Most people, myself included, will keep any great spots they find to themselves as they don't want them to become over populated, though I can tell you, that you can get tons of volatile fires in Mt. Hyjal
Deepholme before the nurf. First two days cata was out I spent like 6 hours total mining and just messing around. Made 50k selling stacks of ore for 400g+ and volatiles for 100g each. Ez cash
Can't do it now cuz its nurfed and ore prices dropped, but that was my farming spot lol