Patch 5.3 removed the minimum skill level required to mine every node in the game.  Players can now level anything they want at skill level 1 and gain skill ups.

Being a level 90 it doesn’t make any sense to go back through old world zones and collect a bunch of ore, even if you want to sell it.  If you’re looking to get to 600 as fast as possible without any effort then you will want to stay in Mists of Pandaria to do your mining.

Use your flying mount to complete the following route circuits.  If you have the Swarmkeeper’s Medallion that adds 10% movement speed, then I recommend you go to Dread Wastes.

Otherwise stick to Jade Forest.  You won’t get Ghost Iron Ore but you’ll get Ghost Iron Nuggets.  Every 10 of them gets you a Ghost Iron Ore.

You can level 1-600 without ever leaving Mists of Pandara.  Enjoy!