GEMOC ARC National Key Centre |
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Technology development
program
BACKGROUND
The Key Centreís Research, Training and Industry Interaction programs require a high level of geochemical analytical technology, which is provided by the state-of-the-art facilities available to the Key Centre. Continual development of both technology and innovative analytical and microanalytical approaches is required to meet the research aims and the needs of industry collaborators. GEMOC continues to develop new analytical strategies for determining the chemical and isotopic compositions of geological materials (both solid and fluid). Special emphasis is being placed on the development of advanced in situ microbeam methods. These developments are transmitted to industry via open and collaborative research, through technology exchange visits and workshops, and as an integral part of the training program.
THE KEY CENTRE brings together the analytical instrumentation
and support facilities of the Macquarie University Geochemical
Analysis Unit (GAU) and the geochemical facilities at the ANU
Department of Geology and CSIRO
Exploration and Mining. Macquarie University is a partner
(with management responsibility) in the Centre for Isotope Studies
housed at CSIRO,
North Ryde.
- The GAU contains:
- a Cameca SX-50 electron microprobe
- a Hewlett Packard 4500 ICPMS (dedicated to U-Pb analysis)
- a new (2000) Agilent 7500 ICPMS (industry collaboration)
- a custom-built UV laser microprobe, usable on either ICPMS
- a Nu Plasma multi-collector ICPMS
- two New Wave laser microprobes (266 nm and 213 nm) for the MC-ICPMS and ICPMS laboratories (industry collaboration)
- a new (2000) Spectro XLAB2000 energy-dispersive XRF
- a LECO H2O-CO2 analyser
- clean labs and sampling facilities to provide the infrastructure required for ICPMS and isotopic analyses of small and/or low-level samples
- Experimental petrology laboratories in GEMOC include piston-cylinder (9, 15 and 40 kb), hydrothermal apparatus, and controlled atmosphere furnaces; each node is well-equipped.
- The Centre for Isotope Studies provides access to thermal ionisation mass spectrometers for analysis of the Rb-Sr, Sm-Nd and U-Th-Pb systems, and extraction lines and gas-source mass-spectrometers for stable-isotope analysis of fluids and minerals.
- The ANU (and ANU INAX) facilities include:
- a Spectro energy dispersive XRF
- an automated Philips XRF
- Australiaís only non-commercial Neutron Activation Laboratory
- atomic absorption spectrophotometry
- sample preparation facilities for mass spectrometric analysis
- access to a Cameca Camebax microprobe, ICPMS and thermal ionisation mass spectrometer facilities through the Institute of Advanced Studies
- LAM-ICPMS - Varian Ultramass
THE GEMOC FACILITY FOR INTEGRATED MICROANALYSIS (FIM) AND MICRO GIS DEVELOPMENT
GEMOC is continuing to develop a unique, world-class geochemical facility, based on in situ imaging and microanalysis of trace elements and isotopic ratios in minerals, rocks and fluids. The Facility for Integrated Microanalysis now consists of four different analytical instruments, linked by a single sample positioning and referencing system to combine spot analysis with images of spatial variations in composition ("micro-GIS"). All instruments in the Facility have been operating since mid-1999.
the facility provides:
Electron Microprobe: for imaging and point analysis of major and minor elements.
Scanning Nuclear Microprobe: for imaging and point analysis of trace elements at ppm levels.
Laser-ablation ICPMS Microprobes: for point analysis of a wide range of trace elements at low ppb levels.
Multi-collector Sector ICPMS with laser microprobe: for high-precision in situ analysis of isotopic ratios.
Micro-GIS system: A key aspect of the Facility is the co-registration of images and point analyses collected on all instruments. All data for a sample, from any of the instruments or from a bench microscope, are in the same coordinate system and can be overlaid in the computer to enhance interpretation. When fully developed, images from one instrument will be read into the computer of another instrument and used to guide the analysis. Major-element maps from EMP, or trace-element maps from the nuclear microprobe, can be linked directly to images from petrographic or cathodoluminescence microscopes, BSE or SEM, or to spot analyses.
current status:
Electron microprobe (EMP): The existing GEMOC EMP is a CAMECA SX50, installed in 1993; it routinely produces high-precision analyses of major and minor elements with a spatial resolution of one micron, as well as high-quality images of major-element (> 0.1 wt%) distribution over areas up to 45 x 45 mm, by stage-scanning with five fixed wavelength-dispersive spectrometers. In early 1999 the EMP was upgraded with an energy-dispersive X-ray detector to allow rapid and simultaneous mapping of all major elements.
