NVCL Spectral Reference Library

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1 MINERAL RESOURCES NVCL Spectral Reference Library Phyllosilicates Part 2: Micas Monica LeGras, Carsten Laukamp, Ian C Lau, Peter Mason. EP st June 2018 National Virtual Core Library

2 Citation LeGras, M., Laukamp, C., Lau, I., Mason, P. (2018) NVCL Spectral Reference Library - Phyllosilicates Part 2: Micas. CSIRO, Australia. Copyright Commonwealth Scientific and Industrial Research Organisation To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO. Important disclaimer CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it. CSIRO is committed to providing web accessible content wherever possible. If you are having difficulties with accessing this document please contact csiroenquiries@csiro.au. NVCL Spectral Reference Library 2

3 Contents Acknowledgments Introduction Analytical Methods Infrared Spectroscopy X-Ray Diffraction Electron Probe Microanalysis Mica Minerals Dioctahedral Mica Trioctahedral Mica Discussion Identifying and Characterising Mica Minerals with Infrared Spectroscopy Observations by X-ray Diffraction Summary and Conclusions Replacements and new candidates for SWIR and TIR SRL Comparison of IR spectroscopy with XRD and geochemistry Further study recommendations include: References 64 NVCL Spectral Reference Library 3

4 Figures Figure 1. ASD spectra for muscovite samples Figure 2. FTIR spectra for muscovite samples Figure 3. ASD spectra for miscellaneous dioctahedral mica samples Figure 4. FTIR spectra for miscellaneous dioctahedral mica samples Figure 5: ASD spectra for biotite samples Figure 6: FTIR spectra for biotite samples Figure 7: ASD spectra for phlogopite samples Figure 8: FTIR spectra for phlogopite samples Figure 9: ASD spectra for lepidolite samples Figure 10 ASD spectra for lepidolite samples Figure 11 ASD spectra for zinnwaldite samples Figure 12 FTIR spectra for zinnwaldite samples Figure 13: Fe-rich zinnwaldite M1597 exhibiting 2200 nm AlOH and 2250 nm FeOH combination bands Figure 14: Al vs position of the 2200nm feature in lepidolites, coloured by 2200nm absorption depth Figure 15: Al vs position of the 2200nm feature in muscovites, coloured by 2200nm absorption depth Figure 16: Mg vs position of the 2200nm feature in muscovites Figure 17: Tschermak exchange vector (calculated from EPMA) vs position of the 2200nm feature in muscovites Figure 18: F vs position of the 2200nm feature in lepidolites, coloured by 2200nm absorption depth Figure 19: F vs position of the 2200nm feature in muscovites, coloured by 2200nm absorption depth Figure 20: Fe vs position of the 2250nm feature in biotite series micas Figure 21: Fe vs position of the 2250nm feature in muscovite Figure 22: Mg vs position of the nm MgOH feature in micas Figure 23: Mg vs absorption depth of the 234 0nm feature in phlogopites, coloured by 2340 nm feature position. One extreme outlier, MES014 has been removed due to darkness in the SWIR region enabling accurate measurement of SWIR absorption features using scalars Figure 24: Fe vs absorption depth of the 2340 nm feature in phlogopites, coloured by 2340 nm feature position. One extreme outlier, MES014 has been removed NVCL Spectral Reference Library 4

5 Figure 25: F vs absorption depth of the 2340 nm feature in phlogopites, coloured by 2340 nm feature position. One extreme outlier, MES014 has been removed Figure 26: Mg vs position of the 2340 nm feature in muscovites, coloured by 2340 nm feature absorption depth Figure 27: F vs Al in lepidolites, coloured by 2200 nm feature position Figure 28: OH stretching fundamental features of biotite series micas in the MIR region Figure 29: Mg vs position of the 2700 nm feature in biotite series micas Figure 30: Fe vs position of the 2700nm feature in biotite series micas Figure 31: Al vs position of the ~2750 nm MIR feature cluster in muscovites Figure 32: Al vs position of the ~2760 nm MIR feature cluster in lepidolites Figure 33: Fe vs position of the ~2740 nm MIR feature cluster in muscovites Figure 34: Stretching fundamental features in the MIR region in zinnwaldites. The upper sample is Fe-rich and the lower samples Fe-poor Figure 35: Al vs position of the 2660nm feature of in lepidolite samples. The feature was not detected in one sample, M Figure 36: Lepidolite sample MES016 before (upper) and after pulverisation Figure 37: Representative spectra of major mica types in the nm region in the TIR. 49 Figure 38: Wavelengths of the two most prominent features of micas in the nm region, as automatically extracted from the spectra using the feature extraction method in TSG. The x-axis and y-axis display the wavelength position of the most intense and second most intense peak, respectively. Sample points are coloured by mineral species as evaluated by means of XRD and EPMA. Samples containing non-mica minerals that manifest features in the TIR region are excluded Figure 39: Fe vs wavelength of the 9130 nm feature in muscovites, coloured by Mg Figure 40: Si/Al ratio vs wavelength of the 9130 nm feature in muscovites, coloured by Al Figure 41: Si/Al ratio vs wavelength of the 9140 nm feature in lepidolites, coloured by F Figure 42: Mg content vs wavelength of the 9780 nm feature in biotite series micas, coloured by Fe Figure 43: The typical appearance of micas at the ~ diffraction peak. Pale green = biotite; blue = phlogopite; brown = muscovite; black = phengite; pink = zinnwaldite; orange = lepidolite; red = paragonite = dark green = margarite Figure 44: The expression of various micas species at their ca peak, as shift in the diffraction angle vs relative intensity (against other major mica diffraction peaks). Samples in which all 5 major peaks could not be measured have been excluded from this figure Figure 45: θ peak intensity of micas vs Tschermak exchange Figure 46: Si/Al ratio vs position of the θ peak in muscovites Figure 47: Si/Al ratio vs position of the θ peak in lepidolites NVCL Spectral Reference Library 5

