In Northern Rhodesia, shale containing rich copper ore gives way laterally to dolomitic rock, believed to represent algal reefs and associated slump deposits. In Katanga, a barren algal reef layer separates cupriferous shale beds. Uranium in the Katherine-Darwin region, Northern Territory, is in limestone reef breccias. At Mount Isa, Queensland, copper occurs in silica-dolomite bodies, here interpreted as reefs, and lead-zinc ore bodies are in shales away from the silica-dolomite bodies. The common denominator in these diverse modes of occurrence is believed to be the mixing of marine and land-derived waters at reef lines, suggesting a syngenetic origin of the deposits.