Transcript
Chapter 6: Recovering the Gold
The miners at Las Médulas used the ruina montium technique again and again, creating a caldera that covered more than ten square kilometers — by far the largest opencast mine in the Roman Empire. Once the gold-bearing strata had been exposed, the miners piled the larger stones into heaps and dug channels along the surface. They lined the bottoms of the channels with gorse branches, then played streams of aqueduct water over the slopes. Gold flakes were washed downhill and caught in the gorse; they were retrieved after the branches were dried and burned.
More than a hundred million cubic meters of sediment were washed down from the mines at Las Médulas. The debris transformed the topography of the plain below, leaving a series of ridges and channels. In channels blocked by later floods, lakes formed. Some, like Lake Somido, are still extant today.
The gold-bearing strata at Las Médulas were not especially rich; by one estimate, they contained only about three grams of gold for every ton of sediment. Around the beginning of the third century, the sheer difficulty of recovering gold from the site seems to have brought mining to an end. Since the mines were never reopened, Las Médulas remains largely as the Romans left it — a monument to both the scale and the limitations of ancient ingenuity.
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.