That's the short hand in the trade for Volcanogenic Massive Sulfides, the type of mineral deposit these systems leave behind. And they are truly spectacular ores of copper, zinc, gold, silver. Not only in their size, but also their grade. Really rich rock.

I spent many years mapping and researching VMS, but the really old ones. Like 1.7 billion years old, which had been metamorphosed and deformed to various degrees. So I tried to study modern examples to guide my work to understand them better. I had the luck to get a tour of the Jerome Copper open pit mine, one the world class deposits of this type. Down at the bottom of the pit was this large outcrop of pyrite, the iron sulfide. It was pretty much 100% pyrite, which is an unusual occurrence. The really neat part, though, was that you could clearly see, despite all the time, heat, pressure, and stress this rock had been through, the structures of black smoker chimneys.

But these chimneys are just what we see on the surface. Below them there is a giant chemical factory going on. That hydrothermal water is moving around through faults, and joints, as moving through the more permeable rocks. It's so hot and acidic that it alters all the minerals, depositing some elements, taking others away.

You might recall that my moniker here is from a particular rock type that is associated with the hydrothermal alteration of metamorphosed black smokers: nodular sillimanite gneiss, AKA podrock.

Thanks for posting that article!