For thousands of years miners used pick and shovel, iron wedges and hammers to follow a vein of ore from near the surface deep into the ground. If they needed to shatter rock and hand tools did not suffice, the miners might build a hot fire up against the rock surface and then quench the heated rock with water (or even vinegar). The technique is called "fire-setting". An interesting source of information about early mining is a 16th-century book "De re metallica" ("On the Nature of Metals") by Georgius Agricola. It's readily available on-line, in English, and contains a wealth of detail.