PHOSPHATE OCCURRENCES ON THE WESTERN AND SOUTHERN COASTAL AREAS AND CONTINENTAL SHELVES OF SOUTHERN-AFRICA

Several different varieties of sedimentary phosphatic deposits of Neogene age occur on the southern and western continental margins of southern Africa. Their origin and distribution were influenced by major transgressions and regressions identifiable in offshore seismic reflection profiles and confirmed by onshore observations. Offshore deposits consist of nodules eroded from outcropping Neogene strata and mixed glauconite/apatite pellets. In addition concretionary masses occur on the South West African shelf associated with siliceous muds. On the western coastal plain the oldest deposit is a Miocene phosphatic sandstone which is unconfonnably overlain by a Pliocene unit containing reworked Miocene material. Small volumes of phosphate-cemented surface sands are found, and a number of deposits of aluminium phosphates occur in the vicinity of Saldanha Bay. The deposits are of the platform type. No tectonic control of mineralization has been identified, but local topographic features have influenced the distribution of ores. Several modes of origin including direct precipitation, replacement, diagenesis, allo-chemical and lithochemical, have been identfied. © 1979 Society of Economic Geologists, Inc.