Planning for a mine’s closure—before it opens

The $2-billion open-pit copper-gold mine is located 95 kilometres west of Mackenzie, B.C.

by Tim Gardner

The advantage of designing and building a new mine these days is that companies can do so while striving for minimal impact on the surrounding environment.

That's what Thompson Creek Metals Company Inc. is trying to do as it constructs British Columbia's first major new metal mine in 15 years. The $2-billion Mount Milligan open-pit copper-gold mine, located 95 kilometres west of Mackenzie, is slated to start commercial production in the late summer of 2013. Its current expected lifespan is 22 years.

"One of the things, from the very beginning of the project, we've taken environmental design very seriously," said Wes Carson, former vice-president for the Mount Milligan project. "We actually started from kind of a closure plan and worked backwards from there. So we started with what we wanted the mine to look like at the end of its life and worked back from that to develop what our environmental plan needed to be."

The process

The benefit of constructing a new mine as opposed to adding to an existing one is that a company can integrate the latest environmentally friendly and cost-saving technologies into the entire operation. Also, Thompson Creek has almost 20 years of baseline data for reference material for its environmental plan, since the project was once approved under a previous owner in 1993, Carson said.

In addition to several environmental studies, mine designers have used community consultation in the mine's development. For example, the project's tailings storage facility location was changed after consultations with local communities and First Nations.

Finally, Mount Milligan's environmental superintendent, Andrew Chewter, is responsible for making sure the mine continues to comply with the roughly one dozen environmental permits that came into force after the mine was allowed to proceed in 2009.

In fact, Thompson Creek conducted a number of prescreening surveys at Mount Milligan prior to construction, including an archaeological impact assessment and wolverine, bear and fisher den surveys, to try to avoid disturbing existing areas of historical importance and wildlife habitat as much as possible. It also conducted native plant surveys to determine what kinds of plants need to be replanted at the mine site during its reclamation process.

Small footprint, zero discharge

An easy example of how the company plans to minimize Mount Milligan's environmental impact can be seen in the footprint of the mine itself. Its compact design will cover an area of less than five square kilometres, reducing potential risks to both fish and water resources.

Carson is also pleased Mount Milligan is being designed to be a zero-discharge facility. The goal is for all water used in mining operations to be continuously recycled on site so that no surface water should be discharged.

The former vice-president is also impressed with some of the energy-conservation measures that are to be introduced at Mount Milligan. For instance, the SAG mill will be outfitted with a wrap-around motor that will run off electromagnetic fields as opposed to a motor equipped with a gear. The new motor should be more power-efficient, run better and require less maintenance.

The truck fleet in the mine's open pit should also be more environmentally friendly than past fleets. Trucks will be equipped with on-board diagnostic systems to measure greenhouse gas emissions. They will also be equipped with software so a shovel filling a truck can automatically instruct it where to take the material.

Protecting the environment

Environmental best practices are also integrated into the company's project planning to protect water, air, land and wildlife. Chewter said just some of the tasks the five-person environmental department does are water-quality sampling—both groundwater and surface water—ambient dustfall sampling and environmental effects monitoring, such as benthic invertebrate sampling in a lake close to the mine's tailings storage facility. Benthic invertebrates are organisms that live in or on the bottom of water-body sediments and have no backbone.

Other initiatives to protect wildlife include a western toad relocation effort and a commitment to restrict certain activities during songbird nesting periods. Also, during summers the department runs a hydrology program to keep track of creek flows around the mine site and to determine how much water may be flowing into the tailings storage facility.

And as part of a fish habitat compensation plan to make up for construction of the tailings storage facility, the department has created an overwintering pond in a creek close to the mine in an area that was previously too shallow to allow fish to overwinter.

Environmental monitoring will continue on the project site after mining ends. A bond for the full cost of closure will be provided to the B.C. government before mining begins.

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