If your level is at or above 55-ish then I would head to Burning Steppes. There are some Mithril, and several small thorium veins. Once you find the small veins, mostly in the Ogre cave Dreadmaul Rock i think, you should get to 275 soon enough to start hitting the Rich viens. Winterspring is valid too, I actually honed my Paladin Wall Crawling Techniques there to move around the Elite Deamons in the South. I don't recommend it though, once I found a good route in Burning Steppes, the reward for risk was way better in BS. When I hit 58, I was already at 300 mining, so on my first trip to Outland, every Fel Iron deposite was in serious jeopardy. Even now at level 64, my two favorite mining spots are Burning Steppes for Thorium and Badlands for Mithril. I average about 20-25 pieces of Thorium and the same or better in Mithril for one trip around those areas. Also, I suggest an add-on to your game. I have been absolutely thrilled with my titan panel mod. There is a gatherer function with the map that marks everywhere you mine or flower pick with an icon so you can see it later. This has made my runs about 40% more time efficient as I no longer have to commit to memory ever spot in every zone I think I have mined something.