Mineralogical Characteristics of Low-Grade
Uranium Ores in Western Australia
Presented by Dr Hal ARAL
29-31 March 2010
IAEA Meeting, Vienna
Outline
• Objective of this presentation
• Characteristics of calcrete type low-grade uranium ores in WA, and
Talk about:
•
•
•
•
HyLoggingTM
XRD – Qualitative and Quantitative
QEMSCAN
Electron microprobe – Mapping and Quantitative Spot Analysis
as major characterisation tools applied on calcrete type uranium ores of WA
Objectives of this presentation
• To give an introductory information about the general characteristics of
low-grade Western Australian uranium deposits.
• To present the application of XRD, HyLogging, QEMSCAN and EPMA
techniques on Western Australian low-grade uranium ores. These
methods are to gather information about the mineralogy, texture and
liberation characteristics of these ores.
Calcrete-hosted uranium ores of WA
by Dr Hal Aral
Dr Mark Pownceby
Dr Ralph Hackl
Calcrete-hosted uranium ores of WA
Typical friable calcrete-hosted uranium ore from Western Australia.
Close to the surface, the calcrete appears similar to dirt or soil, often friable, soft, aggregated
but not densely compacted. With depth, nodular calcrete becomes abundant and is commonly
interbedded with laminar calcrete. The high permeability, as a result of shrinkage cracks and
small vugs, is a characteristic feature of the calcretes in Yilgarn region WA. They generally
form the principal aquifers.
Calcrete-hosted uranium ores of WA
•.
Occur in a broad region extending from Meekatharra in the northwest to
Leonora in the southeast .
Calcrete-hosted uranium occurrences in the northern Yilgarn
district, WA. (Source: Modified after Roberts, 2009)
Calcrete-hosted uranium ores of WA
• Found in Tertiary to Quaternary aged channels which drain the uranium-rich
Archaean granite and greenstone basement of the northern portion of the
Yilgarn Craton.
• The reserves comprise 3 to 7% of known uranium resources in Australia,
ranked 4th after breccia (74%) and unconformity-related (17%).
• Non-pedogenic type and are related to carbonate precipitation at or below the
groundwater table.
• The deposits comprise mostly dolocrete and occasionally calcrete,
which cement and partially or completely replaces the clay and quartz
derived from underlying laterised granitic rocks.
Calcrete-hosted uranium ores of WA
• Yeelirrie (BHPB) and Wiluna (Toro Energy’s Lake Way and Centipede) are
the most important calcrete-hosted deposits in WA.
• In Yeelirrie, the uranium mineralisation is in a horizontal sheet ~9 km long, up
to 1.5 km wide and the ore zone averages 3-4 m thick
• It lies between 4-8 m below surface and 90% below the water table. Around
90% of the mineralisation is at the transition between the calcrete and the
underlying clay-quartz alluvium.
Calcrete-hosted uranium ores of WA
• The uranium and vanadium grades of Northern Yilgarn calcrete-hosted deposits
typically vary from 75 ppm to 650 ppm U3O8 and 70 ppm to 600 ppm V2O5.
• The principal uranium mineral is usually carnotite with the formula
K2[UO2]2.2[VO4].3H2O.
• Once operational, Yeelirrie will increase Australian exports of uranium
significantly and production-wise will approach ERA - Rio Tinto's Ranger
uranium mine in the Northern Territory.
• The Wiluna deposits are expected to come into production within the next few
years.
CSIRO’s HyLoggingTM
Fast Characterisation Tool
by
Dr Kai Yang
Michelle Cardy
Andrew Hacket
HyLoggingTM
• The CSIRO developed HyLogging™ is a non-destructive reflectance
spectroscopy-based method that measures the molecular vibrations
indicative of the chemical bonds in crystalline minerals.
• HyLogging™ identifies mineral species present in the sample and their weight
percentages, mineralogical association and variation and the spatial occurrence.
• The instrument is designed to rapidly measure a large number of drill cores,
chips, or powdered samples within a short time frame. No need for sample
preparation.
HyLogging
•.
TM
The HyLogging™ system
consists of four principal
components:
- a spectrometer covering
from visible-near-infrared
to shortwave-infrared
wavelengths (400-2,500
nm)
- a robotic x-y table for
core/chip tray
- a high resolution digital
linescan camera,
- an in-house developed
software (The Spectral
Geologist – Core),
enables the identification
of minerals by their
specific spectral
absorption features.
HyLoggingTM
HyLogging™ is useful in examining uranium ores in order to define the major
mineral phases present plus their mineral associations and textures.
It is especially suitable for spectral determination of iron oxides and rock-forming
minerals that contain OH-, H2O, CO22- or SO42-, i.e. sheet silicates, clays,
carbonates and sulphates.
