How do miners know where to mine?

Answer 1

The average cost of starting a mine these days is about a billion dollars, so miners must be very sure about where they're mining. The first indications would be noticed by a prospector on the ground, spotting something like an outcrop stained green that indicates copper, or perhaps a ridge of black iron ore. Small samples are taken, to identify the ore minerals, then larger samples, to give a clearer picture of the grade of the ore. Then, if the high cost seems warranted, diamond drilling rigs are brought in to probe the depth and shape of the orebody. If the ore is rich enough, and the ore body is big enough, mining can begin. This is a very simplified explanation; ore bodies are now being discovered that are hidden below ground using sophisticated testing methods, etc.