Depends what are you prospecting for. Sometimes you just want to check what's underneath your base (especially when it's already underground).
But when I am looking for a specific ore from the surface I actually build a map of the surface, look for all the caves in the area, build map of the cave level 1 and have them in a program one above the other, so I can match the surface and underground easily and precisely. And then use rustroot extract starting from convenient points (which I know are easy to reach from the cave). Extract bellow q20 is useless in my opinion as it has very limited range. Just try to find better water, make better extract and then it is not hard to find where the ore is.
What kind of ore it happens to be is another question.

Ore distribution (at least on the 1st level) seems to be quite different from the previous worlds.
Too old to rock-n-roll, too young to die.