A synthesis and analysis of information on inactive hardrock mine sites in Yukon and Northwest Territories: analysis and evaluation of environmental data, volume 1.

Abstract

In the Northwest Territories and the Yukon, mining has, for a long time, been a major industry. The resource industry continues to be a significant economic factor in the Canadian North, and due to increasing environmental awareness, the regulation of mining activities for the protection of the environment is an important issue of debate. In both territories, environmental concerns have been expressed at several lev- els about inactive or abandoned hard rock mining operations, some of which started operations as early as the beginning of the twentieth century, and in the 1930's to 1950's. Mining is associated with the production of waste materials (tailings and waste rock), which could affect, if they are not managed appropriately, the environmental quality in the vicinity of the mine site. It is possible that abandoned mine sites generate environmentally unacceptable conditions. Environmental degradation from past hard rock mining operations can be expected, but this is likely less significant than the environmental problems which may be caused by mine abandonment of both present and future operations, given the difference in scale between past and present activities. It is generally accepted that environmentally sound solutions have to be found for the management of wastes after cessation of the mining activities. Such solutions however, are particularly difficult to perceive in the absence of a technical evaluation of the long term environmental effects of mining wastes. The objective of this work was to obtain a perspective on the magnitude of potential environmental implications inherited from past hard rock (lode) operations. Geographical, historical and environmental data on 21 inactive mine sites in the Northwest Territories and 10 sites in the Yukon have been summarized and evaluated with respect to water quality objectives and metal concentrations reported for background ( 11 non mining environment 11 ) values for sediments and soils. Sites were selected for inclusion in the evaluation based on two criteria. One was that the site had been abandoned before 1983 and the other that the mine site was associated with a mill, i.e. producing tailings. However, inclusion of a site in this report carries no legal implications with respect to decommissioning of the property. Historical and geographical data about each site were assembled from open literature as well as other sources. Environmental data, consisting predominantly of elemental concentrations in water and sediments associated with the mine site and those in tailings, originated mainly from monitoring government and mining company files. In Volumes 11 and 111, historical and geographical information is presented for each mine site for the Northwest Territories and the Yukon, respectively. For each site, topographical maps, aerial and site photographs are associated with a fact sheet, which contains information about the history, geology, milling and tailings. Potential environmental concerns, based on this information, are identified. In Volume I, monitoring data from each site are organized into tables (hard copy and floppies Appendix to Vol. I) from which minimum and maximum concentrations of elements for each site were extracted. These values formed the basis on which the elements As, Cd, Cr, Co, Pb, Ni, Se, Ag , Zn and Hg were evaluated, comparing the concentrations to natural ranges reported for sediments and soils or water quality objectives set for the protection of aquatic life. Other elements (Al, Ba, Ca, Cl, Co, Fe, Mg, Mn, Mo, P, Na, S, Si, Th, Va, U) and physical parameters, (for example pH and electrical conductivity), were recorded and used as descriptive and comparative characteristics of the three environmental components (water, sediment and tailings) evaluated. Milling processes used and the environmental fate of milling reagents- is discussed in relation to long term environmental implications. In one mining operation (Discovery - NWT-5), mercury used in amalgamation is the only process reagent which might have contributed to some environmental degradation. Lead, arser)ic, mercury and cyanide, frequently evoke concerns in relation tomining wastes. These elements are discussed, with a focus on their environmental fate in the long term. The ranges of arsenic and lead concentrations found in the tailings, compared to those in soil, revealed that for both elements, the values generally reflect those of local mineralogy, since the elemental composition of the tailings differs only marginally from that of the host rock. Both arsenic and lead are natural constituents of the mine site environs. Mercury, on the other hand, when concentrations in the tailings are found to be elevated, may be present as a result of past milling practices. Cyanide used in the extraction of gold would be present in the environment of the inactive mine sites in the form of cyano-metal complexes, since these are persistent substances. Given its biological and photochemical degradation, cyanide can be considered an environmental concern strictly related to ongoing operations. For abandoned mine sites, therefore, it is a concern of the past. It was concluded that when local mineralogy and milling processes of the past are thoroughly considered, environmental concerns could not be substantiated by an exhaustive evaluation of available monitory data. Several characteristics, for example, acid generation, which are essential in determining potential environmental concerns relating to abandoned or to be abandoned mining wastes, were identified. The abandoned sites evaluated for both territories were categorized with respect to missing essential environmental information, i.e. where concerns could not be substantiated or refuted based solely on the available data. Conclusions and recommendations were formulated in conjunction with an evaluation of health concerns and safety considerations directly related to human health, such as site location with respect to public access, proximity to potable water supplies, as well as the absence or presence of essential environmental information. In summary, it was concluded, that severe environmental degradation could not be identified at any of the 31 sites in both territories where wastes have remained unattended over at least the past decade. For 5 sites, potential environmental concerns with respect to degradation of land/and or water quality appear warranted, and a focused investigation is recommended for Discovery, Ptarmigan and Thompson-Lundmark in the Northwest Territories, and for Mount Nansen and Venus in the Yukon. The essential components for such an investigation are outlined, with specific reference to that information necessary for a comprehensive assessment of the potential long term environmental concerns. Such information was often missing from the data available for this present study. The data base for inactive hard rock mining operations assembled here, was found to provide a technical basis on which criteria relevant to the development of suitable abandonment procedures for future hard rock mining operations in the Northwest Territories and the Yukon could be formulated. Surely an understanding of the environmental implications of past operations may provide the means for ensuring the future protection of the environment.