Agamenticus

An approximately circular complex some 9 km in diameter, Agamenticus is intruded into Silurian sedimentary rocks and Late Devonian quartz monzonites. The western part of the complex consists of a peralkaline granite of perthite, quartz, arfvedsonite-riebeckite and aegirine-augite, while a homogeneous peralkaline syenite of perthite, less than 2% quartz, the same sodic pyroxenes and amphiboles as the granite, together with accessories, including fayalite, is the dominant rock type in the east. Between the granite and syenite is a ring of variable and heterogeneous quartz syenite which is considered to represent peralkaline granite contaminated by the syenite (Hussey, 1962, p. 41). In the centre of the complex is a plug of porphyritic biotite granite which was probably the last phase of intrusion.