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

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AN OVERVIEW OF VIS-NIR-SWIR
FIELD SPECTROSCOPY AS APPLIED
TO PRECIOUS METALS
EXPLORATION
By
Phoebe Hauff
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AN OVERVIEW OF VIS-NIR-SWIR FIELD SPECTROSCOPY AS APPLIED TO
PRECIOUS METALS EXPLORATION
Phoebe L. Hauff
Spectral International Inc., P.O. Box 1027, Arvada, CO., 80001
303 403 8383 pusa@rmi.net www.pimausa.com
ABSTRACT
Field portable Reflectance Spectroscopy has made a major impact on the
exploration industry because it has changed the way geologists think about their
rocks and about the different alteration systems and relationships between
associated minerals. It has opened new vistas for the field geologist. It allows
him now to "think out of the box" and not be tied to models that are not quite his
deposit type. Portable spectrometers at the outcrop, in the core shack, in the
open pit, give the explorationist instant information about rocks that may all have
similar physical appearances. Portable spectrometers provide in-situ data that
allows the geologist to immediately integrate several data sets - geophysics,
geochemistry and mineralogy - in the field - at the outcrop, where this information
can be quickly applied to a better understanding of what is physically observed -
instant gratification. This was not possible before their invention. Reflectance
spectroscopy is changing the nomenclature of exploration and allowing
geologists to look at mineral associations that provide more in depth
understanding of not only the rocks themselves, but the processes that have
altered them into the precious metal resources so important to the world.
This paper will therefore present an overview of visible through SWIR (Short
Wave Infrared) field spectroscopy with a brief summary of theory and
applications. Emphasis is placed on alteration systems, especially those
associated with low and high sulfidation gold deposits, porphyries, kimberlites,
skarns, IOCG (iron oxide copper gold) and unconformity uranium deposits, all of
which are major successes for reflectance spectroscopy.
Introduction -
Many innovations have occurred in exploration and mining that have contributed
to assisting the industry to find more precious metals resource and to find it
faster. One such innovative technology is that of VIS-NIR-SWIR (Visible – Near-
Infrared - Short-wave Infrared) reflectance spectroscopy. Its use has caused
major changes in the way exploration is done and how explorationists think as
now they are provided with instant information about the minerals in their rocks.
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The utilization of this range (350 to 2500nm) of the Electromagnetic Spectrum for
mineral exploration comes out of remote sensing needs as does the invention
and subsequent refinements of the field spectrometers, which have become the
prime vehicles for this methodology. Initial field units from the GER Mark series
(Geophysical Environmental Resources of Millbrook New York) to the ASD
classics and FieldSpec Pros were developed using solar illumination to
correspond to the satellite and airborne sensors for which they provided ground
truth or verification.
With the addition of an internal light source to eliminate the effects of
atmospheric water spectra, users quickly discovered that the portable
spectrometers had so many more applications then just ground truthing remotely
sensed data and the technology came into its own.
Although there are numerous companies offering instruments in the Visible and
short wave infrared for applications ranging from vegetation, water, forestry,
wood products, paint, carpets, wheat protein content, pharmaceuticals, forensics,
plastics, oil, among others, most are not portable to the field nor general enough
for geologic applications. GER was the company with the Mark series of field
spectrometers, who has always been more involved in the general remote
sensing side of the application rather then specifically targeting the mining
industry. Alex Goetz, at that time of Jet Propulsion Laboratory, Ron Lyon of
Stanford University, Larry Rowan of the U.S. Geological Survey, Robert Agar of
AGARS, Australia, Jon Huntington, CSIRO, Australia, Fred Kruse of AIG, Floyd
Sabins of Chevron, Jim Taranik of the University of Nevada-Reno, and the
present author, among hundreds of others, have all used this instrument for
mostly geologic, but some exploration and mining, applications. At issue has
always been the solar illumination and the corresponding atmospheric water
interference bands that mask out vital components and absorption features in the
mineral spectra. This interference made the application less attractive for
alteration characterization. Even 15 years ago, the solar illumination-based
technology was the best available.
With the introduction of the internal light source, the PIMA-II field spectrometer by
Integrated Spectronics of Sydney, Australia, in the early 1990s, the concept of
portability and field characterization of alteration took on a new perspective and
many new applications. Over 200 PIMAs, the majority of which are still
operational, were pioneering devices for developing new methods of alteration
mapping, core logging, drill well targeting, and field reconnaissance. Most of the
major mining companies worldwide adopted this new technology and utilized it
well for new discoveries and in-depth knowledge of their alteration systems.
In the late 1990s, ASD Inc. (formerly Analytical Spectral Devices, Inc.)
introduced their FieldSpec Pro. This instrument did have an internal light
source probe on it. It was upgraded in 2005 to the “FR3”, which had a refined
probe. Neither of these instruments were designed for the minerals industry, but
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were designed more for general remote sensing with solar illumination as the
prime light source. It was the appearance of the ASD TerraSpec in 2004 with
its flexible and innovative design specifically for minerals and mining that has
brought cutting edge, fast, fiber-optic data collection into the field and core shack.
This paper will review the concepts of reflectance spectroscopy, and look at the
more practical information that can be obtained from the visible, near-infrared,
and short-wave infrared regions of spectra, beyond just simple mineral
identification. Routine applications such as core logging, field reconnaissance,
pit mapping, and remote sensing ground truth will be illustrated with examples.
Selected alteration systems for gold, porphyries, diamonds, unconformity
uranium, IOCGs and skarns will be summarized from a spectral perspective and
mini-case studies discussed, space permitting.
REFLECTANCE SPECTROSCOPY
Spectroscopy is the study of the interaction between energy as electromagnetic
radiation (EMR) and matter. Radiation can be absorbed, emitted or scattered by
matter.
Reflectance spectroscopy can be defined as the technique that uses the energy
in the Visible (0.4-0.7), Near-Infrared (0.7-1.0) and Short-Wave Infrared (1.0-2.5
µm) wavelength regions of the electromagnetic spectrum (Figure 1) to analyze
minerals.
Figure 1. – Highly generalized cartoon of the EMS showing the various regions that
are covered by field portable spectrometers. Source unknown.
The science and techniques of reflectance spectroscopy are based on the
spectral properties of materials. Certain atoms and molecules absorb energy as
a function of their atomic structures. (Hunt, 1977 and Goetz et al, 1982).
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In the visible region, this is caused by electronic transitions such as Crystal Field
Effects (atomic energy level transitions), Charge Transfer (inter-element
electronic transitions), Conduction Band Transitions (electron transfer over
spatially close energy levels) and Color Center Phenomenon (lattice defect
induced energy levels). . Much of this simply involves release of energy when an
electron changes energy levels in an atom.
Absorption features in the SWIR region are a function of the composition of the
mineral. They are a manifestation of energy absorption within the crystal lattice
from vibrational state transitions. Because these vibrational states correspond to
distinct energy levels, the absorption features occur at well-defined wavelength
positions. The energy levels that define these wavelengths are a function of the
size of the ionic radii of the cations bonded to different molecules. The bonds will
vibrate at different wavelengths as a function of the length of the bond. Because
the bond lengths between a specific atom and molecule will be consistent, it is
possible to predict compositions and compositional changes in minerals being
analyzed by the wavelengths and wavelength shifts. (Hunt, 1977)
The transitions between energy levels and compositional differences are
manifested by absorption features at defined wavelengths. The common
absorption feature positions are listed in Table I.
TABLE I – MAJOR ABSORPTION FEATURES
POSITION MECHANISM MINERAL GROUP
~1.4 µm OH and WATER CLAYS, SULFATES
HYDROXIDES,
ZEOLITES
~1.56 µm NH4 NH4 SPECIES
~1.,8 µm OH SULFATES
~1.9 µm WATER SMECTITE
2.02, 2.12 µm NH4 NH4 SPECIES
~2.2 µm AL-OH CLAYS,.
SULFATES, MICAS
~2.29 Fe-OH Fe-CLAYS
~2.31 Mg-OH Mg-CLAYS,
ORGANICS
~2.324 Mg-OH CHLORITES
-2
~2.35 +/- µm CO3
CARBONATES
~2.35+ Fe-OH Fe-CHLORITES
The absorption features occur within a reflectance spectrum, with wavelength
positions and distinctive profiles that can be used to identify mineral and organic
phases. These are shown in Figure 2 below.
Each mineral has a distinctive spectral signature, composed of several
absorption features, which is a function of composition, crystallinity,
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concentration, water content and environmental considerations. For mineral
identification, that signature is compared against characterized references for a
validated identification. This can be done manually by using wavelength tables
and overlaying references on the unknown or it can be done using computer
algorithms operating against a database of references (i.e., a spectral library).
For best results these libraries must be set up for specific deposit types, and not
allow the algorithm to make a wrong choice.
Figure 2 – Example absorption spectrum. The units for the horizontal scale are in
nanometers or microns while the vertical scale is percent reflectance. The absorption
figure shown is a doublet, with two minima or lowest points of the feature. Each
minimum has a distinctive wavelength, which is a function of the chemical
composition. “FWHM” means Full Width at Half Maximum. It can be used for
symmetry determinations that are related to crystallinity.
Although the computer algorithms are useful for data management and
organization, care must be taken when using them for phase identification and
quantification. There are many unaddressed variables and non-user chosen
identifications are not always accurate. Additionally, important information on
crystallinity, water, organics, and iron, among other things, is lost.
VISIBLE RANGE SIGNATURES
There is an abundance of information to be gained from the visible region of the
EMS. This is one of the features that makes the full-range spectrometers so
valuable. Figure 3 shows some of the cations that are recognizable by colors
and corresponding minerals. Although the visible range is constrained from 300-
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720nm, there is additional and complimentary information in the NIR (700 nm to
1000 nm).
Figure 3. – The plot shows some of the more common cations that can be identified in
the visible range.
For example, chlorites are more detectable in the visible range because there is
less interference from other species compared to in the SWIR range where their
signal is usually low unless chlorites are the dominant phase. Iron oxyhydroxides
(Figure 4) have many distinctive features that allow them to be discriminated
from each other. This allows a discrimination of pH zoning and something not
easily done before. The nickel cation also has diagnostic features in the visible
range that can be detected in nickel laterite deposits and correlated to the ore
zones. Chrome in kimberlite minerals such as chrome diopside and G-10
garnets make spectroscopy invaluable to the identification of indicator minerals.
Manganese is also detectable through features in the visible range.
Garnets, pyroxenes, olivine, selected iron and copper oxides, hydroxides,
sulfates, and for heavy element carbonates, a NIR major absorption feature.
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Fe2+ Fe2+ chlorites
Fe3+ hematite, goethite
Ni Chrysoprase
Cr Cr-diopside
Mn Mn-chlorite
Mn rhodonite
Mn rhodocrosite

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A
USGS References
Figure 4 – The plots in [A] show the classic three most common iron minerals encountered in
exploration; jarosite, hematite and goethite. Stronger acidic minerals are shown in [B]. These
include, from top to bottom, schwertmannite, jarosite, copiapite, coquimbite and melanterite.
Rare Earth elements (REE) have
very distinctive signatures in the
visible region as can be seen in
Figure 5. Rare Earth minerals
include such species as bastnesite
(CeFCO 3 ), monzonite (Ce, La,Y,Th)
PO 4 , and xenotime (YPO 4 ). The
two most famous REE mines in the
world are located at Mountain Pass,
California and Bayan Obo, China.
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SPECMIN References
B
Figure 5 – Plots of europium, neodymium oxide,
samarium oxide, praseodymium oxide from the
USGS reference library.

