Coal spectral features in the mid-infrared range

Rodrigues1, Sandra; Fonteneau2, Lionel; Esterle1, Joan

1The University of Queensland, School of Earth and Environmental Science, St Lucia, QLD 4069, Australia; 2CoreScan Pty Ltd, 1/127 Grandstand Road, Ascot WA 6104, Australia

An increasing rank coal suite (from subbituminous to low volatile bituminous coal, LVB) was used to investigate the spectral features of the organic matter in coal in a wide spectral range from 450 nm up to 14300 nm. Different sensors and equipment were used, covering the visible-near and -shortwave infrared (VNIR-SWIR, 450-2500 nm), the mid-infrared (MIR, 2000-8000 nm) and the thermal infrared (TIR, 6000-14300 nm) regions. The MIR and a small portion of the TIR holds the fundamental vibrations for organic materials, while the SWIR only exhibit the overtones and combinations of those fundamental vibrations. Consequently, spectral features (absorption bands) are better defined in the MIR. The 2900 nm absorption feature is attributed to the fundamental –OH stretch in organic materials. This feature is more prominent in the low rank coal and tends to disappear with increasing rank. Therefore, it must be related with the moisture content in the coal samples. The 3280 nm band corresponds to CH stretch in the aromatic fraction. This band develops with increasing coalification, appearing as a deep absorption feature in the LVB coal. A doublet occurs at 3380 nm and 3420 nm, corresponding to CH3 and CH2 asymmetric stretches, respectively, in the aliphatic fraction. In the subbituminous coal sample, these two bands are hard to decouple appearing as an intense absorption band around 3420 nm. In the medium volatile bituminous coal, these bands are clearly separated but become shallower when the LVB coal rank is reached. The 3500 nm absorption band is attributed to CH3 symmetric stretch in the aliphatic fraction, and becomes shallower with increasing rank. In the region between 3280 nm up to 3500 nm the absorption bands seem to be related with the increasing of the aromaticity in the coal, with the loss of the aliphatic components favouring the development of the aromatic. The absorption features described above are the most prominent bands recognised in the MIR region in the coal samples available for the project (ACARP C28045). Other minor bands also occur in the MIR, including the band at 5250 nm, which is an aromatic related feature that does not occur in the subbituminous coal sample. The 6200 nm absorption band is possibly related to the CC aromatic bonding and it is a deeper feature in the LVB coal. On the other hand, the band at 6860 nm correspond to CH2 asymmetric bending and becomes shallower with increasing rank. The results showed that the MIR spectral range has the potential to characterise the rank of the coal though the development and/or disappearance of the spectral absorption features by evaluating the variations in their area, depth and position.


Biography

Sandra Rodrigues is an Organic Petrologist working for the past seven years at The University of Queensland. She has a vast experience working with coal , oil and gas. More recently, Sandra has been applying hyperspectral technologies to the characterisation of the organic matter in the coal.

Deriving Quantitative Alteration Mineralogy from TIR Hyperspectral Data in IOCG Systems

1Stromberg, Jessica, 1Schlegel, Tobias, 1Pejcic, Bobby, 1Birchall, Renee, 1Shelton, Tina

