Mapping bauxite indices using Landsat ETM+ imageries constrained with environmental factors in Foumban area (West Cameroon)

Abstract The present study aims at mapping some western Cameroon bauxites combining results of digital processing of satellite data ( ETM+ of LandSat ) with the geological, structural, mineralogical and geochemical characteristics of the Foumban area. Two categories of encrusted bauxitic surfaces have been identified: ( i ) discontinuous surfaces covering a total area of 11.13 km 2 , and ( ii ) continuous surfaces overlapping 2.41 km 2 . Field observations portray discontinuous surfaces with 5.5 m thick bauxitic mantle subdivided into 1.5 m thick discontinuous duricrust lying on 4.0 m thick continuous duricrust. The continuous surfaces are 4.1 m thick bauxitic duricrust. Mineralogical studies showed that the Foumban bauxites exhibit 78–86% of gibbsite, 7–22% of goethite and less than 7% of kaolinite. Geochemically, Al is the most abundant element with 45.6–58.7 wt.% of Al 2 O 3 ; followed by Fe with 12.9–20.1 wt.% of Fe 2 O 3 and Si with 1.0–3.7 wt.% of SiO 2 . Element mobility stated with enrichment factor (EF) allows differentiating three chemical elements: strongly depleted with EF   1 (Al, Fe, Cr); and with irregular depletion and enrichment behavior with EF ± 1 (Nb, Sr, V, Zr). Based on mass-transport function (M), elements decrease as follows: Sr > Nb > Cr > Al > Zr > V > Zn > Fe > Cu > Si > Ca > K = Na > Mg > Mn. The Foumban encrusted bauxites are classified as laterite and iron-rich high grade orth-bauxites with 45.6–58.7 wt.% of Al 2 O 3 and 1.0–3.7 wt.% of SiO 2 , with bauxite reserves estimated to 75.8 million tons. The mapping approach has shown to be suitable for delineating encrusted bauxitic surfaces within loose laterites in tropical regions.