Geochronology is the vital fourth dimension for geological knowledge. It provides the temporal framework for understanding and modelling geological processes and rates of change. Incorporating geochronological 'observations and measurements' into interoperable geological data systems is thus a critical pursuit. - Although there are several resources for storing and accessing geochronological data, there is no standard format for exchanging such data among users. Current systems are a mixture of comma-delimited text files, Excel spreadsheets and PDFs that assume prior specialist knowledge and frequently force the user to laboriously - and potentially erroneously - extract the required data manually. - Geoscience Australia and partners are developing a standard data exchange format for geochronological data ('geochronML') within the broader framework of Observations and Measurements and GeoSciML that are an important facet of emerging international geoscience data format standards. - Geochronology analytical processes and resulting data present some challenging issues as a rock "age" is typically not a direct measurement, but rather the interpretation of a statistical amalgam of several measurements chosen with the aid of prior geological knowledge and analytical metadata. The level at which these data need to be exposed to a user varies greatly, even to the same user over the course of a project. GeochronML is also attempting to provide a generic pattern that will support as wide as range of radioisotopic systems as possible. This presentation will discuss developments at Geoscience Australia and the opportunities for collaboration.

The current perception is that rocks of the tonalite-trondhjemite-granodiorite (TTG) suite are the dominant Archaean granite type, that only become less important towards the end of the Archaean with the onset of significant reworking of older continental crust and the production of more potassic granites. This broadly established sequence is, however, oversimplified. Clearly different granites, including high-Mg varieties, alkaline/sub-alkaline granites, and granites with A-type affinities, are also important in the Archaean. More importantly, the increasing recognition of granites with evidence for an enriched-mantle component is providing constraints on both crustal growth mechanisms and on possible tectonic environments. Archaean granites in Australia are best known from the Pilbara and Yilgarn Cratons, Western Australia. Both are examples of Archaean granite-greenstone terrains dominated (>65%) by granites (and orthogneisses). This paper compares and contrasts granites from the central and eastern parts of the Pilbara Craton (CEP) with those from the Eastern part of the Yilgarn Craton (EY). Geological data combined with a compilation of >1200 geochemical analyses are utilised to identify both broad regional granite groups and secular changes within the both regions. Although the cratons exhibit different pre-histories it is notable that they share a somewhat similar pattern of granite evolution. It is clear that the granite types in both the CEP and EY exhibit an overall tendency to become more potassic (higher LILE contents), but also more variable in composition with time. This reflects initial continental crustal growth, and subsequent reworking, to produce an increasingly mature and heterogeneous crust, occurring over a long period (eastern CEP), or very rapidly (EY, western CEP). There is also increasing evidence for enriched-mantle components in post 3.0 Ga magma production, in both the CEP and EY, that probably reflect subduction-environment processes. Finally, it is evident that TTG magmatism, often regarded as a voluminous characteristic of Archaean terrains, is, at the present exposure level, relatively poorly represented in both the Pilbara and Yilgarn cratons, and particularly the latter. Volumetrically, more important in these regions, are granites with a high pressure signature, that fall into a more felsic more potassic (LILE-richer) group, best thought of as transitional TTGs. The presence of such granites can be taken as indicative of the involvement of pre-existing felsic crust at the time of their genesis, unlike more typical TTGs.

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 1:100,000 series of maps for Palaeoproterozoic rocks of the Leichhardt River Fault Trough and Lawn Hill Platform of northern Australia arguably form the best set of regional geological maps in the country. Since their release in the 1970?s and early 1980?s they have been extensively used in mineral exploration programs in the Mount Isa Inlier. In this region one of the most obvious lithostratigraphic correlations is based on the assumed equivalence of two sandstone bodies, 1) the Torpedo Creek Quartzite and 2) the Warrina Park Quartzite. Each sandbody forms the basal lithostratigraphic unit of its respective Group (McNamara and Mount Isa) and outcrops as prominent ridges of white quartzite, readily traceable on aerial photographs. The distinctive outcrop character, map patterns and defined stratigraphic relationships have resulted in this correlation forming the `linch-pin? of lithostratigraphic subdivision in the region. Sequence stratigraphic analysis of the Warrina Park and Torpedo Creek Quartzites, the underlying Surprise Creek Formation and overlying fine-grained transgressive siliciclastics has identified a series of chronostratigraphically significant surfaces (sequence boundaries, transgressive surfaces and maximum flooding surfaces) that collectively demonstrate major miscorrelations in the current lithostratigraphic subdivisions. The study demonstrates the potential for major errors associated with lithostratigraphic subdivisions based on the assumed equivalence and continuity of sandbodies. In the case of the Mt Isa region the miscorrelations have resulted in major unconformities with up to 20 my of missing rock record remaining unrecognised in many areas. The consequences of such miscorrelations are inadequate and inaccurate reconstructions of basin geometry, stratigraphic architecture and the mis-identification of synsedimentary growth faults. Because these reconstructions form the essential prerequisites for predictive mineral system models, aimed at constraining the evolution and flow of metal-bearing fluids through these sediments, these inadequacies are of fundamental importance to the exploration industry. This scenario is well recognised in the petroleum industry, where significant effort is made to correctly understand sandbody geometry particularly in reservoir settings where continuity is critical to production and reservoir engineering. The paper provides an example of sandbody miscorrelations in the Palaeoproterozoic successions of northern Australia. Issues raised in this paper are of major significance to the mineral exploration industry as well as state geological surveys and universities involved in mapping programs and basin reconstructions.

