Panning for precious metals
That would be a graphically interesting thing to add to WvW in place of one of the current supply nodes. Can’t see it in PvE though unless its daily capped/fast diminishing returns or it would be gold farmers galore
You could have other materials other than metals that you could pan for. It wouldn’t necessarily have to be metals. If you did have metals you could have gold dust, silver dust etc.. which would you would need to acumulate a lot of before it was processed to actual gold.