Geological, Mineralogical and Geochemical Studies of Pyrite Deposits in the Eastern Part of Douala Sub-Basin (Cameroon, Central Africa)

Abstract

Pyrite deposit of pK27, Douala sub-basin (Cameroon, Central Africa) was studied in a tropical forest setting physically and using X-ray diffraction and X-ray fluorescence spectrometry (XRF) in order to characterize the mineralization for his industrial utilization. The sedimentary materials from the pyrite deposit were grouped into five (05) main lithofacies, including four claystone facies and one conglomeratic facies. The mineralization occurs along the low slopes of valleys in light grey claystone facies situated on the bottom of outcrops with 80 to 200 cm thickness. The particle size distribution of clayey materials host rocks shows that they are essentially constituted of clay and silts fractions. However, their Sorting index (So) more than 4.5 corresponds to poorly sorted sediments and the torrential type; whereas their Coefficient of asymmetry (A) more than 1 indicates that the sorting is carried out towards fine particles. Macroscopically, pyrite in these materials is in crumbly and consolidated piles with aggregate pyrites in oolithic concretions, and globular, cubic, octaedric, massive and fossiliferous forms. The mineralogical compositions of these clayey materials indicate that they are essentially kaolinitic and illitic, followed by goethite, quartz, pyrite, halloysite, anatase and rutile with hematite as accessory minerals. Pyrite in sand fractions is associated with kyanite, grenat, rutile, diopside, muscovite and tourmaline the minerals which recognize the regional metamorphism. However, the specific chemical signature of SO 3 content high in clayey materials and abundant (50.86% - 57.64% SO 3 ) in pyrite is characteristic of the pK27 pyritic formations in the eastern part of Douala sub-basin. Moreover, the Co:Ni ratios of pyrites approximately 0.25 to 0.8 are characteristic of sedimentary pyrites and also suggest an anoxic environment.