No abstract available

Detrital zircon geochronology of high-grade metasedimentary rocks of the Harts Range Group (HRG) in central Australia indicates that its protoliths were deposited during the Neoproterozoic and Cambrian, coeval with sedimentation in the adjacent Amadeus and Georgina basins of the former Centralian Superbasin. The similar provenances of the HRG and basin successions imply that the HRG is the high-grade metamorphic correlative of the basin sequences. Metamorphic zircon formation at ~477 Ma and ~459 Ma appears to reflect peak and retrograde phases of the Early Ordovician Larapinta Event. Palaeogeographic reconstructions indicate that burial and metamorphism took place beneath an epicratonic sea, associated with the formation of a flat-lying foliation in the lower crust and tholeiitic magmatism, consistent with an extensional setting. Burial of the HRG to ~30 km appears to have taken place predominantly by sedimentary loading within an exceptionally deep intracratonic rift basin, the depth of which rivals those of the deepest basins in Earth history. This indicates that lower crustal high-grade metamorphism need not reflect compressional thickening of the crust.

Proterozoic mafic-ultramafic intrusions of the Arunta Region record a protracted period of magmatism during the evolution of this geologically complex and tectonically long-lived terrane in central Australia. New U?Pb zircon geochronology data highlight the episodic emplacement of the mafic-ultramafic systems. Five major events of dominantly tholeiitic mafic magmatism have been recognised at ~1810 Ma, ~1780 Ma, ~1690 Ma, ~1635 Ma, and ~735?460 Ma, and a sixth event at ~1130 Ma has alkaline-ultramafic affinities. Chondrite- and mantle-normalised multi-element patterns of rocks with melt-like compositions have refined the correlations of the magmatic systems indicated by the geochronological framework. The intrusions occur in proximity to major province-wide faults. Differential movements along these faults provide the opportunity to examine geological processes at crustal depths ranging from ~5 km to 25 km (2 kb to 8 kb: Collins, 2000). The intrusions form large homogeneous mafic granulite bodies, granulite bodies interfolded with felsic units, contaminated gabbroic sheets, stacked sequences of high-level doleritic sills, small pods and laterally extensive sheets of amphibolite, and rare plug-like ultramafic bodies. Chilled and contaminated margins and net-vein pillow complexes resulting from the commingling of mafic and felsic magmas indicate that many of the intrusions crystallised in situ and are not tectonically emplaced fault-bounded bodies. Metamorphic overprints range from granulite to sub-amphibolite facies, with a concentration of high-grade mafic granulite bodies in the central Arunta attributed to deeper levels of crust uplifted north of the Redbank Thrust. Mafic rocks in the intrusions of high-metamorphic grade are dominantly two-pyroxene mafic granulites with high clinopyroxene to orthopyroxene ratios and variable amounts of minor hornblende, biotite, quartz, and garnet. In contrast, lower-grade gabbroic intrusions in the western Arunta contain more orthopyroxene, alkali feldspar, and quartz. LREE-enrichment trends with decreasing 147Sm/144Nd ratios and initial ?Nd values (+1.5 to -4.7) indicate that felsic crustal contamination processes were important during the evolution of the latter intrusions. Incompatible trace element trends show that the Arunta intrusions fall into two major geochemical groups that for the first time highlight geographical differences in mineral prospectivity. 1. A S-rich group (~1200 to 300 ppm S: Andrew Young Hills intrusion, Mount Hay Granulite, Mount Chapple Metamorphics) from the western and central Arunta that has potential for orthomagmatic Ni-Cu-Co sulphide associations. 2. A relatively S-poor (<300 ppm S), slightly more primitive group (Attutra Metagabbro, Mordor Complex) from the eastern Arunta that has greater potential for orthomagmatic PGE-sulphide associations. An assessment of various criteria considered important for the formation of different types of Ni-Cu-Co and PGE deposits suggests that ten of the fifteen complexes investigated have potential for basal segregations of Ni-Cu-Co sulphides (Voisey's Bay-type), but only two appear to be prospective for stratabound PGE-bearing sulphide layers (Merensky Reef-type). Potential exists for polymetallic deposits of hydrothermal Cu-Au ? PGEs ? Ag ? Pb spatially associated with mafic-ultramafic rocks (Riddock Amphibolite). The major challenges for finding Ni-Cu-Co sulphide deposits in prospective intrusions, such as Andrew Young Hills and the Mount Hay Granulite, are to determine the pre-deformational geometries of the bodies and to locate favourable mineralised environments (feeder conduits, embayments in basal contacts) concealed by thin (<120 m) alluvial deposits.

The Tarcoola Goldfield is one of several districts included in the recently-proposed central Gawler gold province.

The Yilgarn online GIS displays a wide range of data including geological datasets, topographical data, geophysical images and seismic traverses, whole rock geochemistry and geochronology samples. It provides an aeromagnetic interpretation (lithology distribution and structure) and a geological interpretation of the Archaean Yilgarn Craton, one of Australia's key mineral provinces. The online GIS also focuses on the Leonora-Neale Transect, by providing a detailed solid geology interpretation of the section. The Yilgarn Craton occurs within Western Australia and covers 10% of the Australian continent. Exposure of bedrock is extremely poor throughout the region and most known mineral deposits occur within or adjacent to sparse outcrop.The online GIS provides a view through the poorly magnetised cover to display bedrock distribution. Interpreted rock types of the region include granite, granitic gneiss, layered intrusions and sills. Interpreted structural elements include lithological banding, faults, and dyke swarms. Also presented are several surrounding and partially overlying Proterozoic and Phanerozoic basins and provinces. The Yilgarn Craton is arguably Australia's premier mineral province, attracting more than half the mineral exploration expenditure, and producing two thirds of the gold and most of the nickel mined in the country. For this reason, the online GIS provides the ability to display all deposits in the region or the option of displaying gold or nickel deposits only. Distribution of mineral deposits can be compared to other data layers including geology, and aeromagnetic domains.