"Now when a miner discovers a vena profunda he begins sinking a shaft and above it sets up a windlass, and builds a shed over the shaft to prevent the rain from falling in, lest the men who turn the windlass be numbed by the cold or troubled by the rain."
– Georgius Agricola, de Re Metallica
In order for ores to be smelted into metal, they must first be extracted from within the womb of the earth. Mining allows you to construct Mine Supports and to mine from softened rock and ore surfaces within the mine. Soften darker rock surfaces by lighting a fire by them and letting it burn.
Once you finish mining a cracked wall tile, your character will hold a large boulder which you can drop somewhere and then chip ore or rubble from it; alternatively the player can dump the boulder into a Stamp Mill for automated processing (you won't get Whetstones or Sterling Geodes this way).
Mine Special Conditions:
The purity of a ore is based on the level you are on and the distance from the ladder.
The Purity of the Ore Boulder transfers directly to the Bar of Pig Iron produced in the smelter. Purity also transfers to Bar of Copper, but has no effect in the game right now. The further from the Ladder you get your Ore Boulder, the better chance that it will have higher purity ore in it. If you wear clothing with a bonus to the Mining Artifice, you can get better chances for higher purity ore.
A cave in randomly collapses some mined out tiles around itself, replacing them with mineable tiles. They yield rubble boulders like normal grey tiles. When you mine you run the risk of triggering an impending cave-in, illustrated by dust falling from the mine ceiling. You can prevent the cave-in by building a Mine Support under it. You have in the ballpark of five to ten minutes to build a support before a cave in occurs.
The chance of triggering a cave-in is affected by:
Going further down increases the chance to dig out higher-purity boulders. There are 8 safe mine levels if you wish to keep your mine private; level 9, also known as the Dreamworld, connects all the mines.
To go down a level a Cave Down is needed. Cave down works like a normal Mine Entrance on the surface. But it cannot be built, it has to be mined from a dark tile which need to prepared with a pile of wood before mining. When a cave down is mined, a hexagonal 13x13 space is created around the tile (destroying the mine WALLS). A tip would be to mine out surrounding tiles if you feel they are valuable (like silver ore tiles). Also beware of a cave-in. To be safe place a Mine Support.