Dear Ciprian,

In the zone of aeration above the water table, especially in a comparatively dry atmosphere and in the reactive substances within the gangue or in the ground water, ferric ions greatly predominate. Because the final product observed in gossans and cappings is mainly that derived from ferric rather than from ferrous solutions, the oxidation of piryte, as applied to the leached outcrop interpretation, may be summarized as folows:

1) By oxidation in an inert environment pyrite yields one-half its equivelent in moles of free acid, exports all of its iron, and leaves an empty cavity. Complete leaching takes place.

2) By oxidation and hydrolysis in dilute solutions pyrite may yield twice its equivalent in moles, of free acid. In this case all of its iron remains in the cavity as indigenous limonite (Fe2 O3: hematite or Fe2 O3. H2O: goethite); none is leached.

(Summary extracted from "OXIDATION OF PYRITE BY AIR-WATER PROCESSES" Blanchard, R., 1968)

Ciprian,

There are several papers that address this issue. However, a fundamental work to understand these processes is: Interpretation of Leached Outcrops by Roland Blanchard. Nevada Bureau of Mines. Bulletin 66. 1968.

Regards,

Nilda Urbina