The mine is the second location-effected structure in the game. Costing 12 wood to build, It's used by being plopped over eater an orange or grey-peppered area; once in the building screen, the game will auto-detect what it is and put the mine type as the first building option. Those 2 previously mentioned minerals are Copper and limestone, respectively. Copper is used for high-end military units, and structure upgrades(Farms, Mines, and log foundries, as of 2.0); whereas limestone is used to upgrade passive structures (housing, bakeries, and walls).
In the future it's planed for more minerals to be added in (EX: tin), and as bronze is the combination of copper and tin, more higher-level units and upgrades will incorporate them as the aggressiveness of the Masklings increase.