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Spectral Mapping of Alteration Minerals

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Spectral Mapping of Alteration Minerals S M A M Spectral Mapping of Alteration Minerals A service provided by 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 1) - ”we are looking at different absorption features in the spectra” features (0 features Depth of spectral Depth of spectral 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, micas, chlorites, talc, 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, rock 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 base systems metals Porphyry Greenschist Disseminated IOCG alteration VHMS belts gold systems systems Common alteration minerals we can measure with SMAM Micas • Muscovite-paragonit, biotite, phlogopite Chlorites • Variations in Fe-Mg chlorite Amphiboles • Tremolite, hornblende, actinolite Clays • Illite, illite/smectite, kaolinite, dickite Sulfates • Jarosite, gypsum 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. 1) Mineral occurrence • Important for example if a specific mineral of interest has an established relationship with the target mineralization. Assemblage Histogram Match 0 = Perfect match 0 24 (red) 154 308 462 18 615 769 923 12 1077 Decreasing match Decreasing % % Matches 1231 1385 1538 6 1692 1846 2000 0 Kaolinite Illite Muscovite Actinolite Riebeckite Hornblende FeChlorite IntChlorite Biotite Ankerite Siderite FeTourmaline >2000 Probable TSA Mineral 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 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 mica 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 biotites 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 0.968 1924 0.304 2481 The changing shape of the 0.283 0.261 2469 0.957 0.239 HullQuot biotite spectra is mapping a 2459 0.217 change0.196 from Mg-rich biotite 0.174 Fe0.946 -rich in0.152 the proximal part of the 0.13 0.109 0.935 system0.087 to Fe-rich in the 0.065 2349 0.043 0.924 2257 nm 2257 more distal areas. Distal biotite 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 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.
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