Question about porspecting caves

[Fenrispantom]

here i stand just a mini maps worth away from the entrance at a 3 way tunnel split I've prospected the entrance and at the spot i stand so the question is if i prospect at the entrance does that mean the whole cave has no mine or just near the entrance i know a friend of mine told me once but now i don't remember when i need to so if anyone can tell me I'm wasting my time here please do if not i will carry on with the exploration

[Darkren]

Yo Fenris, I'm really happy for you, I'mma let you finish... But literate people had one of the best punctuation of all time.

Prospecting has confirmed that it covers all ground within a 1000 tile radius, and I'd imagine that would be the same for caves. If a cave reaches further than 1000 tiles away from your character, it's not going to pick up any metal there. (Also, interesting note, if there's metal in a nearby cave <1000 tiles away, prospecting will pick it up, even though you're not in the same cave).