Scanning nuclear microprobe (SNMP): This instrument
has been built by Dr C. G. Ryan as a separate beam line
on the HIAF particle accelerator at CSIRO, North Ryde (built with GEMOC funding contribution).
The design incorporates several complementary types of detector,
a new high-resolution probe-forming system and an innovative optical
system, and provides both images of trace-element distribution
and spot analyses, with a lateral resolution of 1-3 microns.
Current capabilities cover micro-PIXE, micro-PIGE and quantative
element imaging. When fully developed, the capabilities
will include:
(a) micro-PIXE: Proton Induced X-ray Emission (PIXE) using focused MeV proton beams provides non-destructive, simultaneous, quantitative microanalysis and imaging of the spatial distribution of trace elements with concentrations down to the ppm level. The instrument provides simultaneous analysis and imaging of any elements present in a sample above the detection limits. Detection limits as low 0.2 ppm have been achieved in silicates, and 0.5 ppm in sulfides, extracted directly from the quantitative elemental images with 2 µm spatial resolution.
(b) micro-PIGE: Proton Induced Gamma-ray Emission (PIGE) spectra can be collected simultaneously with PIXE analysis. The gamma-rays provide non-destructive analysis of light elements (eg Li, Be, B, F, Na) with detection limits of 10-200 ppm. Other nuclear reaction techniques will provide analysis of anions (H, C, O, S, Cl) which are difficult to analyse by ICPMS and EMP.
(c) CCM: In Channelling-Contrast Microscopy (CCM), MeV energy beams of alpha particles or protons are channelled into the crystal planes and axes of minerals. CCM can be used to yield images of lattice location information or to distinguish elements sited in inclusions from those in solid solution. This capability can be applied to the trace levels detected using ion backscattering, micro-PIXE and micro-PIGE.
(d) Quantitative True Elemental Imaging: The SNMP provides trace-element imaging of areas up to 2.5 mm across; these images are digitised so that any pixel or larger area can be retrieved, and analysed separately for its element concentrations. The Dynamic Analysis method developed by Dr Ryan enables live-time assembly of true elemental images that discriminate against pile-up, inter-element overlap, background and detector artefacts such as escape peaks and tailing.
Laser Ablation ICPMS microprobe (LAM): The existing
GEMOC LAM was installed in December 1994 using a Perkin-Elmer ELAN 5100 ICPMS (later replaced
by an ELAN 6000), attached to a UV laser ablation microprobe
built for GEMOC by Memorial
University, Newfoundland. In 1999 the ICPMS was replaced
by a Hewlett
Packard 4500, and in 2000 an Agilent 7500 ICPMS was added. The
instruments now routinely provide quantitative analyses of >
30 elements at sub-ppm levels in minerals, glasses and metals,
as well as precise U-Pb dating of zircons. Spatial resolution
varies with the application, but typically is on the order of
30-40 microns. The LAM is fitted with a computer-driven
sample stage to provide co-registration of X-Y coordinates with
the other instruments.
Macquarie workshop with Agilent: Simon Jackson, Norm Pearson, Bill Griffin, Richard Myors, Fred Fryer, Suzy Elhlou and Ashwini Sharma (clockwise from front left).
Multi-collector LA-ICPMS microprobe (MC-LAM-ICPMS): A fully-equipped Nu Plasma MC-ICPMS is an integral part of the Facility. This instrument combines a laser ablation microsampler, an Ar-plasma ionisation source, and a multi-collector magnetic-sector mass spectrometer, to provide high-precision in situ analysis of isotope ratios in geological materials. The MC-ICPMS also can be used in solution mode, using either standard nebuliser or a desolvating nebuliser, to supplement the capabilities of the conventional mass spectrometers at the Centre for Isotope Studies.
