USE OF NIR SPECTROSCOPY IN
MINERAL IDENTIFICATION IN SHALE
A comparative look at NIR, XRF and SEM techniques
Somayeh Hosseininejad, Per Kent Pedersen, Ronald James Spencer, Festus Michael Uwuilekhue
Department Of Geoscience, University Of Calgary
CENTRE FOR APPLIED BASIN STUDIES
INTRODUCTION
Paleogeography:
a.
b.
The Upper Cretaceous sedimentary package of interest
was deposited on the eastern margin of the Western
Interior Seaway currently located in central-eastern of
the Saskatchewan province.
Boreal Sea
rn
Weste
60 N
ay
r Seaw
Interio
n
r
e
t
Wes
Study Area
on
s
ud
ay
aw
CANADA
U.S.A.
Se
H
Sask.
Mb.
or
Interi
a: Paleo-geography map of the study area during late
Cenomanian-early to mid Turonian and the position
of the Western Interior Seaway (WIS) during that time.
b: Paleo-map showing the position of the study area
with respect to the position of paleo-shoreline and the
current Cretaceous outcrop (manitoba escarpment)
(modified from Kauffman, 1969).
45 N
y
Seawa
30 N
0 Km 500
Early Turonian Shoreline Position
(after Kauffman, 1969)
Early Turonian Paleolatitude
1000km
Current Outcrop Edge
(Sageman and Arthur,1994)
(after McNeil and Caldwell,1981)
Study Area
Albe
rta
Saskatc
Manitob
a
R13
R11
R9
R7
R5
R3W2
T52
T52
Ma
7-32-50-5W2
T50
aE
16-21-47-11W2
16-12-47-11W2
1-15-47-11W2
Study area is located in east-central
Saskatchewan close to the current
Pasquia Hills outcrop as indicated by
black rectangle (left) and dashed red
line (right).
9-6-47-11W2
T46
T46
R11
R9
R7
Current Pasquia Hills outcrop
R5
R3W2
Viewed Well location
Analyzed Well location
a.
b.
Sea level Changes/OAE’s
McNeil (2009), Dean et al. (1998)
Albian
Early
0
90.4
97.0
upper
Boyne Member
Morden Member
r
pe
up
er
low
Assiniboine Member
Laurier limestone
OAE II
Keld Member
Belle Fourche Member
Base of Fish Scale Zone
Westgate Member
55 30’
O
Skull Creek Member
Swan River Formation
OAE I
USE OF NIR SPECTROSCOPY IN MINERAL IDENTIFICATION IN SHALE
L-Pierre Shale
Gammon Mb.
Boyne member
Carlile Formation
86.6
88.5
100/10-20-001-25/00
Morden member
OAE III
Niobrara cyclothem
Pierre Shale
lower
Conemancian
Cenomanian
MESOZOIC
Late
74.0
83.0
100/10-20-001-25/00
-80
Shallowing
SP
2200
0
R
R
2200
350
m
450
m
400
500
450
550
Keld Assiniboine
Mb.
Mb
Deeping
Favel
Formation
Nicolas, 2009
500
Belle Fourche Mb.
a:Upper-Cretaceous stratigraphic chart and high and low
frequency sea-level curve (after MacNail, 2009 and Dean et
al. 1998). b: Typical induction and resistivity log response
for the studied interval. In this study, the upper part of the
Belle-Fourche Member, Second White Speckled Formation
including Keld and Assiniboine members as well as the
lower part of Carlile Formation were analyzed.
Southwest Manitoba
Ma
Upper Ashville Formation
Period
and Stage
Era
cycles
Stratigraphy:
Carlile
2WS
Formation Formation
R13
Ashville Formation
ou
2-1-48-11W2
Santonian Companian
M
uck
in
nta
T48
2-13-48-10W2
1-3-48-10W2
Arborf ield
Turonian
D
14-10-48-11W2
1-31-47-11W2
t
en
rc
Po
WILDCAT HILL
PROVINCIAL PARK
3-4-49-7W2
4-24-48-11W2
T48
Cretaceous
pm
ar
ills
12-9-50-5W2
15-18-49-6W2
sc
eH
in
up
T50
13-16-50-5W2
11-12-50-6W2
Carrot River
Greenhorn cyclothem
lls
Hi
ob
nit
ia
u
sq
Pa
Study area and
core location:
Movry cyclothem
hewa
n
550
2
Objectives:
What is being measured?
(i) to estimate mineralogical composition specifically clay mineralogy from
the spectra,
A standard spectroscope measures direct transmittance as a
percentage (%T); this represents the percentage of the incident beam
of light transmitted by the sample. This value is then used to calculate
absorbance:
(ii) to qualitatively compare mineral concentrations calculated from XRF
and XRD analyses, as well as mineral groups identified through SEM and
microscopic petrography work with NIR results.
