It can take decades for a large underground mine to move into the black.

There were also at least six underground mines in the valley.

Most of these workers had never worked in an underground mine prior to surface mining.

For underground mines, rehabilitation is not always a significant problem or cost.

The original underground mine opened in 1921, and continued until the mid-1950s.

They live in underground mines, searching for the light of day.

During the years the underground mine has been made gradually deeper.

By 1999, the project operated exclusively as an underground mine.

There is an underground mine employing about 40 people three miles to the west.

The underground mine was finally closed and allowed to flood in 1999.