b'FeatureImaging the supergene search space with ANTFigure 6. Comparison between aeromagnetic intensity image and ANT model with interpretation of structural features. a. Magnetic intensity image across the survey area. Dark dashed lines represent possible north-east-trending fault set that appears to o\x1cset the more north-south-trending magnetic layering. Outline of the magnetic high features is shown in a light grey dashed line. b. ANT model at depth slice of 320 m. c. Structural zones interpreted from the ANT model traced by red dashed lines. Prominent north-east trending features appear to be in\x1fuenced by (o\x1cset) the less prominent, narrower north-west trending features. Also shown is the trace of the magnetic high outlined from the magnetic intensity image.seismic impedance in the upper portion of the model comparedThe ANT model suggests similar seismic velocities extend to the surrounding low velocity suggests that this zone hasacross the model to the south-west and overlap a second pod relatively lower porosity than the adjacent material. Drill holeof mineralisation de\x1ened as AE-5 (Figure 7b). Between the AE-8 information indicates the lowest velocity zones are where the(NP) and AE-5 pods, no signi\x1ecant mineralisation has been yet substrate is cover material such as Eocene sands, or is intensivelyencountered in the drill holes. The ANT velocity model suggests weathered saprolite. Within the upper zone of the main north- that the structure that appears co-located with the other pods east trending feature, however, the drill hole intersections areof mineralisation is continuous across the area and this area predominantly of highly weathered basement. This suggestscould be a target for further drilling.the cover-basement interface is elevated in the region of theDrilling results show that the highest-grade mineralisation north-east trending feature, or that the weathering mineralogyis commonly hosted in sheared pelitic and carbonaceous is di\x1ferent in this zone to the surrounding areas. In terms of themetasedimentary rocks, particularly in areas AE-6, -7 and -8. The model of supergene enrichment, it is possible to envisage thatsheared nature of the metasedimentary rocks and later fault sets the relatively high velocity zone in the uppermost portion ofhave likely facilitated deeper weathering and alteration of the the model may be indicative of the presence of minerals such asbasement, re\x1cected in the lower seismic velocity beneath the iron oxyhydroxides that can form in the leached cap zone abovede\x1ened mineralisation zones. By way of contrast, mineralisation areas of supergene enrichment (Reich and Vasconcelos 2015).in area AE-5 is predominantly in proximity to fault zones within The leached cap may be expressed as a zone of increased seismicinterlayered dioritic and felsic intrusives, with lesser pelitic velocity perhaps as a result of greater interconnectivity of ironsediments. It may be that these host rocks are more competent minerals and associated clays that result in the relative reductionand therefore brittle and oxide mineralisation may be therefore in porosity of this zone compared to the adjacent saprolite. more concentrated along fault zones. The abundance of diorite in the bottom of the holes in area AE-5 may help to explain Structural geometry of the ANT model andthe relatively high seismic velocity in the ANT model beneath relationship to mineral resource estimate this zone of mineralisation, compared to some of the other mineralisation zones.A comparison between the ANT model and the shells de\x1ened by mineral resource estimate drilling shows that areas ofComparison to airborne electromagnetic dataenriched copper grade tend to be spatially related to zones of intermediate velocity (Figure 7a). In particular, the zone ofAn airborne electromagnetic (AEM) survey data is publicly enhanced grade known as AE-8 (NP) sits very clearly withinavailable across the Alford East project area. The survey was \x1cown the upper portion of the main north-east-trending zone ofby Fugro Airborne Surveys for the South Australian Government anomalous velocity. The resource drilling shows that thein 2012 using the TEMPEST system (Lane et al. 1999, 2000). copper and gold mineralisation and associated REE grades areNote that the resolution of the AEM is less than the ANT survey concentrated near the surface and extend down to depthsbecause the AEM was \x1cown for a regional survey, with \x1cightline of at least 200 m. The seismic velocity beneath the de\x1enedspacing of approximately 140 m. The AEM model shows the mineralisation shell remains relatively lower than the adjacentuppermost layers at depths around 20 m are conductive, with country rock at greater depths suggesting the structure thattrends of conductivity in a similar north-northeasterly orientation controls the seismic velocity continues to depth. This furtherto that identi\x1eed in the ANT (Figure 8). The AEM also identi\x1ees supports previous inferences that there is a structural control ona larger region to the east of the de\x1ened mineralisation pods the supergene processes that have localised copper and goldthat is similarly conductive at these shallow depths. The cause of mineralisation in the Alford East project area (Wynne et al. 2019). this conductivity is uncertain; it may be groundwaters residing APRIL 2024PREVIEW 43'