Marine placers are located on present beaches or are related to the Quaternary sea level oscillatory events, which exposed large areas of the continental shelf or covered portions of the coastal plains. The transgressive sea level events drowned alluvial and colluvial deposits including important heavy minerals concentrations further reworked by current and wave action. This mechanism promoted the re-concentration of the denser minerals such as ilmenite, zircon, tin, gold and diamonds. The main exploration activities of marine placers are located on Namibian and South African continental shelves, for diamonds, and on the Southeast Asia, for tin. Important extraction of ilmenite, zircon, rutile and monazite sands occurs in Australia, Sri Lanka and India, as well as on the northern Rio de Janeiro State, Brazil. Gold extraction on beaches and on the continental shelf offshore Alaska ceased during the nineties. The technology involved on the exploitation of marine minerals can be highly sophisticated, as observed in Namibia and South Africa, employing massive ships, with specially designed rotation drills, submarine robots and track-mounted vehicles, equipped with powerful suction pumps, remotely controlled. These equipment are used to extract the gravel substrate containing the diamonds in water depths approaching 200 m. The associated environmental impact in dredged areas is substantial and must be constantly monitored and controlled by an efficient legislation and by the local environmental agencies and controlling organisms. This paper presents a review of the current knowledge about the origin of the marine placers, the main world's and Brazilian occurrences and exploration techniques and the principal environmental impacts associated with its exploitation.
Continental Shelf; Heavy Minerals
