Spectral Mapping
of
Alteration Minerals
A service provided by
S M A M
Applications of SMAM
Case study example
SMAM working procedure
Examples of mineral spectra
SMAM results (alteration zoning)
•
We interpret mineral spectra recieved with a spectrometer
• Both with the help of different softwares and manually
Wavelength in nanometers
Dep
th o
f sp
ectr
al
feat
ure
s (0
-1)
”we are looking at different absorption features in the spectra”
(OH) bearing minerals: clays, micas, chlorites, talc, epidote, amphiboles, sulphates and carbonates
1100 - 2500 nm vibrational processes
Visible and near infrared (VNIR)
400 - 1100 nm electronic processes
Spectral features relevant to mapping of alteration minerals
• By using an ASD TerraSpec spectrometer we are able to measure 1500 - 2000 m of drill core per
day (1 m intervals). One measurement takes about 5 sec.
• Large data sets of spectra (> 50.000) can be compiled quickly at low cost allowing an in-depth
evaluation of the alteration system to be carried out.
• Simplified: We measure the amount of light reflected from the sample.
Sample (e.g. core, rock chip, grab specimens, powders, outcrops and soils)
Light source (visible-SWIR range)
Detector; an optical cable connects the light source with the TerraSpec
The results are then interpreted with The Spectral Geologist software
Introduction to SMAM
Epithermal alteration systems
Porphyry alteration systems
Kimberlites
IOCG VHMS
Shear veins Skarns
Disseminated gold systems
We are using with and software for:
Mapping alteration minerals in order to identify alteration zones and to define ore bodies.
Analysis of a wide variety of deposit types
Greenschist
belts
Carbonate
hosted base
metals
Common alteration minerals we can measure with SMAM
• Muscovite-paragonit, biotite, phlogopite Micas
• Variations in Fe-Mg chlorite Chlorites
• Tremolite, hornblende, actinolite Amphiboles
• Illite, illite/smectite, kaolinite, dickite Clays
• Jarosite, gypsum Sulfates
• Calcite, dolomite, ankerite, siderite Carbonates
• Fe-tourmaline, tourmaline Tourmaline
The sample can be almost anything – but it has to be dry
Since the TerraSpec is field portable, we can work both inside and out in the field
Case study example
SMAM working procedure
Examples of mineral spectra
SMAM results (alteration zoning)
Applications of spectral geology Once the spectral data has been obtained it can be used to identify:
1) Mineral occurrence
• We can map the distribution and/or determine estimates of a particular mineral
species.
2) Changes in mineral proportions
• It is possible to recognize variations in mineral proportions.
3) Mineral composition and crystallinity
• Trends in mineral crystallinity and composition can also be identified in the spectra.
• This allows us to distinguish between different phases of the same mineral.
Dec
reasin
g m
atc
h
1) Mineral occurrence
• Important for example if a specific mineral of interest has an
established relationship with the target mineralization.
Assemblage Histogram
Probable TSA Mineral
% M
atch
es
Kaolinite Illite Muscovite Actinolite Riebeckite Hornblende FeChlorite IntChlorite Biotite Ankerite Siderite FeTourmaline
06
12
18
24
Match
0
154
308
462
615
769
923
1077
1231
1385
1538
1692
1846
2000
>2000
0 = Perfect match
(red)
Assemblage histogram of the mineral distribution as suggested by The
Spectral Geologist software
Mineral occurrence can be viewed for example as
drill-core sections
2) Changes in mineral proportions
Example of muscovite + Fe-chlorite (1) and Fe-chlorite + muscovite (2)
FSFR.2131 Int=3.0 sec
Wavelength in nm
No
rm.
