GEMOC ARC National Key Centre

TECHNOLOGY DEVELOPMENT PROGRAM

BACKGROUND

The Key Centre'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. Further development of both technology and innovative types of analytical and microanalytical methodologies are required to meet the research aims, and the Centre is developing 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 microanalytical methods to extend and integrate the electron microprobe, proton microprobe and laser microprobe instrumentation now available. These developments are transmitted to industry via open and collaborative research, through technology exchange visits and are an integral part of the training program.

RESEARCH FACILITIES

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 Dept. of Geology and CSIRO Exploration and Mining. Macquarie University is a partner (with management responsibility) in the Centre for Isotope Studies housed at the CSIRO, North Ryde.

• The GAU contains:

  * a Cameca SX-50 electron microprobe
  * a Perkin-Elmer ELAN 5100 ICPMS
  * a custom-built laser microprobe attached to the ICPMS
  * an automated Siemens XRF
  * a LECO H2O-CO2 analyser.
  * Newly installed 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 a state-of-the-art thermal ionisation mass spectrometers for analysis of 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 INAX facility includes an automated Philips XRF, Australia's only non-commercial Neutron Activation Laboratory, atomic absorption spectrophotometry, and sample preparation facilities for mass spectrometric analysis. Through the Institute of Advanced Studies, the Department has access to a Cameca Camebax microprobe, ICPMS and thermal ionisation mass spectrometer facilities.

• The HIAF proton microprobe provides ppm-level non destructive, standardless analysis of a range of elements in silicates, oxides, sulphides and individual fluid inclusions.

• ICPMS: Inductively Coupled Plasma Mass Spectrometry (ICPMS) is a rapidly maturing technology, with about 30 instruments now installed in Australia and New Zealand. Development is focussing on improving sensitivity both by improvements to the hardware, and by improved analytical strategies. Many developments are being undertaken in cooperation with the manufacturing company.

• Laser-ablation Microprobe (LAM): A major effort is being invested in the development of reproducible and quantitative in-situ analysis of minerals for a wide range of elements at the ppb level by LAM-ICPMS. The integration of the proton microprobe into this work gives the Centre a special advantage, since the proton probe, while less sensitive, is independent of standards and thus can be used to calibrate the ICPMS methods. A strategy to acquire the instrumentation to enable in situ isotopic ratio analysis is in place.

• In-situ fluid inclusion analysis: The recent development at CSIRO of non-destructive quantitative analysis of single fluid inclusions by proton microprobe (PMP) represents a major advance in the technology available for study of rock- and ore-forming fluids. The method is sensitive to heavy metals at _50 ppm in the fluid. PMP analysis will provide an internal standardisation of LAM-ICPMS data acquired by drilling into the inclusion and hence quantitative analysis of the fluid. These techniques can be used for both natural and synthetic fluid inclusions, to evaluate element partitioning experimentally.

• Scanning Proton Microprobe: The LA-ICPMS and the proton microprobe both provide low-level trace-element analysis of individual spots on mineral grains. Development of a scanning facility for the CSIRO proton microprobe will permit the production of quantitative elemental distribution images down to trace levels. This will complement and extend the high-resolution BSE and X-ray imaging capabilities of the Centre's electron microprobes, and the spot-by-spot analysis capability of the LA-ICPMS.

Summary of analytical capabilities

Precision analysis of most elements from percent levels to parts per billion can be carried out for most geological materials (in-situ for minerals):

• bulk rocks
• silicates
• oxides
• carbonates
• sulfides

In-situ analyses can also be carried out for major and trace element in fluids (eg fluid inclusions). Isotopic analyses (stable and radiogenic) on bulk samples are available through the CIS facility.

Progress since June 1995

• An ELAN 6000 ICPMS was installed (without capital investment from GEMOC) in the Macquarie laboratory by Perkin Elmer Australia, to be used for collaborative development work and for training of PE clients. The Macquarie laboratory will host the Fourth Australasian Symposium on Applied ICP-Mass Spectrometry in 1997.

• Development work on the laser-ablation ICPMS resulted in techniques for fully quantitative analysis of >30 elements in glasses and common silicate and oxide minerals. The analytical protocol eliminates or greatly reduces interelement fractionation, a requirement for reproducible analysis. We achieved excellent agreement between LAM-ICPMS data and those from the proton microprobe, solution ICPMS and NAA. A paper on the methods has been submitted to Geostandards Newsletter, and talks were presented at several conferences (see appendix 5). The laboratory is now participating in a round-robin standardisation of new USGS rock standards.

• The new LAM-ICPMS techniques are now being routinely applied to diamond-exploration samples, where the additional information from the larger number of elements is expected to improve the empirical discriminants developed at CSIRO using proton-microprobe data.

• In a novel application of the technique, the laser has been used to drill into experimental petrology charges, and the ICPMS to analyse the fluids released (see abstract, appendix 5).

• A detailed analysis of the requirements and anticipated applications for a Scanning Proton Microprobe was carried out. This showed that a new beam line was required, rather than a modification of the existing probe. A detailed plan has been drawn up, and a strategy for funding the construction has been developed.