NIR spectroscopy has been widely used in different scientific fields such
as biology and medicine. However, it has been rarely used in mineral
identification in finer sedimentary rocks specifically mudrocks. This work
will allow us to verify the accuracy of this technique compared with XRF
and XRD. The figure below compares NIR with the other methods used
regarding price and ease of use.
Increasing cost of experiment
NIR
Qualitative
XRF
Quantitative
XRD
Quantitative
SEM
Qualitative
Abs=log(1/T)
T=Transmittance=%T/100
A number of things happen when a beam of light comes into contact
with a solid. The beam may be reflected, transmitted, diffused, absorbed,
refracted or polarized. The respective likelihood of these outcomes
depends on the incident beam’s angle of incidence in relation to the solid.
With NIR spectroscopy, it becomes possible to measure the different
percentages of the light reflected, transmitted or absorbed by the
sample, whilst it takes into account the various phenomenon capable of
producing misleading measurements such as diffusion, refraction and
polarization. The spectral range covered is between 350 to 2500 nm.
a.
b.
Increasing ease-of-use
Chart comparing different techniques for mineral identification in this study
including XRF, XRD and SEM along with NIR spectroscopy.
Methodology:
Absorption
Incident beam
Scatter
Transmission
Front
reflection
Refraction
Back reflection
Polarization
What is (Near-Infrared) NIR Spectroscopy?
Visible Near-Infrared spectroscopy is a relatively new nondestructive
method for mineral analysis. The method is based on activating chemical
bonds by irradiating mineral mixtures thereby creating resonance
NIR flowchart
vibration. Accordingly, the energy of the
spectrum is reduced thereby generating
Near Infrared light radiation
an absorption spectrum whose position
in the spectra region indicates the
Chemical bond activation
type of bonds and in many cases the
minerals associated with them. The
non-destructive reflection spectroscopy
Creating resonance vibration
operates in the visible to Near Infrared
region and has been utilized to identify all
Generating an absorbtion spectrum
common clay minerals as well as sulfates,
hydroxides and carbonates (Viscarra et.
al, 2008). Due to their distinct spectral
Data interpretation using software
characteristics, clay minerals are easily
with proper mineral library
identified using this method (Stefano,
2003), in addition to XRD and other
Mineral Identification
mineralogical data, extensive mineral
analysis can be done utilizing the method.
The spectra produced from vis-NIR
spectroscopy are commonly interpreted using appropriate computer
based software with calibrated digital mineral libraries for fast and easy
mineral identification.
Cosmic
Rays
ɣ-Rays
Ultra Violet
10 nm
X-Rays
UV
V
I
S
IR
Radio Waves
Micro
UHF
Short Med Long
10 nm
-7
10 nm
15
10 nm
Infrared
Fundamental
Visi- Near
ble Infrared
380 780
2,500
Far
50,000 nm
a: Types of light Interactions with a solid.
b: NIR reflectance spectra of mineral samples
Equipment and Software
Terraspec 4 Hi-Resolution mineral spectrometer with a contact probe
attachment (for whole core samples) and mug light sampler (for
powdered rock samples) was used in this analysis. Data capture was
achieved using Indico Pro spectral acquisition software. The instrument
(supplied by Analytical Spectral Devices, Boulder Colorado) has a spectral
range between 350 – 2500nm. Prior to scanning, the spectrometer was
calibrated with a Spectralon white tile, this procedure was repeated
every 10 minutes (auto timed for consistency) to ensure accurate mineral
spectral capture. To improve signal to noise ratio, the instrument sample
count rate was set at 200. The acquired spectral data was then analyzed
and interpreted using The Spectral Geologist (TSG) Pro 7.1 software
equipped with digital mineral libraries for mineral identification based on
their unique spectral signatures.
a: Spectrometer device, b: Powder samples used in this study, c: Using spectrometer
on core samples.
USE OF NIR SPECTROSCOPY IN MINERAL IDENTIFICATION IN SHALE
3
RESULTS
Main Minerals
Quartz (wt%)
0
15
30
well ID: 16-21-47-11W2
Toal Clay (wt%)
Calcite (wt%)
45
0
30
60
0
90
25
2
4
6
8
Apatite (wt%)
Siderite (wt%)
Pyrite (wt%)
0
50
10
0
2
3
0
5
1
Gamma Resistivity
Lithology Log
2
Mud
Silt
VF
F
M
C
VC
a.
API-GR
Gravel
Quantitative XRF
Mineralogy:
0
OHM-M
500
1
10
Stratigraphic
Units
Cross plots of major and
Morden Mb.
accessory mineral percentages
vs. depth for the well 16-21-4711W2 using ED-XRF analysis.
