In the western Cameroon, crop out several dyke swarms of Paleozoic–Mesozoic age. These dykes intrude the Precambrian basement in the southern continental part of the Cretaceous Cameroon Volcanic Line. In the Njimom area, two groups of mafic dykes that crosscut the Neoproterozoic basement rocks have been observed. A first group intrudes the mylonites whereas the second group intrudes the granites. The dykes are alkaline basalts and hawaiites. The mineralogical assemblage of both groups of dykes consists of plagioclase, clinopyroxene, altered olivine, and opaque oxides. The dykes that cross-cut the Precambrian mylonitic gneisses show moderate TiO2 (1.7–2.0 wt.%), low MgO (4.4–7.1 wt.%), and compatible trace element concentrations (e.g., Cr = 70–180 ppm; Ni = 30–110 ppm). The dykes that intrude the granites have TiO2 contents between 2.3 and 2.5 wt.% and moderate compatible trace element concentrations (e.g., Cr = 260–280 ppm; Ni = 170–230 ppm). MgO varies from 5.9 to 9.2 wt.%. All mafic dykes are enriched in light lanthanide element and show moderate Zr/Nb and high Zr/Y, Nb/Yb, and Ti/V ratios similar to those of average ocean island basalt (OIB)-type magmas. Some dykes that intrude the mylonites show evidence of contamination by continental crust. The composition of the clinopyroxenes of the dykes that intrude the mylonites clearly indicate different and unrelated parental magmas from dykes that intrude the granites. Contents and fractionation of the least and the most incompatible elements suggest low degrees of partial melting (3–5%) of heterogeneous source slightly enriched in incompatible elements in the spinel stability field. The geochemical features of Njimom dykes (in particular the dykes that intrude the granites) are similar to those of Paleozoic and Mesozoic dykes recorded in the southern continental part of the Cameroon Volcanic Line, suggesting multiple reactivations of pre-existing fractures that resulted in the fragmentation of western Gondwana and the opening of the South Atlantic Ocean.

This study evaluates the fertilizing potential of micaschist powder in sugarcane farming on ferrallitic soils of the Mbandjok area in Cameroon. These soils are poor in exchangeable cations and assimil able phosphorus, very acidic, with low to moderate CEC. An experimental design, which consisted in a randomized Fischer block, is composed of six replications of five treatments:T0: conventional fertilization (Ureemulticote 39 00, 150 kg ha-1; MAP, 125kg ha-1; KCl,250kg ha-1) T0-M1: T0 + 5 t ha-1of Micaschist powder, T0-M2: T0 + 7 t ha-1of Micaschist powder, NP-M1:N and P supply, conventional dose (no KCl) + 5 t ha-1of Micaschist powder, N-M2: N supply, conventional dose (no P and K) + 7 t ha-1of Micaschist powder. The experiment was carried out between October 2015 and February 2019. During this period, soil samples were collected, sugarcane was planted and monitored with great care in order to determine the parameters indicative of the growth and yield of sugarcane plants. The results indicate an important increase of the sugarcane yield during the three years of experiment, on soils where micaschist powder was added, compared to the control. Concerning the percentage of lift and voids, the T0-M1 treatment had 3% of voids compared to the T0 (9%) treatment which is the reference fertilizer; for Tillers parameter, T0-M1 (338 stems) performs very well during the experiment compared to the T0 (297stems) and for the growth parameter, T0-M1 treatment was good increasing from 182 cm in the first year to 280 cm in the second year. This suggests that micaschist powder has a positive and significant effect on the growth components. For the yield of sugarcane, the best result of tons of sugarcane (TC) was obtained with T0-M1 treatment which increased from 77.15 TC ha-1 in the first year to 86.13TC ha-1 in the third year. The overall results indicate that using micaschist powder as fertilizer can enhance sugar cane yield with a long lasting residual effect of rock powder.