The exploitation of placer mineral deposits for their valuable heavy minerals. Placer mineral deposits consist of detrital natural material containing discrete mineral particles. They are formed by chemical and physical weathering of in-place heavy minerals, which are then concentrated through the action of wind or moving water. This concentration can be done through wave and current action in the ocean (beach and offshore placers), glacial action (moraine placers), wind action removing the lighter material (eolian placers), or the action of running water (stream placers). Stream placers are the most important of these deposits because of their common occurrence and their highly efficient concentration mechanisms. Marine placers, primarily beach placers, are the next most economically important, with the potential of offshore placers being the most recent to be recognized and developed.