6 Figure 48: F vs position of the θ peak in muscovites Figure 49: F vs position of the θ peak in lepidolites Figure 50: F vs position of the θ peak in biotite series micas Figure 51: Si/Al ratio vs intensity of the θ peak in phlogopite Figure 52: Mg ratio vs intensity of the θ peak in phlogopite, coloured by Fe Tables Table 1: Location of ions in the mica crystal structure Table 2: Summary of the mica minerals grouping system in TSA Table 3: Regions of the electromagnetic spectrum, their range, mode and instruments they are measured by Table 4: Dioctahedral mica species examined in this report Table 5: XRD mineralogy of dioctahedral mica samples Table 6: The angles (2θ) and relative intensities of the major diffraction peaks of dioctahedral mica samples Table 7: Electron Probe Microanalysis results for white mica samples. All elements are reported in weight % Table 8: Summary of TSA results for dioctahedral mica species measured by ASD and FTIR. The corresponding spectra are displayed in Figures 1 and 2 (muscovite) and Figures 3 and 4 (all other species) Table 9: Trioctahedral mica species examined in this report Table 10: XRD mineralogy of trioctahedral mica samples Table 11: The angles (2θ) and relative intensities of the major diffraction peaks of trioctahedral mica samples Table 12: Electron Probe Microanalysis results for trioctahedral mica samples. All elements are reported in weight % Table 13: Summary of TSA results for trioctahedral mica species measured by ASD and FTIR Table 14: Infrared absorption features of mica group minerals Table 15: Major TIR features of mica group minerals. The intensity of Feature 1 is typically far greater than that of Feature 2, except for muscovite where both features are of approximately equal intensity Table 16: SWIR feature wavelengths and depths for the unknown mica samples Table 17: EPMA-determined quantities and SWIR-determined quantities for Al, F, Mg and Fe in muscovites (weight. %) NVCL Spectral Reference Library 6

7 Table 18: SWIR-TSA 7.05 status and candidates for replacement (all of the proposed new candidates are available for inclusion in a MIR-SRL) Table 19: TIR-TSA 7.05 status and candidates for replacement Table 20: Potential candidates for addition to the SWIR- and TIR-TSA spectral libraries NVCL Spectral Reference Library 7

8 Acknowledgments This work was supported by AuScope Pty Ltd and the National Virtual Core Library (NVCL) project and CSIRO s Mineral Resources Business Unit. Many thanks are given to Malcolm Roberts (UWA) for his assistance in collecting and processing EPMA data at the Centre for Microscopy, Characterisation, and Analysis at the University of Western Australia, and Charles Heath (CSIRO) for his assistance in collecting FTIR data at the Australian Resources Research Centre. Rui Wang (China University of Geosciences) is thanked for providing EPMA results of mica samples. Thank you to Neil Francis (CSIRO) for reviewing the manuscript. NVCL Spectral Reference Library 8

9 1 Introduction Mica group minerals are a common constituent of many rock types, with variations in their chemical and structural composition indicating the nature of their formation environment, and any subsequent alteration processes. Characterising mica minerals is also an important consideration in the geometallurgical processing of ore (Otto & LeGras, 2018). Mica minerals carry some inherent analytical difficulties; due to their sheeted structure, the crystals have a strong preferred orientation and are vulnerable to structural breakdown during pulverisation (e.g. Yariv & Cross, 1979), leading to errors in estimating their abundance with geoanalytical techniques such as X-ray diffraction (XRD) analysis (Otto & LeGras, 2018). The various mica species can also be difficult to differentiate in routine XRD analysis and optical microscopy. A thorough understanding of their infrared characteristics is therefore of great potential value for a wide range of geological applications. Mica minerals are phyllosilicates with a 2:1 layer structure consisting of two tetrahedral sheets enclosing one octahedral sheet. An interlayer of large cations lies between each 2:1 layer (Error! eference source not found.). The negatively charged 2:1 layers are compensated by the positivelycharged interlayers, creating strong bonds between the layers. The magnitude of the resultant layer charge differentiates true micas (ideally -1; compensated primarily by monovalent interlayer cations) and brittle micas (ideally -2; compensated primarily by divalent interlayer cations). True and brittle micas may be further divided into dioctahedral and trioctahedral subgroups based on occupancy of the octahedral layer. The smallest structural unit of the octahedral layer contains three octahedra which may be either two-thirds (dioctahedral) or completely (trioctahedral) filled with small cations (Bailey, 1984). Table 1: Location of ions in the mica crystal structure. Layer Cations Anions Tetrahedral Si, Al, Fe 3+, Be 2+ O Octahedral Mg, Al, Fe 2+, Fe 3+, Li, Mn, Ti, V, Cr, Co, Ni, Cu, Zn OH, F Interlayer K, Na, Rb, Cs, NH4, H3O (true micas), Ca, Ba, Sr (brittle micas) Glauconite and celadonite, are distinguished by their high contents of interlayer K and octahedral Fe 3+. While celadonite and glauconite are classified as dioctahedral, there is chemical evidence suggesting that glauconite and, to a lesser extent, celadonite, may have an intermediate structure between dioctahedral and trioctahedral. Lepidolite and biotite may also occur with intermediate dioctahedral-trioctahedral structures. Illite describes dioctahedral micas where the layer charge (K) for the endmember is 0.9 (per O10(OH)2), whereas other dioctahedral micas have a layer charge of 1 (Meunier & Velde, 2004). The term illite has also been used to describe mica minerals with clay-sized crystallites (e.g. Bailey, 1984). Sericite is often used as a term to describe fine-grained white mica, often observed as alteration product of feldspars, but has no firm definition. NVCL Spectral Reference Library 9

