Northwest of Charbrook, in the Shoreline Ruins chunk, there is a cave of spiders called the Den of Vashat. In this cave there are 6-7 iron nodes and probably 8-10 spider in the low 20's. 6-7 nodes wouldnt be that big of a deal except that by the time you hit the back of the cave, which is pretty small, the front nodes are spawning again. The spawn time on this iron is insane.
Once you get past the entrance guards just hang out in the cave, the spider spawn isnt very fast and you'll have plenty of time to harvest your little heart out.
As an added bonus there are 2 named spiders in the cave, one being Vashat who spawns in the rear, and another is a 3dot (mistress) If I recall. Who spawns on a wooden platform, roughly in the middle. Nohing in here is hard to kill if your in the 20 range. There is a bit of rock in here as well but only 2 nodes or so, again its a really small cave.
Did all my t3 skilling in here in a very short amount of time so check it out miners/harvesters.
Chunk image----
http://vg-en.curse-gaming.com/database/ ... er-hunter/