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  • This GIS results from an AGSO/PIRSA/CRC LEME/Dominion Mining AEM Interpretation Workshop. The workshop focused on AEM data acquired over the Challenger Prospect in South Australia.

  • Presentation to minerals industry representatives at the Geological Survey of Western Australia, 4 May 2010.

  • Diagram produced for the Australian Fisheries Management Authority showing the vessel monitoring system positional data for MV Seawin Emerald 16//8/2006 to 27/8/2006. This diagram is restricted to internal use by AFMA and not for general release.

  • The under-cover geology of the southern Thomson Orogen in north-western New South Wales and south-western Queensland is largely unknown due to the extensive, up to 600 m thick Cenozoic and Mesozoic cover. This cover (mainly consisting of Eromanga Basin and Lake Eyre Basin rocks) results in very restricted basement outcrop, with a subsequent lack of understanding of subsurface lithologies, structures and the potential for the location of economic resources. As a result, this area was selected for a regional, multi-disciplinary project (the Southern Thomson Project) by Geoscience Australia and its State partners the Geological Survey of New South Wales and the Geological Survey of Queensland. The Project reflects the focus of the UNCOVER Initiative (Australian Academy of Science 2012) that aims to form the basis for Australia's potential future discovery and development of new economic mineral resources. The Southern Thomson Project involves many geoscientific disciplines including geophysics, geochronology, geochemistry and stratigraphy to better understand the region and promote mineral exploration by reducing exploration risk. This report focuses on some of the initial reconnaissance and pre-drilling geophysical data collected in 2014 - in particular gravity data, AEM (Airborne Electromagnetics) and MT (Magnetotellurics) along two regional north-south traverses, and a shorter east-west traverse in the northern part of the region. The major aim of this study is to compare AEM and MT electrical conductivity data acquired along these traverses, and integrate them with interpretation of available deep seismic reflection data to generate a series of 2D geological models, which can be tested via forward gravity modelling and subsequent density inversions. This integrative approach allows for a more robust understanding of the crustal architecture and cover thickness (or depth to basement) variations in the Southern Thomson region. The main findings of this report are: 1) Cover thicknesses of 0 to >500 m were initially estimated along various traverses through a combination of AEM and MT data interpretation as well as existing data from drill holes and water bores. Most datasets yield broadly similar results in terms of relative cover thickness variations, although AEM cannot be reliably used when cover thickness is greater than ~150 m due to limitations in the Depth Of Investigation (DOI), and Broadband MT (BBMT) tends to overestimate cover thickness where it is known to be less than 50 m. Cover thickness estimates using MT methods (especially AMT - Audio-frequency Magnetotellurics) agree with other datasets such as existing drill holes/water bores, GABWRA (Great Artesian Basin Water Resource Assessment; Ransley and Smerdon 2012) depth to basement results, and targeted high-resolution ground geophysical surveys (Goodwin et al. in prep). On this regional scale, AMT likely provides the most suitable resolution for estimating cover thicknesses of 0 - 1000 m. 2) Cover thicknesses estimated by AEM and MT conductivity sections have been tested by forward gravity modelling and produce better matches with the observed gravity responses compared to an averaged, uniform cover thickness. This observation shows cover thickness variations can produce discernible variations in gravity responses and need to be taken into account in gravity modelling. Further, this supports the use of a combined approach in using AEM, MT and gravity models to asses cover thickness variations over a broad region. 3) Several alternative interpretations of deep seismic reflection data along the southern part of one of the regional MT traverses (Line 3) were performed to assess crustal architecture. These were tested by forward gravity modelling with subsequent inversions (allowing modelled bodies' density to vary) producing a close match between the observed and modelled gravity responses with reasonable geological densities of crustal units given the limited known and/or inferred rock properties in this region. 4) Two-dimensional (2D) cross-section models along each line were generated by integrating the recent interpretation of basement geology (Purdy et al. 2014) with AEM and MT conductivity sections. These models were tested via forward gravity modelling and subsequent inversions (allowing modelled bodies' density to vary). This approach showed that the most accurate model was a thickened crust north of the Olepoloko Fault (the Southern Thomson region). 5) Many of the 2D forward models produced reasonable matches between the observed and calculated (modelled) gravity responses with respect to the large scale crustal architecture and location of prominent resistive bodies (inferred as felsic igneous intrusions) observed in MT conductivity sections. However, gravity inversions sometimes produced unrealistic densities of crustal units given the (limited) known rock properties in this region. Despite these limitations, the simplistic 2D forward models provide a good starting point for future refinement as more geological, geophysical, geochemical and petrophysical data become available.