10 The SWIR (short-wave infrared; 1000 to 2500 nm) and TIR (thermal infrared; 6000 to nm) spectral reference libraries in The Spectral Geologist software (TSG TM ; are utilised by the software s The Spectral Assistant (TSA) algorithm to match unknown spectra to reference spectra, automatically identifying mineral species and groups. The TSA reference libraries contain spectra identifying white mica group minerals muscovite, phengite and paragonite, and dark mica group minerals biotite and phlogopite (phlogopite in SWIR-TSA only). However, many of the samples from which these spectra were measured are not validated, or locatable (Lau et al., 2016). There are also several important mica species that are not currently represented. To help improve the reliability and range of the TSA spectral libraries, samples representing a variety of mica species including muscovite, biotite, phlogopite, lepidolite, zinnwaldite, paragonite, margarite, celadonite and glauconite have been evaluated. The samples were validated and characterised using FieldSpec3 (also called ASD ), Fourier Transform Infrared Spectrometry (FTIR), X-ray Diffraction (XRD) and Electron Probe Microanalysis (EPMA) instruments. Wavelength ranges collected with the optical instruments comprise the visible near (VNIR; 350 to 1000 nm), SWIR, mid wave infrared (MIR; 2500 to 6000 nm), TIR and far infrared (FIR; to nm) (Table 3). Variations within and between species are assessed to help establish the type and number of mineral samples required to comprehensively characterise mica species using TSA, and guide the interpretation of infrared spectra using TSG. Several of the study samples are suitable for HyLogger measurement and potential addition to the Spectral Reference Library (SRL). TSA groups mica minerals into two classes, White Mica and Dark Mica, which can be differentiated in reflectance spectra by the presence of major absorption features in the SWIR, such as at 2200 nm, 2250 nm, 2350 nm and 2380 nm. In this report, the mica minerals are instead grouped by the structure of their octahedral layer, in accordance with conventional mineralogical classification. Diagnostic SWIR, MIR and TIR absorptions are described in the respective sections of this report. The mica groups and their contained subgroups and mineral species are summarised in Table 2. Suggested additions not currently in the libraries are indicated in italics. Table 2: Summary of the mica minerals grouping system in TSA. TSA Library TSA Class Classification TSA Subgroups SWIR White Mica Dioctahedral Muscovite1 (class 5; 9 members), Muscovite2 (class 6; 3 members), Phengite 1 (class 8; 3 members), Phengite 2 (class 9; 5 members), Paragonite (class 7; 5 members), Celadonite, Margarite, Glauconite Dark Mica Trioctahedral Biotite (class 26; 11 members), Phlogopite1 (class 27; 12 members), Phlogopite2 (class 28; 9 members), Lepidolite, Zinnwaldite TIR White Mica Dioctahedral Muscovite, Phengite, Paragonite, Celadonite, Margarite, Glauconite Dark Mica Trioctahedral Biotite, Phlogopite, Lepidolite, Zinnwaldite NVCL Spectral Reference Library 10

11 2 Analytical Methods 2.1 Infrared Spectroscopy Infrared spectroscopic data was collected at The Australian Resources Research Centre (ARRC) on mineral samples using FieldSpec3 ( ASD ) and Bruker Vertex 80 FTIR instruments (Table 3). Samples were measured whole except for M1631B which was measured as a powder with FTIR and MES016 which was measured as a powder with ASD. Spectra were analysed using TSG TM and The Spectral Assistant (TSA), which is a module for automated mineral identification built into TSG TM (Berman et al., 2017). Absorption features in the SWIR, MIR and TIR reflectance spectra result from stretching fundamentals (e.g. O-H, Si-O) and their corresponding first overtones (e.g. 2 OH), bending fundamentals (e.g. OH) and the respective combination bands of stretching and bending fundamentals ( OH) (Table 3). The characteristic features of each mica species and their relationship to chemical and structural parameters are examined using a variety of scalars (Appendix 1). Table 3: Regions of the electromagnetic spectrum, their range, mode and instruments they are measured by. Region Instrument Range (nm) Mode Visible and near infrared (VNIR) ASD, HyLogger electronic transitions, OH Short wave infrared (SWIR) ASD, FTIR, HyLogger OH, OH Mid infrared (MIR) FTIR, HyLogger4* OH Thermal infrared (TIR) FTIR, HyLogger Si- Far infrared (FIR) FTIR lattice vibrations *HyLogger4 is a hyperspectral drill core line profiling instrument currently being developed by Corescan Pty Ltd. 2.2 X-Ray Diffraction XRD data was collected at ARRC with a Bruker D4 Endeavor instrument fitted with a Co tube, Fe filter and LynxEye position sensitive detector. Each sample was prepared as a powder smeared on a glass slide with ethanol, and measured for ~25 minutes from θ with a step size of 0.02 and a divergence slit of 1. Mineral identification and quantification was completed using Bruker DIFFRAC.EVA software and the Crystallography Open Database. XRD was used to identify and semi-quantitatively determine the abundance of minerals in each sample. Examination of XRD reflection angle and intensity also provides mineralogical information, including chemical composition, crystal structure and crystallinity. NVCL Spectral Reference Library 11

12 2.3 Electron Probe Microanalysis Chemical data was collected using a JEOL8530F Hyperprobe Field Emission Gun Electron Probe Microanalyser at the Centre for Microscopy, Characterisation, and Analysis (CMCA) at the University of Western Australia. The instrument was fitted with five wavelength dispersive spectrometers and operated with a 20 kv accelerating voltage, 40 na beam current and 0 µm spot size. Additional EPMA data from Wang et al. (2017) was collected on the same JEOL8530F Hyperprobe instrument at the CMCA, operated with a 15 kv accelerating voltage, 15 na beam current and 4 µm beam diameter. NVCL Spectral Reference Library 12

