Heavy media separations (HMS) are commonly used in the geosciences to divide crushed rocks or soils into their respective light and heavy specific gravity fractions e.g. gold panning where water provides the medium and the panning action separates the denser gold particles from the lighter, gangue minerals. In the laboratory, HMS are often employed to separate mineral grains prior to further analysis.
The separated heavy minerals provide important indicators of sedimentary rock provenance, sediment pathways and palaeogeography and the degree of diagenesis that sediments have undergone. They may also enable stratigraphic correlation and are particularly useful where biostratigraphic information is absent.
Traditionally, the heavy media employed were halogenated organic solvents (e.g. bromoform, methylene iodide and tetrabromoethane) but these are highly toxic, require strict Health and Safety protocols and are increasingly difficult to obtain.
BGS have therefore researched and replaced halogenated organic solvents with lithium polytungstate (LST) media which offer the following advantages:
Following the isolation of heavy and light fractions, initial analysis is usually undertaken by inspection using optical microscopy or by employing X-ray diffraction techniques. This may be followed by more detailed morphological assessment and micro-geochemical analysis using either scanning electron microscopy or the electron microprobe.
Please contact Simon Kemp for further information