Lots of "ifs" to a question like this. There are chains of various sizes, with the tiny thin ones being the obvious problem. Not that I would want to spend alot of time recovering those. I've melted a couple of those really tiny ones and it resulted in a speck of gold smaller than a BB. Hardly worth the gas in the torch.
Anyway, I don't have any super-thin chains on hand to test, but at pre-set sensitivity (60%) the T-2 will signal on a very small lobster clasp weighing about 1/8 to 1/4 of a gram at 4-5 inches. More gain will add to that range in air tests, but discrimination needs to be set down into the upper iron range for very small gold, as you would expect. On the smallest stuff, you might get slightly more range in all metal mode, but both modes do well, as well as some of the dedicated gold machines using stock coils in fact. I would expect that a smaller DD coil would add to the sensitivity of small gold which should allow you to run higher gain levels than the larger stock coil.
Ralph