All of these are common constituents in low-grade calcrete-hosted uranium ores of
Western Australia.
HyLogging
•.
TM
HyLogging can
be applied on drill
core, chips and
powder samples.
In one application, tens of thousands of metres of samples from diamond and
aircore drilling, each sample representing 0.25-0.50m of drill core, were
measured.
HyLogging
TM
WA Uranium Ores:
The data can be
used to build 3D
mineral
distribution
maps
which cannot be
practically
achieved by any
other methods.
A typical output from CSIRO’s HyLoggingTM system.
HyLoggingTM
Advantages and Disadvantages:
Qualitative POWDER and Quantitative
X-Ray Diffraction
by
Dr Mark Raven
XRD
X-Ray Diffraction (XRD) of WA Ores:
A typical XRD pattern
from a WA calcretehosted uranium ore.
The information at
top right is generated
by comparing the
peak positions in the
pattern with a
database of standard
mineral patterns.
XRD
• XRD is a simple, accurate and relatively cheap tool to identify major and minor mineral
components,
• XRD fails to identify the uranium minerals in the low-grade ore. This is because the
detection limit of XRD is typically on the order of 0.5%. In WA the bulk uranium mineral
content is typically < 0.2%.
• The detection limits of XRD can be lowered to 0.2% by increasing the scanning time for
the pattern collection however halving the detection limit requires four times the
counting time.
• The recognition of minor and trace minerals therefore requires the application of more
sensitive characterisation tools such as QEMSCAN or EPMA.
Quantitative XRD
WA Uranium Ores:
Quartz
Kaolin
Smectite†
Albite
Feldspar‡
Calcite
Dolomite
Halite
11
7
15
3
--
<1
63
1
†1M muscovite, illite-montmorillonite and montmorillonite are reported as smectite.
‡ Microcline or Orthoclase.
In Yeelirrie, the host rock is predominantly dolomite and/or calcite with 15-20%
montmorillonite (swelling type clay) and 5% quartz.
Some gypsum, barite and halite can be found – indicating the prevalance of an arid
environment
XRD
Advantages and Disadvantages:
Another CSIRO Developed Commercial Tool:
QEMSCAN – A powerful characterisation
technology
by Dr Peter Austin
- Demonstration of the capability of the QEMSCAN
- Low-grade uranium images of QEMSCAN are presented
QEMSCAN – A powerful characterisation tool
• QEMSCAN is a scanning electron microscope (SEM) system to provide rapid
automated quantitative mineral analyses. The system is based upon Carl Zeiss SEM’s
fitted with up to 4 energy dispersive X-ray spectrometers and softwares iDiscover and
iExplorer.
• iDiscover software generates information on the chemical and mineral composition of
samples.
• iExplorer is a report generator with powerful graphics.
QEMSCAN provides information about:
- sample mineralogy
- modal mineralogy,
- grain size distribution
- particle shape, compositions, texture
- mineral associations and
- degree of liberation.
QEMSCAN – A powerful characterisation tool
• The measured x-ray energy dispersive spectra are automatically
compared against a database of known SPECTRA and
a mineral or phase name is assigned to each measurement point.
• Grain maps are used to visualise textural relationships, liberation and
locking characteristics between the mineral phases.
• Grains are typically presented in a sorted order of decreasing particle
area.
.
•.
High Resolution
Field Size 1500 µm
.
1 µm Pixel spacing
Then selected one grain for higher resolution analysis and
sanned it at a 1 µm pixel spacing. This grain contained a
high concentration of carnotite.
QEMSCAN – A powerful characterisation tool
Advantages and Disadvantages:
Electron microprobe – Mapping and Quantitative
Spot Analysis
by
Dr Mark Pownceby
Dr Hal Aral
Dr Ralph Hackl
Dr Nick Wilson, Colin MacRae
Aaron Thorpy and Howard Poynton
EPMA (Electron Probe Micro Analysis)
• The EPMA is a microbeam instrument – very low detection limits and very
fine spatial resolutions; quantitatively measure the chemistry of the mineral
phases; provides textural and mineralogical information.
• In contrast to an SEM: EPMA uses wavelength dispersive (WD)
spectrometers to detect the x-ray counts from the sample surface.
• Energy dispersive (ED) spectrometer detects and counts the x-ray signals
for all elements at the same time
• WD spectrometer counts x-ray signals for only one element at a time. It WD
can count many more x-rays for the specific element in the same length of
time and hence is more accurate than ED spectrometry, and has a lower
detection limit.
EPMA
Calcrete-hosted WA ore:
• High-resolution mapping to locate high uranium concentrations and
to provide a visual inspection of the different textural and mineral
associations.
