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Spectral Mapping of Alteration Minerals

Spectral Mapping of Alteration Minerals

S M A M

Spectral Mapping of Alteration

A service provided by

Applications of SMAM

Case study example

SMAM working procedure

Examples of spectra

SMAM results (alteration zoning)

• We interpret mineral spectra recieved with a spectrometer

• Both with the help of different softwares and manually

1) -

”we are looking at different absorption

features in the spectra”

features (0 features Depth of spectral spectral of Depth

Wavelength in nanometers Spectral features relevant to mapping of alteration minerals

Visible and near infrared (VNIR) 400 - 1100 nm electronic processes

1100 - 2500 nm vibrational processes

(OH) bearing minerals: clays, , chlorites, , epidote, amphiboles, sulphates and carbonates Introduction to SMAM

• 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.

The results are then interpreted with The Spectral Geologist software

Detector; an optical cable connects the light source with the TerraSpec

Light source (visible-SWIR range)

Sample (e.g. core, chip, grab specimens, powders, outcrops and soils) 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

Epithermal Carbonate Kimberlites alteration Shear veins Skarns hosted systems metals

Porphyry Greenschist Disseminated IOCG alteration VHMS belts gold systems systems Common alteration minerals we can measure with SMAM

Micas • -paragonit, ,

Chlorites • Variations in Fe-Mg chlorite

Amphiboles • Tremolite, , actinolite Clays • , illite/smectite, ,

Sulfates • Jarosite,

Carbonates • Calcite, dolomite, ankerite, siderite Tourmaline • Fe-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. established • 1)

Important

% Matches occurrenceMineral

Spectral Geologist software Geologist Spectral The by as suggested distribution mineralthe of histogram Assemblage 0 6 12 18 24 Kaolinite

Illite relationship for

Muscovite example Actinolite

with

Riebeckite

if

the a Probable TSA Mineral Probable

Assemblage Histogram Hornblende specific

target FeChlorite

mineralization

IntChlorite mineral Biotite

(red) Perfect 0 = match of Ankerite

. interest

Siderite FeTourmaline

Decreasing match has >2000 2000 1846 1692 1538 1385 1231 1077 923 769 615 462 308 154 0 Match

an

Mineral occurrence can be viewed for example as drill-core sections 2) Changes in mineral proportions

FSFR.2131 Int=3.0 sec Depth 0.5 0.485 0.471

0.9 0.456 0.441 0.426 0.412 0.397 0.382 0.368 2491 0.353 0.338 0.324 0.6 0.309 0.294 2258 0.279 0.265 0.25 0.235 1412 2350 0.221 0.206 0.191

0.3 0.176

Norm. HullQ (Aux. colour: Norm. HullQ) 0.162 0.147 2350nm0.132 1916 0.118 0.103 0.088 2260nm 0.074 Depth of the 2200nm feature >white 2200nm 0.059 0.044

0 1) 2208 0.029 0.015 1400 1600 1800 2000 2200 2400 0 Wavelength in nm

Example of muscovite + Fe-chlorite (1) and Fe-chlorite + muscovite (2)

FSFR.2131 Int=3.0 sec Depth 0.5 0.485 0.471

Depth of the 2250nm feature 0.9 0.456 0.441 0.426 0.412 0.397 0.382 0.368 0.353 0.338 2490 0.324

0.6 0.309 0.294

1411 0.279 0.265 1918 0.25 0.235 0.221 0.206 0.191

2204 0.176 0.3 Norm. HullQ (Aux. colour: Norm. HullQ) 2200nm 0.162 0.147 0.132 0.118 0.103 0.088 2260nm 0.074 0.059 2) 2257 >iron chlorite 0.044 0 2349 2350nm 0.029 0.015 Au values 1400 1600 1800 2000 2200 2400 0 Wavelength in nm 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. Chlorite chemistry Variations in the wavelength of the chlorite 2340nm absorption feature.

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). White mica chemistry Variations in the wavelength of the sericite 2200nm absorption feature. Short wavelength = muscovite Mica Composition, samples 1 to 9 (Aux colour: Index) Aux 8 7.The652 wavelength of 1 7.304 2 6.the957 sericite 2200nm 6.609 6.absorption261 feature is 3 5.913 5.highly565 variable. This 4

5.217 ) 5 4.plot87 shows some of 4.522

Stacked 6 ( 4.the174 variation.

7 3.826 HullQ

. . 3.478

8 3.13 Norm 2.783 2.435 9 2.087 1.739 1.391 1.043 0.696 Long wavelength = phengite0.348 , Mg- and Fe-rich 0 2030 2100 2170 2240 2310 2380 Wavelength in nm NULL

• The presence of acid pushes the equilibrium towards muscovite, neutral pH pushes it to phengite. Kaolinite crystallinity Measure the size of the 2160nm doublet.

