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Detailed field mapping between Cloncurry and Selwyn has established the existence of a common stratigraphic/tectonic history of almost all the geology east of the Overhang Shear Zone, a major suture separating the Cloncurry-Selwyn Zone from the Quamby-Malbon Belt and Mitakoodi Block. The major exception is a discrete tectonic belt in the far south of the region, the Gin Creek Block, which forms an anomalous zone of older stratigraphy and high grade metamorphism enveloped by tectonic boundaries with the surrounding units. The Cloncurry-Selwyn Zone itself could be subdivided into several sub-regions with similar internal characteristics, but for simplicity the key findings reveal that there are two principal supra-crustal packages folded and interleaved together along major faults and intruded by 1550-1510Ma granitic rocks.
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Granulite-facies paragneisses enriched in boron and phosphorus are exposed over a ca. 15 x 5 km area in the Larsemann Hills, East Antarctica. The most widespread are biotite gneisses containing centimeter-sized prismatine crystals, but tourmaline metaquartzite and borosilicate gneisses are richest in B (680-20 000 ppm). Chondrite-normalized REE patterns give two groups: (1) LaN>150, Eu*/Eu < 0.4, which comprises most apatite-bearing metaquartzite and metapelite, tourmaline metaquartzite, and Fe-rich rocks (0.9-2.3 wt% P2O5), and (2) LaN<150, Eu*/Eu > 0.4, which comprises most borosilicate and sodic leucogneisses (2.5-7.4 wt% Na2O). The B- and P-bearing rocks can be interpreted to be clastic sediments altered prior to metamorphism by hydrothermal fluids that remobilized B. We suggest that these rocks were deposited in a back-arc basin located inboard of a Rayner aged (ca. 1000 Ma) continental arc that was active along the leading edge the Indo-Antarctic craton. This margin and its associated back-arc basin developed long before collision with the Australo-Antarctic craton (ca. 530 Ma) merged these rocks into Gondwana and sutured them into their present position in Antarctica. The Larsemann Hills rocks are the third occurrence of such a suite of borosilicate or phosphate bearing rocks in Antarctica and Australia: similar rocks include prismatine-bearing granulites in the Windmill Islands, Wilkes Land, and tourmaline-quartz rocks, sodic gneisses and apatitic iron formation in the Willyama Supergroup, Broken Hill, Australia. These rocks were deposited in analogous tectonic environments, albeit during different supercontinent cycles.
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The Early Cretaceous Gage Sandstone and South Perth Shale formations are a prospective reservoir-seal pair in the Vlaming Sub-basin. Plays include post-breakup pinch-outs in the Gage Sandstone with the South Perth Shale forming top seal. The Gage reservoir has porosities of 18-25% and permeabilities of 1-1340 mD. It was deposited in palaeotopographic lows of the Valanginian breakup unconformity and is the lowstand component of the thick deltaic South Perth (SP) Supersequence. To characterise the reservoir-seal pair, a detailed sequence stratigraphic analysis was conducted by integrating 2D seismic interpretation, well log analysis and new biostratigraphic data. Palaeogeographic reconstructions for the SP Supersequence were derived from mapping higher-order prograding packages and establishing changes in sea level and sediment supply. Higher resolution Gage reservoir reconstructions were based on seismic facies mapping. The Gage reservoir forms part of a sand-rich submarine fan system similar to model proposed by Richards et al (1998). It ranges from canyon confined inner fan deposits to middle fan deposits on a basin plain. Directions of sediment supply are complex, with major sediment contributions from a northern and southern canyon adjacent to the Badaminna Fault Zone. The characteristics of the SP Supersequence differ markedly between the northern and southern parts of the sub-basin due to variations in palaeotopography and sediment supply. Palaeogeographic reconstructions reveal a series of regressions and transgressions leading to infilling of the palaeo-depression. Palaeogeographic reconstructions for the SP Supersequence portray a complex early post-rift depositional history in the central Vlaming Sub-basin. The developed approach is applicable for detailed studies of other sedimentary basins. APPEA
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An extensive AEM survey recently commissioned by Geoscience Australia involved the use of two separate SkyTEM helicopter airborne electromagnetic (AEM) systems collecting data simultaneously. In order to ensure data consistency between the two systems, we follow the Danish example (conceived by the hydrogeophysics group from Aarhus University) of using a hover test site to calibrate the AEM data to a known reference. Since 2001, Denmark has employed a national test site for all electromagnetic (EM) instruments that are used there, including the SkyTEM system. The Lyngby test-site is recognised as a well-understood site with a well-described layered-earth structure of 5 layers. The accepted electrical structure model of the site acts as the reference model, and all instruments are brought to it in order to produce consistent results from all EM systems. Using a ground-based time-domain electromagnetic (TEM) system which has been calibrated at the Lyngby test site, we take EM measurements at a site selected here in Australia. With sufficient information of the instrument, we produce a layered-earth model that becomes the reference model for the two AEM systems used in the survey. We then bring the SkyTEM systems to the hover site and take soundings at multiple altitudes. From the hover test data and the ground based model, we calculate an optimal time shift and amplitude scale factor to ensure that both systems are able reproduce the accepted reference model. Conductivity sections produced with and without calibration factors show noticeably different profiles.
