The Yukon Workers' Compensation Health and Safety Board says as many as 180 people may have been exposed to lead while cleaning up the former Sa Dena Hes mine.
The lead-zinc mine north of Watson Lake operated between 1991 and 1992. Remediation at the site started in 2013.
The project was issued a temporary stop work order in July after it received medical reports showing some of the workers had lead poisoning. It was originally reported that at least 10 workers had been contaminated.
But Richard Mostyn at the Workers' Compensation Board says many more may have been exposed.
"It's one of the largest occupational exposures we've had in the territory's history," says Mostyn. "Its going to be a long process."
2014 was not a good year for workplace safety in Yukon.
Mostyn says there were five workplace deaths during the year. That's the most workplace deaths the territory has had in a single year in over two decades, Mostyn says.
"That's far too many for a jurisdiction our size."
The deaths happened in separate incidents and across a range of industries including retail, trucking and mining.
Mostyn says the board investigates every death to try to find out how it happened and to try to prevent a re-occurrence.
There was about 1,700 reported workplace injuries in 2014 and a 10 per cent jump in claims (based on statistics available at the end of November). Mostyn says part of the increase in claims resulted from the workers exposed to lead at the mine site.
An injury counter outside the board's office in Whitehorse shows as of Friday morning there has been five reported workplace injuries in the territory.