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

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SWIR RANGE SIGNATURES
The field spectrometers are probably the best tools invented in the last 10 years,
aside from GPS, for field reconnaissance and core logging. They can be taken
to the field, to the pit and to the outcrops. They operate from a backpack or from
the field vehicle. They can be set up in a field camp, in a core shack, or on an
outcrop. They are versatile and flexible and provide the explorationist with “on
the spot”, in-situ information, right at the outcrop, so there is instant gratification
and instant knowledge of the composition of the outcrop or the drill core.
Alteration types are instantly identified, mixtures are seen, zoning can be tracked,
mineral transition zones characterized. Ten years ago, this was just becoming a
possibility. Now it can be done in a tenth of a second.
What can be seen? Table II, from Thompson and Thompson (1996) summarizes
the majority of the common infrared-active minerals that can be detected in the
SWIR range.
Table II – Summary of Infrared Active Minerals with SWIR Absorption Features
Environment of formation Standard terminology SWIR active mineral assemblage (key minerals are in bold)
Intrusion-related
High-sulfidation epithermal
Low-sulfidation epithermal
Mesothermal
Potassic (biotite-rich), K silicate,
biotitic
Biotite (phlogopite), actinolite, sericite, chlorite, epidote,
muscovite, anhydrite
Sodic, sodic-calcic Actinolite, clinopyroxene (diopside), chlorite, epidote, scapolite
Phyllic, sericitic Sericite (muscovite-illite), chlorite, anhydrite
Intermediate argillic, sericite-
chlorite-clay (SCC), argillic
Sericite (illite-smectite), chlorite, kaolinite (dickite),
montmorillonite, calcite, epidote
Advanced argillic Pyrophyllite, sericite, diaspore, alunite, topaz, tourmaline,
dumortierite, zunyite
Greisen Topaz, muscovite, tourmaline
Skarn Clinopyroxene, wollastonite, actinolite-tremolite, vesuvianite, epidote,
serpentinite-talc, calcite, chlorite, illite-smectite, nontronite
Propylitic Chlorite, epidote, calcite, actinolite, sericite, clay
Advanced argillic — acid sulphate Kaolinite, dickite, alunite, diaspore, pyrophyllite, zunyite
Argillic, intermediate argillic Kaolinite, dickite, montmorillonite, illite-smectite
Propylitic Calcite, chlorite, epidote, sericite, clay
“Adularia” — sericite, sericitic,
argillic
Advanced argillic —
acid-sulphate (steam-heated)
Sericite, illite-smectite, kaolinite, chalcedony, opal,
montmorillonite, calcite, dolomite
Kaolinite, alunite, cristobalite
(opal, chalcedony), jarosite
Propylitic, zeolitic Calcite, epidote, wairakite, chlorite,
illite-smectite, montmorillonite
Carbonate Calcite, ankerite, dolomite, muscovite (Cr-/V-rich), chlorite
Chloritic Chlorite, muscovite, actinolite
Biotitic Biotite, chlorite
Sediment-hosted gold Argillic Kaolinite, dickite, illite
Volcanogenic massive sulfide
Sediment-hosted massive sulfide
Sericitic Sericite, chlorite, chloritoid
Chloritic Chlorite, sericite, biotite
Carbonate Dolomite, siderite, ankerite, calcite, sericite, chlorite
Tourmalinite Tourmaline, muscovite
Carbonate Ankerite, siderite, calcite, muscovite
Sericitic Sericite, chlorite
Albitic Chlorite, muscovite, biotite
Minerals are grouped by assemblages of alteration minerals, and keyed to commonly used terminology; Complete assemblages are in
Thompson and Thompson (1996)
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