Illite, mixed-layer Illite-smect itc and chloritc are the major clay minerals of the Devonian shales of the Lower Amazonas Basin. The absence of chlorite in the radioactive section of the Barreirinha Member (Curuá Formalion) is atributed to syndepositional processes (anoxic conditions) that also originated kaolinite and mixed-layer illite-smectite.These rocks are at a high stage of diagenesis and consequently the most evident alterations caused by the intrusion of basic igneous magma are the apperance of pyrophyllite and paragonite derived respectively from kaolinite and mixed-layer illite-smectite. The width of the metamorphic aureole adjacent to the sills at least equals the thickness of the intrusives bodies. At the same time, several alterations occur within the intrusives as they incorpotate fluids from surrounding rocks.Resumo indisponível.