Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

1 Publication
Hyperspectral imaging for structural geology: An example for more interdisciplinary data analysis in mineral exploration
Zimmermann, R.ORC; Herrmann, E.; Rosa, D.; Kirsch, M.; Gloaguen, R.
Since the applications of hyperspectral imaging found their way into geological investigations, mineral mapping has reached a completely new level of spatial and spectral resolution. Thanks to increasing technological developments in hyperspectral imaging, system resolutions steadily became better at lower prices. Although these methods are already frequently applied in the field of economic geology and petrology, so far, these techniques have rarely been used for structural mapping and interpretation. The actual tool of choice, photogeology, makes just the use of true-color RGB images. However, detailed mineral and lithological maps from hyperspectral imaging can bring a new dimension. Hyperspectral imaging can highlight small mineralogical differences in rocks that cannot be picked-up in traditional RGB images and thus allow lithological contacts to be easily identified. Potential applications include, e.g., mapping dykes of different spectral signatures and their genetic relations or folds in (inaccessible) homogeneous rocks like marbles or quartzites. Furthermore, different types of alteration, associated with structural information can allow the detection of pathways for mineralising fluids and their structural control, one of the most important application of applied structural geology in mineral exploration. Potential methods include mapping absorption wavelength, spectral unmixing and non-linear classifications. All hyperspectral results are integrated into 3D point-clouds for interpretation. We exemplify the interdisciplinary analysis of hyperspectral data, independent of scale and source and their use for structural geology.
In the first case the barely accessible, 1000 m high marble cliffs of Maarmorilik/Greenland were scanned with a ground-based hyperspectral imaging (HSI) system. In certain structural positions a Pb-/Zn-mineralisation is hosted. A preliminary analysis with focus on carbonate mineralogy using absorption wavelengths identified fold structures of calcite-rich and dolomite-rich marbles, which are not visible in standard RGB images. Furthermore, some marble horizons are rich in evaporite minerals (e.g., anhydrite). The distribution of those horizons is mapped using spectral unmixing techniques and can be used to elucidate the structural relationship between deformation, mineralising fluids and ore emplacement.
At the inaccessible mine-pit of Peña de Hierro/Spain hyperspectral imaging is used to enhance the understanding of ore emplacement in relation with faults. Various mineral mapping methods, e.g., Spectral Feature Fitting, and non-linear unsupervised clustering, e.g., Self-Organising Maps, are applied. Faults and folds can easily recognised in RGB images here. However, in hyperspectral data we observe a degradation of hydrothermal activity around faults and orebodies that lead to a better understanding of the interaction between faulting and ore emplacement. Small scale structures in overlying meta- sedimentary rocks are highlighted in hyperspectral images too. They give indication of post-mineralisation deformation and, thus, pathways for secondary alteration and ore replacement.
  • Poster
    10th EARSeL SIG Imaging Spectroscopy Workshop, 19.-21.04.2017, Zürich, Schweiz

Publ.-Id: 24905 - Permalink