June/July 2007

Engineering Exchange

AMEC – leaders in responsible practice

By H. Weldon

Victor construction site

AMEC is an international project management and services company that designs, delivers, and supports mining industrial and infrastructure projects worldwide. For more than a decade, AMEC has provided complete design services to virtually all of the world’s major mine developers and operators, as well as mid-sized mining companies, juniors, and lending institutions. Just about anywhere you find diamonds in Canada, you’ll find AMEC engineers.

AMEC has provided everything from exploration and testwork services, through to comprehensive engineering, procurement, and construction management (EPCM) and environmental services, for most of the diamond mines under development in Canada. AMEC was there when the very first Canadian diamonds were brought to the surface at BHP Billiton’s EKATI mine and, responsible for EPCM, played an integral role.

AMEC is currently providing EPCM services for the Victor Diamond project in Ontario under an alliance agreement with De Beers. Since the early exploration phase, AMEC’s earth and environmental specialists have played a key role in the approvals/permitting process, with the federal EA and three Provincial Class EAs completed without a hitch. Experienced individuals consulted with the First Nations communities, overcoming hurdles and paving the way to EA approval. The six AMEC employees from the Mississauga office involved in this aspect of the project earned the AMEC Spring 2004 Excellence in Client Service award. With AMEC’s assistance, the Victor project has provided employment for 600 people from First Nations and other northern Ontario communities during its construction phase.

Not just a diamond specialist

AMEC’s expertise extends beyond the diamond industry. Take the Pogo project, situated 85 miles southeast of Fairbanks, Alaska. Pogo posed many challenges as a greenfield underground mine and processing facility in a remote area of environmental sensitivity. Joint owners Teck Cominco and Sumitomo placed top priority on environmental stewardship for this project.

AMEC engineers successfully designed and oversaw the building of the Pogo project. By minimizing environmental impact, Pogo met its goals of addressing long-term land sustainability and maximizing acceptability by the Alaskan public.

One of Pogo’s notable design aspects is a surface gold mill for recovery through gravity concentration, flotation, and cyanide leaching. Compared to traditional whole ore leaching, applying a high gravity concentration effort followed by flotation reduces the amount of material to be leached by cyanide.

Keeping the environment in mind, AMEC paid special attention to water and waste management. An innovative tailings system eliminated the need for a tailings pond at Pogo. The waste is divided into two parts: material with any residual cyanide from processing, or potentially reactive, naturally occurring sulphides mixed with cement for disposal as low-permeability paste underground. The rest of the tailings material is filtered and dry-stacked in a surface storage facility. At the end of mine operations, the dry-stack tailings will be reclaimed, minimizing environmental impact.

The Goodpaster River passes directly through the Pogo property and is the natural drainage river for the site, posing yet another engineering challenge. AMEC used Monte Carlo simulation to determine the probability distributions of water flows in a project-specific water model. The model was used to estimate discharge rates and water quality under various conditions. Process water, mine water, surface water, and runoff, as well as dry-stack runoff, were all incorporated in the containment and treatment strategy. The gold plant maximizes the use of recycled water, drastically cutting down the need to add fresh water by using hose pumps instead of standard centrifugal slurry pumps. This technology has helped to reduce the amount of water requiring treatment and discharge.

The collection system for mine drainage, surface, and runoff water was designed to prevent untreated water from entering the Goodpaster River. All water first passes through the treatment facility that removes contaminants before discharging into the river. The facility includes a high-density sludge process to achieve enhanced co-precipitation of metals including arsenic; lime softening, and recarbonation to remove calcium and magnesium.

Plans are already in place for reclamation once operations cease at Pogo. It is intended to re-establish the designated post-mining land for wildlife habitat and recreation. This will be done by reclaiming and stabilizing any areas that have been disturbed by exploration activities, stabilizing and protecting soil from erosion by wind and water, and establishing long-term self-sustaining vegetation and minimizing long-term closure requirements. Re-establishing the wildlife habitat is expected to take five to fifteen years, first by stimulating the growth of early successional vegetation and stands of aspen. These will then provide a habitat for moose and other game, ruffed grouse, voles, and raptors.

The overall footprint of Pogo is  small by design. The mill and water treatment facilities have compact and space-efficient layouts, predominantly organized in a single narrow bench. AMEC has helped to ensure that Pogo’s legacy will be how many ounces of gold it produced in its mine life, not a story of what was left behind.

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