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

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Alteration types associated with Porphyry Copper Deposits
ALTERATION MINERALOGY:
Early formed alteration can be overprinted by younger assemblages. Central and
early formed potassic zones (K-feldspar and biotite) commonly coincide with ore.
This alteration can be flanked in volcanic host rocks by biotite-rich rocks that
grade outward into propylitic rocks. The biotite is a fine-grained, “shreddy”
looking secondary mineral that is commonly referred to as an early developed
biotite (EDB) or a “biotite hornfels”. These older alteration assemblages in
cupriferous zones can be partially to completely overprinted by later biotite and
K-feldspar and then phyllic (quartz-sericite-pyrite) alteration, less commonly
argillic, and rarely, in the uppermost parts of some ore deposits, advanced argillic
alteration (kaolinite-pyrophyllite) . Panteleyev (1995):
Potassic - biotite rich Alteration (Thompson and Thompson, 1996)
This alteration type is found in the core of porphyry deposits. It may form large
peripheral alteration zone in wall rocks (without K-spar) and zones out to
propylitic alteration. Minerals include biotite, phlogopite, K-spar, magnetite,
quartz, anhydrite, albite-sodic plagioclase, actinolite, rutile, apatite, sericite,
chlorite, and epidote.
Figure 35 - Potassic alteration shows
Actinolite, biotite, phlogopite, epidote, ironchlorite,
Mg-chlorite, muscovite, quartz,
anhydrite, magnetite.
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Figure 36 - Potassic - K-silicate alteration
includes "albite", anhydrite, quartz, muscovite
and epidote.