Applications in use and under development include:
Laser Analysis (in situ point analysis)
- U-Pb dating of zircon, monazite, apatite
- Hf isotope analysis in zircon for studies of crustal generation, mantle evolution and crust-mantle interaction
- Re-Os dating of sulfides in mantle-derived xenoliths
- Nd isotope analysis in apatites, titanites and other REE-rich minerals
- Sr isotope analysis of carbonates, feldspars, apatites, pyroxenes
- Pb isotopes in sulfides and silicates
- Stable isotope ratios of Zn, Cu and other cations in hydrothermal systems
Solution Analysis
- Re-Os ó mapping of mantle depletion ages in whole rocks and chromites
- Lu-Hf ó crustal genesis, mantle metasomatism; Lu-Hf dating of garnet peridotites, eclogites, granulites
- Rb-Sr, Sm-Nd, U-Pb ó faster and simpler than TIMS; simplified low-blank chemistry, no time-dependent mass fractionation, hence greater precision
PROGRESS IN 2000
1. Facility for Integrated Microanalysis
a. MC-ICPMS: A multi-collector magnetic sector ICPMS for in situ (laser-ablation) and solution analysis of isotopic ratios was installed in November 1998. The instrument is the Nu Plasma, designed and manufactured by Nu Instruments of Wrexham, UK. The instrument was producing good data after only a few days of installation, and has continued to do so. Merchantek EO (now New Wave Research) have provided a 266 nm UV laser microprobe (under a collaborative agreement; see below) for use with the MC-ICPMS and a new 213 nm laser microprobe was purchased in 2000. Major applications developed during 1999-2000 (seeResearch Highlights) include the high-precision analysis of Hf in zircons to trace lithosphere evolution and magma-mixing histories in granitic rocks, a survey of copper-isotope composition in a range of ore bodies, the analysis of Sr isotopes in carbonate fossils for stratigraphic control, and Re-Os dating of single grains of Fe-Ni sulfides in mantle-derived rocks.
During 2000 the precision of the in situ Re-Os analyses was improved significantly by the use of multiple ion-counters, and we completed a major study of complex sulfide assemblages in xenoliths from the Massif Central. A collaborative research proposal to study the range of stable-isotope variation in copper and iron in ore deposits was begun in November 2000, with five industry sponsors.
The in situ analysis of the Rb-Sr, Lu-Hf, Sm-Nd and Re-Os systems by laser ablation microprobe has required the development of corrections for isobaric overlaps (eg 87Rb on 87Sr), and has demonstrated that these corrections can be done with very high precision in the MC-ICPMS. This has opened the possibility of greatly simplifying the ion-exchange chemistry traditionally used to obtain clean element separations for standard mass-spectrometry analysis. Tests during the year have led to a simplified scheme for the dissolution of rocks and separation of Sr, Nd, Hf and Pb for isotopic analysis using the MC-ICPMS in solution mode. This provides whole-rock analyses that are faster, simpler and ultimately cheaper than those obtained by traditional methods.
b. Scanning Nuclear Microprobe: On the first day of operation, a spot-size of 1.3 µm was obtained at a beam current of 0.5 nA, suitable for fluid inclusion analysis and imaging. The spot-size grows to just 1.8 µm at 10 nA (3 MeV protons), ideal for mineralogical samples. PIXE detection limits down to 0.2 ppm were achieved in silicates (40 ppb in diamond) in quantitative high resolution trace element images. Recent advances include the commissioning of the PIGE system for light element detection. This operates simultaneously with the PIXE system, and provides spatial distribution images for the elements Li, Be, B, F, Na, Mg, Al and Si. Detection limits of 6-8 ppm have been achieved for F and Na extracted directly from images with 2 µm spatial resolution. The system has proved a powerful tool for non-destructive fluid inclusion analysis, providing images of the internal structure of individual fluid inclusions, now including elements such as F and Na. The result is a quantitative analysis of the homogeneous trapped fluid with detection limits as low as 20 ppm.
c. Laser-ablation ICPMS microprobe: The laser microprobe on the ELAN 6000 ICPMS, provided by Perkin-Elmer Australia (under a collaborative agreement), operated at full capacity until September 1999, while the Elan 5100 ICPMS was used for solution analysis. In October 1999, the ELAN 6000 was replaced with a Hewlett Packard 4500 ICPMS, under a new collaborative agreement whereby GEMOC will serve as a demonstration and development facility for Agilent Technologies with a second instrument to be installed later. In late 1999 GEMOC, together with the University of Newcastle and with significant support from Macquarie University, was successful in an RIEFP application for funds to replace the old ICPMS and laser microprobe in 2000. Following negotiations with Agilent , we purchased both the existing 4500 and the new 7500 ICPMS, and retired the Elan 5100. The new 7500 ICPMS was successfully tested, and went into "production mode" mid-year. It provides a major increase in sensitivity that will benefit all of GEMOCís projects. The 4500 instrument is now dedicated primarily to U-Pb dating of zircons, where its stability and ease of operation provide a high throughput. RIBG funding also provided a New Wave 213 nm laser microprobe, portable enough to be used on both the quadrupole ICPMS instruments and the MC-ICPMS. Under contract with Agilent Technologies, GEMOC currently is completing a detailed test of the capabilities of the 7500 ICPMS as a laser microprobe instrument, using both the 266 nm and the 213 nm lasers.
