Placer deposits represent concentrations of heavy minerals of certain elements, particularly of gold, uranium, and platinum, by sedimentary processes. Depending on the age and the state of their consolidation, the deposits are empirically classified as paleoplacers if they formed in ancient coarse siliciclastic rocks, or as modern placers if they are a part of Pliocene to Recent unconsolidated clastic sediments. According to the main commodities and the host environments the placers are subdivided into 1.1 Paleoplacer uranium, gold, and 1.2 Placer gold, platinum. Paleoplacer deposits are further subdivided into uraniferous and auriferous pyritic quartz pebble conglomerates and sandstones (subtype 1.1.1) which contain detrital pyrite and are older than 2.4 Ga; and auriferous hematitic conglomerates and sandstones (subtype 1.1.2) which are younger, and contain hematite in place of pyrite. The transition from pyrite to hematite with time marks the increase in oxygen in the Earth’s atmosphere.