Hu
llQ
(A
ux.
co
lou
r: N
orm
. H
ull
Q)
1400 1600 1800 2000 2200 2400
00.3
0.6
0.9
2258
2491
1412 2350
1916
2208
Depth
0
0.015
0.029
0.044
0.059
0.074
0.088
0.103
0.118
0.132
0.147
0.162
0.176
0.191
0.206
0.221
0.235
0.25
0.265
0.279
0.294
0.309
0.324
0.338
0.353
0.368
0.382
0.397
0.412
0.426
0.441
0.456
0.471
0.485
0.5
1) 2260nm
2350nm
2200nm >white mica
FSFR.2131 Int=3.0 sec
Wavelength in nm
No
rm.
Hu
llQ
(A
ux.
co
lou
r: N
orm
. H
ull
Q)
1400 1600 1800 2000 2200 2400
00.3
0.6
0.9
2204
1411
2490
1918
2257
2349
Depth
0
0.015
0.029
0.044
0.059
0.074
0.088
0.103
0.118
0.132
0.147
0.162
0.176
0.191
0.206
0.221
0.235
0.25
0.265
0.279
0.294
0.309
0.324
0.338
0.353
0.368
0.382
0.397
0.412
0.426
0.441
0.456
0.471
0.485
0.5
2)
2200nm
2260nm
2350nm >iron chlorite
Depth of the 2200nm feature
Depth of the 2250nm feature
Au values
3) Mineral composition and crystallinity • Variations in chemical composition can be detected
as the wavelength positions of features shift consistently
with elemental substitution.
• This provides discrimination of different phases of the
same mineral, based on variations in composition and/or
crystallinity.
• These can be very important indicators in alteration
systems, for example when looking for vectors towards
prospective parts of the alteration system.
In the enhancement you can see the change in composition from Mg- to
Fe- chlorite, as the wavelength increases from 2330 nm (Mg) towards 2350
nm (Fe).
Chlorite chemistry Variations in the wavelength of the chlorite 2340nm absorption feature.
The wavelength of
the sericite 2200nm
absorption feature is
highly variable. This
plot shows some of
the variation.
White mica chemistry Variations in the wavelength of the sericite 2200nm absorption feature.
• The presence of acid pushes the equilibrium towards muscovite, neutral pH pushes it to phengite.
Mica Composition, samples 1 to 9 (Aux colour: Index)
Wavelength in nm
No
rm. H
ullQ
(S
tac
ke
d)
2030 2100 2170 2240 2310 2380
Aux
0
0.348
0.696
1.043
1.391
1.739
2.087
2.435
2.783
3.13
3.478
3.826
4.174
4.522
4.87
5.217
5.565
5.913
6.261
6.609
6.957
7.304
7.652
8
NULL
1
2
3
4
5
6
7
8
9
Short wavelength = muscovite
Long wavelength = phengite, Mg- and Fe-rich
Kaolinite crystallinity Measure the size of the 2160nm doublet.
Kaolinite, samples 1 to 4 (Aux colour: Index)
Wavelength in nm
Hu
llQ
uo
t (S
tac
ke
d)
1500 1800 2100 2400
Aux
0
0.13
0.261
0.391
0.522
0.652
0.783
0.913
1.043
1.174
1.304
1.435
1.565
1.696
1.826
1.957
2.087
2.217
2.348
2.478
2.609
2.739
2.87
3
NULL
1
2
3
4
Poorly ordered Kaolinite
Well ordered
Kaolinite
2160 nm
Comparison of different biotites
• Short wavelength to long wavelength.
• Besides the shift in the wavelength of
the 2250nm feature, the spectrum also
changes symmetry.
