Oil and gas discoveries in Australia's offshore basins are concentrated on the North West Shelf (Northern Carnarvon, Browse and Bonaparte basins) and Bass Strait (Gippsland, Otway and Bass basins). While discoveries have been made in a few regions outside these areas (e.g. Perth Basin), a large proportion of Australia's offshore basins remain exploration frontiers. However, the decline in oil production from the North West Shelf and Bass Strait basins since 2000 has led to an increasing exploration interest in the frontier basins. In order to improve our knowledge of the offshore frontiers and encourage exploration to these areas, from 2003-2011, Geoscience Australia was funded by the Australian Government to undertake a series of pre-competitive data acquisition and analyses programs in frontier basins around the Australian margin. This Record presents a comprehensive inventory of the geology, petroleum systems, exploration status and data coverage for 35 frontier basins, sub-basins and provinces, that draws on the results of those pre-competitive data programs, as well as exploration results and the geoscience literature. The Record also provides an assessment of the critical science and exploration questions and issues for each area. The results of each basin assessment are summarised in a prospectivity ranking. The availability of data and level of knowledge in each area is reflected in a confidence rating for that ranking. While the prospectivity of some areas is widely acknowledged to be high (e.g. Ceduna Sub-basin), the perception of prospectivity in many basins is negatively affected by the amount or quality of data available; in these basins, the acquisition of new data or targeted research could make a significant difference to the understanding of petroleum potential and likelihood of success. Therefore, recommendations for future work that could assist in addressing key knowledge or data gaps are included in each basin assessment.

Recent acquisition of deep crustal seismic and magnetotelluric data in the southern Northern Territory, in conjunction with current and previously completed studies, has led to an increased knowledge of the geological and geodynamic framework of the region. This improved understanding has been used to assess the potential for the presence of uranium and geothermal energy systems within the southern Northern Territory. Four uranium mineral systems were considered: sandstone-hosted, uranium-rich iron oxide-copper-gold, unconformity-related and magmatic-related. The analysis for uranium systems was undertaken in a 2D, GIS-based environment and employed a mineral systems approach consisting of four key components: 1) sources of metals, fluids and ligands, 2) drivers of fluid flow, 3) fluid flow pathways and architecture, and 4) depositional sites and mechanisms. Two geothermal systems were targeted: hot rock geothermal and hot sedimentary aquifer. For the assessment for hot rock geothermal systems, temperatures at depth were predicted in 3D using the 3D GeoModeller software package. Hot sedimentary aquifer potential was assessed using the modelled temperature at the basal contact of sedimentary basins containing favourable aquifer units.

This quarter, with its favourable climatic conditions, has seen the greatest activity in the field for the year. Thirteen geologists and five geophysicists, together with many assistants, have operated in the area on many prospects. The Darwin office and laboratory are well-established and providing many services to the public such as assaying, instrument repair, and geological and geophysical advice. Detailed geological and geophysical work has been commenced or continued at the following prospects: A.B.C., Edith River, Burrundie, Brock's Creek and Adelaide River, while minor investigations have been carried out at many other localities. Three drills have operated throughout the quarter. Regional geological mapping has been continued over a wide area. The amount of work being done will decrease during the coming quarter due to the approach of the "wet" season.

Crustal magnetism is predominantly caused by the abundantly distributed ferrimagnetic mineral magnetite which posses the property of spontaneous magnetisation. Such magnetisation is dependent on temperature, which if high enough, will cause magnetite minerals to lose their magnetic property of spontaneous magnetisation and become paramagnetic. This temperature, known as the Curie point isotherm, occurs at ~580oC for magnetite. As temperature increases with depth in the crust, the Curie point can be taken as the depth at which the crustal magnetism ceases to be recorded. Using power spectral analysis of aeromagnetic data, we have generated a Curie point depth map for the Olympic Dam region in South Australia, host to the world's largest iron oxide-copper-gold-uranium deposit. The map shows an approximately 55 km long by 35 km wide and 40 km deep hemispherical depression in the Curie point depth beneath Olympic Dam, from a background average of around 20 km. Olympic Dam is notable for its large iron and uranium content, and it is located in a region of unusually high heat flow (av. 73 mWm-2). With such high heat flow one would expect the Curie point depth to be shallow. The paradox at Olympic Dam is that the Curie point depth is deep, raising questions about the geothermal gradient, depth-integrated abundance of heat-producing elements, and the source of the iron. A possible solution to the paradox is to interpret the deep Curie point depth as a giant hydrothermal alteration zone, where the heat-producing elements have been scavenged and concentrated into the upper crust, along with the gold and copper. The iron must have a significant mantle source as it is measured throughout the full crustal column. As iron is electrically conductive, such an interpretation is supported by the high conductivity measured deep beneath Olympic Dam.