Assiniboine
This analysis was done on
Mb.
powder samples using mortar
and pistol to achieve higher
accuracy. Also showing the
lithology log along with gamma
Keld Mb.
and resistivity log. Straight
L-Colorado Unit
horizontal lines are indicating
the boundaries between
Belle Fourche
MB.
different members within
the studied interval. Major
mineralogical changes occur
along these boundaries indicating a change in sediment source as a result of sea-level fluctuation or change in the oceanographic state of the sea.
55
60
65
70
75
80
85
90
The highest values for resistivity correspond to the highest carbonate content in the rock and highly cemented intervals. The abnormally high gamma
values are related to thick to thin fish bone and bentonite beds.
The inverse relationship between quartz and carbonate contents indicates different sources. In these sediments quartz is mainly detrital and different
forms of carbonate minerals are mainly present as parts of calcareous fossil fragments as well as carbonate cement. Clay minerals are shown in more
detail in the next figure.
b.
Clay Minerals
Illite
0
30
well ID: 16-21-47-11W2
Kaolinite
Smectite
60 0
2
4
6 0
3
5
well ID: 13-16-50-5W2
Total Clay
8
10 0
25
50
Stratigraphic
Units
Illite
0
Kaolinite
Smectite
30
60 0
2
4
6 0
3
5
Total Clay
8
10 0
25
Stratigraphic
Units
50
Morden
Mb.
Morden
Mb.
Assiniboine
Mb.
Assiniboine
Mb.
Keld Mb.
Keld Mb.
L-Colorado Unit
L-Colorado Unit
BF Mb.
BF Mb.
Cross-plots of clay minerals vs.
depth for the two wells of 16-2147-11W2 and 13-16-50-5W2 using
the XRF technique. Values are in
weight percentages. Highest clay
contents usually occur at the base of
each parasequence, indicating the
progradational nature of these units.
Lower ratios of illite and smectite
indicate lower depth of burial and
lack of maturity in the sediments. In
these sediments kaolinite is usually
present as cement in pore spaces.
Qualitative SEM Mineralogy:
Scanning electron microscopic images showing different groups of minerals including silicates, carbonates, sulfates and phosphates. SEM helps to
study different minerals within the fabric of the rock.
Silicate minerals include quartz and clay with minor amounts of feldspar. Quartz is present both as detrital grains and replacement cement. Clay minerals
are mostly autogenic.
Carbonates are in different
forms such as calcite, as the
most prominent, dolomite,
siderite and ankerite.
Minor mineral groups include
pyrite and phosphates.
Phosphate is present in two
forms of apatite grains and
fish fragments.
Silicates
Silicates
Albite
Albite
Carbonates
Carbonates
Clay minerals
Clay minerals
Kaolinite
Kaolinite
Ankerite
Ankerite
Albite
Albite
Feldspar
Feldspar
Kaolinite
Kaolinite
Sulfates
Sulfates
Clay minerals
Clay minerals
Calcite
Calcite
Pyrite
Pyrite
Ankerite
Ankerite
Ankerite
Ankerite
Kaolinite
Kaolinite
Phosphates
Phosphates
Kaolinite
Kaolinite
Calcite
Calcite
Quartz
Quartz
Phosphatic
Phosphatic
fish bone
fish bone
Phosphatic
Phosphatic
fish bone
fish bone
Apatite
Apatite
Dolomite
Dolomite
Silicfied shell fragment
Silicfied shell fragment
Quartz
Quartz
Sm
e
Sm
eccttite
ite/Illi
/Illite
te
Calcite
Calcite
Quartz
Quartz
Calcite
Calcite
kaolinite
kaolinite
kaolinite
kaolinite
Calcite
Calcite
Calcite
Calcite
Feldspar
Feldspar
kaolinite
kaolinite
USE OF NIR SPECTROSCOPY IN MINERAL IDENTIFICATION IN SHALE
4
RESULTS AND DISCUSSION
Quantitative NIR Mineralogy:
Assiniboine
16-21-47-11W2
Muscovite
Montmorilonite
Gypsum
Gypsum
Montmorilonite
13-16-50-5W2
16-21-47-11W2
Muscovite
13-16-50-5W2
Morden
Muscovite
Montmorilonite
Gypsum
Siderite
Muscovite
Montmorilonite
Gypsum
Siderite
13-16-50-5W2
Calcite
Calcite
Montmorilonite
Siderite
Ankerite
Montmorilonite
Gypsum
Gypsum
16-21-47-11W2
Belle Fourche
Muscovite
13-16-50-5W2
16-21-47-11W2
Keld
Muscovite
Gypsum
Montmorilonite
Montmorilonite
Gypsum
Spectrum plots for individual minerals present within each unit. Each mineral has a specific spectral signature, however, there are some overlaps
in the spectral band produced by the minerals which makes the distinction between minerals a more challenging process.
Despite the presence of significant amounts of carbonate in the Assiniboine, this mineral has not been detected in this unit for unknown reasons.