1CSIRO Mineral Resources, Kensington, Australia

Identifying alteration mineral zonation around hydrothermal ore systems is critical to the mineral exploration process. Hyperspectral methods are commonly used to map alteration because they are fast, inexpensive, and require little to no sample preparation compared to other mineralogical techniques such as scanning electron microscope (SEM) based mineral mapping, for example. The visible-near and shortwave infrared (VN-SWIR, 350-2500 nm) spectral regions are most used as they are sensitive to hydrated mineral phases including chlorite and white micas. However, in mineral systems which are iron oxide-rich or where key alteration assemblages include abundant anhydrous phases, such as in iron oxide-alkali-calcic alteration systems, using this spectral range can be problematic. In this case, the thermal-infrared (TIR) spectral range (6000-14500 nm) may be more appropriate as it is sensitive to anhydrous silicates such as quartz and feldspars. However, there are inherent challenges in unmixing hyperspectral data for deriving quantitative mineral abundances. In particular, when the quantification of minor or spectrally similar phases are key to the alteration assemblages, such as in the quantification of different feldspars. This can be overcome with the use of a calibration dataset such as quantitative X-ray diffraction or SEM-based quantitative mineralogy in combination with Partial-Least Square (PLS) regression methods. In developing such models, scale is of critical importance. Variability in the sampling area and volume between datasets is one of the greatest challenges in validating hyperspectral data with quantitative mineralogy, and in integrating any geoscience datasets. In this work, we used several hyperspectral and spectroscopic instruments (HyLogger, Agilent 4300 FTIR, Bruker Vertex FTIR, ASD Fieldspec Pro) to evaluate the impact of scale on hyperspectral data validation in IOCG systems. In this process we developed a methodology for creating the first scale-consistent dataset of VNIR-SWIR, TIR, and SEM-based quantitative mineralogy data on drill core samples. This dataset comprises 250 samples from a world-class IOCG deposit in which the key mineral phases, assemblages, and alteration patterns were identified using the SEM-based quantitative mineralogy. Hyperspectral data was processed using The Spectral Geologist Software (TSGTM) software and even with a scale consistent dataset, and a constrained mineral library based on the SEM-based mineralogy, conventional unmixing methods such as the The Spectral Assistant (TSATM) were unable to reproduce key alteration patterns for vectoring towards ore. Using the SEM-based mineralogy data, PLS modelling was applied to derive predictive models for key mineral phases from the TIR hyperspectral data. The resulting models produced quantitative mineralogy with r2 > 0.94 for key phases including quartz, K-feldspar, albite, calcite, and >0.80 for magnetite, biotite, and plagioclase. More importantly, the key mineral assemblages change with distance to ore and the relative abundance feldspar species (albite, K-feldspar, plagioclase) identified by the SEM-based mineral mapping were reproduced using PLS-derived mineral abundances in a validation drill core. This method and the models generated will provide a framework for improving the application of hyperspectral data for mapping alteration in IOGC systems.


Biography

Jessica is a Research Scientist in the Mineral Footprints team at CSIRO Mineral Resources where she leads Activity 5 of the NVCL and works on projects across multiple commodities applying the combined use of lab and field-based spectroscopic and geochemical techniques to address industry-specific challenges.

Modelling of petrophysical from hyperspectral drill core data collected from the Osborne Cu-Au deposit, Mount Isa Inlier, Queensland

Laukamp, Dr Carsten1, Francis, Neil1, Hauser, Dr Juerg1, Gopalakrishnan, Dr Suraj2, Mule, Shane1

1CSIRO, Perth, Australia, 2Geologial Survey of Queensland, Brisbane, Australia

The combination of magnetic susceptibility and density allows identification of iron oxide copper-gold (IOCG) mineralisation by estimating proportions of magnetite, sulphide and hematite alteration which can be indicative of IOCGs. In the frame of the National Virtual Core Library project, hyperspectral reflectance spectra acquired from drill core of the Osborne Cu-Au deposit, Mount Isa Inlier, Queensland using a HyLogger3 at GSQ’s Exploration Data Centre were compared with magnetic susceptibility and density measurements. In this study we explore the feasibility of inferring the petrophysical data from the 1) visible-near (VNIR), shortwave (SWIR) and 2) thermal (TIR) infrared wavelength regions. Specifically, we seek to predict magnetic susceptibility and density values in drill core sections where petrophysical data are not available and potentially extrapolate these to other hyperspectral data sets, such as those acquired by field or Earth Observation instruments.