13 3 Mica Minerals 3.1 Dioctahedral Mica For this report, six species of dioctahedral micas were examined (Table 4). There are three dioctahedral mica species, muscovite, phengite and paragonite, in the White Mica group of the SWIR-TSA spectral reference library and two, muscovite and phengite, in the TIR-TSA SRL. The White Mica group in the SWIR-TSA SRL is divided into five subgroups; Muscovite1, Muscovite2, Phengite1, Phengite2 and Paragonite. Proposed new dioctahedral subgroups to be added to the SWIR- and TIR- TSA spectral libraries are margarite, celadonite and glauconite. Table 4: Dioctahedral mica species examined in this report. Mineral Name Celadonite Glauconite Margarite* Muscovite Paragonite Phengite** Chemical Formula KMgFe 3+ Si4O10(OH)2 (K,Na)(Fe 3+,Al,Mg)2(Si,Al)4O10(OH)2 CaAl2Si2Al2O10(OH)2 KAl2(Si3Al)O10(OH)2 NaAl2(Si3Al)O10(OH)2 K(AlMgFe 2+ )2(SiAl)4O10(OH)2 *Margarite is a brittle mica. All other dioctahedral and trioctahedral mica species studied in this report are true micas. **Phengite describes intermediate phases between muscovite and celadonite New Reference Sample candidates Muscovite The SWIR-TSA spectral library Muscovite1 subgroup consists of 9 samples, all of which have to be replaced (Lau et al., 2016). The Muscovite2 subgroup consists of 3 samples, none of which are validated as the respective samples are not available for validation (Lau et al., 2016).. In the TIR-TSA spectral library, muscovite is represented by three spectra measured from two untraceable samples. Therefore, all of the muscovites in the TIR-TSA have to be replaced. NVCL Spectral Reference Library 13

14 The new candidates for reference muscovite samples for the SWIR, MIR and/or TIR include: 1. Erwan3, locality unknown 2. M1582, Delaware County, Pa., USA 3. M1583, Mica Creek, Mt. Isa, Qld., Australia 4. M1584, Coleman River, Qld., Australia 5. M2188, Bowen, Qld., Australia 6. M2427, Goteborg, Sweden 7. MT7380, Bradshaw Mountains, Arizona, USA 8. MT8387, Bradshaw Mountains, Arizona, USA 9. WARDS 46E 1063, Keystone, South Dakota, USA Phengite In the SWIR-TSA spectral library the Phengite1 subgroup consists of 3 samples and the Phengite2 subgroup of 5 samples, none of which have been validated. There are two untraceable paragonite spectra in the TIR-TSA spectral library. No suitable phengite samples have yet been located for further study. Paragonite There are five paragonite samples in the SWIR-TSA spectral library, however, no details or samples associated with these spectra could be located. The reference paragonite samples include: 1. M1615, Monte Campione, Tessin, Switzerland 2. MES013, Gassetts, Windsor Co., Vermont Celadonite There are no celadonite samples currently in the SWIR- or TIR spectral libraries. The reference celadonite samples includes: 1. MES017, Ametista do Sul, Rio Grande do Sul, Brazil Glauconite There are no glauconite samples currently in the SWIR- or TIR spectral libraries. The reference glauconite samples include: 1. G1, Fiji 2. M1631B, New Jersey, USA Margarite There are no margarite samples currently in the SWIR- or TIR spectral libraries. The reference margarite samples include: 1. M8E6, Chester, Massachusetts, USA NVCL Spectral Reference Library 14

15 3.1.2 XRD XRD analysis of dioctahedral mica samples indicate that most of the samples consist of pure mica, making them suitable candidates for the SRL (Table 5). The celadonite and margarite samples are mixtures, however, there are distinct zones of pure mica that may be targeted for analysis. The glauconite samples are unsuitable for characterisation in the TIR region due to inseparability of their quartz component, but are suitable for characterisation in the SWIR where quartz does not express any absorption features. MES013 is unsuitable due to its mixture of paragonite and muscovite micas. Detailed diffraction angle and relative intensity data for the major diffraction peaks are summarised in Table 6. Table 5: XRD mineralogy of dioctahedral mica samples. Sample ID Mica Species XRD Mineralogy (%) Suitable for SWIR SRL Suitable for TIR SRL MES017 Celadonite Quartz (77), celadonite (16), calcite (4), diopside (4) Yes Yes G1 Glauconite Glauconite (>80%), quartz (10%-15%) Yes No M1631B Glauconite Glauconite (>80%), quartz (10%-15%) Yes No m8e6 Margarite Margarite (64), tetradymite (28), chlorite (8) Yes* Yes* Erwan3 Muscovite Muscovite (100) Yes Yes M1582 Muscovite Muscovite (100) Yes Yes M1583 Muscovite Muscovite (100) Yes Yes M1584 Muscovite Muscovite (100) Yes Yes M2188 Muscovite Muscovite (100) Yes Yes M2427 Muscovite Muscovite (100) Yes Yes MT7380 Muscovite Muscovite (100) Yes Yes MT8387 Muscovite Muscovite (100) Yes Yes 46E 1063 Muscovite Muscovite (100) Yes Yes WR-1 Muscovite Muscovite (100) Yes Yes M1615 Paragonite Paragonite (100) Yes Yes MES013 Paragonite Paragonite (61), muscovite (30), quartz (5), chlorite (4) No No *Considering the scarcity of reference samples for this mica species. NVCL Spectral Reference Library 15

16 Table 6: The angles (2θ) and relative intensities of the major diffraction peaks of dioctahedral mica samples Sample ID Species angle intensity angle intensity angle intensity angle intensity angle intensity MES017 Celadonite N/A* N/A* N/A* N/A* N/A* N/A* G1 Glauconite N/A* N/A* N/A* N/A* N/A* N/A* M1631B Glauconite N/A* N/A* N/A* N/A* N/A* N/A* m8e6 Margarite N/A* N/A* N/A* N/A* N/A* N/A* Erwan3 Muscovite M1582 Muscovite M1583 Muscovite M1584 Muscovite M2188 Muscovite M2427 Muscovite MT7380 Muscovite MT8387 Muscovite E 1063 Muscovite WR-1 Muscovite N/A* = peak unidentifiable NVCL Spectral Reference Library 16

