Heavy minerals: from `Edelstein' to Einstein

• Published in: Journal of geochemical exploration 1998-06, Vol.62 (1), p.81-103
• Main Author: de Meijer, R.J
• Format: Article
• Language: English
• Subjects: exploration; heavy minerals; natural radioactivity; processing; sediment dynamics; sediment transport
• ISSN: 0375-6742; 1879-1689
• DOI: 10.1016/S0375-6742(97)00073-3

Identification in 1982 on the Dutch Frisian Island of Ameland of beach sand with an enhanced level of natural radioactivity, due to concentrations of heavy minerals, inspired a multi-disciplinary research project. A joint research effort in geochemistry, sedimentology, hydrodynamics, solid-state physics and nuclear physics has revealed new aspects in the use of natural radioactivity in heavy-mineral exploration and processing, as well as in understanding sediment transport processes in the coastal zone. This paper describes radiometric methods and techniques, such as thermoluminescence dating and a method known as radiometric fingerprinting. Initially our focus was on relationships between natural radioactivity and grain size, and between radioactivity and mineral species. Additionally the distribution of heavy minerals along the Dutch coast was mapped. One of the first substantial findings was that the concentrations of K, U and Th in light and heavy minerals differ by two orders of magnitude. Thus the total heavy-mineral mass fraction (THM) could be accurately determined radiometrically. Attempts to determine THM radiometrically resulted in identifying regions of provenance, or origin for coastal sand minerals. This stimulated studies of transport processes and their selectivity. Investigations were conducted on the beach, under laboratory conditions and on the seafloor. Moreover, the enhanced radionuclide concentrations in, e.g., zircons make them particularly suitable for thermoluminescence dating young dune and beach sediments. This knowledge may aid better management of coastal zones, and may help to identify the genesis conditions of heavy-mineral placers. The instrumentation development has resulted in MEDUSA a towed detector system used for radiometric seafloor mapping. MEDUSA revealed 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 allows a quantitative assessment of mineral suites during various stages of wet and dry separation. This industrial application of MEDUSA is being considered in Australia and South Africa.