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IGC 2012 Presentation on the reflectance spectroscopic characteristics of zircons and the tools for finding them as possible aids as geological chronometers.
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Government of Western Australia Department of Mines and Petroleum
Geological Survey of
Western Australia
Hyperspectral data – a tool
for identification of
geological chronometers
Lena Hancock (GSWA)
Chris Kirkland (GSWA)
Jon Huntington (CSIRO)
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Outline
• Introduction – analytical tools and samples
• Zircon reflectance spectra at: – Visible-near-infrared VNIR (380-1000 nm)
– Shortwave-infrared SWIR (1000-2500 nm)
– Thermal-infrared TIR (6000-14 000 nm)
• Applications: – Heavy mineral sand
– Minnie Creek granite
– Cummins Range carbonatite
• Conclusions
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Outcome of this study
• The use of hyperspectral data as a rapid tool to:
– search for zircon
– quantify its abundance
– determine its composition (crystal state)
• Determine diagnostic spectral features of zircon that can
be used both for targeting core sections for positive
geochronology sampling and accurate age determination
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Quick zircon detection in drill core
Type Duration Units Zr U SiO2
TestAll Geo 122 sec ppm 324430 < LOD 380339
Portable
XRF
SW UV
light
Courtesy of Peter Downes, WA Museum Harold Moritz - Creative Commons Non-Commercial Share
SW UV light
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Analytical tools
HyLogging is a new, highly automated method
designed by CSIRO through the AuScope
program to determine drillcore mineralogy
using rapid reflectance spectroscopy
•GSWA HyLogger 3-2, Perth WA
Zircon samples
validation:
SEM-EDX
Portable XRF
Zircon trace-elements
analyses:
LA-ICP-MS
•HyChips 3-1, CSIRO
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Zircon samples and composition
ZrSiO4
ZrO2 – 67.1%
SiO2 – 32.9%
Zircon isomorphous varieties:
U3O8 – more than 1.5%
ThO2 – up to 7%
HfO2 – up to 24%
Ca, Y, Nb, Ta, Dy substitute to
Zr4+
H2O – 4% altered hydrous
zircon
Ti substitute to Si4+
Pb – common and radiogenic
WA Museum Private and company collections
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Other datable minerals
There are range of U bearing minerals that can be used as geological chronometers:
VNIR-SWIR spectrum VNIR-SWIR spectrum
VNIR-SWIR spectrum VNIR-SWIR spectrum
Baddeleyite, ZrO2
Zirconolite, CaZrTi2O7
Monazite, (Ce,La,Nd,Th)PO4
VNIR spectrum
Xenotime, YPO4
Apatite, Ca5(PO4)3(F,Cl,OH)
Zr oxides Phosphates
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
VNIR zircon spectrum
653 nm feature can be
detected in individual
zircon grains as small as
1 mm
Note: strong ferric
iron absorption
around 660 nm can
have influence on
the depth of the
VNIR spectral
features of zircon
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Zircon spectrum at VNIR
• Crystalline zircon spectral features are related to presence of
U4+: absorption lines at 481, 515, 535, 565, 617, 654, 691,
877, 913 nm (Smith, 1980; Anderson, 1983). These numbers are
constant for most zircons and change only in intensity
• Metamict zircon anomalous spectrum influenced by U4+. U4+
is located within inclusions formed within damaged crystals
(Platonov et al., 1984). Spectrum at 653.5 nm is weaker and
broader
• Electron defects, colour centres, and REE3+ /Y3+
isomorphism are other effects on the zircon VNIR spectra (Hanchar and Hoskin, 2003)
Examples for time-resolved spectra of emission lines of
rare-earth elements in zircon (Nasdala et al., 2003).
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Zircon spectrum at SWIR
Crystalline zircon:
1107 nm – strong
1500 nm – very intense and sharp
2069 nm – strong
Intermediate zircon:
1114 nm – intense
1473 nm – broad
1500 nm – slightly broad, intense
1900 nm – water band
2065 nm – strong
Metamict zircon:
1118 nm – wide broad
1475 nm – broad
1900 nm – water band
2067 nm – broad
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Zircon spectrum at SWIR
Ming Zhang et al, 2002:
Absorption bands near 1107 and 1500 nm are related to U5+ impurity-
induced new transitions rather than radiation-damage-induced signals;
decreased dramatically with metamictization. 1500 nm feature is recovered
after high-temperature annealing.
