When Galileo Mining (ASX: GAL) defined the maiden resource at its Callisto discovery in October 2023, it established that the company’s wholly owned Norseman ground contained a significant and unusual Australian palladium, platinum, gold, rhodium, nickel and copper deposit. The discovery provided a tangible foundation for the company, but it also raised a broader question. Was Callisto an isolated mineralised intrusion, or the first recognised deposit within a much larger system?
Galileo’s exploration during 2026 has increasingly focused on answering that question. Deep drilling beneath Callisto has identified another mineralised intrusive unit, repeated sulphide intersections have been recorded at Mission Sill, and prospecting has located mineralised fresh rock at surface approximately two kilometres from the existing resource. None of these developments yet amounts to a second economic discovery, but together they strengthen the interpretation that Callisto may form part of a wider mineralised district.
That change in emphasis is important for the investment case. Galileo is no longer simply attempting to add tonnes around the margins of one known deposit. It is using the geological characteristics of Callisto as a guide to identify separate intrusions across the wider Norseman PGE and Nickel Project, where Callisto, Mission Sill, Jimberlana and several emerging prospects sit within a substantial and largely underexplored land position.
The immediate challenge is to turn that increasingly persuasive geological model into another material discovery. A programme of approximately 4,500 metres of aircore drilling was completed during June across Mission Sill and South Callisto, while drilling is also being planned around the newly identified North Callisto outcrop. The next results will therefore test whether Galileo has merely identified widespread low-grade PGM anomalism, or whether one of these targets can develop into a second deposit capable of adding meaningfully to Callisto.
Callisto Remains the Foundation of the Investment Case
Despite the growing regional exploration story, Callisto remains the asset against which Galileo must be assessed. Its maiden Indicated and Inferred Mineral Resource Estimate comprises 17.5 million tonnes at 1.04 grams per tonne of combined palladium, platinum, gold and rhodium, together with 0.20% nickel and 0.16% copper. Expressed on a palladium-equivalent basis, the resource grades 2.3 grams per tonne and contains approximately 1.27 million ounces.
The contained metal inventory includes approximately 585,000 ounces of the four precious metals, 35,000 tonnes of nickel and 28,000 tonnes of copper. Around eight million tonnes, or 46% of the resource, is classified as Indicated, providing a stronger level of geological confidence across a substantial part of the deposit. Galileo has also reported that approximately 95% of the resource falls within an optimised pit shell, while mineralisation remains open below the current model.
Callisto also benefits from a location that is considerably more favourable than many early-stage Australian discoveries. The broader Norseman Project lies around ten kilometres from the established mining town of Norseman and close to sealed roads, rail, gas, water and electricity infrastructure. The deep-water Port of Esperance is approximately two hours to the south, providing potential access to an established export route should the project eventually progress towards development.
A defined resource and favourable location do not, however, establish economic viability. Further metallurgical work, resource development, engineering studies and assessment of the recoverability and payable value of the different metals will be required before Callisto can be viewed as a development project. For now, its greatest strategic value is twofold: it provides Galileo with an existing mineral inventory and supplies the geological template being used to search for additional deposits across Norseman.
Deep Drilling Reveals a Separate Mineralised Intrusion
The most important development beneath Callisto came from diamond hole 26NRDD525, which was drilled to 772 metres to test whether the geological structures responsible for the existing deposit had also accommodated mineralised intrusions at depth. The hole passed through the known resource before intersecting a separate ultramafic pyroxenite sill within the underlying volcano-sedimentary sequence. That newly recognised unit returned 109 metres at 0.21 grams per tonne of palladium, platinum and gold from 426 metres, including 8 metres at 0.50 grams per tonne from 486 metres.
Sampling through Callisto itself provided a useful comparison with the deeper intrusion. The hole returned 38 metres at 1.57 grams per tonne of palladium, platinum and gold, together with 0.24% copper and 0.27% nickel from 124 metres. This included 13 metres at 2.37 grams per tonne, 0.38% copper and 0.37% nickel from 146 metres, reinforcing Callisto’s position as the most strongly mineralised intrusive unit identified at Norseman to date.
The deeper interval is substantially lower grade than the existing resource and cannot presently be treated as a new Callisto-style discovery. Its significance lies instead in what it reveals about the broader geology. Galileo now interprets the Callisto and Mission Sill trends as complexes containing numerous intrusive sills, emplaced along deep-seated structures, rather than as single isolated rock bodies. At least one of those intrusions hosts the existing Callisto deposit, while the latest drilling confirms that other PGM-bearing units occur beneath and around it.
That interpretation expands the search beyond simply extending the current resource down dip. Galileo can now target separate intrusive units along the approximately 20 kilometres of prospective geology surrounding Callisto, using gravity, magnetic and drilling information to distinguish the most favourable locations. The result does not prove that another economic deposit exists, but it provides direct geological evidence that Callisto is not the only mineralised intrusion within the system.
