michael shaffer inco innovation centre memorial university st. john’s, [email protected]...
TRANSCRIPT
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Michael ShafferINCO Innovation CentreMemorial UniversitySt. John’s, Newfoundland [email protected]
Advanced Techniques in EPMA Seminar
August 7, 2010University of Oregon
Eugene, Oregon
A brief introduction to theFEI Mineral Liberation Analyzer™:
the technique & results
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MLA:points of interest
Particle analysis Rocks crushed, sized and representative Most accurate E.G, iron ore from Labrador
“Large particle” analysis e.g., 25x45mm section Questionably representative Large grain sizes textures E.G, Himalayan garnet shist
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BEI: Fe-rich minerals
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Fe-rich minerals of interest& spectral ambiguity
Hematite & magnetite [Fe2O3 versus Fe3O4] Generally not distinguishable with x-ray spectra Associations important to client
Titano-magnetite Distinguishable with x-ray spectra BSE similar to Hm Titanium important to client
Goethite or limonite [FeO(OH)•(H2O)n] Generally with minor Al, Si, Mg, and usually
distinguishable with x-ray spectra BSE darker than Hm (BSE classification would be
helpful) Siderite [FeCO3]
Generally with Ca, Mg, Mn, and usually distinguishable with x-ray spectra
BSE darker than Hm (BSE classification would be helpful)
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Mineral modes
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Mineral Wt%Hematite 4.57Magnetite 38.54Ti_magnetite 0.09Goethite 0.17Limonite 0.08Ilmenite ndRutile ndCorundum ndQuartz 35.55Aluminosilicate ndMisc_silicates 0.11Siderite 0.06Siderit-Mn 0.11Rhodochrosite ndRhodo-FeMg 0.01Rhodo-MgFe 0.00Siderit-MgMn 7.37Siderit-Mg 0.96Ankerite 0.06Calcit-MgMn ndDolomit-FeMn 11.48Magnesit-FeMn 0.22Dolomite 0.15Calcite 0.08Unknown 0.02
Mineral Wt%Pyrolusite 0.00Bixbyite_lo-Mn ndBixbyite_hi-Mn ndOther_oxides 0.00Olivine 0.00Garnet 0.00Cpx 0.01Opx 0.02Amphibole 0.00Biotite 0.03Feldspar 0.03Muscovite 0.04Serpentine ndChlorite 0.14Mn-rich_clay ndCalcit-REE ndPyrite 0.00Pyrrhotite ndChalcopyrite ndSphalerite ndMisc_sulfides ndApatite 0.08Miscellaneous 0.00Misc_metals 0.01Total 100.0
Mineral Wt%Magnetite 38.54Hematite 4.57Hm_or_Mt 0.00Goethite 0.17Limonite 0.08Other_oxides 0.09Quartz 35.55Misc_silicates 0.38Carbonates 20.50Sulfides 0.00Misc 0.09Unknown 0.02Total 100.0
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The particle table
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4k to 20k particles
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Properties of particles
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DensityWt%Area%Area (microns)Area (pixels)PerimeterMax SpanLength (MBR)Breadth (MBR)Hull AreaHull PerimeterEE Minor AxisHull EE Minor AxisEE Major Axis (P&A)EE Minor Axis (P&A)EE PerimeterEC DiameterAngularityEnclosed Length DeltaForm Factor
All minerals (Wt%)e.g., Hematite (Wt%)
Magnetite (Wt%)Goethite (Wt%)Limonite (Wt%)Quartz (Wt%)…Misc (Wt%)Unknown (Wt%)
All elements (Wt%)e.g., Al (Wt%)
Ca (Wt%)Cr (Wt%)Cu (Wt%)F (Wt%)Fe (Wt%)H (Wt%)K (Wt%)La (Wt%)Mg (Wt%)Mn (Wt%)Na (Wt%)Ni (Wt%)P (Wt%)S (Wt%)Si (Wt%)Ti (Wt%)…Zn (Wt%)
Free Boundary, all mineralse.g., Hematite (%)
Magnetite (%)Goethite (%)Limonite (%)Quartz (%)…Misc (%)Unknown (%)
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datamining the particle table
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3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.30.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Si content for particles of density greater than SG
SF+100
SF+200
specific gravity of particles
Si %
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Large sections
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Spectral discrimination ~ garnet
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grain boundaries resolved with BEI
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grain boundaries not resolved with BEI
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Grain associations
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Mineral Qtz Biot Plag Ksp Gt_Mg
Qtz - 30 20 7.3 1.3
Biot 35 - 24 7.3 1.7
Plag 32 32 - 8.9 0.9
Ksp 29 25 23 - 0.3
Gt_Mg 14 17 6.7 0.8 -
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The grain table
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More than 52,000 grains
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Properties of grains
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DensityCenter XCenter YWt%Area%Area (microns)Area (pixels)PerimeterMax SpanMax Span AngleWt% (Particle)Area% (Particle)Wt% (Mineral)Area% (Mineral)Particle Max SpanParticle PerimeterLength (MBR)Breadth (MBR)Angle Length (MBR)
Hull AreaHull PerimeterEE Minor AxisHull EE Minor AxisHull EE PerimeterEE Major Axis (P&A)EE Minor Axis (P&A)EC DiameterAspect RatioAngularityEnclosed Length DeltaForm FactorBoundaries with other mineralse.g., Quartz (%)
Orthoclase (%)Garnet (%)Biotite (%)…free surface (%)
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datamining the grain table:mineral textures
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0 30 60 90 120 150 1800.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
