2009
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This report outlines the level survey completed during the visit to Funafuti, Tuvalu January 2009. This is the third EDM Height Traversing levelling survey of the deep bench mark array in Funafuti, Tuvalu. This is also a repeat survey and on eight previous occasions, from 1993 to 2003 the Tuvalu levelling survey was performed by the National Tidal Centre (NTC) using the Precise Differential Levelling technique. This project is sponsored by the Australian Agency for International Development (AusAID), managed by the Bureau of Meteorology (BOM) and supported by the National Geospatial Reference Systems Project (NGRS), Geospatial Earth Monitoring Division, GEOSCIENCE AUSTRALIA.
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In 2008, as part of its Onshore Energy Security Program, Geoscience Australia and PIRSA acquired 262 km of vibroseis-source, deep seismic reflection data as a single north-south traverse (08GA-C1) in the Curnamona Province in South Australia. This line started in the south near outcrop of the Willyama Supergroup, ran to the east of Lake Frome along the Benagerie Ridge, and ended in the north to the northeast of the Mount Painter and Mount Babbage Inliers. Almost the entire route of the seismic traverse was over concealed bedrock, with only a few drillholes which could be used as control points. Overall, the crust imaged in the seismic section is relatively reflective, although the central part of the section contains an upper crust which has very low reflectivity. The lower two-thirds of the crust contain strong, subhorizontal reflections. The Moho is not sharply defined, but is interpreted to occur at the base of the reflective package at about 13 s two-way travel time (TWT), about 40 km depth. The highly reflective crust can be tracked, from the southern end of the seismic section, northwards for a distance of about 200 km. In the north, where rocks of the Mount Painter and Mount Babbage Inliers are exposed close to the section, the crust has a marked lower reflectivity, compared to the rest of the line. This contrast in crustal reflectivity suggests that the crust beneath the Mount Painter region is different to that beneath the Willyama Supergroup of the Curnamona Province in the south, raising the possibility of an ancient crustal boundary between the two regions.
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Palaeoproterozoic magmatic rocks from the Mary Kathleen Fold Belt of the Mount Isa Inlier record different magmatic textures and variations in tectonic strain associated with extension and the development of crustal-scale detachment zones. New SHRIMP U-Pb zircon geochronology for magmatic rocks, combined with field relationships, refine the duration of this extension to between 1780 and 1740 Ma. The initial stages of this tectono-magmatic event are co-incident with mafic magmatism, basin formation and rapid sedimentation of the ~1780-1765 Ma Myally Supersequence of the Leichhardt Superbasin in the adjacent Leichhardt River Fault Trough. The Ballara Quartzite and Corella Formation represent a period of sag phase sedimentation during the later part this event, and facies models, sequence stratigraphic interpretations and detrital zircon geochronology data confirm the time equivalence of these units to the Quilalar Supersequence of the Leichhardt River Fault Trough. These correlations permit the Eastern and Western Successions of the Mount Isa Inlier to be correlated at this time. Locally, the Corella Formation is intruded by 1740 Ma granites, suggesting that at least the lower parts of this package were deposited during the 1780-1740 Ma extensional event. By linking deep crustal extension processes in the Mary Kathleen area with near-surface basin formation in the adjacent Leichhardt River Fault Trough, it is possible to develop crustal-scale architecture models which provide insights into the development and migration of ore-bearing fluids.
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Over the last 20 years, it has become common practice to treat SIMS measurements of <sup>207</sup>Pb/<sup>206</sup>Pb in zircon as unfractionated. Consequently, uncertainties associated with composite <sup>207</sup>Pb/<sup>206</sup>Pb values are often limited only by population statistics of the weighted mean, and citation of 95% confidence limits of 1- (or less) on Meso- to Paleoarchean mean ages is increasingly commonplace. In such cases, the presence of undiagnosed SIMS instrumental mass fractionation of <sup>207</sup>Pb/<sup>206</sup>Pb of similar magnitude (1-2-) could have serious ramifications for the accuracy of the measured age: in extreme cases, the 'true' <sup>207</sup>Pb/<sup>206</sup>Pb may not even lie within the artificially narrow 95% confidence interval of the measured value. This possibility has important implications for high-precision zircon geochronology via SIMS, and the correlation of Precambrian events. Our previous work has characterized (via ID-TIMS) a Paleoarchean igneous zircon reference material ('OG1'). Its reference <sup>207</sup>Pb/<sup>206</sup>Pb is 0.29907 ± 0.00011 (3465.4 ± 0.6 Ma) for natural (air-abraded) zircon, and 0.29939 ± 0.00012 (3467.1 ± 0.6 Ma) for zircon annealed and chemically abraded using the Mattinson technique. The corresponding reference <sup>206</sup>Pb/<sup>238</sup>U ages are 3440.7 ± 3.2 Ma and 3463.3 ± 3.6 Ma respectively.
