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  • Obtaining reliable predictions of the subsurface will provide a critical advantage for explorers seeking mineral deposits at depth and beneath cover. A common approach in achieving this goal is to use deterministic property-based inversion of potential field data to predict a 3D subsurface distribution of physical properties that explain measured gravity or magnetic data. The non-uniqueness of inversions of potential field data mandates careful and consistent parameterization of the problem to ensure realistic solutions. Including all prior geological knowledge as constraints on the inversion also helps ensure that the recovered predictions are consistent with both the geophysical data and the geological knowledge. We review how potential field inversions are best applied for mineral exploration problems using the UBC-GIF inversion algorithms. We use examples to emphasise the importance of mesh design and applying appropriate data processing, and identify the approach for defining key parameters such as data uncertainty, potential field weighting functions, and numerical parameters that approximate prior geological knowledge of in situ trends, geometries and properties. Consistent application of these techniques will ensure the most reliable predictive physical property models for explorers.

  • Cocos (Keeling) Island is located approximately 3,685km almost due west of Darwin. It is a mid-ocean atoll with a coral reef, and a very shallow (1 - 20 m) shelf surrounds the island. Bathymetry data are required in this area to help identify major seabed processes and habitats. The data are also required to enable modelling of tsunami as they interact with the shelf around the island and the coast. This report describes the methodology employed in creating detailed bathymetry data grids of the Cocos (Keeling) Island region. It covers data collection, quality control and gridding. Descriptions are provided of each dataset employed, the methods used to integrate the different datasets and the attributes of the new bathymetry models. Four new bathymetry grids are presented, including grids that integrate bathymetry with the island's topography.<p><p>This dataset is not to be used for navigational purposes.

  • Australian Phanerozoic basins have been under-explored for uranium. As a result, Geoscience Australia has been conducting research into uranium systems in the Frome Embayment, with the aim of developing a series of models and exploration techniques to assist uranium exploration in other basins. The transport and depositional mechanisms are relatively well understood for sandstone-hosted uranium deposits; uranium is transported by oxidised meteoric fluids and precipitated by either an in situ reductant or by mixing with a reduced fluid. Using the concept that an oxidised fluid will progressively oxidise the rock that it passes through and, in turn the fluid will be reduced by wall rock interactions, potentially we can use drillhole logs to identify and map the redox state of the rocks and hence identify depositional sites. A pilot study was undertaken to determine whether the open file geological logs could be used to map the redox state. A list of oxidised and reduced keywords was identified from the logs. Logs were digitised and oxidised words were given a value of one and reduced words given a value of negative one. Where there was combination of oxidised and reduced words, zero was used to designate the intermediate redox state. Where redox state could not be determined from the logs, a null data value was used. The redox values were imported into gOcad and gridded using DSI and IDW for comparison purposes. The technique identified north-south trending features in the Namba Formation interpreted to be previously unmapped paleochannels. This technique of mapping redox conditions of sediments using open file drilling reports is able to be applied in other basin settings, assisting in the targeting of sandstone-hosted uranium systems.

  • In 2008-2009 Geoscience Australia, contracted Fugro Airborne Surveys and Geotech Airborne, to respectively acquire TEMPEST and VTEM airborne electromagnetic (AEM) data with broad line spacings covering more than 71 000 km² in the Pine Creek region, Northern Territory. The Pine Creek survey (Figure 1) is the second regional AEM survey funded by the Onshore Energy Security Program (OESP) at Geoscience Australia. Geoscience Australia funded the flying of 19 500 line km, subscriber companies funded 10 400 line km. The 5 000 m line spacing provide regional information with 1 666 m, 555 m and closer line spacing providing detail for mineral systems analysis and deposit scale mapping. One of the main survey objectives was to reduce exploration risk and encourage exploration in the region by mapping, under cover, in areas where gravity and magnetics are quiet. Geological targets included detecting: conductive unites within the Pine Creek Orogen (PCO) sequence; Kombolgie Sandstone / PCO unconformity; Tolmer Group/ Finniss River Group unconformity. Geoscience Australia undertook conductivity logging (Figure 2) in the Pine Creek region. Conductivity logs were processed and as input into forward models, ground truth AEM results and for geological interpretations. To facilitate interpretation, subsurface electrical conductivity predictions using a layered earth inversion (sample by sample) algorithm developed by Geoscience Australia (GA-LEI) were derived from the AEM survey data. Conductivity characterisation of large regional units using the AEM data show: the Rum Jungle Complex is a consistently resistive area with an average conductivity value of less than 2 m/S; the Mt Partridge Group has a conductivity value up to 100 m/S; the Kombolgie Sandstone has a conductivity range of less than 2 m/S in more areas. Detecting conductivity contrasts in areas with known uranium prospectivity aids in a mineral systems analysis and geological interpretation of uranium deposits.

