Swartbooisdrif

Immediately south of the Kunene River numerous sodalite-bearing carbonatite dykes, one of which is 9.5 km in length, and many narrow veins occur in an area of 10x10 km within anorthosites of the Kunene Intrusive Complex. They are clearly depicted on a map in von Seckendorff et al. (2000, Fig. 2). The dykes are strikingly coloured by irregular, impersistant bands rich in blue sodalite, white ankerite, pink analcime and yellow cancrinite (Menge, 1986). The dykes are generally up to 50 m thick but, as indicated by a geological map of part of one dyke (Menge, 1986, Fig. 3), may vary rapidly. They are vertical or steeply dipping bodies and commonly multiple with several phases of carbonatite, various types of foid syenite and lamprophyre. According to Toerien (in Verwoerd, 1967) nepheline syenite with biotite, sodalite and cancrinite was the first intrusive phase. This was followed by brown carbonatite which brecciated the nepheline syenite, of which numerous xenoliths are distributed throughout the carbonatite. Associated with this episode was the emplacement of dykes of biotite-phyric lamprophyre. A final carbonatite phase was then intruded which is characterised by evenly distributed and occasional bands of feldspar and by more intense reaction along contacts. Discontinuous areas of blue sodalite and yellow cancrinite are widespread and, in the opinion of Toerien (Verwoerd, 1967), appear to have replaced nepheline syenite. Menge (1986) describes three dykes in detail and illustrates the structural and textural complexity including photographs, in colour, illustrating the intimate intermingling of the principal minerals, for the genesis of which he invokes processes of liquid immiscibility as well as replacement. A detailed study of the oxide and sulphide minerals in the sodalite-bearing rocks, including mineral chemistry and petrographic data, with many illustrations of textural relationships, is that of von Seckendorff et al. (2000).