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Cu oxidation/weathering question

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jennifercindrich:
Hallo,

I digging in a location that has a natural outcrop of a quartz vein. The location is central texas in the llano uplift near packsaddle mountain. The vein contains pyrite and chalcopyrite. The pyrite has mostly altered to lots of jarosite, relics of pyrite in the quartz are rarely seen. Chalcopyrite is present, unaltered and transformed to covellite.
My question is: Why would it seem that the final products of weathering are almost absent, as I see no malachite, brochantite, or chrysocolla?
The climatic condition of the area is semi-arid.

Thank you for any help.

Jennifer

smaragd123:
There was probably no intrusion of carbonate containing water which would alter the chalcopyrite and cause it to react to copper carbonates.

harzgeist:
Interesting question!
Should'nt the atmospheric CO2 enaugh to form copper carbonates - assuming the pH isn't too low. In that case one should expect brochantite to be formed, in analogy to the forming of the jarosite, that obviously happens.

Thomas

Fabian99:
Hi there,

I think that's it.

Jarosit growths at a pH round about 3, Carbonates need more than 4 to be stable.

BR

smaragd123:
Can anyone tell me the reaction equation for the formation of malachite?

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