  • Geoscience Australia collects and manages large amounts of data for Australia's marine zone, including bathymetry data and the legal boundaries of petroleum acreage release areas. Communicating this information to non-specialists can be difficult. To overcome this communication problem Geoscience Australia uses innovative visualisation techniques, including 3D flythroughs and video editing, to integrate raster and vector geospatial data into enhanced multimedia products. Geoscience Australia has used these techniques for a number of years and the resulting products are highly regarded by stakeholders interested in marine zone management and petroleum exploration. This paper examines four case studies where these innovative techniques were used to effectively communicate marine zone information with a wide audience.

  • A 3D map of the Cooper Basin region has been produced over an area of 300 x 450 km to a depth of 20 km (Figure 1). The 3D map was constructed from 3D inversions of gravity data using geological data to constrain the inversions. It delineates regions of low density within the basement of the Cooper/Eromanga Basins that are inferred to be granitic bodies. This interpretation is supported by a spatial correlation between the modelled bodies and known granite occurrences. The 3D map, which also delineates the 3D geometries of the Cooper and Eromanga Basins, therefore incorporates both potential heat sources and thermally insulating cover, key elements in locating a geothermal play. This study was conducted as part of Geoscience Australia's Onshore Energy Security Program, Geothermal Energy Project. This 3D data release constitutes the first version of the Cooper Basin region 3D map. A future data release (version 2 of the 3D map) will extend the area to the north and east to encompass the entire Queensland extension of the Cooper Basin. The version 2 3D map will incorporate more detailed 3D models of the Cooper and Eromanga Basins by delineating the major internal sedimentary sequences within the basins. Thermal properties will then be incorporated into the 3D map to produce a 3D thermal model. The goal is to produce a 3D thermal model of the Cooper Basin region that not only matches existing temperature and heat flow data in the region, but also predicts regions of high heat flow and elevated temperatures in regions where no heat flow or temperature data exists.

  • PowerPoint presentations presented at the NORTH QUEENSLAND SEISMIC AND MT WORKSHOP in Townsville, June 2009.

  • This presentation summarises results of 3d petroleum systems modelling of the northwestern Ceduna Sub-basin, Bight Basin, offshore southern Australia, using Schlumberger Petromod software. The model builds on two 2D models for the northern and central Ceduna Sub-basin published in Totterdell et al. (2008).

  • Several scenarios of an original 3D model based on the petroleum systems model of Fuji et al. (APPEA 2004) were simulated using the PetroMod 3D V.10 modeling software. In general the results of the modelling study presented here confirms the modelling results of Fuji et al. (2004) with respect to the timing of generation in the different sub-basins as well as present day maturity. The main differences between the work of Fuji et al. (2004) and the work presented here are based on the use of PhaseKinetic models for the individual source rock formations and the ensuing compositional predictions of the fluids in different fields. Source rock transformation ratios as well as the bulk generation rates indicate that the source rocks are presently still generating. The Central Swan Graben area is presently more mature than the other kitchen area of the Vulcan Sub-basin, the Cartier Trough. The locations of predicted accumulations coincide with the locations of most of the proven fields. In many cases accumulation sizes and predicted column heights are large, mainly due to the fact that the resolution of the numerical model is low which leaves rather large volumes of the cells to be filled. Modelling results predict a series of accumulations at locations which have, as yet, not been tested. However, most of them depend on fault closure, thus increasing exploration risk. The main risks as observed from this modelling exercise are: 1) source rock presence and definition, 2) definition of the traps, 3) resolution of the input model, 4) cap rock properties, which are still largely unconstrained. The different scenarios modelled show distinct variations with respect to predicted petroleum distribution as well as the physical properties of the accumulated fluids.

  • A technical user manual for volcanic ash dispersion modelling using python-FALL3D.