From 1 - 10 / 839
  • A laboratory study has been conducted to determine the best methods for the detection of C10 to C40 hydrocarbons at naturally occurring oil seeps in marine sediments. The results indicate that a commercially available method using hexane to extract sediments and gas chromatography to screen the resulting extract is effective at recognizing the presence of migrated hydrocarbons at concentrations between 50 to 5,000 ppm. When the oil charge is unbiodegraded the level of charge is effectively tracked by the sum of n-alkanes in the gas chromatogram. However, once the charge oil becomes biodegraded, with the loss of n-alkanes and isoprenoids, the level of charge is tracked by the quantification of the Unresolved Complex Mixture (UCM). The use of GC-MS was also found to be very effective for the recognition of petroleum related hydrocarbons and results indicate that GC-MS would be a very effective tool for screening samples at concentrations below 50 ppm oil charge.

  • Executive Summary Between the 6th and 10th December 1999, the Australian Geological Survey Organisation, in collaboration with the NSW Environment Protection Authority and the Department of Land and Water Conservation, conducted a field survey of Durras Lake, South East, NSW. The objectives of the survey were to: (i) measure the net fluxes of sediment metabolites from the major sediment facies; (ii) estimate the rate and significance of denitrification; and (iii) field test modifications to AGSO automated benthic chambers. Eight chambers were deployed on two sediment facies (sand and mud). Time series of water samples collected from these chambers were used to determine nutrient flux rates and sediment respiration. The following observations were made: At the time of the survey, the deep mud basin was stratified with an anoxic, saline bottom layer and fresher well oxygenated surface waters.. Respiration dominated (ie oxygen demand of the sediments was greater than production via photosynthesis) in each chamber incubation in the mud and sand facies. TCO2 fluxes ranged between 13.3 ?57.4 mmol m-2 day-1 in the mud facies and 39.0 ?106.3 mmol m-2 day-1 in the sand facies. Organic carbon being degraded in the deeper mud basin was primarily of a diatomaceous composition. Dark respiration in the sand facies was not consistent with a mainly diatomaceous origin of organic carbon. Denitrification efficiencies were relatively low in both the sand and mud facies. Low denitrification rates in the mud facies may be related to the low concentrations of dissolved oxygen in the water overlying the sediments. Tests of AGSO system for direct measurement of denitrification using benthic chambers and N2 measurement by quadropole mass spectrometer were successful.

  • The ENE-trending Mallina Basin developed in the central part of the Pilbara Craton, NW Australia, between c. 3010 and 2940 Ma, over the boundary between two distinct terrains characterised by greenstones aged c. 3120 and older. The basin preserves an association of igneous rocks characterised by an unusual combination of high-Mg and high LILE concentrations, that provides valuable insight into the geological evolution of the region. The oldest dated components of the Mallina Basin are c. 3010 Ma volcaniclastic rocks found only in the far northwest. Geochronology and field relationships indicate that the main basin deposition, of clastic rocks, occurred from 2970 to 2955 Ma. Towards the end of this depositional phase, siliceous high-Mg basalts (SHMB) formed the upper part of the stratigraphy in the northwestern part of the basin (Whim Creek Belt), and their subvolcanic equivalents intruded the southern part of the basin. Sedimentation was terminated by ESE?WNW compression at c. 2955-2950 Ma. Rocks with boninitic compositions and spatially associated low-Ti tholeiitic gabbro formed sub-volcanic sills in coarse siliciclastic rocks in the southern part of the basin, probably during the waning stages of compression. Immediately after compression, an extensive alkaline granite complex was emplaced into the central and northern part of the basin, coeval with intrusion of a 2955-2945 Ma high-Mg diorite (or sanukitoid) suite. Renewed extension also resulted in renewed basin sedimentation between 2945 and 2935 Ma. Voluminous high-K monzogranite swamped the region between c. 2935 and 2930 Ma, particularly adjacent to, and south of the basin, and was early- to syn-tectonic with respect to SE-NW compression. Monzogranite magmatism becomes systematically younger and less voluminous away from the Mallina Basin.

  • Dataset for the Southeast Region Release area contains biostratigraphic, reservoir facies, and organic geochemistry from wells in the release region.

  • Dataset for the Southwest Region Release area contains biostratigraphic, reservoir facies, and organic geochemistry from wells in the release region.

  • The NGMA Cooper-Eromanga Basins project is a co-operative undertaking between the agencies of the Commonwealth and Queensland, South Australia, New South Wales and Northern Territory governments. The aims of the project are to provide uniform regional data sets and to develop an understanding of the hydrocarbon generation potential of the Cooper and Eromanga Basins. This product provides an interactive environment in a GIS format where gas and oil show data, oil geochemistry data and geological data can be readily interrogated using a project-designed graphical interface

  • During the 1953 field season geochemical prospecting techniques were employed as an additional tool in the search for ore deposits in the Northern Territory. Areas of particular interest were those at which radio-active minerals had already been discovered or at which radiometric anomalies were being investigated. The work thus included the already proved Rum Jungle field as well as the new prospects at Brodribb, Waterhouse, Edith River, and Coronation Hill. A direct chemical test for uranium in soils was not used, the discovery of the radio-active areas being left to the sensitive ratemeters now in use. The close association between copper and uranium was used to advantage as it is present at many of the uranium prospects in the Northern Territory. It is a logical step to use the geochemical techniques to locate new copper mineralization, and then to carry investigations further by attempting to locate uranium in the vicinity of the copper, particularly in areas covered by deep soils where ratemeters are of no use. A field test for cobalt, a metal often closely associated with both copper and uranium, was developed, but of the many samples tested for this element only one gave a positive test. It is possible that the cobalt, an element which is extremely mobile in the oxidized zone, has been completely leached and dispersed from the radio-active minerals.