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Spatially Resolved X-ray Analysis of Minerals

2D X-ray spectrometry offers a wealth of information on mineral samples, allowing to pinpoint elements within a sample, even if they are present in low concentrations and only at a few locations. Depending on application and spatial resolution required, either micro X-ray fluorescence spectrometry (µ-XRF) or energy-dispersive X-ray spectrometry (EDS) on the scanning electron microscope (SEM) can be used. µ-XRF allows to scan large samples with minimal preparation and can detect trace concentrations in the ppm range with a spatial resolution of down to 25 µm. EDS requires sample preparation but can provide a resolution range of 10s of nm.

Hyperspectral Imaging

Element Map of a Granite Sample
Element map of a granite sample, showing some of the main constituents
Comparison of Sum and Maximum Pixel Spectra of a Granite Sample
Comparing sum spectrum and Maximum Pixel Spectrum. The Maximum Pixel Spectrum clearly shows the presence of thorium, lanthanum and cerium, which cannot be detected in the sum spectrum due to their low overall concentration

Spectrum Images or hyperspectral images (HyperMap) provide complete spectra for each pixel of the image, allowing data mining. For instance, the element identification can be improved by using the Maximum Pixel Spectrum function (Bright and Newbury, 2004). This function synthesizes a spectrum consisting of the highest count level found in each spectrum energy channel. Even elements which occur in only a few or just one pixel of an element map can be easily identified.

Hyperspectral Imaging

Monazite Particles in Granite
Monazite particles identified
with the help of Maximum
Pixel Spectrum

The M4 TORNADO µ-XRF spectrometer and QUANTAX for SEM (EDS) support these analytical methods. Application examples in minerals and mining include:

  • Mineral identification through quantitative element maps
  • Determination of major and minor constituents

Analysis can be further refined using chemical phase mapping (Autophase), which detects similarly composed spectra with the help of mathematical methods (principal component analysis or cluster analysis) or user defined areas. This tool is most valuable for quantification of phases in a mineral sample.

Automated particle analysis

Image of an Iron Ore Pellet Overlaid with Chemical Classification Results
Backscattered electron
image of a single analysis
field of an iron ore pellet
overlaid with color coding
according to chemical
classification. The phase
list in the table in the
image in the right column
can be used as a color

The ESPRIT software for QUANTAX for SEM provides a powerful and universally configurable particle analysis package with ESPRIT Feature. ESPRIT Feature can be set up to perform unattended measurement runs, analyzing large sample quantities or large areas. Configurabilty supports all operating modes from quick overview to analysis in full detail. The user simply returns to the lab after analysis completion to find all results compiled to reports and measurement data on disk. Data can be reviewed or particles revisited immediately and individually for verifying results.

Chemical Classification Results of an Iron Ore Pellet
Chemical classification
results of the analysis of
all fields of the sample

ESPRIT Feature combines morphological measurement with chemical classification. The package provides individually configurable feature detection methods, consisting of image filters, versatile binarization, morphological and property filters to segment measurement data according to particle geometry and brightness.

Chemical classification adds element composition to every particle by quantitative EDS analysis. The user has the option of either analyzing the particle as a whole (average spectrum) or by using a point spectrum. Chemical classes can be set up individually, for example as composition ranges of minerals sought after.

All parameters, including morphological filters and sizing setup as well as chemical classes can be stored for re-use.

More info

View a recording of our "X-ray Expeditions into Geoscience" webinar to learn more

Download Application Note #4 on "Identification of trace elements and corresponding phases with hyperspectral imaging"

Download Application Note #5 on "Specific small particle search by mineral grain feature analysis and chemical evaluation"