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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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The SWIR method does not detect minerals per se, but the vibrational energy of
the chemical bonds between atom and molecule in the octahedral layer of a
compound. This gives more flexibility in detecting amorphous materials.
Therefore, it is possible to detect Si-OH bonds and thus look at amorphous
silicas, such as opaline phases.
SWIR is also very sensitive to water, which will be illustrated in a later section.
This is particularly valuable when tracking fluid migration through a deposit.
The common molecules detected are H2O, OH, CO3, and NH4. Selected sulfates
are seen when an OH bond is present, as are phosphates (Figure 6). Table II
lists most of the common infrared-active
minerals. The groups most likely
encountered, with selected mineral
examples, include clays (illite,
illite/smectite, kaolinite, smectites,
dickite) and all pyllosilicates, carbonates
(calcite, dolomite, ankerite, siderite,
malachite, azurite, cerrusite), micas
(muscovite, biotite, phlogopite,
paragonite), chlorites (Mg, Fe, Al),
Sulfates (alunite, jarosite, gypsum, Fesulfates),
tourmaline (schorl, elbaite,
dravite, rubellite), amphiboles (tremolite,
actinolite, hornblende), pyroxenes
(diopside, augite, hypersthene), garnets
(pyrope, almandine, grossularite),
pyroxinoids (rhodonite, sodalite)
selected silicates (talc, topaz, scapolite,
pyrophyllite, zunyite, epidote, olivine,
serpentines, dumortierite , idocrase)
evaporates (sulfates, niter, anhydrite,
gypsum, borax minerals),hydroxides
(diaspore, brucite), zeolites (stilbite,
heulendite, clinoptilolite), and silica
(opal, quartz, sinter)
pl
Figure 6. – These are plots of
common alteration minerals.
(Thompson et al, 1999).
Limits of detection will vary with the
matrix composition and the active versus
inactive components. It varies between
mineral mixtures. It is very difficult to do
accurate quantitative mixtures without first
building calibration files of percentage
mixtures.
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SPECTRAL INFORMATION
Field Spectrometers, whether they are based on an integrating sphere or fiber
optic cable, allow the collection and presentation of spectral data. Although the
primary objective of this operation is the identification of the minerals found in
different alteration systems, there is other information that can be obtained from
the data and which is of great significance in the interpretation of the spectral
information. These include chemical substitution, crystallinity, effects of water,
paragenesis and temperature.
CHEMISTRY
The ability to discern compositional differences in mineral groups that have solid
solution substitution is very useful. Some examples are the carbonates,
amphiboles, chlorites, illite/micas, tourmalines, smectite clays, alunites, all of
which exhibit wavelength shifts with cation substitution (Figure 7A, 7B, and 7C).
A B
Figure 7 – The spectral plots in [A] are for alunites of different compositions from Ca to Na
to K to NH4. Note that the diagnostic feature ranges from 1495nm for Ca to 1460nm for
NH4 . In Figure 7B, the diagnostic wavelength shift occurs in the 2330 nm range for Mgchlorites
shifting to 2350+ for Fe-chlorites. The carbonate group is shown in [C]. These
mineral show a significant shift with different cation compositions ranging from (top to
bottom) aragonite (Ca), Dolomite (Mg, Ca), calcite (Ca), rhodocrosite (Mg), stronianite (Sr),
magnesite (Mg), cerrusite (Pb), siderite (Fe), ankerite (fe, Mg), malachite (Cu), and azurite
(Cu).
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IRON OXYHYDROXIDES AND SULFATES
Iron oxides, hydroxides, oxyhydroxides and sulfates are very important not only
to precious metals exploration, but also in the determination of oxidation states
and acid drainage creation potential. They can be used in the field to provide
approximate pH's in an environment, especially along a stream, as shown in the
cartoon below. The three most common iron minerals are plotted in Figure 9.
PYRITE
SOURCE
SPRING
PH = 2.3-2.8
JAROSITE
KFe III (SO4)(OH)6
melanterite
copiapite
Bigham et al, 1996
pH = 3
pH = 4
SCHWERTMANNITE
Figure 8 - This cartoon shows pH changes along a stream from a sulfide metals source through
neutralization of acid waters by dilution and volume effects.
703
Fe8 III O8(SO4)(OH)6
745
766
862
894
920
Source: US Geological Survey data base.
pH = 4
12
No jarosite
FERRIHYDRITE
~Fe3O8.4H2O
pH = 6
pH = 7
STREAM
GOETHITE
α = FeOOH
Lepidocrocite
Maghemite
Figure 9 - The three most
common iron minerals
encountered in gold and copper
deposits are jarosite, goethite
and hematite. The plot shows
spectral profiles and
wavelengths for these minerals
in the visible range, where most
of their diagnostic features
occur. The emission features
are more consistent and
reproducible then the
absorption features. These
features all have a range.
These minerals are usually
mixtures of each other and
therefore a wavelength range is
more applicable to defining
them.

435
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430
430
468
430
B
560
518
IRON OXIDES OXYHYDROXIDES
795
782
769
761
748
920
855
961
922
959
ACID IRON SULFATES
733
682
655
713
776
874
871
917
927
A
Lepidocrocite
Ferrihydrite
Maghemite
Goethit
Hematite
Schwertmannite
Jarosite
Copiapite
Coquimbite
Melanterite
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Figure 10 - For most of these iron
species, the definitive features are
found in the visible region. The more
common iron oxides and hydroxides are
plotted in Figure 10A and include
lepidocrocite, ferrihydrite, maghemite.
Goethite and hematite.
The iron sulfates are very useful for help
in determining pH of their environment
and potential acid drainage factors.
They are plotted in Figures 10B for
Visible range and 10C for SWIR range
and include schwertmannite, jarosite,
copiapite, coquimbite and melanterite.
Except for jarosite, they show mostly
water features in the SWIR. A full range
spectrometer is therefore essential for
their definitive identification.
C
Schwertmannite
Jarosite
Copiapite
Coquimbite
Melanterite

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Another perspective of this shift is the aluminum substitution in illites and Al-micas.
Figure 11- Aluminum content of illites can be
estimated from the 2.2 µm absorption
feature, which shifts relative to the percent
aluminum present. There appears to be a
deposit-specific correlation in that when
illite/”sericite”/muscovite alteration is present,
there are higher amounts of aluminum
apparently associated with the ore zones.
This also has been documented by Post and
Noble (1993) and their data is plotted below
against spectral wavelength values collected
from their published samples.
Figure 13 – Selected Georgia kaolinites,
showing decreasing crystallinity down the
plot. Crystallinity index is based on work
done by Murray and Lyons (1956). Note
how water content increases with
decreasing crystallinity.
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Figure 12- Feature positions for a cross section
of muscovites and illites from SPECMIN range
from 2198nm to 2212 nm, with the majority falling
within 2200-2204 nm.
The illites plotted in Figure 9 are from different
environments and from top to bottom are [A] Hog
Ranch, Nevada, epithermal gold deposit; [B]
Chuquicamata, Chile, porphyry copper; [C]
Leadville, Colorado, gold vein system; [D]
Cananea, Mexico, porphyry copper deposit; [E]
Round Mountain, Nevada, disseminated gold
deposit; [F, G, H] sedimentary illites from Illinois
shales.
Degree of crystallinity can be determined
from change in the profile, using a
calibration data set for comparison
(Figure 13 ).
Note how the kaolinite doublet in the
2200 nm region softens and broadens
from a sharp, well-defined minimum to a
shoulder as ordering decreases.
This change in profile can be
mathematically defined and utilized as an
index. It is a function of random and
sporadic filling of metal sites in the
octahedral layer of the mineral. Empty
and random sites decrease order and,
therefore, the sharpness of the profile.

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PARAGENESIS AND WATER
Profiles also give information related to paragenesis and, indirectly, temperature
(Figure 15). Broad, open absorption features coupled with large water features
such as those found in smectites, zeolites, and opaline silica minerals indicate
ambient to low temperatures from low energy environments. As the profile
sharpens and becomes well defined, such as in muscovites, pyrophyllite,
epidote, and dickite, the temperature of formation increases and the crystal
lattice becomes ordered in a high-energy environment.
Figure 15 - plots showing changes in profile
As a function of ordering in the crystal lattice,
From broad, low temperature smectites to
higher temperature mica and pyrophyllite.
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Figure 14 - A very important series is the
one from montmorillonite (A) through to
muscovite [I]. This goes through mixed
layer smectite/illite [B] and illite/smectite
[C, D] to illite [E, F, G, H]. The plot
summaries the species in this series and
shows the information that can be gained
by the wavelength shift indicating
changes in aluminum content. This is
the most complicated series commonly
worked with in alteration systems.
Changes in water content, profile shape
and wavelength are all subtle between
the different species in the series. They
are difficult to distinguish and can only
be differentiated by comparison against
references.
Figure 16 - plots different water sites from
channel water in beryl to molecular water
in gypsum to zeolite channel water to
interlayer water in smectite to surface
water.