Abstract for initial submission; see Geocat 71429 for conference paper version

Brown's Deposit is the westernmost known area of mineralization in the Rum Jungle area. It is situated approximately two miles northeast of Rum Jungle Railway Siding and one mile southwest of White's Deposit in an area known as Brown's Workings, which was worked for copper in the early part of the century. In June 1950, preliminary geophysical investigations revealed that a radiometric anomaly was present at the eastern end of the old copper workings, and in October 1940, a self-potential survey (Allen 1950) indicated the presence of two distinct bodies of sulphide mineralization. During 1950 a geological map of the area on a scale of 100 feet to an inch was prepared, and in 1951 mapping of the area on a scale of 40 feet and 20 feet to an inch was commenced. This work at present remains unfinished due to other commitments. Three diamond drill holes, part of an extensive programme of diamond drilling planned for the area were drilled towards the end of 1951.

The Brodribb anomaly was first detected by the Bureau of Mineral Resources' aerial scintillometer survey over the Rum Jungle area in 1952. The prospect lies six miles due west of the 40 mile peg on the Stuart Highway and can be reached easily in the dry season by means of the Brodribb track. However, for several months during the wet season the track is quite impassable to heavy vehicles necessary to maintain drilling operations. Ground parties made a preliminary inspection of the area in September, 1952 and by the end of October a combined preliminary detailed geological and geophysical survey was completed (Frankovich, 1952). The results of the surveys and the consequent costeaning indicated that drilling should be carried out for a complete investigation.

The prospect is an existing cooper lease (M.L.69B) held by Messrs. J.W. Watson and K. Cooper who carried out some mining in the area in 1950. The area was first visited in 1953 by I.A. Mumme whose interest was aroused by the pre-existing copper prospects and the close proximity of the Shoobridge granite. Further examination was carried out by Mumme and the writer early in November, and detailed mapping was done on a scale of 100 feet to the inch by the writer and D.N. Smith. Radioactive rocks and the secondary uranium mineral torbernite were discovered at this prospect, which is a copper mine, on October 25th 1953 by I.A. Mumme. A survey plan of the mine shafts, pits and costeans and lines of mineralization was prepared by I.A. Mumme on the 5th and 6th of November so that a suitable base line could be chosen for magnetic and self-potential test traversing. Three magnetometer traverses were completed. P. Rosenhain visited the area on the 5th November and inspected the shafts, stopes and costeans and carried out geological mapping from the 16th November to the 19th November. Further magnetic and self-potential traversing and some reconnaissance radiometric field work was carried out during the two periods 16th November to 20th November, and 24th November to 28th November.

The area prospected is shown in plan on Plate 2 and a locality map is given in Plate 1. The prospecting was done by geologists D.E. Gardner and N.O. Jones, and survey hands S.J. Quain of the geological party, and B. Brewster and E. Rigby of the geophysical party. In order to cover the area systematically, it was subdivided into small topographic units, bounded by such features as creeks and the crest of ridges. Each unit of the area was traversed by one or more members of the prospecting party, who used Geiger-counters or ratemeters to test shear zones and outcropping quartz veins for radio-activity. Prospects were examined by either of the two geologists, who also made general notes on the geology of each unit of the prospecting area. Twelve uranium prospects were discovered within an area 4 miles long by 1.25 miles wide in Cullen granite adjacent to the contact with Brocks Creek sediments. An additional prospect was previously known to occur there. They are all small, and judging from the surface counts, appear to be low in grade.

Sediments of the Brock's Creek Group and of the Phillips Creek Formation, and volcanics of the Edith River Formation were prospected with carborne radiometric equipment. A comparatively high background count was recorded in the Edith River Volcanics, but no significant radiometric anomaly was found. A geological party prospected ten shear zones south east of the Edith Siding, including a cupriferous one, and a strongly fractured belt near the granite contact. No radiometric anomaly was found. Future prospecting should be directed towards major faults within the sediments.