Abstract
A workflow incorporating hyperspectral reflectance data, hull corrections, absorption feature extraction and clustering is presented. The workflow is applied to dense hyperspectral datasets, as collected by hyperspectral drill core logging systems. The extracted absorption features of the reflectance spectra collected from drill cores are shown to form assemblage clusters when plotting the wavelength position of the first, second and third deepest absorption features in two and three dimensions. Using an unsupervised clustering method to establish clusters based on the extracted absorption features yields viewable down hole distributions of similar mineral assemblages. The proposed workflow has the potential for the rapid identification of differing lithologies, alteration and/or weathering overprints. Application of the workflow with no a-priori assumptions about the composition of the potential mineral assemblages provides a means of generating an informative overview of the dataset that is not biased or constrained by preconceptions. The workflow can easily be added to the current workflows of geologists whom are working with dense hyperspectral data to provide an overview of the potential down hole mineral assemblages and aid in the visual logging process or assist in quickly identifying areas for more detailed observation. Furthermore, key mineralogical parameters for resource characterisation, such as the presence of clay minerals can be assessed in a cost and time efficient manner. The proposed workflow is applied to spectra collected from four different drill cores collected in the Gawler Craton located in South Australia and demonstrates the potential outlined above.
Highlights
Hyperspectral drill core sensing systems have enabled geologists to objectively and cost-effectively characterise mineral assemblages that can allow the explorer, or geologist, to rapidly classify potential minerals, down hole assemblages and possible regions of interest for further analysis [1,2,3,4].Initial spectrometer systems employed for collecting reflectance spectra from drill cores were handheld and led to datasets comprising tens or hundreds of reflectance spectra [5,6,7]
In each case the down hole lithology as logged by a geologist is plotted in conjunction with the results
The short-wave infrared (SWIR) wavelength region is restricted to absorptions defined by alteration minerals, it is shown that good correspondence can be found between the results and logged lithology
Summary
Initial spectrometer systems employed for collecting reflectance spectra from drill cores were handheld and led to datasets comprising tens or hundreds of reflectance spectra [5,6,7]. The development of dedicated instruments such as the HyLoggerTM [8,9], for automated collection of reflectance spectra from drill cores, has yielded datasets comprised of tens of thousands to millions of reflectance spectra with hyperspectral imaging systems [10]. Due to the large volume of reflectance spectra in such datasets it is desirable to develop workflows and methodologies to automate the initial processing so high-level overviews that can be used for further assessment. A high-level overview of large reflectance datasets is crucial to providing insight into more targeted approaches if required, and to aid in driving deeper analysis in a productive manner from the outset. A successful workflow creates the overview of the mineralogical complexity for (1) geological interpretation or (2) to prepare the dataset for further processing
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