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.

Legacy product - no abstract available

No abstract available

Poorly exposed Paleoproterozoic sandstones and siltstones of the Killi Killi Formation record developement of a large turbidite complex. Killi Killi Formation sediments were eroded from the uplifted ~1860 Ma Nimbuwah and Hooper Orogens as indicated by detrital zircons with sediment deposition at ~1840 Ma. Facies analysis, isopach maps and detrital zircon populations, combined with Sm-Nd data from the Tanami region and Halls Creek Orogen, confirm the previously suggested correlation of the Paleoproterozoic successions in the Eastern zone of the Halls Creek Orogen and the Tanami region. Detrital zircons from the Aileron Province suggest the turbidite complex extends into the Arunta region, however, high metamorphic grade precludes direct facies comparisons in the Arunta region. Portions of the turbidite complex in the Tanami region are dominated by mudstones, consisting of low-density turbidites and associated hemipelagites, that potentially acted as a redox boundary to gold-bearing fluid. Gold prospectivity in turbiditic systems is increased within these mudstone sequences with the potential for further gold discoveries.

The North Australia Project (NAP) was initiated in July 2000 following negotiations between the Northern Territory Geological Survey (NTGS) and the Australian Geological Survey Organisation (now Geoscience Australia). The NAP was a joint project undertaking geoscientific studies in the Tanami, Arunta and Tennant regions of central Australia to help encourage mineral exploration. The project continued until June 2004, when the Geological Survey of Western Australia (GSWA) began regional data acquisition in the western Tanami region. In July 2004, the Tanami Project, a joint initiative between Geoscience Australia, NTGS, and GSWA to increase mineral exploration replaced the NAP. Although NTGS and GSWA have continued interests in the Tanami and Arunta regions, the collaborative Tanami Project will finish in December 2006. The purpose of this product is to provide reports and datasets summarising the results of the project at this time. The only major products not included in this DVD are the results of the Tanami seismic survey and modifications to the on-line 3D models required by the seismic results. These will be released separately, beginning in August 2006. As this report is intended to be as up-to-date as possible, it refers to a number of manuscripts that are either in press or in preparation. Although these manuscripts cannot be provided here, much of the data upon which the conclusions are based are presented in summary, either in abstracts, presentations, or data tables.

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New SHRIMP U/Pb zircon ages of 472.2 ± 5.8 Ma and 470.4 ± 6.1 Ma are presented for the age of peak metamorphism of Barrovian migmatite units. Magmatic advection is thought to have provided significant heat for the Barrovian metamorphism. Published U/Pb emplacement ages for Grampian-age igneous units of Scotland and Ireland define a minimum age range of c. 473.5 to c. 470 Ma for Barrovian metamorphic heating. The new U/Pb ages are consistent with attainment of peak Barrovian metamorphic temperatures during Grampian magmatism. U/Pb-calibrated 40Ar/39Ar ages for white mica from the Barrovian metamorphic series vary systematically with increasing metamorphic grade, between c. 465 Ma for the biotite zone and c. 461 Ma for the sillimanite zone. Microstructural work on the timing of metamorphism in the Barrovian metamorphic series has shown that peak metamorphism occurred progressively later with increasing peak-metamorphic grade. Younging metamorphic age with increasing metamorphic grade across the Barrovian metamorphic series requires that the sequence was cooled in the lower-grade regions while thermal activity continued in the high-grade regions. This thermal scenario is well explained by the presence of a large-scale extensional detachment that actively cooled units from above while the Barrovian metamorphic heating continued at greater depth in the footwall. The spatio-temporal thermal pattern recorded by the Barrovian metamorphic series is consistent with regional metamorphism during crustal extension.

The Nolans Bore deposit, located in the Aileron Province of south-central Northern Territory, is an emerging Australian rare earth development. It consists of steeply northwest dipping apatite veins hosted by ~1806 Ma granite gneiss. A preliminary ~1240 Ma U-Pb age for apatite may correspond to a major global period of alkalic magmatism between 1300 and 1130 Ma, including emplacement of the Bayan Obo deposit in China. Low ?Nd and 87Sr/86Sr in the mineralisation is reminiscent of modern EM-1 ocean island basalts and may indicate a link to carbonatitic magmatism. Oxygen isotope thermometry indicates a mineralisation temperature of 410°C, with '18Ofluid of ~8.0'. Fertilisation of the mantle to produce the EM-1 source may relate to subduction associated with convergence along the southern margin of the North Australian Craton.

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.