The Matjieskloof uranium anomaly, Fraserburg district

The Matjieskloof uranium anomaly (GT-7) is situated on the slopes of Groottafelberg at the base of the Nuweveld Escarpment in the Fraserburg District of the Cape Province. It lies within, or immediately adjacent to, the Poortjie Member of the Teekloof Formation, Beaufort Group. The deposit is associated with a succession of fluvial tabular sandstones interbedded with red, purple, and green mudstones and siltstones. Mineralization (uraninite, coffinite with minor molybdenum) is of a URAVAN type and occurs as pods within abandoned loops of a meandering channel system. The geometry of the ore body suggests that coalescence between sandstones played a major role in the location of ore pods. It is proposed that a weak REDOX front developed in the sandstone body during the mixing of discrete oxidizing and reducing fluids at the time of coalescence. Free carbon within this weak REDOX zone controlled the fixing and preservation of the uranium. An ore reserve of about a million tons is estimated