b
Wavelength in nm
Hu
llQ
uo
t
1500 1800 2100 2400
0.9
1
19211395
2490
2497
2388
2476
2249
2326
Depth
0
0.022
0.043
0.065
0.087
0.109
0.13
0.152
0.174
0.196
0.217
0.239
0.261
0.283
0.304
0.326
0.348
0.37
0.391
0.413
0.435
0.457
0.478
0.5
b
Wavelength in nm
Hu
llQ
uo
t
1500 1800 2100 2400
0.9
24
0.9
35
0.9
46
0.9
57
0.9
68
0.9
79
0.9
9
1398
2459
2488
24811924
2469
2349
2257
Depth
0
0.022
0.043
0.065
0.087
0.109
0.13
0.152
0.174
0.196
0.217
0.239
0.261
0.283
0.304
0.326
0.348
0.37
0.391
0.413
0.435
0.457
0.478
0.5
Proximal biotite
Distal biotite
Mg-rich
Fe-rich
2248 nm
2257 nm
• The 2250 feature gets larger as it
shifts to longer wavelengths and a
secondary feature at 2390nm, which is
always present in Mg minerals,
becomes less and less apparent as the
2250 wavelength increases.
•The changing shape of the biotite
spectra is mapping a change from Mg-
rich biotite in the proximal part of the
system to Fe-rich in the more distal
areas.
SMAM working procedure
Examples of mineral spectra
SMAM results (alteration zoning)
Comparison of different biotites
Short wavelength to long wavelength
The changing shape of the biotite spectra is mapping a change from Mg-rich biotite in the proximal part of the system to Fe-rich in the more distal areas.
b
Wavelength in nm
Hu
llQ
uo
t
1500 1800 2100 2400
0.9
1
19211395
2490
2497
2388
2476
2249
2326
Depth
0
0.022
0.043
0.065
0.087
0.109
0.13
0.152
0.174
0.196
0.217
0.239
0.261
0.283
0.304
0.326
0.348
0.37
0.391
0.413
0.435
0.457
0.478
0.5
b
Wavelength in nm
Hu
llQ
uo
t
1500 1800 2100 2400
0.9
24
0.9
35
0.9
46
0.9
57
0.9
68
0.9
79
0.9
9
1398
2459
2488
24811924
2469
2349
2257
Depth
0
0.022
0.043
0.065
0.087
0.109
0.13
0.152
0.174
0.196
0.217
0.239
0.261
0.283
0.304
0.326
0.348
0.37
0.391
0.413
0.435
0.457
0.478
0.5
Proximal biotite
Distal biotite
Mg-rich
Fe-rich
2248 nm
2257 nm
Cross section of the Fäboliden Au-deposit
Biotite wavelengths plotted along drill holes, short wavelength biotite (blue) correlates with the Au-mineralization.
Examples of mineral spectra
SMAM results (alteration zoning)
Theoretical example of picking diamond drill holes and surface samples for SMAM work
- One section along mineralisation zone.
- Sections with ~ 200 m space perpendicular to mineralisation and in major mineralisation zone ~ 100 m spacing.
- Holes situated ~ 25 m to both sides from the section to be included in spectral mapping program.
- Few selected holes from periphery.
- Also surface samples such as grab samples and trench samples can be included to get an surface study.
Project planning
Typical working procedure
1. The project starts with collecting spectral data from for example drill-core, rock chips, powder or crushed material. One measurement takes only a few seconds.
2. The data is then imported into The Spectral Geologist software for interpretation. In TSG you can view your results e.g. as spectra, scatter plots, charts etc.
Fe-chlorite Sericite
Amphibole
Biotite
3. The combined information can then be presented in different formats
Since the TSG data can be exported for use in other softwares, the integration of spectral and for example geochemical data allows relationships between target mineralization and the spectral characteristics of the alteration to be investigated.
On the other hand, you can also work in the opposite direction by importing other necessary data into TSG.
Drill-core sections
Mineral Mapping Pty Ltd
The spectral data can also be
imported to your GIS or 3D software.
2D maps
3D models
SMAM results (alteration zoning)
OH
Water peak
H2O/OH
Al-OH (White mica)
Fe-OH (Chlorite)
Mg-OH (Chlorite)
Example: Sample with White mica and Chlorite
Amphibole features: Near 1400 nm, and a pair near 2310 and 2380 nm (tremolite has a doublet at ~2315 nm).
Biotite features: A major feature at 2330 nm, commonly with a shoulder near 2380 nm. A subordinate feature is present around 2245-2260 nm.
