New evidence for the early onset of supergene alteration along the kalahari unconformity

The manganese ore of the Hotazel Formation in the Kalahari Manganese Field, which has been thrust along the Blackridge thrust fault, has been subjected to various degrees of pre-thrusting hydrothermal and post-thrusting supergene alteration. Coarse-grained apatite, which appears to be formed under supergene conditions on textural grounds, is present in the thrusted manganese ore in previously unrecorded abundances. U-Pb dating of this apatite within the thrusted manganese ore has placed the onset of chemical weathering of the succession at a 77 ± 7.5 Ma, approximately 35 million years earlier than previously thought for the area. This implies that erosion along the Post-African I land surface, as well as the effects of supergene alteration in the Kalahari Manganese Field must have commenced within the late Cretaceous Period, subsequent to earlier erosion along the African land surface.