If you're up to Chapter 3 in the legendary questline you will have to do a quest called Orb of Dominion and The Shadow War.
you will be lead into a cave where you will need to kill certain amount of mobs.
The mobs do hardly any damage and each mob drops anywhere between 70silver - 1.5gold. You can simply pull the whole cave and aoe it down within 1 min or so if u have speed buff to aggro all the mobs.
I've had the whole cave drop gold between 15g-45g with blues and green that sell for 7g-30g each.
The mobs also have a very fast re-spawn timer as well.
I cant say how much gold per hour this is but its definitely not the usual 10silver or so you get from killing normal Dreanor mobs.
I'm not sure if you can see the mobs if you're not up to that quest or if they re-spawn as fast as they do if you're on the quest line.