17 3.1.3 EPMA EPMA (Table 7) was used to definitively identify the species of each dioctahedral mica sample. The data is additionally used to examine the relationship between the chemical composition of micas and their infrared and XRD features. Table 7: Electron Probe Microanalysis results for white mica samples. All elements are reported in weight %. Sample ID Mineral ID F Cl Ca Rb Si Mg Al Mn Na Ti K Ba Cr Fe Ni V O MES017/C1* Celadonite N/A N/A N/A 0.00 N/A G1/WR-2* Glauconite N/A N/A N/A 0.00 N/A M1631B Glauconite M8E6 Margarite Erwan3 Muscovite M1582 Muscovite M1583* Muscovite N/A N/A N/A 0.00 N/A M1584* Muscovite N/A N/A N/A 0.00 N/A M1585* Muscovite N/A N/A N/A 0.01 N/A M2188 Muscovite M2427* Muscovite N/A N/A N/A 0.00 N/A MT7380 Muscovite MT8387 Muscovite P-2* Muscovite N/A N/A N/A 0.01 N/A PH-1* Muscovite N/A N/A N/A 0.00 N/A WARDS46E 1063 Muscovite WR-1* Muscovite N/A N/A N/A 0.00 N/A M1615 Paragonite *Analysed by Rui Wang NVCL Spectral Reference Library 17

18 3.1.4 Infrared Spectroscopy Dioctahedral mica spectra in the VNIR, SWIR, MIR and TIR were collected for muscovite (Figure 1 and Figure 2), celadonite, glauconite, margarite and paragonite (Figure 3 and Figure 4). The SWIRand -TIR TSA classifications of these spectra are summarised in Table 8. All muscovite samples were correctly classified by the SWIR-TSA, with the exception of slightly low-al M1582 which was classified as phengite. TIR-TSA correctly classified all samples as Muscovite for Min1 while a selection of incorrect minerals appear as Min2. Paragonite was correctly identified by SWIR-TSA and classified as muscovite (with minor rutile and augite) TIR-TSA, in the absence of a TIR paragonite reference spectra. The margarite sample was classified as muscovite by SWIR-TSA. Chlorite, which was detected in the sample by XRD analysis, was also correctly identified SWIR-TSA. TIR-TSA incorrectly classified the same samples as edenite and olivine-mg. A major constituent of this sample, tetradymite, has no reference spectra in the SWIR or TIR spectral libraries. However, being a Bitelluride, no major absorption features are expected in the SWIR or TIR. One glauconite sample was classified as mica (muscovite) by SWIR-TSA. Otherwise, the SWIR and TIR classifications suggested only non-mica minerals for both glauconite samples. No mica was identified in the celadonite sample. SWIR-TSA identified ankerite (calcite was detected in XRD analysis) and TIR-TSA identified quartz (also detected in XRD analysis). A variety of incorrect minerals were also identified NVCL Spectral Reference Library 18

19 Table 8: Summary of TSA results for dioctahedral mica species measured by ASD and FTIR. The corresponding spectra are displayed in Figures 1 and 2 (muscovite) and Figures 3 and 4 (all other species). SWIR-TSA (stsas) TIR-TSA (stsat) Sample ID Species Min1 Min2 Min3 Error* Min1 Min2 Min3 Error* Erwan3 Muscovite Muscovite NULL NULL 325 Muscovite NULL NULL 18 M1582 Muscovite Phengite NULL NULL 140 Muscovite NULL NULL 79 M1583 Muscovite Muscovite NULL NULL 104 Muscovite Gypsum NULL 50 M1584 Muscovite Muscovite NULL NULL 218 Muscovite NULL NULL 22 M2188 Muscovite Muscovite NULL NULL 118 Muscovite NULL NULL 32 M2427 Muscovite Muscovite NULL NULL 235 Muscovite NULL NULL 21 MT7380 Muscovite Muscovite NULL NULL 106 Muscovite Magnesite NULL 663 MT8387 Muscovite Muscovite NULL NULL 90 Muscovite Dolomite NULL E 1063 Muscovite Muscovite NULL NULL 199 Muscovite NULL NULL 52 MES017 Celadonite Ankerite Saponite NULL 170 Antigorite Quartz Montmorillonite 83 G1 Glauconite Ankerite Saponite NULL 249 Lizardite Epidote NULL 62 M1631B Glauconite Muscovite Dolomite NULL 103 Calcite Magnesite Rutile 253 M8E6 Margarite Muscovite Chlorite-Fe Kaolinite-PX 519 Edenite Olivine-Mg NULL 206 M1615 Paragonite Paragonite NULL NULL 183 Muscovite Rutile Augite 74 * Error refers to the goodness-of-fit (Standardised Residual Sum of Squares) measure for each match reported by TSA, with lower scores indicating better matches. NVCL Spectral Reference Library 19

20 Figure 1. ASD spectra for muscovite samples. Figure 2. FTIR spectra for muscovite samples. NVCL Spectral Reference Library 20

21 Figure 3. ASD spectra for miscellaneous dioctahedral mica samples. Figure 4. FTIR spectra for miscellaneous dioctahedral mica samples. NVCL Spectral Reference Library 21

