So long, Robertson headframe: Yellowknife landmark comes down Saturday

Con Mine's Robertson headframe, the tallest structure in the Northwest Territories, will be levelled by a controlled explosion Saturday afternoon.

At 76 metres tall, the white and black mine shaft with a red top hat can't be missed from nearly any vantage point in Yellowknife.

Built in 1977, the headframe'sdays have been numbered since the closure of Con Mine in 2003, but the structure had several reprievesdue to public outcry and possible preservation options by the city of Yellowknife and the territorial government.

Ultimately, no one wanted to take on the liability.

But that doesn't mean people won't miss the headframeas an emblem of the city's gold mining past and a wayfinding landmark.

The public can't be on the mine site during demolition, but Miramar Northern Mining Ltd., a subsidiary of Newmont Mining, which owns the site, says people can get as close as Robertson Drive, which runs right in front of the property.

Demolition isscheduled for between 4:30 and 5:30 p.m. Saturday, just before dusk.

How will it happen?

The company hired to take down the headframe Rakowski Cartage and Wrecking has been preparing for Saturday's big blast for weeks now. That's included inspecting the building to make sure there isn't any hazardous waste leftover (all asbestos and arsenic were removed and buried by 2011).

Workers have also had to remove leftover equipment inside the building, as well as remove the steel sides and roof of the headframe, which was done Friday evening and Saturday morning.

Before the demolition of the headframe, workers will douse the structure and its surrounding area with water in order to control the dust from the explosion. There will also be water shoots installed around the headframe that will spout water about 10 metres in the air.

Then... BOOM.

What's in the dust

There is always a chance of contaminated waste being in the dust produced by a blast, according to John Sandlos, a Memorial University assistant professor who has studied the history of Giant Mine.

Up until the mid '80s, the Robertson headframewas insulated with asbestos. According to the hazardous waste documents from Miramar, the asbestos from every building on the Con Mine site was removed.

"Con Mine is now asbestos free, with completion of the last asbestos removal campaign at the lakeshore pumphouse in the first quarter of 2011," Miramar's hazardous waste plan says.

The mine also did use arsenic when processing its ore into gold, but in a different way from how it was used at Giant Mine. That mine's operationsleft behind237,000 tonnes of toxic arsenic trioxide dust buried underground.

At Con Mine, the arsenic was mixed with water to create a "sludge," which meant there was less residual arsenic dust that people could immediately breathe in.

The hazardous waste documents say there was anundisclosed amount of residual arsenic found in rocks on the site in 2009, but those rocks werepressure washed, buried by cleaned rocks and moved to the hazardous waste site on the mine property.

"No further arsenic-bearing hazardous wastes are expected to be encountered on site for disposal of at this facility," the document says.

Demolition crews plan to monitor the dust following the explosion Saturday and will continue to use water to suppress it.