The most mineral diversity has been detected in the Keld (only major plots are presented here).
Comparison:
XRF
XRD
SEM, normal and
Fluorescent light Petrography
Illite
Smectite
Carbonate
Pyrite
Quartz
Illite/Smectite
Kaolinite
Feldspar
Pyrite, Apatite, Siderite
Quartz
Illite/Mica
Kaolinite
Feldspar/Plagioclase
Pyrite
Quartz
Illite
Kaolinite
Feldspar/Plagioclase
Pyrite
Second White Speckled
Formation
NIR
Assiniboine
Member
Calcite (Carbonate)
Ankerite (Carbonate)
Siderite
Smectite
Kaolinite
Gypsum, Pyrite, Zoisite (Epidote)
Calcite
Quartz
Illite/Smectite
Kaolinite
Pyite, Apatite, Siderite
Quartz
Illite/Mica
Kaolinite
Feldspar/Plagioclase
Pyrite
Quartz
Calcite, Dolomite, Ankerite
Illite/smectite
Kaolinite
Feldespar/Plagioclase
Pyrite, apatite, phosphate
Carbonate
Illite
Smectite
Siderite
Gypsum, Pyrite
Calcite
Quartz
Illite/Smectite
Kaolinite
Pyrite, Apatite, Siderite
Quartz
Illite/Mica
Kaolinite
Feldspar/Plagioclase
Pyrite
Quartz
Calcite, Dolomite
Illite/smectite
Kaolinite
Feldespar/Plagioclase
Pyrite, apatite, phosphate
Belle Fourche
Formation
Carlile Formation
Stratigraphic
Units
Smectite
Belle-Fourche Illite
Member
Gypsum, pyrite
Quartz
Illite/Smectite
Kaolinite
Pyrite, Apatite, Siderite
Quartz
Illite/Mica
Kaolinite
Feldspar/Plagioclase
Pyrite
Quartz
Illite
Kaolinite
Feldespar/Plagioclase
Pyrite, Gypsum
Morden
Member
Keld
Member
USE OF NIR SPECTROSCOPY IN MINERAL IDENTIFICATION IN SHALE
5
Conclusion:
•
NIR includes the least amount of sample preparation as well as measurement time. This feature makes the NIR one of the best techniques used for
quick mineral identification in the field. Use of the NIR instrument in laboratory conditions is usually associated with higher levels of noise.
•
The NIR instrument predicts different minerals present in the sample as a function of their near infrared (NIR) diffuse reflectance spectra. Minerals
that do not have detectable response within that wavelength will not be detected. For example NIR is unable to identify quartz content as this
mineral does not have a spectral response in the UV-vis-NIR range.
•
NIR spectroscopy is found to be accurate and reliable in clay mineral identification compared with XRF and XRD method.
•
NIR, unlike XRF and XRD, is a qualitative technique and one of the main difficulties to apply the NIR spectroscopy obtained from mudrock in
quantitative form is the presence of broad and superimposed bands and the low absorption intensities.
•
The fact that the spectra are strongly impacted by physical parameters (e.g., particle size, density, and moisture content) is the reason that NIR is
not widely used in laboratory work specifically with fine grained mudrock samples.
•
Another factor that interfere the NIR spectra from minerals is presence of organic material in the context of rock. Shale and mudrocks are one of
the richest rock-types in terms of organic matter content. This fact makes the use of NIR spectroscopy more challenging for mudrock samples.
•
The other challenge associated with the NIR technique is making use of the proper software with an appropriate mineral library (calibration) to
interpret the data. In fact, NIR is only able to predict the minerals within the diversity of samples in the library. In order to achieve the best results
from NIR spectroscopy, it is crucial to create a library specifically designed for each study. To create a complete designated library one has to use
other available techniques such as XRF or XRD prior to using NIR.
•
Table comparing different methods of analysis for mineral identification in this study including XRF, XRF, NIR and SEM. There is a good correlation
in clay mineralogy between NIR method and the other techniques. NIR proves poor in major mineral detection such as calcite and quartz.
Acknowledgements
The authors would like to thank Analytical Spectral Devices, Boulder Colorado, for granting us the spectrometer and providing technical support. This
study was supported by funds from Questerre Energy Corporation.
References
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Pg. 623-630.
Stefano, C. J., Calrson, E. H., Ortiz, J. D., 2003, Clay Mineral Identification by Diffuse Spectral Reflectance, Geological Society of America, Abstracts with Programs, Vol. 35, No.
2, Pg. 18.
Viscarra Rossel R.A., Walvoort D.J., McBratney A.B., Janik L.J., Skjemstad J.O., 2006, Visible, Near Infrared, Mid Infrared or Combined Diffuse Reflectance Spectroscopy for
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USE OF NIR SPECTROSCOPY IN MINERAL IDENTIFICATION IN SHALE
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