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LWIR and SWIR imaging spectroscopy applied to drill core and cuttings samples of Li-pegmatites to characterize their modal mineralogy and to discriminate between coarse-spodumene and fine-spodumene crystals pegmatite

Weah, Jerome W. (2022) LWIR and SWIR imaging spectroscopy applied to drill core and cuttings samples of Li-pegmatites to characterize their modal mineralogy and to discriminate between coarse-spodumene and fine-spodumene crystals pegmatite.

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Embargo date:1 September 2023
Abstract:Spodumene is considered one of the most critical lithium-bearing minerals due to its high lithium content and extraction rate. The growing demand for lithium-ion batteries (LiBs) in electric vehicles and short-term supply shortages has led to spodumene mineral being the most explored mineral nowadays and listed lithium companies as a top investment priority. Most junior mining and exploration companies are immensely working to fill the current lithium supply shortage gap. However, the establishment of lithium mines is, without debt, a significant challenge. The ability to extract lithium from spodumene minerals requires efficient and effective geological and metallurgical optimization of block models, which is crucial to the effective development of most mining operations. Data flow into the model requires earlier knowledge of spodumene ore, geo-domain ( Coarse and fine spodumene crystals size ), and waste characterization is crucial. Imaging spectroscopy has been employed as an alternative technique in mapping and characterizing spodumene crystal sizes instead of conventional methods. However, with the limited studies on spodumene mapping and crystals size characterization, this research investigates the usefulness of LWIR and SWIR imaging spectroscopy applied to drill core and cuttings pegmatite samples from Birimian supergroup sequences within the cape Coast Basin of Ghana in West Africa to map and characterize spodumene crystal sizes (coarse and fine) and other associated minerals. These samples were considered because Berimian supergroup sequences consist predominantly of granites and pegmatites, the key host lithologies of spodumene minerals. The study objectives are to develop a method to characterize spodumene and other associated minerals and to discriminate coarse and fine-spodumene crystals pegmatites based on mineralogy and possibly mineral chemistry. A total of 3 drill cores and 25 cuttings samples were used to acquire hyperspectral images in the VNIR, SWIR, and LWIR wavelength ranges. Only SWIR and LWIR datasets were investigated since important spectral features of the silicates and hydrothermal alteration minerals present in pegmatite host rocks. In addition, 50g of each 25 cuttings samples were used to acquire XRD data for comparison, and five stretched-out powder samples from specific regions on the core for XRD validation. Spot checks on a few pixels from both SWIR and LWIR datasets were applied to manually validate spectral angle mapper(SAM) classification results. The acquired LWIR and SWIR images were preprocessed for noise reduction and reflectance to emissivity conversion. Red, Green, and Blue(RGB) composites of the out MNF bands were used to facilitate endmembers extraction. The extracted endmembers were then compared to reference spectral libraries for mineral identification and naming, applying spectral normalization and continuum removal by division approach. After the endmembers were named, spectral Angle Mapper (SAM) was applied to generate mineral classification images and mineral quantification based on the dominant minerals species in each pixel, where each pixel represents one mineral species or a mixture. Imaging spectroscopy analysis results identify spodumene minerals by their four reststrahlen features. The deepest but narrow feature at 9038nm and two broad, shallow features at 8322 nm and 11663 nm, followed by a broad weak feature near 10506 nm in the LWIR spectral range. Other identified minerals from LWIR core and cuttings datasets include quartz, microcline, and albite, and a host of mineral mixtures comprised of all identified minerals. SWIR core and cuttings datasets identified hydrothermal alteration minerals, including muscovite, ammonio smectite, montmorillonite, and lepidolite. Mineral spectral differences were based on wavelength position and shape (width, depth, and symmetrical). Their diagnostic reflectance and emissivity features that reflect variability in their mineral composition were used to distinguish identified minerals. One limitation of mineral mapping using hyperspectral LWIR and SWIR lies in the selection of mapping algorithms. Wrong classification lead to misclassification and unclassified pixels resulting in wrong interpretation. ii XRD analysis identified all minerals from the LWIR dataset. Muscovite and lepidolite were the only SWIR minerals observed from XRD. However, both minerals overlap in their peaks, creating difficulties in distinguishing them. SAM-LWIR cuttings (sieved and washed) were compared to XRD whole-rock cuttings (unsieved and unwashed) data. All identified cuttings minerals from both datasets revealed no statistically significant, positive, or negative relationship, with R2 < 0.5. Linear correlation results of SAM-LWIR modal mineralogy against the mean spodumene crystals size revealed no statistically significant, positive, or negative relationship between modal albite and microcline. Modal spodumene and quartz show a statistically significant positive or negative relationship with spodumene crystal size, with R2 = 0.4439 and R2 = 0.1259. Spodumene crystal's size distinction was based on a predefined threshold value. The mean of spodumene crystals size >=100mm2 in a 10cm interval; the interval is described as coarse spodumene crystal pegmatite (P1), otherwise deemed as a fine-crystal pegmatite (P2). Visual inspection of the classified LWIR images shows that dominant quartz and albite-rich zones were associated with ‘P1’, and dominant quartz-microcline-rich zones were associated with ‘P2’. Keywords: Hyperspectral, LWIR, SWIR, imaging Spectroscopy, Spodumene, Crystal size, Endmembers, XRD
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Subject:38 earth sciences
Programme:Geoinformation Science and Earth Observation MSc (75014)
Link to this item:https://purl.utwente.nl/essays/92959
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