From 1 - 10 / 269
  • Deep seismic reflection profiles provide a unique view of the architecture of the crust and upper mantle, leading to inferences regarding its geodynamic evolution. The Eastern Goldfields Superterrane (EGST) in Western Australia is a classic Archaean granite-greenstone terrane that hosts some of the world's best gold and nickel deposits. Defining the geodynamics and its resultant architecture are two critical components in understanding these major mineral systems. Two major across strike seismic transects totalling 614 km (91EGF01 and 01AGSNY1) have been acquired, and these are augmented by numerous shorter seismic traverses. The result is a comprehensive grid of traverses that have been integrated with the geology and the potential field geophysics to create a series of 3D models (maps). The post seismic paradigm for interpreting the folds (domes) and faults was one of thrust duplexing in an overall cyclic contractional-extensional tectonic setting. One of the features of the general map patterns, preservation of stratigraphy, the metamorphic isograds and exhumation of high-grade rocks, and the meso- to macro-scale structures suggests that extension played a more important role in creating the essential architecture of the terrane (and hence the seismic fabric) that initially thought. A key moment in the importance of interpreting extension in terms of the seismic data became apparent as a result of the reprocessing of the upper 2 seconds of the data. Careful velocity analysis revealed a hitherto unknown fabric to the seismic events which could be traced into a well-exposed mine developed during extensional tectonics. Tracing these seismic events to depth changed the thinking of the entire seismic line, which better matched the emerging new geological understanding of the region. The result of this geological-geophysical integration (especially the targeted re-processing) has been an improved systems understanding of this most endowed piece of crust. Similar seismic patterns are observed in the Superior Province of Canada, although they are traditionally described in terms of a contractional tectonic mode. Careful reprocessing of the seismic data, together with a reappraisal of the geology may also similarly change paradigms in Canada?

  • The oil and gas exploration and development industry is a significant Australian industry. In 2000 the value of oil and gas produced was $10.5 billion. This meant that Australia remained more than self sufficient in petroleum, contributing to economic activity and avoiding the balance of payment pressure that importing that amount of petroleum would represent. There is thus an incentive to maintain a healthy petroleum exploration and production industry. R&D for the upstream petroleum industry however, needs to be targeted to the requirements of the differing facets of the industry under the diverse conditions in which the industry operates or could operate. These conditions include changes in oil prices and perceptions of prospectivity, uncertain access to gas markets and the effects of international agreements such as the United Nations Framework Convention on Climate Change. Different petroleum companies also have differing exploration and production portfolios and different needs. Petroleum service industry companies try to meet industry?s needs. Governments have their own goals in promoting and regulating the industry and derive considerable revenues for economic rent applied to reserves held by the Crown. In the above context, a range of scenarios was considered in a planning process prioritising future needs for petroleum R&D in Australia. In this context two groups of senior petroleum industry, research and government representatives carried out scenario planning workshops in 1998 and 1999 to define scenarios and associated R&D priorities to assist in planning and identifying opportunities for petroleum R&D. The results of this study highlight core areas of R&D that are required under most of the scenarios. These are considered highest priority and high priority areas. Given the long time frame (in the order of 10 years) needed to develop and maintain R&D capability, this highlights for government, academia and industry the sustained effort needed for development and maintenance of capability particularly in these core areas of R&D. In 1998 and 1999 when the workshops that formed the basis of this study were undertaken, Australia was arguably in the `low oil and gas price scenario?. This scenario puts an onus on government to support regional studies to promote exploration and most priority petroleum R&D. Under this scenario support from industry is substantially aimed at reducing cost. Although oil prices have increased, coincident increases in stock market pressures for competitive profits from the industry has arguably left the industry in 2001 still in the low oil and gas price scenario. Thus there remains a strong need to maintain a local petroleum R&D capability to meet Australia?s needs.

  • The world class Callie lode gold mine is one of several gold deposits located at the Dead Bullock Soak goldfield in the Northern Territory Tanami Desert, about 550km northwest of Alice Springs. Its high grade and high tonnage make it an important system to understand in terms of regional mineralising processes. The aim of this research was to elucidate the important factors contributing to the formation of such a large deposit, and what features might be important for refining exploration strategies in the region.

  • Most of the rocks of the Eastern Succession of the Mt Isa inlier described in this report were formed between 1760 and 1500 Ma, post-dating the Archaean and early Palaeoproterozoic history. The geodynamic settings of both the depositional and orogenic parts of this history have been extensively debated in the past and are still unresolved at present. Progress has been made in this report through an examination of the isotopic signatures of crustal blocks comprising the basement to the cover sequences, by analysing the geodynamic implications of mafic rocks and the voluminous late-orogenic felsic magmatism, and by a more detailed examination of the tectonothermal evolution.

  • This Bulletin summarises the results of regional mapping by teams of the Bureau of Mineral Resources and the Geological Survey of Queensland from 1961 to 1967 over an area of some 67 000 km2 near Townsville. Small areas of high-grade metamorphics may be Precarnbrian, or may be correlatives of the oldest dated rocks (Late Cambrian to Early Ordovician). These early strata occupied a major east-west basin which was destroyed by orogeny and granitic intrusion in Middle Ordovician time. A further period of granitic intrusion consolidated the Lolworth-Ravenswood Block as a major east-west structural high. Of the Palaeozoic sedimentary basins, the Burdekin Basin received sediments from Givetian to Tournaisian times. Ranging in tectonic activity between a mildly unstable shelf and a yoked intracratonic basin, it presented an alternation of marine and continental conditions as it gradually expanded northwards. South of the Lolworth-Ravenswood Block, a miogeosyncline formed in the Middle Devonian. In the Tabberabberan Orogeny a geanticline rose in the geosynclinal belt, and the Drummond Basin formed on its western side. This transverse basin received sediments from Late Devonian to Middle Carboniferous times in three well-marked cycles, each beginning with torrential sediments and ending with mature ones. In its later life, it possibly emptied into the Burdekin Basin. The Broken River Embayment received sediments more or less continuously from Silurian to Carboniferous times, but only the lowest and highest units occur in the map area. The lowest units are shelf and trough sediments, the highest is shallow-marine and lacustrine. At the latest stage in its development the Embayment reached its greatest extension to the southeast and may have connected with the Burdekin Basin. The Late Devonian to Early Carboniferous sediments and volcanics near the coast represent the northern extremity of a basin probably connected with the Yarrol Basin. These basins were destroyed in the Kanimblan Orogeny, and from Late Carboniferous to Early Permian times the area was dominated by igneous activity. The Bowen Basin developed in the Permian volcanic episode, and passed through a series of marine incursions to a continental environment. Local coastal conditions during the first marine incursion produced the Collinsville Coal Measures. Possible correlatives of Bowen Basin units are widespread, although some of the relationships are tenuous. Triassic orogeny ended deposition in the Bowen Basin, and was followed in the south coastal area by a period of igneous activity in the Early Cretaceous. Quiet conditions followed, and by the end of the Cretaceous the area was topographically mature. In the early Cainozoic some earth movement continued, producing the Hillsborough Basin and resulting in erosion of much Triassic sandstone. The mature topography re-established by mid-Tertiary was the base for the subsequent lateritic episode, interrupted by further erosion and deposition. The evolution of the area was completed by Cainozoic volcanism followed by slight erosion. The physiography of the coastal area is dominated by corridors between high ranges. Faulting can be reasonably suspected as a cause, and in some cases there is some evidence. The inland area is occupied mainly by the Burdekin catchment, which developed its present form by movements in the Cainozoic but still retains some northeasterly trends from Palaeozoic structures.