b'FeatureImaging the supergene search space with ANTImaging the supergene search space with Ambient Noise TomographyAnthony ReidAdebayo Ojo Fleet Space Technologies, Beverley, South AustraliaFleet Space Technologies, Beverley, South Australia& Department of Earth Sciences, The University ofE adebayo.ojo@eet.spaceAdelaide, Adelaide, South AustraliaE anthony.reid@eet.space Gerrit Olivier Fleet Space Technologies, Beverley, South AustraliaBronwyn MurphyE gerrit.olivier@eet.spaceFleet Space Technologies, Beverley, South AustraliaE bronwyn.murphy@eet.space Doreen Mikitiuk DXplorer, Eatons Hill, QueenslandNicole Galloway-WarlandE dm@dxplorer.com.auThor Energy PLC, Norwood, South AustraliaE nicole@thorenergyplc.comOverview chalcocite, covellite, digenite as well as native copper. Conductive minerals such as these can be imaged by electrical geophysical Supergene mineralisation is an important contributor to themethods such as induced polarisation, and also by airborne economic viability of many mines. Supergene enrichmentelectromagnetic methods (Witherly 2023). Complications in processes can produce elevated copper, gold, rare earthEM methods caused by chargeability of sur\x1ecial, weathering elements (REE) and other commodities in the near surfacematerials (Soerensen et al. 2018) and conductive saline environment via a combination of acidic groundwaters andgroundwaters (Chandra et al. 2020) need to be screened from bacterial activity. Australia has widespread, deep weatheringelectromagnetic datasets when ranking conductivity drill targets. pro\x1eles that in places extend tens of metres into the bedrock.Furthermore, oxide supergene minerals are less conductive, and Where this weathering has overprinted near-surface sulphidemay not be imaged by electrical geophysics.accumulations there is potential for supergene enrichment. However, these weathered pro\x1eles are typically buried byWeathering can produce a signi\x1ecant reduction in density of younger materials, and geophysical methods are required tothe bulk rock package. This will cause a decrease in seismic investigate the weathering pro\x1ele. Here, we focus on Ambientvelocity, which can be detected by seismic methods. Both active Noise Tomography (ANT) as one method that can be appliedre\x1cection seismic and passive seismic methods are able to to see through cover and image the seismic velocity of theimage the cover-basement interface. For instance, the thickness subsurface in 3D. In the example of the Alford East project,of weathering pro\x1eles can be estimated by using a low-cost in South Australias Yorke Peninsula, the ANT models are ablepassive seismic method that measures horizontal-to-vertical to detect zones of where the cover-basement interface isspectral ratios (Nelson and McBride 2019). Here we focus on relatively deep, and where drilling has intersected these zones,another passive seismic method, Ambient Noise Tomography they typically comprise strongly weathered and mineralised(ANT). The method is appealing for use in mineral exploration rock with enrichment in copper and REE. It appears basementdue to its versatility: it is possible to not only image the cover-structural controls may have localised weathering intobasement interface, but also variations of seismic velocities in susceptible metasomatic rock types, leading to the supergene enrichment detected in the area by drilling and, by extension, ANT. This survey is a demonstration of the bene\x1ets of combining ANT with other geological and geophysical tools to image the structural architecture of the subsurface and has expanded the search space for buried supergene mineralisation in the region.IntroductionUpgrading of primary sulphide mineralisation can occur in the weathering environment (Figure 1). In many deposits, it is the supergene cap mineralisation that makes a mining operation economically viable, as a consequence of the early cash \x1cows that can be generated from mining these uppermost portions of the orebody. Weathering processes can concentrate copper signi\x1ecantly, and the grades of supergene ores can be higher than the disseminated hypogene mineralisation in the basement (Sillitoe 2005; Reich and Vasconcelos 2015).Weathering of a crystalline rock changes its petrophysical Figure 1. Schematic image of supergene alteration and weathering above a properties. As a result, deep weathering pro\x1eles may be visible inprimary (hypogene) disseminated sulphide zone (Reich and Vasconcelos 2015). geophysical surveys. For example, in Andean porphyry deposits,Zones of iron oxide, oxide and sulphide form in response to deep weathering and the supergene zones are rich in sulphide minerals such aswill potentially have a distinct geophysical signature to the primary rock type.APRIL 2024PREVIEW 39'