Pobibilities and challenges of remote sensing for exploration of carbonatite-hosted REE deposits


Pobibilities and challenges of remote sensing for exploration of carbonatite-hosted REE deposits

Zimmermann, R.; Brandmeier, M.; Gloaguen, R.

Remote sensing data can provide valuable information about ore deposits and their alteration zones at surface level. However, small-scale, structurally controlled ore deposits require remotely sensed data with a very high spatial and spectral resolution. Due to their economic importance, carbonatite-hosted HREE deposits have become a focus of interest and provide a challenge for traditional remote sensing methods. Thus, in this study we focus on developing and testing new remote sensing exploration methods to detect carbonatites as potential host rocks in a well known deposit: Lofdal/Bergville Farm in the northern part of Namibia. The HREE-hosting carbonatite dykes have widths of 0.5 to 3 m. HREE got enriched within these small dykes and fractures during a post-carbonatite intrusion hydrothermal mineralization stage [1].

Several classification and unmixing algorithms were tested on airborne HyMap data. We observe a significant improvement of classification results by using a combination of spectral, textural and geomorphometric information in an expert-based approach compared to "traditional" classification algorithms. The extent of major dykes and the main intrusion could be reproduced very accurately. Thus, we recognize that carbonatites are associated with specific geometric patterns that help to improve classification results. Furthermore, the structures found by Automated lineament extraction (TecLines Toolbox [2]) agree with the orientation of mapped structures in the area and provide more detail to the original mapping.

However, a major difficulty that arised during this study was the still inadequate spatial resolution of 5 m for mapping most of the dykes. Small-scale alteration zones and narrow dykes cannot be detected or mapped correctly. Furthermore, the spectral signature of the surrounding host rocks is similar to the carbonatites and the fenitization zone. Including geometric information into the classification does not lead to significant improvement.

High spatial and spectral resolution is essential for accurate mapping of those narrow mineralized structures. Therefore, we hope to handle these problems by using high-resolution drone-borne systems for hyperspectral imaging, geophysics and 3D photogrammetry.

References
[1] Anthony-Jones, W., Bau, M. and Wall, F. (2014): Rare Earth Element deposits. Proceedings of the 13th Freiberg Short Course in Economic Geology, TU Bergakademie Freiberg

[2] Rahnama, M. and Gloaguen, R. (2014): TecLines: A MATLAB-Based Toolbox for Tectonic Lineament Analysis from Satellite Images and DEMs, Part 1: Line Segment Detection and Extraction, Remote Sensing 6: 5938–5958

  • Lecture (Conference)
    IAMG 2015 - The 17th annual conference of the International Association for Mathematical Geosciences, 08.09.2015, Freiberg, Deutschland
  • Contribution to proceedings
    IAMG 2015 - The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland
    Proceedings of IAMG 2015, 978-3-00-050337-5, 773-783

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Publ.-Id: 22396