Metasedimentary rocks of the Banfora belt are examined for their petrography geochemistry and genesis. Main formations are pelite meta pelites sandstone- and metagrauwackes. The first ones show a fine interlocking layering with unclear graded bedding in the sandstone compared to the metapelites, while the metagrauwackes show a clearly discordant graded bedding of light grey to light pink colour. The low SiO2/Al2O3 ratios (3.67 to 6.60) suggest their low sedimentary maturity. The meta pelites sandstone-pelites show moderate Na2O/K2O values (10.13 - 22.69) indicating moderate chemical maturity; in contrast, the metagrauwackes show low Na2O/K2O values (1.94 - 5.80) suggesting low chemical maturity. The meta pelites sandstone-pelites and metagrauwackes have Rb/Sr ratios of 0.866 - 0.004 and 0.173 - 0.607 respectively, indicating a moderate to low degree of chemical alteration. The chemical alteration index (CIA = 58 - 83) and the plagioclase alteration index (PIA = 53 - 81) suggest weak to moderate alteration of the source rocks. This alteration is different from simple alteration as the sole control on chemical composition, but is associated with metasomatism. The meta pelites sandstone- show a mixture of mafic and intermediate igneous sources which indicate that the protoliths could be basalts and andesites, but the metagrauwackes would be derived from the erosion of a mixture of andesitic to granitic rocks. The studied rocks generate from young undifferentiated to differentiated arcs. They are of low to moderate sedimentary and chemical maturity

Metasediments, Banfora Belt, Source, Alteration, Geotectonic Environment