Morphological, mineralogical and geochemical characterization of the Danfili-Mambal duricrust formations (Adamawa-Cameroon)

Abstract

In the present study, duricrust formations of Danfili-Mambal are characterized on morphological, mineralogical and geochemical point of view, in order to identify the different facies and to determine their potential mining. To this end, four hills were explored and samples collected for analysis. The morphological characterization allows to distinguish four facies : massive to sub-nodular, nodular massive, massive and vacuolar. These facies show a spatial distribution : the massive and vacuolar facies occupy the top and the upper slope of the hills, the nodular facies are found at the mid-slope and the sub-nodular facies at the down slope. The mineralogical analysis revealed that all these facies include gibbsite, kaolinite, goethite, quartz, hematite, magnetite and anatase. Gibbsite appears as the most dominant mineral. Geochemically, aluminum oxides (Al2O3) and iron oxides (Fe2O3) are the most abundant (Al2O3 : 29.92% - 56.59%; Fe2O3% : 8.87% - 46.55%). The SiO2 contents as well as Alkali and alkali earth elements were very low. The most represented trace elements are Ba, Sr, V and Zr. Light rare earths were more concentrated than heavy rare earths respectively: 629.66 ppm and 8.30 ppm. The high values of CIA and MIA (> 99.94) associated to the low content of alkali and alkali earth elements supported an intense weathering origin of duricrust. The presence of gibbsite and kaolinite suggested that the main cristallochemical mecanisms are allitisation and monsiallitisation. The average Al2O3 contents (>40%) associated to low content in SiO2 indicates that they are bauxites.