Greydwarves except for Shaman and Brutes are afraid of fire and will run from it. Place multiple camp fires around the copper node. Copper nodes are frequently guarded by trolls but once you kill the troll that spawns nearby it takes at least 3 game days before another one can spawn.

During the day there can only be 3 active greydwarves in a 64 x 64 tile radius but at night (or during a raid) there can be 6. Greydwarves have a visual perception range of 30 tiles and alert at 20 tiles distance but their hearing perception range is 64 tiles (max render distance). Mining is noisy. It will attract creatures from maximum range. If you are seeing something different than this you either have a bug or a mod conflict (if you are running mods).