From 1 - 10 / 2216
  • 1. Blevin et al.:Hydrocarbon prospectivity of the Bight Basin - petroleum systems analysis in a frontier basin 2. Boreham et al : Geochemical Comparisons Between Asphaltites on the Southern Australian Margin and Cretaceous Source Rock Analogues 3. Brown et al: Anomalous Tectonic Subsidence of the Southern Australian Passive Margin: Response to Cretaceous Dynamic Topography or Differential Lithospheric Stretching? 4. Krassay and Totterdell : Seismic stratigraphy of a large, Cretaceous shelf-margin delta complex, offshore southern Australia 5. Ruble et al : Geochemistry and Charge History of a Palaeo-Oil Column: Jerboa-1, Eyre Sub-Basin, Great Australian Bight 6. Struckmeyer et al : Character, Maturity and Distribution of Potential Cretaceous Oil Source Rocks in the Ceduna Sub-Basin, Bight Basin, Great Australian Bight 7. Struckmeyer et al: The role of shale deformation and growth faulting in the Late Cretaceous evolution of the Bight Basin, offshore southern Australia 8. Totterdell et al : A new sequence framework for the Great Australian Bight: starting with a clean slate 9. Totterdell and Bradshaw : The structural framework and tectonic evolution of the Bight Basin 10. Totterdell and Krassay : The role of shale deformation and growth faulting in the Late Cretaceous evolution of the Bight Basin, offshore southern Australia

  • The Tanami Region of northern Australia has emerged over the last two decades as the largest gold producing region in the Northern Territory and one of the top three Palaeoproterozoic gold provinces in the world. Gold occurs in epigenetic quartz veins hosted by metasediments and mafic rocks, and in sulphide-rich replacement zones within iron formation. Many of the deposits are hosted in the hinges of pre-existing anticlines; others are hosted within zones of extensive structural reworking or in highly competent rocks. Limited geochronological data suggests that mineralisation occurred at about 1810 Ma, during a period of extensive granitoid intrusion. Most deposits are associated with D5 faults and shear zones that formed in a sinistral transpressive structural regime with ?1 oriented between ESE-WNW and ENE-WSW. Structures active during D5 include ESE-trending sinistral faults that curve into north-trending reverse faults localised in supracrustal belts between and around granitoid domes. Granitoid intrusions also locally perturbed the stress field, possibly localising structures and deposits. The reverse faults are interpreted as relay faults, and forward modelling indicates that all faults extend into the mid-crust. In areas characterised by the north-trending faults, orebodies also tend to be north-trending, localised in dilational jogs or in fractured, competent rock units. In areas characterised by ESE-trending faults, the orebodies and veins tend to strike broadly east at an angle consistent with tensional fractures opened during ESE-directed transpression. Many of these deposits are hosted by reactive rock units such as carbonaceous siltstone and iron formations. Ore deposition occurred at depths ranging from 1 to 11 km from generally low to moderate salinity carbonic fluids with temperatures from 200 to 430?C, similar to lode gold fluids elsewhere in the world. We interpret these fluids as the product of metamorphic dewatering caused by enhanced heat flow, although it is also possible that the fluids were derived from coeval granitoids. Lead isotope data suggest that the ore fluids had a similar source to the granitoids, possibly a mid-crustal reservoir. Gold deposition is interpreted to be caused by: (1) CO2 effervescence and reduction of ore fluids caused by interaction of the moderately oxidised fluids with carbonaceous siltstone; (2) sulphidation of host iron formations; (3) depressurisation and effervescence of fluids caused by pressure cycling in shear zones; and (4) boiling and fluid mixing at shallow levels. Deposits in the Tanami Region may illustrate the continuum model of lode gold deposition suggested by Groves (1993) for Arch?an districts.

  • Nature and origin of the lithogeochemical halo across section 110 of the Broken Hill Zn-Pb-Ag deposit - Darin Evans, BSc (Hons) thesis, La Trobe University

  • pmd*CRC Project T1 Final Report - Targeting new mineral deposits in western Victoria

