Characterization of Pyroclastic Deposit from Three Different Areas within Foumbot Region (West-Cameroon): Comparative Studies of Their Effects as Pozzolanic Materials in Mortars and Cement Manufacture

Pyroclastics which are known natural pozzolanic materials due to amorphous contents, are present in several areas of the Mbepit Massif in West Cameroon. In this work natural pozzolan from three zones namely Pouoloum, Njimbouot and Nkouonja were characterized. A comparative study was then developed to attest the effect of these pyroclastics as partial substitution in portland cement. The mixtures were made at different pozzolanic proportions (00%, 10%, 15%, 25% and 35%) of substitution of the cement. The compressive and flexibility strength was carried out at 7, 28 and 90 days on mortar specimens (4 × 4 × 16 cm3). The results revealed apozzolanicactivity index of 81.99 %, 83.47% and 74.54% respectively for rock sample from Pouoloum (PCB), sample from Njimbouot (PCC) and sample from Nkouonja (PCN). After 90 days, for a substitution rate of 25% compressive strength are respectively 55.69 MPa, 60.4 MPa, 53.34 MPa for PCB, PCC and PCN. According to the American Society for Testing and Materials (ASTM) C618 classification, the pyroclastics are in accordance with all the criteria to be classified as pozzolan. Independent of the substitution rate, the mechanical performance increases with age in PCB, PCC and PCN. However PCC is most reactive than PCB and PCN. This may be due to the amorphous reactive content in this material and can be linked to the eruptive dynamisms which were more explosive in some areas than in others. The amorphous content is 32.01%, 36.99%, 24.84% for PCB, PCC and PCN respectively. These results also prove that Natural Pozzolan is interesting in the manufacture of composite cement CEM II, CEM IV in accordance with EN197-1 or can be added in mortar for buildings and sustainable environmental management.

Petrography and Mineralogy of the Quartz and Quartz-Feldspar Sulphide Veins in the Pan-African Syenitic Massif of Guider (North Cameroon)

In the syenitic pluton of Guider (593 ± 4 Ma) in the North-West Cameroon domain of Central African Fold Belt, mineralized N-S to NE-SW vertical or sub-vertical quartz and quartz feldspar veins has been recently identified. In this contribution, we present petrography and mineralogy of these veins, in order to constrain their genesis and emplacement mechanisms based on detailed field work, petrographic studies and chemical characterization of minerals by using an electron probe microanalyser (EPMA). Field observations and vein microstructures show that the emplacement of the veins has been controlled by the dextral N-S trending strike-slip shear zones related to the regional D2 deformation phase. The results of mineralogical analysis reveal the co-presence of silicates and metallic minerals that include magnetite, ilmenite, pyrite, bismuthite, galena (very rare) and sulphide complexes (BiPbS, BiAgPbS, FeBiPbCuS, BiFe(TeS), FeBiPbS, BiPbCuS). The gangue is represented by quartz (quartz 1, quartz 2 and quartz 3), feldspars, sericite, chlorite, yellowish brown clay minerals, and hematite. The textural relationships between sulphides, quartz and alteration products show that the mineralization is essentially syn- to late-D2 and suggest that syenitic country rock and dextral shear zones have played an important role in the metallogenesis of these veins. This mineralization shows characteristics for copper-bearing calc-alkaline deposits, but differs from these by its more extensive alteration and its abundance in hematite. Substitutions of Al(IV) by Si(IV) in sericite associated with the sulphide mineralization and cataclastic deformation suggest that the temperature of trapping of the fluids is between 230°C and 275°C.