So battling has an opportunity to drop Pandora's Box. Which when opened give you a random tier based equipment. Now here comes the Vault of Erebus(I know, I'm stealing it from AoM). Essentially the TS version of Pandora's Box. But instead of tier based equipment, we get a random amount of one of the four resources.
We still need to hammer out the amounts, but I think between 1 and let's say 500k resources would be a good starting point.