Requirements:
Mining 65
Able to kill lvl 20-22 creatures
A few hours time
Must be alliance or a gutsy horde
Location:
Wetlands
I say mining 65 because you need that to mine tin. Not sure what the minimum requirement to mine incendicite is. There are about a dozen nodes that constantly spawn in the cave. The incendicite is for a mission so they spawn enough for everyone to complete their mission. They also give you exp for mining it. I got from 100-150 in about an hour without smelting (can't smelt incendicite).
A stack of 10 incendicite sells for a few silver so dont expect to make mad cash on those. However you can speed up your process by offereing the ones that actually need the incendicite what you have so they will get out of your hair. There are spiders in this cave that drop spidersilk and venom sacks. So you can also make good cash on the sold drop items or level up your rogue poisons if you need to.
Everytime I go in there this cave is empty. Though I'm sure thats soon to change.