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Climate change is expected to increase severe wind hazard in many regions of the Australian continent with consequences for exposed infrastructure and human populations. The objective of this paper is to provide an initial nationally consistent assessment of wind risk under current climate, utilizing the Australian/New Zealand wind loading standard (AS/NZS 1170.2, 2002) as a measure of the hazard. This work is part of the National Wind Risk Assessment (NWRA), which is a collaboration between the Australian Federal Government (Department of Climate Change and Energy Efficiency) and Geoscience Australia. It is aimed at highlighting regions of the Australian continent where there is high wind risk to residential structures under current climate, and where, if hazard increases under climate change, there will be a greater need for adaptation. This assessment is being undertaken by separately considering wind hazard, infrastructure exposure and the wind vulnerability of residential buildings. The NWRA will provide a benchmark measure of wind risk nationally (current climate), underpinned by the National Exposure Information System (NEXIS; developed by Geoscience Australia) and the wind loading standard. The methodology which determines the direct impact of severe wind on Australian communities involves the parallel development of the understanding of wind hazard, residential building exposure and the wind vulnerability of residential structures. We provide the current climate wind risk, expressed as annualized loss, based on the wind loading standard.
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The Australian Government formally releases new offshore exploration areas at the annual APPEA conference. In 2012, twenty-seven areas in nine offshore basins are being released for work program bidding. Closing dates for bid submissions are either six or twelve months after the release date, i.e. 8 November 2012 and 9 May 2013, depending on the exploration status in these areas and on data availability. As was the case in 2011, this year's Release again covers a total offshore area of about 200,000 km2. The Release Areas are located in Commonwealth waters offshore Northern Territory, Western Australia, South Australia, Victoria and Tasmania (Figure 1). Areas on the North West Shelf feature prominently again and include underexplored shallow water areas in the Arafura and Money Shoal basins and rank frontier deep water areas in the outer Browse and Roebuck basins as well as on the outer Exmouth Plateau. Following the recent uptake of exploration permits in the Bight Basin (Ceduna and Duntroon sub-basins) Australia's southern margin is well represented in the 2012 Acreage Release. Three new blocks in the Ceduna Sub-basin, four blocks in the Otway Basin, one large block in the Sorell Basin and two blocks in the eastern Gippsland Basin are on offer. Multiple industry nominations for this Acreage Release were received, confirming the healthy status of exploration activity in Australia. The Australian government continues to support these activities by providing free access to a wealth of geological and geophysical data.
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Australia has a rich uranium endowment. Amongst other favourable geological conditions for the formation of uranium deposits, such as the presence of intracratonic sedimentary basins, Australia is host to widespread uranium-rich felsic igneous rocks spanning a wide range of geological time. Many known uranium deposits have an empirical spatial relationship with such rocks. While formation of some mineral systems is closely associated with the emplacement of uranium-rich felsic magmas (e.g., the super-giant Olympic Dam deposit), most other systems have resulted from subsequent low temperature processes occurring in spatial proximity to these rocks. Approximately 91% of Australia's initial in-ground resources of uranium occur in two main types of deposits: iron-oxide breccia complex deposits (~ 75%) and unconformity-related deposits (~ 16%). Other significant resources are associated with sandstone- (~ 5%) and calcrete-hosted (~ 1%) deposits. By comparison, uranium deposits associated with orthomagmatic and magmatic-hydrothermal uranium systems are rare. Given the paucity of modern exploration and the favourable geological conditions with Australia, there remains significant potential for undiscovered uranium deposits. This paper discusses mineral potential of magmatic- and basin-related uranium systems.
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As part of initiatives by the Australian and Queensland Governments to support energy security and mineral exploration, a deep seismic reflection survey was conducted in 2007 to establish the architecture and geodynamic framework of north Queensland. With additional support from AuScope, nearly 1400 km of seismic data were acquired along four lines, extending from near Cloncurry in the west to almost the Queensland coast. Important results based on the interpretation of the deep seismic data include: (1) A major, west-dipping, Paleo-proterozoic (or older) crustal boundary, which we interpret as a suture, separates relatively homogenous, thick crust of the Mt Isa Province from thinner, two layered crust to the east. This boundary is also imaged by magnetotelluric data and 3D inversion of aeromagnetic and gravity data. (2) East of the Mt Isa Province the lower crust is highly reflective and has been subdivided into three mappable seismic provinces (Numil, Abingdon and Agwamin) which are not exposed at the surface. Nd model ages from granites sampled at the surface above the western Numil and central Abingdon Seismic Provinces have very similar Nd model ages, suggesting that both provinces may have had a very similar geological history. By contrast, granites sampled above the eastern Agwamin Seismic Province have much younger Nd model ages, implying a significantly younger component in the lower crust; we consider that the Agwamin Seismic Province contains a strong Grenvillean-age component.
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After CO2 is injected into the saline aquifer, the formation water inside the porous media becomes more acidic. This will significantly affect the original chemical equilibrium underground, and induce or speed up various processes of dissolution and precipitation depending on the reservoir pressure, temperature and salinity of formation water. The Early Cretaceous Gage Sandstone has been identified as a potential reservoir unit suitable for large-scale CO2 storage in the offshore southern Perth Basin. This study assesses the contribution of mineralisation trapping to CO2 storage capacity of the Gage Sandstone through a comprehensive geochemical modelling.
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Open Geospatial Consortium (OGC) web services offer a cost efficient technology that permits transfer of standardised data from distributed sources, removing the need for data to be regularly uploaded to a centralised database. When combined with community defined exchange standards, the OGC services offer a chance to access the latest data from the originating agency and return the data in a consistent format. Interchange and mark-up languages such as the Geography Markup Language (GML) provide standard structures for transferring geospatial information over the web. The IUGS Commission for the Management and Application of Geoscience Information (CGI) has an on-going collaborative project to develop a data model and exchange language based on GML for geological map and borehole data, the GeoScience Mark-up Language (GeoSciML). The Australian Government Geoscience Information Committee (GGIC) has used the GeoSciML model as a basis to cover mineral resources (EarthResourceML), and the Canadian Groundwater Information Network (GIN) has extended GeoSciML into the groundwater domain (GWML). The focus of these activities is to develop geoscience community schema that use globally accepted geospatial web service data exchange standards.