Genesis of porphyry copper deposits: key roles for plagioclase and anhydrite in metasomatism

[@jfvanschalkwyk]

Love the detail ... !!!

[@jfvanschalkwyk]

Great video - great contents - great piece of research - you nailed it ! It is obvious that these reactions produce HCl and H2SO4 - highly acid gas / fluids that will cause alteration and leaching as they infiltrate and move through the surrounding rock pile ! Could these be the same acidic gas that ends up causing advanced argillic alteration in the lithocap...?

[@SteveJohnson-CU-CSM]

Anhydrite from breakdown of labradorite! If the base of a porphyry is albitic does that suggest an underlying intrusive driving the process?

[@milenaresources4244]

We have drilled through considerable HS alteration associated with a porphyry finger in Chile showing just the same minerals...and bornite/cpy with veinlets of anhydrite...we have possible digenite and a bit of tourmaline in some big breccia pipes. Strangely, we got a show of lazulite in drill core. There is a big blue cliff outcrop of lazulite adjacent to the km sized breccia pipe. There does not seem to be much of a potassic core...if any in drill core. We bottomed one hole in albite actinolite...which we assumed was the edge of the system. I suspect we might have APS minerals beside the anhydrite and lazulite. So...maybe that's how to connect APS systematics with porphyry systems. Labradorite? What? Not one bit of carbonate to be seen anywhere.

[@milenaresources4244]

So....where does the oxygen come from to get SO2? I have a bit on this issue discussed in Researchgate and also came to the conclusion that anhydrite is a required reaction product...and your reactions indicate SO2 is a required reactant. So...has anyone seen CuCl in say fluid inclusions? There are some fascinating examples of Cu carbonates in something called "K-2 Jasper" from Pakistan. The Cu carbonates are megascopic 1 cm sized blue azurite bearing and somewhat malachite stained round stain bubble features in a silicious sulfide free foliated altered "granite gneiss" that no longer has FeMg's to speak of. It is called "jasper" because the silica content is high enough to hold a nice polish. So...usually we have low oxygen conditions at the base of the crust...where might that oxygen come from? Ringwoodite/Bridgemanite/Enstatite recrystallization above the Mantle Transition Zone in vertical plunging slabs? Could there be some strange production of H and OH ionic constituents? Interesting you say that the whole rock chemistry seems to be constant. I always shudder when I hear the term Metasomatism...it is not a chemical process. The notion of replacement is not a very coherent geochemical process either. Ionic diffusion and molecular substitution are viable processes. I see the point you make about invariant crystallographic orientations going from labradorite to albite...but I do think there are problems with the Unit cell configurations. They should change...and that would certainly affect the properties of the new material. You might play around with the garnet/pyroxene transformative process that might control the redox reactions of iron according to a number of folks who say it does oxidize things nicely. Those garnet peridotite reactions seem likely to underly the neogene Andean deposits based on REE signatures using principal component analyses...per AGU. Those would be the big copper bearing ones...not the shallow or thinner skinned Eocene Andean and Indonesian systems with much higher gold abundances.