Minto tackles water treatment problems

For the past two years, mines in Alaska and Northwest Canada have encountered problems with unusually large volumes of stormwater runoff or snowmelt during spring breakup, but it's too soon to determine if it is a trend.

This year, the Minto Mine just east of the Yukon River in west-central Yukon Territory, ran into troubles when excess water, over and above what could be contained in the mine's water storage pond, had to be diverted into its open pit during breakup in order to prevent a non-compliant discharge.

Capstone Mining Co. subsidiary Minto Explorations Ltd. operates the copper-gold-silver mine, which is located 240 kilometers, or 149 miles, north of Whitehorse.

Capstone said the diversion of water was anticipated in its 2009 budget, but the snowpack was greater than usual, resulting in more water being diverted into the open pit than planned. Minto received approvals from regulators to discharge the excess water.

During the emergency, Yukon environmental inspectors ordered the miner to dump about 750,000 cubic meters, or 198.1 million gallons, of water into Minto Creek and the Yukon River, when the wall of one of the mine's water storage pits partially collapsed due to melting permafrost.

Meeting requirements and more

The discharge upset environmental groups who immediately called for the mine to be closed until its wastewater system could be repaired.

Instead, Capstone developed a new water management plan for the mine with the aid of BioteQ Inc., a Vancouver, B.C.-based environmental technology firm, which it submitted to regulators in July 2009 along with an amended version that Yukon regulators are currently considering.

"The application should be public once (the Yukon Water Board and the Yukon Environmental and Socio-economic Assessment Board) have deemed it adequate," Quin told Mining News Oct. 20. He said the amended plan might be completed "in a month or so" but could not give a firm date because the regulators have raised additional questions.

Robert Holmes, director of the Mineral Resources Branch of Yukon Territory's Ministry of Energy, Mines and Resources, told Mining News Oct. 21 that Capstone and Minto Explorations, remained in compliance with their licenses throughout the period when they were dealing with the water problems.

"I would even say that they utilized best practices to go beyond their license requirements in order to minimize any risk to the environment. Planning, environmental assessment and licensing updates are planned to occur over this winter to prevent a similar event from occurring again," Holmes said.

Water treatment guarantee

Capstone said its plan incorporates a new onsite water-handling network to minimize interaction of unaffected water with water affected by mining operations.

In addition to helping to assess long-term water treatment options for the site, BioteQ provided water treatment services for the 2009 season, treating water containing suspended solids and dissolved metals. Water treatment operations are seasonal, typically from May to October.

Capstone also hired Bioteq to install a water treatment plant at the mine that will treat 4,000 cubic meters, or 1.1 million gallons, of water a day. The project will cost C$4.9 million in 2009 (for pumps, piping and water treatment plant fabrications) and another C$1 million in 2010 (for additional piping and water treatment plant commissioning). The miner said the investment is intended to eliminate the need for one-off discharge approvals. BioteQ is guaranteeing that water coming out of the Minto mine will meet environmental standards.

Capstone President Stephen Quin told reporters Oct. 8 that the new water treatment plant will handle significantly larger volumes of water with the aim to treat any water that comes into the system and be able to discharge it.

The plant will employ BioteQ's sulphide treatment process to meet extremely low concentrations of metals in treated water that is discharged into the environment. The process also is expected to deliver lower life-cycle costs for water treatment compared to alternative processes.