Lead and Silver Mining
Too full of a day, so this one will be a very short follow-up to an earlier post about lead in water pipes and cognitive decline.
The basis of the earlier post had to do with how easy it is to fashion lead into pipes, how the ancient Romans surely did this to bring water into their living spaces, and how the inevitable health risks (including a loss of brain function) may have contributed to the fall of the Roman Empire. The post ends with a discussion of the challenges the EPA is facing in replacing the last of the lead pipes still in use in the United States (think Flint, Michigan).
There is a new study reported yesterday (6 January 2025) in the journal Proceedings of the National Academy of Sciences, and summarized this morning in the New York Times. The study doesn’t dispute the dangers of ANY exposure to lead, but questions whether lead water pipes were the primary source of the contamination in ancient Rome.
Their alternate source? Silver mines, which would have released lead into the atmosphere during the mining operations. According to the study, producing a single ounce of silver (the base of Rome’s economy) produced 10,000 ounces of lead! I didn’t know this and remain mostly ignorant about the numbers (although the linkage of lead and silver is well known).
It’s uncertain where Rome got all of its silver, but the historic mines in Spain are probably the source for much of it. A likely suspect is the historic Rio Tinto-Nerva Silver Basin in Spain — a classic volcanogenic massive sulfide deposit. And the area is indeed historic: silver mining at Rio Tinto dates back several thousand years to ancient Rome, and beyond to the Copper and Bronze Ages.
Be that as it may, the extent of the atmospheric contamination was not restricted to southern Europe. Joseph McConnell — an environmental scientist at the Desert Research Institute, a nonprofit group based in Nevada, and the primary author of the new research — reports that he and his colleagues have detected lead in layers of ice collected in Russia and Greenland that date to the time of the Roman Empire.
The levels of lead that Dr. McConnell and his collaborators measured were extremely low, roughly one lead-containing molecule per trillion molecules of water. But the ice samples were collected thousands of miles from southern Europe, and lead concentrations would have been highly dispersed after such a long journey.
Using computer models, Dr. McConnell estimates that somewhere between 3,300 to 4,600 tons of lead were emitted into the atmosphere each year by Roman silver-mining operations. The researchers then estimated how all that lead would be scattered across the Roman Empire.
The Times summary goes into great detail about this, as well as the effects of lead on IQ numbers, especially in infants and children. I encourage you to take a look at it.
Gotta run.
While I was part of efforts to limit acid water drainage, cyanide, and metals emissions from modern gold and silver mines, it is impossible to totally eliminate releases into the environment. Back in the day, though, it was …. holy moly … yikes! Mercury in ores and as a part of ore processing has had and is having big impacts. Using mercury to recover gold goes back at least to the Romans too. The Comstock Lode in Nevada and associated deposits spawned hundreds of mills in the 1800’s, most of which used Mercury as part of the metal recovery process. It is estimated that about 7000 short tons of mercury was discharged onto hillsides and into the Carson River drainage, and there it sits in a superfund site. There is no safe level of exposure to mercury. Don’t eat the fish from the Carson River. Google “CARSON RIVER MERCURY SITE
DAYTON, NV”. Trying to remediate this big site might make things worse than leaving it alone.
I worked one season in a gold telluride mine in Colorado. One of the minerals in the ore was an extremely low temperature epithermal mineral – mercury telluride – or coloradoite. I could find this mineral on the surface waste dump from the 1800’s and 1900’s. This mineral decomposes if you look at it funny. Back in the 1970’s some guys found a nice bonanza ore shoot in the mine with native gold and gold tellurides, along with mercury telluride. They were in such a hurry to get their gold that they smelted it at the underground mine face in a frying pan, and that wasn’t the stupidest thing they did with their addled brains.
And mercury occurs naturally and is in coal combustion products too. Mercury gets into the atmosphere and cirulates worldwide. As with alot of earth processes, the mercury is selectively absorbed by biological and chemical sinks – which can be peat deposits, many of which are incorported in permafrost. Other processes are going on, but global warming is releasing some of the reservoirs of mercury into waters and air at a pretty good clip now.
No doubt, “zero discharge” has always been an elusive target, and is especially problematic when the materials of concern are part of the process. They called him “The Mad Hatter” for a reason…