Subduction of oceanic crust at an unusually low angle (flat-subduction) has been proposed as a general model for the growth of continental crust older than about 2.5 Ga. At modern zones of flat subduction, magmatic additions to new crust come from partial melting of both the subducting oceanic crust (slab) and the thin wedge of mantle above the slab. Evidence for both a slab and wedge source is commonly preserved in some, but not all, late Archaean (3.0-2.5 Ga) terrains, but we find little evidence that a mantle wedge contributed to early Archaean (>3.0 Ga) crustal growth. In contrast to most modern terrains and some late-Archaean terrains, early Archaean continental crust evolved through direct melting of thick mafic crust.

The northern Pedirka Basin in the Northern Territory is sparsely explored compared with its southern counterpart in South Australia. Only seven wells and 2500 km of seismic data occur over a prospective area of 73,000 km2. In this basin three petroleum systems have potential related to important source intervals in the basal Jurassic (Poolowanna Formation), Triassic (Peera Peera Formation) and Early Permian (Purni Formation). They are variably developed in three prospective depocentres, the Eringa Trough, the Madigan Trough and the northern Poolowanna Trough. New basin modelling techniques indicate oil and gas expulsion responded to increasing early Late Cretaceous temperatures in part due to sediment loading (Winton Formation). Using a composite kinetic model, oil and gas expulsion from coal rich source rocks were largely coincident at this time when source rocks entered the wet gas maturation window. The Purni Formation coals provide the richest source rocks and equate to the lower Patchawarra Formation in the Cooper Basin. Widespread well intersections indicate that glacial outwash sandstones at the base of the Purni Formation, herein referred to as the Tirrawarra Sandstone, have regional extent and are an important exploration target as well as providing a direct correlation with the prolific Patchawarra/ Tirrawarra petroleum system found in the Cooper Basin. An integrated investigation into the hydrocarbon charge and migration history of Colson-1 was carried out using CSIRO Petroleum's OMI (Oil Migration Intervals), QGF (Quantitative Grain Fluorescence) and GOI (Grains with Oil Inclusions) technologies. In the basal Jurassic Poolowanna Formation between 1984 and 2054 mRT, elevated QGF intensities, evidence of oil inclusions and abundant fluorescencing material trapped in quartz grains and low displacement pressure measurements collectively indicate the presence of palaeo-oil and gas accumulation over this 70 m interval. This is consistent with the current oil show indications such as staining, cut fluorescence, mud gas and surface solvent extraction within this reservoir interval. Multiple hydrocarbon migration pathways are also indicated in sandstones of the lower Algebuckina Sandstone, basal Poolowanna Formation and Tirrawarra Sandstone. This is a significant upgrade in hydrocarbon prospectivity, given previous perceptions of relatively poor quality and largely immature source rocks in the Basin. Conventional structural targets are numerous but the timing of hydrocarbon expulsion dictates that those with an ?older? drape and compaction component will be more prospective than those dominated by Tertiary reactivation which may have resulted in remigration or leakage. Preference should also apply to those structures adjacent to generative source ?kitchens? on relatively short migration pathways. Early formed Tirrawarra Sandstone and Poolowanna Formation stratigraphic traps are also attractive targets. Cyclic sedimentation in the Poolowanna Formation results in two upward fining cycles which compartmentalise the sequence into two reservoir ? seal configurations. Basal fluvial sandstone reservoirs grade upwards into topset shale/ coal lithologies which form effective semi-regional seals. Onlap of the basal cycle onto the Late Triassic unconformity offers opportunities for stratigraphic entrapment.

