Gold Mine, as its name suggests, mines Gold. It provides a steady stream of gold when the player is offline. Generated gold is stored in the mine, and requires the user to “collect” them manually, which is then transferred to the Gold Vault.
Other than Gold Vaults, Gold Mines are another prime target during a Resources Raid, especially those bases that contains high level Gold Mines. In fact, Gold Mines are often the better target than Gold Vaults as players usually spent all their gold before they went offline. In this case, most of the gold that can be raided would be those in the Mine, not the Vault. Also, in most bases, Gold Mines are usually less protected than Gold Vaults, which makes them the best target for fast gold raids.