Cleaning up historic tailings sites can’t be done with a one-solution-fits-all approach, especially for Goldcorp Inc.’s Porcupine properties in Timmins.
When the company took over 100 per cent ownership of the properties from Kinross Gold Corporation in 2007, it was left with 30 historic tailings areas and 20 mine sites, totalling more than 30,000 hectares.During a June 10 Ontario Land Reclamation Symposium field trip, Goldcorp environmental manager László Götz and strategic development officer Dave Bucar took more than 80 participants on a tour of the company’s land reclamation projects.
Coniaurum project
The company’s most recent success story was the Coniaurum mine tailings reclamation project, completed in 2008 and winner of a Timmins Chamber of Commerce Nova Business Excellence Award. This former underground gold mine produced one million ounces of gold from approximately 4.2 million tons of ore. Erosion concerns resulted in excavation of the benign tailings, which were reinforced and contoured with proper drainage systems added to prevent further erosion. Biosolids from the Abitibi Bowater pulp and paper mill in Iroquois Falls were placed on top and seeded with various grasses. Now, lush grassy fields abound as far as the eye can see.
The Porcupine mining camp was host to numerous gold mines during the last century. Past practices did not call for closure plans and reclamation work. Under current legislation, liability defaults to the new owner. After performing an environmental risk assessment of its properties, Goldcorp decided on three priorities: the Hollinger tailings and McIntyre Concentrate Dump, the Delnite tailings and the Broulan Reef tailings site.
Hollinger/McIntyre tailings
Bucar described the Hollinger and McIntyre tailings areas as a “complex system” due to the acidic nature of the tailings and erosion issues. The two sites are located in the middle of the city, are highly visible and the subject of social and environmental concerns. A volunteer group called the Porcupine Watchful Eye is in monthly communication with company representatives, promoting greater transparency in the company’s operations and reclamation efforts.
The site has been studied for closure over a nine-year period. Both mines had been in production since the early 1900s and collectively produced more than 30 million ounces of gold throughout the 20th century, according to Ann Wilson’s presentation: A Century of Mining in the Porcupine Camp.
During the Hollinger Mine’s life, tailings were deposited in Gilles Lake, which is now one-third its original size. Later, Highway 655 was built over part of it. Further upstream, highly acidic tailings from the McIntyre site were deposited into land depressions over a 60-year span, resulting in acid rock drainage and metals leaching into the ground and draining into the Hollinger tailings.
Approach
Other past issues were a series of storm and flooding events that occurred in the early 1960s. Tailings dams were breached, causing them to wash downstream. A number of walking and biking trails now exist where the tailings migrated. Consequently, the company is taking a “downstream-up approach” to clean up the migrated tailings and return them to the Hollinger tailings pond, which will ultimately be placed under a water cover.
“We probably own about half of the surface rights through the tailings and downstream areas,” Bucar said. “A lot of it is relocation of tailings and addressing erosion conditions in the event of a major storm event. We want to ensure we can convey water off the site in an appropriate manner and discontinue the erosion that carries the tailings downstream. One of the major environmental concerns is the low pH of the water and the metals that are leaching out. So we’re trying a combination of things to contain the tailings and manage the water quality.”
The clean-up has already begun and will continue in two phases over a four to five year period. Phase one consists of retrieving downstream tailings and designing engineered channels to control water flow off the site properly. Phase two will focus on the relocation of the downstream tailings and the McIntyre Concentrate Dump tailings underwater into the tailings pond. By using a water cover, oxygen is reduced along with the acid generation. All of the tailings going into the pond will be treated with lime, and the water leaving the pond will be treated until it meets discharge targets.
Final costs were not determined as of July when the project was put out to tender. However, Bucar estimates it will be more than $10 million.
“Over the next couple of years, people will see dramatic changes to the landscape, which is a good thing,” Bucar said.
The other two properties receiving immediate attention are the Delnite and Broulan Reef tailings areas.
Delnite tailings
The Delnite tailings site is a result of almost 30 years of mining during the mid-20th Century. The Delnite Mine produced just shy of one million ounces of gold, leaving about three million cubic metres of tailings over 27 hectares. It was moved up on the list of priorities due to concerns about arsenic leaching and excessive dust that were voiced by community members from the nearby Delnite subdivision. The underground mine ran from 1937 to 1964 and resulted in the milling of 3.8 million tons of ore. It later reopened in the ‘80s and operated for one year.
The Delnite orebody contains arsenopyrite, a naturally occurring mineral prominent in that area. However, it is slowly releasing its arsenic content out of the tailings mass to nearby surface and ground water sources.
A meeting in 2007 with Delnite subdivision residents led to a temporary, voluntary plan to address their most urgent concerns. This involved keeping children and house pets away from ponded water, improving the safety of the steep south dam, more sampling, monitoring and ground water studies, as well as a human health risk assessment, which had not been received at the time of the interview.
“The tailings site had a different look a year ago,” Götz said. “It had some steep faces, not vegetated or controlled. The tailings could be easily washed away by rain.”
Also, agricultural crops were grown on some test plots to determine whether or not they would stop the arsenic leaching.
“Several years ago, we formed a consortium with government, different mining companies and Laurentian University to study the possibility of growing biofuel-type plants on top of tailings that would have been enhanced with the pulp and paper biosolids.”
Götz said the scientists wanted to see how the crops behaved in different types of tailings. Unfortunately, with one-metre thick biosolids placed on top (to yield the best biofuel crops), tests showed the arsenic leaching was accelerated. Since the symposium, Götz has received calls from various consultants suggesting a thinner layer of biosolids would stop the leaching problem. Presently, he is waiting for more information on the topic. Requests for quotes were sent out in early July to ascertain final solutions to close out this site.
The company’s third priority is the 23-hectare Broulan Reef property. Deacon towers to regulate water flow stand like sentries among 2.3 million cubic metres of tailings. Off in the distance, the old head frame marks the horizon, awaiting its buyer to dismantle and remove it from the property.
Götz said the mine operated for 50 years beginning in 1915 and produced 240,660 ounces of gold. In 1951, the Broulan Reef mill processed ore from the Broulan, Monetal, Reef and Bonwhit operations, resulting in 2.1 million tons of ore milled. In 1966, the mill undertook a contract with Kam-Kotia and Texasgulf’s Kidd Creek Mine to process silver-lead-zinc ore on a trial basis. This resulted in 110,000 tons of copper-lead-zinc tailings, highly sulphidic in nature being deposited in the Broulan Reef. These tailings were deposited at the end of the mill’s life and left exposed to oxidize, resulting in acid generation on the site.
Environmentally, it is a hot spot, but no one lives near the site, making it third on the list of risk assessment priorities for clean-up.
“There will be some fancy engineering required there to have it closed,” Götz said. After the risk assessment last fall, Goldcorp budgeted money to have the engineering completed so negotiations and consultations with the government, Ministry of Environment and Ministry of Northern Development, Mines and Forestry, the Delnite residents, the City of Timmins, Aboriginal people and other interested parties could begin in order to obtain permits to close it down. Requests for quotes were sent out in early July to begin rehabilitation of the site.
