June/July 2010

Engineering Exchange

Expanding up: Increasing tailings capacity by adding new layers to an existing facility

By H. Ednie

East Lake tailings facility

Proposed layout of the East Lake tailings facility

Some problems are nice to have. Such is the case for Claude Resources’ Seabee Gold Project at Laonil Lake, Saskatchewan, where continued exploration success has resulted in a challenge to expand tailings facilities to meet the extended mine life capacity.

Seabee Mine entered production in 1991, with a planned mine life of three years. Now, almost 20 years later, it is still going strong, with no end in sight. The original tailings facility, designed for three years of operation, was modified in 1997 (including changes in the mill) to handle production up until 2004, at which point a new facility that would carry production through 2009 was designed and constructed.

However, with permitting underway (since obtained) at the Santoy 8 — another satellite gold deposit — combined with continued extension of reserves in the main Seabee Mine, the need for greater tailings capacity was imminent. Golder Associates helped with the permitting of the Santoy 7 satellite deposit and was retained again in 2007 to find options for another facility.

Finding the solution

Leon Botham, principal, Canadian mining sector leader for Golder Associates, says his team looked at a number of options to expand tailings capacity at Seabee. They investigated the local area for opportunities to build a new facility, but found nothing they deemed reasonable without using another lake, which was not ideal. No options were presented at an acceptable cost to meet the needed capacity.

So, the team returned to the existing tailings facilities and got creative. East Lake was part of the original construction and was filled to capacity in 2004. A second facility at Triangle Lake was nearly, but not quite, full. With creative juices flowing, Botham’s team turned their sights on expanding the Triangle Lake facility. Although the dams’ design required modification, it was the easier of the two to expand.

“The original dams are essentially concrete walls, which made it easier and less costly to raise the existing topography,” Botham explains. “We went from concrete walls to rockfill dams with geomembrane liners. By raising the structure, we were able to give three more years’ capacity to the Triangle Lake facility.”

At East Lake, there is high ground on the west side and dams all the way around the rest. The challenge was what to do with the existing topography on the west side. “We chose a method that had been used in other places, such as in eastern Canada, but never in Saskatchewan,” Botham says. “We will build rockfill dykes on top of the existing tailings. New tailings produced will be deposited in cells on top of the existing tailings facility and the water will flow down.” In the stacked tailings, the dykes will contain the solids, and the water from the tailings slurry will flow through the dykes to be collected in the existing pond.

In total, the two expansions will allow for about five and a half years’ additional tailings capacity for Seabee. Knowing the mine plan is most likely to extend beyond that, plans for a second Triangle Lake tailings facility expansion are already in place. Although this second expansion has not yet been permitted, the plan is to dam off an adjacent low lying area and use the same tailings stacking method employed at East Lake.

The first Triangle Lake and East Lake facilities expansions recently received regulatory approvals, with construction set to start when the snow melts. A remote camp, there is an ice road in the winter, but only fly-in access the rest of the year. Claude Resources will use their own on-site equipment to build the new tailings management structures.

During construction, the biggest challenge will be at the East Lake facility. “The tailings we’re building on are still saturated, so when we build on them, pore pressure will increase,” Botham says. “We’ll need to allow that pressure to dissipate as we go. So a key part is going to be getting the timing correct, by controlling the rate at which the fill is placed.”

Going forward, the plan is for the East Lake tailings facility to operate in the summer and the Triangle Lake facility in the winter. The objectives are to get both facilities built as quickly as possible and into use this year.

“This will be a demonstration project for the Saskatchewan regulators as the stacking method is new to the province and will show it does work safely,” Botham adds. “The success of the East Lake expansion will enable easier permitting for the second expansion of Triangle Lake.”

Permitting was a challenge, as the stacking method at the East Lake facility was new. It required a truly collaborative effort to keep the government informed. Botham says that Claude Resources Inc. and Golder Associates are a real team and worked as one to communicate with the government to ensure their proposal was well-understood.

“It’s been an educational project for me and an interesting challenge,” Botham adds. “It’s exciting — we’re not just looking at an additional five-year life, but we’re focused on the horizon, and we’ve identified how to keep going forward.”

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