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Type of water present also can be tracked relative to profile and wavelength
(Figure 16). As seen in the figure, different types of water (channel, structural,
interlayer, surface, silica, encapsulated), have different profiles which provide
information about how the water was formed and where it resides.
II. DATA COLLECTION AND ANALYSIS Applications Examples
Outcrop mapping - Pamel
Pamel: An alteration study of the Pamel prospect in the Western Cordillera
of Peru was conducted for Candente Resource Corp. The results from
approximately 12 samples were integrated with geologic information and
outcrop patterns. Based on 3 days work, combined with the previous
geologic data, an alteration map was created for the property. The results
clearly showed distinct alteration zones and helped delineate zones of
interest (Figure 17). The alteration varies, from silicification to alunite-dickite,
to alunite-kaolinite, to kaolinite dominant, and outward to sericite, illite,
and chlorite. Small amounts of diaspore, topaz, and tourmaline were also
noted locally (Thompson et al., 1999).
Figure 17. - alteration map created by A. Thompson from PIMA outcrop samples.
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Core Logging
Spectral core logging is one of the major applications of reflectance
spectroscopy. Figure 18 presents a spectral core log..
HIGH SULFIDATION SYSTEM DRILL HOLE :: GOLD vs MINERALOGY
DEPTH Wave Au Kl Dik Alk Ill Sm Sil Jar Ch ALT Minerals
40 2206 0.005 x x 1 Jarosite, trace gyp, illite?
68 2206 0.005 x x 1 Illite + silica
74 2206 0.009 tr x x 1 Illite, silica tr gyp tr kaolinite
80 2206 0.024 x x x 1 Illite -> kaolinite, gyp, silica
81 2204 0.024 x x 1 Illite, gypsum - - jarosite?
94 2210 0.007 x 1 Illite
100a 2206 0.013 x x 1 Illite, jarosite
117 2206 0.008 x 1 Illite
124 2204 0.025 x x 1 Illite jarosite
140 2212 0.005 x x 1 Illite, jarosite, gypsum?
146 2192 0.011 x x 1 Illite, silica
150 2164 0.011 x 1 Kaolinite
164 2166 0.099 x 1 Kaolinite, well x/n
170 2168 0.099 x 1 Kaolinite, MW
173 2180 1.473 x x x 4 Dickite, alunite, kaolinite
175 2180 1.473 x x 4 Alunite + dickite
178 2170 1.473 x x 5 Alunite + silica
181 2177 0.133 x x x 4 Dickite and alunite silica
182 2181 0.133 x tr 3 Dickite, trace alunite
183 2180 0.133 x 3 Dickite
186 2166 0.035 x 1 Best kaolinite
196 2167 0.013 x x 1 Kaolinite + silica
204 2167 0.005 x 1 Kaolinite
214 2177 0.099 x tr 1 Kaolinite tr dickite
218 2166 0.099 x x 1 Kaolinite - poor illite
224 2166 0.016 tr x 1 Smectite + minor kaolinite
229 2167 0.016 x 1 Kaolinite
235 2164 0.196 x 1 Kaolinite - still wet
238 2164 0.196 x 1 Kaolinite
244 2164 0.007 x 1 Kaolinite
Pit Bench Mapping - Blast Holes
Considerable information can be gained through the analysis of blast holes in an
open pit mine. Although blast holes are assayed, in-situ mineralogical analysis
can provide alteration types, which if spectrally defined, will give the metallurgist
information needed for efficient mill recovery or heap leach pad blending.
17
A
B
C
D
E
F
Figure 18 - An Excel chart
that shows mineralogy
against alteration type
against gold assay values.
Plotting the minerals in this
way gives an excellent
comparison of the
presence of gold related to
mineralogy. The alteration
classifications are
indigenous to the high
sulfidation system and
represent mineral
associations.
Figure 19 - This plot is a compilation of
different alteration types from a copper
mine, defined using spectroscopy.
These include [A] muscovite, [B]
weathered muscovite shown by large
water feature, [C] illite with very minor
kaolinite overprint, [D] illite - kaolinite
mixture, [E] kaolinite – illite mixture, [F]
kaolinite. By matching metallurgical
data to the clay type, it was possible to
determine that too much kaolinite
would cause recovery losses.

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ALTERATION SYSTEMS FROM THE SPECTRAL PERSPECTIVE
The more common deposits that can be defined by reflectance spectroscopy
include epithermal gold, low and high sulfidation systems; porphyries,
kimberlites, IOCG (Iron Oxide-Copper-Gold), skarns, and uranium (both
sandstone hosted sediment and unconformity types). Although there are
numerous other deposit and alteration types that can be analyzed successfully
with this method, space constraints allow only an overview of the above list.
This section therefore presents a very brief definition of the deposit type,
reference to a graphic model, list the better-known deposit examples, and
discuss the alteration from the spectral perspective. The information presented
here as background to the deposit type and alteration systems has been
compiled from references and from websites.
Definition of deposit type
EPITHERMAL GOLD - LOW SULFIDATION
Epithermal gold deposits form in hydrothermal systems related to volcanic
activity. These systems, while active, discharge to the surface as hot springs or
fumaroles. Epithermal gold deposits occur largely in volcano-plutonic arcs
(island arcs as well as continental arcs) associated with subduction zones, with
ages similar to those of volcanism. The deposits form at shallow depth,

________________________________________________________________
Boiling of liquid in the LS geothermal environment leads to precipitation of gold
in veins accompanied by a variety of features such as adularia and bladed
calcite cementing colloform and brecciated quartz. Silica sinters may be the
surface expression of such veins and may be accompanied by nearby zones of
surficial steam-heated acid alteration
These deposits form in both subaerial, predominantly felsic, volcanic fields in
extensional and strike-slip structural regimes and island arc or continental
andesitic stratovolcanoes above active subduction zones. Near-surface
hydrothermal systems, ranging from hot springs at surface to deeper, structurally
and permeability focused fluid flow zones are the sites of mineralization. The ore
fluids are relatively dilute and cool solutions that are mixtures of magmatic and
meteoric fluids. Mineral deposition takes place as the solutions undergo cooling
and degassing by fluid mixing, boiling, and decompression.
http://www.em.gov.bc.ca/mining/Geolsurv/MetallicMinerals/MineralDepositProfile
s/profiles/h05.htm Panteleyev (1996):
Model for Low Sulfidation Epithermal Vein Systems
Figure 20 - Figure shows a model for a low-sulfidation epithermal gold system. Note distribution
of alteration zoning and know deposits. (Corbett and Leach, 1998)
19

________________________________________________________________
Major Global Deposits
EL PEÑON, Chile MARTA, Peru
ESQUEL, Argentina ROUND MOUNTAIN, Nevada
CERRO VANGUARDIA, Argentina COMSTOCK, Virginia City, Nevada
HISHIKARI, Japan SLEEPER, Nevada
GOSAWONG , Indonesia MIDAS, Nevada
KUPOL, Russia WAIHI , New Zealand
ROSIA MONTANA, Romania GOLDEN CROSS, New Zealand
LIHIR, PNG CERRO BAYO, Chile
TRES CRUCES, Peru KORI KOLLO, Bolivia
COMMON ALTERATION MINERALS in LOW SULFIDATION SYSTEMS
ILLITE KAOLINITE CHLORITES
ILLITE/SMECTITE BUDDINGTONITE EPIDOTE
Montmorillonite ADULARIA* ZEOLITES
QUARTZ CALCITE HEMATITE
*Adularia is not infrared active.
Alteration types associated with Low Sulfidation Systems
Silicification is extensive in ores as multiple generations of quartz and
chalcedony and commonly is accompanied by adularia and calcite. Pervasive
silicification in vein envelopes is flanked by sericite-illite-kaolinite assemblages.
Intermediate argillic alteration [kaolinite-illite-montmorillonite (smectite)] forms
adjacent to some veins; advanced argillic alteration (kaolinite-alunite) may form
along the tops of mineralized zones. Propylitic alteration dominates at depth and
peripherally. Panteleyev, A.(1996). Buddingtonite can also be present.
QSA Quartz-Sericite-
Adularia
Figure 21 - Plot shows illite, mixed layer
illite/smectite, montmorillonite, quartz, calcite,
dolomite, kaolinite and pyrite.
20
Silicic
Figure 22 - Silicic alteration is pervasive
replacement of the rock by silica minerals.
Minerals include opal, chalcedony, quartz,
hematite, and pyrite.

________________________________________________________________
This assemblage also contains adularia. The chemical bonds for feldspars are
not detectable in the SWIR range. This varies from alteration around veins,
fractures and permeable zones to selective replacement of plagioclase in
alteration envelopes.
Figure 23 - QSA alteration plot shows quartz, illite,
muscovite with quartz, and pyrite.
Argillic
QSA Quartz-Sericite-Adularia
This type of alteration occurs as wall rock alteration around veins and
replacement zones in permeable lithologies. This may show the change in
aluminum content and temperature change away from the vein in a progression
from illite illite/smectite smectite. Carbonates are also important in these
systems and may reflect condensation of CO2 from deeper boiling zones.
In these systems is also seen amethyst, quartz pseudomorphs after calcite,
barite, fluorite, Ca-Mg-Mn-Fe carbonate minerals such as rhodochrosite.
Panteleyev (1996):
21
Argillic
Figure 24 - Argillic alteration plot shows
illite, illite/smectite, montmorillonite,
calcite, dolomite, kaolinite, and pyrite.

________________________________________________________________
Steam Heated Argillic
This alteration type is found above the water table and forms an extensive area.
It is related to the condensation and oxidation of gases (H2S). It is found in
geothermal areas with mud pots, fumeroles and native sulfur.
Weathered outcrops are often characterized by resistant quartz ± alunite 'ledges'
and extensive flanking bleached, clay-altered zones with supergene alunite,
jarosite, and other limonite minerals. Panteleyev (1996):
Propyllitic
Steam Heated Argillic
Figure 25 - Steam Heated Argillic alteration
plots sulfur, pyrite, chalcedony, opal,
kaolinite, alunite and jarosite.
Propylitic alteration occurs in the outer zone of alteration around a deposit. It can
have regional extension.
22
Propylitic
Figure 26 - This plot of propylitic alteration shows
Mg-Chlorite, Fe-Chlorite, epidote, illite/smectite,
zeolite. Montmorillonite and calcite.