Mission Sill Becomes the Leading Regional Discovery Target
Mission Sill has emerged as the most advanced regional target outside Callisto because drilling has repeatedly encountered shallow PGM-bearing sulphides across a large prospective trend. Initial four-metre composite assays included 44 metres at 0.78 grams per tonne of palladium, platinum and gold from 4 metres in NRC514, including 8 metres at 1.33 grams per tonne. NRC513 returned 40 metres at 0.92 grams per tonne from surface, including 8 metres at 1.20 grams per tonne from 8 metres.
Follow-up one-metre sampling provided a more detailed view of the sulphide zones in fresh rock. Results included 8 metres at 0.42 grams per tonne from 24 metres in NRC518, including 2 metres at 0.88 grams per tonne, and 17 metres at 0.36 grams per tonne from 79 metres in NRC519, including 5 metres at 0.61 grams per tonne. A further hole returned 16 metres at 0.27 grams per tonne from 88 metres, with the reported intersections remaining open along strike and at depth.
The grades are not yet comparable with Callisto, but their distribution is geologically encouraging. Galileo reports that the disseminated sulphides occur within discrete pyroxenite intrusions and become more concentrated towards the centres of those units, resembling the pattern observed at the existing resource. Results have been recorded across sections separated by kilometres, while the wider Mission Sill trend extends for approximately 12 kilometres, leaving a substantial area only lightly tested.
Mission Sill therefore represents a large mineralised system rather than a defined deposit. The exploration challenge is to locate the parts of the intrusive sequence where sulphide development and PGM grades strengthen sufficiently to support a meaningful discovery. Galileo completed approximately 4,500 metres of aircore drilling across Mission Sill and South Callisto in late June, with the results intended to refine the strongest targets before deeper follow-up drilling.
Geophysics Turns a Large Tenement Position into Defined Targets
Galileo’s Norseman tenure covers approximately 255 square kilometres, but the scale of that landholding only becomes valuable if the company can identify where mineralised intrusions are most likely to occur. During 2026, Galileo has increasingly combined gravity, magnetic and induced-polarisation data with drilling and geological mapping to convert long prospective trends into more specific targets. This work is particularly important because much of the project is concealed beneath transported cover, limiting the usefulness of surface observation alone.
At Mission Sill, gravity data outlines the contact between mafic and ultramafic rock units, while induced-polarisation results show a strong chargeability response close to known sulphide intersections. Galileo interprets these contact zones as favourable locations for the development of PGM-bearing sulphides, based partly on the geological setting observed at Callisto. The convergence of geophysical responses and existing drill results therefore provides a more credible basis for follow-up drilling than either dataset would provide independently.
Gravity coverage also supports an approximately 20-kilometre prospective trend extending north and south of the Callisto resource. Within that corridor, Galileo is attempting to identify individual intrusive units, structural positions and contact zones that could host stronger mineralisation. The company’s November 2025 presentation similarly described the Callisto and Mission Sill trends as extending for approximately 20 kilometres and 12 kilometres respectively, with campaign drilling and geophysical surveying being used together to progress new targets.
Geophysics cannot establish grade, thickness or economic continuity, and strong anomalies may ultimately reflect barren sulphides or variations in rock type. Its practical value is in reducing the search area and improving the order in which targets are tested. For Galileo, the next measure of success will be whether this increasingly detailed targeting process leads to intersections materially stronger than the broad, lower-grade mineralisation already identified at Mission Sill.
North Callisto Introduces a Potentially Shallower Discovery Route
North Callisto adds a different type of exploration opportunity because mineralised fresh rock has been identified at surface approximately two kilometres along strike from the existing resource. Rock-chip sampling returned values of up to 1.87 grams per tonne of palladium, platinum and gold, with mineralised outcrop recognised across approximately 40 metres of strike. Galileo describes this as the first mineralised fresh-rock outcrop identified within the Norseman project area.
The contrast with Callisto is significant. The existing resource was discovered beneath approximately 100 metres of cover, whereas the North Callisto target is exposed at surface. Previous drilling around 140 metres north of the outcrop returned 62 metres at 0.22 grams per tonne 3E, while drilling approximately 170 metres to the south included 100 metres at 0.19 grams per tonne. These intersections are low grade, but they indicate that anomalous PGM mineralisation occurs beyond the limited area of exposed rock.
Galileo’s interpretation is that the local stratigraphy dips eastwards, meaning any continuation of the mineralised unit may lie beneath and east of the outcrop, where drilling remains limited. An initial aircore programme is being planned to test the area surrounding the surface mineralisation, supported by further mapping and prospecting along strike. The objective will be to establish whether the outcrop represents an isolated mineralised exposure or the surface expression of a broader intrusive body.
