Vryheid (2287) is in the centre of a highly mineralized district.
Many fossils are mineralized with pyrites, which has evidently been reduced by the action of decomposing organic matter on a solution of ferrous sulphate, or perhaps less directly on ferrous carbonate dissolved in water containing carbonic acid, in the presence of certain sulphates.
Near the crest of anticlines is commonly an enriched portion of the ground in mineralized districts; and, in the case of water supply, the tilt of the strata determines the direction of the underground flowage.
There are several highly mineralized areas in the country.
In the older formations the phosphates tend to become more and more mineralized by chemical processes.