The main Tambani body, which consists of nepheline syenite gneiss, is some 20x6 km with several outlying areas and is orientated parallel to the trend of the surrounding paragneisses (Cooper and Bloomfield, 1961). Contacts with the surrounding rocks are conformable and transitional but there are places which are cross-cutting, including occurrences of nepheline syenite dykes cutting the adjacent paragneisses that Cooper and Bloomfield (1961) ascribe to mobilisation of the nepheline gneiss. The nepheline gneisses are typically migmatitic with in places mobilisation apparently obliterating the gneissic structure. Concordant bands of typical country rock biotite and hornblende gneisses occur throughout the body and pegmatites up to a metre thick are also widespread. A typical example consists of microcline perthite, nepheline, biotite, muscovite and accessory zircon, magnetite, corundum and apatite; blue sodalite occurs in some areas. A range of other minerals including betafite, uraninite and monazite have been found in the area (Cooper and Bloomfield, 1961); they give analyses of two nepheline gneisses.