This mine closed in 1990 but continues to affect the region.

Some mines continued to operate into the 1960s, but the volume never reached the same levels as in the earlier boom years.

At this rate the mine continued to work for the following one and a half decades.

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

Without the limits, the mine would continue operations in various stages for well over another one hundred years until approximately 2133.

This mine has continued to be worked to the present time with varying results.

The abandoned mines continue to be environmental and health hazards.

The mines continued to work until the late 19th century.

The mines, which have a combined work force of 820 employees, will continue normal operations during the sale, the company said.

These mines continued operating until the end of the 19th century.