• Then, quantitative WD analysis to determine the composition of
individual U-rich mineral phases as well as to determine if uranium
occurs in trace amounts in any of the gangue mineral phases.
• Elements that were not measured by WD spectrometry were
measured using two parallel ED spectrometers. Measuring both ED
and WD signals simultaneously ensured complete spectral
information.
EPMA
• The data is analysed using an automated clustering procedure
to group the elements into statistically different mineral phases.
• The phases identified by the clustering procedure are then
transferred back onto the map to show the distribution of each
mineral phase.
EPMA
EPMA maps
showing the
occurrence of
carnotite (red)
in low-grade
calcrete-hosted
uranium ores
from Western
Australia.
500 µm
Dolomite
Talc
Mg aluminosilicate
Quartz
100 µm
Carnotite
Gypsum
K feldspar
Kaolinite
OUTPUT: single element distribution scatter plots or mineral maps.
JEOL 8500
FEG EPMA
equipped with 5
WD detectors,
2 solid state ED
detectors.
EPMA
The mapping data is displayed using the CSIRO’s software CHIMAGE. The data
presented as combined element maps to make correlations between elements readily
detectable.
EPMA
Averaged quantitative (wt %) EPMA analyses for 20 carnotite grains.
Wt%
K
U
V
O
Na
Si
Ca
Mg
Al
Fe
Total
Sample1
Average
6.64
48.67
11.99
14.49
0.3
0.37
0.33
0.18
0.09
0.12
82.95
Sample 2
Average
6.65
49.04
11.71
14.26
0.38
0.2
0.54
0.2
0.03
0.04
82.81
K2[UO2]2.2[VO4].3H2O
Analyses obtained using an accelerating voltage of 20 kV and a beam current of
40 nA and a focussed (<1 μm) beam. Counting times for uranium were 60 secs
on the peak and 30 secs on the background.
Stoichiometric carnotite contains 8.7%K, 52.8%U, 11.3%V, and 5.99% H2O.
However, the above data show the phase analysed contains, on average, only
~6.7%K, ~49%U and 11.8%V.
EPMA
Advantages and Disadvantages:
Newly emerging characterisation technology:
LA ICP-MS
by
Cheryl McHugh
Laser Ablation (LA-ICP-MS)
The New Wave UP213 Laser
• .(LA) systems are specifically
Ablation
designed to be coupled with an ICPMS (Inductively Coupled Plasma
Mass Spectrometer)
¾ This technique is more commonly
•Laser Ablation (LA-ICP-MS)
known as LA-ICP-MS
¾ Previously our ICP-MS instrument
could only be used for solution or
digested solids analysis
¾ Now we can conduct direct solid
sample analysis of minor and trace
components using the LA-ICP-MS
system
Laser Ablation (LA-ICP-MS)
¾ The• sample
is placed in an ablation cell
.
¾ A laser is focused through an optical beam path on to a sample and the laser
starts ablating the sample
¾ The particles of the sample are swept in a carrier gas (helium) towards the
plasma of the ICP-MS system
¾ Ionisation takes place in the plasma and quantitative analysis can be obtained
with the ICP-MS
¾ Viewing optics are provided through a video camera coupled to a monitor
¾ This ensures visual focus of the sample and allows identification of the areas to
be analysed as well as the observation of laser ablation process
¾ The UP 213 model has a neodymium-doped yttrium aluminium garnet laser
(Nd:Y3Al5O12) and is more commonly known as a ND:YAG laser
¾ Laser operates in UV region at 213nm
Laser Ablation (LA-ICP-MS)
¾ LA is suitable for different types of solid samples
¾ Bulk analysis of geological samples, silicate minerals, metals, alloys, ceramics etc
•.
¾ Two samples cells
¾ Quick change drawer – large volume cell 60mm ID, 50mm Deep
¾ Supercell – small volume cell (good for fast purge out)
¾ Minimum sample preparation is required
¾ Samples may only need to be cut to size to fit into the sample cells
¾ Potted samples (as used in Microscopy)
¾ Fused beads/pressed powders
¾ Spot sizes down to 4um
¾ Isotopic analysis with ICP-MS
¾ Precision Depth profiling
¾ Geological dating
¾ Sample mapping
¾ Manual/Automatic focus option
¾ Computer controlled laser parameters, sample viewing ( down to 2um), stage positioning
and gas routing functions
Ablation Pattern - Spot
•.
Ablation Pattern - Traverse.
•.
Ablation Pattern – Grid of spots
•.
Thank you
Minerals Down Under National
Research Flagship
Dr Hal ARAL
Principal Research Scientist
Stream Leader
Phone: +61 3 9545 8823
Email: [email protected]