The Semarule syenite complex lies within one of the large granite plutons in southeastern Botswana that are known collectively as the Gaborone granite. Semarule is post-granite in age but syenites and granites are complexly intermingled as illustrated by the map of King (1955, fig. 1), with various facies distinguishable, mainly by textural criteria. Certain of the syenites contain aegirine-augite and/or melanite, and in some melanocratic varieties wollastonite and abundant calcite are present. Aegirine-augite and melanite also occur in some of the abundant suite of syenitic dykes and pegmatites. King (1955) considered that the complex was formed by alkali metasomatism and mobilisation of Gaberone granite. The complex is partly overlain by remnants of a Karoo dolerite sill.