40Ar/39Ar dating of mica-bearing pyrite from thermally overprinted Archean gold deposits

Benthic habitats on the continental shelf are strongly influenced by exposure to the effects of surface ocean waves, and tidal, wind and density driven ocean currents. These processes combine to induce a combined flow bed shear stress upon the seabed which can mobilise sediments or directly influence organisms disturbing the benthic environment. Output from a suite of numerical models predicting these oceanic processes have been utilised to compute the combined flow bed shear stresses over the entire Australian continental shelf for an 8-year period (March 1997- February 2005 inclusive). To quantify the relative influence of extreme or catastrophic combined flow bed shear stress events and more frequent events of smaller magnitude, three methods of classifying the oceanographic levels of exposure are presented: 1. A spectral regionalisation method, 2. A method based on the shape of the probability distribution function, and 3. A method which assesses the balance between the amount of work a stress does on the seabed, and the frequency with which it occurs. Significant relationships occur between the three regionalisation maps indicating seabed exposure to oceanographic processes and physical sediment properties (mean grain size and bulk carbonate content), and water depth, particularly when distinction is made between regions dominated by high-frequency (diurnal or semi-diurnal) events and low-frequency (synoptic or annual) events. It is concluded that both magnitude and frequency of combined-flow bed shear stresses must be considered when characterising the benthic environment. The regionalisation outputs of the Australian continental shelf presented in this study are expected to be of benefit to quantifying exposure of seabed habitats on the continental shelf to oceanographic processes in future habitat classification schemes for marine planning and policy procedures.

Australia's nickel sulfide industry has had a fluctuating history since the discovery in 1966 of massive sulfides at Kambalda in the Eastern Goldfields of Western Australia. Periods of buoyant nickel prices and high demand, speculative exploration, and frenetic investment (the 'nickel boom' years) have been interspersed by protracted periods of relatively depressed metal prices, exploration inactivity, and low discovery rates. Despite this unpredictable evolution, the industry has had a significant impact on the world nickel scene with Australia having a global resource of nickel metal from sulfide ores of not, vert, similar 12.9 Mt, five world-class deposits (> 1 Mt contained Ni), and a production status of number three after Russia and Canada. More than 90% of the nation's known global resources of nickel metal from sulfide sources were discovered during the relative short period of 1966 to 1973. Australia's nickel sulfide deposits are associated with ultramafic and/or mafic igneous rocks in three major geotectonic settings: (1) Archean komatiites emplaced in rift zones of granite-greenstone belts; (2) Precambrian tholeiitic mafic-ultramafic intrusions emplaced in rift zones of Archean cratons and Proterozoic orogens; and (3) hydrothermal-remobilized deposits of various ages and settings. The komatiitic association is economically by far the most important, accounting for more than 95% of the nation's identified nickel sulfide resources. The ages of Australian komatiitic- and tholeiitic-hosted deposits generally correlate with three major global-scale nickel-metallogenic events at not, vert, similar 3000 Ma, not, vert, similar 2700 Ma, and not, vert, similar 1900 Ma. These events are interpreted to correspond to periods of juvenile crustal growth and the development of large volumes of primitive komatiitic and tholeiitic magmas caused by large-scale mantle overturn and mantle plume activities. There is considerable potential for the further discovery of komatiite-hosted deposits in Archean granite-greenstone terranes including both large, and smaller high-grade (5 to 9% Ni) deposits, that may be enriched in PGEs (2 to 5 g/t), especially where the host ultramafic sequences are poorly exposed. Analysis of the major komatiite provinces of the world reveals that fertile komatiitic sequences are generally of late Archean (not, vert, similar 2700 Ma) or Paleoproterozoic (not, vert, similar 1900 Ma) age, have dominantly Al-undepleted (Al2O3/TiO2 = 15 to 25) chemical affinities, and often occur with sulfur-bearing country rocks in dynamic high-magma-flux environments, such as compound sheet flows with internal pathways facies (Kambalda-type) or dunitic compound sheet flow facies (Mt Keith-type). Most Precambrian provinces in Australia, particularly the Proterozoic orogenic belts, contain an abundance of sulfur-saturated tholeiitic mafic ± ultramafic intrusions that have not been fully investigated for their potential to host basal Ni-Cu sulfides (Voisey's Bay-type mineralization). The major exploration challenges for finding these deposits are to determine the pre-deformational geometries and younging directions of the intrusions, and to locate structural depressions in the basal contacts and feeder conduits under cover. Stratabound PGE-Ni-Cu ± Cr deposits hosted by large Archean-Proterozoic layered mafic-ultramafic intrusions (Munni Munni, Panton) of tholeiitic affinity have comparable global nickel resources to many komatiite deposits, but low-grades (< 0.2% Ni). There are also hydrothermal nickel sulfide deposits, including the unusual Avebury deposit in western Tasmania, and some potential for 'Noril'sk-type' Ni-Cu-PGE deposits associated with major flood basaltic provinces in western and northern Australia.

