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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 disti nguish 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: y i t il n l ta s ry c g i n s a e r c I n
Kaolinite
Smectite Illite-Smectite
Dickite ) d e k c a t S (
) d e k c a t S (
Illite
Q l l u H . m r o N
Pyrophyllite
Q l l u H . m r o N
Sericite
i s a e r c I n
Alunite
1900 nm 1500
1800
Wavelength in nm
2200 nm 2100
2400
1500
1800
2100
2400
Wavelength in nm
Fig. 1. Illite crystallinity; we can Fig. 2. Changing acid mineral phase measure the ratio of the depth of the with increasing temperature. 2200 nm feature to the 1900 nm feature.
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. M
Low Temperature disordered kaolinite
ordered kaolinite
Kaolinite
Smectite
DH1
DH2
M
Low crystallinity mica
Illite-Smectite
The oca on o he mag nary dr ho es (DH 1 and DH 2) s us ra ed n g 4
Dickite
Illite Alunite Pyrophyllite
Sericite
High crystallinity mica Long wavelength mica
Short wavelength mica
High Temperature Low pH
F g 4 Overv ew of an ep herma sys em w h a era on m nera s ha can be measured w h SMAM Genera recommenda on; measure 1 spec rum every me er on every exp ora on dr ho e o nav ga e your way n he sys em
F g 3 S mp f ed phase d agram of an ep herma sys em
Increasing pH DH 1
DH 2
M
IncreasingKaolinite crystallinity
M
Kaolinite (Steam-heated)
Illite-Smectite Kaolinite Illite-Smectite
IncreasingIllite abundance
Dickite
Illite
Increasing Illite Crystallinity Illite wavelength = 2206nm
Alunite + Silica
Pyrophyllite Muscovite Decreasing Mica AlOH wavelength
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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. Potassic alteration
Alteration mineralogy mineral ogy in Porphyry Cu-Mo-Au Systems: Fe ch bo e
Vertical zonation from Potassic,, (biotite + K feldspar) to Potassic Phyllic,, (sericite) to Phyllic Advanced argillic, argillic, (pyrophyllite, dickite, quartz Topaz in F-rich systems) or Argillic,, (illite-smectite) Argillic
M D
m
Mg ch bo e
Phyllic alteration Muscov e
Pheng e M A
A A
A w
Lateral Zonation from Potassic to Propylitic,, (actinolite, chlorite, epidote, Propylitic albite, calcite)
D ck e
Advanced argillic alteration
Topaz
B o e (po ass c a era on): bes des he sh n he 2250 nm ea ure Mg-ch or e shows a secondary ea ure a 2390 nm
m M
Wh e m ca (phy c a era on): he wave eng h sh s n h s examp e rom 2194 nm n muscov e o 2222 nm n pheng e D ck e (advanced arg c a era on): ma or ea ures a 1380 1415 2180 and 2208nm; opaz: ma or ea ures a 1405 and 2080 nm Seedorff Seedor ff et a
2005
Ch or e compos on (propy c a era on): n examp e; Mg-ch or e 2324 nm Fe-ch or e 2350 nm
hs
Propylitic alteration
Fe ch o e
Mg ch o e
w
m
M m
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