Taseko Mines reported on November 5 that it had been advised by Knight Piésold that a negative environmental assessment by a Federal Review Panel of Taseko’s New Prosperity gold-copper project in southwestern British Columbia appeared to have relied on the wrong design in its analysis of seepage rates from the project’s tailings storage facility. On November 18, the company reported that it had complied with a November 13 request from the Canadian Environmental Assessment Agency (CEAA) to explain the company’s position that the panel had erred in its finding on the technical aspects of New Prosperity’s tailings seepage and water quality.

While the CEAA posted the request for information on its web site and acknowledged to Taseko receipt of letters dated November 8 to Canada’s Environmental Minister Leona Aglukkaq (15 pages) and November 15 to the CEAA (8 pages), it did not post these documents on the CEAA website. 

Taseko then posted the letters on the New Prosperity project website.

Taseko President and CEO Russell Hallbauer said, “We expect to be treated fairly and objectively in this process. Publicly requesting information and then choosing not to release the results of the request in a similar manner creates an inaccurate portrayal of Taseko and an impression in the minds of the public that our critique of the panel’s findings is somehow flawed. We have therefore posted the specific documents related to this matter to ensure that our shareholders, community stakeholders, and the general public are fully aware of the facts.”

The letters address in detail Taseko’s plans for the New Prosperity tailings storage facility.

The Federal Review Panel’s assessment of the New Prosperity tailings storage facility relied heavily on modeling by Natural Resources Canada (NRCan), indicating that seepage into Fish Lake from the facility would cause significant adverse effects on fish and fish habitat, wetlands, and aboriginal interest in the Fish Lake area. However, the NRCan design was not Taseko’s proposed design.

NRCan assumed that a low-permeability basin liner would not be included in the tailings storage facility and that seepage would readily leak into more pervious overburden and fractured bedrock. However, Taseko’s proposed tailings storage facility does include a continuous, low-permeability, compact soil liner to restrict such seepage losses. 

“Knight Piésold is one of the pre-eminent engineering firms in the world. Our other consultants on the project are similarly among the best in the world in their specific areas of discipline. NRCan and the panel have chosen to ignore the Taseko design for the tailings basin that has been developed and reviewed by these very experienced, reputable tailings dam engineering and construction experts,” Taseko stated in its November 5 press release.

In its November 15 letter to the CEAA, Taseko describes the panel’s error in failing to base its conclusions on Taseko’s proposed design as being “so outrageous as to be nearly unfathomable.”

The New Prosperity project is located 125 km southwest of Williams Lake, British Columbia. Taseko proposes to develop the project as a conventional open-pit mine and 70,000-mt/d concentrator producing an annual average of 247,000 oz/y of gold and 108 million lb/y of copper in concentrates over a 20-year mine life. The project also includes an approximately 125-km-long power transmission line corridor.

Taseko has been working on the current New Prosperity design since it began improving its design after the federal government initially rejected the project in 2010.