North Callisto should not yet be presented as a discovery. Rock-chip samples are selective by nature and do not demonstrate width, continuity or average grade beneath the surface. Even so, the target is strategically important because it may offer Galileo a shallower and potentially more direct route to testing mineralisation than the deeper targets beneath Callisto, while also supporting the wider argument that PGM-bearing intrusions recur along the broader trend.
A Funded Explorer with Time to Test the Geological Model
Galileo ended the June 2026 quarter with A$7.476 million in cash and no debt or financing facilities. Exploration expenditure during the quarter was A$730,000, while total exploration expenditure for the financial year reached approximately A$2.996 million. Based on the June-quarter spending rate, the company estimated that it had funding available for around 10.3 quarters of activity.
That funding position gives Galileo time to test several targets without an immediate requirement to return to shareholders for fresh capital. The company can continue follow-up work at Mission Sill, drill the North Callisto target, advance metallurgical testing at Callisto and maintain broader target generation across Norseman. For an exploration company, this reduces the risk that individual drilling decisions are dictated primarily by short-term financing pressure.
Galileo also received A$1 million during the financial year under its lithium farm-in and joint venture agreement with Mineral Resources. The parties subsequently agreed to suspend the earn-in period for up to two years, although Mineral Resources may continue low-impact exploration and can restart the earn-in by paying Galileo a further A$1.5 million. If restarted, Mineral Resources would be required to spend A$12.5 million to increase its interest to 55%.
The cash position is supportive, but it does not remove the need for disciplined allocation. Galileo now has numerous targets across Callisto, Mission Sill, North Callisto, South Callisto and Jimberlana, and not every anomaly warrants deeper drilling. The value of the balance sheet will depend on whether management concentrates expenditure on targets capable of producing a second material discovery rather than simply maintaining a high level of exploration activity.
Fraser Range and Lithium Provide Optionality, Not the Main Story
Galileo’s wider portfolio includes its Fraser Range interests and the Norseman lithium joint venture, but neither currently provides the central investment narrative. The latest exploration announcements are overwhelmingly focused on the wholly owned Norseman PGM project, where Callisto supplies an established resource and the company is pursuing additional discoveries across several intrusive trends.
The Fraser Range Project remains prospective for nickel and copper sulphide mineralisation and is held through joint ventures with interests associated with Mark Creasy. Its location within the same broader province as the Nova-Bollinger deposit gives the ground strategic relevance, but the recent announcement flow does not indicate a comparable level of active drilling or near-term resource work. It should therefore be recognised as a potentially valuable exploration option rather than treated as an immediate catalyst.
The Mineral Resources lithium joint venture offers a different form of optionality. Galileo has already received cash payments, retains exposure to future third-party-funded exploration and may receive a further A$1.5 million if the earn-in is restarted. However, the agreed suspension means that full-scale lithium exploration is not currently progressing on the timetable originally envisaged.
These assets broaden Galileo’s commodity exposure and may create future value without requiring the company to fund all exploration itself. Even so, the current investment case rests primarily on the PGM, nickel and copper potential at Norseman. Fraser Range and lithium should therefore be presented as additional strategic options, not as substitutes for progress at Callisto and the surrounding targets.
The Next Results Will Test Whether Norseman Is a District
The immediate test of Galileo’s district-scale interpretation will come from assays generated by the approximately 4,500 metres of aircore drilling completed at Mission Sill and South Callisto in late June. The programme was designed to refine the location of shallow PGM-bearing sulphides and identify areas suitable for deeper follow-up drilling. Results were expected during August, although laboratory demand had created some delay.
North Callisto provides a second near-term test. Mineralised fresh-rock outcrop has now been identified approximately two kilometres from the resource, and Galileo is planning aircore drilling around the exposed zone. A significant subsurface continuation would strengthen the case for repeated mineralised intrusions along the Callisto trend, while weak or discontinuous results would suggest that the surface occurrence is more limited.
Further prospecting, mapping and geophysical interpretation will continue across the approximately 20-kilometre Callisto trend and the extensive Mission Sill corridor. The metallurgical samples collected from the deep Callisto diamond hole also provide an opportunity to reassess the existing resource using current metal prices and improved processing information. These programmes give Galileo several routes to strengthen the project, even if a second discovery is not immediate.
The geological case has advanced during 2026, but it remains unproven at the district level. Callisto demonstrates that substantial PGM, nickel and copper mineralisation exists at Norseman, while the deeper intrusion, Mission Sill sulphides, geophysical trends and North Callisto outcrop suggest that the system may repeat elsewhere. The next phase will be judged by whether one of those targets develops into a coherent deposit capable of adding materially to Galileo’s existing 1.27 million ounce palladium-equivalent resource.
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