The traveling prospecting along the M’vunzi River has collected samples of the greenstone which have been the subject of macroscopic and microscopic observations of the thin sections made in the petrography laboratory. The present study has enabled us to identify in addition to the three types of rocks previously described by our predecessors, a fourth petrographic type which is a chloritoschist. In addition, two new minerals have been identified including «garnet» and «cordierite», respectively in an amphibolite and in a chloritoschist. The mineralogical paragenesis of the different petrographic types described to date in the M’vunzi valley composed of: epidote-chlorite-quartz, epidote-plagioclase-albite-chlorite-calcite, chlorite-biotite-quartz and chlorite-biotite-albite-quartz are typically secondary mineral paragenesis and indicate that all basic lavas in the study area were affected by regional greenschist facies metamorphism which is clearly justified by the appearance of chlorite in each mineralogical paragenesis. These results allowed us to deduce that the M’vunzi valley is lined with Gangila green rocks, the main ones being amphibolites, chloritoschists, micaschists and epidotites. It is therefore, for the most part, ancient basaltic lavas very rich in plagioclase which subsequently transformed into green rocks. The latter are the products due to the regional metamorphic gradient of Low Pressure and High Temperature (LP-HT).