Basal Proterozoic units as fossil time markers and their use in uranium prospection

Pyritic, uranium-bearing, quartz-pebble conglomerates have been found in Canada, in South Africa, in Brazil and in Australia. All are similar in lithology and mineralogy. All overlie a contorted greywacke-greenstone sequence and are overlain by rock units containing red clastics and shales. All are of similar age, where datable, being developed between 2800 m.y. and 2200 m.y. Uranium content derives from detrital, heavy minerals carried to and preserved in the rocks because of an anoxygenic atmosphere prior to 2200 m.y. Recognition of the environment of origin reflected by the conglomerates or the change in environment reflected by the sequence of rock units described permits assignment of an age range, frequently more meaningful than that derivable from usual dating methods. Uraniferous conglomerate ores can only be found below the oldest red-colored rock units. (author)