New mineral discoveries in the Dawson Range have been heavily supported by soil geochemistry. The use of soil augers to penetrate through loess-rich units and into locally derived weathered bedrock has been important in the successful application of this technique. To assist the mineral exploration industry, we characterized the surficial geology, soils and permafrost of the northern Dawson Range. Mapping indicated that widespread loess is present in the study area and the thickest deposits are located in basins on the south side of the Dawson Range near the Donjek and White rivers. A mantle of weathered bedrock covers virtually the entire landscape. The texture of fluvial deposits is affected by stream order and base level changes along the Yukon River. By understanding the effects of slope, aspect, elevation and permafrost processes on surficial materials, a landscape model can be developed that will facilitate geochemical exploration and mineral development in the region.

Results of surficial geology investigations in Wellesley basin and the Nisling Range can be summarized into four main highlights, which have implications for exploration, development and infrastructure in the region: 1) in contrast to previous glacial-limit mapping for the St. Elias Mountains lobe, no evidence for the late Pliocene/early Pleistocene pre-Reid glacial limits was found in the study area; 2) placer potential was identified along the Reid glacial limit where a significant drainage diversion occurred for Grayling Creek; 3) widespread permafrost was encountered in the study area including near-continuous veneers of sheet-wash; and 4) a monitoring program was initiated at a recently active landslide which has potential to develop into a catastrophic failure that could damage the White River bridge on the Alaska Highway.

Quaternary geology investigations in the Coal River map sheet (NTS 95D) during the 2009 field season focused on characterizing surficial materials and their distributions, with attention to the eastern half of the map sheet which has not been previously mapped. Moraine deposits are relatively thin in valley bottoms (<2 m) and become thinner and more intensely colluviated on upland surfaces. Streamlined glacial landforms and till plains are pronounced in the southern half of the map sheet. Surficial deposits are limited in many east-trending meltwater canyons, and in the northeastern corner of the map sheet. The map area was glaciated most recently by the Cordilleran Ice Sheet, which advanced from the south and west. Meltwater from montane glaciers and the Laurentide Ice Sheet in adjacent map sheets likely contributed to extensive glaciolacustrine, glaciofluvial and glaciodeltaic deposits in north-trending valleys that were dammed by the Cordilleran Ice Sheet.

The McQuesten River region in the northern part of the McQuesten and Mayo map areas (scale 1:250 000) is underlain by Upper Proterozoic to Mississippian rocks that were deposited in an offshelf setting during the formation of the northern Cordilleran continental margin, deformed during the Mesozoic, and intruded by pre and post-kinematic intrusions. The Selwyn Basin phase of evolution of the continental margin is represented by rock units that correlate with units defined in the eastern part of Selwyn Basin. Dark clastic and rare felsic metavolcanic rocks of the Deconian-Mississippian Earn Group unconformably overlie rocks of the Selwyn Basin phase and are overlain conformably by the Mississippian Keno Hill quartzite. Dark, fine-grained metaclastic rocks of unknown age locally overlie Keno Hill quartzite. Four episodes of plutonism can be distinguished in the area, the earliest probably Early Paleozoic in age, another mid-Triassic in age, and two phases of Cretaceous granitic magmatism. Early Paleozoic bodies are typically metre-scale, fine-grained diabasic dikes and sills intruding rocks of the Hyland Group. Mid-Triassic diorite to gabbro occurs in discontinuous pods of various sizes, primarily in the Tombstone Thrust sheet where they intrude Devonian and Mississippian rocks. The most voluminous and widespread granitic rocks are the early Late Cretaceous Tombstone intrusions (92 ± 2 Ma). Typical Tombstone intrusions are weakly porphyritic, medium-grained hornblende-biotite granite to granodiorite, but they range from syenite to granodiorite and are locally peraluminous. The latest episode of granitic magmatism, the 65 ± 3 Ma McQuesten intrustions, is not yet fully delineated but includes five stocks of peroluminous potassium feldspar megocrystic granite. Paleozoic and Mesozoic structures occur in the region. The Sprague Creek Fault, a pre-Late Cambrian normal fault, is inferred from stratigraphic relationships. A possibly Jurassic phase of shortening is represented by west-northwest-trending, south-vergent folds that pre-date Jura-Cretaceous structures. The most pervasive and important phase of deformation is Jura-Cretaceous in age and kinematically complex. The Robert Service and Tombstone thrusts and Tombstone Strain Zone formed between the Late Jurassic and early Late Cretaceous during northward and northwestward displacement of more southerly hanging wall rocks. The McQuesten River region has numerous mineral occurrences, a long history of mining and mineral exploration and good potential for further discoveries.

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.

Surficial geological mapping in the central Kluane Ranges was undertaken to better understand the distribution and character of surficial materials. Upland surficial materials in the area are dominated by near-source bedrock derivatives. Valley bottom settings, including Shakwak trench and Duke River valley, are characterized by broad open valleys with thick deposits of Quaternary sediment. Permafrost is discontinuous in the study area and its character is affected by slope and aspect, topography and material texture. Mass wasting processes in the study area include rockfall and avalanches, debris flows, debris avalanches and active layer detachment slides. The distribution and character of surficial materials are significant for soil geochemical sampling programs, mineral exploration, infrastructure and development.

An integrated bedrock mapping and regional soil sampling program in the Mount Mervyn map area (106C/04) was undertaken in 2010. It is the first year of a multi-year initiative called the South Wernecke mapping project (SWP), which will cover ten 1:50K map sheets in the southern Wernecke Mountains area in central Yukon. Field work in the first year served to highlight the complexities of the bedrock geology in the region, and identify areas of mineral potential. The Mount Mervyn map sheet is underlain by Proterozoic and Paleozoic siliciclastic and carbonate rocks that have been deformed into an east-trending fold-and-thrust belt. Regional soil geochemical data coupled with bedrock observations highlight new areas of mineral potential (i.e., Ni and Au) that have not been previously identified.

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Surficial geological mapping in the central Kluane Ranges was undertaken to better understand the distribution and character of surficial materials. Upland surficial materials in the area are dominated by near-source bedrock derivatives. Valley bottom settings, including Shakwak trench and Duke River valley, are characterized by broad open valleys with thick deposits of Quaternary sediment. Permafrost is discontinuous in the study area and its character is affected by slope and aspect, topography and material texture. Mass wasting processes in the study area include rock fall and avalanches, debris flows and avalanches and active layer detachment slides. The distribution and character of surficial materials has significance for soil geochemical sampling programs and infrastructure and implications for mineral exploration and developments are addressed.

This summary of geological studies in the Mt. Hundere area of central Watson Lake map sheet was undertaken as part of a Master's thesis completed at Queen's University in 1977. Mapping of the area was extended in August 1978. This report presents the results of the most recent mapping.