Great Southern Mining Launches Largest Ever Drill Program at Duketon

Great Southern Mining Fires Up Its Largest Ever Drill Program as Gold Discoveries Show Expanding Potential

Great Southern Mining Limited (ASX: GSN) has announced the imminent launch of its most ambitious drilling campaign since acquiring its Duketon Project tenure in 2021. This Great Southern Mining largest drill program at Duketon gold projects involves a reverse circulation (RC) program of up to 20,000 metres targeting three separate gold projects in the Laverton region of Western Australia.

The announcement is accompanied by new diamond drilling results from the Golden Boulder discovery that extend known mineralisation at depth and redefine the structural understanding of the system, opening the door to materially greater depth potential. With the company fully funded following the recent settlement of a $4.6 million equity placement, the stage is set for what could be a pivotal period for GSN shareholders.

The Largest Drill Campaign in the Company's History

The upcoming first phase of the RC program — between 15,000m and 20,000m — will be the largest the company has undertaken. Three project areas will be targeted, each at a different stage of development and each offering a distinct value-creation pathway.

All three projects sit within trucking distance of multiple gold processing facilities — a practical advantage that materially improves the economics of any future development pathway.

"The upcoming major drill program is aimed at unlocking this value by extending mineralisation in proven gold-bearing systems, which offers shareholders a compelling risk-return opportunity."
— Matthew Keane, Managing Director, Great Southern Mining

Golden Boulder: Depth Potential Comes Into Focus

The headline result accompanying the drilling announcement is a diamond drill hole — 26GBDD001 — completed into the Golden Boulder Main Line trend in April 2026. The 201.6m hole was designed to interrogate the geology and structure controlling gold mineralisation rather than simply confirm grade, and it has delivered a result that changes how the company interprets the system.

Key Assay Intercepts from 26GBDD001

Critically, the hole extended the westernmost gold lode — the most continuous lode identified at Golden Boulder to date — by approximately 40 metres down-dip. While the grade intercepts are themselves encouraging, the more significant outcome is structural: measurements from the diamond core now indicate the gold-bearing lodes dip steeply at 70–85° toward the east-northeast, rather than the previously interpreted moderate-to-shallow orientation.

This reinterpretation has significant implications. Steep-dipping lodes in shear-hosted systems tend to persist at depth, and the target zone between the Betelgeuse and Rosemont fault zones — which has so far been tested to less than 150m below surface — now presents a compelling target corridor for extensions going into the upcoming RC program and beyond.

The mineralisation style is consistent with what geologists describe as an orogenic gold system: gold hosted in intensely sheared basaltic units within quartz-carbonate veining, with associated hydrothermal alteration and fine disseminated pyrite and arsenopyrite.

Understanding Orogenic Gold — Why Does the Geology Matter?

What Is an Orogenic Gold System?

Orogenic gold deposits form during major tectonic events — periods of mountain building or continental collision — when deeply circulating fluids carry dissolved gold and deposit it along fault and shear zones in the crust. The gold tends to concentrate in quartz veins or as fine disseminations in chemically reactive rock packages.

Why Does This Matter for Investors?

Orogenic gold systems are the source of some of the world's most significant gold deposits — including the mines that define the Eastern Goldfields of Western Australia, such as Regis Resources' Rosemont deposit (which exceeds 2 million ounces and sits on the same north-south structural trend as Golden Boulder). These systems are characterised by:

• Steep dip persistence: Mineralisation that dips steeply tends to continue at depth, making step-out drilling at depth a high-value activity
• Multi-lode potential: Parallel lodes along shear corridors can multiply the overall resource footprint
• Near-surface grades: Mineralisation that starts near surface (as is the case at both Golden Boulder and Amy Clarke) reduces the cost barrier to early-stage economics

The structural reinterpretation at Golden Boulder — confirming steeper dip angles — is precisely the kind of geological update that opens up a larger three-dimensional target for future drilling.

Furthermore, understanding the key technical terminology is essential for contextualising these results:

• Orogenic gold: Gold deposited in shear zones during tectonic events
• Shear zone: A zone of intense rock deformation acting as a conduit for mineralising fluids
• Quartz-carbonate veining: Veins of quartz and carbonate minerals that often carry gold in orogenic systems
• RC drilling: Reverse Circulation drilling — a fast and cost-effective method used to collect rock chips from depth
• Diamond drilling: A technique that recovers intact core, allowing detailed geological and structural analysis
• Down-dip: The direction in which a geological structure descends into the earth

Three Projects, Three Value Levers

Golden Boulder — Extending a Multi-Kilometre System

Golden Boulder carries significant historical pedigree: the area hosts over 50 historical workings across a ~3.7km strike, with recorded production from 1900–1955 of 1,915 tonnes at 28.6 g/t Au. Modern drilling in 2025 extended mineralisation over a 3.5km strike along the Main Line trend alone, returning standout intercepts including:

• 5m at 14.6 g/t Au from 41m, including 1m at 70.9 g/t Au (hole 25GBRC009)
• 5m at 5.1 g/t Au from 25m, including 1m at 23.9 g/t Au (hole 25GBRC030)
• 6m at 6.7 g/t Au from 48m, including 1m at 34.5 g/t Au (hole 25GBRC054)

The upcoming RC program at Golden Boulder has four defined objectives:

1. Prove mineralisation continuity in the northern 1.9km of the Main Line trend
2. Extend mineralisation at depth along the Main Line
3. Infill broadly spaced drill lines in the southern 1.6km of the Main Line
4. Extend mineralisation at depth and to the south along the Eastern Line trend

Amy Clarke — 4.7km of Near-Surface Mineralisation Awaiting Its First RC Test

Amy Clarke is located approximately 8–10km from Regis Resources' Garden Well gold processing facility and represents one of the most strategically positioned targets in the portfolio. Two aircore campaigns have now outlined gold mineralisation across a 4.7km strike, with the vast majority of drilling penetrating less than 50m below surface.

