Underground mining in the area has a long history and was largely carried out by the Cape Breton Development Corporation, or Devco, a Federal Crown Corporation formed by an Act of Parliament in 1967.

The Donkin block is located in the Sydney Coalfield in Eastern Canada which contains 12 major coal seams ranging in thickness from 0.9 meters to 2.1m. Eleven seams have been mined historically and the resource block lies adjacent to the eastern boundary of prior underground mining operations.

Donkin is the most eastern extension of the coalfield that is accessible from the north coast of Cape Breton and is the last primary block of un-mined coal accessible from the coast.

Underground mining operations in the Sydney coalfield last took place in 2001 when the last operating mine closed. When Devco stopped coal mining it surrendered the mineral rights to areas it previously held. Most of the mining was conducted by room and pillar and longwall methods.

During the late 1970s and 1980s, Devco spent C$100 million evaluating the mining potential of the Donkin Coal Resource Block. Two exploratory tunnels were driven down to the coal seams beneath the sea floor and extensive exploration was carried out to define the coal resource, access the coal deposit, and evaluate potential mining operations.

Mining production was put off as the price of coal fell and markets for Cape Breton’s high-sulphur coal failed to materialize.

The tunnels, one of which is four kilometres long, were left to flood.

In December the Department of Natural Resources called for proposals from interested parties to make submissions for the exploration and development of the Donkin resource block.

Exploiting the Donkin resource will require undersea mining operations which have a long history of success in the Cape Breton area.

But the Department of Natural Resources warned developing a coal deposit for undersea mining operations posed unique challenges. Conventional surface borehole drilling for exploration for example, is impossible. Drilling by drill ship is difficult and expensive, and sterilizes a significant block of coal within the coal seam making it unmineable in the future. Historical mine development was based on inference from existing mining areas and very limited drilling.

“The risks of exploring, re-accessing the tunnels, and developing an economic undersea coal mining operation should be thoroughly understood by proponents,” the department warned.

Many of the previous assets, such as mining equipment, is available through Devco. To date a number of undisclosed companies are reportedly interested in Donkin.