readvances. Differential retreat of the Cassiar and Coast Mountain ice lobes enabled the Cassiar lobe to penetrate, and at times readvance, up-gradient into Coast Mountain valleys. This pattern of deglaciation created ice dams and a series of proglacial lakes that submerged valleys under as much as 300 m of meltwater.

The nature and extent of past glaciations are depicted on the glacial limits map of Yukon.

The physiography and glacial history of Yukon bear directly on the geological setting, grade and economic viability of Yukon placer deposits. The limits of several advances of the Cordilleran Ice Sheet are evident in south central Yukon in the form of deposits and ice-marginal features left successively southeast by retreat of the three main glacial episodes. The oldest, including multiple glaciations, was the pre-Reid at up to 3 Ma, succeeded by the Reid at up to 200 Ka, and the McConnell which ended approximately 10.3 Ka. Yukon placer deposits are grouped into five broad categories based on age, gemorphic and sedimentologic characteristics. These are 1) Pliocene to early Pleistocene alluvial placer deposits preserved as high level terraces buried beneath non-auriferous overburden; 2) Pleistocene non-glacial alluvial placer deposits that occur as valley-bottom fill and low to high level terraces in unglaciated terrain; 3) Interglacial placer deposits that occur as valley-bottom alluvial fill or low terraces in drainages that have escaped the effects of glacial erosion; 4) Glacial placer deposits that have formed when gold from regional bedrock or paleoplacer sources was incorporated into glacial drift; and 5) Recent placer deposits that are found as colluvial deposits, valley-bottom alluvial blankets in gulches and tributary valleys, bar deposits in major river systems and beach and nearshore marine deposits. Ten major regions produce placer gold in Yukon:: Indian River; Klondike; west Yukon (Sixtymile/Fortymile/Moosehorn); Lower Stewart; Clear Creek; Mayo; Dawson Range; Kluane; Livingstone and Whitehorse South. Since 1886, these areas have produced over 15 million crude ounces of placer gold, mainly from the unglaciated Klondike, west Yukon and Lower Stewart regions. Many areas in Yukon remain unexplored for new placer gold deposits, both in unglaciated and glaciated areas. Areas of exploration potental in unglaciated areas include abandoned channels, oxbows and point bars, high level terraces, and tributary gulch and creek placers. In and along the margins of glaciated areas, pre-glacial or interglacial placer deposits may lie buried by glacial and glaciofluvial drift. Lower-grade placer deposits may have formed by glaciofluvial reworking of pre-glacial or interglacial placers. Non-glacial placer deposits may be found unconformably overlying glacial drift. Deeply incised interglacial valleys oriented obliquely to paleo-ice flow directions are also favourable locations for the preservation of economic placer deposits in glaciated areas. Interest in exploring for new gold reserves has been sparked by new placer research and surficial mapping programs initiatied by the Yukon Geology Program and the Geological Survey of Canada. As this research continues to add to the understanding of placer gold deposits, exploration activity is expected to continue and new reserves in both unglaciated and glaciated areas may be found.

Preliminary investigation of surficial geology in northern Kluane Range has resulted in new interpretations of Pleistocene ice cover including extensive unglaciated terrain and restricted glaciation during the Last Glacial Maximum. Two glacial limits are identified: a higher limit recording the most extensive glaciation of the area; and a lower limit that records younger, less extensive glaciation. This paper describes Pleistocene limits of the Donjek Glacier and the distribution of surficial materials in the upper Quill, Maple, and Wade creek drainages. The source and transport mechanism of surface materials has particular significance for surficial geochemistry sampling programs and implications for mineral exploration are addressed.

Late Wisconsinan McConnell glaciation (ca. 24-11 ka) occurred in four phases in the Pelly Mountains of southern Yukon. Phase 1 marked the onset of ice accumulation in cirques above 1524 m above sea level (a.s.l.). These local glaciers expanded and fed valley glaciers that extended into the surrounding lowlands (after 26.3 ka). At glacial maximum or phase 2, the development of ice-divides to the east and south of the Pelly Mountains permitted Cordilleran ice lobes to invade the lesser glaciated Pelly Mountains, which resulted in up-valley ice-flow. This ice-flow arrangement continued into early deglaciation (phase 3), a period characterized by re-advances of the invading ice lobes. Following retreat of the ice lobes from the Pelly Mountains, some local cirque glaciers above 1600 m a.s.l. resumed limited down-valley flow (phase 4). For drift prospecting purposes, the dominant glacial dispersion trajectory in these high relief areas is controlled by the last phases of ice-flow (either phase 3 or 4).