First off, where are you in the game? You have two major hunts that require you to go through there and basically complete it. You get the key to access the next third of the mines during the "Antlion Infestation" hunt (bring Areoga...trust me...) and the other one is the awesome "Ancient Man of Mystery" hunt, to finish it you need the last key to get it... (SPOILER)You need to talk to the man at the Phon Coast who fell from the sky.