________________________________________________________________
Definition of deposit type
HIGH SULFIDATION SYSTEMS
High sulphidation Au + Cu ore systems develop from the reaction with host rocks
of hot acidic magmatic fluids to produce characteristic zoned alteration and later
sulphide and Au + Cu + Ag deposition. Ore systems display permeability controls
governed by lithology, structure and breccias and changes in wall rock alteration
and ore mineralogy with depth of formation. One of the challenges is to
distinguish the mineralized systems from a group of generally non-economic
acidic alteration styles including lithocaps or barren shoulders, steam heated,
magmatic solfatara and acid sulphate alteration.
Original definitions (Heald et al.,1987) suggest that epithermal deposits formed at
temperatures < 300°C and therefore at shallow depths, typically < 1 km.
The term epithermal is therefore used in field exploration studies to describe Au ±
Ag ± Cu deposits formed in magmatic arc environments (including rifts) at
shallow depths, most typically above the level of formation of porphyry Cu-Au
deposits (typically < 1 km), although in many instances associated with
subvolcanic intrusions. Higher level epithermal deposits are commonly formed
later in a deposit paragenesis, and may be telescoped upon deeper earlier
formed deposits, including in some instances porphyry systems which are older,
or part of the same overall magmatic event (e.g., Lihir, Corbett et al., 2001b). In
strongly dilational structural environments porphyry-related systems may be
telescoped outwards into the deeper “epithermal” environment (e.g., Cadia,
Maricunga Belt).
In brief, high sulphidation deposits develop in settings where volatile rich
magmatic fluids rise to higher crustal levels without significant interaction
with the host rocks or ground waters. Volatiles (SO2) evolved from the
depressurising fluids oxidize to form a two stage hot acid fluid, the initial stage
of which reacts with the host rocks to produce the characteristic zoned acidic
alteration at epithermal crustal levels (Corbett and Leach, 1998). A later liquiddominated
fluid phase deposits sulphides which are characterised by pyrite
with enargite, or the latter’s low temperature polymorph luzonite.
Magmatic rocks are interpreted to represent the ultimate source of ore fluids as
demonstrated by the commonly association of HS deposits with felsic domes
and phreatomagmatic breccias within flow-dome complexes. Many HS deposits
display associations with porphyry Cu-Au systems of similar ages (Nena), or are
collapsed upon and form part of the porphyry ores. Fluids responsible for the
formation of HS deposits rarely evolve to Au- rich lower sulphidation style ores.
23

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Model for High Sulfidation Gold Systems
Figure 24 - FUIIIIIIIIIIIIIIIIIIIIIYiuuuuuuuuuuuuuuuuuuuuuuu
Figure 27 - Model for High Sulfidation Gold System showing alteration zones and feeder
structure. Source: Henley and Ellis, 1983
List of Well Known Deposits - Distribution
GOLDFIELD , Nevada ZIJINSHAN, China
YANACOCHA, Peru SIPAN, Peru
SUMMITVILLE, Colorado TAMBO, Chile
LEPANTO, Phillipines TANTAHUATAY, Peru
PASCUA-LLAMA, Chile-Argentina AQUA RICA, Argentina
PIERINA, Peru QUIMSACOCHA, Ecuador
PUEBLO VIEJO, Dominican Republic MARTABE, Indonesia
ALTA CHACAMA< Peru VELADERO, Argentina
LA COIPA, Chile RODIQUILAR, Spain
MULATOS, Mexico FURTEI, Sardinia
ALTERATION TYPES (Corbett 2000)
Acid alteration contains a suite of minerals formed in low-pH conditions (e.g.,
kaolin-dickite, alunite, pyrophyllite, dickite) and may be grouped as styles
including: Barren high sulphidation alteration described as lithocaps or barren
shoulders are a common source of difficulty for explorationists, especially as
these may crop out in the vicinity of low and high-sulphidation epithermal Au and
also porphyry Cu-Au mineralization. Barren shoulders comprise a class of nonmineralized
advanced argillic (silica-alunite + pyrophyllite etc.) alteration derived
24

________________________________________________________________
from magmatic volatiles venting from intrusive sources at depth (Corbett and
Leach, 1998). These alteration zones are characterized by high temperature
minerals such as pyrophyllite-diaspore, zunyite, topaz, locally including
corundum and andalusite. Silica characteristically occurs as a massive form
rather than vuggy silica, typical of mineralized high sulphidation deposits.
Examples include Lookout Rocks, Horse Ivaal at Frieda River, Vuda, and Alum
Mountain. Lithocaps (Sillitoe (1995, 1999) may extend to higher crustal levels,
include additional lower temperature argillic alteration, and are interpreted
(Sillitoe, op cit) to locally conceal epithermal or porphyry mineralization.
Shoulders and lithocaps crop out as variably dipping bodies termed ledges
developed by the exploitation of permeable lithologies (typically flat dipping), or
dilatant structures (typically steep dipping). These alteration zones are
distinguished from mineralized high sulphidation systems in the field by the lack
of vuggy silica and generally coarse grained and higher temperature layered
silicates (e.g., alunite, pyrophyllite, dickite). The presence of high temperature
alteration minerals such as alunite or corundum is distinctive. PIMA, Terraspec
and XRD studies are therefore useful for the delineation of alteration zonation
and provision of vectors towards where mineralization should occur in ore
systems.
25

________________________________________________________________
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.

________________________________________________________________
1998). Mineralogies dominated by pyrophyllite-diaspore-dickite may be
indicative, but not exclusively, of higher temperature (deeper) conditions,
whereas lower temperature (opaline) pervasive silicification or alunite-kaolin
dominate in cooler (higher level) settings. Similarly, thin alteration zones may
suggest that fluid conditions have changed rapidly, possibly in a quenched higher
level system (or distal to the fluid upflow), whereas wide zonation characterizes
slower changing fluid conditions more typical of deeper levels (or more proximal
to the fluid upflow).
Figure 30 - Advanced Argillic Alteration spectra show
pyrophyllite, topaz, zunyite, dickite, alunite, quartz,
hematite, and pyrite.
27
Figure 31 - Intermediate Argillic Alteration shows
kaolinite, illite, illite/smectite, montmorillonite, quartz,
pyrite

________________________________________________________________
Argilic — Intermediate Argillic
This alteration zone is found between propylitic and and advanced argillic. It can
be progressive outward from illite illite/smectite montmorillonite. It may
also show gradations from illite + illite/smectite into a chlorite envelope
around the illite vein (Comstock Lode, Virginia City, Nv).
Figure 32 - Argillic alteration contains
kaolinite, illite, illite/smectite,
montmorillonite, quartz, and pyrite.
Propylitic Alteration
Propylitic can be regional, but it is usually found in the outer-most alteration
zone. It will show different wavelengths for the chlorites as opposed to those
chlorites in the intermediate argillic suite.
28
Figure 33 - Propylitic Alteration shows Mg-Chlorite,
Fe-chlorite, epidote, calcite, pyrite.

________________________________________________________________
Porphyry Copper Deposits
Porphyry copper deposits form at 2-5 km below the earth's surface at
temperatures of >500-600 degreed C from hypersaline (40-60 wt % NaCl equiv.)
near neutral magmatic fluids (Hedenquist and Lowenstein, 1994). Aqueous
magmatic vapors containing CO2, SO2, H2S, and HCl separate from fluids and
ascend to the surface. Ore bodies range in size from several hundred meters to
more than a kilometer in diameter. Grades tend to be low, and the ore minerals
are usually disseminated through a quartz stockwork within the upper part of the
host porphyry intrusive.
Alteration around the ore body is usually concentric and may be described by the
Lowell and Guilbert (1970) model for porphyry copper deposits. Zoned
assemblages that were formed as reactive, metal-bearing magmatic fluid, which
moved away from the intrusion, cooled and reacted with the country rock.
In the core of the deposit, over the mineralizing intrusion, there is a potassic zone
(biotite + magnetite ± orthoclase ± albite ± anhydrite ± chalcopyrite ± bornite)
which represents late magmatic K-metasomatism of the host intrusives. This
passes upwards into extensive quartz stockwork and a transitional zone
characterized by intermediate argillic alteration (chlorite + hematite/sulfides +
quartz ± illite).
This is usually overprinted by the phyllic zone which dominates the stockwork.
The phyllic zone is acid-leached and characterized by quartz + sericite +
tourmaline + pyrite ± chalcopyrite. The sericite may be composed of either illite +
montmorillonite or fine grained muscovite. Above the phyllic zone, the rock is
capped by an advanced argillic zone where leaching is oxidized acidic water
(generated by the absorption of magmatic vapor in to meteoric waters) has been
particularly intense and may reach to the paleosurface. It is characterized by the
assemblage quartz + alunite ± pyrophyllite ± kaolinite/dickite. Surrounding the
potassic, intermediate/phyllic and advanced argillic zones is the deuterically
(propylitic) altered country rock. The propylitic zone is characterized by green
coloration and the assemblage: chlorite + epidote ± albite ± actinolite ± calcite ±
hematite.
Hypogene copper sulphide mineralization is characterized by chalcopyrite
[although bornite occurs when the sulfur activity is low as indicated by the
absence of pyrite]. Magnetite is common in the potassic zone and pyrite in
phyllic zone in the advanced argillic zone, sulphides have been decomposed and
leached, or replaced by limonite.
Supergene leaching of hypogene alteration and mineralization occurs after the
hydrothermal event. It is distinguished here from weak secondary alteration (due
to later near neutral meteoric water percolation) which does not produce strong
leaching, but may result in a modest overprint of montmorillonite, kaolinite, in the
29

________________________________________________________________
hypogene and supergene zones. The principal mechanism of strong supergene
leaching is the oxidation of pyrite in water, which produces limonite and
generates sulphuric acid. The effect of this acid on acid stable hypogene
minerals (quartz, alunite, kaolinite) is subtle. However, there may be
decomposition of biotite and feldspars in the potassic zone. Feldspars and
chlorite in the propylitic zone and illite in the phyllic zone, producing a supergene
leached cap that is characterized by the assemblage quartz + alunite + kaolinite
+ gypsum. This is not always easy to distinguish from the hypogene leached cap
of the advanced argillic zone.
Figure 34
Infrared Active Alteration Minerals Associated with Porphyries
Infrared-active alteration minerals associated with porphyries include quartz,
sericite/muscovite, biotite, phlogopite, anhydrite/gypsum, magnetite, actinolite,
chlorite, epidote, calcite, clay minerals (illite, kaolinite, smectite), tourmaline.
Gangue minerals in mineralized veins are mainly quartz with lesser biotite,
sericite, magnetite, chlorite, calcite, epidote, anhydrite and tourmaline. Leached
cap and lithocap minerals can include jarosite, alunite, pyrophyllite, diaspore,
zunyite, topaz and dickite.
30

________________________________________________________________
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.
31
Figure 36 - Potassic - K-silicate alteration
includes "albite", anhydrite, quartz, muscovite
and epidote.

