University of Twente Student Theses
Reflectance spectra in synthetic mineral mixtures : an implication for the feasibility of remote detection of rare earth elements in hematite rich carbonatites
Weeranayake, Sachinthani (2024) Reflectance spectra in synthetic mineral mixtures : an implication for the feasibility of remote detection of rare earth elements in hematite rich carbonatites.
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| Abstract: | Reflectance spectroscopy and remote sensing have become significant for identifying REE-minerals and analysing REEs in various mineral phases and geological settings. Carbonatites are one of the primary geological environments with the potential to contain rare earth element (REE) minerals such as monazite, bastnäsite, and parisite. Detecting REEs in carbonatite with proximal sensing and remote sensing is challenging due to the presence of iron oxide and iron-bearing minerals, as they mask spectral absorption features of REE ions in the Visible and Near Infrared region (VNIR). This study attempts to understand the influence of varying concentrations of hematite and carbonates on absorption feature parameters of the REEs-bearing minerals using laboratory-synthesised powdered mineral mixtures. Additionally, this study explores the possibility of using REE ion absorption features in VNIR and short-wave infrared (SWIR) regions to detect REEs in carbonatites using various operational airborne and spaceborne sensors. Laboratory-synthesised monazite and bastnäsite from a precipitation method were used as REE minerals. Powdered mineral mixtures with different mineral abundances were prepared in the laboratory, followed by an acquisition of reflectance spectra using an ASD Fieldspec 3 spectroradiometer. The AVIRIS and EnMap, representative of hyperspectral sensors, and Landsat Next and WorldView3, representative of multispectral sensors, were considered for resampling laboratory spectra to evaluate remote sensing capabilities. In this study, a linear relationship of depth of the REE-related absorption features with monazite abundance is found in the SWIR region in synthetic mineral mixtures, and these features are not masked by the presence of hematite. So, while most spectroscopic studies so far have focussed on the application of REE-related absorption features in the VNIR region, the current study highlights that REE-related absorption features in the SWIR range are particularly well suited for detecting monazite in mineral mixtures resembling natural REE ores. These findings are formalized in a novel Praseodymium band ratio (PrR) for mapping absorption features in the SWIR region caused by electronic transitions in the Pr3+ ion. Our analysis shows that this ratio effectively detects REE even in hematite-bearing carbonatites using hyperspectral data from laboratory spectrometers, but probably also from airborne or spaceborne hyperspectral sensors. Moreover, the findings of this study also reveal the capability of a multispectral satellite for detecting REEs in nature-like REE ore rocks: the SWIR 2 band of the WorldView 3 multispectral sensor detecting the Pr feature centred at 1580 nm. In contrast, even though the new Landsat Next platform has several bands in the SWIR range, this study indicates that the band centred at 1610 nm is too wide (90 nm, FWHM) to detect the Pr feature. Any future multispectral sensors with a bandwidth smaller than 20 nm and with bands centring around 1570 nm with adjacent bands around 1700 nm would have the capability of detecting REEs, so these results should perhaps be considered in future sensor designs. Keywords: carbonatites, synthetic monazite, hematite, remote sensing, WorldView 3, Landsat Next, resampling, mineral mixtures |
| 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/104744 |
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