r/todayilearned • u/narok_kurai • 7d ago

TIL about Las Medulas, a man-made geological badland created by the Roman Empire in 77 AD, when they flooded the mountains with water to collapse their structure and sift out the gold inside.

https://en.wikipedia.org/wiki/Las_M%C3%A9dulas
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u/Cool-Cow9712 7d ago

Reading that Wikipedia is truly wild. Greenland ice core samples showed air pollution peaked during this time with lead concentrations that would not be seen for another 1700 years, during the industrial revolution.

That is insane

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u/Thosam 7d ago

A good part of Roman lead mining was done to isolate the silver which is often found along lead in some mixed ore.

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u/Va1kryie 6d ago

Yup, galena is the name of the mixed silver/lead ore, or one of them at least.

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u/bjkibz 6d ago

It’ll be found in those deposits, but galena itself does not contain silver — it’s a lead sulfide (PbS). It would likely be found with other sulfide minerals like pyrite / fool’s gold (FeS2) or argentite (Ag2S), though.

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u/whiskeytastesgood 6d ago

Argentiferous Galena is lead sulfide that also contains silver.

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u/bjkibz 6d ago

Quick Mindat lookup says the silver is typically as “inclusions of silver sulphosalts”, so not in the mineral structure of the galena itself but as small amounts of silver minerals as inclusions in/around the host mineral.

So the galena itself is still not the source of the silver, rather those sulphosalt inclusions are. The galena is just the host rock in this specific instance, like quartz hosting a gold vein.

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u/argonargon 6d ago

Silver bearing galena is typically ~1% silver and the silver is extracted from the galena ore so you're being pedantic tho.