b'AEGC 2021Short abstractsmagnetite. Remanence is subordinate to magnetic susceptibility1 School of Physical Sciences, University of Adelaideat Osborne because multidomain magnetite grains are the main2 University of Adelaidecarrier. Therefore, remanence does not contribute significantly to3 Scripps Institution of Oceanographythe total magnetisation of the deposit. 4 Geological Survey of South Australia, Department for Energy Statistical relationships between density and magneticand Miningsusceptibility (R2 of 0.87 or better), breaks down at high K-values5 Mineral Systems Branch, Geoscience Australiaof 1.5SI i.e. parts of the Lower and Intermediary Ironstone.With the completion of AusLAMP in South Australia, we have a This suggest that neither the AMS fabric, nor remanence isgood understanding of the resistivity structure across the State. the cause of the mismatch between the location of the oreAn outcome of AusLAMP is the identification of a major arcuate-body and the TMI magnetic anomaly, which subsequentlyshaped high conductivity feature that follows the northern made the initial drill siting difficult. It is instead related to theand eastern extents of the boundary of the Gawler Craton. The self-demagnetisation effect, and/or local modification of theeastern part of this conductor is interpreted as the fossilised magnetic field, which are both due to the extreme magneticfluid pathways of the Olympic Domain, a world-class region for susceptibilities observed. IOCG mineralisation.215: The resistivity structure of the Gidyea SutureTo the south-west lies the roughly N-S crustal Eyre Conductivity and its relationship to the Carpentaria ConductivityAnomaly (~250 km in length and ~50 km wide), and to the east, two major parallel conductivity anomalies that together Anomaly contribute to the major Flinders Conductivity Anomaly, Dr Janelle Simpson , Mr Dominic Brownand A/Prof Karen~300 km in length and ~50 km in width, extending from mid-1 2Connors crust to shallow upper mantle depths. At the point of vergence 3between these three major elongated conductivity anomalies, 1 ASEG a lack of MT station coverage due to the shallow gulf waters 2 Geological Survey of Queensland has so far hampered efforts to constrain the offshore extents of 3 W.H.Bryan Mining & Geology Research Centre these conductivity features.The Gidyea Suture is a structure that lies on the eastern marginA previous land-based broadband MT survey just south of the Mount Isa Province. It was first recognised in deep crustalof Mt Hope on western Eyre Peninsula to Tumby Bay at seismic, and subsequent authors have used magnetotelluricthe eastern edge of the Eyre Peninsula resolved the Eyre (MT) data to further support its existence. It is considered toConductivity Anomaly in detail, with correlations to known be a highly conductive zone that is part of the broad-scalegraphite deposits suggesting grain-boundary graphite films Carpentaria Conductivity Anomaly (CCA). New, high-resolutionas the primary conductive cause. This transect has now been MT data in the Cloncurry region, together with a more detailedextended eastward into the Spencer Gulf- completing an interpretation of the location of the Gidyea Suture from theamphibious MT transect, ~240 km in length, with 36 terrestrial deep crustal seismic data provides additional constraint on theMT sites (~2 km spacing) and 12 marine MT (~10 km spacing). conductivity structure of the Gidyea Suture. We discuss the resistivity structure of the Spencer Gulf and the implications for constraining the aforementioned three major The crustal conductivity feature typically attributed to theconductivity anomalies and their associated mineral systems. Gidyea Suture varies considerably along the strike of the suture.We also touch on the logistics of deploying the first marine The conductivity feature typically sits in the Numil terrane,MT deployments in over 15 years, and the scope for future which underlies the suture to the east. The conductivity featureoffshore MT ventures.extends into the upper crust. In contrast, to the west of the suture in the Cloncurry area, there is a resistive upper crust and a broad region of conductive lower crust that is largely220: Gaining value from historical AEM dataconfined between the suture and Quamby Fault. To the north where the Gidyea Suture is offset laterally by the Quamby Fault,Mr Shane Mul 1 and Dr Timothy Munday2the upper crustal conductor is present both to the west and east of the suture. A significant conductivity feature was also1 Mineral Resources, CSIROimaged in the mid to upper crust along the Quamby Fault.2 CSIROThis feature may be associated with upper crustal graphiticAustralia is covered with a significant number of AEM surveys, shale basins or alteration along the fault. All these differentprimarily acquired over the last three decades. Most of these conductive structures are within the zone typically considereddata were collected with now obsolete systems or system to be the CCA. The complex and variable nature of resistivityvariants. Unfortunately, many of these historical datasets structures along and around the Gidyea Suture indicates itcontain unknown, uncertain or poorly measured system cannot simply be thought of as an anomaly related solely toparameters and undocumented or poorly documented the suture. metadata such as acquisition and processing methods. With an increased emphasis being put on getting more information from AEM datasets, their quantitative use requires that they 216: Continental shelf marine MT feasibility study in thebe interpreted using full non-linear inversion methods. Spencer Gulf, South Australia Unfortunately, that requires information on system geometry, transmitter waveform, and other processing parameters. Prof Graham Heinson1, Dr Kate Robertson 2, Mr Goran Boren1,Where this information is lacking, uncertainties in derived Prof Steven Constabl3, Mr Jake Perez3, Mr Ben Kay1, Dr Stephanmodels for the conductivity structure increase. In recent years, Thiel4, Mr Jingming Daun5 and Mr Darren Kyi5 state geological surveys, and government water departments 99 PREVIEW AUGUST 2021'