The mine is a basic tile improvement that is available at Mining. This improvement increases the yield of a tile by +2. Mines can be built on any hill tile or on any resource that must be mined, like Copper, Iron, Mithril and Gems.
Mines recieve one extra hammer upon research of blasting powder. They also recieve an +1 with the civic arete running. They also recieve an +1 with blasting powder.
Building a mine gives access to metal and gem resources (i.e. iron, gems, gold) In addition, mining a hill without a bonus resource on it has a small chance of creating a new resource on that tile. This chance is greatly increased (though still small) with access to earth mana.