[pfdietz]

It's sulfides like pyrite that, when exposed to air, are oxidized by bacteria to sulfate.

There's an enormous belt of pyrite in Spain that has caused a river, the Rio Tinto, to be one of the most acid rivers on the planet.

https://en.wikipedia.org/wiki/Rio_Tinto_(river)

[cyanydeez]

Yes, and it's not just "random" sulfur, it's integral to the geologic complexes that miners look for to get the minerals they want.

Think of it like the husk of a corn cob, or the cob of your corn. It's a byproduct of the very things we're looking for in mining.

The only other activity that could get hose minerals is indistinguishable from magic.

[mapt]

I'm not sure the belt of pyrite is best labelled as the cause here.

It might have something to do with the inferred activities of Rio Tinto, a transnational corporation that is one of the largest mining firms in the world.

[duskwuff]

The river was polluted millennia before the Rio Tinto company came into existence. There's been mining operations along the Rio Tinto since ca. 3000 BC.

[mapt]

Yes. Sure.

But before the mining operations? Probably not very polluted. It's the mining doing the polluting, not the belt of pyrite simply existing.

[pfdietz]

> But before the mining operations? Probably not very polluted.

From the wikipedia page:

"The discovery of multiple oxide terraces mediated by microorganisms at up to 60 metres above the current water level, and as far away as 20 kilometres from the current river's path, may suggest that the unusual ecosystem is a natural phenomenon since before human mining activities started in this region.[9]"