plagioclase orientation
angle for MBR
% p
lag
ioc
las
e
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Applications at MUN Mineral modes & associations Mineral locking & liberation Mineral searching (e.g., zircon, baddeleyite, monazite)
Includes x-y coordinate export Precious mineral searching (e.g., Au, PGM)
Includes associations with host minerals Provenance determinations
Sourcing continental river & till sediments (mineral prospecting)
Sourcing offshore sediments with onshore (oil & gas) Lateral correlation of offshore sediments (oil & gas)
Some thought toward … Accurate determination of trace minerals (e.g., apatite,
corundum) Invisible gold with a FEG MLA Long-count EDX Auxillary inputs …, e.g., WDX, μXRF
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Acknowledgements
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The MUN MLA team:
David GrantAlan Maximchuk
Dylan Goudie
&thank you for your interest!
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A typical frame, BSE relative to Ni metal
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Is it possible with XBSE & MLA spectra?
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0
1
2
3
4
5
6
7
8
0.35 0.45 0.55 0.65 0.75 0.85
eV
Co
un
ts (
20
00
sp
ec
tra
l co
un
ts)
Hematite
Magnetite
0
5
10
15
20
25
6.10 6.30 6.50 6.70
eV
Co
un
ts (
20
00
sp
ec
tra
l co
un
ts)
Hematite
Magnetite
Difference is only
24 counts(2σ ~ 34)
15 counts (2σ ~ 58)
72 wt% Fe versus 70%
28 wt% O versus 30%Sensitive to absorption
Sensitive to charging
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The spectral-classification result
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Red implies mineral grain is either hematiteormagnetite
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BSE classification
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Cumulative or “full”
histogram
QtzHm
Other silicates, carbonatesand hydroxides
Mt
“reliable” histogram
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BSE-classification results – good & bad
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MagnetiteHematite“Darks”
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MLA BSE mode results – good & badthe smallest size fraction: -200 mesh
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Before “Merge Overlay”
Mode BSE data
acquisition
Classified data, modes, …
Processed via
gray level segmentation
Mode XBSE data
acquisition
Classified data, modes, …
Processed via
Spectral matching
ORMerge
Overlay
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MLA “merge overlay” tool
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Results from Merge Overlay
Spectrally classified “Hm-or-Mt” becomes: Hematite, or Magnetite, or “Fe-ox_no-ID”
Which can generally be justified and grouped with limonite or goethite (… although pure siderite is also a possibility)
Smaller size fractions evaluated independently Hm:Mt modal ratio might be assumed from
larger SFs or their trends27
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Reproducibility: mineral modes same samples – 6 months between
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Samples A, B, C & D
Qtz
Hm Mt
no-ID Qtz
Hm Mt
no-ID Qtz
Hm Mt
no-ID Qtz
Hm Mt
no-ID
0
5
10
15
20
25
30
35
40
45Size +100M mineral modes
2008
2009
Wt%
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Reproducibility: mineral modes same samples – 6 months between
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Samples A, B, C & D
Qtz
Hm Mt
no-ID Qtz
Hm Mt
no-ID Qtz
Hm Mt
no-ID Qtz
Hm Mt
no-ID
0
5
10
15
20
25
30
35
40
45Size +200M mineral modes
2008
2009
Wt%
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Hm
with
Mt
Hm
with
Qtz
Mt w
ith H
mM
t with
Qtz
Hm
with
Mt
Hm
with
Qtz
Mt w
ith H
mM
t with
Qtz
Hm
with
Mt
Hm
with
Qtz
Mt w
ith H
mM
t with
Qtz
Hm
with
Mt
Hm
with
Qtz
Mt w
ith H
mM
t with
Qtz
0
5
10
15
20Size +100M mineral associations
2008
2009
Per
cen
tag
e o
f g
rain
bo
un
dar
ies
Reproducibility: mineral associations same samples – 6 months between
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Samples A, B, C & D
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Hm
with
Mt
Hm
with
Qtz
Mt w
ith H
mM
t with
Qtz
Hm
with
Mt
Hm
with
Qtz
Mt w
ith H
mM
t with
Qtz
Hm
with
Mt
Hm
with
Qtz
Mt w
ith H
mM
t with
Qtz
Hm
with
Mt
Hm
with
Qtz
Mt w
ith H
mM
t with
Qtz
0
5
10
15
20
25
30
35
40Size +35M mineral associations
2008
2009
Per
cen
tag
e o
f g
rain
bo
un
dar
ies
Reproducibility: mineral associations same samples – 6 months between
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Samples A, B, C & D
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Results comparison:MLA v. Rietveld XRD
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Qtz Mt Hm Qtz Mt Hm Qtz Mt Hm Qtz Mt HmSample ASF+100M
ASF+200M
Sample BSF+100M
BSF+200M
0
5
10
15
20
25
30
35
40
45
50Rietveld 1
Rietveld 2
MLA
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Results comparison:MLA v. Rietveld XRD
Average absolute errors
XRD sampling XRD-v-MLA0
2
4
6
8
10
12
14
16
18
20
Quartz
Magnetite
Hematite
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Sources of data processing error
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Sources of instrumental error:electron beam illumination
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195 = Hm198 = Mt