Chlorite features: There are two major absorption features for chlorite; at 2260 nm and 2350 nm for Fe-chlorite; or at 2250 nm and 2330-2340 nm for Mg-chlorite.
Epidote features: The major feature is near 2340 nm with a sharp, but lesser, absorption near 2258 nm. In these respects it is similar to chlorite, with which it can sometimes be confused. Epidote, however, has its third most diagnostic feature near 1550 nm and fourth feature near 1884 nm.
Muscovite (sericite) features: Fairly sharp features near 1408, 2200, 2348, 2442 nm. A broad "dimple" can occur near 2100 nm.
Scapolite features: Major features at 1420,1478, 2340 and 2358 nm.
Calcite features: Major features at 1880, 1990 and 2340 nm.
Fe-tourmaline: Major features at 2200, 2245, 2300 and 2370 nm.
Spectral features
Minerals are classified by comparing different absorption features, e.g. the wavelength of the minimum, the depth and width of the features etc
Biotite Chlorite, sericite
Examples of mineral spectra
Tremolite, sericite Biotite, sericite
Examples of mineral spectra
Examples of mineral spectra
Calcite Calcite + epidote + sericite
Typical calcite with a broad feature at ca 1400 nm.
Epidote features at 1550 nm, 1830 nm and 2250 nm, sericite feature at 2200 nm.
Dolomite, CaMg(CO3)2
Dolomite = ca 1858 nm, while calcite has ca 1875 nm
Dolomite = ca 1978 nm, while calcite has ca 1995 nm
Dolomite = ca 2320 nm,
while calcite has ca 2330 nm
Results: Wavelength of the 2200nm absorption feature in sericite, plotted against depth
down hole
• Topaz, dickite, pyrophyllite is an assemblage that forms in very acidic conditions.
• The wavelength of the 2200nm absorption feature in sericite reflects the pH of the alteration fluid.
• Topaz-bearing assemblages
have very short mica
wavelengths. In contrast,
albite-rich alteration zones
(alkaline) have very long mica
wavelengths.
• The muscovite to phengite
reaction is controlled by pH.
• In sericite zones, muscovite
means acid fluid; phengite
means alkaline fluid.
• The shift in the white mica
wavelength can be used as a
hydrothermal pH indicator. Depth
Scope 1:782; 782 points, R² =0.325; Aux: Au
Easting
Nort
hin
g
3240 3280 3320 3360
12320
12360
12400
12440
12480
0
0.074
0.148
0.222
0.296
0.37
0.444
0.519
0.593
0.667
0.741
0.815
0.889
0.963
1.037
1.111
1.185
1.259
1.333
1.407
1.481
1.556
1.63
1.704
1.778
1.852
1.926
2
NULL
Scope 1:782; 782 points, R² =0.325; Aux: Wav e_AlOH
Easting
Nort
hin
g
3220 3240 3260 3280 3300 3320 3340 3360 3380
12320
12360
12400
12440
12480
2206
2206.148
2206.296
2206.444
2206.593
2206.741
2206.889
2207.037
2207.185
2207.333
2207.481
2207.63
2207.778
2207.926
2208.074
2208.222
2208.37
2208.519
2208.667
2208.815
2208.963
2209.111
2209.259
2209.407
2209.556
2209.704
2209.852
2210
NULL
Au values AlOH wavelength
1) 2)
Incre
asin
g
Au
va
lue
s
De
cre
asi
ng
wa
ve
len
g
th
TSG scatter plot of Au values (1) and AlOH wavelength (2), horizontal section. The
relationship between high Au values (red and yellow dots) and low AlOH wavelengths (red
and yellow dots) are highlighted in the pictures (© Copyright CSIRO Australia, 2008).
