The following is reprinted from Beyond Borders, Barrick Gold's magazine of sustainable development. Click BarrickBeyondBorders.com to read other articles in the August 2015 issue.
ONTARIO - Visitors to the former David Bell mine near Marathon, Ontario, would never know that there used to be a mine there. Hundreds of saplings dot re-contoured areas, and it’s not uncommon to see black bears rummaging through reclaimed fields for tasty native grasses to snack on.
“This is a part of our commitment to our local stakeholders and the general public – to remediate the land back to what it was when we received it,” says Shane Hayes, mine closure co-ordinator at Barrick’s Hemlo operation, and part of the team that spearheaded the remediation.
The Hemlo property actually consists of three mines: David Bell, Williams and Golden Giant. Mining operations at David Bell ended in 2010, while operations at Golden Giant concluded in 2014.
Barrick was responsible for rehabilitating the David Bell mine and various areas of the former Golden Giant site. This involved removing the rock used to build the foundations for several facilities at the site, which had been excavated during the initial development of the mine – and some of it contained gold.
Rather than discard this material, Hemlo processed 30,000 tonnes of it and ended up recovering 1,000 oz of gold. In addition, the decision to process this material eliminated the risk of this sulphide-based rock producing acid rock drainage. (Acid rock drainage occurs when sulfide-based ore is exposed to air and water, which acidifies water.)
Because David Bell and Golden Giant were underground mines, equipment and materials stored below the surface were removed, and 13 access points to the surface were capped with large, heavy concrete blocks. Under the environmental team’s leadership, specialized contractors demolished the mine’s headframe and mill, and local contractors oversaw various earthwork projects such as laying down 50,000 tonnes of topsoil to begin re-seeding vegetation.
“We also received help from 75 grade eight students from the Pic River and Pic Mobert First Nation communities, and the towns of Manitouwadge and Marathon,” Hayes says. “They helped us plant more than 3,000 white spruce and jack pines last year.”
Each year for the past 10 years, approximately 80 students from these First Nations and other local communities have joined the environmental team to plant trees and support other remediation efforts. In that time, the students have helped plant 30,000 trees.
As part of the 2014 remediation efforts, the environmental team planted 1,400 white birch, willow and dogwood trees over areas that contained rocks that could generate metal accumulation in plants and trees. These trees, indigenous to the area, exhibit a process called “phytostabilization,” whereby metals in the soil that may be harmful to the tree are confined to the tree’s roots. This process “locks” these elements at the trees’ roots and ensures that these elements do not enter the food chain. In addition, these trees help prevent erosion.
An even more innovative approach to reclamation at Hemlo lies on the horizon.
“Because we don’t have a lot of topsoil in the Boreal forest where we’re located, we’re working with Laurentian University to develop technosol to grow these trees in,” says Jeremy Dart, Hemlo’s environmental superintendent.
Technosol is artificially created topsoil. In this case, the technosol is comprised of non acid generating rock from Hemlo and wood bark from a local wood mill that is ground and blended together. The project began three years ago at the David Bell site. Each year, two post graduate students and two professors have worked on improving the technosol for eventual use for tree growth.
Results at test plots have been positive so far, supporting the growth of grasses and mosses. Representatives from Hemlo will be meeting with government regulators later this year to determine whether the technosol can be included as part of the mine’s eventual closure plan and remediation strategy.
“We’re always looking to improve our environmental performance, and this is one of the many elements we’re looking at to enhance closure at the site,” says Andrew Baumen, general manager of Hemlo.
Hemlo’s environmental team will monitor the site for at least 10 years, examining soil, water and plant samples throughout that time. If results demonstrate that the environment is stable over that period, the mine property could be relinquished back to the Ontario government.