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Detrital zircon from sandstone bodies intersected in three recent exploration wells on the North West Shelf were analysed and dated using the SHRIMP (Sensitive High Resolution Ion Microprobe) at Geoscience Australia to test the technique as a tool for understanding the provenance and sediment transport pathways of reservoir facies in the region. Chevron, Hess and Santos, the operating companies for exploration permits WA- 365-P, WA-390-P and WA-281-P respectively, collected 3-5 kg of cuttings from the wells Guardian-1 and Hijinx-1 (Triassic Mungaroo Formation on the Exmouth Plateau of the Carnarvon Basin) and Burnside-1 (Jurassic Brewster Sands from the Browse Basin). All three wells were drilled in 2009-2010. Samples were prepared at Geoscience Australia with 70-80 zircon grains randomly selected for analysis following standard data acquisition and processing procedures to provide a statistically meaningful representation of detrital ages in each sample.

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Multiple new geophysical (airborne electromagnetics, borehole gamma and NMR), geospatial (LiDAR), sonic drilling and geochronological datasets have been used to map and resolve the nature of Quaternary fluvial deposition in the Lower Darling Valley (LDV), NSW. The LDV Cenozoic sequence contains Paleogene and Neogene shallow marine, fluvial and shoreline sediments overlain by Quaternary lacustrine, aeolian and fluvial units. In the LDV Quaternary fluvial sequence, multiple scroll-plain tracts are incised into higher, older more featureless floodplains. Prior to this study, these were respectively correlated to the Coonambidgal and Shepparton Formations of the Riverine Plain in the eastern Murray Basin and associated with the subsequently discarded Prior Stream/Ancestral River chronosequence of different climatically controlled depositional styles. In contrast to that proposition, we ascribe all LDV Quaternary fluvial deposition to lateral-migration depositional phases of one style, though with more variable stream discharges and channel and meander-scroll dimensions. Successively higher overbank-mud deposition through time obscures scroll traces and provides the main ongoing morphologic difference. A new morphostratigraphic unit, the Menindee Formation, refers to the mostly older and higher floodplain sediments, where scroll traces are obscured by overbank mud which continues to be deposited by the highest modern floods. Younger inset scroll-plain tracts, with visible scroll-plain traces, are still referred to the Coonambidgal Formation. Another new stratigraphic unit, the Willotia beds, refers to even older fluvial sediments, now above modern floodplain levels and mostly covered by aeolian sediments. This work provides important insights into hydrogeological processes and the nature of Australian Quaternary fluvial deposition.

Aspects of the tectonic event history of Palaeo- to Mesoproterozoic Australia are recorded by metasedimentary basins in the Mt Isa, Etheridge, and Coen Provinces in northern Australia and in the Curnamona Province of southern Australia. Based on similarities in depositional ages and stratigrapy, these basins are interpreted to have been deposited in a tectonically-linked basin system. However, in deformed and metamorphosed basins, field correlations are difficult, making independent data, such as Nd isotope data and detrital zircon U-Pb geochronology essential to discriminate tectonic setting and sediment provenance.

As part of the National Geoscience Agreement with the Northern Territory Geological Survey, Geoscience Australia is evaluating the geological setting of the mafic-ultramafic intrusions in the Arunta Province. The major aims of this study are to constrain the various mafic-ultramafic magmatic systems within the event chronology of the Arunta, and to provide a geoscientific framework for assessing the resource potential of the intrusions. SHRIMP U-Pb geochronology results of thirteen mafic-ultramafic bodies have highligted the episodic emplacement of the Arunta intrusions during the Proterozoic. Five major magmatic events from 1810 Ma to 1130 Ma have been identified. Geochemical discrimination diagrams show that the Arunta intrusions fall into two major geochemical groups that highlight geographical differences in prospectivity for Ni-Cu and platinum-group element mineralisation.

This volume incorporates the Abstracts of papers presented at the BHEI annual meeting, May 2000.

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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