  • This study undertook geochemical and isotopic analyses on a wide selection of oil stains from the Thorntonia Limestone, Arthur Creek Formation and the Arrinthrunga Formation and its lower Hagen Member in order to define geochemical inter-relationships between the oils, characterize their source facies and to determine the extent of post-emplacement alteration. Oil stains were collected from BHD-4 and -9, Elkedra-2 and -7A, Hacking-1, MacIntyre-1, M13 PD, NTGS99/1, Owen-2, Randall-1 and Ross-1 over a depth range from 91 to 1065 m and were analysed for bulk, molecular (biomarkers) and carbon isotopic compositions. Gas chromatograph of the saturated hydrocarbon fraction clearly showed biodegradation as the main alteration process in the shallow reservoirs. Unaltered oil stains show a dominance of medium weight n-alkanes with a maximum at n-C15. Biodegradation results in a progressive loss of the lighter hydrocarbons and an accompanying shift in n-alkane maximum to C27, to finally a complete loss of n-alkanes and a large unresolved complex mixture (UCM). The absence of 25-norhopanes suggests a mild level of biodegradation. The low ratio of saturated hydrocarbons/aromatic hydrocarbons (<1, down to 0.42) compared to high ratios (up to 4.35) for oils with abundant lower molecular weight n-alkanes is consistent with biodegradation. However, low ratios are also seen for otherwise pristine oils, suggesting a complex charge history of initial biodegraded and subsequent re-charge with n-alkane-laden oil. The level of biodegradation is not too severe as to overtly affect the distribution of the biomarkers C19 - C26 tricyclic terpanes, C24 tetracyclic terpane, C27 - C35 hopanes, C30 triterpane (gammacerane) and C27- C29 desmethylsteranes, enabling their use in oil-oil correlation and definition of oil populations. To clarify the inter-relationships among the Georgina Basin oil stains multivariate statistical analysis was used involving a wide range of biomarker ratios that are source-specific and environmental indicators. Resulting oil populations showed a strong correlation with their reservoir unit across the basin, suggesting juxtaposition of source and reservoir within the same stratigraphic unit. Oil-source correlation based on biomarker, bulk carbon isotopes of saturated and aromatic hydrocarbons and n-alkane-specific carbon isotopes identified Thorntonia(!), Arthur Creek(!) and Hagen(.) Petroleum Systems. The latter petroleum system is characterised by relatively high gammacerane, indicating an evaporitic depositional environment. Alternatively, an evaporatic organic facies from an Arthur Creek Formation source may have sourced the Hagen Member oil stains, considering that other oil stains reservoired within the Arrinthrunga Formation show a close affinity with oil stains from the Arthur Creek(!) Petroleum System, suggesting an inter-formational Arthur Creek-Hagen Petroleum System at Elkedra-2. An Arthur Creek-Hagen(!) petroleum system is evident at Elkedra-7A while there is a mixed Thorntonia Limestone and Arthur Creek source contribute to the oil stain at Ross-1.

  • Geophysical data were acquired by Australia and Japan from 1994-2002 on the deep-water continental margin offshore from Queen Mary Land, East Antarctica in the general locality of Bruce Rise. This paper presents a regional interpretation of these data and outlines the tectonic history.

  • Solid geology interpretation of the north-western part of the Red River 1:250 000 sheet area. Solid geology based on interpretation of geophysical data.

  • Geoscience Australia and the National Oceans Office carried out a joint project to produce a consistent, high-quality 9 arc second (0.0025° or ~250m at the equator) bathymetric data grid of those parts of the Australian water column jurisdiction lying between 92º E and 172º E and 8 º S and 60º S. As well as the waters adjacent the continent of Australia and Tasmania, the area selected also covers the area of water column jurisdiction surrounding Macquarie Island, and the Australian Territories of Norfolk Island, Christmas Island, and Cocos (Keeling) Islands. The area selected does not include Australia's marine jurisdiction off the Territory of Heard and McDonald Islands and the Australian Antarctic Territory.

  • Controversy continues on the origin of gold deposits in metamorphic belts and the role of magmatism in these regions. We adopt a Minerals Systems approach to analyse and compare some chemical processes related to the formation of major Australian Au-dominated deposits that have been classified as either orogenic or intrusion-related. Fluid inclusion data was compiled from deposits in the Archaean Yilgarn Craton, the Proterozoic Tanami, Pine Creek and Paterson areas, and the Palaeozoic western Lachlan Fold Belt. On a regional scale, and a deposit scale, the dominant lithologies in each area are mafic and felsic igneous rocks, graphite-bearing clastic sediments and banded iron-formations. Significantly, evaporites are absent from all areas. A clear spatial association exists in the Tanami, Telfer and Pine Creek regions with reduced granites. The complied data show that the deposits form over a wide range of temperature-pressure conditions (<200 to >600ºC, <1.4 kbar) and that they involve fluids with broadly similar major chemical components (i.e. H2O+NaCl+CO2± CH4 ± N2). The main difference is that Telfer, Tanami and Pine Creek deposits have higher salinity fluids. Elsewhere, deposits classified as orogenic gold deposits have low salinity fluids (typically <10 wt.% NaCl eq.) with CO2 contents ranging from 10 to 25 mol.% (Ridley & Diamond, 2000), whilst intrusion-related gold deposits may show evidence of higher CO2 and/or high salinity fluid inclusions (Thompson & Newberry, 2000). Processes thought to cause gold precipitation in both types of deposits are fluid-rock interaction (e.g. desulphidation), phase separation, or fluid mixing. We have re-examined the impact of the H2O-NaCl-CO2 system on the nature of the dominant gold precipitation mechanisms at different crustal levels (Fig. 1). The latter infers different roles of chemical (fluid-rock interaction) vs rheological (phase separation and/or fluid mixing) host-rock controls on gold deposition. This also implies that at the site of deposition, similar precipitation mechanisms operate at similar crustal levels for both orogenic and intrusion-related gold deposits