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The Kef Essennoun deposit is characterized by a thick layer (~ 35 m) of Upper Than phosphorites, which is itself, divided into 3 sub-layers known in all Djebel Onk district according to the P₂O₅ and MgO contents. From the bottom to the top, these sub-layers are:

- The basal sub-layer (BL): It consists of an alternation of marl, phosphorites and dolomite, about 2 m thick. The phosphorites have a relatively low P₂O₅ content (from 16 to 22%) and a high MgO content (3 to 5%). Heterogeneous phosphorite grains are cemented by marl and clay matrix.

- The main sub-layer (ML):  It has a thickness of 25 to 30 m and is mined for phosphorites. It is characterized by high P₂O₅ content (26 to 29 %) and low MgO content (less than 4%). Homogeneous phosphorite particles are cemented by clay or carbonaceous cement.

- The upper sub-layer (SL): It consists of a phosphatic dolomite layer with a relatively low P₂O₅ content (16 to 24%) and a high MgO content (6 to 11 %). This sub-layer is also characterized by a high SiO₂ content, ranging from 1 to 6 %. The phosphorite particles are heterogeneously grained.

The different analysis techniques applied to these types of minerals have shown a close relationship between the petrographic and mineralogical phases and between the particle size distribution and evolution of chemical contents and, on the other hand, developed a method for homogenization of the three sub-layers, which offers a wide variety of mixes that can meet the exploitability criteria.