The Division Mountain area is underlain primarily by Jurassic to Cretaceous(?) sedimentary rocks of the Laberge Group and Tantalus Formation. The Laberge Group is divisible into the following informal units: the Richthofen, Nordenskiöld, Conglomerate, and Tanglefoot formations. The Tanglefoot, which comprises a large portion of the exposed strata at Division Mountain, is here subdivided into the lower and upper members. The lower member consists of quartz-rich sandstone, grit, polymicitic conglomerate and laminated siltstone. The upper member is coal-bearing and typified by white grit, sandstone, and carbonaceous shale. The overlying Tantalus Formation is characterized by thick packages of resistant chert pebble conglomerate with intercalated sandstone beds, which form local highlands at Cub, Corduroy, Division, and Vowel mountains. The strata at Division Mountain are folded into several upright, tight northwest-trending anticlines and synclines with amplitudes of 2 to 7 km. The folded strata are intruded by feldspar-hornblende andesite sills and dykes. Organic matter identified within coal and siltstone of the Tanglefoot and Tantalus formations consists of Type III and subordinate Type I kerogen, suggesting the material is largely gas-prone. A combination of thermal maturation indicators (vitrinite reflectance and Tmax ) suggests that the coal and related strata are in the early to late stages of thermal diagenesis. Samples of the underlying Richthofen formation contain Type III kerogen matured beyond the oil window. Local folding and thickening of the Tanglefoot and Tantalus strata, as well as local intrusions in the Tanglefoot, may play a key role in the determination of hydrocarbon potential of the Division Mountain area.

Coal was discovered in the Rock River Basin by Sulpetro Minerals Ltd. In July 1980, and five holes sunk to delimit coal occurrences in September 1981. Samples were collected from all five holes for palynologic analysis and the undisrupted core from three holes examined in the field to determine the depositional setting of the coal and provide a basis for evaluation of the coal potential of this area.

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Coal is found in Mississippian, Jurassic, Cretaceous and Tertiary non-marine sequences which underlie as much as 37,000 km² of the Yukon Territory (Long, 1985). However, very little of this vast area of potential coal-bearing rocks has been examined in any detail and the extent of coal deposits is largely unknown. Coal occurrences are known in seven areas: 1) in the Paleogene Amphitheatre Formation in the Kluane area; 2) within Jura-Cretaceous sedimentary rocks of the Laberge Group and Tantalus Formation deposited in the Whitehorse trough in the Carmacks, Braeburn and Whitehorse areas; 3) in Tertiary sedimentary rocks in the Dawson, Pelly River, Ross River and Watson Lake areas located in the Tintina Trench; 4) within Late Cretaceous sedimentary rocks in the Indian River area; 5) in Eocene sedimentary rocks of the Rock River Basin; 6) within the mid-Cretaceous to Tertiary strata of the Bonnet Plume basin; and 7) in Mississippian sedimentary rocks of the Kayak Formation in northern Yukon. Minor coal is also known to exist in Mississippian map unit Mo. (Norris, 1982) in the Snake River area; in the Neocomian "coal-bearing division" (Jeletzky, 1961; Norris, 1981) in the northern Richardson Mountains; in the Upper Cretaceous Moose Channel Formation in the northernmost Yukon; and within Paleocene Reindeer Formation in the Mackenzie Delta area. The Mississipian Mattson Formation, which hosts coal in the Northwest Territories, is known to occur in the southeastern Yukon, however no coal occurrences of any significance have been noted in the Yukon portion. This report is accompanied by a 1:2 000 000-scale Yukon Coal Inventory map including coal occurrences for the Yukon Territory.

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This is a product of the Gold and base metals–southeastern Yukon (Selwyn basin) project funded jointly by the Geo-mapping for Energy and Minerals (GEM) program of Natural Resources Canada, and the Yukon Geological Survey (Government of Yukon).

The Valley deposit is located in east-central Yukon, 367 km northeast of Whitehorse. In 2012, Golden Predator Mining Corp. originally sampled gold-mineralized quartz veins in outcrop at what is now known as the Valley deposit. Snowline Gold Corp. subsequently followed up on the mineralization through diamond drilling from 2021 to present. The Valley deposit is a reduced intrusion-related gold system characterized by sheeted quartzcarbonate veins hosting free gold and associated lead-bismuth-tellurium sulphides, within a multi-phase, reduced granodiorite intrusion. The phases of the intrusion are physically and chemically distinct, exhibiting the evolution of a magma over time. Gold mineralization is strongly associated with vein density, whereby vein densities of >10 veins per metre correlate with gold grades of >1 g/t. In June 2024, the initial mineral resource estimate defined an Indicated Mineral Resource of 76 Mt at 1.66 g/t Au for 4.05 Moz Au, and an Inferred Mineral Resource of 81 Mt at 1.25 g/t Au for 3.26 Moz Au using a 0.4 g/t Au cut-off grade (Burrell et al., 2024).

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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.