The only problem with this was the material used to construct these devices was itself contaminated by fallout from the nuclear weapons tests of the postwar era. You simply could not find metal ores that were not already saturated with fission products from nuclear testing. The radiation emitted by this residual fallout would overwhelm the radiation from the test samples and it was impossible to get a good reading. In other words, an additional level of “background” radiation was superimposed on the radiation from natural sources and it often totally obscured the radiation from the sample being tested.

The problem was solved by building the sample chambers for this equipment out of steel recovered from the thick armor plating of pre-1945 mothballed battleships. The armor plating was removed, the outer layers were milled off, and the resulting uncontaminated steel was not only free from weapons test debris, it also provided shielding from any other radiation present in the environment. Any radioactivity present in this metal was strictly from natural sources, it had always been there, and could be subtracted as “background”.

Scientific American

When oceanic crust subducts, there is smear (not a geologic term). It’s not a discrete boundary between the plates. The frosting gets scraped off the cake, so to speak, and as it does, it gets all f**ked up. And then, if this winds up getting smashed between two continental slabs, and spending some quality time at high P/T under a 20,000 foot mountain whose roots are deep and melting, it winds up as part of the continental crust.

Continental plates are not homogenous. They are demolition derby cars made of clay.

I was always under the impression the deep ocean basins were extruded from mid-ocean ridges and eventually slid under the continents, and the continents were made up of lighter rocks that floated on top of the basaltic abyssal plains.

If you can visit these sites on foot, they somehow must have found themselves lifted up onto the continents.

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!