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| Titel |
Application of Automated SEM-EDS Based Mineral Identification Systems to Problems in Metamorphic Petrology |
| VerfasserIn |
Robert Fairhurst, Wendy Barrow, Gavyn Rollinson |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043834
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| Zusammenfassung |
| Automated scanning electron microscopy-energy dispersive x-ray spectrometer (SEM-EDS)
based mineral identification systems such as QEMSCAN have been in development for
over 20 years, primarily as a tool to understand mineral liberation and element
distribution in metal mining industry. This powerful technique is now being used in
non mining applications such as metamorphic petrology where accurate mineral
identification and metamorphic fabrics are key to deciphering the metamorphic history of
samples.
The QEMSCAN was developed by CSIRO for application in the mining industry where it
is used to understand mineralogy, texture, mineral associations, the presence of gangue
minerals and deleterious elements that may potentially interfere with mineral processing and
planning, and the overall impact of mineralogy on grinding and flotation processes. It
is capable of identifying most rock-forming minerals in milliseconds from their
characteristic x-ray spectra. The collected x-ray spectra are compared to entries in a
database containing the species identification profiles (SIPs) and are assigned a label
accordingly. QEMSCAN is capable of searching large sample areas at high resolution
resulting in the accurate and precise determination of all minerals present. Reports that
were originally developed for the mining geologist can be equally useful to the
petrologist, e.g. phase/mineral maps, modal mineral abundances and mineral association
reports.
Identification of key minerals is of great importance to determining the petrologic history
of a sample. These key minerals may be few in number and present as small microinclusions
(less than 100 μm) making them difficult to identify, if at all, with the petrographic
microscope. Therefore, imaging by electron-microprobe or scanning electron microscope are
the methods traditionally used. However, because of the small field of view available on these
instruments at a magnification necessary to resolve micron sized relicts and textures, the
search for a few microinclusions may be extremely time consuming, tedious and
costly. QEMSCAN with its ability to provide large quantitative data sets and search
large sample areas at high resolution means that whole thin sections can have their
mineralogy accurately and precisely determined in hours. For instance in metamorphic
petrology once relict minerals of earlier metamorphic assemblages are located;
thermobarometry and geochronology can then be applied; resulting in a wealth of
information on previous segments of the pressure-temperature-time-deformation path.
The relict mineral textures and their relationship to the fabric of the entire thin
section can be easily seen in the phase/mineral map yielding important textural
information.
We have developed a SIP database to be used to study metamorphic samples from the
Central Metamorphic terrane (CMt) of the eastern Klamath Mountains, northern California.
The CMt was chosen because recent work has resulted in the discovery of relict rutile grains
and ilmenite-plagioclase-amphibole symplectites textures interpreted as the decomposition of
either garnet or omphacite during exhumation from eclogite facies conditions. The
QEMSCAN is being used primarily to search for these relict garnet and omphacite grains.
Although only a few samples have been run, no garnet or omphacite have been located
thus far. However, in a very short period of time the modal mineral abundances
and overall fabric have been determined to a degree never previously achieved. |
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