An overview of vis-nir-swir field spectroscopy - Spectral International

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Alteration Types Associated with High Sulfidation Systems
Vuggy Silica
This alteration type occurs in structural zones or as replacement bodies in
permeable lithologies, usually in the core of zones of advanced argillic alteration.
This extreme form of acid leaching occurs in the higher levels of epithermal
deposits. It is also found in the upper parts of telescoped porphyry systems.
Figure 28 - Vuggy Silica Alteration shows alunite,
jarosite, quartz, sulfur, pyrite, hematite.
Silicic
Vuggy Silica
Silicification adds silica to a vuggy, acid leached rock and fills the vugs created
through intense leaching. Silicification is common in high sulfidation systems. It
can be confused with intense quartz stockwork at the top of some porphyry
deposits.
. Advanced Argillic
This alteration type is found in the upper regions of a high sulfidation system. It
can occur in the lithocap of a porphyry system.
The progressive neutralization and cooling of high sulphidation fluids by rock
reaction produces alteration moving away from the core in which zonation is
characterized progressively outwards by mineral assemblages dominated by:
alunite, pyrophyllite, kaolin, and illitic and chloritic clays (Corbett and Leach,
26
Silicic
Figure 29 - The silicic alteration plot shows quartz,
chalcedony, alunite, barite, hematite, pyrite.
Barite has only water features and does not have
a diagnostic spectrum.