Using The Spectral Geologist (TSGTM) software, partial least squares (PLS) was employed to derive predictive models using 23 unique magnetic susceptibility and density measurements, that were assigned to all nearby spectral measurements (+/- ~10cm). The values of the input magnetic sustainability and density values ranged from 0 to 2.3 K (Si) and 2.7 to 4.9 g/cm3, respectively. The hyperspectral data were not spatially re-sampled to fit with the drill core interval measured for petrophysical data. Instead, the original 1 cm spatial resolution was used to evaluate the variability of hyperspectral data within the petrophysical sample intervals. The correlation between the 23 measured and corresponding modelled magnetic susceptibility (n = 157) for the same 23 depth intervals was high for the VNIR-SWIR (r2 = 0.95) and the TIR (r2 = 0.969), but the PLS-modelled magnetic susceptibility values showed a large variance (± 0.8 and ± 0.5, respectively). Similarly, the correlation between the measured and modelled density was high for the VNIR-SWIR (r2 = 0.958) and the TIR (r2 = 0.989), with the PLS-modelled density values showing a large variance (± 0.4 g/cm3 for both wavelength ranges). However, HyLogger3 high-resolution RGB imagery showed that the predicted value ranges were sufficiently different to discriminate drill core intervals dominated by magnetite-rich rocks, from magnetite-rich breccia and least-altered (non-mineralised) rocks. PLS models based on the VNIR-SWIR wavelength ranges were mainly driven by depth changes of electronic transition absorption features related to iron and copper in the VNIR, which are most intense in the highly altered, magnetite- and/or sulphide rich rocks. PLS models based on the TIR wavelength ranges were highly influenced by the thermal background typically associated with iron oxides and sulphides. Density values modelled from VNIR-SWIR compared to those modelled from TIR showed a good correlation (r2 = 0.729), whereas the correlation between magnetic susceptibility modelled from VNIR-SWIR and TIR was comparably low (r2 = 0.518). While the small amount of data used to infer the models discussed here means that their predictive power needs to be assessed comprehensively, our results nevertheless indicate a high potential for successfully inferring petrophysical from hyperspectral data and cost-effective mapping of IOCG-related alteration. 


Biography

Carsten Laukamp is a senior research geoscientist at CSIRO Mineral Resources, based in Perth, Australia and is project leader of the National Virtual Core Library. Carsten explores the potential for combined use of reflectance spectroscopy, geochemistry and geophysics for tracing hydrothermal alteration signatures through cover and advancing ore body knowledge.

HIGH RESOLUTION VS. STANDARD RESOLUTION: How an increase in spectral resolution using a field portable spectrometer affects quality of data – a case study on Nickel exploration

Shelton Pieniazek, Lori1

1Spectral Evolution, United States

Standard resolution of a field portable spectrometer at 3nm (UV), 8nm (VIS) and 6nm(NIR) has been used successfully in the geological remote sensing and mining industry for a variety of applications. Alteration mapping has been key for finding different mineral assemblages that indicate an area of interest. Using a higher resolution field spectrometer has proven to be beneficial in understanding and identifying new features in a variety of different mineral groups and subgroups.

A study was conducted using three different field spectrometers, each with different resolutions. As you increase resolution, features that are not visible with a standard resolution spectrometer appear in all three ranges (UV,VIS,NIR) thus yielding a better understanding of alteration changes and geochemical conditions


Biography

Mrs. Lori Shelton Pieniazek is the Geologist for Spectral Evolution. She received her degree in Geosciences from Tennessee Technological University. Her main focus is on applying spectral geology applications to the mining and geological remote sensing industries.

HyLoggerTM mineralogy from chips: A RoXplorer pilot study

Moltzen, Jake1

1Geological Survey Of New South Wales, Londonderry, Australia

The RoXplorer® coiled tube drilling system is scheduled to be used for MinEx CRC drilling activities in New South Wales (NSW) from 2022 for National Drilling Initiative (NDI) areas South Cobar, North Cobar, Mundi, Forbes and Dubbo. This recently developed system provides a faster and more cost-effective alternative to conventional diamond and reverse circulation drilling, while also offering safety advantages and reduced environmental impacts (Hillis et al. 2014). Ongoing technology development within MinEx CRC will maximise RoXplorer® production during MinEx CRC drilling campaigns, with 5 km spaced holes planned throughout NDI areas to better understand basement and cover sequence geology and the potential for undiscovered ore deposits buried beneath cover.

In this pilot study, two trial drillholes from the RoXplorer® system were scanned using the HyLogger-3TM instrument to determine the best method for scanning RoXplorer® chips and to assess the quality of visible-near infrared to shortwave infrared (VNIR-SWIR) and thermal infrared (TIR) spectra for routine interpretation. Downhole chip samples produced by the RoXplorer® range in size from ~10 µm to ~4 mm (Tiddy et al. 2019), however a separated coarse fraction with sizes ranging from ~1 mm to ~4 mm was used for both drillholes. Outcomes from this study included:

  • VNIR‒SWIR and TIR spectra were found to be reliable for routine mineral identification, tracking mineral chemistry and identifying lithological variations downhole.
  • Black plastic chip trays produced better spectral results than clear or white trays.
  • Larger 50 mm x 50 mm chip compartments produced better spectral results than standard 25 mm x 50 mm chip compartments.
  • Regular linescan mode produced spectra with higher reflectance and therefore better sensitivity, than chip scanning mode.
  • Rinsing chips with water to remove clinging fines increased TIR reflectance by up to 40% and reduced volume scattering effects.