22 3.2 Trioctahedral Mica The trioctahedral mica species evaluated in this report are summarised in Table 9. In the SWIR-TSA SRL the Dark Mica group includes reference spectra for trioctahedral micas biotite and phlogopite. Biotite is also represented in the TIR-TSA library. Proposed new trioctahedral mica subgroups to be added to the SWIR- and TIR- TSA spectral libraries are lepidolite and zinnwaldite. Table 9: Trioctahedral mica species examined in this report. Mineral Name Phlogopite Biotite* Lepidolite** Zinnwaldite*** Chemical Formula KMg3(AlSi3O10)(OH)2 K(Mg,Fe)3(AlSi3O10)(OH)2 K(Li,Al)3(Si,Al)4O10(F,OH)2 KLiFe 2+ Al(AlSi3)O10(F,OH)2 *Biotite describes intermediate phases between annite and phlogopite **Lepidolite describes intermediate phases between polylithionite and trilithionite ***Zinnwaldite describes intermediate phases between siderophyllite and polylithionite Reference Samples Biotite The eleven biotite spectra in the SWIR-TSA Spectral Library consist of 2 unknown spectra, 3 unknown samples from the NSW Geological Survey, which could no longer be traced, 3 untraceable GER IRIS samples, 2 untraceable museum samples and a USGS sample. None of the eleven samples is accessible for validation and all need replacement. In the TIR-TSA Spectral Library, biotite is represented by one spectra taken from sample D03523, which is not available for validation work. The new candidates for reference biotite samples include: 1. M1593, Torington, NSW, Australia 2. M2400 biotite, Bancroft, Ontario, Canada 3. MES001, Yilgarn Craton, WA, Australia 4. MT8288, Faraday Township, Ontario, Canada Phlogopite In the SWIR-TSA Spectral Library, the phlogopite spectra were separated into two groups of 12 and 9 spectra (Lau et al., 2016). The 2250 nm absorption feature is only present in group phlogopite1, but not in group phlogopite2. Some of the samples were measurements of a suite of samples that were part of a Chlorite-Biotite-Phlogopite CSIRO study by McLeod. However, 6 of group NVCL Spectral Reference Library 22

23 phlogopite1were from an unknown spectrometer and many of the other samples were untraceable. In group phlogopite2, only one spectrum was collected using an unknown spectrometer, but two samples were from untraceable measurements with a CSIRO ASD. There are no phlogopite spectra in the TIR-TSA library. The new candidates for reference phlogopite samples include: 1. M1589, Musgrave Ranges, SA, Australia 2. M1591, USA (precise locality unknown) 3. M1592, Eganville, Ontario, Canada 4. M1594, Quebec, Canada 5. MES004, S Burgen, Ontario, Canada 6. MES014, Maria Mine, nr., Milford, Beaver Co., Utah 7. MT8392, Hybla, Ontario, Canada Lepidolite There are no lepidolite samples currently in the SWIR- or TIR SRLs. New candidates for reference lepidolite samples include: 1. M1596, San Diego County, California, USA 2. M2817, Grosmont mine, Londonderry pegmatite, Coolgardie, WA, Australia 3. MES016, Minas Gerais, Brazil 4. M2027, Ubini amblygonite mine, Coolgardie, WA, Australia 5. M2526, Grosmont lepidolite locality, Coolgardie district, WA, Australia Zinnwaldite There are no zinnwaldite samples currently in the SWIR- or TIR SRLs. New candidates for the reference zinnwaldite samples include: 1. M1597, Zinnwald, Bohemia, Czech Republic 2. M1844, Cocanarup, Ravensthorpe, WA, Australia 3. M2084, Cocanarup, Ravensthorpe, WA, Australia XRD XRD analysis of trioctahedral mica samples indicate that most of the samples consist of pure mica, making them suitable candidates for the SRL (Table 10). Three very mixed samples, Erwan1, Erwan2 and LE-1, have been excluded as candidates. Detailed diffraction angle and relative intensity data for the major diffraction peaks are summarised in Table 11. NVCL Spectral Reference Library 23

24 Table 10: XRD mineralogy of trioctahedral mica samples. Sample ID Mica Species XRD Mineralogy (%) Suitable for SWIR SRL Suitable for TIR SRL Erwan1 Biotite Biotite (70), quartz (19), albite (9), chlorite (2) No No Erwan2 Biotite Biotite (65), quartz (25), albite (7), chlorite (3) No No M1593 Biotite Biotite (100) Yes Yes M2400 Biotite Biotite (100) Yes Yes MES001 Biotite Biotite (99), kaolinite (1) Yes Yes MT8288 Biotite Biotite (100) Yes Yes LE-1 Lepidolite Mica, albite, minor palygorskite No No M1596 Lepidolite Lepidolite (100) Yes Yes M2027 Lepidolite Muscovite/lepidolite (100) Yes Yes M2526 Lepidolite Lepidolite (100) Yes Yes M2817 Lepidolite Lepidolite (100) Yes Yes MES016 Lepidolite Lepidolite (100) Yes Yes M1589 Phlogopite Phlogopite (100) Yes Yes M1591 Phlogopite Mica (100) Yes Yes M1592 Phlogopite Mica (100) Yes Yes M1594 Phlogopite Mica (100) Yes Yes MES004 Phlogopite Mica (99), vermiculite (1) Yes Yes MES014 Phlogopite Mica (100) Yes Yes MT8392 Phlogopite Mica (100) Yes Yes MES002 Phlogopite Biotite (99), kaolinite (3) Yes Yes M1597 Zinnwaldite Zinnwaldite (100) Yes Yes M1844 Zinnwaldite Mica (100) Yes Yes M2084 Zinnwaldite Mica (100) Yes Yes NVCL Spectral Reference Library 24

