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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
Pétrographie et géochimie comparées des pellets phosphatés et de leur gangue dans le gisement phosphaté de Ras-Draâ (Tunisie). Implications sur la genèse des pellets phosphatés
Swiss Journal of Geosciences, Volume 103, No. 3, Year 2010
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Description
Paléocène-Early Eocene phosphate outcrop in the Ras-Draâ deposit (Tunisia) comprises alternances of P-rich strata (P2O5 ≥ 18%) and P-poor ones (P2O5 ≤ 2%). In phosphate rich strata, P is concentrated in rounded grains-so-called pellets-(28% ≤ P2O5 ≤ 38%) embedded in a matrix-so-called exogangue-much poorer in P (P2O5 # 7%) than pellets. The study of pellets (whose size lies mainly between 100 and 500 μm), of their surrounding matrix and of poorly phosphatic sediments, interlayered between the phosphatic strata, has been performed by optical microscopy and various chemical analyses, ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) and punctual chemical analyses by EDS (Energy Dispersive Spectroscopy). Mineralogical and chemical studies of the Tunisian phosphatic pellets show that the basic mineralogical component of these grains is carbonate-fluor-apatite, or francolite. The structural formula of a representative specimen of francolite in the basin is as follows: (Ca4.63Mg0.13Na0.22)(PO4) 2.51(CO3)0.48(OH0.77F 0.23). The mineralogy of the constituents of the sediment surrounding pellets comprises carbonates, clays, silica (opal, quartz). Microscopic observations of Ras-Draâ phosphorites, added to geochemical results, establish that pellets are small bodies, allochtonous to their matrix and whose composition is independent of that of this matrix. Fecal cylindrical bodies and subspherical pellets, the latest being supposed to proceed from the fecal bodies by fragmentation, are considered to have been formed by fishes, as P-rich and organic matter-rich faeces. These faeces turn out to be resistant to mechanical dispersion and to chemical diffusion of soluble elements from and in direction of sea water. This closeness is responsible for the strong reducing conditions having prevailed inside and during the pellets diagenesis. © 2010 Swiss Geological Society.
Authors & Co-Authors
Ben Hassen Trabelsi, Aida
Tunisia, Hamam Lif
Centre de Recherches et Des Technologies de L'energie
Trichet, Jean G.
France, Tours
Université de Tours
Disnar, Jean Robert
France, Tours
Université de Tours
Bélayouni, Habib
Tunisia, Tunis
Université de Tunis el Manar, Faculté Des Sciences de Tunis
Statistics
Citations: 21
Authors: 4
Affiliations: 3
Identifiers
Doi:
10.1007/s00015-010-0029-x
ISSN:
16618726
e-ISSN:
16618734
Research Areas
Environmental
Study Locations
Tunisia