b'AEGC 2021Short abstracts247: Magnetic inversion constrained by probabilisticOften during the development of a mining operation there is a magnetotellurics models: methodology and application need to identify if additional mineral resources are in the vicinity and if the resources identified can be explained by existing Dr Jeremie Giraud 1, Dr Hol Seill2, Dr Vitaliy Ogarko3, Drgeophysical data. There is also the additional complication Gerhard Visser4, Dr Mark Lindsay5,6 and Prof Mark Jessell5,6 whereby the development of the mine results in a higher degree of complexity than expected initially and can these areas 1 Centre of Exploration Targeting (School of Earth Sciences), Thebe detected within existing data sets.University of Western Australia, 35 Stirling Highway, Crawly, WA, 6009, Australia In this case history we look at several generations of 2 CSIRO, Deep Earth Imaging FSP, Australian Resourcesgeophysical data acquired over a large time period over Research Centre, 26 Dick Perry Avenue, Kensington WA 6151,a mine site in Finland. The data sets include several Australia. generations of gravity, magnetic (ground and airborne), 3 International Centre for Radio Astronomy Research, UniversityInduced Polarisation, magnetotelluric and seismic data. Care of Western Australia, 35 Stirling Highway, Perth 6009 WA,has been taken to reduce all data to a common projection, Australia where necessary and possible combine smaller surveys into 4 CSIRO Deep Earth Imaging Future Science Platform, 26 Dicka unified data set, and obtain time specific topographic data Perry Av., Kensington, WA 6155, Australia valid for the survey acquisition and mine development at 5 Centre of Exploration Targeting, School of Earth Sciences,the time.University of Western Australia, 35 Stirling Highway, Perth 6009 WA, Australia All data has been inverted in 3D primarily as unconstrained 6 Mineral Exploration Cooperative Research Centre (MinEx CRC),3D inversions. Limited constrained inversions have also been School of Earth Sciences, University of Western Australia, 35completed. The efficacy of the inversions is evaluated and the Stirling Highway, Perth 6009 WA, Australia results combined to provide an unique view of the physical We present a cooperative inversion workflow that integratesproperties of not only the deposit, but the surrounding magnetotelluric-based electrical resistivity models into gravitygeology as well.inversion. The sensitivity of these two geophysical methods complement well, the gravity being suitable to resolve lateral variation of density, while the magnetotelluric (MT) is primarily251: Evaluation of ore deposit models using sensitive to variations of the electrical conductivity across horizontal interfaces. Considering petrophysical and structuralgeophysical, geological and geochemical inputs and prior information, we developed a workflow that leveragesthe implications for exploration activitiesstand-alone inversions and knowledge about the resistivity andMr Robert Hearst , Mr George Brabecand Ms Karen Gilgondensity of rocks observed in the studied area. 1 1 1The workflow consists in 1) performing 1-D probabilistic1 Southern Geoscience Consultants Pty Ltdinversions of MT data for each sounding to create an ensembleA common question often being asked at the present time by of 1D resistivity models, all compatible with the data withinmany mineral prospects for which ore deposit models have uncertainty. We then 2) cluster the models from these ensemblesbeen created prior to development is:to derive lithologic classes, which are used to calculate interface probabilities between rock units. We interpolate theseDo the ore deposit models faithfully reflect the ore potential probabilities over the whole survey area and, given the establishedpresent? This can be a difficult question to answer given the petrophysical relationships between density and resistivity, wenature of drilling to determine the deposit models. In this case define spatial and petrophysical constraints to 3) perform gravitystudy we set out to take existing ore deposit models and the inversion. In such case, inversion applies spatially-varying multiplerock physical properties assigned and complete forward and bounds constraints using the alternating direction method ofinverse modelling of the geophysical properties assigned in the multipliers as implemented in the Tomofast-x engine. deposit model and compare the results to the actual acquired The workflow is first tested against a realistic synthetic model.geophysical data sets available.The resulting MT-constrained gravity inversion model shows the presence of the deep horizontal interfaces as suggested byThe most geophysical datasets used in the case histories the MT models but unrecoverable using stand-alone gravityconsist primarily of gravity and magnetic data. The ore inversion as well as clear vertical contacts that were not welldeposit models generated from drilling activities and the defined by the MT models only. This demonstrates the potentialassociated rock physical properties from cores specimens value of cooperative inversion of geophysical datasets withand assay values are used to first generate 3D forward different sensitivity and resolution such as MT and potentialgeophysical models. The results of the 3D forward modelling field data. We then apply our workflow to an E-W profileare then inverted to attempt to recover the ore deposit crossing the Eucla Basin and Albany-Fraser Range (Westernmodel. The acquired field geophysical data is inverted in 3D Australia), where we model over 130 broadband MT soundingsas both unconstrained and constrained by the ore deposit and high-resolution gravity data. model. The results are then evaluated, compared and analysed using geophysical, geological and geochemical 248: The 3D inversion and integration of geophysicaldata sets.data in an active mine environment The results of the analysis have an impact on near deposit Mr Robert Hearst 1 and Ms Karen Gilgon1 exploration in addition potential optimising of exploration techniques and providing realistic type models for target 1 Southern Geoscience Consultants Pty Ltd identification along the same or similar trends.105 PREVIEW AUGUST 2021'