Remote sensing exploration of Nb-Ta-LREE-enriched carbonatite (Epembe/Namibia)

Remote sensing exploration of Nb-Ta-LREE-enriched carbonatite (Epembe/Namibia)

Zimmermann, R.; Brandmeier, M.; Andreani, L.; Mhopjeni, K.; Gloaguen, R.


On the example of the Epembe carbonatite-hosted Nb-Ta-LREE deposit we showcase the use of hyperspectral reflectance data and geomorphic indicators to improve the remote sensing exploration of structurally controlled critical raw material deposits. It further demonstrates how exploration can benefit from a combination of expert knowledge and remotely sensed relief as well as imaging data. In a first stage, multi-source remote sensing data feed lithological mapping based on \textit{kohonen} Self-Organizing maps. We show that morphological indices such as Topographic Position Index, and spatial coordinates are crucial parameters to improve the accuracy of carbonate classification by 10%. The resulting lithological map shows the spatial distribution of the ridge forming carbonatite dyke, the fenitization zone, syenite plugs and mafic intrusions. In a second step, the internal zones of the carbonatite complex were identified using multi-range spectral feature fitting (MRSFF) algorithm and a specific decision tree. This approach allowed detecting potential enrichment zones characterized by an abundance of fluorapatite and pyroxene as well as dolomite-carbonatite (beforsite). Cross validation of the mineral map with field observations and radiometric data confirm the accuracy of the proposed method.

Keywords: Carbonatite; REE; Self-Organizing Maps; Decision Tree; Spectral Feature Fitting; Geomorphology; Namibia; HyMap; SRTM