NON- DESTRUCTIVE IN SITU ANALYTICAL TECHNIQUES
ELECTRON MICROPROBE (EMP)
An electron microprobe uses a high-energy focused beam of electrons to generate
X-rays characteristic of the elements within a sample from volumes as small as 3
micrometres (3 x 10-6 m) across.
• Chemical composition is determined by comparing the intensity of Xrays from standards (known composition) with those from unknown
materials.
• The electron microprobe is ideally suited for quantitative analysis of the
major element (>1 wt%) and minor element (0.1-1 wt%) contents of
minerals, glasses, etc.
• The electron microprobe is the “workhorse” for in situ analysis of
minerals and glasses in thin section.
Woah! Look at
•
Used to identify minerals, determine phase compositions, document
that zoned Plag!
chemical zoning within minerals for petrologic, growth, and diffusion
studies, and locate rare phases.
The electron beam
or probe does not
How it
merely interact with
Works:
the surface of the
specimen, but
penetrates into it =>
What it can do:
Pros: Cheap, simple sample preparation, speed and ease of use, high sample
throughput, good spatial resolution, excellent for characterizing major elemental
abundances.
Cons: Worse precision and accuracy for light or trace elements, must have well
characterized standards.
$- Electron microprobe is the “workhorse” of analytical equipment—giving you a lot
of bang for your buck.
Other non-destructive analytical techniques include: Scanning electron microscopy
(SEM), Cathodoluminescence microscopy (CL), and Particle-induced X-ray emission
analysis (PIXE)
LASER ABLATION INDUCTIVETLY COUPLED PLASMA MASS SPECTROMETRY
DESTRUCTIVE IN SITU ANALYTICAL TECHNIQUES
(LA-ICP-MS)
•
•
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A microanalytical technique for the determination of trace elements in solid
materials.
A pulsed laser (“light amplification by the stimulated emission of radiation”)
beam is used to ablate (physically excavate) a small quantity of sample
material, which is then transported into the Ar plasma (high-T ionized
gaseous discharge) of the ICP-MS instrument.
Used for in situ trace element concentrations in minerals and glasses, isotopic
ratios for tracer geochemistry and geochronology in major minerals
(plagioclase, clinopyroxene) and accessory minerals (e.g. zircon, monazite,
rutile), depth profiling through zoned minerals, analysis of fluid and melt
inclusions trapped in minerals, analysis of micronuggets (PGE-rich) in
sulphides.
45 m spot
Pros:
Simple sample preparation, speed and
ease of use, high sample throughput,
high sensitivity, reasonably good
precision and accuracy, multi-element
capability.
75 m spot
Cons:
Low spatial resolution compared to
electron microprobe and ion probe, need
for well-characterized homogeneous
standards, need for prior knowledge of
internal standard concentrations in
samples and standards, interferences.
Laser=>
ICP-MS=>
PCIGR Laser and ICP-MS
What are these tracks in this
clinopyroxene?!?!
$$--More expensive than the microprobe, but less expensive than SIMS and
SHRIMP
SECONDARY ION MASS SPECTROMETRY (SIMS) &
SENSITIVE HIGH RESOLUTION ION MICROPROBE (SHRIMP)
DESTRUCTIVE IN SITU ANALYTICAL TECHNIQUES
•
•
•
•
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Secondary Ion Mass Spectrometry (SIMS) is used for the chemical analysis
of (VERY) small volumes of material.
In SIMS the surface of the sample is bombarded under vacuum with a finely
focused beam of primary ions (Cs+, O+, O- or Ar+).The collision cascade
results in the ejection (sputtering) and ionization of atoms and molecules from
the surface layers of the sample – micrometre-scale resolution!
The SIMS can quantitatively analyze nearly all elements in the periodic table
from H to U; for many elements the detection limits are in the ppb range
(MUCH better than EMP!).
