Geochemistry

Geochemistry is the study of the chemical processes which form and shape the Earth. It includes the study of the cycles of matter and energy which transport the Earth's chemical components and the interaction of these cycles with the hydrosphere and the atmosphere.

Geoscience Australia maintains a variety of high quality, state-of-the-art facilities for geochemical analysis of natural systems to help discover how and when the various parts of the Australian continent were formed and how these were shaped by later events such as deformation, alteration, mineralisation and regolith formation. Geochemistry is used also to help understand how petroleum and mineral systems operate and in the study of groundwater, marine and coastal habitats, and other environmental issues.

Geoscience Australia also stores a large amount of geochemical data collected from both onshore and offshore parts of Australia and selected other countries. Geochemical modelling is used also to test and predict the effects of various geochemical processes in both space and time.

Inorganic geochemistry

Inorganic chemistry is concerned with the properties of all the elements in the periodic table and their compounds, with the exception of organic compounds (compounds containing C-H bonds). Inorganic chemistry investigates the characteristics of substances that are not organic, such as nonliving matter and minerals found in the Earth's crust.

Inorganic geochemistry laboratories

The inorganic geochemistry laboratories specialise in the identification and analysis of rocks, minerals, soils and the fluids trapped in rocks. This information is used to support Geoscience Australia's national and regional programs, mineral systems research and regolith studies.

These laboratories use analytical techniques which are acknowledged as among the most powerful, most sensitive and most cost effective available. Expertise and facilities available for the preparation and analysis of geochemical samples include:

Sample preparation

Rocklabs hydraulic splitter: This unit is equipped with tungsten carbide blades and is used to clean weathered samples and to split large samples to fit the swing-jaw crusher.

Rocklabs swing-jaw crusher: The swing-jaw crusher is used to reduce samples from 100mm diameter to less than 20mm diameter. The jaw faces are made of low contaminant mild steel.

Boyd crusher: The Boyd crusher with attached rotary sample divider reduces samples from less than 50mm to less than 4mm grains. The sample divider can be set to sample between 2% and 50% of the fine crush.

Rocklabs vibratory ringmill: This unit is used to produce a very fine powder from the coarse product from the Boyd crusher. Three grinding mediums are available. These are:

Geochemical analysis

X-Ray fluorescence (XRF) spectrometry: The Philips PW 2404 XRF spectrometer with automated sample loader and online data processing is used for analysing fusions and pressed powder samples for elements with an atomic mass greater than 9. The equipment can measure concentrations as low as 1ppm and as high as 100%. A semi-automatic Initiative Scientific Products Fusilux 4X4 Fusion Machine is used in the production of fused discs and an Activon Automated Speca press for producing powder pellets.

Laser ablation and solution inductively coupled plasma - mass spectrometry (ICP-MS): The Agilent Technologies 7500 ICP-MS with automated sample loader and online data processing is used in conjunction with the X-ray Fluorescence (XRF) spectrometer for the analysis of a wide range of trace elements. Detection limits down to ppb levels can be obtained routinely. The ICP-MS is traditionally used with solutions, made by acid digestion of fused glass disks. The ICP-MS is also equipped with a Newwave UP-193 solid state laser ablation system for analysis of solid samples.

Leco RC-412 multiphase carbon / hydrogen / moisture analyser: The Leco C/H/moisture analyser is used for the determination of organic and inorganic carbon as well as bound water in rock and soil samples. This instrument not only determines total carbon and hydrogen but also the amount of the two elements given off and the temperature at which the two elements are given off.

Volumetric, gravimetric and electrochemical methods: Supplementary analyses such as moisture, ferrous iron, fluoride, loss on ignition and specific gravity also are available.

Other specialised techniques may be used upon request.

Mineralogical and fluid inclusion facilities

Laser Raman microprobe (LRMP): The HORIBA Jobin Yvon SuperLabram laser Raman microprobe has a fully confocal microscope and is used for the rapid and non-destructive analysis of solids, liquids and gases. The high spatial resolution of this instrument (¿ 1 micron) makes it particularly suitable for the identification of gases and solids in fluid inclusions. The laser Raman microprobe is equipped with a motorised stage also, which allows Raman mapping of selected areas of the sample. An optical-fibre probe can be attached to the spectrometer and used for probing larger samples that do not fit under the microscope, such as hand specimens and drill core.

X-ray diffraction spectrometry: The Seimens D500 X-ray diffractometer (XRD) is used to identify and determine the amount of minerals in powdered samples. The Siroquant software package is used to quantitatively determine the amount of each mineral identified by its X-ray diffraction pattern.

Portable infrared mineral analyser (PIMA): The Integrated Spectronics PIMA is a field-portable, shortwave infrared spectrometer which provides rapid data on rocks and minerals. The accompanying software contains a library of PIMA mineral spectra allowing easy interpretation of unknown spectra. Measurements can be made on all types of samples including diamond drill-core, RC and RAB chips, powders and soil samples.

Electron probe micro-analyser (EPMA): The Cameca SX-100 electron probe micro-analyser is a shared Geoscience Australia-Australian National University facility used for the analysis of elements in very small areas such as individual mineral grains. It is equipped with four wavelength dispersive X-ray spectrometers and an energy dispersive spectrometer. Cathodoluminescence and backscattered electron images also may be obtained in the scanning mode. This instrument is primarily used for major element microanalysis with detection limits typically exceeding 50-100ppm. However, detection limits may be extended into the trace element range by the use of longer counting times and precise background corrections.

Heating and freezing stages: These laboratories contain the following heating and freezing stages which are used mainly for fluid and melt inclusion studies:

• Linkam MDS (IR-adapted) 600 stage (-196°C to +600°C). This stage is mounted on an infrared microscope equipped with a Hamamatsu IR camera and a mercury lamp for UV illumination. The Linksys software is used for automated temperature control and capture of digital images at specified time or temperature intervals
• Linkam TS 1500 stage (20 to 1500°C). This stage is automatically controlled with a TS94 programmer
• Fluidinc modified USGS gas flow stage (-196 to +700°C). This stage is mounted on a microscope equipped with a Sony video camera for viewing
• ChaixMeca stage (-196 to +600°C)
• Leica 1350 stage (25 to 1350°C).

Transmitted and reflected light microscopes: These laboratories contain a range of research-grade, polarising microscopes and binocular microscope including:

• Leica DMRX polarising microscope which can be operated in transmitted or reflected or both simultaneously and is equipped with a Leica DFC 320 digital camera for microphotography
• Leitz Orthoplan polarising microscope equipped with mercury lamp for UV illumination
• Leitz Orthoplan polarising microscope equipped with a Leica DC100 digital camera and diamond-coated microdrill for cutting small sections from petrological thin sections
• Olympus BX60 polarising microscope equipped with IR Optics and IR camera (400 - 2200nm) and mercury lamp for UV illumination
• Wild M400 Photomakroskop - stereo binocular microscope.

Inorganic geochemistry database

This is a database of whole-rock and stream-sediment geochemistry for samples which are mainly from Australia, Antarctica, Papua New Guinea and the Solomon Islands. Both major and trace element analyses are included. Analyses are added from:

• Projects carried out by Geoscience Australia
• university theses
• collaborative projects with the Northern Territory and State Geological Surveys
• geochemical data published in scientific journals and reports.