So using them for searching for cables/pipes or lost items is “allowed, sort of” - you can readily buy metal detectors in Ireland for these purposes.
Prospecting for gold, on the other hand, is a legally thorny subject in Ireland. Finds above a couple of grams have to be reported and handed in.
If you happen to “stumble across” historical artefacts on your land you are meant to stop doing whatever caused you to find them (eg construction), report it, and then wait forever while archaeologists eventually show up and spend ages poring over the find to ensure you don’t destroy anything of historic value.
Prospecting for gold, on the other hand, is a legally thorny subject in Ireland. Finds above a couple of grams have to be reported and handed in.
If you happen to “stumble across” historical artefacts on your land you are meant to stop doing whatever caused you to find them (eg construction), report it, and then wait forever while archaeologists eventually show up and spend ages poring over the find to ensure you don’t destroy anything of historic value.