Carbonated rocks of Mintom constitute the upper series of Dja [2] - [4] . A part from the sedimentary formations, the area reveals the presence of metamorphic rocks (gneiss, schist, mica) and plutonic rocks (gabbro, granite). Structurally, the region is crossed by numerous of tectonic structures such as faults, folds and mylonite. The work of [5] show that this basin is limited at North by the Pan African belt and at south by the Congo Craton (Figure 2). The main geological formations (shales, dolomites and limestones) are covered with argillites and laterite. Two main soils run throughout the area including yellow lateritic soils in land and hydromorphic soils in the lowlands [1] [6] [7] .

The study of [4] led to subdivide the upper Dja series in four lithological units from bottom to top, there are: The unity of Kol, made with diamictite on its base and pelit on the summit; Metou unit composed of massive dolomite; Mominbolé unit that has an alternation of limestone and clay: it is a pelitic limestone and the Atog Adjap unit composed of clear limestone and yellowish gray band. From the photogeological analysis [2] [4] , it appears that, the different features which form the sedimentary basin of Mintom stick out in a powerful soil layer near the Dja River. The survey S1 of [2] in BI was used to estimate the relative thickness of limestone feature (Figure 3). Thus, the massive limestone has a thickness of 21 m, while the banded limestone features extends over a thickness of 24 m.

The methodology of work is divided into two major activities including field campaigns and laboratory work.

They took place in four stages. The first phase consisted of an exploration of the study area in order to locate outcrops; the second was used to determine the sampling points and the two last stages were devoted to sample in previously defined sampling points. The samples were collected by geological hammer at three points defined on various features. Then, they were packed in sampling plastic bags. Field campaigns have also helped to give the description of the different features encountered.

Laboratory work concern the analysis of different samples collected in the field. These analyzes were performed in different laboratories. The Table 1 gives the synthesis of laboratory analysis.

Several geological structures and outcrops were encountered (block, slab, escarpment, cleavage, bend, fault) (Figure 4).

Three major features have been described from outcrops and geological structures (Figure 5). They are:

・ Massive limestone feature

It is observed mainly in Atog-Adjap where it is very extensive. It is a hard gray rock and very effervescent in HCL. Its structure shows alternating benches separated by thin layer of dark argillite. In optical microscope, the rock is homogeneous and composed with very small crystals (<20 microns).

・ Banded limestone feature

It is a dark gray rock characterized by alternating light and dark bands. The thickness of a band varies between 10 - 15 cm. In thin blade, the texture is cryptogranular with small calcite crystals (0.03 mm). We also note the presence of veins (e = 60 microns) filled with black politic material.

・ Dolomite feature

It is a massive ocher rock, very resistant to hammer and very low effervescence in HCl. In microscope, the bottom is dolomicritic with many microcracks showing dolomite and quartz recrystallization. It is noted the

presence of micro-cracks and wall rock piles in pyrite grains.

The X-ray diffraction analysis sample’s powders obtained from different features gave the results that are illustrated by corresponding diffractograms. From these results (Figure 6), it appears that calcite, mica and smectite constitute the major elements of massive limestone. The banded limestone is composed of calcite; mica and smectite while the mineralogical composition of dolomite is made only by dolomite and smectite.

Chemical analyzes of samples have identified the different chemical compositions of the different features expressed as percentages of oxides. Table 2 presents the summary of the results. The analysis of these results shows that the massive limestone is rich in CaO and SiO₂, the massive limestone in CaO. For dolomite, the most important elements are the CaO and MgO. These contents can be the basis for various industrial uses.

The exploitation of mechanical results (Table 3) shows that the massive limestone rock is a low-wear, resistant to both, fragmentation, and compression and relatively dense. The banded limestone meanwhile is a rock with high wear, weakly resistant to both fragmentation, and compressive strength and low density. Concerning dolomite, it is a rock with very low wear, very resistant to both, fragmentation and compression and relatively dense.

The main uses recognized for carbonated material and the main uses of specifications are presented below:

For massive limestone

It can serve as raw material for the production of clinker (CaO ˃ 42% MgO < 2% Fe₂O₃ ˃ 1% Al₂O₃ ˃ 2% SiO₂ ˃ 6%); Agriculture’s amendments and production of quicklime. Mechanically, its low wear (MDE = 17%), high resistance to fragmentation (LA = 20%), its high compressive strength (MPa = 107) and its high density, predispose it in civil engineering work.

For banded limestone

Their high wear MDE = 48%), low resistance to fragmentation (LA = 27.5%), their low density and compressive strength MPa = 49) showed that the main uses of this material are recruited in the areas of ornamental stones.

For dolomite

Geochemical properties of dolomite show that it can be used in the steel industry or agriculture as amendments. Its mechanical properties notably its low wear (MDE = 11%) its high resistance to fragmentation (LA = 19%), its high compressive strength (MPa = 118) and high density, describe it as good material in civil engineering.