The characterisation of benthic habitats based on their abiotic (physical and chemical) attributes remains poorly defined in the marine environment, but is becoming increasingly central in the development of marine management plans in Australia and elsewhere in the world. The current study tested this link between physical and biological datasets for the southern Gulf of Carpentaria, Australia. The results presented were based on a range of physical factors, including the sediment composition (grain size and carbonate content), sediment mobility, water depth and organic carbon flux, and their relationship to the distribution and diversity of benthic macrofauna was tested. The results reveal the importance of process-based indices, such as sediment mobility, in addition to other environmental factors in defining the distribution of the benthic macrofauna. The distribution of the benthic macrofauna changes gradationally across the south-eastern Gulf, associated with changes in the per cent mud and gravel, the seabed exposure and the water depth. Patterns of diversity also reveal the importance of physical processes such as sediment mobility in defining benthic habitats. The species' environment relationships observed at the small scale of the current study are consistent with broader associations observed for other organisms within the Gulf.

Evaluation of 40Ar-39Ar quartz ages: Implications for fluid inclusion retentivity and determination of initial 40Ar/36Ar values in Proterozoic samples

The purpose of this study is to determine the potential of tsunami inundation from historical and potential submarine mass failures of the NSW coast based on the findings from the October 2006 Continental Slope Survey conducted by GA. The learnings from this study are intended for use by the Australian Tsunami Warning Project and NSW emergency managers.

Presented at the Evolution and metallogenesis of the North Australian Craton Conference, 20-22 June 2006, Alice Springs. The Warumpi Province is an east-trending 1690 Ma - 1600 Ma terrane which extends for >500 km along the southwestern margin of the Arunta Region. It is interpreted to be an exotic terrane that accreted onto the southern margin of the North Australian Craton (NAC) at 1640 Ma (Scrimgeour et al 2005a). The evolution of the Warumpi Province from 1690 Ma to 350 Ma has been constrained through integrated lithological, structural and metamorphic mapping, geochemical and isotopic analysis, and geophysical interpretation (Scrimgeour et al 2005b). The Warumpi Province has been subdivided into three domains that have differing protolith ages and structural and metamorphic histories: the amphibolite facies Haasts Bluff Domain in the south and east, the granulite facies Yaya Domain in the north, and the greenschist facies Kintore Domain in the west. The Warumpi Province can be viewed as greenfields in terms of minerals exploration and has the potential to host a variety of mineralisation styles including base metals (BHT, VMS), IOCG, and diamonds. No modern mineral exploration has been undertaken within the Warumpi Province. <p>Related product:<a href="https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&amp;catno=64764">Evolution and metallogenesis of the North Australian Craton Conference Abstracts</p>

Presented at the Evolution and metallogenesis of the North Australian Craton Conference, 20-22 June 2006, Alice Springs. The Pine Creek Orogen (PCO) is part of the North Australian Craton and is correlated with other Palaeoproterozoic domains of northern Australia. Archaean (>2.5 Ga - 2.7 Ga) granite and metamorphics are overlain by Palaeoproterozoic strata comprising sandstone, mudstone, and minor carbonates and volcanics. Its age is constrained between 2.5 Ga and 1.86 Ga, and the succession is divided into two supergroups. The older Woodcutters Supergroup comprises <2.5 Ga to 2.02 Ga arenites, stromatolitic dolostone, and pyritic carbonaceous shale. The younger Cosmo Supergroup comprises BIF, mudstone, and tuff, succeeded by a monotonous flysch sequence. Zircons from the tuff beds provided an age of 1863 Ma, confirming a major depositional break of about 150 million years. <p>Related product:<a href="https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&amp;catno=64764">Evolution and metallogenesis of the North Australian Craton Conference Abstracts</p>

Noble gas and halogen constraints on mineralizing fluids of metamorphic versus surficial origin: Mt Isa, Australia

Presented at the Evolution and metallogenesis of the North Australian Craton Conference, 20-22 June 2006, Alice Springs. The 2005 Tanami Seismic Collaborative Research Project produced four regional deep seismic reflection traverses, 05GA-T1 through 05GA-T4, totalling 724 line-km. Traverse 05GA-T1, a 354.3 km long northwest-southeast regional transect started in Western Australia and ended in the Northern Territory. It was located close to Tanami Gold's Bald Hills deposits and Newmont's Tanami and The Granites mine sites. This traverse provided cross-strike information on the geometry of the Coomarie and Frankania granite complexes as well as many of the region's fault systems. The traverse ended at the southern edge of the Willowra Gravity Ridge. The cross-traverses, 05GA-T2 (101.8 km long), 05GA-T3 (179.2 km long) and 05GA-T4 (84.4 km long) provide orthogonal three-dimensional control on the geometry of the region's main fault systems. The project objectives are to: - Image the geometry of the main faults; - Determine a deformation sequence for these faults; - Identify any through-going crustal structures; - Determine stratigraphic thicknesses of the Tanami Group and granite body geometries; - Determine relationships of the various stratigraphic packages to controlling structures; - Investigate the relationship of mineralised domains to crustal scale structures; - Identify Archaean basement and its relationship to the overlying Tanami Group stratigraphy; - Investigate the character of the Tanami-Arunta boundary. <p>Related product:<a href="https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&amp;catno=64764">Evolution and metallogenesis of the North Australian Craton Conference Abstracts</p>