________________________________________________________________
Potassic - K-silicate
This alteration occurs in the core of porphyry systems, particularly when hosted
by felsic intrusions - granodiorite, quartz monzonite,granite, seyenite. Minerals
include K-feldspar, quartz, albite, muscovite, anhydrite, epidote. Feldspars do
not have detectable bonds in the SWIR region and therefore their profiles do not
have distinctive features.
Sodic, Sodic-Calcic
Occurs with minor mineralization in the deeper parts of some porphyry systems
and is a host to mineralization in porphyry deposits associated with alkaline
intrusions.
albite, actinolite, diopside, quartz, magnetite, titanite, chlorite, epidote , scapolite
Figure 37 - Sodic- Calcic alteration plots
Albite, actinolite, Fe-chlorite, epidote,
Mg-chlorite, marialite, mizzonite,
diopside, quartz, magnetite.
32
Figure 38 - Phyllic alteration includes:
Illite, muscovite, iron chlorite, Mgchlorite,
gypsum, anhydrite, quartz,
pyrite.

________________________________________________________________
Phyllic
Phyllic alteration commonly forms a peripheral halo around the core of porphyry
deposits. It may overprint earlier potassic alteration and may host substantial
mineralization. Detectable minerals include muscovite, illite, quartz, pyrite,
chlorite, hematite, and anhydrite.
Intermediate Argillic
Intermediate argillic alteration generally forms a structurally controlled to
widespread overprint on other types of alteration in many porphyry systems. The
detectable minerals include illite, muscovite, dickite, kaolinite, Fe-chlorite, Mgchlorite,
epidote, montmorillonite, calcite, and pyrite.
Figure 39 - Intermediate argillic alterations
contains muscovite, illite, chlorite, kaolinite,
dickite, montmorillonite, calcite, epidote, and
pyrite.
33
Figure 40 - Advanced argillic alteration for a
porphyry system will contain higher temperature
minerals such as Topaz, pyrophyllite, andalusite,
dumortierite, tourmaline, along with alunite,
diaspore, quartz, hematite, and pyrite.

________________________________________________________________
Advanced Argillic
This is an intense alteration phase, often in the upper part of porphyry systems.
It can also form envelopes around pyrite-rich veins that cross cut other alteration
types. The minerals associated with this type are higher temperature and include
pyrophyllite, quartz, andalusite, diaspore, corundum, alunite, topaz, tourmaline,
dumortierite, pyrite, and hematite.
Propylitic
Forms the outermost alteration zone at intermedite to deep levels in the porphyry
system. It can be mineralogically zoned from inner actinolite-rich to out epidote
rich facies. chlorite, epidote, albite, calcite, actinolite, illite, clay pyrite
Figure 41 - Propylitic alteration for porphyry systems
includes; Fe- chlorite, Mg-chlorite, epidote, actinolite,
calcite, illite, montmorillonite, albite, and pyrite.
34
Figure 42 - Copper carbonates in porphyry
systems can include azurite, malachite,
aurichalcite, and rosasite.

ARSENATES
________________________________________________________________
Supergene
Secondary (supergene) zones carry chalcocite, covellite and other Cu2S minerals
(digenite, djurleite, etc.), chrysocolla, native copper and copper oxide, carbonate
and sulphate minerals. Oxidized and leached zones at surface are marked by
ferruginous “cappings” with supergene clay minerals, limonite (goethite, hematite
and jarosite) and residual quartz. Panteleyev, A. (1995):
Minerals include: antlerite, bisbeeite, brochantite, chalcoalumite, claringbullite,
conichalcite, crednerite, cuprite, delafossite, graemite, nantokite, paramelaconite,
paratacamite, rosasite and spangolite, aurichalcite, connellite, cyanotrichite,
malachite and shattuckite are additional supergene copper. Those available in
the database are plotted in this section.
The best way to display the variations in the supergene environment is by group.
The following plots are divided into copper carbonates, chlorides, arsenates,
phosphate, silicates and sulfates.
CHLORIDES
Figure 43 - Copper chlorides includes
atacamite, connellite, and cumengite.
ARSENATES
35
PHOSPHATES
Figure 44 - Copper phosphates include
libelhenite, pseudomalachite, and
turquoise.
Figure 45 - Copper arsenates
include bayldonite, chenevixite,
conichalcite, clinoclase and
olivenite.

________________________________________________________________
SILICATES
Figure 46 - Copper silicates include chrysocolla,
dioptase, papagoite, and shattuckite
36
SULFATES
Figure 47 - Copper sulfates include antlerite,
brochantite, chalcanthite, cyanotrichite,
kroehnite, spangolite.

________________________________________________________________
LEACHED CAP
Minerals in the leached cap environment include alunite, kaolinite, illite, diaspore,
iron oxides, copper sulfates, and copper hydroxides.
Figure 48 - Leach cap minerals include goethite,
hematite, jarosite, kaolinite, chrysocolla,
antlerite, brochantite, diaspore, turquoise.
alunite.
Exotic copper mineralization is a complex hydrochemical process linking
supergene enrichment, lateral copper transport, and precipitation of copper oxide
minerals in the drainage network of a porphyry copper deposit.
37
Figure 49 - Other leach cap minerals are copper
bearing and include atacamite, azurite, malachite,
chrysocolla, kaolinite.

________________________________________________________________
DIAMONDS - KIMBERLITES
DEPOSIT DEFINITION
Kimberlites are a group of volatile-rich (dominantly carbon dioxide) potassic
ultrabasic rocks. Commonly, they exhibit a distinctive inequigranular texture
resulting from the presence of macrocrysts (and in some instances megacrysts)
set in a fine-grained matrix. The megacryst/macrocryst assemblage consists of
rounded anhedral crystals of magnesian ilmenite, Cr-poor titanian pyrope, olivine,
Cr-poor clinopyroxene, phlogopite, enstatite and Ti-poor chromite. Olivine is the
dominant member of the macrocryst assemblage. The matrix minerals may
include second generation euhedral primary olivine and/or phlogopite, together
with perovskite, spinel (titaniferous magnesian aluminous chromite, titanian
chromite, members of the magnesian ulvospinel-ulvospinel-magnetite series),
diopside (Al- and Ti- poor), monticellite, apatite, calcite, and primary late-stage
serpentine (commonly Fe rich). Some kimberlites contain late-stage phlogopites.
The replacement of early-formed olivine, phlogopite, monticellite, and apatite by
deuteric serpentine and calcite is common. Evolved members of the clan may be
devoid of, or poor in, macrocrysts, and composed essentially of calcite,
serpentine, and magnetite together with minor phlogopite, apatite, and
perovskite. (From Mitchell 1986)
http://www.geology.ubc.ca/research/diamonds/kopylova/intro/morphology.html
Kimberlites can be divided into 3 distinct units based on morphology and
petrology. These units are: 1) Crater Facies Kimberlite ,2) Diatreme Facies
Kimberlite; 3) Hypabyssal Facies Kimberlite (Mitchell 1986). Kimberlite occurs
in the Earth's crust in vertical structures known as kimberlite pipes.
Kimberlites are divided into Group I (basaltic) and Group II (micaceous)
kimberlites, along mineralogical grounds, the difference in mineralogy being
caused by the preponderance of water versus carbon dioxide. Group I
kimberlites are of CO2-rich ultramafic potassic igneous rocks dominated by a
primary mineral assemblage of forsteritic olivine, magnesian ilmenite, chromian
pyrope, almandine-pyrope, chromian diopside, phlogopite, enstatite and of Tipoor
chromite. Group-II kimberlites (or orangeites) are ultrapotassic, peralkaline
rocks rich in volatiles (dominantly H2O). The distinctive characteristic of
orangeites is phlogopite macrocrysts and microphenocrysts, together with
groundmass micas that vary in composition from phlogopite to Fe-rich
phlogopite.
38

________________________________________________________________
Figure 50
DEPOSIT MODEL
Diamonds are mined in about 25 countries. India was the initial source, followed
by Brazil and then South Africa. Africa is the richest continent for diamond
mining, accounting for roughly 49% of world production. The major sources are in
the south with lesser concentrations in the west-central part of the continent. The
major producing countries are Congo Republic (Zaire), Botswana, South Africa,
Angola, Namibia, Ghana, Central African Republic, Guinea, Mali, Sierra Leone,
Tanzania and Zimbabwe. Canada is starting to come on line now with Ekati and
Diavik.in the northern part of the country. Australia has one producing mine, the
Argyle. There are major resources in Russia. The United States has very minor
deposits in Colorado, Wyoming and Arkansas.
(http://www.amnh.org/exhibitions/diamonds/other.html)
39

________________________________________________________________
ALTERATION MINERALS
Common alteration minerals associated with kimberlites include: Carbonates,
Phlogopite, Biotite, chlorites, Serpentine, richterite, other amphiboles, talc,
septechlorite, smectite, saponite, apophyllite, zeolites (analcime), vermiculite.
Figure 51 - This plots shows Serpentine,
calcite, magnesite, phlogopite, biotite,
chamosite, clinochlore, saponite, Mgsilicate,
vermiculite, Fe-amphibole.
INDICATOR MINERALS
Several minerals, when found in glacial sediments, are useful indicators of the
presence of kimberlite, and to a certain extent, an evaluation of the diamond
potential of kimberlite. These minerals are far more abundant in kimberlite than
diamond, survive glacial transport, and are visually and chemically distinct. Crpyrope
(purple colour, kelyphite rims), eclogitic garnet (orange-red), Cr-diopside
(pale to emerald green), Mg-ilmenite (black, conchoidal fracture), chromite
40
Figure 52 - Other alteration minerals include
pyrope garnet, richterite, phlogopite, olivine,
diopside. Cr-diopside

________________________________________________________________
(reddish-black, irregular to octahedral crystal shape), and olivine (pale yellowgreen)
are the most commonly used kimberlite indicator minerals in drift
prospecting. Kimberlite indicator minerals are recovered from the medium to very
coarse sand-sized fraction of glacial sediments, and analyzed by electron
microprobe to confirm their identification.
(source: http://sts.gsc.nrcan.gc.ca/page1/miner/kirk/indic.htm)
Garnets
Pyrope, Almandine, Grossular
Diopside
Chrome-diopside, diopside
Others to consider
Zircon, Olivine, Orthopyroxenes (Harzburgite?),Chromite??, Ilmenite??,
Perovskite??
Figure 53 - This plot includes
almandine, grossularite, pyrope garnets;
diopside, Cr-diopside, and olivine. Figure 54 - Garnet comparisons
\
41
The indicator garnet for the presence of diamonds in
kimberlites is a G-10. This has a diagnostic chrome
feature in the visible, indicated by the arrow.

