The magnitude of systematic uncertainties inherent in comparisons of Proterozoic 40Ar/39Ar- and U-Pb-based ages is illustrated via a consideration of age constraints on two contrasting styles of Palaeoproterozoic mineralization in northern Australia. Published 40Ar/39Ar ages for Au-Cu-Bi-mineralization in the Tennant Creek region range from1825 to 1829 Ma, apparently younger than the timing of deformation bracketed by 207Pb/206Pb zircon ages of igneous rocks at ~1850 Ma. Despite this apparent age offset, propagation of systematic uncertainties in the 40Ar/39Ar ages shows that they are indistinguishable from the ~1850Ma zircon ages. Recalculation using revised estimates of the 40K decay constant and age of the 40Ar/39Ar standard shifts the 40Ar/39Ar ages to 1847-1851 Ma, in excellent agreement with 207Pb/206Pb zircon ages from Tennant Supersuite igneous rocks and with local geological constraints. To the south of Tennant Creek, in the Davenport Ranges, numerous smallWprospects have been interpreted to be coeval with post-tectonic granites of the Devils Suite at ~1710-1720 Ma. New 40Ar/39Ar ages from muscovite selvages on wolframite-bearing veins range from 1697 to 1703 Ma. These ages shift to 1711 to 1717Ma when recalculated using revised estimates for 40K decay constant and age of standard material, bringing them into agreement with existing 207Pb/206Pb zircon ages for Devils Suite granitoids, and consistent with field and geochemical interpretations. These examples highlight the importance of considering systematic sources of uncertainty when comparing radiometric ages determined via different isotopic methods, particularly in the Proterozoic and Archean parts of the timescale. Ongoingwork to calibrate the 40Ar/39Ar and U-Pb-based timescales will further enhance the application of multiple isotopic methods to constrain geological processes.

Uranium mineralization at Coronation Hill is associated with rhyolitic rocks of Upper Proterozoic and sediments of Lower Proterozoic Age. The mineralization at and near the surface is in the form of Autunite and Torbernite; it occurs in a zone of strong fracturing, which effects rocks of both Lower and Upper Proterozoic age. Rubble and soil covers most of the area of interest at Coronation Hill and openings available to date do not allow a full appreciation of the geology of the prospect. A preliminary programme of diamond drilling is recommended to test and prospect and further testing should be guided by such information as is obtained from this drilling. The discovery of uranium mineralization in volcanic rocks of Upper Proterozoic age at Coronation Hill opens up an entirely new province for exploration for uranium in the Katherine-Darwin region of the Northern Territory. The linear belt of fracturing, the South Alligator Fault Zone, on which the Coronation Hill is situated, suggests an obvious zone to which future prospecting effort should be guided.

Geophysical surveys of the magnetite deposits of Australian Magnetite Pty. Ltd. at Gulgong were made by the Bureau in 1952 and 1953, and revealed that the Tallawang deposit was the most important one. The present report gives the results of a detailed magnetic survey which was made over this deposit in August, 1953. Results show that three concentrations of very strongly magnetic material exist within the Tallawang deposit. The southern concentration is unlikely to contain considerable reserves beyond those in sight. The central concentration has been partly worked and could yield reserves of ore from the west wall of the quarry. The northern concentration, which has not been worked, could yield limited reserves. It is shown that the deposit, as a whole, pitches northwards. Some exploratory drilling is recommended on each of the three concentrations.

Sediments of the Brock's Creek Group and of the Phillips Creek Formation, and volcanics of the Edith River Formation were prospected with carborne radiometric equipment. A comparatively high background count was recorded in the Edith River Volcanics, but no significant radiometric anomaly was found. A geological party prospected ten shear zones south east of the Edith Siding, including a cupriferous one, and a strongly fractured belt near the granite contact. No radiometric anomaly was found. Future prospecting should be directed towards major faults within the sediments.

Gold deposits in the Archaean Eastern Goldfields Province in Western Australia were deposited in greenstone supracrustal rocks by fluids migrating up crustal scale fault zones. Regional ENE-WSW D2 shortening of the supracrustals was delaminated from lower crustal shortening at a regional sub-horizontal detachment surface below the base of the greenstones. Major gold deposits lie close to D3 strike slip faults that extend through the detachment surface and into the middle to lower crust. The detachment originally formed at a depth corresponding to the brittle/ductile transition. In orogenic systems the brittle/ductile transition correlates with a low permeability pressure seal separating hydrostatic fluid pressure gradients in the upper crust from suprahydrostatic fluid pressure gradients in the lower crust. Fluid pressures near the base of the low permeability pressure-seal can intermittently exceed lithostatic pressures, leading to tensile strength failure and fluid filled extension fractures. In orogens, the extension fractures will be sub-horizontal, have poor vertical connectivity and become fluids reservoirs. This would create an ideal depth to nucleate a regional detachment surface in a deforming crust. Seismic bright spots at ~6s TWT in Tibet and the western United States are probable examples. If the low permeability pressure seal is subsequently broken by a through going fault, the fluids will be drained into the upper crust. Large, deeply penetrating faults are therefore ideal for focussing fluid flow into the upper crust.

Y4 Presentation of introduction to Targeting and the terrane-scale targeting (presented to sponsors at the final PDT Meeting in Kalgoorie May 2007)

Initial 'straw man' used in the targeting exercise and developed from earlier Y4 (PDT) Meeting in May 2007

Australian Proterozoic Mineralising events on Australian Proterozoic Regions base, 1:4 000 000 July 2007 Version

<p>In February 2009, Geoscience Australia released a new national radiometric map and dataset. This improved radiometric map, shows the distribution of potassium (K), uranium (U) and thorium (Th) at the Earth's surface as measured using the airborne gamma-ray spectrometric method. The gridded data that underpin the map cover over 80 % of the Australian continent at 100m spatial resolution. These data were calibrated to be consistent with an Australian radioelement datum based on an Australia wide airborne geophysical survey (AWAGS2) completed in 2008, which was conducted under the Australian Government funded Onshore Energy Security Initiative. AWAGS provides the baseline for stitching and levelling of all publicly available airborne radiometric (and magnetic) surveys across Australia, which are of a range of ages and qualities, and for future airborne surveys. The new grids of K, eTh and eU can be used to reliably compare the radiometric signatures observed over different parts of Australia, enabling the assessment of key mineralogical and geochemical properties of bedrock and regolith materials from different geological provinces and regions across the continent. These data support a range of different applications including exploration, geological mapping, geomorphological studies and environmental mapping. </p> <p>Presented at AusIMM Uranium Conference, Darwin, 10 June 2009.</p>

Plans for the National Geochemical Survey of Australia were presented to the geoscience agencies of all States and the Northern Territory in early 2007. The presentation entitled National Geochemical Survey of Australia: outline of a new proposal was given to: Primary Industries and Resources South Australia in Adelaide on 20 February 2007 Geological Survey of Western Australia in Perth on 21 February 2007 New South Wales Department of Primary Industries in Maitland on 29 March 2007 Geological Survey of Queensland in Brisbane on 2 May 2007 Northern Territory Geological Survey in Darwin on 3 May 2007 Minerals Resources Tasmania in Hobart on 16 May 2007 GeoScience Victoria in Melbourne on 17 May 2007