The best I can say is keep looking for a way underground, what zone are you in... I know in the searing gourge that the nortern part of the map is accassable underground though a few caves in the molten crater(center part of the zone). The best I can recomend without you telling us where the "menny" underground veins are nobody can help you, I know of a few ways to access cirten caves that are relevent to me (alliance) and may be able to help you. without that the best I can say is when you see a vein on your minimap stand over it, then look at your world map, take note of where you are standing. Find a cave , look at your world map and try to get standing on your wold map where you were when you were standing over the vein.
Hope it helps