hyperspectral data a tool for identification of geological chronometers l hancock et al igc

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


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


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


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


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


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


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


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).


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


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


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


Mud Tank zircon pebbles spectra

SWIR TIR


Zircon-quartz mixtures

Pure quartz

sand

Pure zircon

sand

Zircon 90 wt%

Zircon 10 wt%


VNIR-SWIR spectra for zircon-quartz mixture

Zircon 10% Quartz 90%


Single sample acquisition (100 spectral samples)


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


TIR spectra for zircon-quartz mixture

Quartz 100%

Zircon 100%




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+


Heavy mineral sand

Using 654 nm feature depth Zircon grains distribution and abundance

HyChips 3-1 Pixel size 1.5 mm, 30X30 samples


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


Zircon in Minnie Creek granite batholith XRF spot analysis vs. spectral signature

124 ppm

134 ppm

209 ppm

104 ppm

210 ppm


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


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


Acknowledgments

• CSIRO, NVCL team

• AuScope

• GSWA staff

• Peter Downes, WA Museum

• Michael Verrall, ARRC

• David Vaughan

• Frank Doedens

hyperspectral data a tool for identification of geological chronometers l hancock et al igc

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