________________________________________________________________
DEPOSIT TYPE DEFINITION
SKARNS
http://www.wsu.edu:8080/~meinert/aboutskarn.html#Definitions
There are many definitions and usages of the word "skarn". Skarns can form
during regional or contact metamorphism and from a variety of metasomatic
processes involving fluids of magmatic, metamorphic, meteoric, and/or marine
origin. They are found adjacent to plutons, along faults and major shear zones, in
shallow geothermal systems, on the bottom of the seafloor, and at lower crustal
depths in deeply buried metamorphic terranes. What links these diverse
environments, and what defines a rock as skarn, is the mineralogy. This
mineralogy includes a wide variety of calc-silicate and associated minerals but
usually is dominated by garnet and pyroxene.
The composition and texture of the protolith tend to control the composition and
texture of the resulting skarn. In contrast, most economically important skarn
deposits result from large-scale metasomatic transfer, where fluid composition
controls the resulting skarn and ore mineralogy.
One of the more fundamental controls on skarn size, geometry, and style of
alteration is the depth of formation.
Major skarn types:
Fe Skarns ,Au Skarns, W Skarns, Cu Skarns, Zn Skarns, Mo Skarns.
The vast majority of skarn deposits are associated with magmatic arcs related to
subduction beneath continental crust. Plutons range in composition from diorite
to granite although differences among the main base metal skarn types appear to
reflect the local geologic environment (depth of formation, structural and fluid
pathways) more than fundamental differences of petrogenesis (Nakano et al.,
1994). In contrast, gold skarns in this environment are associated with
particularly reduced plutons that may represent a restricted petrologic history.
42

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ALTERATION TYPES ASSOCIATED WITH SKARNS
RETROGRADE ALTERATON
The term retrograde alteration refers to an alteration stage in which higher
temperature, generally anhydrous, minerals are replaced by lower temperature,
generally hydrous, minerals. In some cases this process is largely metamorphic,
i.e. the bulk composition stays roughly the same but mineral "A" is replaced by
mineral "B". In other cases, retrograde alteration is concurrent with strong
metasomatism, such as during mineralization with various sulfide minerals
Retrograde skarn mineralogy, in the form of epidote, amphibole, chlorite, and
other hydrous phases, typically is structurally controlled and overprints the
prograde zonation sequence. Thus, there often is a zone of abundant hydrous
minerals along fault, stratigraphic, or intrusive contacts. This superposition of
later phases can be difficult to discriminate from a spatial zonation sequence due
to progressive reaction of a metasomatic fluid.
SKARN MODEL
Figure 55 - Zonation of most skarns reflects the geometry of the pluton
contact and fluid flow. Such skarns are zoned from proximal endoskarn to
proximal exoskarn, dominated by garnet. More distal skarn usually is more
pyroxene-rich and the skarn front, especially in contact with marble, may be
dominated by pyroxenoids or vesuvianite. Meinert, L.D., 1992
43

________________________________________________________________
In general, retrograde alteration is more intense and more pervasive in shallower
skarn systems. In some shallow, porphyry copper-related skarn systems,
extensive retrograde alteration almost completely obliterates the prograde garnet
and pyroxene skarn (Einaudi, 1982a,b)
Porphyry copper Skarn
Alteration potassic alteration
phillic alteration
advanced argillic alteration
propylitic alteration
Figure 56 - From Murakami (2005)
The main differences between amphiboles in different skarn types are variations
in the amount of Fe, Mg, Mn, Ca, Al, Na, and K. Amphiboles from Au, W, and Sn
skarns are progressively more aluminous (actinolite-hastingsite-hornblende),
amphiboles from Cu, Mo, and Fe skarns are progressively more iron-rich in the
tremolite-actinolite series, and amphiboles from zinc skarns are both Mn-rich and
Ca-deficient, ranging from actinolite to dannemorite. For a specific skarn deposit
or group of skarns, compositional variations in less common mineral phases,
such as idocrase, bustamite, or olivine, may provide insight into zonation patterns
or regional petrogenesis (e.g. Giere, 1986; Silva and Siriwardena, 1988;
Benkerrou and Fonteilles, 1989).
44
Prograde
Retrograde
Vein system A vein:biotite vein
Dominant in sallower part of
B vein:Quartz-molybdenite (no alteration halo skarn system
along vein)
C vein:chlorite (or green smectite bearing
mixed layer clay) + sulfides (partly pyrite
+molybdenite)
D vein: phillic alteration (sericite alteration
along Quartz vein)
Related intrusion Generally, porphyry, sometimes depend on
depth of formation
Depend on depth of formation

________________________________________________________________
PROGRADE ALTERATION
The minerals found in prograde systems include: Scapolite-meionite, scapolitemarialite,
scapolite-mizzonite, diopside, hedenbergite, olivine, rhodonite,
grossularite, andradite, wollastonite, vesuvianite
Figure 57 - Scapolite-meionite, scapolite-marialite, scapolite-mizzonite, diopside, hedenbergite,
olivine, rhodonite, grossularite, andradite, wollastonite, and vesuvianite.
45

________________________________________________________________
RETROGRADE SKARN ALTERATION
Retrograde alteration commonly replaces earlier skarn alteration, but may also
affect adjacent wallrock, which is many cases is limestone.
The minerals observed in these suites include illite/smectite, montmorillonite,
nontronite, pyrite, epidote, clinozoisite, tremolite ->actinolite, prehnite, chlorite,
vesuvianite, biotite, phlogopite, quartz, calcite, dolomite, ankerite, siderite, Fedolomite.
These are plotted in Figures 58, 59, and 60.
CLAY SERIES
Figure 58 - Illite, Illite/smectite,
montmorillonite, nontronite, and pyrite.
46
CARBONATE SERIES
Figure 59 - Ankerite, calcite, dolomite,
Fe-dolomite, and siderite.

________________________________________________________________
Figure 60 - Actinolite, tremolite, epidote,
clinozoisite, Fe-Chlorite, Mg-chlorite,
biotite, phlogopite, vesuvianite, and
prehnite
47
Figure 61 - Forsterite, serpentine, talc, calcite,
tremolite, and magnetite
MAGNESIUM SKARN
Magnesium skarns are developed as
metasomatic replacements of dolomitic
limestone. High temperature magnesium
skarns are characterized by forsterite, and
diopside and low temperature magnesium
skarns contain serpentine and talc. Both of
which occur as retrograde minerals after
forsterite and clinopyroxene.
Figure 61 plots forsterite, serpentine, talc,
calcite, tremolite, magnetite.

________________________________________________________________
Definition of deposit type
IRON OXIDE COPPER GOLD (IOCG)
Iron oxide copper-gold (IOCG) deposits encompass a wide spectrum of sulphidedeficient
low-Ti magnetite and/or hematite ore bodies of hydrothermal origin
where breccias, veins, disseminations and massive lenses with polymetallic
enrichments (Cu, Au, Ag, U, REE, Bi, Co, Nb, P) are genetically associated with,
but either proximal or distal to large-scale continental, A- to I-type magmatism,
alkaline-carbonatite stocks, and crustal-scale fault zones and splays. The
deposits are characterized by more than 20% iron oxides. Their lithological hosts
and ages are non-diagnostic but their alteration zones are, with calcic-sodic
regional alteration superimposed by focused potassic and iron oxide alterations.
The deposits form at shallow to mid crustal levels in extensional, anorogenic or
orogenic, continental settings such as intracratonic and intra-arc rifts, continental
magmatic arcs and back-arc basins. Margins of Archean craton where arcs and
successor arcs were developed appear to be particularly fertile.
http://gsc.nrcan.gc.ca/mindep/synth_dep/iocg/index_e.php
The 3810 Mt Olympic Dam deposit in Australia is the deposit that guides most
mineral exploration worldwide (Hitzman et al., 1992; Western Mining Corporation,
2003). Currently known metallogenic IOCG districts occur in Precambrian
shields worldwide as well as in Circum-Pacific regions (e.g., Carlon, 2000;
Fourie, 2000; Porter, 2000, 2002a and papers therein; Strickland and Martyn,
2002; Gandhi, 2004c; Goff et al., 2004).
The recognition of this deposit type was triggered by the 1975 discovery of the
giant Olympic Dam deposit in Australia (Roberts and Hudson, 1983) followed by
the discovery of Starra (1980), La Candelaria (1987), Osborne (1988), Ernest-
Henry (1991), and Alemao (1996). The early discoveries served to define this
group of deposits as the IOCG deposit type in the 1990s (Hitzman et al., 1992).
source: Mineral Deposits of Canada
Source: Iron Oxide Copper-Gold (+/-Ag,+/-Nb,+/-REE,+/-U) Deposits: A Canadian
Perspective
Louise Corriveau Geological Survey of Canada
http://gsc.nrcan.gc.ca/mindep/synth_dep/iocg/index_e.php
This appears to be a website publication only.
48

________________________________________________________________
IOCG PROPOSED MODELS
Figure 62 - Schematic illustrations of flow paths and hydrothermal features for alternative models for IOCG deposits. Shading in arrows
indicates predicted quartz precipitation (veining) for different paths in different quartz-saturated rocks which provides a useful
first-order indication of path (cf,. Barton el al., 1997, Barton and Johnson,2000)..
________________________________________________________________
Page 49

