November 2008    Print this article

Aldermac mine site restoration:
A $16.5 million project

Johanne Cyr,
Direction du développement et du milieu miniers

Restoration of the Aldermac mine site began in September 2008 and will continue over a two-year period. The total cost of the project is estimated at $16.5 million and will be financed by the gouvernement du Québec 's contaminated site restoration fund.

Firmly rooted in sustainable development principles, this project will help restore the site to its natural state and promote the creation of wildlife habitats.

History

Located 15 kilometers west of Rouyn-Noranda and 3 kilometers northeast of Arntfield, the Aldermac mine site is one of the most problematic abandoned1 mine sites in the Abitibi-Témiscamingue region.

The Aldermac property is named for two prospectors who first staked out the site in 1922 – 1923: W. Alderson and A.A. Mackay. Discovered in 1925, the Cu-Zn deposit was mined from 1932 to 1943 by two companies—Aldermac Mines Limited and Aldermac Copper Corporation Ltd. The first was dissolved on December 13, 1937 , and the second was liquidated in January 1946.

Average copper content varied from 1.47 to 1.65%, average silver content was 6.47 g/t, and average gold content 0.17 g/t. The concentrator produced 28,041 tons of copper, 10,675 ounces of gold, 389,100 ounces of silver, 63,753 tons of silica, and approximately 505,600 tons of pyrite.

Problems give rise to a major challenge

Characterization work and many studies have made it possible to clearly identify the environmental issues facing the Aldermac mine site. An estimated 1.5 Mt of mine tailings produced on the Aldermac site have resulted in acid mine drainage. Mine tailings deposited without any containment precautions now cover a 76 hectare area.

These mine tailings consist of approximately 50% sulfurous minerals and contain significant concentrations of arsenic, cadmium, copper, molybdenum, zinc, and sulfur. The sectors affected by acid mine drainage are Rivière Arnoux and its tributaries, lakes Arnoux and Dasserat, and areas adjacent to the mine tailings.

The major environmental damage caused by mining at this site requires considerable corrective measures. This site also represents an indirect public health risk, as the food chain has been affected (sport fishing). As none of the operators can be directed to restore or redevelop the site under the Mining Act, it is considered abandoned. MRNF was therefore forced to take responsibility.

In planning the Aldermac site restoration project, MRNF considered the following objectives:

Chosen solutions

The Aldermac mine site is located in a shallow valley running north-south and bordered by many rock outcrops to the east and an esker nearly 2 kilometers long to the west. A gravel mine is in operation at the southern tip of this esker. A watercourse drains the tailings site into Stream 1, which flows into Rivière Arnoux.

The tailings site starts in the south near the former mine facilities and extends 1,900 meters further north. It presents a 25 meter difference in level from south to north, and significant changes in elevation can be observed at the transitions between sectors.

A restoration approach has been chosen for each of the four distinct sectors of the Aldermac site:

South sector – impervious covering

The rugged south sector features zones of rock outcrops. It is located at the source of the tailings spill, upstream from the intermediate sector. The south sector has a significant proportion of the total volume of tailings, as well as various waste and debris associated with the former mine and concentrator buildings. The tailings layer is up to 6 meters thick at the former discharge point.

An impervious covering will be placed over a portion of the south sector. It will consist of a geomembrane, a protective geotextile, a layer of granular materials, and a topsoil horizon on steeper inclines. The eco-efficiency of such a system has been proven. This type of covering is highly effective in reducing the supply of water and oxygen, and preventing acid mine drainage. Waste and debris will be removed and disposed of in accordance with current environmental regulations.

Intermediate sector – excavation of sulfurous tailings

Tailings in the intermediate sector will be excavated and transported to the north sector. The terrain will then be limed and revegetated in harmony with the site environment. A water body will cover part of the intermediate sector after restoration. This efficacy of this method hinges on the complete removal of the source of the acid mine drainage.

North sector – saturation of sulfurous tailings

The north sector encompasses the bulk of the area to be restored—approximately 26.5 hectares. Most of the tailings there are already saturated due to the high groundwater level. This sector will remain a wetland developed on two terraces. Tailings will be covered with a granular material designed to maintain the water table near the surface while reducing runoff and evaporation. This method is effective in preventing tailing acidification and, consequently, acid mine drainage.

To establish a high groundwater level, existing dikes will be enhanced and new ones built. Agricultural lime will be added to the tailings surface to minimize the impact of the release of acids and heavy metals in any tailings deposits carried in from the intermediate sector and Stream 1. Special efforts will be made in landscaping this sector to ensure its integration into the environment and the return of wildlife.

Stream 1 – cleanup

The Stream 1 sector can be divided into two segments. The first runs south to north along a 700 meter stretch with a greater than 2% grade, while the second runs east to west over approximately 1.9 kilometers with an average grade of approximately 0.2% and includes a floodplain varying between 20 and 100 meters in width.

The tailings accumulated in the 2.6 kilometers of Stream 1 will be excavated and transported to the north sector. The terrain will then be limed and revegetated to obtain plant cover in tune with the site environment.

The restoration plan was designed by SNC LAVALIN Inc. in partnership with Journeaux, Bédard & Ass. and Écogénie Inc. The Norascon construction firm in Amos has been tasked with completing the site work.

References

SNC LAVALIN, Plan de restauration du site minier Aldermac, final report, October 2007.

Bédard, Isabelle, Techniques de réhabilitation des zones d'épanchement du parc à résidus miniers Aldermac, master's thesis; Civil, Geological, and Mineral Engineering Department, École Polytechnique de Montréal, September 2000.

CONSOR, Rapport de caractérisation – Parc à résidus miniers Aldermac, January 1995.

An inactive mine site is deemed "abandoned" when, under the Mining Act, no responsible party is able to restore it either because such parties no longer exist legally or no longer have the required financial resources.

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© Gouvernement du Québec, 2008