Current coal production is being stockpiled on site, and trucked and stored up at the Provincial Energy Ventures port in Sydney, Cape Breton, for export.
Citing delays in permits from the Greek government, the company said no additional investment would be made into the Olympias and Skouries projects or the Stratoni mine, which it acquired in 2012.
A preliminary economic assessment (PEA) of the Ekati mine in Canada's Northwest Territories has the iconic diamond operation staying open seven more years.
When the company's Pine Cove pit mine stops producing in about eight months, work will begin to turn it into a tailings storage facility with capacity of up to 7 million tonnes.
President John Magufuli has asked for a review of a local contract belonging to Petra Diamonds and ordered senior officials to resign over the outcome of a probe into the diamond and tanzanite sector.