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1) 2)Spectral Mapping (SMAM) in Epithermal and Porphyry Copper Systems - Vectors toward the mineralized zone
Ab Scandinavian GeoPool Ltd
1) Epithermal Systems
Many hydrothermal minerals are stable over limited temperature and/or pH ranges. Therefore, by mapping the distribution of alteration minerals in areas of epithermal prospects, it is possible to reconstruct the thermal and geochemical zonation, leading to a model of the hydrology of the extinct hydrothermal system. Alteration minerals are also crucial to distinguish the style of deposit, low sulfidation or high sulfidation.
Common alteration minerals in epithermal systems are e.g. kaolinite, dickite, pyrophyllite, alunite, smectite, illite-smectite, illite and sericite, and these can all be measured with the TerraSpec spectrometer.
Examples of what we can measure with SMAM:
The results can be used to map pH and temperature
variations, which will help to navigate your way in the
epithermal system and locate the mineralized zone.
2) Porphyry Copper Systems
Infrared-active alteration minerals associated with porphyries include sericite/muscovite, biotite, phlogopite, actionolite, chlorite, epidote, calcite, clay minerals (illite, kaolinite, smectite) and tourmaline.
Fig. 1. Illite crystallinity; we can measure the ratio of the depth of the 2200 nm feature to the 1900 nm feature.
© Copyright 2008, Ab Scandinavian GeoPool Ltd
Illite
Muscovite
Kaolinite
Dickite
Pyrophyllite
Alunite +Silica
Kaolinite(Steam-heated)
Increasing Kaolinite crystallinity
Increasing Illite Crystallinity
Increasing Illite abundance
Illite-Smectite
Illite-Smectite
Illite wavelength = 2206nm
Decreasing Mica AlOH wavelength
DH 1 DH 2
Smectite
Illite-Smectite
Illite
Sericite
Kaolinite
Dickite
Pyrophyllite
Alunite
Low Temperature
High Temperature
Low pH Increasing pH
disorderedkaolinite
orderedkaolinite
Low crystallinitymica
High crystallinitymica
Short wavelengthmica
Long wavelengthmica
DH1DH2
Fig. 2. Changing acid mineral phase with increasing temperature.
Wavelength in nm
No
rm.H
ullQ
(Sta
ck
ed
)
1500 1800 2100 2400
Kaolinite
Dickite
Pyrophyllite
Alunite
Wavelength in nm
No
rm.H
ullQ
(Sta
ck
ed
)
1500 1800 2100 2400
Smectite
Illite-Smectite
Illite
Sericite
Inc
rea
sin
g c
rys
tallin
ity
Inc
rea
sin
g t
em
pe
ratu
re
1900 nm2200 nm
Fig. 3. Simplified phase diagram of an epithermal system.
The location of the imaginary drill holes (DH 1 and DH 2) is illustrated in fig. 4.
Fig. 4. Overview of an epithermal system with alteration minerals that can be measured with SMAM. General recommendation; measure 1 spectrum every meter on every exploration drill hole to navigate your way in the system.
Mineral Mapping Pty Ltd
Mineral Mapping Pty Ltd
Vertical zonation from Potassic, (biotite + K feldspar) toPhyllic, (sericite) to Advanced argillic, (pyrophyllite, dickite, quartz Topaz in F-rich systems) orArgillic, (illite-smectite)
Lateral Zonation from Potassic to Propylitic, (actinolite, chlorite, epidote, albite, calcite)
Seedorff et al., 2005
Fe-rich biotiteDistal
Mg-rich biotiteProximal
Muscovite - AcidicAdjacent to Adv. argillic (shallow)
PhengiteAdjacent to potassicor propylitic (deep)
Dickite –Advanced Argillic Topaz
Advanced Argillic(in F-rich systems,eg Porphyry Mo)
Fe Chlorite –Low temp,Acid
Mg Chlorite(overprinting actinolite)High tempneutral
Alteration mineralogy in Porphyry Cu-Mo-Au Systems:
Muscovite
Phengite
Fe-richbiotite
Mg-richbiotite
Potassic alteration
Phyllic alteration
Dickite
Topaz
Advanced argillic alteration
Fe-chlorite
Mg-chlorite
Propylitic alteration
Biotite (potassic alteration): besides the shift in the 2250 nm feature, Mg-chlorite shows a secondary feature at 2390 nm.
White mica (phyllic alteration): the wavelength shifts in this example from 2194 nm in muscovite to 2222 nm in phengite.
Dickite (advanced argillic alteration): major features at 1380, 1415, 2180 and 2208nm; topaz: major features at 1405 and 2080 nm.
Chlorite composition (propylitic alteration): in this example; Mg-chlorite 2324 nm, Fe-chlorite 2350 nm.