________________________________________________________________
ALTERATION
Following is a summary of alteration zoning associated with many IOCG
deposits. Please note that reflectance spectroscopy does not detect the silicate
bonds found in the feldspars.
The principal ore minerals are hematite (specularite, botryoidal hematite and
martite), low-Ti magnetite, bornite, chalcopyrite, chalcocite and pyrite.
Subordinate ones include Ag-, Cu-, Ni-, Co-, U-arsenides, autunite, bastnaesite,
bismuthinite, brannerite, britholite, carrolite, cobaltite, coffinite, covellite, digenite,
florencite, loellingite, malachite, molybdenite, monazite, pitchblende, pyrrhotite,
sulphosalts, uraninite, xenotime, native bismuth, copper, silver and gold, Ag-, Bi-,
Co-telluride, and vermiculite.
Gangue mineralogy consists principally of albite, K-feldspar, sericite, carbonate,
chlorite, quartz (crypto-crystalline in some cases), amphibole, pyroxene, biotite
and apatite (F- or REE-rich) with accessory allanite, barite, epidote, fayallite,
fluorite, ilvaite, garnet, monazite, perovskite, phlogopite, rutile, scapolite, titanite,
and tourmaline. The amphibole includes Fe-, Cl-, Na- or Al-rich hornblende
(edenite), actinolite, grunerite, hastingsite, and tschermakitic or alkali amphibole.
Carbonates include calcite, ankerite, siderite and dolomite. Late-stage veins
contain fluorite, barite, siderite, hematite and sulphides.
There are 3-6 alteration types associated with IOCG deposits. These include
sodic, sodic-calcic, potassic, quartz-tourmaline, and albite-calcite. Figure 63
shows the minerals associated with the different alteration types.
MINERAL Sodic Sodic-calcic Potassic Qzt-Tourmaline Albite-Calcite
albite
K-spar
amphiboles
bastnaesite (REE carbonates)
biotite
calcite
chlorite
epidote
garnet (andradite, Fe-rich garnet)
hematite
monazite
muscovite
quartz
scapolite
tourmaline
magnetite
Figure 63 – Minerals associated with alteration types for IOCG deposits.
________________________________________________________________
Page 50

________________________________________________________________
Sodic Alteration. The minerals are albite, magnetite, and epidote.
Sodic
Alteration
Figure 64 - With sodic alteration,
spectroscopy sees magnetite and epidote.
Sodic-Calcic Alteration early stages
There is strong albitization (± clinopyroxene, titanite, calc-silicate (clinopyroxene,
amphibole, garnet) - alkali feldspar (K-feldspar, albite) ± Fe-Cu sulphides, and
various assemblages including albite, actinolite, magnetite, apatite and late
epidote. Ca-rich host-rocks are present, with Fe-rich garnet-clinopyroxene ±
scapolite skarn.
Scapolite-actinolite-magnetite
Albite - actinolite-magnetite
Albite-chlorite-epidote-calcite
This is very complex system or systems.
Iron Stage
This stage is largely sterile except for iron ore and apatite. There is an influx of
magnetite ± biotite.
51
Sodic-Calcic
Figure 65 – Sodic-calcic alteration is more complex.
The plot shows actinolite, iron-chlorite, epidote,
diopside, magnetite, mizzonite, marialite, calcite
and pyrope.

________________________________________________________________
The minerals include
iron oxide (magnetite and hematite), iron carbonate (siderite and
ankerite) and iron silicate (chlorite and amphibole, in particular grunerite
and hastingsite).
IRON STAGE
Figure 66 - The iron stage of alteration shows
biotite, iron-chlorite, cummingtonite, ankerite,
siderite, hematite, and magnetite.
Potassic Alteration
The main ore stage is associated with potassium-iron alteration zones in which
either sericite (at Olympic Dam and Prominent Hill) or K-feldspar (most common)
prevail as the potassic-bearing phase.
K-feldspar-biotite-pyrite-chalcopyrite
At Olympic Dam,
Potassic alteration occurs with hematite, sericite, chlorite, carbonate ± Fe-Cu
sulphides ± uraninite, pitchblende and REE (bastnaesite) minerals prevail. It is
locally superimposed on a magnetite-biotite alteration (Reynolds, 2000; Skirrow
et al., 2002). The intense chloritization destroys the biotite. Quartz, fluorite,
barite, carbonate, orthoclase, epidote and tourmaline can also be present.
Titanite, monazite, perovskite and rutile may occur. The main uranium mineral is
uraninite (pitchblende) with lesser coffinite and brannerite.
52
POTASSIC ALTERATION
Figure 67 - Potassic is the most
complex of the alteration phases. It
includes tourmaline, biotite, iron-chlorite,
epidote, REE-carbonate, monazite,
muscovite, calcite, hematite, quartz.

________________________________________________________________
Quartz-Tourmaline Alteration
The minerals in this suite include tourmaline-magnetite-quartzchalcopyrite-pyrite,
chlorite, and chalcopyrite.
Quartz-Tourmaline
Alteration
Figure 68 - Quartz-tourmaline alteration
plot with magnetite, quartz, tourmaline,
and Fe-chlorite.
Albite-Calcite Alteration
This phase is post ore - retrograde.
The minerals include albite-calcite-bornite-chalcocite and dolomite in
quartz veining.
53
Albite-Calcite
Figure 69 - Albite-calcite alteration is post-ore
and contains calcite, dolomite, and quartz.

________________________________________________________________
UNCONFORMITY URANIUM DEPOSITS
Unconformity-associated uranium (U) deposits consist of pods, veins, and semimassive
replacements of uraninite which are overlain by zoned, quartz
dissolution, kaolinite, sudoite, illite, dravite, quartz alteration halos and located
near unconformities between Paleo- to Mesoproterozoic siliciclastic basins and
metamorphic basement.
In major producing basins (e.g. Athabasca, Kombolgie) the 1-2 km, flat-lying,
and apparently un-metamorphosed, mainly fluvial strata include red to pale tan
quartzose conglomerate, arenite and mudstone deposited from ~1730 to > Au, Pt, Cu, REE and Fe.
(Source: by C.W. Jefferson1, D.J. Thomas2, S.S. Gandhi1, P. Ramaekers3, G.
Delaney4, D. Brisbin2, C. Cutts5, P. Portella5, and R.A. Olson6: Mineral
Deposits of Canada, Unconformity Associated Uranium Deposits
http://gsc.nrcan.gc.ca/mindep/synth_dep/uranium/index_e.php)
The paleo-weathered basement immediately below the Athabasca Group has a
vertical profile ranging from a few centimeters up to 70 meters thick, with much
deeper pockets and slivers developed along fault zones. The following
description is after Macdonald (1980, 1985). The regolith is variably affected by
diagenetic iron reduction resulting in a bleached zone at the top, interpreted as
hematite removal from the upper "red zone" of the paleo-weathered basement
section. This bleached zone, always present immediately below the
unconformity, is composed of buff-colored clay and quartz. It crosscuts and
therefore post-dates the red zone beneath. Below this, the upper portion of the
regolith profile exhibits a strong red hematitic alteration that grades into
underlying greenish chloritic alteration. In profiles developed on the basement
meta-arkose, a white zone of white clay replacement of feldspars and mafic
minerals separates the red and green zones. A downward progression from this
kaolinite to illite and chlorite is common through the regolith profile.
Discussion continues regarding the respective contributions of paleo-weathering,
diagenesis and hydrothermal processes to the alteration preserved at the
unconformity. Cuney et al. (2003) stated that the regolith may represent a redox
front controlled by the degree of percolation of the oxidized diagenetic brines in
the basement, and that the lack of Ce-anomalies is not in favour of a lateritic
54

________________________________________________________________
origin. It is here preferred that the red-green alteration was indeed regional, a
result of lateritic weathering as proposed by Macdonald (1980), and was
overprinted by hydrothermal alteration (the white zone of Macdonald) that
increases in intensity close to and is genetically related to the bleaching
alteration associated with U deposits (Macdonald, 1985). This interpretation is
based on field relationships noted by Macdonald (the white zone transects down
across the red and green along fractures).
Deposit Distribution
The new uranium production is likely to come from deposits in Canada, Australia,
Niger, the United States, and Kazakhstan.
Table III - Global Distribution of Uranium Deposits
Olympic Dam Australia breccia
Jabiluka Australia unconformity
Ranger Australia unconformity
Kintyre Australia
Athabasca, Thelon Canada unconformity
Kazakhstan sandstone
Niger, sandstone
Uzbekistan, sandstone
Franceville Basin Gabon sandstone
Karoo Basin). South Africa sandstone
Wyoming, New Mexico USA Sandstone
Alteration mineralogy and geochemistry
Alteration mineralogy and geochemistry of Australian and Canadian unconformity
associated deposits and their host rocks in the Athabasca and Thelon basins,
and the Kombolgie Basin have been compared by Miller and LeCheminant
(1985), Kotzer and Kyser (1995), Kyser et al. (2000) and Cuney et al. (2003).
Early work on alteration mineralogy in the Athabasca Basin is exemplified by
Hoeve and Quirt (1984), and Wasilyuk (2002) has set the modern framework of
exploration clay mineralogy. Intense clay alteration zones surrounding deposits
such as Cigar Lake constitute natural geological barriers to U migration in ground
waters (Percival et al., 1993) and are important geotechnical factors in mining
and ore processing (Andrade, 2002) Figure 70.
Alteration halos are developed mainly in the siliciclastic strata and range between
two distinctive end member types: 1) quartz dissolution + illite ( NE Athabasca)
55

