GEMOC's 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 develops new analytical strategies as required, to determine the chemical and isotopic composition of geological materials (both solid and fluid) in solution and in situ. 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 CSIRO Exploration and Mining. Macquarie University is a partner (with management responsibility) in the Centre for Isotope Studies housed at CSIRO, North Ryde.
|"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 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 types of analytical instrument,
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 FIM have been operating since mid-1999.
Major instruments will be replaced or upgraded in 2002-2004 through the
$5.125 million DEST Infrastructure grant awarded to Macquarie University
with the Universities of Newcastle, Sydney, Western Sydney and Wollongong
the facility provides:
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.
Norm Pearson in a panoramic view of the MC-ICPMS lab
Guillaume Delpech at the Electron Microprobe
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. The EMP will be replaced in 2002 (see below).
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 original 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
Packard 4500, and in 2000 an Agilent
7500 ICPMS was added. These two 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 µm. The LAM is fitted with a computer-driven sample stage
to provide co-registration of X-Y coordinates with the other instruments.
On-line data reduction with the GEMOC-developed "GLITTER"
software enhances laboratory productivity and data interpretation; the
software is marketed internationally by New
|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
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.
Stephanie Touron surrounded by the LAM-ICPMS
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 Fe, Mg, Zn, Cu and other cations in appropriate minerals from hydrothermal systems and mantle rocks
- Re-Os - mapping of mantle depletion ages in whole rocks, illmenites and chromites
- Lu-Hf - crustal genesis, mantle metasomatism; Lu-Hf dating of garnet peridotites, eclogites, granulites; basaltic gneiss
- Rb-Sr, Sm-Nd, U-Pb - faster and simpler than TIMS; simplified low-blank chemistry, no time-dependent mass fractionation, hence greater precision
PROGRESS IN 2001
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 213 nm laser microprobe was purchased in 2000. Major applications during 2001 (see Research Highlights) included the high-precision analysis of Hf in zircons to trace lithosphere evolution and magma-mixing histories in granitic rocks, the analysis of copper and iron isotope composition in minerals from 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. We carried out major Re-Os studies of sulfide assemblages in xenoliths and xenocrysts from the Slave, Kaapvaal and Siberian cratons, in alpine-type peridotites from the Norwegian and Swedish Caledonides, and in ocean-ridge peridotites. A collaborative research project, with five industry sponsors, studied the stable-isotope variation in copper and iron in several ore deposits. A major study of U-Pb and Hf-isotope systematics of mid-Proterozoic rocks in S. Norway provided a new view of the tectonics of southern Scandinavia (see Research Highlights)
The rapid growth of the TerraneChronTM application (Research Highlights) and its use of in situ Hf-isotope analysis, (see Research Highlights) coupled with the demand for in situ Re-Os analysis and stable isotope analysis, has led to competition for instrument time on the MC-ICPMS. An order will be placed during 2002 for a second instrument, funded by the DEST infrastructure grant.
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. During the year we further developed and modified 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: Development of the SNMPÝhas concentrated on aspects of quantitative trace-element imaging and on web access to the instrument. Proton induced X-ray emission (PIXE) yields from major- and trace-elements are dependent on sample composition and geometry. Methods have been developed to correct PIXE images for the changing sample composition across an image area. This is an iterative process, making use of the initial PIXE images to provide a measure of the proportions of end-member components in each pixel of the images. Corrections can then be made to the calculated yields, improving the accuracy of the deduced concentrations. This process converges within 2-3 iterations to yield sample compositions accurate to within 3% of electron microprobe analysis. Sample structure can also affect detected X-rays, (and hence deduced elemental concentration) because X-rays from beneath the sample surface may exit through neighbouring pixels on their way to the detector. They can therefore experience absorption effects related to the neighboring pixelís composition. Correction for this effect also is an iterative process, and an algorithm has been developed for the purpose. These corrections are now part of a software product called GeoPIXE II.
A web server has been established, with the collaboration of CSIRO Minerals, that enables the SNMP to be accessed via the world-wide web. Along with electron-beam instruments in Clayton, this constitutes "The Australian Microscopy Virtual Laboratory". The server provides video feed from a room camera and the SNMP online microscope. Now users interstate or overseas can effectively have a seat at the instrument, and watch as their samples are analysed. The next stage of development will include serving outÝPIXE and PIGE spectra and real-time images.Ý
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 with Agilent Technologies. In 2000 GEMOC, together with the University of Newcastle and with significant support from Macquarie University, received ARC RIEFP funds to replace the old ICPMS and laser microprobe. Following negotiations with Agilent, we purchased both the existing 4500 and the new 7500 ICPMS, and retired the Elan 5100. The new 7500 ICPMS went into "production mode" mid-2000. It provided a major increase in sensitivity that has benefited 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 carried out 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 2001, the laboratory produced large volumes of data for eight Macquarie PhD thesis projects, several projects carried out by international visitors and Honours students, 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 in situ analysis of diamonds, and the completion of a major project on the trace-element signature of diamonds.
d. Software: Esmé van Achterbergh and Chris Ryan
further refined the GLITTER
(GEMOC Laser ICPMS Total Trace Element Reduction) software, our on-line
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. Fourteen copies of GLITTER were sold worldwide
in 2001, and the sales rate is increasing steadily, to the point of achieving
industry-standard status. Recently Finnegan Instruments announced
a new software system designed to support GLITTER on their ICPMS instruments.
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, and the purchase of a rocker furnace for sample preparation.
3. Laser development
GEMOC continues to benefit from an 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 donated their 266 nm Nd:YAG UV laser ablation sampling system to 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 were carried out in 2001, and the sample cell design of the 213 nm laser was modified to improve signal stability. A Merchantek/New Wave Research 193 nm EXCIMER system based on an OPtek laser is on order, and should be delivered in March 2002.
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 to prepare solutions for radiogenic isotope analysis by MC-ICPMS, 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 2001 on diamonds from Canada, Brazil and Venezuela.