Natural Land Reclamation for Mineral Exploration Properties & Placer Mines in Yukon

The Canadian Environmental Assessment Act legislates that development activities requiring federal permits be assessed through environmental screening, and environmental impacts mitigated with existing technology. The implementation of Mining Land Use Regulations on mineral claims in Yukon will require routine environmental impact assessment within a permitting system. A database of known environmental impacts related to mineral exploration and placer mining will thus make the screening process more efficient. This particular project focuses on three different mining districts of Yukon, and provides information on soil, overburden, vegetation, slope stability, and permafrost conditions on disturbed and undisturbed surfaces related to mineral exploration and placer mining. Disturbances included in this study consist of trenches (dating from 1912 to 1993), drill pads (dating from 1967 to 1993), ripped and compacted surfaces associated with roads and camps, and placer mine highwalls and tailings piles (dating from 1911 to 1993). Observations include detailed vegetation description(tree, tall shrubs, low shrub, dwarf shrub, herb, graminoid, and mosses and lichens layers), soil texture and basic chemistry, slope, height, width and age of the trenches, elevation, aspect and latitude of the site, and description of any active processes such as slope erosion, permafrost degradation, failure, sheet erosion and gullying. The preferred sites and rates of natural revegetation by pioneer species were related to disturbance characteristics, such as trench orientation, surface compaction, and presence or absence of permafrost. Recommendations on site abandonment and treatment were formulated using analysis of the above data. Factors most important to the natural revegetation of sites were identified as elevation (alpine versus subalpine), at least 20 centimetres of soil with at least 20% fine-grained matrix, and stable slopes with angles of 45 degrees or less. Trench design, mixture of organic matter with the surface material, aspect and slope position of the disturbance are significant factors, but of lesser importance. Placer mined sites located in fine-grained, organic and ice-rich sites were found to reclaim both cuts and tailings successfully within five to ten years. The least intrusive approach to site reclamation is to abandon disturbances in a state such that natural colonization could take place within a few years, and the site re-integrated to its ecosystem within a reasonable period of time. However, in some cases, slopes will not reach stable profile without the help of surface vegetation. More aggressive revegetation procedures may then be required (contouring and/or seeding), especially when dealing with high alpine sites. A revegetation strategy should take into consideration the local ecosystem and plant succession. Species imported to the area should facilitate, not eliminate, the re-entry of local pioneer forb, grass and shrubs species. A program designed to test the optimum conditions for site abandonment could provide further information on physical requirement for physical design of abandoned features and possible seed/fertilizer mixtures in alpine and subalpine areas.