U4+ signals near 1475 and 2069 nm are induced by radiation-damage
Note influence of:
•Fe2+ absorption, such as in carbonate and amphibole, to 1107 nm band
•Hydroxyl to 1475 and 1500 nm features
• Chlorites, talc, topaz, pyrophyllite to 2069 nm band
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Zircon spectrum at TIR
• 10.3 and 11.2 um reflectance peaks due to (SiO4)4- internal stretching modes
(Woodhead et al, 1991; Hanchar and Hoskin, 2003)
• 9.8 um peak shift towards shorter wavelengths with increasing OH content due to
weight lost during replacement of SiO4 by (OH,F)4 (Caruba et al, 1985)
• Variations in presence of 9.2 um feature due to crystal crystallographic orientation
(Andy Green, pers. comment)
Note:non-uniqueness of zircon TIR spectrum in very “busy” interval, also overlapping with carbonate peak at 11.2 um
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Mud Tank zircon pebbles spectra
SWIR TIR
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Zircon-quartz mixtures
Pure quartz
sand
Pure zircon
sand
Zircon 90 wt%
Zircon 10 wt%
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
VNIR-SWIR spectra for zircon-quartz mixture
Zircon 10% Quartz 90%
Zircon 90% Quartz 10%
Single sample acquisition (100 spectral samples)
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Spectrum of Zircon 1%-Quartz 99% mixture
TIR (no zircon)
The HyLogger’s limitation in
detection of zircon spectra:
about 1% of zircon in
spectral sample
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
TIR spectra for zircon-quartz mixture
Quartz 100%
Zircon 100%
Zircon 10% Quartz 90%
Zircon 60% Quartz 40%
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Applications
Search for zircon spectra in mineral sand and core
using 654 and 1500 nm absorption features
Note:
654 nm – strong influence from background noise
1500 nm – missing in metamict zircon, also related to Y3+
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Heavy mineral sand
Using 654 nm feature depth Zircon grains distribution and abundance
HyChips 3-1 Pixel size 1.5 mm, 30X30 samples
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Zircon in Minnie Creek granite batholith MSD1 drillhole
Tray 7
PFIT scalar created on 1500 nm zircon absorption feature and applied to the HyLogging dataset
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Zircon in Minnie Creek granite batholith XRF spot analysis vs. spectral signature
124 ppm
134 ppm
209 ppm
104 ppm
210 ppm
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Zircon in carbonatites
1500 nm 653 nm 653 nm
?
Mud Tank carbonatite Cummins Range carbonatite
Mud Tank single grain
U – 13
Th - 6
Hf – 7584
Y – 50
Dy – 7
Cummins Range core
U – 291
Th – 399
Hf – 23 598
Y – 1642
Dy - 254
Average of 5 analyses each, in ppm:
Normal values for
zircon in carbonatite
(Belousova et al., 2002)
Influence from very
strong absorption of Fe-
bearing carbonate and
amphibole
TIR
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Conclusions
• Zircon has a distinctive absorption spectrum in the VNIR and SWIR range
• 654, 1115, 1500, 2069 nm spectral features, related to U4+/U5+ content, can
be used to detect zircon in mineral sand and core
• The HyLogger’s limitation in spectral detection of zircon is c. 1% or 0.1 mm
grain size. However, with respect to background noise and strong influence
from matrix spectra, the realistic threshold would be 10% or 1 mm grain size
• Metamict zircon can be distinguish by much weaker and broader bands,
especially 1500 nm; important as these grain yield poor geochronology
• Recommended search scalars are based on 654 and 1500 nm features and
their combination
Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum
Acknowledgments
• CSIRO, NVCL team
• AuScope
• GSWA staff
• Peter Downes, WA Museum
• Michael Verrall, ARRC
• David Vaughan
• Frank Doedens