Denmark - Civilian Buildings
 

Gold Mine, Coal Mine, Iron Mine

To begin extracting coal, iron, or gold, build a mine on a deposit. Then assign peasants to the mine to let them begin extracting the required resource. To increase the limit of workers a mine can hold, carry out a series of upgrades to the mine's infrastructure. The final (7th) mine upgrade allows 95 peasants to work in a single mine.

You should defend your mines, because they can be captured by the enemy.