I've never tried to go after that particular resource there before, but I think Pankoki has a good idea in that it's too close to the surface. With all the troubles, why not add one or two more lvls down into the cave to signify their digging deeper for more of the mineral if adventurers are mining it all away, and with all the dust and such it's kicking up to do the dig, make it a no-resting zone, and leave the Primal as it is right by it. The giants, with their tough constitutions, won't be bothered all that much by the dust, but it'll be too much for a lesser race to rest comfortably.
Mapping up and attaching a new area might take a while, but it's an idea all the same.
Edit: Oh, another Idea. Cuz of all the dust, people moving around, even invis, would be easily spotted, so make it a prohibited spell on the last two levels or something, forcing players to test their abilities, rather than just sneaking in, make the strike, and sneak back out.