b'AEGC 2023Short abstractsResolving basement crustal architecture andthe fluid pathway footprint is generally expressed as district-scale extensional tectonics using 3D inversion modellingalteration and geochemical haloes. However, it is generally difficult of airborne gravity data in the Otway Basin region,to focus successful exploration due to the extensive geochemical Victoria. smoke. In addition, many seemingly attractive accumulations of iron oxide alteration are often barren or at best host low metal Mark McLean1,2 Glenn Pears3, Matt Boyd1 and Ross Cayley1 grades, and it is rarely obvious which iron oxide masses might host economic Cu and Au deposits.1 Geological Survey of Victoria 2 The University of MelbourneOur solution for successfully identifying the fire in IOCG 3 Mira Geoscience systems of the Gawler Craton of South Australia is to apply a range of methodologies that combine the strengths of Seismic reflection surveys are used to image the sub-surfaceboth empirical and conceptual, process-based targeting. Our crustal architecture of sedimentary basins. This often includesintegrated Mantle to Mine approach minimises interpretation the top of basement which is an important interface forbias and reduces the reliance on specific deposit models.understanding structural controls imposed on basin fill and basin system prospectivity since the basin base represents theSpecifically, we have utilised a data-driven methodology lower boundary of effective pore space. However, seismic data(machine learning) that systematically tests for the relative has limitations and meaningful interpretation can becomeimportance of a large number of geological factors on known problematic where the basin is thick or where seismic data isdeposits, which is additionally guided by an integrated mineral vintage, noisy, or does not penetrate deeply. Airborne gravitysystems approach that analyses the processes operative in the gradiometry (AGG) data gives insight into crustal geometriespassage of ore fluids and metals to their eventual deposition and can be used to complement seismic interpretation in thesesites. Finally, we have utilised an analogue-driven methodology scenarios. to test geological processes (geomechanical modelling) that The 3D geometries of geological structures can be testedsimulates rock failure and ore fluid flow at potential metal quantitatively against AGG using a 3D forward modelling andtrap sites in the upper crust to further hone district-scale inversion approach. This iterative process involves constructiontargeting. As an independent test of their accuracy, the results of geological models, assigning rock property data, andof the machine learning and geomechanical modelling were calculating the synthetic gravity response of the theoreticalcompared with the location of known mineral occurrences and model. The challenge with meaningfully interpreting gravitygeochemical anomalies. The hit rate was very high in the case of data is that it measures the cumulative response of everythingboth methodologies and this test has given us confidence in the including basin fill, base-of-basin topography and geologicalpredictions made for less well-known zones.complexity within underlying basement, including Moho geometry. Neglecting basement geological complexity, can result in incorrect interpretation of base-of-basin geometry. Characterisation of metavolcanic megaclast structures within the Moyston Fault hangingwall mlange This study provides a workflow to tackle the problem of(Moornambool Metamorphic Complex), western superposition of geophysical anomalies. We use the Otway Basin in southeast Australia as a laboratory to provide aVictoria: Insights from potential field modelling and systematic approach for interpreting basin and underlyingmachine learning.basement geometry using AGG data in conjunction with other geoscientific datasets. A new regional 3D model of theTom McNamara 1 Mark McLean1,2 and Ross Cayley2Otway Basin is presented which is consistent with AGG data,1 University of Melbourne legacy seismic and drilling data. It also integrates current2 Geological Survey of Victoriaunderstanding of the crustal architecture with previous seismic interpretations of basin and basement, previous basement 3DWestern Victorias goldfields are a world-renowned historical geological framework models, and insights gained throughgold endowment. Sites across the region are undergoing surface mapping. The workflow identifies the possibilitynew development in deeper prospects, as advances in data of previously unrecognised basin depocenters and wherequality, geophysical techniques and modelling have made additional data are required to reduce interpretation ambiguity. these prospects viable exploration targets. The Stawell Corridor (stratigraphically the Moornambool Metamorphic Complex) Mantle to mine: an integrated machine learning,is a multi-million-ounce goldfield of western Victoria, with large-scale mining operations and exploration programmes minerals systems and geomechanical approach tofor additional resources active within the corridor. The largest copper and gold exploration. of these is Stawell Gold Mine, producing 62 tonnes of gold just John McLellanPaul Pearson since reopening in 2016. The total endowment of the Stawell 1,2 3Corridor is estimated at up to 900 tonnes.1 Director, GMEX 2 Adjunct Senior Research Fellow, Economic Geology Reserach Unit,The corridor is a ~15 km wide Cambrian high-strain zone James Cook University bounded to the west by the Moyston Fault, and east by the 3 Director, New Mine Exploration Coongee Fault. The most abundant mineralisation along the corridor is controlled by kilometre-scale dome structures Many mineral deposits lie under thick accumulations of post- comprised of Cambrian metavolcanics, raised within the mineral cover, making exploration expensive and risky. ExplorationMoyston and Coongee fault hangingwalls as mlange targeting is thus often focused mainly on various combinations ofmegaclasts torn from the metavolcanic basement. The gravity and magnetic anomalies. In the case of IOCG style depositscompetency contrast between the metavolcanics and overlying FEBRUARY 2023 PREVIEW 120'