25 Table 11: The angles (2θ) and relative intensities of the major diffraction peaks of trioctahedral mica samples Sample ID Species angle intensity angle intensity angle intensity angle intensity angle intensity Erwan1 Biotite N/A* N/A* Erwan2 Biotite N/A* N/A* M1593 Biotite M2400 Biotite MES001 Biotite MT8288 Biotite M1589 Phlogopite M1591 Phlogopite M1592 Phlogopite M1594 Phlogopite MES004 Phlogopite MES014 Phlogopite MT8392 Phlogopite MES002 Phlogopite M1615 Paragonite N/A** N/A** N/A** M1596 Lepidolite M2817 Lepidolite MES016 Lepidolite M2027 Lepidolite M2526 Lepidolite LE-1 Lepidolite M1597 Zinnwaldite M1844 Zinnwaldite M2084 Zinnwaldite N/A* = peak unidentifiable N/A** = peak overlapping another phase NVCL Spectral Reference Library 25

26 3.2.3 EPMA EPMA data (Table 12) was used to definitively identify the species of each trioctahedral mica sample. The data is additionally used to examine the relationship between the chemical composition of micas and their infrared and XRD features. Table 12: Electron Probe Microanalysis results for trioctahedral mica samples. All elements are reported in weight %. Sample ID Mineral ID F Cl Ca Rb Si Mg Al Mn Na Ti K Ba Cr Fe Ni V O M1593 Biotite M2400 Biotite MES001* Biotite N/A N/A N/A 0.00 N/A MT8288 Biotite M1589 Phlogopite M1590* Phlogopite N/A N/A N/A 0.00 N/A M1591 Phlogopite M1592 Phlogopite M1594 Phlogopite MES004 Phlogopite MES014 Phlogopite MT8392 Phlogopite LE-1* Lepidolite N/A N/A N/A 0.00 N/A M1596 Lepidolite M2027 Lepidolite M2526 Lepidolite M2817 Lepidolite MES016 Lepidolite M1597 Zinnwaldite M1844 Zinnwaldite M2084 Zinnwaldite *Analysed by Rui Wang NVCL Spectral Reference Library 26

27 3.2.4 Infrared Spectroscopy Reflectance spectra of trioctahedral mica in the VNIR, SWIR, MIR and TIR were collected for biotite (Figures 5 and 6), phlogopite (Figures 7 and 8), lepidolite (Figures 9 and 10) and zinnwaldite (Figures 11 and 12). The SWIR- and TIR TSA classifications of these spectra are summarised in Table 13. Half of the biotite samples were correctly identified by SWIR-TSA as Min1 (with phlogopite occasionally appearing as Min2) with the remaining samples identified as aspectral or NULL. This may be due to the low reflectance values of the samples in the SWIR. All of the biotite samples were correctly identified as Min1 by TIR-TSA, with a variety of incorrect classifications as Min2 (quartz is correctly identified as Min3 in sample Erwan2). All of the phlogopite samples were correctly classified as phlogopite by SWIR-TSA (with the exception of M1589, identified as NULL). All of the phlogopite samples were classified as biotite for Min1 by TIR-TSA, which lacks phlogopite reference spectra. A variety of incorrect Min2 and Min3 classifications appear in both the SWIR and TIR. The lepidolite and zinnwaldite spectra were classified by TSA as a variety of mica (and occasional non-mica) minerals in the SWIR and TIR. NVCL Spectral Reference Library 27

28 Table 13: Summary of TSA results for trioctahedral mica species measured by ASD and FTIR. SWIR-TSA (stsas) TIR-TSA (stsat) Sample ID Species Min1 Min2 Min3 Error* Min1 Min2 Min3 Error* Erwan1 Biotite Biotite Phlogopite NULL 74 Biotite Riebeckite Edenite 7 Erwan2 Biotite Biotite Phlogopite NULL 67 Biotite Actinolite Quartz 28 M1593 Biotite Biotite NULL NULL 78 Biotite Apatite NULL 49 M2400 Biotite Aspectral NULL NULL 169 Biotite NULL NULL 41 MES001 Biotite Aspectral NULL NULL 32 Biotite Kaolinite-WX NULL 66 MT8288 Biotite NULL NULL NULL NULL Biotite NULL NULL 57 LE-1 Lepidolite Paragonite NULL NULL 118 N/A N/A N/A N/A M1596 Lepidolite Muscovite Kaolinite-PX NULL 405 Muscovite NULL NULL 26 M2027 Lepidolite Muscovite NULL NULL 185 Muscovite Phengite NULL 11 M2526 Lepidolite Phengite NULL NULL 734 Phengite Nontronite NULL 17 M2817 Lepidolite Phengite NULL NULL 747 Nontronite Magnesite NULL 105 MES016 Lepidolite MuscoviticIllite Montmorillonite NULL 169 Phengite Nontronite Muscovite 9 M1589 Phlogopite NULL NULL NULL NULL Biotite Apatite NULL 63 M1591 Phlogopite Phlogopite NULL NULL 151 Biotite Riebeckite NULL 33 M1592 Phlogopite Phlogopite NULL NULL 21 Biotite Talc Antigorite 14 M1594 Phlogopite Phlogopite NULL NULL 153 Biotite Riebeckite NULL 32 MES004 Phlogopite Phlogopite Biotite Hornblende 82 Biotite Riebeckite NULL 41 MES014 Phlogopite Phlogopite Zoisite NULL 153 Biotite Chlorite-Fe NULL 25 MT8392 Phlogopite Phlogopite NULL NULL 61 Biotite Dolomite NULL 81 M1597 Zinnwaldite Biotite Muscovite NULL 131 Muscovite NULL NULL 26 M1844 Zinnwaldite Paragonite Montmorillonite NULL 257 Muscovite Phengite NULL 6 * Error refers to the goodness-of-fit (Standardised Residual Sum of Squares) measure for each match reported by TSA, with lower scores indicating better matches. NVCL Spectral Reference Library 28

29 Figure 5: ASD spectra for biotite samples. Figure 6: FTIR spectra for biotite samples. NVCL Spectral Reference Library 29

30 Figure 7: ASD spectra for phlogopite samples. Figure 8: FTIR spectra for phlogopite samples. NVCL Spectral Reference Library 30

