Silver Mine is a natural resource that contains coin in Age of Empires III. Silver mines are more common on the map than Gold Mines, which contain twice the amount of coin. Each Silver Mine has 2000 coin in them, which can be mined by Settlers, Villagers, Coureur des Bois, as well as Miners.
"The mountain called Cerro Rico housed a fabulously rich silver mine. The mining town of Potosi, in what is now Bolivia, mushroomed to service these mines. Spanish viceroys - charged with overseeing Spain's interests - exploited the Incan concept of public service, mita, to work the mines. Much of the silver siphoned back to Spain from the New World was from the mines of Potosi."