There are several highly mineralized areas in the country.
In a general way it is supposed that the lands lying between the lower St Paul's river and the Sierra Leone frontier are not much mineralized, except that in the vicinity of river mouths there are indications of bitumen.
Similarly there is a difference of opinion as to the conditions under which the organisms have been mineralized, some holding that the process has taken place at a high temperature and under great pressure; but the lack of practical evidence in nature in support of these views has led many to conclude that petroleum, like coal, has been formed at moderate temperatures, and under pressures varying with the depth of the containing rocks.
Vryheid (2287) is in the centre of a highly mineralized district.
In the older formations the phosphates tend to become more and more mineralized by chemical processes.