Spot gold this a.m. is $132.46/gram, so that's $397.38 per ton excavated.
Assuming he means imperial/short tons, that comes to 0.106 ounces avdp or 0.096 Troy ounces per ton of sediment. That's about 302,000 parts soil to one part gold (by weight). Not much ROI.
Stories like this remind me how invested the Romans were in monetizing human suffering. I suppose it wasn't that unusual for the era, but in the end, the Romans just had so much more to show for it.
There was an old phosphate hydraulic mine near where I grew up. Between the water cannon blasting and the Ph of the tailings piles, it was craggy and barren, like moonscape. And it attracted kids on dirt bikes from all over the region, ... until they were forced to close the place over litigation concerns.
Actually it shows that the Romans used water to do a lot of the work to extract a lot of gold over a few centuries, pretty smart.