The SE Asia Research Group remains focused on field and laboratory based studies that aim to improve our understanding of the tectonic development and geological history of the SE Asia region. Recent projects have increasingly made use of developments in Sedimentary Provenance and Thermochronological techniques to support field programmes. Both approaches require systematic handling, processing, separation, and ultimately dating, of samples gathered during field programmes.
To this end, the SE Asia Research Group has been heavily involved in developing and maintaining departmental facilities for sample processing and mineral separation. Exisiting sample processing facilites and protocols have been upgraded and updated and the research group has developed new mineral separation facilites, capable of handling large volumes of material, based on those used by colleagues in the Department of Earth Sciences at the University of Melbourne, Australia.
Sample Processing
Rock Crushing
Crushing is the first step for all lithified samples. Material is first broken into smaller pieces using a Pneumatic Splitter, and then crushed using a new ‘Retsch’ Jaw Crusher with a variable gate. Multiple passes with progessively finer spacings produce a good crush with plenty of monomineralic material without over crushing or obliterating the sample.
Disagregation/acid dissolution
To aid in the breakdown and removal of clays, sedimentary samples are washed using distilled water. Unwanted carbonate material is remved using acetic acid.
Wet and Dry Sieving
Samples are routinely wet sieved to remove any unwanted plant material, bugs etc. (modern sediment samples) and/or fine dust generated during crushing (originally lithified rocks). Both can have adverse affects on later separation phases stages. In order to minimalsie potential contamination all samples are processed using disposable nylon sieve meshes, held with a split brass collar. We use 63, 100 and 250 micron meshes, most commonly working on the 100-250 micron fraction, but retaining all fractions for any future use. Samples are dried in a low-temperature oven. Dried samples are often dry sieved to remove any remaining fine (<63 micron) material before the mineral separation phase.
Mineral Separation
Mineral Separation is achieved using a combination of magnetic, density and other separation techniuqes, the order and usage of which varies depending upon both the sample material and the required end products.
Magnetic Separation
Magnetic Separation is normally carried out in two stages. An intial ‘bulk’ separation, using a weak magentic filed, aims to remove only the most magnetically susceptible minerals before more precise separation.
Bulk separation is performed using a hand magnet Further, more precise and detailed separation, is performed using the Frantz Isodynamic Separator (above). A wide range of separations can be performed by altering the many different features of the Frantz including the magnetic field, the forward and side tilt of the slide and its vibration.
Heavy Liquid Separation
We regularly use two heavy liquids for density separations: Sodium Polytungstate (SPT) with a maximum density of ~2.89 and Di-iodomethane (DIM) with a maximum density of ~3.31. Both are recycled after use.
Both sedimentary provenance and thermochronology projects require relatively large volumes of mineral separates. As such, we use a bulk SPT set-up featuring 2L separation funnels with stirrers to agitate what is a relatively viscous liquid and encourage separation. Despite the large (2L) volume, each sample commonly requires multiple ‘runs’ through the SPT to produce sufficient quantities of the desired heavy minerals. Where necessary, the ‘heavy’ SPT fraction can be further separated using DIM.
photos: K.D’Souza