No abstract available

Abstract: The multiply-deformed (D1-D3) Palaeoproterozoic Willyama Supergroup in south-central Australia incorporates upper and lower ca. 1700 Ma metasedimentary sequences with contrasting early tectonothermal histories that invite comparisons with the metamorphic core complexes and younger extensional orogens of western North America and Europe. A detachment surface of D1 age separating these two sequences has the deduced geometry of an extensional shear zone, juxtaposing rocks subjected to bimodal magmatism, sillimanite to granulite grade migmatisation, and Na-Fe metasomatism against a less intensely metamorphosed upper plate lacking both migmatites and bimodal magmatism. Syn-extensional metamorphism took place under low pressure-high temperature conditions, producing regionally extensive andalusite- and sillimanite-bearing mineral assemblages before further high grade metamorphism accompanying D2 recumbent folding and crustal thickening. D2 folding locally inverted the original D1 thermal structure so that sillimanite-grade lower plate rocks now lie structurally above andalusite-grade rocks of the upper plate, rendering recognition of the original detachment surface and associated thermal structure difficult. U/Pb dating of synextensional metabasites intruded into lower plate rocks just below the detachment surface indicate that extension and related bimodal magmatism peaked around 1690-1670 Ma. This is 70-90 m.y. earlier than some previously published 1600-1590 Ma ages for the onset of regional deformation and related low P-high T metamorphism and which we equate with events that overprinted the first phase of deformation and metamorphism at 1690-1670 Ma. A regionally extensive redox boundary associated with the detachment surface served as the locus for fluid flow and Pb-Zn mineralisation.

The 42 element, 1190 sample Mobile Metal Ion subset of the National Geochemical Survey of Australia database was used to develop and illustrate the concept of Degree of Geochemical Similarity of soil samples. Element concentrations were unified to parts per million units and log(10)-transformed. The degree of similarity of pairs of samples of known provenance in the Yilgarn Craton were obtained using least squares linear regression analysis and demonstrated that the method successfully assessed the degree of similarity of soils related to granitoid and greenstone lithologies. Exploratory Data Analysis symbol maps of all remaining samples in the database against various reference samples were used to obtain correlation maps for not only granitoid- and greenstone-related soil types, but also to distinguish between for example samples derived from marine vs regolith carbonate. Likewise, the distribution of soil samples having a geochemical fingerprint similar to mineralised provinces (e.g., Mt Isa) can be mapped and this can be used as a first order prospection tool. Sensitivity analysis confirmed the method to produce robust results without undue influence from either single elements with anomalous concentrations or elements with a high proportion of censored values.

The Bight Basin contains a thick, prospective Jurassic-Cretaceous sedimentary section. Recent work by both Geoscience Australia and the petroleum exploration industry has increased our understanding of the structural and stratigraphic development, and the range of opportunities available in this frontier basin. The presence of thick deltaic units and indications of active petroleum systems further enhance its prospectivity. Although the basin is being tested by new drilling it remains one of the least explored passive margins in the world, and will require much more exploration to fully assess its potential.

No abstract available

The potential for using a single high precision atmospheric station for detecting CO2 leaks has been investigated using a variety of statistical approaches. Geoscience Australia and CSIRO Marine and Atmospheric Research installed an atmospheric monitoring station, Arcturus, in the Bowen Basin, Australia, in 2010 and have collected over 3 years' worth of atmospheric concentration measurements. The facility is designed as a prototype remote baseline monitoring station that could be deployed in areas targeted for commercial scale geological storage of carbon dioxide. Two Picarro gas analysers are deployed in the station to continuously monitor CO2, CH4 and CO2 isotopes. An automated weather station and an eddy covariance flux tower have also been installed at the site. Atmospheric CO2 perturbations, from simulated leaks, have been modelled to determine the minimum statistically significant emissions that can be detected above background concentrations at Arcturus. CO2 leakage was simulated from January to December (2011) using a 3D-coupled prognostic meteorological and pollutant dispersion model (TAPM). Simulations were conducted for various locations, emission rates and distances (1-10 km) from the station. The simulated leaks were simulated using an area source (100 m x 100 m) and a point source located in the optimum wind direction (SSE), which showed the largest perturbation. To better understand the observed CO2 signal, a statistical model combining both a regression and time series model was constructed. The regression model is a time dependent generalised additive model relating the CO2 to other observed atmospheric variables (e.g. wind speed, temperature, humidity). It accounts for seasonal trends through the inclusion of dummy variables. The time series model is based on a seasonal auto-regressive integrated moving average (ARIMA) model, but with the additional complexity of allowing auto-regressive relationships to depend on the time of day. A non-parametric goodness of fit approach using the Kolmogorov-Smirnoff (KS) test was then used to test whether simulated perturbations can be detected against the modelled expected value of the background for certain hours of the day and for particular seasons. The developed regression model allows us to pre-whiten the CO2 time series. Pre-whitening reduces both the variance and skew of the marginal distribution of the signal. This improves the power of the Kolmogorov-Smirnoff (KS) test when attempting to detect simulated perturbations against the background signal. The KS test calculates the probability that the modelled leak perturbation could be caused by natural variation in the background. For hours between 10am and 2pm in the winter of 2011, minimum detectable leaks located 1km from the measurement station improve from 44 to 22 tpd for an area source and 33 to 14 tpd for a point source at a p-value of 0.05. These are very large leaks located only 1 km from the station. Additionally, this approach results in a high false alarm rate of 56%. An alternative p-value could be chosen to reduce the false alarm rate but the overall conclusion is the same. A long term, single measurement station monitoring program that is unconstrained by prior information on possible leaks, and based on detection of perturbations of CO2 alone due to leakage above a (noisy) background signal, is likely to take one or more years to detect leaks of the order of 10kt p.a.

