im 230 mining so cant mine thorium yet...although ive seen some in tanaris and un goro crater ....in tanaris go all the way south to the dew collectors..theres 1 deposit
in un goro go south-west and travel along the mountainrange...i think theres 2 deposits there.
well could use more advises on more places..............
The most ive seen is in Winter, but you probly dont wana go ther as a lvl 40, might wana wait till 50s. Other than that Un'goro Crater is my best guess, but then again lvl 50 area..
Thorium for lvl 40, the best place you you would probably be Blasted Lands. Although the mobs maybe hard to go up aginst, yoou will find many small thorium veins littered accross the landscape.
Stil...lvl 40 and need thorium already? Thats pretty darn fast.Like said above,Blasted lands would be good but u would die couple of times because of higher lvl mobs.