The findings of this work will be used to help develop a consistent approach to scanning future RoXplorer® drillholes across the state and territory Geological Survey HyLoggerTM nodes.

References

Hillis R. R., Giles D., Van Der Wielen S. E., Baensch A., Cleverley J. S., Fabris A., Uvarova Y. (2014). Coiled tubing drilling and real time sensing – enabling prospecting drilling in the 21st Century? Society of Economic Geologists Special Publications, 18, 243–259.

Tiddy C. J., Hill S. M., Giles D., van der Hoek, B. G., Normington V. J., Anand R. R., Baudet E., Custance K., Hill R., Johnson A., McLennan S., Mitchell C., Zivak D., Salama W., Stoate K. Wolff K. (2019). Utilising geochemical data for the identification and characterisation of mineral exploration sample media within cover sequence materials, Australian Journal of Earth Sciences, DOI: 10.1080/08120099.2019.1673484


Biography\

Jake completed undergraduate studies at Curtin University and honours at the University of Tasmania before spending 4 years working for Mineral Resources Tasmania with the HyLoggerTM team. He is currently employed as a spectral geologist with the Geological Survey of NSW to oversee the delivery of the NVCL project.

Validation of spectral data: A critical step towards accurated prediction

Ramanaidou, Erick1

1Mineral Resources – Discovery | CSIRO, Kensington, WA, Australia

The last three decades have seen the emergence of spectral mineralogy as a valued tool for the exploration and mining companies. From the past luggable GER IRIS and portable PIMA we now have access to an extended suite of small, fast, light and accurate field spectrometers such as the ASD and Spectral Evolution spectrometers covering the visible, near infrared and short-wave infrared – VNIR-SWIR 380 to 2500 nm range. In parallel, automated systems to scan diamond cores and drill chips have been developed such as the hyperspectral point analyser, the HyLogging System™, the hyperspectral imaging spectrometers, the Corescan™ Core Imager Mark III, SpecIm SisuROCK, Neo Hyspex and HCIS Terracore are commercially available for use by the exploration and mining companies. As well as VNIR-SWIR, the thermal infrared -TIR range (8 to 14 µm) is now available with the HyLogging System™ 3 providing the detection minerals such as quartz, felspar, olivine, pyroxene and garnet. Large volumes of diamond cores and drill chips have been measured by the exploration and mining companies and the spectral geologist research community has responded by providing automated ways of processing large number of spectra. The CSIRO- developed the spectral geologist or TSG™ offers two ways of processing the spectra (1) through the automated spectral analysis program or The Spectral Assistant (TSA) or through customised scripts, algorithms that use depth and minimum wavelength of absorptions to uniquely identify specific minerals. The TSA is applied for HyLogging System™ spectra on measured areas on around a few cm2 where mineral mixture is likely. On the other hand, the hyperspectral imaging Corescan™ Core Imager Mark III captures many pure pixels at a resolution of 500 µm and the mineral mapping processing is performed using a dedicated expert system program.

Reflectance spectra acquired using these systems are often the complex results of many absorptions embedding not only mineralogical but also particle size information. Although quite powerful, the processing methods previously mentioned require validation by more classical methods such as x-ray diffraction, Raman spectroscopy, X-ray fluorescence (XRF) and µXRF mapping to improve prediction.

Through examples selected from the iron ore and nickel laterite industries, it will be demonstrated that complementary and cross validated methods are essential to ensure that validation of spectral data is undertaken as a critical step towards accurate mineralogical prediction and that it is good to have redundant information.


Biography

Dr. Erick Ramanaidou is the Commodity Research Leader for iron ore and nickel laterite. He has been involved in spectral research for the last 25 years and has concentrated his effort to the understanding of the spectral properties of iron oxides and gangue minerals in iron ores.

About the GSA

The Geological Society of Australia was established as a non-profit organisation in 1952 to promote, advance and support Earth sciences in Australia.

As a broadly based professional society that aims to represent all Earth Science disciplines, the GSA attracts a wide diversity of members working in a similarly broad range of industries.