The Nifty Cu deposit, hosted in Neoproterozoic shales and dolomitic mudstones of the Paleo-Neoproterozoic Paterson Province, Western Australia, has features that have led both syngenetic (pre-tectonic) and syn-tectonic genetic models. Here we report radiogenic isotope data (Sm-Nd, Rb-Sr, U-Pb) for vein apatite coeval with Cu minerals which provide absolute age constraints on apatite deposition, and therefore Cu mineralization. Fluorapatites from two structurally and mineralogically similar vein sets have similar 87Sr/86Sr (0.7213-0.7238) and 208Pb/204Pb (37.90-38.04) ratios, unusual roof-shaped REE patterns and very high Sm/Nd ratios. Sm-Nd isotope data for apatite samples from the two veins yield a pooled age of 791 ± 42 Ma (-Ndi = +0.6 ± 3.7). Pb isotope data for apatites from one of the samples are U-rich and, together with galena, yield a 207Pb-206Pb isochron age 822±23 Ma, within error of the Sm-Nd age. These mineral ages, combined with independent age constraints on the sedimentary host rocks, and textural observations suggest early- to syn-tectonic emplacement of Cu mineralization in the period 850-790 Ma. We suggest that mineralization occurred during the early stages of basin inversion, the Miles Orogeny. Relatively high -Nd values in vein apatite suggest that ore fluids are derived from, or reacted with, high--Nd mafic igneous rocks, as represented by a suite of gabbros and basalts (830-815 Ma) emplaced into the Neoproterozoic sequence. By contrast, 87Sr/86Sr ratios (~0.723) imply extensive re-equilibration of ore fluids with local sedimentary host rocks. A possible Cu source in mafic igneous rocks is consistent with inferred Cu sources for other sediment-hosted Cu deposits; however, it is unclear if the ore fluids are modified ortho-magmatic fluids or if Cu was leached from mafic source rocks by basinal fluids.

The 42 element, 1190 sample Mobile Metal Ion subset of the National Geochemical Survey of Australia database was used to develop and illustrate the concept of Degree of Geochemical Similarity of soil samples. Element concentrations were unified to parts per million units and log(10)-transformed. The degree of similarity of pairs of samples of known provenance in the Yilgarn Craton were obtained using least squares linear regression analysis and demonstrated that the method successfully assessed the degree of similarity of soils related to granitoid and greenstone lithologies. Exploratory Data Analysis symbol maps of all remaining samples in the database against various reference samples were used to obtain correlation maps for not only granitoid- and greenstone-related soil types, but also to distinguish between for example samples derived from marine vs regolith carbonate. Likewise, the distribution of soil samples having a geochemical fingerprint similar to mineralised provinces (e.g., Mt Isa) can be mapped and this can be used as a first order prospection tool. Sensitivity analysis confirmed the method to produce robust results without undue influence from either single elements with anomalous concentrations or elements with a high proportion of censored values.