HEAVY MINERALS - FROM EDELSTEIN TO EINSTEIN

Identification in 1982 on the Dutch Frisian Island of Ameland of beach sand with;ln enhanced level of natural radioactivity, due to concentr ations of heavy minerals, inspired a multi-disciplinary research proje ct. A joint research effort in geochemistry, sedimentology, hydrodynam ics, solid-state physics and nuclear physics has revealed new aspects in the use of natural radioactivity in heavy-mineral exploration and p rocessing, as well as in understanding sediment transport processes in the coastal zone. This paper describes radiometric methods and techni ques, such as thermoluminescence dating and a method known as radiomet ric fingerprinting. Initially our focus was on relationships between n atural radioactivity and grain size, and between radioactivity and min eral species. Additionally the distribution of heavy minerals along th e Dutch coast was mapped. One of the first substantial findings was th at the concentrations of K, U and Th in light and heavy minerals diffe r by two orders of magnitude. Thus the total heavy-mineral mass fracti on (THM) could be accurately determined radiometrically. Attempts to d etermine THM radiometrically resulted in identifying regions of proven ance, or origin for coastal sand minerals. This stimulated studies of transport processes and their selectivity. Investigations were conduct ed on the beach, under laboratory conditions and on the seafloor. More over, the enhanced radionuclide concentrations in, e.g., zircons make them particularly suitable for thermoluminescence dating young dune an d beach sediments. This knowledge may aid better management of coastal zones, and may help to identify the genesis conditions of heavy-miner al placers. The instrumentation development has resulted in MEDUSA a t owed detector system used for radiometric seafloor mapping. MEDUSA rev ealed unknown large quantities of heavy minerals on the Dutch seafloor . These minerals are present in layers up to 40% in thickness and with concentrations up to 20%. Radiometric fingerprinting of minerals allo ws a quantitative assessment of mineral suites during various stages o f wet and dry separation. This industrial application of MEDUSA is bei ng considered in Australia and South Africa. (C) 1998 Elsevier Science B.V,AII rights reserved.