During 2000, the laboratory produced large volumes of data for six PhD thesis projects, several projects carried out by international visitors, and in-house funded research projects. It also routinely provides data for projects related to mineral exploration (diamonds, base metals, Au), as a consulting service to the industry. New developments included improvements in the quantitative analysis of bitumens and diamonds and the in situ analysis of Platinum Group elements in mantle-derived sulfides, and the analysis of a range of "new" trace elements (including Li and Ge) in mantle minerals was made possible by the sensitivity of the new Agilent 7500 ICPMS.
d. Software: Esmé van Achterbergh and Chris Ryan further refined the on-line version of the GLITTER (GEMOC Laser ICPMS Total Trace Element Reduction) software, our interactive program featuring linked graphics and analysis tables. This package provides the first real-time interactive data reduction for LAM-ICPMS analysis, allowing inspection and evaluation of each result before the next analysis spot is chosen. In 2000, its capabilities were expanded to include on-line reduction of U-Pb data. The use of GLITTER has greatly increased both the flexibility of analysis, and the productivity of the laboratory. New Wave Research now market the software together with their laser microprobe equipment; GEMOC provides customer service and backup through Macquarie Research Limited. Six copies of GLITTER were sold worldwide in 2000, and the sales rate is increasing steadily.
2. Energy Dispersive XRF
A Spectro XLAB2000 energy-dispersive X-ray spectrometer was
installed in November 2000 in a joint venture with Tasman Resources.
Like the earlier model instrument installed in the laboratory
at the ANU, this utilises the polarisation of scattered
X-rays to substantially reduce backgrounds and enhance detection
limits. The XLAB2000 uses a specially designed 300 W palladium
X-ray tube that improves its performance for the lighter trace
elements, and also for major elements, relative to the earlier
instrument. In addition, this spectrometer is fitted with
a silicon detector of a type recently developed that eliminates
the low-energy "tail" from the lightest elements, and
enables all major elements to be measured in a fused glass to
levels below 0.01%. The capability of this new instrument
to apparently provide major element analyses of a quality at least
comparable to the more expensive conventional crystal spectrometers
is being thoroughly evaluated. This instrument will provide
highest-quality data for major elements and for most trace elements
to sub-ppm levels. The operation of the equipment is enhanced
by a 100 position sample loader, one of the first to be installed
on a Spectro instrument.
XRF history: Keith Norrish (right) constructed the first XRF and Bruce Chappell (back left) is continuing to develop XRF methodologies with Spectro. Norm Pearson (front) is the GAU manager
3. Laser development
GEMOC continues to benefit from a industry partnership with New Wave Research (formerly Merchantek EO), a major US manufacturer of laser ablation systems, which has made Macquarie its Alpha Test Site. New Wave has maintained their 266 nm Nd:YAG UV laser ablation sampling system at GEMOC and their new 213 nm system was delivered early in 2000. Both lasers can be coupled to the Nu Plasma MC-ICPMS, allowing high precision isotope ratio determinations to be performed on minerals in situ. The mobility of the probes has allowed them to be used on the quadrupole ICPMS instruments as well, in a range of applications. Detailed tests of the relative advantages of the 213 nm and 266 nm lasers for the analysis of different materials with the 7500 ICPMS are in progress.
4. Centre for Isotope Studies (CIS)
The Centre for Isotope Studies (CIS) is a consortium operated
by the geoscience departments of the New South Wales Universities,
CSIRO Exploration and Mining, and Petroleum Resources using jointly-purchased
mass-spectrometers housed at the CSIRO in North Ryde. The facility
allows staff and students to obtain both radiogenic and stable
isotopic analyses and uses technical staff jointly funded by the
University members under an agreement arranged by Professor Peter
Bergquist (Deputy Vice-Chancellor Research Macquarie University)
and Dr Richard Flood (University Consortium Convenor).
GEMOC has developed its own clean laboratories for the preparation
of solutions for radiogenic isotope analysis but uses the stable
isotope separation facilities at North Ryde. Of particular importance
for GEMOC is the technique developed by Dr Anita Andrew for C-isotopic
analysis of diamonds using very small sample sizes (0.1 mg), which
allows analysis of microdiamonds or multiple fragments of different
zones of small stones. This is now an essential part of
GEMOC capabilities and over 100 analyses were carried out in 2000
on diamonds from Canada, Brazil and Venezuela.
5. ANU Developments
Australian Earth Data On-Line AEDOL continued development to provide automated processing facilities for the acquisition, harmonisation, generation and dissemination of commercially valuable spatial products including GIS datasets and geocoded images. By automating the processing, delivery and commerce of these products, AEDOL can significantly lower the cost to the user. This will drive technology take-up by eliminating transport costs and minimising delays and importantly, it will put the power of the system directly into the hands of the end-user.