  • Diatoms are important primary producers within pelagic, benthic end epiphytic communities and their siliceous frustule leads to rapid sinking to the sediment. As a consequence, diatoms play a critical role in nutrient and carbon cycles in shallow and deep water environments. In this study, benthic nutrient and gas fluxes, water column and sediment properties were studied in a coastal lagoon of south-eastern Australia to identify control mechanisms coupling benthic and pelagic processes, in particular, how nutrients become fractionated by processes affecting benthic nutrient fluxes. During late spring, the water column of St. Georges Basin was oligotrophic, primary production was likely P limited and the phytoplankton community was dominated by cyanophytes. Molar ratios of TCO2 : Si benthic fluxes, however, were equal to the molar composition of diatoms suggesting that diatoms preferentially sink and deliver the most labile organic matter fraction to the sediment. The congruent release of Si and C implies a coupling of processes mobilizing Si and C. It is argued that extracellular polymeric substances surrounding the silicious frustule are the primary labile organic matter fraction and their rate of mineralization limits the dissolution of the silicious frustule. As decomposing biomass in sediments lead to net N2-production and very efficient burial of P, the fate of diatoms significantly contribute to the removal of bioavailable nutrients. High DIN:DIP benthic flux ratios of 290 to 900 promote P limitation particularly in shallow water bodies with long water residence times.

  • The Whundo Group, in the Pilbara Craton of northwestern Australia, is exceptional amongst Mesoarchaean, or older, volcanic sequences in that it preserves geochemical characteristics that are extremely difficult to interpret in any way other than reflecting modern-style subduction processes, most likely at an intra-oceanic arc. The group includes boninites, interlayered tholeiitic and calc-alkaline volcanics, Nb-enriched basalts, adakites, and shows evidence for flux melting of a mantle wedge. The geochemical data are also consistent with geological relationships that infer an exotic terrane with no felsic basement. These data provide clear evidence for modern-style subduction processes at 3.12 Ga.

  • Airborne electromagnetic (AEM) systems are increasingly being used for mapping conductivity in areas susceptible to secondary salinity, with particular attention on near-surface predictions (ie those in the top 5 or 10 metres). Since measured AEM response is strongly dependent on the height of both the transmitter loop and receiver coil above conductive material, errors in measurements of terrain clearance translate directly into significant errors in predicted near-surface conductivity. Radar altimetry has been the standard in airborne geophysical systems for measuring terrain clearance. In areas of agricultural activity significant artifacts up to five metres in magnitude can be present. One class of error, related to surface roughness and soil moisture levels in ploughed paddocks and hence termed the ?paddock effect?, results in overestimation of terrain clearance. A second class of error, related to dense vegetation and hence termed the ?canopy effect?, results in underestimation of terrain clearance. A survey example where terrain clearance was measured using both a radar and a laser altimeter illustrates the consequences of the paddock and canopy effects on shallow conductivity predictions. The survey example shows that the combination of the dependence of AEM response on terrain clearance and systematic radar altimeter artefacts spatially coincident with areas of differing land-use may falsely imply that land-use practices are the controlling influence on conductivity variations in the near surface. A laser altimeter is recommended for AEM applications since this device is immune to the paddock effect. Careful processing is still required to minimise canopy effects.

  • Airborne electromagnetic data (AEM) are used in many and diverse applications such as mineral and energy exploration, groundwater investigations, natural hazard assessment, agriculture, city planning and defence. Unfortunately, many users do not have access to a simple workflow for assessing the quality of the data that they are using. This poster outlines the main quality assurance and quality control (QA-QC) procedures used by Geoscience Australia for our 2008-11 AEM surveys. Minor processing errors can dramatically reduce the quality of the data to the point that interpreters will be unable to use the data, or worse still, will be misled by features or characteristics produced during acquisition and processing. These scenarios not only impact the application at the time of interpretation, but can seriously impact the reputation and perceptions of the AEM industry. Every effort should be made to ensure that maximum fidelity is preserved in the data during acquisition and processing so that the best possible data are available for interpretation. Geoscience Australia is embarking on a project to upgrade the National Airborne Geophysical Database to better manage the data from major AEM surveys. This will better preserve the data and associated documentation to allow users to access and take advantage of the data well into the future. The quality of historical data included in this endeavour will unfortunately be variable and dependent on the QA-QC standards of the time. Geoscience Australia currently holds over 150 000 line kilometres of AEM data funded by the Commonwealth Government, State Governments and industry. Much of this data is available online for download, but is not available via the Geophysical Archive Data Delivery System (GADDS). Geoscience Australia is planning the expansion of GADDS to accommodate AEM data into the future. It is hoped the procedures outlined on the poster will be widely accepted by users, in particular new users, as a set of minimum requirements to help ensure that AEM data will be of a consistent quality and to a higher standard acknowledging it as the valuable resource it is. Key words: Airborne electromagnetic data; National Airborne Geophysical Database; AEM; QA-QC.