The production of acid rock drainage (ARD) from mine tailings is a significant environmental concern at various abandoned mine sites in Yukon. Leachate with low pH and high dissolved metals concentrations deriving from mine tailings impoundment areas can negatively impact various groundwater and surface water resources. The presence of both oxygen and water is required for ARD to develop. Therefore, the reduction of the oxygen source and the water source from the mine tailings through the use of a low permeability cover (which acts as an oxygen/infiltration barrier) will limit ARD production. This is the basis of the design and recent reclamation (1998-99) of the Arctic Gold and Silver Tailings Site in Carcross, Yukon that EBA has been involved with in association with PWGSC.

The effects of permafrost degradation in Yukon have serious negative implications for the structural integrity of vertical infrastructure. This is especially pertinent for critical buildings such as hospitals, schools, etc., in small communities that are situated on top of warm, ice-rich permafrost. Projections of mean annual air temperature over the next few decades, based on regional climatic models, indicate that air temperature will rise, hastening the thaw of permafrost. The combination of rising of air temperatures and buildings situated on warm permafrost has prompted this investigation into the vulnerability of Yukon Government vertical infrastructure. The application of DC resistivity and ground penetrating radar in conjunction with borehole drilling indicates that in Dawson there is warm ice-rich permafrost beneath the Palace Grand Theatre; the Old Territorial Administration building is underlain by primarily unfrozen sediment; and permafrost under the St. Andrew’s Church is characterized by high variability. A deep active layer was observed at Ross River School and geophysical surveys indicate that warm water drainage from the roof is contributing to the thaw of the underlying permafrost.

The presence and proper classification of permafrost is essential to mine planning, operation, and abandonment in the Yukon Territory. This paper discusses the current state of practice regarding permafrost delineation and classification, presents information regarding design and monitoring of structures on permafrost (with particular reference to mining), and includes examples of Yukon and other northern mines where permafrost has affected operations. Permafrost in the Yukon is particularly sensitive to disturbance, as it is generally ¿warm¿ and discontinuous. It is therefore extremely critical that planning for new mines include provisions for the proper classification of permafrost on the mine property, as it will directly affect operations and abandonment of the site, with corresponding financial implications.

Placer mining has over a one hundred year history in the Yukon Territory. The majority of placer mining has taken place in the zone of discontinuous permafrost. Within the discontinuous permafrost zone, vegetated valley flats and north-facing slopes generally are underlain with permafrost. The permafrost thickness is highly variable and may reach depths of 60 meters. The active layer covering the permafrost also varies greatly in thickness. To access gold bearing gravels, the removal of extensive quantities of overburden is usually required. Once this insulative cover is removed, the thermal equilibrium of the permafrost is disrupted and thawing occurs. This affects the stability of soils and vegetation and slope failure may occur. The extent that exposed permafrost melts depends partly on the amount and form of ice content. As melting progresses, the potential for mass movement of soil increases. Melting permafrost usually results in a wetter environment than was initially present, which further affects the natural revegetation process. Bioengineering is the use of living plant materials to perform engineering functions such as erosion control and stabilization of steep slopes. Although bioengineering methods are now commonly used in the stabilization of steep problem slopes in more moderate climates (Polster, 1997), experimentation with these techniques in areas underlain with permafrost is still required. Advantages of using bioengineering systems are that they can be installed without machine access (which in permafrost areas would disturb the site even more), they strengthen with age, and they are less expensive than traditional hard engineering practices.