Critically, mineralisation at Amy Clarke is identified in saprock and near fresh-rock — not dispersed through a deeply weathered saprolite — which suggests a hard rock primary system awaiting its first RC test. Selected previous highlights include:

• 17m at 1.4 g/t Au from 20m, including 1m at 11.2 g/t Au (hole 25ACAC0105)
• 2m at 23.9 g/t Au from 10m (hole 25ACAC0007)
• 3m at 5.7 g/t Au from 8m (hole 25ACAC0132)

Initial interpretation suggests gold is hosted in steep quartz veins on the contact of sedimentary schists and porphyries — a structural setting with strong depth potential that the RC program will test for the first time.

Mon Ami — A Resource With Development Optionality

Mon Ami is the most advanced asset in the near-term development sense. The project sits on a granted Mining License (M38/1256), holds a JORC-compliant resource of 1.56Mt at 1.11 g/t Au for 55.5Koz, and has already had key mining studies completed including flora, fauna and heritage assessments.

Located approximately 14km from the Granny Smith gold processing facility (operated by Goldfields Ltd, NYSE: GFI), Mon Ami is well positioned within a well-serviced gold production corridor. The company has identified the nearby Ida H deposit — located just 8km north along the same Barnicoat Shear — as the most applicable analogue for Mon Ami's depth potential.

Ida H was one of the highest-grade mines in the Laverton District, having historically produced 229,900 tonnes at 22.6 g/t Au for 170,650 ounces from underground mining to approximately 450m vertical depth. The upcoming RC program at Mon Ami will consequently:

• Test depth extensions to known gold-bearing lodes within the modelled resource
• Follow up on high-grade intercepts including 10m at 2.7 g/t Au from 241m and 2m at 25.1 g/t Au from 173m
• Test the Blanc Platt target for a potential repeat lode to the north along the Barnicoat Shear

GSN is also actively investigating options to monetise the Mon Ami deposit, including a small-scale mining venture.

Fully Funded and Ready to Drill

A practical concern for many exploration-stage investors is whether a company can execute its stated program. In this case, the answer is straightforward: Great Southern Mining is fully funded for all planned drilling activities, having settled the final tranche of a $4.6 million equity placement in early June 2026. This financial certainty underpins the significance of the Great Southern Mining largest drill program at Duketon gold projects and removes a key risk factor for shareholders.

Upcoming Catalysts and Program Timeline

The combination of near-term drill results from three separate project areas provides multiple potential newsflow catalysts across the second half of calendar 2026.

The Investment Thesis: Scale, Proximity, and a Structural Tailwind

Several factors combine to create a compelling case for following GSN's progress through this drill cycle.

1. Discovery-scale strike lengths with minimal depth testing
Both Golden Boulder (3.5km) and Amy Clarke (4.7km) have been defined primarily through shallow drilling — less than 150m and less than 50m below surface respectively. The upcoming RC program represents the first serious test of the depth dimension at both systems.

2. Structural reinterpretation strengthens depth case
The diamond hole at Golden Boulder has shifted the geological interpretation from shallow-dipping to steeply-dipping lodes. In practical terms, this is the kind of update that expands the three-dimensional search space and underpins a more aggressive depth-extension drilling strategy.

3. Location within a proven gold corridor
Golden Boulder sits on the same structural trend that hosts Regis Resources' Rosemont deposit (>2Moz), Baneygo (380Koz) and Ben Hur (390Koz). This regional context provides meaningful precedent for the scale of system that can develop along this trend.

4. Proximity to processing infrastructure across all projects
All three project areas sit within trucking distance of multiple operating gold processing facilities. This is a material advantage for any future development scenario, reducing the capital intensity of a path to production and broadening the range of commercial options available to the company.

5. Mon Ami as a near-term monetisation option
With a defined JORC resource, a granted mining licence, and key studies already completed, Mon Ami offers a potential near-term value realisation pathway that sits alongside the longer-runway exploration upside at Golden Boulder and Amy Clarke.

Why Investors Should Keep a Close Eye on Great Southern Mining

The confluence of factors at play for GSN in mid-2026 is notable. A company embarking on the Great Southern Mining largest drill program at Duketon gold projects — fully funded, with two multi-kilometre discoveries at shallow depths awaiting their first proper depth test, and a structurally reinterpreted flagship target that now presents a more compelling three-dimensional geometry — represents an active and catalyst-rich situation.

The Laverton region of Western Australia is one of the country's most established gold mining corridors. The infrastructure is in place. The geological precedents for large systems along these shear trends are well documented. And for GSN, the structural work completed through the recent diamond drilling has materially upgraded the understanding of what might lie beneath the surface at Golden Boulder.

However, the next several months of drill results will ultimately determine whether this structural promise translates into a material resource expansion. In summary, Great Southern Mining has positioned itself as an active explorer in one of Western Australia's most productive gold corridors, with multi-kilometre discoveries at Golden Boulder and Amy Clarke yet to be tested at meaningful depth. With the Great Southern Mining largest drill program at Duketon gold projects now commencing and the company fully funded, investors have a clear set of upcoming catalysts to monitor through the second half of 2026.

Ready to Follow Great Southern Mining's Biggest Drill Program?

With three gold projects spanning kilometres of untested strike, a structurally upgraded flagship discovery, and the company's largest ever drill program now underway, Great Southern Mining (ASX: GSN) is entering one of the most catalyst-rich periods in its history. To learn more about the Duketon Project, the upcoming RC program, and what this drilling campaign could mean for shareholders, visit Great Southern Mining's official website.