31 Figure 9: ASD spectra for lepidolite samples. Figure 10 ASD spectra for lepidolite samples. NVCL Spectral Reference Library 31

32 Figure 11 ASD spectra for zinnwaldite samples. Figure 12 FTIR spectra for zinnwaldite samples. NVCL Spectral Reference Library 32

33 4 Discussion 4.1 Identifying and Characterising Mica Minerals with Infrared Spectroscopy Absorption features in the SWIR, MIR and TIR wavelength regions of the infrared spectrum arise from, and allow analysis of, mineral structure and chemistry. Examination of these features allows a variety of mica minerals to be identified and characterised. Hydroxyl bonds in the octahedral layer can be observed as stretching fundamentals in the MIR, bending fundamentals in the TIR/FIR, and stretching overtones and combination bands in the SWIR. In addition, Si-O stretching fundamentals are recorded in the TIR. SWIR and MIR features described in the literature are summarised in Table 14, however, these features and their assignments did not always correspond with those observed in the test samples. TIR features, as described in the literature, were available only as transmission measurements and are not included due to large wavelength shifts. NVCL Spectral Reference Library 33

34 Table 14: Infrared absorption features of mica group minerals. group mineral series nm cm-1 assignment comments literature SWIR dioctahedral phyllosilicate white mica M-OH reflectance Vedder (1964) dioctahedral phyllosilicate white mica [M,Li] 2OH reflectance Martinez-Alonso et al. (2002) dioctahedral phyllosilicate white mica (Al) 2OH reflectance Vedder (1964) dioctahedral phyllosilicate white mica (Al,Fe 3+ ) 2OH reflectance Martinez-Alonso et al. (2002) dioctahedral phyllosilicate white mica (Al,Mg) 2OH reflectance Martinez-Alonso et al. (2002) dioctahedral phyllosilicate white mica (Al,Fe 2+ ) 2OH reflectance Martinez-Alonso et al. (2002) MIR trioctahedral phyllosilicate ("10Å phase") dark mica (M)2OH [AlFe 3+ ], [AlMg] Robert & Kodama (1988) dioctahedral phyllosilicate white mica [M,Li] 2OH Martinez-Alonso et al. (2002) trioctahedral phyllosilicate ("10Å phase") dark mica (M)2OH [AlFe 3+ ], [AlMg] Robert & Kodama (1988) trioctahedral phyllosilicate ("10Å phase") dark mica (M)2OH [AlFe 3+ ], [AlMg] Robert & Kodama (1988) dioctahedral phyllosilicate white mica Al 2OH Martinez-Alonso et al. (2002) dioctahedral phyllosilicate white mica AlMgOH Martinez-Alonso et al. (2002) trioctahedral phyllosilicate ("10Å phase") dark mica (M) 2OH [AlFe 3+ ], [AlMg] Robert & Kodama (1988) di- and trioctahedral phyllosilicate mica Mg 2OH Besson & Drits (1997) dioctahedral phyllosilicate white mica AlFe 3+ OH Martinez-Alonso et al. (2002) dioctahedral phyllosilicate white mica AlFe 2+ OH Martinez-Alonso et al. (2002) di- and trioctahedral phyllosilicate mica MgFe 3+ OH Besson & Drits (1997a,b) di- and trioctahedral phyllosilicate mica Fe 2+ MgOH Besson & Drits (1997a,b) di- and trioctahedral phyllosilicate mica Fe 3+ OH Besson & Drits (1997a,b) di- and trioctahedral phyllosilicate mica Fe 2+ Fe 3+ OH Besson & Drits (1997a,b) di- and trioctahedral phyllosilicate mica Fe 2+ 2OH Besson & Drits (1997a,b) MOH OH stretching fundamental; MOH - OH bending fundamental; MOH 1 st overtone of OH stretching fundamental NVCL Spectral Reference Library 34

35 4.1.1 SWIR In the SWIR, mica minerals exhibit combination features related to OH molecules bonded to cations in the octahedral sheet. These features are commonly coined AlOH (2200nm), FeOH (2250nm) and MgOH (2340nm) (Vedder, 1964, Martinez-Alonso et al., 2002). Due to their close proximity and significant Al-Fe differences in most micas, the AlOH and FeOH features often cannot be delineated, with the smaller feature being overwhelmed by the larger. However in one particularly iron-rich zinnwaldite sample (generalised chemical formula KLiFe 2+ Al(AlSi3)O10(F,OH)2), M1597, both the AlOH and the FeOH features are prominent (Figure 13). The Li-OH related absorption feature at around 2146 nm, proposed by Martinez-Alonso et al. (2002) is barely recognisable. Figure 13: Fe-rich zinnwaldite M1597 exhibiting 2200 nm AlOH and 2250 nm FeOH combination bands. The AlOH feature is prominent in Al-rich micas muscovite, lepidolite, paragonite and margarite. In muscovites and lepidolites, Al content is related to both the position and depth of this feature, shifting to shorter wavelengths and increasing in depth as Al increases (Figures 14 and 15). In muscovites, Tschermak exchange vector (Al VI Si IV /(Mg,Fe) VI Si IV ; Duke, 1994) (Figure 16) and Mg content (Figure 17) can also be predicted, as was established by Vedder & McDonald (1963). Note the heteroscedasticity of the data in Figure 16, potentially indicating two populations of muscovite differentiated by Tschermak exchange. In species that incorporate significant amounts of F, such as lepidolite, the feature shifts to longer wavelengths and shallows as OH is replaced by F (Table 18). In muscovites, increasing F also shifts the feature to longer wavelengths but has no relationship with absorption depth (Figure 19). This demonstrates a capability of SWIR instruments such as ASD not achievable with the much more widely-used X-ray Fluorescence (XRF), which struggles to detect F. NVCL Spectral Reference Library 35