|Title||Optimizing remediation of gold mine tailings in Nova Scotia|
|Author||Parsons, M B; Jamieson, H E; DeSisto, S L; Kavalench, J|
|Source||Nova Scotia Department of Natural Resources, Mineral Resources Branch, Report 2010-2, 2010 p. 19|
|Links||Online - En ligne|
|Links||Historic Gold Mines Advisory Committee|
|Alt Series||Earth Sciences Sector, Contribution Series 20100255|
|Meeting||Geology Matters 2010, Nova Scotia Department of Natural Resources Open House; Halifax; CA; October 25-26, 2010|
|Media||paper; on-line; digital|
|Subjects||environmental geology; hydrogeology; Health and Safety; tailings; tailings disposal; tailings analyses; tailings geochemistry; waste disposal; groundwater; groundwater pollution; heavy metals
contamination; arsenic; human health|
|Program||Program management and Transition Activities, Environmental Geoscience|
|Abstract||In recent years, Canadians have demonstrated an increased awareness of the potential impacts of mining activity on environmental and human health. This has led to more stringent regulations, and
technological development supporting environmental stewardship and improved remediation within the mining sector. Establishing acceptable environmental solutions for active and past-producing mine sites has become imperative to meet both public
expectations and international scrutiny. However, there remain significant gaps in our understanding of the long-term behaviour of mine wastes and uncertainty regarding the most appropriate strategies to monitor the success of remediation efforts.
Recent studies of historical gold districts throughout the Meguma Supergroup in Nova Scotia have identified several areas where exposure to mine wastes may represent a potential risk to ecosystem and human health. Arsenopyrite (FeAsS) occurs
naturally in the ore and surrounding bedrock in these gold deposits, and was concentrated in the tailings during milling operations. In 2005, the Province of Nova Scotia established the Historic Gold Mines Advisory Committee, consisting of five
provincial and five federal departments (http://www.gov.ns.ca/nse/contaminatedsites/ goldmines.asp), to examine these risks in more detail. Since that time, detailed studies have been carried out to examine the concentration, chemical form and
bioaccessibility of arsenic (As) in tailings, airborne particulates and forest soils near these sites. The results have clarified the spatial extent of mine tailings, the mineral hosts for As, and the fate of windblown tailings dusts. Environmental
assessments have also been completed at two mines (Montague and Goldenville) where dusty, high-As tailings are located close to residential areas and are used for recreational activities (e.g. off-road vehicle racing).
In 2008, Natural Resources
Canada partnered with Queen's University, Trent University, the University of Ottawa, AMEC, SRK Consulting, and Nova Scotia Environment to develop optimized remediation methods for arsenic-rich gold mine tailings. Remediation strategies for mine
wastes at publicly accessible sites like those in Nova Scotia typically employ clean soil covers to reduce human exposure and dust generation. However, burying the tailings under soil may trigger dissolution of some As-bearing minerals and lead to
accelerated release of As to local streams and groundwater. Other conventional tailings remediation designs such as flooding, removal or fencing are also problematic because of the high solubility of some As minerals, dust hazards, expenses
associated with removal, and community desire to maintain site access. The present study is using laboratory experiments and field tests to investigate the biogeochemical stability of different tailings types to design the best plan to protect
downstream surface waters and groundwaters and reduce risks to human health.
Preliminary results show that the mobility of As under various cover scenarios is strongly controlled by the mineral hosts for As in the tailings. When leached with
natural rainwater, highly weathered tailings containing secondary minerals such as scorodite (FeAsO4·2H2O) produce acidic drainage (pH ~ 2.5) with high As concentrations. In contrast, weathered tailings with relatively high Ca/As ratios and Ca-Fe
arsenates such as yukonite (Ca7Fe12(AsO4)10(OH)20·15H2O) produce leachates with near-neutral pH values and moderate As concentrations. Tailings containing As mainly as arsenopyrite oxidized within six months to generate acidic leachates (pH < 3) with
extremely high concentrations of As. These results will be combined with data from ongoing field and laboratory tests to provide experimentally tested remediation options applicable to active and abandoned lode gold mines across Canada.