Poorly orderedKaolinite Kaolinite, samples 1 to 4 (Aux colour: Index) Aux 1 3

2 2.87 2.739 2.609 2.478 2.348 3 2.217 4 2.087 1.957

) Well ordered 1.826 Kaolinite 1.696

Stacked 1.565 ( 1.435 1.304

1.174 HullQuot 1.043 0.913 0.783 0.652 0.522 0.391 0.261 2160 nm 0.13 0 1500 1800 2100 2400 Wavelength in nm NULL b Depth

1 0.5 0.478 0.457 0.435 Comparison of different 24970.413 1921 1395 0.391 2490 0.37 0.348 • Short wavelength to long wavelength. 0.326 0.304 2476 0.283 • Besides the shift in the wavelength of 0.261

0.239 HullQuot

0.9 the 2250nm feature, the spectrum also Mg-rich 0.217 0.196 changes symmetry. 0.174 2249 2248 nm 0.152 0.13 2388 0.109 0.087 0.065 Proximal biotite 0.043 2326 0.022 • The 2250 feature gets larger as it 1500 1800 2100 2400 0 Wavelength in nm shifts to longer wavelengths and a b Depth secondary feature at 2390nm, which is 0.5 0.478 always present in Mg minerals, 0.457 0.99 0.435 becomes less and less apparent as the 0.413 1398 0.391 2250 wavelength increases.

0.979 0.37 2488 0.348 0.326

0.968 1924 0.304 2481 0.283 0.261 2469

0.957 0.239 HullQuot 2459 0.217 Fe-rich 0.196

0.174 0.946 0.152 0.13 •The changing shape of the biotite

0.109 0.935 0.087 spectra is mapping a change from Mg- 0.065 Distal biotite 2257 nm 2349 0.043 rich biotite in the proximal part of the 0.924 2257 0.022 1500 1800 2100 2400 0 system to Fe-rich in the more distal Wavelength in nm areas.

SMAM working procedure

Examples of mineral spectra

SMAM results (alteration zoning)

b Depth

1 0.5 0.478 0.457 0.435

24970.413 1921 1395 0.391 Comparison of different 2490 0.37 0.348 biotites 0.326 0.304 2476 0.283 0.261

0.239

HullQuot 0.9 Mg-rich 0.217 0.196 0.174 2249 2248 nm 0.152 0.13 Short wavelength to long 2388 0.109 0.087 0.065 wavelength Proximal biotite 0.043 2326 0.022 1500 1800 2100 2400 0 Wavelength in nm

b Depth 0.5 0.478 0.457

0.99 0.435 0.413 1398 0.391

0.979 0.37 2488 0.348 0.326 The changing shape of the 0.968 1924 0.304 2481 0.283 0.261 biotite spectra is mapping a 2469

0.957 0.239 HullQuot 2459 0.217 change from Mg-rich biotite Fe-rich 0.196 0.174 0.946 in the proximal part of the 0.152 0.13 0.109 0.935 system to Fe-rich in the 0.087 2257 nm 0.065 more distal areas. Distal biotite 2349 0.043 0.924 2257 0.022 1500 1800 2100 2400 0 Wavelength in 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)

Project planning Theoretical example of picking 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.

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.

Fe-chlorite Sericite 2. The data is then imported into The Spectral Geologist software for Biotite interpretation. In TSG you can view your results e.g. as spectra, scatter plots, charts etc. Amphibole Since the TSG data can be exported for use in other softwares, the integration of spectral and for example geochemical data allows 3. The combined information can relationships between target mineralization and the spectral then be presented in different characteristics of the alteration to be investigated. formats On the other hand, you can also work in the opposite direction by importing other necessary data into TSG.

Drill-core sections 2D maps The spectral data can also be imported to your GIS or 3D software.

Mineral Mapping Pty Ltd

3D models

SMAM results (alteration zoning)

Example: Sample with White mica and Chlorite

Water peak H2O/OH

OH Mg-OH Al-OH Fe-OH(Chlorite) (White mica) (Chlorite) 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

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. Examples of mineral spectra

Chlorite, sericite Biotite Examples of mineral spectra

Tremolite, sericite Biotite, sericite Examples of mineral spectra

Calcite + epidote Calcite + sericite

Typical calcite with a broad feature at ca Epidote features at 1550 nm, 1830 nm and 1400 nm. 2250 nm, sericite feature at 2200 nm. 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

Dolomite, CaMg(CO3)2

Results: Wavelength of the 2200nm absorption feature in sericite, plotted against depth down hole

• Topaz, dickite, 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

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

Au values AlOH wavelength

Scope 1:782; 782 points, R² =0.325; Aux: Au 2 Scope 1:782; 782 points, R² =0.325; Aux: Wave_AlOH 2206 1.926 2206.148 1.852 2206.296 1) 1.778 2) 2206.444 1.704 2206.593

