Heap leach pads are piles of mine-derived rock that is placed on a liner and flushed with solutions to liberate the gold, copper, or nickel in the rocks. At this link I have written extensively about the design, construction, operation, and closure of heap leach pads.

But I say nothing in the course about placing a “synthetic liner” over the pile at closure and reclamation. Yet here is a link to a story about the old Wood Gulch mine in Nevada where Barrick has done just that. Here are some extracts from the report:

Barrick returned to the site this summer to install the liner to prevent melting snow from traveling through the leach pad and picking up old cyanide solution at the small mine near Mountain City that hasn’t produced gold since the end of 1990. “We were still seeing a large volume of drain-down solution from the snow so we’re trying to cut off any more water from entering the pad,” she said.

Rory Lamp, a supervisory wildlife biologist for the Nevada Department of Wildlife, said the original concern at Wood Gulch was that contaminated water would reach a nearby stream, which could threaten the red band trout in Badger Creek. “They are trying to resolve that risk,” Lamp said.

Sierra Geosynthetic Services Inc. installed the special liner supplied by Agru and designed for better drainage. Logan Jensen of the engineering firm Knight Piesold said roughly 430,000 square feet of liner went on the pad. High Mark Construction worked to finish covering the liner with waste rock that will then be recovered with topsoil and reseeded. The company earlier removed topsoil on the pad, regraded and compacted the material so the liner could be laid and welded to an original liner under the pile of rock and ore.

Wood Gulch was a small mine, so the leach pad covers only 12 acres. The mine was the first and only one Homestake Mining Co. developed under a small mines division, Brito said. Barrick acquired Wood Gulch when it acquired Homestake in 2001. The mine started in mid-1988, closed for the 1988-89 winter, and went into continuous operation from April 1989 to November 1990. During operation, the mine produced 34,852 ounces of gold and 66,955 ounces of silver, according to Barrick. Reclamation began in 1991. The heap was rinsed in 1991 and 1992, and horizontal drains were drilled in 1993 before the pit highwall resloped, and the heap was covered with growth soil and seeded.

The interesting part of this story is how long it took after mine closure to decide they needed to reduce infiltration to the old, so-called, closed pile. You can almost hear the panic in the voice of the person talking to the reporter–also obviously a young and impressionable person who wrote the following:

She said the decision to install the liner over the Wood Gulch leach pad made sense for the location. “This is very site specific,” she said, adding that others in the mining industry were concerned the Barrick work would set a costly precedent. Modern mines place synthetic liner down before starting a heap leach pad or expanding an existing pad, but they cap the heaps with soil mixtures. Lamp said Nevada mines continue to learn from leach-pad closures, but Wood Gulch was reclaimed years ago. “We have 20 years of information now. It’s been a learning process as we go along,” he said. Brito said that while the synthetic liner topping a leach pad is a first for mining in Nevada, the liner has been used for projects elsewhere and is commonly used at landfills. “We borrowed the idea,” she said.

I would love to get details of how they intend in the long-term to keep the soil in place on the slopes over the “liner.” Sadly this report gives no indication of the type of geosynthetic used as a “liner,” so can make no inferences. I once put a layer of Claymax down as part of the top cover of a uranium mill tailings pile, but have never been able to persuade myself or any client to do likewise on the sideslopes of a mine waste facility. Maybe I will phone Logan Jensen of Knight Piesold, a consulting company that started life in South Africa as F.E. Kanthack, changed its name to Watermeyer, Legge, Piesold, and Uhlman, and then again to Knight Piesold.