TAILINGS MANAGEMENT AT THE IRON MINE OF MOUNT WRIGHT

Frédéric Choquet, David Bédard, Desheng Deng, Claude Bédard, Serge Thériault, Sébastien Moreau

In the proceedings of: GeoQuébec 2015: 68th Canadian Geotechnical Conference & 7th Canadian Permafrost Conference

Session: Uncertainty, Reliability, and Risk / Incertitude, fiabilité, et risque

ABSTRACT: The tailings storage facility (TSF) of the Mount Wright mine, a property of ArcelorMittal Mining Canada, has been active since 1976. It is located in the Fermont area and spreads across 15 km² which makes it one of the largest impoundments in North America. Tailings are more than 100 m thick in some areas. The tailings deposition rate has been greater than 30 Mm³ per year since 2014. Different methods are used to raise the eight kilometers of dams that confine the tailings. This paper discusses the choice of the appropriate raising method depending on the site conditions, the environmental constraints and the borrow materials available. It also introduces the systems implemented to monitor the structures. Indeed for some of them have been monitored for 25 years.

RÉSUMÉ: Le parc à résidus de la mine du Mt-Wright, actif depuis 1976, est opéré par ArcelorMittal Exploitation Minière. Situé dans la région de Fermont sa superficie de 15 km² en fait l™un des plus grands en Amérique du Nord. L™accumulation de résidus atteint par endroit plus de 100 m d™épaisseur. Depuis 2014, le parc accueille près de 30 Mm³ de résidus par an. Plusieurs méthodes de construction de digues et de barrages de parc à résidus sont utilisées pour ériger les huit kilomètres d™ouvrages de retenu qui ceinturent le parc. L™article présente le choix des différentes méthodes de construction ou de rehaussement des digues et barrages en fonction des conditions du terrain, des contraintes environnementales et de la disponibilité des matériaux de construction. Il introduit les différents systèmes de suivi des ouvrages. En effet, certains la banque de données pour certains d™entre eux couvre plus de 25 ans. 1 SITE PRESENTATION The tailings storage facility of the Mt-Wright mine, a property of ArcelorMittal Mining Canada, has been active since 1976. The Mt-Wright mine site is located in the area of Fermont, north of the 53rdThe following paragraph describes the main features of the TSF. The circled number written after the name refers to Figure 1. parallel within 50 km of the border with the Province of Newfoundland and Labrador. The climate is subarctic, with an average snow fall equivalent to 344 mm of water per year and an average rainfall of 586 mm per year. The mine produces about 24 Mt of iron concentrate per year and generates 44 Mt of tailings per year. The tailings are slurried and pumped from the mills (1) to the south-east corner of the TSF (2). Sediments settle as the slurry progresses westward. At the west end of the TSF lies a sedimentation pond named Hesse Nord (3), with an average capacity of 12 Mm³. The pond is delineated by two dams named Dam A (4) and dam Hesse 4 (5). A control structure has been built in the dam Hesse 4 (5). It allows the TSF operator to control the water level of the pond.Waters passes through Hesse 4 decant structure (5) and is brought into the process water pond named Hesse Centre (6) through the process water channel (7). From Hesse Centre (6), water is pumped back to the plant (1). As required by law, more than 90% of the water is recycled. Over a year, the water balance is in excess and a treatment plant (8) is required to keep the water level within the safety range. The treated water goes into the polishing pond named Hesse South (9) before being released into the local watershed through the final effluent (10). Figure 1: Overall presentation of the TSF features a b c

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