Person discovers that they can sense the presence of metal ores in the ground if given a familiarization sample first.
Only can sense one type at a time (whichever was the last sample they had held) and limited in scope (ie cant sense it 1000 miles away but might be able to sense it 1000 meters away).
What time period is this person in? How did this person discover their ability? How does this person take advantage of this ability? How does this person prevent others from taking advantage of them?
