CMT general manager Scot Clyde said the mine had received approval from WorkSafe Tasmania to restart development at the end of June and commence mining by late July.

"A new mining method is a significant change to mine design and operation, including the introduction of remote mining equipment and new technology to remove people from the risk of mud in-rush," he said.

"While this is good news for the bulk of our employees, the local community and suppliers, it will significantly reduce ore production over the next two years and unfortunately this requires fewer employees."

Roughly 303 employees of CMT and mining contractor Barminco have been on standby arrangements since February, with a mix of care and maintenance, redeployment to other sites and leave and standby wages.

In January a worker was killed in a mudslide at the mine and in December another two employees died after falling 35m from a maintenance platform in the mine's main shaft.

Clyde and Barminco CEO Peter Stokes said Mt Lyell would employ around 239 people.

They said around 64 positions would be affected across the operation and a further 24 were likely to be at risk in the new year.

CMT and Barminco said they would consult workers and unions over the next two weeks and retrenchment would be considered a last resort.

The companies are also working with the state government and other stakeholders on how they might be able to assist the mine and its employees.

CMT said it was undertaking exploration drilling and feasibility studies to help secure a long-term future for the mine.

"This is a major financial commitment by the company and buys time to develop the new resource to extend the life of the mine," Clyde said.

The historic mine, which began operations in 1896, was reopened by Copper Mines of Tasmania in 1995.

Previous operations involved a sub-level caving mining method with work being carried out at 1000m below the original surface of 600m below 0m.

Production before the closure was about 2.7 million tonnes per annum of ore at 1.25% copper grade.

Copper Mines of Tasmania is part of the Vedanta group of companies.