________________________________________________________________
(Percival, 1989; Andrade 2002; Cuney et al., 2003), and 2) silicified (Q2) +
kaolinite + dravite (Key Lake, McArthur River) (Matthews et al. 1997, Harvey and
Bethune, 2000).
Ore-related illitic alteration is reflected in anomalously high illite proportions
(Hoeve et al. 1981a, b, Hoeve and Quirt 1984, Percival et al., 1993) and resultant
anomalous K2O/Al203 ratios in the sandstone (Earle and Sopuck 1989). Sudoite,
an Al-Mg-rich di-tri, octahedral chlorite (Percival and Kodama, 1989), is present
in both alteration types. Local silicification fronts are also present in some of the
larger de-silicified alteration systems, e.g. Cigar Lake (Andrade 2002).
Deposit-related silicification (Q2 event), recorded notably by drusy quartz-filled
fractures (McGill et al. 1993) and pre-ore tombstone-style silicification (Q1; Yeo
et al. 2001b; Mwenifumbo et al., 2004, 2005), are particularly intense in
Athabasca sandstone sequences above or proximal to basement quartzite. The
tombstone silicification of the Athabasca Group preserves diagenetic hematite
and dickite (Mwenifumbo et al. 2005) and microbial laminae (Yeo et al. 2005a)
very close to the McArthur River deposit.
Figure 70 - Two end-member sandstone alteration models for egress-type deposits in the eastern
Athabasca Basin (modified from Matthews et al. 1997, Wasyliuk, 2002 and Quirt, 2003). UC =
unconformity, Reg = regolith profile grading from red hematitic saprolite down through green
chloritic alteration to fresh basement gneiss, Up-G = upper limit of graphite preserved in footwall
alteration zone. Cap = secondary black-red earthy hematite capping ore bodies. Fresh = fresh
basement: Fe-Mg chlorite biotite paragneiss.
Illite-kaolinite-chlorite alteration halos are up to 400 m wide at the base of the
sandstone, thousands of meters in strike length, and several hundreds of meters
vertical extent above deposits (Wasilyuk, 2002, for McArthur River; Kister et al.,
56

________________________________________________________________
2003, for Shea Creek; and Bruneton, 1993, for Cigar Lake). This alteration
typically envelops the main ore-controlling structures, forming plume-shaped or
flattened elongate bell-shaped halos that taper gradually upward from the base of
the sandstone (Hoeve and Quirt, 1987) Figure 70. Potassium, magnesium and
aluminum ratios are diagnostic of the different clay types.
Hydrothermal, ore-related alteration effects are superimposed on pre-existing
alteration assemblages, including the paleo-weathering alteration recorded by
the red-green profile below the basal unconformity, and the initial detrital clay
mineralogy that is locally preserved in silicified zones (Mwenifumbo et al., 2005).
This has led to confusion as to which process generated the red-green transition
at the basement-sandstone unconformity. Ore-related white clay alteration is
superimposed on the red hematitic paleo-weathering alteration (McDonald,
1980). Very dark coarse grained hematite alteration forms a cap over ore
deposits such as Cigar Lake (Andrade 2002).. This very dense, crystalline,
hydrothermal hematite alteration contrasts with the brick red, fine-grained
hematite that is interpreted as a detrital or very early diagenetic mineral, and is
intimately interlayered with clay minerals to form micro-laminae in oncoidal
hematite beds (Yeo et al., 2005a).
Figure 71 - Simplified mineral paragenesis of the Paleo- to Mesoproterozoic Athabasca, Thelon
and Kombolgie basins, after Figure 10.21 of Kyser et al. (2000). The ages of primary uraninite,
the first deposition of U in a given deposit, may be different for different deposits, hence U1
(~1500-1600) and U1' (~1350-1400) might both be primary in the Athabasca Basin. Depositional
ages in the Athabasca Group are Zv: U-Pb on volcanic zircon in Wolverine Point Formation, and
Os-Re: primary organic matter in Douglas Formation.
57

________________________________________________________________
INFRARED ACTIVE ALTERATION MINERALS ATHABASCA BASIN
Figure 72 - The common alteration minerals found in the Athabasca Basin deposits include
dravite (magnesiofoitite Mg end member), illite, kaolinite and dickite.
Figure 73 - Chlorites found in the Athabasca
suite. Mg-chlorite and the unique sudoite are
plotted.
58
Figure 74 - Other minerals observed are quartz,
hematite, monazite (REE), dolomite and siderite.

________________________________________________________________
DISCUSSION
Starting with the PIMA, it took about four hard years to introduce the technology
to the industry. It was very alien to users initially, as most universities do not
teach infrared analytical methods. Those that do, usually treat the subject very
briefly, as most departments do not have expensive infrared instrumentation.
Once applications, case studies, spectral libraries, some simple mineral
identification software, and a well-documented training course and manuals were
developed, it became easier to sustain the method.
As more and more companies utilized the technology, word spread via the
"grapevine". Most companies would not cite PIMA analyses in their public
presentations and papers. They all considered reflectance spectroscopy their
"secret weapon".
With the introduction of the TerraSpec, some of the secrecy has dissipated and
companies are more willing to acknowledge the application of reflectance
spectroscopy to their exploration programs. Additionally, VNIR analysis has been
used for over 10 years and is no longer so exotic.
Spectroscopy is used for field and core reconnaissance, core logging, target
generation, vectoring, blast hole logging, and remote sensing ground truth. It has
its biggest successes in epithermal gold systems, porphyry, IOCG, skarns,
kimberlites and unconformity uranium.
Reflectance Spectroscopy has changed the way exploration is done, how core is
targeted, drilled and logged and alteration systems modeled. It has made some
impact on mine metallurgy, grade control and production. It has opened the
important world of alteration mineralogy to a rapid, non-invasive, identification of
alteration minerals in-situ and instantly, in the field, in the core shack, on the pit
benches and faces and underground in the tunnels. It has expanded the
geologist’s knowledge about the minerals in alteration systems, their
associations, and the environments in which they form, therefore leading to a
better and more predictive understanding of mineral deposits. Now, clays,
phyllosilicates, and carbonates, minerals that have similar physical appearances
and have always been difficult to identify by hand lens, are known in 3, 5, or 10
seconds. This analysis can be in-situ in the field, at the outcrop, and/or in the
core shack.
Reflectance spectroscopy has been used by all the major and many smaller
companies in some capacity. There are nearly 400 instruments in the industry
between the different manufacturers. Following is a partial list of companies who
own or have owned spectrometers and many have more than one (apologies to
those left off the list) : Alamos Gold, Almaden, Anglo American, Anglo-Gold-
Ashanti, Barrick, BHP, Balkan Minerals, Battle Mountain, Billiton, Bolnisi,
Buenaventura, Codelco, Collahausi, Cornerstone, CRA, Crystallex, Cyprus, De
Beers, Depromisa, El Dorado, Formicruz, Gencor, GoldCorp, Goldfields,
Gryphon Gold, Hecla, Hemlo, Homestake, Hochschilds, Iamgold, Incor, Inmet,
59

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Ivanhoe, Kennecott, Lac, La Coipa, Linear Gold, Mantos Blancos, Mantos Oro,
Metallica, Metallic Ventures, Mineral Mapping, Minera Paramount, Minnova,
Newcrest, Newmont Exploration, Newmont Gold, New Sleeper, Noranda,
Normandy Posieden, North, Nova Gold, Oro Candente, Oro Peru, Penoles,
Phelps Dodge, Placer Dome, QVX, Rio Tinto, Romarco, Santa Fe, Southern
Peru Copper, Teck-Cominco, WMC, and Western States.
Many more companies have either rented instruments or used consultants who
have done spectral analysis for them.
The uranium companies are where spectroscopy makes a major contribution to
drill target and core logging of alteration to vector to mineralization. The
alteration minerals and clays occur in unique relationships to ore and
spectroscopy is the major way to define these relationships and establish
vectors. The companies include Areva, Cameco, Can-Alaska, Forum Uranium,
Jabiru, JNR, Triex, Uranium City, Uravan, Uex. There are over 30 instruments in
Canada and Australia dedicated to this task alone.
DeBeers funded the original PIMA development and then used close to 20
PIMAs to characterize alteration in kimberlite pipes globally. G-10 garnets, as
diamond indicators, have a distinctive chrome feature in the visible, easily
analyzed by the Terraspec.
The alteration model for Pierina was done with the PIMA. Newmont at
Yanacocha evolved from PIMA core logging into using the Terraspec to
define their alteration and drill taregets. Novagold used the FieldSpec Pro (FR)
at Donlin Creek, as did Barrick at Alta Chicama and Ivanhoe at Oyu Tolgoi. It
goes on with Lac and Barrick in the El Indio belt where they redefined alteration
and mineralization episodes finding major advanced argillic alteration throughout
the belt; Placer Dome logged core at La Coipa. At Valedaro, in Argentina, no
hole was drilled before adjoining holes had been checked with the spectrometer
as they had discovered a unique silica signature associated with gold zones. At
Tres Cruces in Peru, Oro Peru defined mineralized zones and degrees of
alteration using the presence of ammonia in illite or buddingtonite. Noranda and
Rio Tinto use their FR's for remote sensing ground truth, as has Buenaventura,
Newmont, Teck-Cominco, WMC and Barrick..
Perhaps the greatest use for spectroscopy is in core logging. One of the major
success stories, as mentioned, is in the unconformity uranium deposits where
companies have to drill blind targets through glacial till and sandstone down
through the unconformity, where the ore lies, to the basement. The alteration
mineralogy zoning is very diagnostic relative to proximity to ore. The
spectrometers are the most rapid, economic way to vector to the ore bodies and
define them.
Reflectance spectroscopy has become a robust method, routinely used in a wide
variety of applications in the industry,
60

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Acknowledgements
This paper is dedicated to all those field geologists who persevered from PIMA to
Terraspec; who collected thousands of spectra and applied their new found
knowledge to better understanding their deposits and alteration systems. I
acknowledge all of you for your individual and collective contributions to this
wonderful discipline of field spectroscopy.
A special acknowledgement to Graham Hunt, who gave me the first taste of
reflectance spectroscopy years ago at the U.S. Geological Survey. Also to
Alexander F.H. Goetz, who has not only given me knowledge and opportunity,
but taught me a great deal about instrumentation and was supportive in the
creation of the fabulous TerraSpec. And to the Team of engineers, scientists,
and technical support people at Analytical Spectral Devices who created the
Terraspec.
Acknowledgement as well to Terry Cocks of Australia, who with his CSIRO
colleagues, created the PIMA, the first innovative step in this mini-revolution.
Another special salute to Anne Thompson, whose tireless and absolutely top
notch efforts through the years has made reflectance spectroscopy an accepted
analytical tool for all those Canadian Juniors doing very grassroots exploration,
pioneers in their own rights.
The reader also is referred to the paper “Alteration Mapping in Exploration:
Application of Short-Wave Infrared (SWIR) Spectroscopy”, by Anne J.B.
Thompson. Phoebe L. Hauff and Audrey Robitaille, SEG Newsletter, 1999,
Number 39, published by the Society of Economic Geologists, Littleton,
Colorado.
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