1.63 2206.741

12480 12480 1.556 2206.889 1.481 2207.037 1.407 2207.185

1.333 2207.333

1.259 2207.481 12440 12440 1.185 2207.63 1.111 2207.778 1.037 2207.926

0.963 2208.074

Northing

Northing 0.889 2208.222 12400

12400 0.815 2208.37

Decreasi ng waveleng th

Increasing values Au 0.741 2208.519 0.667 2208.667 0.593 2208.815

0.519 2208.963 12360 12360 0.444 2209.111 0.37 2209.259 0.296 2209.407 0.222 2209.556

0.148 2209.704 12320 12320 0.074 2209.852 0 2210 NULL NULL 3240 3280 3320 3360 3220 3240 3260 3280 3300 3320 3340 3360 3380 Easting Easting 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). Norm. HullQ

Results: Down hole profile, mineralogy/alteration vs. Au, TSG data exported Au gt Depth NormalNorm.Depth HullQ HullQ Au values Classification Auv Epidote 27 Sulphide (asp) 28 Chlorite 29 Epidote 30 Integration of 31 Sulphide (asp) Amphibole_chlorite

------32 33 Chlorite spectral and 34 Amphibole 35 Sulphide (asp) 36 Chlorite geochemical data 37 Chlorite 38 Chlorite 39 Amphibole 40 Amphibole 41 Sulphide (asp) 42 Chlorite

43 Sulphide (asp) Altered zone Altered 44 Sulphide (asp) 45 Chlorite Down hole 46 Chlorite 47 Chlorite Sulphide (asp) direction

------48 49 Chlorite 50 Amphibole_muscovite 51 Amphibole 52 Amphibole 53 Amphibole 54 Amphibole 55 Chlorite 56 Amphibole_muscovite 57 Amphibole_muscovite 58 Amphibole 59 Amphibole_muscovite 60 Amphibole_muscovite 61 Amphibole_muscovite 62 Amphibole_muscovite 63 Amphibole 64 Amphibole 65 Amphibole_muscovite 66 Amphibole_muscovite 67 Amphibole_muscovite 68 Amphibole_muscovite 69 Amphibole 70 Amphibole 71 Amphibole_muscovite 72 Amphibole 73 Amphibole 74 Amphibole 75 Amphibole 76 Amphibole 77 1500 2000 2500 Amphibole_muscovite 78 Amphibole 79 Wavelength 80 Amphibole_muscovite 81 Amphibole_chlorite 82 Epidote 83 NULL 84 NULL 85 NULL 86 NULL 87 NULL 88 NULL 89 NULL 90 NULL 91 NULL 92 NULL 93 NULL 94 NULL 95 NULL 96 NULL 97 NULL 98 NULL 99 NULL 100 NULL 101 NULL 102 NULL 103 NULL 104 NULL 105 NULL 106 NULL 107 NULL 108 NULL 109 NULL 110 NULL 111 NULL 112 NULL 113 NULL 114 NULL 115 0 1.1 NULL 2.2 1500 2000 2500 NULL Simplified phase diagram of an epithermal system

Low Temperature

disordered kaolinite Kaolinite Smectite Low crystallinity DH1 mica ordered kaolinite DH2 Illite-Smectite Dickite

Illite

Alunite Pyrophyllite Sericite High crystallinity mica

Short Long High Temperature wavelength wavelength mica mica Low pH Increasing pH Example of an epithermal system with alteration minerals that can be measured DH 1 DH 2

Increasing Kaolinite crystallinity Kaolinite (Steam-heated)

Illite-Smectite

Kaolinite

Illite-Smectite

Increasing Illite abundance

Dickite Illite Increasing Illite Crystallinity Illite wavelength = 2206nm

Alunite + Silica

Pyrophyllite Muscovite Decreasing Mica AlOH wavelength

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 ) to

Lateral Zonation from Potassic to Propylitic, (actinolite, chlorite, epidote, albite, calcite)

Seedorff et al., 2005 Advanced Argillic Alteration (vertical zonation)

Dickite – Advanced Argillic

Topaz Advanced Argillic (in Fe-rich systems, e.g. Porphyry Mo) Phyllic Alteration (vertical zonation)

Muscovite - Acidic Adjacent to Adv. argillic (shallow) Short 2200 nm wavelength

Phengite Adjacent to potassic or propylitic (deep) Longer 2200 nm wavelength Potassic Alteration (lateral zonation)

Fe-rich biotite Distal 2255nm

Mg-rich biotite Proximal 2245nm Propylitic Alteration (vertical zonation) Longer wavelength

Fe Chlorite – Low temp, acid

Shorter wavelength

Mg Chlorite (overprinting actinolite) High temp, neutral Simplyfied schematic model of how to navigate in alteration systems

Sericite zonation Cu-Pb-Zn VMS Wavelength measured with ASD Sediment

Au-As Deposit

Andalusite

Intense alteration zone, but no metal

Scale 1km 3D snapshot

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