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Shared geological and geochemical processes are involved in the formation of particular groups of uranium deposits. Three families of uranium mineral systems are recognised: magmatic-, metamorphic- and basin-related. End-member fluids in each family are magmatic-hydrothermal, 'metamorphic' (including fluids reacted with metamorphic rocks at elevated temperatures), and surficial fluids such as meteoric water, lake water and seawater. Most well known uranium deposit types can be accommodated within this tripartite framework, which explicitly allows for hybrid deposit types.
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The southwest corner of Western Australia consists of Protozoic geology with the area undergoing no tectonic activity in the last 40Ma. It has not been glaciated in the last 20Ma and has had a cool dry climate for at least 200ka, thus providing an ideal environment to preserve fault scarps. High resolution DEM data has been used to identify over 50 new features that are thought to be scarps of surface rupturing earthquakes. Half of these scarps have been the subject of some field work with one new feature being fully verified. Using recently developed fault scaling relations the fault length and displacement are used to estimate the magnitude and, in many cases, identifying multiple events. This has been used to generate a neotectonic earthquake catalogue. Non-extended stable continental region (SCR) and extended continental crust (ECC) and have separate catalogues The SCR catalogue is considered to have a magnitude of completeness (Mc) of M6.5 with ~55 earthquakes of M6.5 or greater. The data has typical truncated GR recurrence characteristics, with a slope (b) of 0.9-1.0, between magnitude 6.5 and 6.9, and rapid decrease in recurrence above M6.9. SCR data has an asymptote of M7.2 suggesting a Mmax of M7.1-M7.3. The ECC data has a Mc of M7.2 and has 15 events of this magnitude or greater. The recurrence rapidly decreases above M7.4 with an asymptote of M7.6 suggesting a Mmax of M7.5-M7.7. The large number of SCR events gives us confidence in the proposed Mmax of M7.2.
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The Paterson drill hole database was compiled to constrain interpretation of airborne electromagnetic data acquired over the outcropping province and immediate surrounds. The data were sourced from the Geological Survey of Western Australia's WAMEX database while loges were captured from pdfs of exploration reports. The database contains locations for over 6500 drill holes with geological logs compiled for approximately 4300. There are two resources available: 1. GA Record 2009/031 - A drill hole database for the Paterson airborne electromagnetic (AEM) survey, Western Australia in PDF format 2. Drill hole database ZIP File (includes CSV files suitable for import into GIS, drill hole management or mine planning software)
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Overview of work program between 2007 to early 2009.
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This report describes the geology of the area covered by the SKIPTON 1:100 000 sheet area (7522) in western Victoria. Geomorphology, stratigraphy, structure, metamorphism and economic geology of the area are described. Brief outlines of the regional geological setting and geological history are also presented. The Skipton 1:100 000 sheet area comprises an inlier of early Palaeozoic meta-sediments and intrusives, unconformably overlain by surficial Cainozoic sediments and volcanics. The exposed bedrock forms the westernmost part of the Lachlan Fold Belt. Exposed bedrock comprises Cambrian-Ordovician turbidites of the Warrak and Pyrenees Formations of the Saint Arnaud Group. These units were deformed and regionally metamorphosed to low-grade during the Silurian Benambran deformation and later intruded by Devonian fractionated I-type granite plutons. A transgressive fluviatile to marine sequence of Tertiary rocks overlies older units in the centre and west: units distinguished are the White Hills Gravel, Dilwyn Formation, Heytesbury Group and Moorabool Viaduct Sand. Quaternary units cover most of the sheet area and comprise basalt flows and scoria deposits of the Newer Volcanics, and a range of fluvial and lacustrine sediments including: older alluvial terrace deposits; older alluvial and colluvial deposits; colluvial deposits; swamp and lagoonal deposits; stream alluvial deposits; and lunette deposits. Late Pleistocene aeolian clay, the Windgelli Clay, forms a thin veneer over the most of the Palaeozoic rocks and the Newer Volcanics. The previously worked tungsten, gold, bismuth and silver - bearing vein deposit at Pittong is the only metalliferous occurrence known in SKIPTON. However, the area contains more significant nonmetalliferous deposits including the Pittong clay deposit and deposits of sand, granite, basalt, and scoria.
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This is an article written as a contribution to the IEA GHG R&D Programme's quarterly newsletter (for publication in the June 2009 edition), at the invitation on the IEA GHG R&D Programme. It describes the release of Australia's offshore acreage for greenhouse gas storage.