SETTLERS add a MINE to hills, mountains, or desert tiles.
Mining raises PRODUCTION (shields) — most on hills and mountains, where the ore lies.
A tile cannot be both mined and irrigated; pick shields or food.
Shields build your units, city improvements, and wonders, so mined hills power an industrial heartland.
Ring a production city with mines and a food city with irrigation, then link them by road.
A mine pays only while a citizen works the tile. On a resource tile nobody works, a CAMP pays instead: mine the tile you work, camp the tile you don't.