The Mine is a resource gathering building, which allows Citizens to gather Metal. It becomes available in the Classical Age, along with the resource itself.
A Mine may only be built next to a mountain or cliff that does not already have a friendly (own or allied) mine next to it. Mines of neutral or enemy nations do not count against this limit, however. A mine provides 2 to 10 worker slots, depending on the size of the mountain or cliff. Note that cross-border mining spots lying partially in enemy territory may provide fewer worker slots. In this case, as the borders change, so can the number of worker slots that each mine provides.
By default, each worker produces 10 Metal per 30 seconds, up to the nation's Commerce Cap.
If a Mine is placed within a city's economic radius, its productivity can be increased by building a Smelter in the same city. Without further research, a Smelter adds 50% to the production of all Mines in the same city, increasing the gather rate to 15 Metal per worker per 30 seconds. By researching metallurgy technologies at any Smelter, the bonus can be increased to 100% (20 per worker), 150% (25 per worker), and 200% (30 per worker).
Also, a one-time bonus of 30 Metal is granted whenever completing or destroying/razing a mine.