Results: Horizontal maps created with The Spectral
Geologist, Au values imported to the software
• In this example the high Au values correlate with short AlOH
wavelengths
AuvEpidote
Sulphide (asp)
Chlorite
Epidote
Sulphide (asp)
Amphibole_chlorite
Chlorite
Amphibole
Sulphide (asp)
Chlorite
Chlorite
Chlorite
Amphibole
Amphibole
Sulphide (asp)
Chlorite
Sulphide (asp)
Sulphide (asp)
Chlorite
Chlorite
Chlorite
Sulphide (asp)
Chlorite
Amphibole_muscovite
Amphibole
Amphibole
Amphibole
Amphibole
Chlorite
Amphibole_muscovite
Amphibole_muscovite
Amphibole
Amphibole_muscovite
Amphibole_muscovite
Amphibole_muscovite
Amphibole_muscovite
Amphibole
Amphibole
Amphibole_muscovite
Amphibole_muscovite
Amphibole_muscovite
Amphibole_muscovite
Amphibole
Amphibole
Amphibole_muscovite
Amphibole
Amphibole
Amphibole
Amphibole
Amphibole
Amphibole_muscovite
Amphibole
Amphibole_muscovite
Amphibole_chlorite
Epidote
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
Wavelength
Au gt
0 1.1 2.2
Norm. HullQ
1500 2000 2500
Depth27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
Norm. HullQ
1500 2000 2500
Depth Normal HullQ Au values Classification
Down hole direction --
----
--A
lte
red
zo
ne
----
----
Integration of spectral and geochemical data
Results: Down hole profile, mineralogy/alteration vs. Au,
TSG data exported
Smectite
Illite-Smectite
Illite
Sericite
Kaolinite
Dickite
Pyrophyllite Alu
nit
e
Low Temperature
High Temperature
Low pH Increasing pH
disordered kaolinite
ordered kaolinite
Low crystallinity mica
High crystallinity mica
Short wavelength mica
Long wavelength mica
Simplified phase diagram of an epithermal system
DH1 DH2
Illite
Muscovite
Kaolinite
Dickite
Pyrophyllite
Alunite + Silica
Kaolinite (Steam-heated)
Increasing Kaolinite crystallinity
Increasing Illite Crystallinity
Increasing Illite abundance
Illite-Smectite
Illite-Smectite
Illite wavelength = 2206nm
Decreasing Mica AlOH wavelength
Example of an epithermal system with alteration minerals that can be measured
DH 1 DH 2
DH 1: With SMAM you are able to see the change from smectite-illite, and the decrease in mica AlOH wavelength, which helps you to navigate in the system and
localize the ore body (DH 2).
Example Porphyry Cu-Mo-Au Systems Vertical zonation from Advanced argillic, (pyrophyllite, dickite, quartz Topaz in F-rich systems) or Argillic, (illite-smectite) Phyllic, (sericite) to Potassic, (biotite + K feldspar) to Lateral Zonation from Potassic to Propylitic, (actinolite, chlorite, epidote, albite, calcite)
Seedorff et al., 2005
Advanced Argillic Alteration (vertical zonation)
Topaz Advanced Argillic (in Fe-rich systems, e.g. Porphyry Mo)
Dickite – Advanced Argillic
Phyllic Alteration (vertical zonation)
Phengite Adjacent to potassic or propylitic (deep)
Muscovite - Acidic Adjacent to Adv. argillic (shallow) Short 2200 nm
wavelength
Longer 2200 nm wavelength
Potassic Alteration (lateral zonation)
Mg-rich biotite Proximal
Fe-rich biotite Distal
2245nm
2255nm
Propylitic Alteration (vertical zonation)
Mg Chlorite (overprinting actinolite) High temp, neutral
Fe Chlorite – Low temp, acid
Longer wavelength
Shorter wavelength
Sediment
Rhyolite
Cu-Pb-Zn VMS
Au-As Deposit
Andalusite
Sericite zonation
Wavelength measured
with ASD
Intense alteration
zone, but no metal
Scale 1km
Simplyfied schematic model of how to navigate in alteration systems
3D snapshot
THE END