From 1 - 10 / 839
  • Legacy product - no abstract available

  • ABSTRACT: Building on method developments achieved during a series of precursor pilot projects, the National Geochemical Survey of Australia (NGSA) project targets catchment outlet (overbank) sediments as a uniform sampling medium. These transported, fine-grained materials are collected (from a shallow and a deeper level) near the lowest point of 1390 catchments, which cover 91% of the country. Dry and moist Munsell® colour, soil pH and electrical conductivity and pH of 1:5 (soil:water) slurries are recorded and laser particle size analysis and infrared spectroscopy are performed. The dried samples are sieved into two grain-size fractions (<2 mm and <75 mm) that are analysed by x-ray fluorescence (XRF) and inductively-coupled mass spectrometry (ICP-MS) (multi-element, total analyses), by ICP-MS after aqua regia digestion (multi-element, including low level gold), and specialised methods for platinum group elements, fluorine and selenium. At the time of writing, 78% of the samples have been collected and most analyses are completed for the first 25% of samples. The project is due for completion in June 2011.

  • There is a general acceptance amongst the analytical community that geological materials must be reduced to less than 75 microns grain size to reduce particle-size effects and to reduce minerals sufficiently to provide a representative analysis of the sample. This study examines several aspects of this assumption, by comparing the XRF analysis of pressed powder pellets and fused glass discs of the same samples in coarse- and fine-grained form; quantifying the grain-size difference between these samples by laser particle size analysis. An examination of the effect that overloading a grinding head can have on the efficiency of grinding was also carried out. Coarse- and fine-grained aliquots of the same samples were pressed into powder pellets and trace elements analysed by a Philips PW2404 X-ray Fluorescence spectrometer. These same samples were fused into Lithium meta/tetra Borate discs and analysed for major elements by XRF. A sub-sample of this glass disc was acid-digested and trace elements analysed on an Agilent 7500CE ICP-MS. Results obtained were compared. Grinding head efficiency was examined by pulverising increasing weights of the same rock sample in a Rocklabs TC-200 Tungsten Carbide grinding head in a Rocklabs Standard Ring Mill. The same methodology as outlined above was then used to analyse the fractions and compare the results. A Malvern 2000E Laser Particle Size analyser was used to quantify the grain size of the samples analysed. Analytical results will be presented, highlighting the effects of the varying grain size.

  • A new continental-scale geochemical atlas and dataset for Australia were officially released into the public domain at the end of June 2011. The National Geochemical Survey of Australia (NGSA) project, which started in 2007 under the Australian Government's Onshore Energy Security Program at Geoscience Australia, aimed at filling a huge knowledge gap relating to the geochemical composition of surface and near-surface materials in Australia. Better understanding the concentration levels and spatial distributions of chemical elements in the regolith has profound implications for energy and mineral exploration, as well as for natural resource management. In this world first project, a uniform regolith medium was sampled at an ultra-low density over nearly the entire continent, and subsamples from two depths and two grain-size fractions were analysed using up to three different (total, strong and weak) chemical digestions. This procedure yielded an internally consistent and comprehensive geochemical dataset for 68 chemical elements (plus additional bulk properties). From its inception, the emphasis of the project has been on quality control and documentation of procedures and results, and this has resulted in eight reports (including an atlas containing over 500 geochemical maps) and a large geochemical dataset representing the significant deliverables of this ambitious and innovative project. The NGSA project was carried out in collaboration with the geoscience agencies from every State and the Northern Territory under National Geoscience Agreements. .../...

  • Legacy product - no abstract available

  • This data package comprises data sets which cover the Wangaratta 1:250 000 map sheet (WANGARATTA). This area has recently been covered by airborne geophysical surveys by the Geological Survey of Victoria and these data sets intend to compliment this data.

  • During April/ May 1988 the Bureau of Mineral Resources will conduct a 22 day geochemical research programme in the Otway and Gippsland Basins. This programme follows previous preliminary studies (January-February 1987) which examined the distribution and molecular composition of light hydrocarbon gases within deep water surficial sediments in the Otway Basin.The major thrust of the forthcoming cruise will be to obtain shallow water (continental shelf) geochemical data from both the Otway and Gippsland Basins, to test ideas generated from the previous programme, and, inparticular, to integrate the results with in house BMR geohistory and maturation modelling studies. The objectives are, therefore: 1.To develop new information on source rocks, maturation, and hydrocarbon migration on the Mussel and Crayfish Platforms and Voluta Trough in the Otway Basin. 2.Specifically, to test the relationship between variations in sourcerock maturation (as indicated by well data and geohistory analyses) andthe surface hydrocarbon gas composition and distribution within sediments from the Otway and Gippsland Basins. The majority of the programme will be focussed on the Otway Basin, with the final 4-5 days of the cruise spent in the Gippsland Basin. Sampling will becarried out along previously shot BMR multi-channel seismic lines, and will consist of vibracoring in shallow water (<150m) and combinations of piston and gravity coring in deeper water. In the Otway Basin, four key profiles will be sampled (see Fig.1). The two western profiles (A & B) run from the Crayfish Platform into the VolultaTrough, whereas the eastern profiles (C & D) run from the Mussel Platform into the central Voluta Trough. On all of these profiles the basal Early Cretaceous, considered the section with the best source potential, becomes progressively deeper buried (towards A" etc.), with maturity increasing from VR =1.0-1.3 (peak oil generation) on the Platform margins to over mature (VR = 3.0-4.0) in the central Voluta Trough. Similarly, the Late Cretaceous sequences (eg. Belfast Mudstone), which are immature on the Platform margins, are ideally placed within the oil window in the central Voluta Trough. The molecular compositions of the thermogenic gases withinthe surface sediments along these profiles may thus provide important cluesto the nature of the principal source horizons within the Otway Basin. For example, a dry gas signature in the central Voluta Trough would argue against a Late Cretaceous source, and support the contention that the Early Cretaceous is the major source horizon. In addition to the above profiles, specific areas will be studied indetail. These include previously defined hydrocarbon anomalies andpotential seafloor seeps off Port Douglas (see Fig.1). The Gippsland Basin programme will consist principally of sampling from the southern shelf, through the Central Deep, and onto the Lakes Entrance Platform (see Fig.2). Latrobe Group source rocks vary from immature toovermature along this transect, and the objective is to determine whetherthis change in maturity is reflected in the composition of the surface hydrocarbon gases. The Gippsland programme will allow a comparison of theresults obtained from a frontier exploration area, the Otway Basin, withthose from a major oil/gas producing province. In both the Otway and Gippsland Basins, high resolution seismic data willbe collected over selected hydrocarbon anomalies, in order to better definenear-surface structure, particularly faulting. This data will be acquiredwith either a 15 or 80 cubic inch water gun.