The instrument may also be used to determine the isotopic ratios of elements
(e.g. C, O, Si, B, Li, S) to a precision of <0.05% in suitable material.
The SHRIMP is an enormous version of the SIMS that is mainly used for hard
to analyze things like U-Pb geochronology. It is also bigger (which is
sometimes better).
Difference in Sample Size:
SIMS is much better than other
destructive analytical techniques!
Pros: Excellent spatial resolution, isotopic capabilities, accuracy and precision.
Cons: Expensive! Technical and touchy sample preparation, not all elements in all
substrates can be analyzed because of interfereances.
$$$- Both techniques are very expensive
Scenario 1:
DESTRUCTIVE IN SITU ANALYTICAL TECHNIQUES
The Smithsonian (or equivalent Canadian well know national museum) was recently
gifted with a new anthropological find of the oldest homo sapiens specimen ever
found. Needless to say, this museum and research piece is a very valuable and
very fragile sample. You are charged with assessing the diet, living conditions, and
locality of habitation of this unique human by assessing the major and trace
element composition of the bones. You have an unlimited budget and may use any
instrument(s) to accomplish your goals. Create a research plan.
Scenario 2:
PCIGRGold Company has hired you to get them the information they need to know
on a budget. You are given several sawed rock samples showing mineralization
along veins of a porphery deposit. Your job is to identify the ore minerals in these
veins and determine the grade of any precious metals (Au, Ag, and the platinum
group elements Pt, Pd, Os, Ir, Rh, Ru) as cheaply as you can. Go!
Scenario 3:
Dominique wants you, her student, to assess the petrology of a suite of Hawaiian
picritic basalts (basalts with olivine phenocrysts in them) that were just
spectacularly erupted along the southeast rift of Mauna Loa. Based on what you
know about Harker diagrams, assessing the extent of fractional crystallization
that has taken place in a suite of samples, and the origin of Hawaiian lavas, what
would be the best way to start an exploratory study?
Scenario 4:
A recent study has just uncovered a rock near the Acasta gneiss that is older!
They have named it the PCIGR gneiss in honor of the lab that dated the whole
zircons. However, before being published, some reviewers pointed out that the
zircons may be complex aggregates of several stages of growth similar to what
was seen with the Jack Hills Zircons. How would you assess if the PCIGR gneiss
zircons are zoned and, if so, date the individual zones to defend your publication?
Scenario 5:
DESTRUCTIVE IN SITU ANALYTICAL TECHNIQUES
You are charged with completing a paleo-oceanography study to determine the
temperature of past oceans over time. Fortunately, oxygen isotopic ratios are an
excellent proxy for temperature, so all you must accomplish is measuring the
oxygen isotope ratios of different layers in banded iron formations from the
Archean. Unfortunately, each layer in your sample of banded iron formation is
only about a millimeter thick. How would you accomplish this?
Scenario 6:
A new type of meteorite has recently impacted an unpopulated area in the
Northwest Territories. You are given a very small thin section to characterize
that you must return in one year to the Royal Ontario Museum. You notice some
interestingly shaped and colored condrules and want to assess their major and
trace element chemistry. Go!
Scenario 7:
You are unfortunately burdened with helping one of your TAs with her study of
the Li isotopic signature of Hawaiian basalts. She tells you to please find a way to
assess where (aka in what minerals) and how much of Li, her element of study,
resides in her samples of Hawaiian basalt. How would you accomplish this goal?
Scenario 8:
It is important for hazard assessment and mitigation along active arcs to
understand how volcanic activity in arc systems works. You are charged with the
job of figuring out the past activity of a Cascade Arc lava chamber that is
currently a major threat to a large metropolitan area, Mt. Rainier, Washington.
One way to decide how many new pulses of magma are injected into an active lava
chamber is to look at the zoning in magmatic minerals and the resulting changes in
composition across single mineral grains. You want to study the changes in trace
element abundances across grains of plagioclase and clinopyroxene. What
instrument should you use?