192 = Hm195 = Mt
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Sources of instrumental error:varying e-beam current
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195 = Hm198 = Mt
192 = Hm195 = Mt
3rd frame 143rd frame
2 hoursLater …
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Remedying BSE problems
Non-uniform illumination No remedy if the SEM manufacturer did
not anticipate applications in quantitative BSE
Except to use high magnification Difficult to remedy if the SEM
manufacturer did not provide alignment tools for uniformity
FEI Quanta SEMs: Centering the illumination provided by e-
gun tilt Tetrode & gun alignment should be
accurate Illumination gradients worse for large spot
sizes
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Remedying BEI problems
Varying beam current Very common depending on age of
filament … Stability generally monotonic, i.e., not
erratic … allows for breaking the BSE JKF file into 2
to 4 files, thereby creating more reliable histograms that represent time periods during analysis.
Note also that this method is quite dependent on a significant amount of Hm-Mt in the sample, which builds a more accurate reliable histogram
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Anticipating problems we haven’t yet encountered, and possible
improvements
MUN IIC has not yet applied this method to mineral assemblages other than the minerals discussed here I.E., a severe complication would arise for
significant amounts of titano-magnetite, thereby blurring the distinction of Hm in the reliable histogram
A very helpful improvement, which would allow the same tools to be applied to other applications, would be for the spectra-classified result to mask the minerals of interest to be classified with BSE
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MLA Mode BSE conclusions
Hm – Mt BSE discrimination works … And Hm-Mt associations are possible
… but not specifically with other minerals
and, by itself, cannot discriminate most other minerals because of average atomic number (i.e., BSE ambiguity)
However, it presents a suitable solution for augmenting spectral classification (mode XBSE)
How to augment with spectral classification? …
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Summary
Hm–Mt BEI discrimination is possible … Hm-Mt associations are possible, and with all minerals Mineral modes and associations can be reproduced with
acceptable accuracy A comparison with quantitative XRD is within errors
associated with the difficulty associated with representative down-sampling (XRD sampling independent of MLA sampling)
However, a well-aligned and stable SEM is necessary … Electron beam illumination must be uniform over 1 – 2mm Beam current must be stable over the 2 – 3hr analytical time
(although data processing can accommodate a monotonic variation)
This technique is more generally applicable, even to more complex mineral assemblages when chemistry (x-ray spectra) aids in masking the minerals of interest
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Consider an independent approach …
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Exported BEI frames into 3rd-party software
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The masked & cleaned frames
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A clean histogram allows for automatic thresholding
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Independent software resultsfortunate & unfortunate
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Independent BEI conclusions
Hm – Mt discrimination works … Associations Hm-Mt are not possible Minerals of similar atomic number,
identified by XBSE, do not affect calculated Hm:Mt
However, results can be biased if: one mineral does not polish as well, or if one mineral’s grain size is typically smaller
Not the best solution, but should be in the analyst’s toolbox 47
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The results for the client
Primary modes and associations come from mode XBSE.
Whereas we had been providing Hm:Mt via the independent method … Because titano-magnetite and pyrite are
minimal and correctable, we do not augment XBSE with additional BSE results.
The good news is that Hm-Mt associations are provided but the bad news is that Hm-Mt-Qtz associations are not.
What is needed …48
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Results comparison:MLA v. Rietveld XRD
49Rietveld 1 Rietveld 2 MLA Rietveld 1 Rietveld 2 MLA
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Sample 1SFs +100 & +200
sampling error
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Results comparison:MLA v. Rietveld XRD
50Rietveld 1 Rietveld 2 MLA Rietveld 1 Rietveld 2 MLA
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Sample 2SFs +100 & +200
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Merge JKF dialog
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3rd-party results can sometimesbe a necessary tool
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MLA BSE mode results – good & badminerals of similar atomic number
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Results comparison:MLA v. Rietveld XRD
Largest absolute errors
XRD sampling XRD-v-MLA0
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