This study investigated the natural attenuation of zinc in mine drainage at the Galkeno 300 mine site, located at the northern limit of the discontinuous permafrost zine in central Yukon Territory. The mine drainage contains ~150 mg/L Zn where it exits the mine; where these same waters enter the receiving environment of Christal Creek, the Zn concentrations have been reduced to ~2 mg/L. The research program examining this natural attenuation consisted of two phases. Phase 1 was comprised of a site investigation along with the collection of samples for chemical analyses and laboratory testing. Phase 2 consisted of laboratory characterisation and testing of samples collected during Phase 1. The Phase 1 site investigation was carried out during summer 2000. A climate station was established to monitor precipitation and temperature during the study period. Site water balance was monitored through the erection of two weirs; input exceeded outputs by and averages of 16%, indicating a minor degree of dilution. Water samples collected at sites along the longitudinal mine drainage flowpath showed no temporal trends, but clearly outlined a dramatic decrease in Zn concentrations with distance from the adit. Soil samples of upper organic and lower mineral horizons were collected from within and immediately adjacent to the flowpath. Chemical analysis of aliquots of these samples clearly showed elevation of Zn concentrations in samples in contact with mine drainage; upper organic horizons samples in particular were found to contain highly anamalous Zn levels. The Phase 2 laboratory investigation subjected the collected samples to physical and chemical characterisation, as well as batch adsorption testing and column leaching with synthetic and natural mine drainage. Batch adsorption tests showed the organic soils to have the highest Zn attenuation capacity; in particular, organic soils from the midpoint of the site (site C) were found to have the highest adsorptivity. Similar results were obtained in the column leaching and desorption test; organic samples from site C had both the highest Zn attenuation capacity and and the greatest degree of Zn retention under increasingly aggressive desorbing conditions. Selective extractions of the collected soils showed that the oxide fraction was the repository for much of the soil zinc. In the organic sils in particular, the oxide fraction dominates the geochemical fractionation of Zn in Galkeno 300 soils. High concentrations of Mn are removed form the mine drainage simultaneously with Zn; the coprecipitation of Mn-Zn oxides appears to be the dominant process of natural attenuation of Zn at the Galkeno 300 site.

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.

Reclamation testing was carried out on 3 mineral exploration sites in Yukon: an alpine site at the Red Ridge property in the Whitehorse area, and 2 subalpine sites, a boreal forest site at the Nucleus property in the Carmacks area, and a site in moist permafrost at the Hawk propeerty int he Dawson City area.

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.

Yukon’s northern oil and gas basins remained unglaciated during the Pleistocene. The absence of coarse aggregate material generated by glaciation, coupled with continuous permafrost, has required expensive programs of crushing and hauling bedrock for road and infrastructure development. This study examines fluvial deposits associated with the late-Pleistocene Eagle River meltwater channel as potential sources of aggregate for regional development. In particular, it applies a process-depositional model of meltwater channel development to understand the distribution and potential quality of aggregate resources in the area. We identify three zones with meltwater channel development: (i) an upper erosional zone (~ 50 km) of scoured bedrock associated with initial development of the channel; (ii) a middle zone (~ 35 km) of coarse deposition on high terraces associated with initial channel incision; and (iii) a lower zone (~ 75 km) dominated by fine lacustrine and deltaic deposits that likely overlie coarse fluvial deposits with up to 30 m of clay, silt and sand.

This report summarizes the results of geological mapping and preliminary petrological studies of an exposure of ultramafic rocks, the Buffalo Pitts Peridotite (BPP), in the eastern Dawson Range, central Yukon. The BPP is characterized by fresh spinel peridotite. Plagioclase mantles on spinel grains are interpreted to have developed during decompressive metamorphism during exhumation from sub-crustal depths to mid- to upper-crustal depths. The peridotite body forms a foliaform lens 580 m by 100 m that is enclosed in and intruded by leucocratic, biotite-garnet-corundum blue orthogneiss.The peridotite and blue corundum orthogneiss are in turn hosted in a north-dipping panel of amphibolite-grade metamorphic rocks that are included in the pericratonic Devono-Mississippian Wolverine Creek metamorphic suite, part of the Yukon-Tanana Terrane. Quartzite, quartz-mica schist and amphibolite with minor marble and calc-silicate units occur largely south of, and structurally beneath the peridotite body. Leucocratic tonalite gneiss, part of the ~357 Ma Selwyn Gneiss, occurs north of, and structurally above the BPP. Tonalite veins intrude the blue corundum orthogneiss and are interpreted as marginal intrusions of the Selwyn orthogneiss. Intrusion of dykes derived from the Selwyn Gneiss requires exhumation and emplacement of the BPP and the enclosing blue corundum orthogneiss in or prior to the earliest Mississippian.